350 sbc bogs and sputters at moderate acceleration

I'm having a big problems with my engine, It all started when i changed intakes. it sputters and bogs when it gets under load in gears. Idles and revs fine in Part unless I cant seem to adjust the idle speed to anything less than 850 rpm's Carburetor is Holley Truck Avenger and the distributor is MSD Street Fire HEI that is new with Taylor wires and the plugs are gapped at 0.040" It dies not matter if the ignition timing is at 35° or 38° w/o vacuum advance connected. 14° / 17°base time. What i think is the problem is either the carburetor or spark plugs. Because it didn't get any better when i changed back to the intake I had on it earlier. It pulls around 16" vacuum at idle. A little less i would say. Suspect a little vacuum leak maybe ?

Best regards.


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It also seems to run fine from dead stop at wot through 1-2 gears. but while cruseing it starts to bog and sputter if i go anything more than maybe 3/8 open throttle ? It idle's and revs without all problems in Park and Neutral gears.
I did lent in a backfire while changing intake manifold because not all them plug wires were in their right places. Could that have damaged my Power valve and it could be root to all my problems ?

Sounds more like a timing issue to me, maybe a bad vacuum advance canister or stuck mechanical advance. Have you verified timing throughout the rpm range with a timing tape or dial back light? If it is always a partial load situation, I would lean toward the vac can... or you might have a leak somewhere that is really throwing it off.

It does it with the vacuum advance disconnected also. The distributor is maybe 4 month's old so i highly doubt it's the distributor itself that's making my life living hell. Did put in new spark plugs and wires also at that same time.
Mechanical advance is also good. at least when i put the timing light on it. It has tape on the damper. I'm suspecting a vacuum leak but with 15-16" Hg vacuum i find it not very likely.

Could this be related to it running rich ? these days we have very cold weather, around 18-19° F And one thing that keep's me anxious about this it that i cant get it to idle below 900 rpm. Then it's like it doesn't matter how far out i screw the idle adjustment screw !!! I'm also only getting 15" Hg vacuum at idle

350 chevy - bored .030" over
11:1 compression
L98 Aluminum heads 58cc
Edelbrock Streetmaster intake. Low rise single plane
Holley Truck avenger 670 cfm carb. 69 Jets front 6.5" Pv 89 jets rear and 31# squirter
MSD Streetfire Hei distributor. New with Taylor spiro pro wires. 14° idle and 35° at 3000 rpm.
Spark plugs are black and sooty but they do not have oil or fuel on them.
Headers and dual 3" exhaust
drove it around earlier today and it only sputters when under load at mid engine speed. It runs clean and seems to work very well at Wot.

Hope this clears things out as i'm getting really furstrating about this engine.

When the engine is fully warmed up is the electric choke completely open? It sounds like the choke fast idle cam on the passenger side is engaging, causing the high idle speed that cannot be lowered using the curb idle screw adjustment.

Look closely at the passenger side of the carb and find the fast idle cam and assembly. Be sure it's disengaged once the engine is warmed up and the choke is off. You might need to adjust the choke cover to a "leaner" setting.

Thank you for your advice sir
If the fast idle cam does not engage would that be enough just to leaner the fast idle mixture ? (slowing things down) to let the fast idle cam disengage ?
It certanly might be my problem it it runs with the choke on a bit all the times. Than atleast it would be rich as hell. I will let you know how the status will be tomorrow. after i Will thoroughly go through this carburetor

BEST regards

The choke has to be FULLY open once the engine is warm.

If the fast idle cam is engaged, it is just like you turned the idle speed screw to raise the idle speed- except it is on the other side of the carb. If you adjust the cap on the electric choke so the choke is fully open when the engine is warmed up, the fast idle (if it's adjusted correctly) should not be engaged anymore, and the idle would then be controlled normally, by the idle speed screw on the driver side- the one you're used to using.

Instructions on setting the choke is HERE, Page 9.

The choke plate is not fully open when warm, How do i fix this problem ? It's maybe 1/4 open

You have to turn the black plastic choke cap clockwise. It's all in the instructions I linked to in my previous post.

The choke needs electricity to work. Be sure the choke is connected to a 12V switched source.

Thanks again sir. I did that and it opened up. But i still find the adjustment on the fast idle cam strange. If i turn the cap counter clockwise it opens the choke plate as it should and then i can just play with the fast idle cam with hand... If i put it all the way down as the choke plate would open up the engine just dies..

Another problem, When adjusting the float on this carburetor. Is it normal that when i loosen up on the lock screw on the needle assembly gasoline just pours up through the needle hole. But still theres no gas coming out of the side hole on the fuel bowl ?

Best regards.

On the choke fast idle deal, I'm not sure if I'm following you. From HERE:

If you're saying the engine dies w/the choke on and the fast idle off, that's normal- the engine needs to have a higher idle w/the choke on.

HERE is a post on setting the choke on an Avenger, also you might want to do a search there and elsewhere for info on setting the choke.

You can get leakage at the adjusting nut/lock screw of the needle and seat when setting the fuel level. I don't know if you would call it "normal" but it happens to me all the time.

You don't want fuel spilling from the hole w/the carb level. The fuel level should be right at the bottom of the sight hole.

i now have adjusted the floats and i am still experiencing hesitation upon acceleration off idle, what's the best way to cure that problem ? could it solve the problem going with bigger jets in the primaries ?

Hesitation off idle is usually the accelerator pump circuit. It's controlled by the shooters and the pump cam. Holley's instructions are on page 6 and 7 HERE.

thank for your help sir, by this reeding it seems to me i should try to decrease the size of the squirter, i'm running 31" squirter now, i'm also going to put the cam in position nr 2, also seems to me it would be ok to go to bigger jets in this cold climate im in. Im running 65 front 79 rear with 8,5" power valve, im pulling about 16-17" hg vacuum at idle now.