Thread: Secondary woes

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Originally posted by 79C10
Okay heres the deal, I have a fairly new SBC 350 slightly modded with an Edelbrock performer intake, headers and a rebuilt quadrajet. The deal is that I'lll be cruising down the freeway around 65MPH and I'll open up the secondaries and the engine will start making a popping noise (backfiring/too rich?) at the same time the engine shutters slightly, It only seems to do this when im around 65-70MPH. On the other hand I can be cruising around 45MPH with it whining at 5000 RPM with the secondaries open and it performs top notch. So I don't think its related to engine speed.

EDIT:

It won't shutter/pop at anything slower than 60MPH

And if it matters Im running a 700R4 tranny.

Sounds like jets and/or secondary spring need tuning. Also, you need to check fuel level in the bowl. Sounds lean. Could be in the accelerator pump also.

Yea, I ruled out the "lack of fuel" thoery, my fuel pump is fine and I've removed my external filter, as my internal one is brand new.

Originally posted by 79C10
Yea, I ruled out the "lack of fuel" thoery, my fuel pump is fine and I've removed my external filter, as my internal one is brand new.

Don't rule out 'lack of fuel' just yet. The carb jetting and squirter and accelerator pump needs to be checked out. Jeg's sells a hi-performance calibrating kit for your carb. You may need it and a good manual on Quadrujets. That's a lean pop and it may just be caused by the secondaries opening too fast or the jet's too lean in the secondary side.

Originally posted by 79C10
Yea, I ruled out the "lack of fuel" thoery, my fuel pump is fine and I've removed my external filter, as my internal one is brand new.

if you have the brass filter you can't look at it and tell whether its stopped up or not. they will stop up from sitting and look good. if you don't know how long it's been in the carb. put a new one in anyway. same thing with the paper one also.

Originally posted by lt1s10
if you have the brass filter you can't look at it and tell whether its stopped up or not. they will stop up from sitting and look good. if you don't know how long it's been in the carb. put a new one in anyway. same thing with the paper one also.

I just recently had the carb rebuilt and im pretty sure its brand new because I can look at it and see that its pretty clean, Its one of these http://store.summitracing.com/partde...=115+%2D128245

I pulled the plugs and they look like...

http://www.xylicon.com/box/otherstuf...hand_small.jpg
http://www.xylicon.com/box/otherstuff/spark.jpg
http://www.xylicon.com/box/otherstuff/spark2.jpg

Originally posted by 79C10
It only seems to do this when im around 65-70MPH. On the other hand I can be cruising around 45MPH with it whining at 5000 RPM with the secondaries open and it performs top notch. So I don't think its related to engine speed.
It won't shutter/pop at anything slower than 60MPH

i have no real chevy-specific experience yet (just european engines), but ill put my 10 cents worth in as ive been taking advice with out giving any...

it seems very strange that it never happens below 60mph. as you say, it looks like its not related to engine speed. could there be something that happens to your ride only over 60mph? by this i mean some kind of wheel speed related vibration which then causes some other prob with the carb? prehaps wheel bearing or something? i know most fuel bowls really dont like been shaken around too much (even if its only a small high frequency vibration that aint that noticeable)

prehaps the increased air pressure/ram effect through the grill at speeds over 60mph (and prehaps therefore the airpressure into the airfilter/carb) can cause probs with the carb operation when the secondaries are opened?

i'll be quiet now and crawl back into my beginners box

lobster