qjet or distibutor issues on 455

[wskirvin]

Okay guys i'm lost here and looking for some advice. I have a early 70's qjet that i bought "rebuilt" from a guy, well it ran pig rich and couldnt lean it out at all. so i took it to a shop here in Indy and they went through it again, found the choke linkage was bent as well as the wrong float was installed and was sticking. well they got it back together. i bolted it on my 455 (bored .030 with a 230/236 and 112.0 lobe sep) and it fires up, idles great around 850-900rpm. put it in drive and it stays around 650-700rpm until the engine is hot (above 180) then in gear it starts to bog out and almost die. I can power brake it and it will stay running... let off and it will die down again and barely stay running. put it back in neutral or park and it does the same until i bump the rpms up and then itll idle again just fine. shut the car off and then go to restart it and you have to give it some gas to start back up again. i'm kinda lost on where to look next..... not sure if its a carb issue or possibly an vacuum advance issue on the distributor. this only seems to happen after being in gear and driving. itll idle in park no issues at all other than smelling just a tad rich. short of sending the carb off to be rebuilt again(this time by everyday performance)...... im not sure what else to check. The distributor is used, it was in the engine before rebuilding it. only thing thats been done to it was I put in the pertronix HEI tune up kit. i never changed the springs or bushings in it though. and when i set the timing, with the advance unhooked and plugged, the it is about 12*before tdc on the timing pointer. seems to like it there the best and when i hook the advance up, it idles great. i dont believe it is a choke issue but i could very well be wrong too. anyone have any pointers or ideas on where to start? getting tired of just throwing money at it with the same results.

 

[pagrunt]

First question to ask is did they mess with any of the linkage screw stops? Might have to readjust back to a setting for idle. I'm just going with a general trouble shooting suggestion to see if it's just something simple.

 

[wskirvin]

First question to ask is did they mess with any of the linkage screw stops? Might have to readjust back to a setting for idle. I'm just going with a general trouble shooting suggestion to see if it's just something simple.

i honestly have no idea. i'm not sure if they have been touched or not. i'm very new with quadrajets and i know the mixture screws as well as the idle screw for the throttle but any other adjustments are greek to me lol last carb i had was an old 600 cfm edelbrock on a 307 about 12 years ago.

 

[pagrunt]

Then it might just be better off to get the engine to operating temp (atleast 180) & do a basic set of the idle & timing again. Might need to adjust the air/fuel mixture.

 

[fleming442]

I think the idle is too low for the cam duration. Bump it up some.

 

[olds307 and 403]

I put the idle at 1000 in park minimum. How old is the fuel pump, it could be dying. Also use an inline filter vs the one in the inlet housing. You could try one light and one medium spring or two medium springs and go from there. That is also low initial timing, you could be way short on total timing. Some Olds HEI have more mechanical advance, most do not. Be happy that carb idles at all with that much cam. My 403 carb would barely idle with the 204/214 cam just upping the compression from 8 to 9.6 to 1.

 

[wskirvin]

I put the idle at 1000 in park minimum. How old is the fuel pump, it could be dying. Also use an inline filter vs the one in the inlet housing. You could try one light and one medium spring or two medium springs and go from there. That is also low initial timing, you could be way short on total timing. Some Olds HEI have more mechanical advance, most do not. Be happy that carb idles at all with that much cam. My 403 carb would barely idle with the 204/214 cam just upping the compression from 8 to 9.6 to 1.

I'll definitely try that. What carb are you using now and do you still have any issues? i've kicked around the idea of swapping to a holley or a quick fuel carb after reading with the size cam i have there was a chance the qjet would have issues.

 

[wskirvin]

Then it might just be better off to get the engine to operating temp (atleast 180) & do a basic set of the idle & timing again. Might need to adjust the air/fuel mixture.

yeah i've done that 3 times now and all the same results. thats what has me stumped.

 

[GPNX]

first thing i would do is get total timing set right without vacuum advance you will have to turn throttle screw up with no vacuum advance hooked up. initial timing doesn't mean much on a non stock engine. i start at 30 degrees full advance run wide open throttle. keep bumping it up 2 degrees until you hear denotation or loose power then back it off a couple of degrees. After that hook vacuum advance to full manifold adjust throttle screw. drive around at cruising speed and if you can adjust vacuum advance canister do the same thing as the full timing bump up around 2 degrees until you loose power or hear denotation. then back off a couple of degrees. if it is a pontiac engine you should have around 32-36 for total timing without vacuum advance and 12 more with vacuum. after that make sure you have the right size metering rods and jets in carburetor. cliff ruggles quadrajet book is great on how to set one up. after that you can set the idle mixture screws. quadrajets are in my opinion the best carburetor but can be time consuming to set up right.

 

[olds307 and 403]

I'll definitely try that. What carb are you using now and do you still have any issues? i've kicked around the idea of swapping to a holley or a quick fuel carb after reading with the size cam i have there was a chance the qjet would have issues.

I had Everyday Performance go through the 403 Qjet and retune/rebuild it, night and day difference. Also check for slop in the throttle linkage on the carb, it may be worn enough and causing a vacuum leak. Worn throttle shafts are a known issue on Qjets.