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Discussion Starter · #1 ·
Well the car has been finished for awhile now and most of the bugs are worked out of it. The problem I need to correct now is the engine performance. It is a 351 Cleveland 4V. Everything is new or rebuilt including the carb and distributer. The car lacks power and seems to stumble during acceleration. I put a remanufactured stock Autolite carb on it and tinkered with the settings. It has a new stock distributor, but I did not take it to the machine shop to check the curve. I set the timing at 15 degrees but runs like crap so I tune it by ear. Think the curve on the distributor is out? I am running a pentronix ignition. Any specific settings I should be looking at to get this thing running right? If I have the curve set at the machine shop, what should the settings be? Motor is all stock.
 

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mach_foster said:
I put a remanufactured stock Autolite carb on it
That's most likely your problem, the Autolite 4300 is a POS.
 

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4V Clevelands tend to stumble at low rpms. You really have to work with them to get rid of the stumble.

They like a LOT of initial timing (15 degrees is a good start) and they like a really aggressive advance curve. Plus a big pump shot from the accelerator pump.

If you have 3.00 gears with an auto with a tight converter it will exacerbate the problem. Personally I would run AT LEAST 3.50 rear gears with a 4V. And a 2500 stall converter.

I have been playing with the 4V Cleveland in my 73 vert for 15 years now. I ended up doing all the things above and the low end stumble is gone. I've used both Holley and Edelbrock VS carbs and they work fine once tuned. I also had a Boss 351 and it loved a 650 Holley DP but it had a manual and 3.91 gears.
 

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Discussion Starter · #4 ·
That is very helpful info. Any idea what the distributer curve should look like. What RMP should it be all in at?
 

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Hello,
Nice Mach!! The original carb, like Hemikiller says, has a bad designed accelerator pump. I personally use the 600cfm Carter AFB competition series carb. After some air/fuel mixture tuning, it runs flawlessly with the 351C 4V. I will check my Mallory mechanical advance settings later today. It's been awhile since everything been set up, so I'm a little rusty with the settings.
 

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mach_foster said:
That is very helpful info. Any idea what the distributer curve should look like. What RMP should it be all in at?
As early as your fuel will allow. The fuel will be the determining factor IME.

Better to get a performance carburetor where the pump shot volume and duration can be easily adjusted. Critical for off-idle performance with the 4V heads. We used 4 hole 1" carb spacers on our racing iterations with good success (on the starting line). An adjustable plenum divider helped with single plane intakes.

Hope your compression ratio is up there. 11:1 is a good serviceable CR for a 4V 335.

As noted, minimum 3.50 gear and a 10" converter (or a loose 11") for reasonable performance driving around. The 4V Cleveland is a racing engine de-tuned for the street.

Pat
 

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I had a similar stumble on mine, could not set the timing with a light. when I advanced it by ear it ran much better. Later I found out the balancer outer ring had spun giving false readings. Check that your balancer is reading true TDC.
With a new balancer in place I run 16 degrees at idle with 22 degrees of mechanical advance.
the total 38 degrees is all in by 3000 rpm. Runs very well like this with no stumble and I can still advance more if I wanted to race it.

Sorry I cant help with the carb tuning, I have only worked on Holleys
 

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If the plug read indicates proper mixture, advance can be easily set using the detonation sensing method. Downside is, depending on safety margin, atmospherics can push the engine into detonation.

The above, and the lack of a computer to continually monitor and change operational parameters, is why I always ran racing fuel in serious street and racing engines. Much easier and more pleasant to tune and the engines lasted longer and ran better at their peak torque/hp levels.

335's/385's can tolerate a lot of advance IME. Numbers in the mid 40's aren't uncommon...

Pat
 

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Cannot comment on the autolite but I went with a 650 thunder series and tuned it with a Innovate AFR unit. Even the 650 required quite a bit of leaning out to eliminate stumbling. I got it to a good level where stumbling is gone but only after the engine is warm. 12 deg advance, MSD 6A, 3:25, Performer intake.
 

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Unless the pump shot is huge or there is a gross failure in the carb's metering system, I've never heard of "leaning out" a carb to eliminate off-idle stumble, especially in a 335 series engine.

If anything, the carbs based on the old AFB go lean off-idle instead of rich, but I'm happy to be corrected. :)

Specifics are greatly appreciated!

Pat
 

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1972vert said:
I run 16 degrees at idle with 22 degrees of mechanical advance.
the total 38 degrees is all in by 3000 rpm. Runs very well like this with no stumble and I can still advance more if I wanted to race it.

Sorry I cant help with the carb tuning, I have only worked on Holleys
Hello,
I checked my dizzy, and I'm running this same set up with the initial and total advance. Though I run 104 octane boost, and it seems to keep the denotation to a minimum.
 

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Discussion Starter · #12 ·
Thanks for all the info guys. I am going to start working with it as soon as the weather clears.
 
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