I am sure someone can put their finger on this. I have a mildly modded rebuilt 289, 4.030 bore 9.1:1 compression, edelbrock performer rpm cam/heads/intake, and edelbrock 600cfm carb, and a rebuilt AOD.
my problem is that from a stop under hard acceleration, the car runs pretty good. but when crusing at ~50mph in 3rd of 4th, SOMETIMES it will stumble when giving it pretty good gas and then "catch up" about a second later. It is not every time, only SOMETIMES, so it makes me think its the carb, but could it be a timing issue? I am running 15 degrees at idle (1000rpm) in park, and 36 total at 3000rpm. I haven't messed with the vacuum much...
I wonder if I should switch to a holley carb or the edelbrock is good enough.
Install a known-good Holley or 4100 and compare. Could be the air valve timing/operation or accelerator pump circuit. Any difference between part-throttle acceleration in 3/4 vs full-throttle as far as stumble?
i was thinking about getting a 80457 from summit which is a holley based on the 4160.
as far as the throttle difference, i don't think there is much difference between how much throttle i give it, it stumbles for a second before catching up...almost like the transmission is shuttering is what it feels like. i will say that full throttle seems to catch up just slightly quicker.
My bet is you'll need to get the Edelbrock tuning kit and try a different combo of jet/rod/spring. Lots of anecdotes on the Net about your issue. Try the Mopar forums, as Mopar folks have used Carter and later Edelbrock carbs a lot.
a lot of guys were saying that it needs a stiffer spring. i dont really understand how that affects it and might cure the problem? it comes in the calibration kit and i guess i could try that...
A stiffer spring means the metering rod lifts more quickly in response to falling intake manifold vacuum as the throttle plates are opened. Stumbles usually result from lean conditions, though occasionally from rich conditions. Faster rise on the metering rod means more fuel flow. There are also variables of metering rod diameter and taper and jet size. Take some time to watch the video and read the instructions with the kit and you'll learn a bunch
The engine in my D-coder is a stock long block with a Cobra intake, Autolite 4100 carb and JBA shortie headers. The only time I had a intermediate RPM stumble with the 4100 was when there was some debris in the intermediate circuit. Otherwise, flawless. I have it set up for a long pump shot, since the car has a stock converter and 3.0's.
Race car is likely irrelevant but has a 3310 (780cfm) Holley with a ton of modifications. Reo pump, dial-a-pod and a bunch of internal mods. Engine is a highly modified 351W.
I've never run Carter-based carbs so know very little about them other than helping my Mopar race buddies sort them in the distant past. I know there are different jets, metering rods and springs. Each plays a role in the overall metering scheme. Beyond experimenting, I really can't offer you any definitive advice....
well i got a holley 80457 today (which is a 4160 i guess) and I think it runs much better honestly. My biggest issue now is that I have a pretty good rpm drop when I put it in gear...park is 1200rpm and drops to about 750rpm in gear. I already have 16 deg advance initial on an edelbrock 7122 cam (about 224 duration). Its an AOD with about a 1500-1800 stall i think, unless the builder put a different one in that i didnt ask for.
Verify no vacuum leaks around the carb ports and mounts.
Also, I found I had a more stable idle with racing camshafts and an automatic with a relatively tight converter when going to a 4-corner idle circuit and independently adjusting the secondary throttle blades in order to balance airflow without the primary blades invading the transfer slot. IIRC, my A333 is 224 intake and 234 exhaust @ .050.
Thanks but I think I may have found my problem. No vacuum leaks anywhere that I could find and sprayed carb cleaner just about everywhere on the engine to be sure. I have a vacuum gauge hooked up to manifold for testing and what I see is a needle that vibrates about 1-2inches no matter what rpm it is at. Almost so fast that it blurs and looks steady. I read somewhere to check the ignition. I checked the cap and rotor and they were both burnt/charred and scored. Think that is the problem?
What did the vacuum gauge read at idle out of gear? In gear? Do you note engine vibration visibly? Generally, an ignition system problem will cause idle misfire, resulting in low vacuum readings and noticeable vibrations.
The cap and rotor are cheap to replace and I'd surely suggest doing that. Keep us posted. Check your numbers before and after replacement with no other changes. If the cap and rotor are bad, there's a chance the other ignition system components (points/condenser/wires/spark plugs) needs service as well. Do you know the last time the ignition system was serviced?
idle in park was about 14, vibrating between 13.5 and 15 I would guess at about 1100rpm. Too fast to really see. In gear it was about 6, vibrating still over about 1.5 inhg at about 700rpm. The engine does vibrate pretty rough, but mainly only once it is in gear or i adjust the idle below 800rpm.
The cap and rotor didn't really help much. Everything on the engine is brand new so all ignition is well. However, I wonder what the symptoms of a faulty coil are (pertronix flamethrower 40,000V)? I am also curious is I adjusted my rockers properly...
The AutoGuide.com network consists of the largest network of enthusiast-owned enthusiast-operated automotive communities.
AutoGuide.com provides the latest car reviews, auto show coverage, new car prices, and automotive news. The AutoGuide network operates more than 100 automotive forums where our users consult peers for shopping information and advice, and share opinions as a community.
289 stumble
