new carb issue

[fdbdw]

71 c10 350 hei
Just installed a performer eps manifold and 1406 carb, previously had a 2bb roch. It seems to bogg down a little when I step on it, was wondering if the timming should be advanced more than prev carb and or go a little tighter on the lifters, I have the timming set at 10btc manual calls for 8 but living at high altitude 10-12 works better, valves set at 1/2 turn after zero lash, wodering if 3/4 and or 12-14 btc would be better for my new app, any thoughts or ideas, thanks

[hilandr452]

Shout out to a fellow Colorado Springs guy!

I've always used the 1 degree advancement for every 1000 feet above sea level, which would put you at 14 or so since we're at 6000 feet here. You can fine tune it after that on the carb side usually.


Dan

[fdbdw]

Hey dan, thanks, its good to get info from someone who also has to deal with altitude issues

[ChevLoRay]

1406....manual choke? If so, it's jetted richer than the 1405, which has an automatic choke. I had the manual choke model on my 350 in my '69, and it had issues with running rich and gas-fouling spark plugs. A change to an Edelbrock Q-Jet solved those problems, even though I went from a 600cfm to a 750cfm.

[nicolas72gmc]

I'm having that same issue right now only on a 1407 and I am about 800 ft. above sea level. I have my timing at 14 degrees. What you describe is exactly what mine is doing. Does it level out and kick hard after the stumble?

[fdbdw]

na 1406 is electric choke 2% leaner than the 1405 manual choke, it doesnt run bad its just that it sounds a little bogged when secondaries kick in, has me leaning toward more timming advancedment, planning on getting headers soon Im sure the old ram horns are holding it back a bit also

[jim zag]

Accelerator pump and squirter size kind of typical EDELBROCK tuning problem. You need more initial SQUIRT!!!

[dznucks]

Not tryin to hijack here......but i have an EPS manifold and a 1406 and i have pulled all my hair out trying to fix this same problem.

mine runs great as long as your in the cruise mode. In part throttle and WOT it doesn't feel quite right. its a very slight stumbling is the only way i know to describe it. as soon as you back out of the secondaries and the vacuum overcomes the step up springs, returning to cruise mode, it takes off like a scalded dog. i have been all over the calibration chart, moved my timing from 10* all the way up to 18* (16* gives me a max mechanical of 36*). tried every dizzy wieght spring combo and i still cant get it to act right.

Does this sound similar to your porblem? i am not at altitude but i am almost to the point of shooting the damn thing. i am very interested in knowing the solution.

[dznucks]

do you have a fuel pressure regulator? edlebrocks are notorious for being picky about their pressure. i have been running mine at 5.5psi as edelbrock recommends. but i just read a post from 70rs/ss where he sais to keep it at 4 psi or else it will run rich.

i am going to dial mine back and see it that helps.

good luck and keep us (me) posted on what you find out.

[fdbdw]

advanced the timming to about 14 hard to know exactly cause its off the mark, did tell some difference gonna try about 16 or 18 also gonna order some headders. with secondaries bringing in more air Im thinking ram horns cant get it out

[mclairmo]

I always thought a stumble was usually caused by a too rich condition, especially at high altitude where you have less oxygen to mix with the fuel. Less oxygen demands less fuel. I would focus on the carb since that it what was changed. If you had no stumble with the 2 barrel, the new carb must be the culprit. Maybe lean out the secondary circuit or have it come in later? Headers should help as will getting more cool and dense air into that carb.

[dznucks]

I dropped my fuel pressure to 4 psi from 5.5psi and that got rid of that stumble in part throttle and WOT. now it seems to run out of steam at WOT. i might need to fatten up my secondaries.

from my experience the ram horns are about as good as your going to get unless you've got a tricked out motor. i had shortie block huggers before and went back to my ram horns.

[fdbdw]

my understanding is that if you want to noticable difference you need to go with long tube headers and that shoties and ram horn yeild about the same results, i hoping that a set of long tubes will lean it out just enough and provide some better air flow, any thoughts on this

[dznucks]

Ram horns were used on the older vettes with 4 barrell carb'd engines that put out more power than our stock engines do.

Your right the long tube headers have different flow and thermal characteristics than rams or shorties. I have always understood that long tube headers are better for high torque or high rpm applications. ie. racing, highway driving, towing. not a DD.

I have a manual tranny so i could never go with long tube headers without using a slave cylinder or switching to auto. so i cant speak form experience.

I am not saying the headers wont improve things, but i doubt the problem you originally described will be solved with them.

Have you read the Timing FAQ? if not check that out, its pretty good. Again if you dont have a fuel pressure regulator on the edelbrock carb, you are running rich regardless of the tune. your stock fuel pump puts out way too much pressure causing fuel to blow by the needle and seats, especailly in the secondaries. check your 1406 owners manual, they say 5.5 but that is way too much as i just found out. 4 psi works much better. i have been chasing your same problem ever since i put on my 1406.

[dznucks]

hopefully it attached, but here is a pic of my regulator, its on the passenger fender.
its a holley regulator and a glycerin filled gage from grainger. you can get both for under $60 total.

[fdbdw]

put in a pressure regulator, tried every pressure from 5.5 and lower ran out of juice wot, advanced the timming more and ran pretty good, either the pressure wasnt the issue or the regulator is bad, thanks for all the help