I don't know why Holley did that but they sold a lot of extra jets to people that thought they needed them.
Comp Cams makes a Maxjet where each jet actually corresponds with the drill size and their flow rating is supposed to be more precise.
Looking for help fixing engine hesitation. I'm lost.
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Comp Cams makes a Maxjet where each jet actually corresponds with the drill size and their flow rating is supposed to be more precise.
I looked it up and base timing of the early 70's Olds 350 was anywhere from 8-14* depending on the horsepower rating. Of course the fuel was a bit better back then, but you should be able to run the same. Usually the more performance items you add to an engine like intake, cam, heads, headers, etc. the more initial they like to a point. I would say 12* is a good starting point, but I wouldn't be opposed to adding more. Usually I try to run as much base timing as I can and limit total to 35-40 without vacuum advance, as long as the engine doesn't start hard and such. I run 18 initial on my pickup with 10.3:1 compression and 35* locked on my SS, neither have a problem cranking.
That power valve is way low I imagine unless that cam is lopey with lower vacuum.
Caution Long Post! Here is a copy of a quick guide to Holley tuning...
Part 1:
Tuning the float level
On Holleys this adjustment is very easy as it can be done without dismantling. With the engine idling take out the sight plug on the side of the fuel bowl. Be ready with a rag to catch the fuel that might run out if the float level is too high. With the sight plug removed, use a big screwdriver and a 5/8”/16mm wrench to adjust (the screw should just be loosened, adjustment is done on the nut). Adjust so that fuel is up to the level of the sight plug hole and just slowly trickles out. Note that if the level is too high and you adjust down, you have to wait until the fuel is consumed or trickled out, which can be an issue especially on the secondary fuel bowl. Also note that if you adjust down too low the nut loses its grip on the float bolt and when you try to get it back up it won’t work. In that situation, stop the engine, take off the screw and nut entirely and screw the float bolt up with your fingers. You may need a new gasket after doing this.
When both floats are adjusted as specified above, you can screw in the sight plugs.
Tuning the choke
Engine should be off during this session. Chokes are tuned by loosening the normally 3 screws, and then turning the round choke housing. Which direction is rich and which is lean is normally seen marked with arrows, if not, try turning it, and note when the choke plate closes (you may need to slightly open the throttle for the choke plate to move), that’s the rich condition, since closing for the air richens the fuel/air mixture, just what a cold engine likes. Try placing the choke housing in the middle of the scale. Then start the engine and drive a normal trip. Note that the engine has to be totally cold, this means not started for 4-5 hours. This means that testing several settings of the choke normally takes days, we often try a new setting when we come back from a trip, then leave it until next morning, and then test.
How does the engine behave. Is there a lot of smoke from exhaust it’s much too rich. If it stumbles, spits, and is not easy to drive, it’s too lean. If it runs fine, then you’re close, but you should try the next leaner setting until it starts to stumble, spit etc., because having too rich a choke setting costs fuel and fouls your spark plugs.
So choke tuning is really trial and error approach. Set it as lean as you can live with.
Tuning the idle mixture
Start with engine off and warm, the choke must have heated enough to not be affecting the fuel/air mixture. Slowly and softly turn the idle screws all the way in, noting how many turns. Make sure you down force them in too hard, it’ll ruin the finely tapered ends, and then you need new idle screws. Were they a similar amount of turns out? In the future they should be. Most carbs we dealt with should start the tuning 1-1½ turn out. If your carb ran fine and it was 2 turns out previously, start there. But in general, turn out both screw 1½ turn.
You now need to hook up your vacuum gauge. If you don’t have one, buy one, see section Vacuum gauge, the wonder tool. Most people that tune cars and don’t have a vacuum gauge, use the tach instead, but tuning based on rpm is a lot more difficult, inconclusive and inaccurate than tuning with vacuum. The vacuum gauge hose should be attached to a permanent vacuum port on the intake or on the carburetor. Do make sure it’s not ported vacuum, or on cars from the 70-80s with plenty of vacuum hoses, some were affected by temperature. Do use the correct port.
Start the engine and let it idle. Automatic transmission cars need to be in drive, so have a friend in the car with a foot on the brake, the parking brake is not sufficient. Look at the vacuum gauge. It should be high and steady. If the needle is floating back and forth more than 2-3 it’s rich. If it’s steady but occasionally drops a little, it’s too lean. If it’s totally steady you’re close to the right setting. If the needle does strange things, troubleshoot your engine.
Now turn the screws 1/8 of a turn. If the vacuum gauge indicates too lean, turn out and vice versa. If the needle is steady, turn in. Do both screws at the same time, then give the engine 30 seconds to settle with the setting. If you got a higher or a more steady vacuum, you’re going in the right direction, try once more. If not, try the other direction. Turn only 1/8 at a time, it’s a lot for the carb. When you get close to the absolute right setting, go to 1/16 increments.
Vacuum gauge Idle Action
Steady, high Good Try either direction for higher steady needle
Steady, high, occasional drop Lean Try 1/8 out until needle is steady with no drop
Floating more than 2-3 Rich Try 1/8 in until needle is steady
When this is done, you’ll end up with a strong steady idle and probably at a higher rpm. So you need to reduce the idle speed to the required level by adjusting the idle screw (not the idle mixture screws we just tuned…).
Some engines with long duration camshafts will not be able to obtain a high steady vacuum. On those engines you need to settle for the highest vacuum you can get, and it wont be 100% steady. That’s the price you pay for a long duration camshaft (but the idle sounds great).
Now you have tuned not only your idle, but also your 0-60 mph driving circuit, and if done correctly, the car will feel much stronger in that area. But as we see in part 2, we’re not satisfied with “feeling” faster, we will test and verify it..
Long Post Part 2:
Tuning the Power valve
As mentioned there are many “power”-systems, many different constructions. On Holleys it’s separate valves you have to buy, install and test.
Holley power valves are not tunable with regards to volume of fuel, only when it’ll start flowing, at which vacuum.
If you car feels strong at part throttle, also up a long hill, then there’s no tuning needed. The power valve is not the main player at fast acceleration, that’s more the accelerator pump, idle circuit and jets. The power valve is to cover for when you take that long hill or overtake on the freeway. If you in those situations feel a stumble or just lack of power, then you should go to a power valve that comes on sooner, at a higher vacuum. Let’s just reemphasize, when you press the pedal down you decrease vacuum, and when the vacuum gets below the vacuum stamped on the power valve it’ll open for extra fuel. Most Holleys come with a 6.5 power valve as standard. Rule of thumb is that you should have a power valve that is at half the vacuum at idle. So if you have 15 vacuum at idle, you should have a 7.5 power valve. The 6.5 power valve will work fine (unless you feel the stumble and lack of power as mentioned) in most cars. But some hi perf engines, especially those with a long duration camshaft, will idle at maybe 10-12, then you need to go a 4.5 or 5.5 power valve.
Some “racers” think it’s smart to take out the power valve and install a plug instead, and then richen up the carb with jets to get to the same end result. Only problem with that is that the carb will be rich all the time, also when it’s not needed, so fuel economy goes out the window, and spark plugs foul. Not recommended
Tuning the accelerator pump
Again here we would say the set up when buying would in 80% be perfect. But if you bought too big a carburetor as many people do, then there’s a bigger “hole” to cover when you smash the pedal to the floor, so more pump shot is needed. There are many things you can change on the accelerator pump. The total volume, standard is 30cc, a bigger pump can be bought pumping 50cc. We’ve so far never seen an engine needing more than the 30cc though. Secondly the speed of the “arm” can be adjusted by changing or moving the colored plastic cam on the throttle shaft. It determines the volume in relation to throttle position. A Holly kit contains the following cams (least pump shot->white, blue, red, orange, black, green, pink, brown->most pump shot). Thirdly the size of the holes in the shooter determines how fast the fuel is squirted into the bores. So adjustments are infinite. Which makes things easier but also more complex. This is not just a screw you can turn.
One thing before we start. Regardless of which colored plastic cam and size of pump (30/50cc) it’s critical to adjust end play when throttle is fully depressed. If end play is too much you lose pump action, if it’s to little you end up destroying the pump. End play is determined by opening the throttle fully (engine off) and then seeing how much further you can press the accelerator pump at the are situated on the fuel bowl. You should be able to create a gap of 0.4mm, adjust spring just above to obtain that.
You need to tune the accelerator pump based on two sets of info. Is it too little or too much? Is it too soon or too late? This must be based on experience when flooring the pedal. First though, let’s get rid of a myth. People that experience a stumble when suddenly accelerating often describes it as “it wont take the gas”. It is in fact the opposite that happens, the engine doesn’t get enough gas to cover the “hole” when the pedal is pushed down, throttles open and vacuum drops. So what’s your experience? Does it stumble or is there smoke out the exhaust? And is that condition immediate or after few seconds?
Stumble Smoke
Immediate 1) 2)
After a few seconds 3) 4)
1) Here the accelerator comes in with too little to late. This can be solved by either changing the cam to one that provides more shot earlier, or a shooter with bigger holes. Notice the spring on the accelerator pump arm? Fluid can’t be depressed, so when the pedal is floored, the spring depresses and only extends as fast as the holes in the shooter allow. So if you need to get more shot faster, it’s the cam or the shooter size. The cam comes in kits, normally with data on each cam. If not, put them on top of each other, you can clearly see which has the most aggressive profile. Shooters are starting around size 0.025”. Go up approx 0.003” at a time until the problem is cured. What’s best, cam or shooter. Well a cam kit is a lot cheaper than various shooters, and in 90% on the cases it solves the problem.
2) This is the reverse of 1). Except that here it’s our experience that decreasing shooter size is more effective than cam changes, maybe because there are no cams radically less aggressive than the standard cam. Anyway, 2) is a rare occasion
3) So initially it’s OK, but after a few seconds it stumbles. This is because all the fuel in the accelerator pump is used up. This results either from too big holes in the shooter or too little total volume of the accelerator pump. If you see smoke on the immediate throttle opening, your shooter is too big, squirting too much fuel in too soon and running out of fuel. If there’s no smoke on the immediate throttle opening, that part is perfect, then there’s just not enough fuel for your engine’s demand, and you need to increase form 300cc pump to 50cc pump. As mentioned this is rare, never happened to us. But then again, we never buy our carburetors too big for the engine, that would necessitate the bigger pump.
4) This is also a rare condition. The shooter size is OK, the immediate reaction shows that. But then it just pumps on and on and thereby too much. It would be logical to decrease pump size from 50cc to 30cc, but we never seen anybody go that way, against human nature maybe. We suggest a milder cam, one that gives less arm travel per throttle movement. Find a cam where the initial lift is the same but the lift after that is less.
If all this doesn’t solve a stumble, it could be because the secondaries are opening too quickly, so let’s look at that.
Tuning the secondaries
First let’s talk about secondaries on double pumpers. You can’t (shouldn’t) adjust the linkage, point of primary throttle position that the secondary throttle start to open should not be changed. Only thing to check is that when the primary throttles are fully open (engine off), the secondary throttles should also be fully open. If there is a problem with the secondaries on a double pumper, it’s usually the secondary accelerator pump that needs adjustment, see previous chapter. We haven’t ever had a need to adjust anything on the secondaries on double pumpers except the mentioned full throttle opening.
Let’s discuss the other type, the vacuum secondaries. In fact some models open based on vacuum, others on flow through the bores. Holleys are the latter, but we still name them vacuum secondary carburetors. Some carburetors keep the plates closed until demand is there with springs, others use weights. Common is that they can be adjusted as to how soon and how much they open. If they open too late, you lose power. If they open too early you get a stumble. On some carbs changing the spring/weight is easy and aids tuning, but on others like the Holley it’s tricky to do on the engine and the choke has to be removed. Fortunately Holley’s made a kit to avoid that, a quick change kit so you can change the spring in 1 minute.
Regardless of whether it’s springs or weight, the procedure is simple. First you should adjust the manual linkage from primary throttle axle to secondary throttle axle. Yes, there is a linkage, also on a vacuum secondary carb, but it doesn’t open the secondary throttles, in fact the opposite, it ensures that they close when the primary throttles are being closed. This is to avoid the engine running on when you release the pedal. What you need to adjust is so that at idle it’s closing the secondary throttle all the way.
Then you can start tuning with the springs/weights. If your car has no stumble you try softer springs/lighter weights until it does, then you go one spring/weight heavier. If you have a stumble, you try heavier spring/weight until that stumble is gone. So you aim for the softest spring/lightest weight that doesn’t make the engine stumble.
Just to clarify, what is a stumble here as compared to what we talked about when tuning the accelerator pump? A stumble here is something that is felt when cruising and the quickly pressing down the pedal slightly, like an overtake manoeuvre, since the extra angle of the throttle axle is small, the accelerator pump doesn’t help much, and maybe the power valve doesn’t even come into play. But the engine will only stumble like this if the secondaries open too early, which in fact more than doubles the size of the carburetor.
Tuning the jets
When everything above is perfect, only then can we start to look at changing the jets.
When the carb is perfectly tuned as described above and smoke comes out the exhaust when the engine is warm, it’s probably too rich. And if the spark plugs are too dark, that would indicate the same thing. Are the spark plugs too white, it indicates too lean condition
Tuning the Power valve
As mentioned there are many “power”-systems, many different constructions. On Holleys it’s separate valves you have to buy, install and test.
Holley power valves are not tunable with regards to volume of fuel, only when it’ll start flowing, at which vacuum.
If you car feels strong at part throttle, also up a long hill, then there’s no tuning needed. The power valve is not the main player at fast acceleration, that’s more the accelerator pump, idle circuit and jets. The power valve is to cover for when you take that long hill or overtake on the freeway. If you in those situations feel a stumble or just lack of power, then you should go to a power valve that comes on sooner, at a higher vacuum. Let’s just reemphasize, when you press the pedal down you decrease vacuum, and when the vacuum gets below the vacuum stamped on the power valve it’ll open for extra fuel. Most Holleys come with a 6.5 power valve as standard. Rule of thumb is that you should have a power valve that is at half the vacuum at idle. So if you have 15 vacuum at idle, you should have a 7.5 power valve. The 6.5 power valve will work fine (unless you feel the stumble and lack of power as mentioned) in most cars. But some hi perf engines, especially those with a long duration camshaft, will idle at maybe 10-12, then you need to go a 4.5 or 5.5 power valve.
Some “racers” think it’s smart to take out the power valve and install a plug instead, and then richen up the carb with jets to get to the same end result. Only problem with that is that the carb will be rich all the time, also when it’s not needed, so fuel economy goes out the window, and spark plugs foul. Not recommended
Tuning the accelerator pump
Again here we would say the set up when buying would in 80% be perfect. But if you bought too big a carburetor as many people do, then there’s a bigger “hole” to cover when you smash the pedal to the floor, so more pump shot is needed. There are many things you can change on the accelerator pump. The total volume, standard is 30cc, a bigger pump can be bought pumping 50cc. We’ve so far never seen an engine needing more than the 30cc though. Secondly the speed of the “arm” can be adjusted by changing or moving the colored plastic cam on the throttle shaft. It determines the volume in relation to throttle position. A Holly kit contains the following cams (least pump shot->white, blue, red, orange, black, green, pink, brown->most pump shot). Thirdly the size of the holes in the shooter determines how fast the fuel is squirted into the bores. So adjustments are infinite. Which makes things easier but also more complex. This is not just a screw you can turn.
One thing before we start. Regardless of which colored plastic cam and size of pump (30/50cc) it’s critical to adjust end play when throttle is fully depressed. If end play is too much you lose pump action, if it’s to little you end up destroying the pump. End play is determined by opening the throttle fully (engine off) and then seeing how much further you can press the accelerator pump at the are situated on the fuel bowl. You should be able to create a gap of 0.4mm, adjust spring just above to obtain that.
You need to tune the accelerator pump based on two sets of info. Is it too little or too much? Is it too soon or too late? This must be based on experience when flooring the pedal. First though, let’s get rid of a myth. People that experience a stumble when suddenly accelerating often describes it as “it wont take the gas”. It is in fact the opposite that happens, the engine doesn’t get enough gas to cover the “hole” when the pedal is pushed down, throttles open and vacuum drops. So what’s your experience? Does it stumble or is there smoke out the exhaust? And is that condition immediate or after few seconds?
Stumble Smoke
Immediate 1) 2)
After a few seconds 3) 4)
1) Here the accelerator comes in with too little to late. This can be solved by either changing the cam to one that provides more shot earlier, or a shooter with bigger holes. Notice the spring on the accelerator pump arm? Fluid can’t be depressed, so when the pedal is floored, the spring depresses and only extends as fast as the holes in the shooter allow. So if you need to get more shot faster, it’s the cam or the shooter size. The cam comes in kits, normally with data on each cam. If not, put them on top of each other, you can clearly see which has the most aggressive profile. Shooters are starting around size 0.025”. Go up approx 0.003” at a time until the problem is cured. What’s best, cam or shooter. Well a cam kit is a lot cheaper than various shooters, and in 90% on the cases it solves the problem.
2) This is the reverse of 1). Except that here it’s our experience that decreasing shooter size is more effective than cam changes, maybe because there are no cams radically less aggressive than the standard cam. Anyway, 2) is a rare occasion
3) So initially it’s OK, but after a few seconds it stumbles. This is because all the fuel in the accelerator pump is used up. This results either from too big holes in the shooter or too little total volume of the accelerator pump. If you see smoke on the immediate throttle opening, your shooter is too big, squirting too much fuel in too soon and running out of fuel. If there’s no smoke on the immediate throttle opening, that part is perfect, then there’s just not enough fuel for your engine’s demand, and you need to increase form 300cc pump to 50cc pump. As mentioned this is rare, never happened to us. But then again, we never buy our carburetors too big for the engine, that would necessitate the bigger pump.
4) This is also a rare condition. The shooter size is OK, the immediate reaction shows that. But then it just pumps on and on and thereby too much. It would be logical to decrease pump size from 50cc to 30cc, but we never seen anybody go that way, against human nature maybe. We suggest a milder cam, one that gives less arm travel per throttle movement. Find a cam where the initial lift is the same but the lift after that is less.
If all this doesn’t solve a stumble, it could be because the secondaries are opening too quickly, so let’s look at that.
Tuning the secondaries
First let’s talk about secondaries on double pumpers. You can’t (shouldn’t) adjust the linkage, point of primary throttle position that the secondary throttle start to open should not be changed. Only thing to check is that when the primary throttles are fully open (engine off), the secondary throttles should also be fully open. If there is a problem with the secondaries on a double pumper, it’s usually the secondary accelerator pump that needs adjustment, see previous chapter. We haven’t ever had a need to adjust anything on the secondaries on double pumpers except the mentioned full throttle opening.
Let’s discuss the other type, the vacuum secondaries. In fact some models open based on vacuum, others on flow through the bores. Holleys are the latter, but we still name them vacuum secondary carburetors. Some carburetors keep the plates closed until demand is there with springs, others use weights. Common is that they can be adjusted as to how soon and how much they open. If they open too late, you lose power. If they open too early you get a stumble. On some carbs changing the spring/weight is easy and aids tuning, but on others like the Holley it’s tricky to do on the engine and the choke has to be removed. Fortunately Holley’s made a kit to avoid that, a quick change kit so you can change the spring in 1 minute.
Regardless of whether it’s springs or weight, the procedure is simple. First you should adjust the manual linkage from primary throttle axle to secondary throttle axle. Yes, there is a linkage, also on a vacuum secondary carb, but it doesn’t open the secondary throttles, in fact the opposite, it ensures that they close when the primary throttles are being closed. This is to avoid the engine running on when you release the pedal. What you need to adjust is so that at idle it’s closing the secondary throttle all the way.
Then you can start tuning with the springs/weights. If your car has no stumble you try softer springs/lighter weights until it does, then you go one spring/weight heavier. If you have a stumble, you try heavier spring/weight until that stumble is gone. So you aim for the softest spring/lightest weight that doesn’t make the engine stumble.
Just to clarify, what is a stumble here as compared to what we talked about when tuning the accelerator pump? A stumble here is something that is felt when cruising and the quickly pressing down the pedal slightly, like an overtake manoeuvre, since the extra angle of the throttle axle is small, the accelerator pump doesn’t help much, and maybe the power valve doesn’t even come into play. But the engine will only stumble like this if the secondaries open too early, which in fact more than doubles the size of the carburetor.
Tuning the jets
When everything above is perfect, only then can we start to look at changing the jets.
When the carb is perfectly tuned as described above and smoke comes out the exhaust when the engine is warm, it’s probably too rich. And if the spark plugs are too dark, that would indicate the same thing. Are the spark plugs too white, it indicates too lean condition
So I need to vent. I HATE ALL THE CHAIN AUTOPARTS STORES IN MY TOWN!!! AUTOZONE, O'REILLYS, ADVANCE, AND CARQUEST NOBODY HAS JETS FOR A 4160. Isn't the 4160 carb a very common carb? Autozone didnt even have a vacuum gauge!!!! For now on I'm ordering my parts online. Last time I went to the chain stores looking for a trans gasket for a 200-4r nobody had those either. Just pisses me off. So now Im putting my carb back together with what I have so I can drive it tomorrow. 😡
So got the carb back together with the same gets unfortunately. Got the car started and set the timing to what I believe is 12 degrees. The mark on the block only goes 0-10 before and 0-4 after. I set it where I believed 12 would be about. When I started it seemed to be around 16-18 it was pretty far from the mark on the block. Then hooked up the vacuum gauge. Highest reading I was getting was bouncing between 8-10 with the mixture screws one full turn out from seated. Anything farther out it would stay steady at 8. Reved it up by moving the throttle by hand and still have the hesitation. I think I may have another un related problem also that I'm very worried about. After I reved it up and it was coming down it sounded like there was something rattling around in the passenger side valve cover. I checked and the oil says full on the dipstick. Anything for me to start checking there?
Edit: Just started the car again and the idle vacuum is now running around 12-13 which seems more correct cause tje cam paperwork says it shold be at 12. I will order a 6.5 power valve when I order new jets later. Or should I go with a 5.5?
Edit again: I know why there was a difference in vacuum the second time I did it. Not thinking the car was in park idling. The first time the gf was in the car with it in drive and foot on the brake like the holley instructions said. So which vacuum reading should I use to decide power valve? If I go with the 8-10 reading I would say the 4.5 thats in the carb ia good. If I use the 12-13 I should go up in power valve size.
Edit: Just started the car again and the idle vacuum is now running around 12-13 which seems more correct cause tje cam paperwork says it shold be at 12. I will order a 6.5 power valve when I order new jets later. Or should I go with a 5.5?
Edit again: I know why there was a difference in vacuum the second time I did it. Not thinking the car was in park idling. The first time the gf was in the car with it in drive and foot on the brake like the holley instructions said. So which vacuum reading should I use to decide power valve? If I go with the 8-10 reading I would say the 4.5 thats in the carb ia good. If I use the 12-13 I should go up in power valve size.
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You go off of your vacuum in gear, so yep the 4.5 PV according to your readings.
Just a quick question, does your idle speed drop a lot when put in gear compared to Park? Reason I am asking is because I think the converter is too tight and causing some of your lag down low. I know a new converter costs some coin, but getting the right converter for a setup makes a hell of a difference compared to one that's not quite right. Not saying this is the cure all but I'll bet it's some of the problem.
Just a quick question, does your idle speed drop a lot when put in gear compared to Park? Reason I am asking is because I think the converter is too tight and causing some of your lag down low. I know a new converter costs some coin, but getting the right converter for a setup makes a hell of a difference compared to one that's not quite right. Not saying this is the cure all but I'll bet it's some of the problem.
It depends if the car is warm or not. If the car isnt warm and I put it in drive from park it idles at 800 and drops down to 6-700. When it's warmed up there isn't a noticable difference. im running a 200-4r trans fresh rebuild with shift kit and some other stuff from midwest converters. Just put in this spring.
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