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Discussion Starter · #1 ·
Ive got an 86 El Camino with a 305 . I just swapped the cam for a summit 1102 and new Edelbrock performer intake, im trying to get the old quadrajet dialed in. It sputters and tries to die when you stab it like its not getting enough fuel. I think stock primary size is 72 summit has a 73 or a 76 . Does anyone have a guess on what jet size it may need?
Thanks for your time.
 

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I am really not an expert on the Qjet as there is so many variables on what metering rods and jets are in them as they were all calibrated for what ever said vehicle they were put on since they were a factory made and tuned carburetor vs an aftermarket carb which will have a starting tune out of the box that will have to be changed and adjusted for whatever the application its going to be on. First off you might want to check your timing and make sure your ignition system is all up to par and that you have the correct timing curve with your engine before messing with your carb. Timing plays a very critical role in how the carb and everything else will respond.

I once had a problem after I changed out my coil and moved my distributor and thought I put it back in the right spot where I marked it and I also put a different carb on and for the life of me understand why I had a big stumble and no amount of adjusting my carb would change it and I was chasing my tail on it. I finally got my timing light out and checked it and even though I was almost spot on with my mark I still was off enough to have ten degrees of timing lost because I did not have it advanced enough at idle. Once I reset it all my problems went away. As far as your Qjet goes I could not tell you where your carb would be at factory settings as it would have been calibrated most likely with emissions put in the tune and most likely won't be correct for anything for performance wise.

Get the book listed below and it has a lot of great information on tuning and modifying them to work on performance builds and such. I wish I could help out more but I honestly don't know where to start on that one as unless the carb is stock trim from what it came with the factory it could be anything and just like an Edelbrock there are different metering rods that work in relation to the jets and many different combos can be done there. I also would maybe check to see if your secondary air valve is not opening up to quickly causing the bog your talking about. You stated it when your getting into it real fast and that could be the secondary side opening up to fast causing the bog or stumble.

I would recommend the book by Cliff Ruggles called "
How to build and modify Rochester quadrajet carburetors" by Cliff Ruggles
 

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Discussion Starter · #4 ·
Thanks guys. I replaced the old electronic advance distributor with a vacuum and couldn't really say where i set the initial timing. I advanced it to where it got the best vacuum at idle. Timing is a good place to start and doesn't cost a thing to adjust.
 

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Discussion Starter · #6 ·
Yes i broke in the cam. I ran it 10 min at around 2800 10 minutes at 2500 and 10 at 2000rpm with maxima break in oil. These numbers are approximate as i dont have a tachometer. Then fresh lucas classic car oil with zink. It seams to have been successful, i don't hear any valve chatter at all.
 

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My last 305 at sea level liked 14 Initial.
at elevation you likely need more. You gotta start the burn earlier.
and you might need to lean down the jetting.
bump your timing up first.
 

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That’s a pretty mild cam it shouldn’t be creating problems with jetting or timing.

The stumble is it all the time or just momentarily with the throttle at WOT?

Temporary stumble is usually accelerating pump settings. All the time is lack of power enrichment which on the Q-Jet is where the metering rods raise to the rich setting, that is a manifold vacuum versus spring pressure on the vacuum piston in the carb. This can also be too much secondary air valve too soon.

Stumbles and stays that way can be main metering which encompasses metering rod and secondary air valve timing as described above but the stumble doesn’t go away or it can be ignition from module and coil issues to secondary high voltage plug wires to the plugs themselves often fouled or gapped too wide. Plug gaps of .030 to .035 is plenty, forget this .060 stuff.

Bogie
 

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Discussion Starter · #13 ·
That’s a pretty mild cam it shouldn’t be creating problems with jetting or timing.

The stumble is it all the time or just momentarily with the throttle at WOT?

Temporary stumble is usually accelerating pump settings. All the time is lack of power enrichment which on the Q-Jet is where the metering rods raise to the rich setting, that is a manifold vacuum versus spring pressure on the vacuum piston in the carb. This can also be too much secondary air valve too soon.

Stumbles and stays that way can be main metering which encompasses metering rod and secondary air valve timing as described above but the stumble doesn’t go away or it can be ignition from module and coil issues to secondary high voltage plug wires to the plugs themselves often fouled or gapped too wide. Plug gaps of .030 to .035 is plenty, forget this .060 stuff.

Bogie
Thanks bogie, It stumbles and stays when i try to go from idle to WOT, it wont pick up until i let off. At partial throttle it runs great. It seams very possible its getting too much from the secondaries too soon, but im not sure how to adjust those. Or it could just as well be metering rods
 

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Discussion Starter · #14 ·
Well gents im back feeling like a dog chasing his tail. I set timing at 14 degrees initial no change. I disabled the secondaies and it still stumbled with no power. Im back to thinking it's too rich or more likely too lean. 1 size larger primaries 4 sizes thinner rods? Any feedback?
 

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How fresh are the plugs and what is their gap?

Whose distributor are you using by model or part number, same for coil if not native to the distributor.?

Where is the ignition primary voltage coming from?

Bogie
 

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Discussion Starter · #16 ·
Summit 850001-1 distributor. The plugs are a little old and crusty but they worked before the cam swap. I think the distributor power is coming from the ignition, it's the factory wiring.
 
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