71 c10 carb troubles

[71_bowtie]

hey guys, i could use some ideas.....I recently put an edlebrock performer rpm manifold on my stock 350 with a holly 4160 carb. it ran great for a while then had some issues. then i switched to a 1406 edelbrock and it is running pretty good, but it seems like it wants to sputter and backfire when shifting in to secound. by the way it has a turbo 350 trans. but higher rpms seem to be fine. you guys have any ideas on what to try? thanks for any input you may have.

[CC69Rat]

Where's the timing now? When you put the intake on, you had to remove the dizzy .. maybe it's a tooth off? I'd be curious to put it on a timing light and start there .. Try it at about 12deg btdc. Was it originally a 2 barrel 350? (assuming so) With that intake you should be able to handle a little more timing because you are pushing a little more gas / air mixture down it's neck. Headers or anything? Tells us more about the motor. Just a stock 350 with the intake and carb? Is your 1406 right out of the box?

[oldblue1968chevy]

timing light and fuel pressure.......

[domeier]

Check your vacuum lines and distributor advance dashpot. I just had mine go bad a little while back. Caused it to run a little rough at idle, and hesitation when accelerating.

[71_bowtie]

sorry, i posted in a hurry this morning. the manifold is a performer eps, not an rpm like i posted. yes was a 2 barrel.yes it has headers with glass packs and side exit exhaust (true duals) new points & condenser(set @ 31*) (.019 point gap), new cap, new rotor, distributor is correct, vac lines are new, fuel pump is new(and the stock 4brl replacement) new fuel line & filter to carb, timing is @ 8*btdc, adjusted the carb like they showed on dvd, it appears the problems are on the even side of the motor....the backfiring is on the even bank of engine....i used the carb on another car and it work awesome. am i needing to check my valves? could my tranny modulator be causing this? thanks again

[domeier]

Originally Posted by 71_bowtie

...i used the carb on another car and it work awesome.

So, just put that other engine in it.

Kidding. Don't shoot.

A burned valve would do that, but it would have been the same when you had the 2bbl on it. If there's nothing internal wrong, I'm guessing manifold leak, exhaust or intake... or maybe a bad plug? You could swap the plugs from left to right and see if the problem moves.

[CC69Rat]

Broken rocker arm or possibly weak valve spring (?) Something is causing it to fire with the exhaust valve open too early. Is it always the same cyl? I'd pull the plug and maybe see if one plug looks different? A good clean fire should be a chocolate milk brown color. Does it have a big cam in it? Wow, tough one.

[71_bowtie]

stock cam as far as i know, just put new plugs in it. after i put the edelbrock manifold on i put a holley 650 on it...it ran good and sounded sweet. but then it started to backfire on then even side. so got a new edelbrock and put it on, still had the sputter/backfire on the even side. the edelbrock is a 600 and the exhaust sounds louder then with the holley. it's hard to tell over the exhaust, but there may possibly be a slight tic on that side also. the plugs i took out were about a year old and didn't look that bad.i'll try to post a couple pics of the truck...i call it copperhead

[domeier]

If I were you... I'd think about the following:

1) You put the carb on another engine and it worked properly, so you can rule out the carb.

2) You're pretty sure the ignition and vac lines are all good, so you can rule those out too, (only if you're dead positive it's all good.)

3) So it's either a valve problem or something simple that you're passing by.

What about the carb gasket? I had one suck partway into the manifold once, before I got the right adapter under my 1406. Do you need an adapter plate for that manifold/carb setup?

4) Big PITA, but you could always put your 2bbl manifold and carb back on just to see what happens.

It sure sounds like a vacuum leak to me.

Good luck.

[RUSHNBOBO]

great advise from above ....one thing that jumps out at me is when you said "shifting into second"....your vacuum drops off at this point and if your secondaries have crashed in to soon it will overwhelm the engine's air fuel needs. I've never had a edelbrock carb but holley type carbs will do the same thing.

Diagnose by going one step at a time to a stiffer spring on the secondaries ...or whatever system edelbrock uses...until the "bog" goes away, then you know it's set. Heavy trucks amplify this issue and almost never run right out of the box.

I run a BG speed demon and had to go 1 spring stiffer to get rid of the secondaries crashing in to soon. This bog , if bad enough will damn near sound like the motor wants to die until it catches up to the added carb flow.

Just a thought...and easy to check...could certainly be something else as noted above though...good luck

[71_bowtie]

thanks for the ideas. one other thing ...the edelbrock says it id designed for 6psi fuel pressure. the stats on the new fuel pump i put on are 7.5psi. you think a regulatur is needed? thanks again... i'll keep checking things over again.

[MacGyver72]

I'll give you one more thing to check and to consider. Do a leak down test to make sure you haven't got a valve stuck open. Also, check your heads for intake size. If I'm not mistaken, two barrel motors used 1.72 intakes. You need 1.94 for a four barrel at least. 2.02 are the high horsepower double-hump heads everyone looks for. Check the numbers on yours and research them. You may not be burning all the fuel.

[oldblue1968chevy]

I noticed a big differnce when first starting the truck (wouldnt idle for crap when I had8psi or whatever it was from stock fuel pump).

Started/idled alot better I set mine at 5.5psi

Check and make sure your adv in your distributor under your rotor button isnt siezed up.