I just installed a 421 sbc in my 88 Olds Cutlass. After breaking in the cam, running the engine at 2000-2200 rpms for 20 minutes, I went to adjust the idle speed screw to bring it down to idle. When I got to about 1500 the engine just cut off. When you squirt some fuel in by pressing the gas pedal twice and try to start it. It seems to try to start then nothing. While I was breaking in the cam and had the engine at 2000 rpm i the timing was at 25 degrees. After adjusting the idle speed screw I just can't seem to figure out why it won't idle. It is basically and new speed demon, I only had it on my previous engine a week before I bent a valve in it. I dumped the fuel out of the bowls before it was stored for a year or so. Any help would be great.
Engine won't idle
- Thread starter 88olds421
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I'd take the carb apart and clean it...you may have some gel in the idle circuit from fuel left there while it was on the shelf...
check for vacuum leaks , If you just got it running to break in your cam, you may need to adjust the initial timing on it also.
Even with 25 degrees at 2000 rpm. The distributor was set up to be all in at 3000 with 20 degrees of mechanical advance. Do you guys think 3 or so degrees would keep a car from idling. In my previous experience I usually ran between 12 and 14 degrees of initial advance, the engine would still idle at 8 degrees of advance. So you think I should advance the timing more than 18 degrees initial just to get it to idle.
Well, after messing with the timing and advancing it still the same result. You can hear a few cylinders fire but then just stops, sometimes the engine will spin over backwards after stopping. Looks like it is time for a rebuild of the carb.
88olds421 said:
if it's spining backwards looks like to much advance, also if you are running a holley check to make sure your squirter is working i had this issue once before myself
It is a demon carb, the squirter works fine. That is what I thought as well that I had a bit too much timing, even when I retard it some still just a few cylinders fired then nothing. So at this point I have the carb disassembled and ahve soaked the parts in parts cleaner over night. I am going to finish cleaning them up tonight. Probably going to have to order the new gaskets cause all the parts stores around here have just the holley gasket sets and not ones for demon.
Well, after having the 650 demon apart many times, I went and bought a new 750 Holley and thinking that would fix my issues, well it didn't. I am completely lost. I had someone crank the engine and I put the timing gun on it and have it at 13 degrees initial. I check for spark on the #1 and #2 cylinders, and I do not have any vacuum lines running from the car, everything is plugged just like the Holley came from the factory. I just cannot figure out why it will only fire a few cylinders then stop. There are also new plugs, wires, and cap and rotor. Any help would be great.
You weren't very specific about your engine specs so I'll have to make some assumptions. A 421 is a huge SBC so it probably has a huge (long duration) cam. That means low manifold vacuum - especially at lower RPMs. Carburetors are vacuum operated. Pull all your plugs and see if they are fuel fouled. If they are, replace them and see if you can get it started again. Then it's time to make some adjustments.
I had a similar situation while breaking in a small block with a long duration cam and a stock tuned carb. At anything below @1800 it would choke out. The low vacuum was causing 2 things; the power valve would open (go rich) and fuel would pull through the primaries. This would cause the engine to die and be nearly impossible to start. I dropped down to a 5.5 power valve from the 7.5 that was stock in my 3310. You probably have a 6.5. I then adjusted my secondaries open just a crack. That allowed the primaries to be closed which let the idle circuit work properly. At that point I was able to run it enough to do jetting changes as necessary. Good luck.
I had a similar situation while breaking in a small block with a long duration cam and a stock tuned carb. At anything below @1800 it would choke out. The low vacuum was causing 2 things; the power valve would open (go rich) and fuel would pull through the primaries. This would cause the engine to die and be nearly impossible to start. I dropped down to a 5.5 power valve from the 7.5 that was stock in my 3310. You probably have a 6.5. I then adjusted my secondaries open just a crack. That allowed the primaries to be closed which let the idle circuit work properly. At that point I was able to run it enough to do jetting changes as necessary. Good luck.
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