CJ5 misfires at high RPM/hard acceleration

I guess Holley doesn't know anything about carbs either, since they recommend a 570 CFM carb for that combination, using their online carb selector.

Also, you might want to look at

which is a manifold for Ford 302 engine and look at what carb Holley recommends for that. Yeah, 570 or 600 CFM. I have personally set up several 302 Fords and 318 Dodges with Holley

600 carbs, and they work great.

The other thing you are wrong about is that too big of a carb does NOT go rich when it gets to its flow range, unless the power circuit activates. A carburetor is a dumb piece of metal, and doesn't know how fast the engine it is mounted to is spinning. It is calibrated to meter a specific amount of fuel to a specific amount of air. The reason a big carb does not work on a small low RPM engine is because it takes a higher air flow to start the fuel flowing through the main jets. This is because the bigger throttle bore and venturi do not create as much of a pressure drop as a small throttle bore and venturi. Imagine putting a very small hole in the side of a straw, and sucking through the straw, then do the same thing with a piece of garden hose. The air speed through the garden hose is much slower, and it does not create as much of a suction through the small hole. This is not the "exact" way a venturi works, but it is similar.

What usually happens on a carb that is too big for an engine is that when the throttle is pressed, the accelerator pump dumps too much fuel, and eventually that fuel passes through the engine. What happens then it the engine goes lean because it is getting all the air it needs, but the airflow is not creating enough of a pressure drop across the venturi to start the main circuits flowing.

Holley vacuum secondary carbs are quite forgiving as far as sizing, and you can over carburate somewhat without any problems. I'm not saying you can hang a 900 CFM vacuum carb on a 304 or 318 that is relatively stock and have it work, but a 600 is definitely doable.

By the way, you should probably invest $16 in this book

so you understand how a carburetor works. Most of what I typed here is basically in that book, although I do have an older version that doesn't cover fuel injection. Chris

Ditto. The only thing I've seen them work OK in are the old VW Bugs. Where America plugs seemed to pull the heli-coils, unless you held your mouth just right. God Bless America, Bill O|||||||O mailto: snipped-for-privacy@aol.com

I think you should buy a mechanic's repair manual. I start by plugging number one spark plug hole with my finger. Then clicking a remote starter button or a friend hitting the starter via the ignition until I feel the compression leak by my finger then very quick starts, until the timing marks line up on the front balancer pulley. Usually the distributor cap has a number one marked on it, or use the manual's picture as to where the rotor will point when it's dropped in. Start the distributor in one notch counter clock wise, then slide it in and if it looks will right, spin the engine so it will drop into the oil pump's drive notch. God Bless America, Bill O|||||||O mailto: snipped-for-privacy@aol.com

wrote in message news: snipped-for-privacy@n2g2000hse.googlegroups.com...

I don't wanna know.

Oh, you hold your mouth right, alright...right around my pubic nest, Tubby boy

You're just too young. It's an old mechanic's saying...really.

-- Old Crow "Yol Bolsun!" '82 FLTC-P "Miss Pearl" '95 YJ Rio Grande BS#133, SENS, TOMKAT, MAMBM

Emphasis on old. God Bless America, Bill O|||||||O mailto: snipped-for-privacy@aol.com

The problem is fixed. I'm not 100% sure what it was, but I have a pretty good idea. The vacuum advance was plugged into manifold vacuum & had been ever since I can remember. The problem is that the vacuum advance was bad to begin with, so it was probably never noticed. I received my new carb today (a Holley 4412) & ensured it was plugged into ported vacuum this time around. I also timed it by ear + vacuum this time rather than the light. In the end, I came out with about 12 degrees BTDC initial advance (with the vacuum advance disconnected, not that it matters now with ported vacuum) instead of the 5 degrees that my Haynes manual states. Dwell angle is about 40 rather than the recommended 31 now too. It will stall with anything lower than 35. I get about 20" vacuum at around 700rpm idle now & it performs better than I ever remember it when it was running correctly, probably due to the carb & maybe the headers? Anyway, I wonder what the possibility is that I have some aftermarket cam with a heavier lift/duration due to all of these non standard settings required to get it running good.

Once again, I greatly appreciate everyone's help. I doubt I would have realized it wasn't getting enough advance without everyone's help & I learned a few things from everyone's experience. I even went out & bought some Champion truck plugs!

Thanks again guys,

-Matt

Sounds like you got it pretty much sorted out. I'll lay money that if you put the 600 back on there now that the timing is correct, or close to correct, it will run good(assuming it is rebuilt properly). A 500 2 barrel actually flows 350CFM when it is flow rated as the same vacuum drop as a 4 barrel is rated, so in essence you have half of a 700 4 barrel.

I kind of screwed up on the ported vacuum thing. I normally use manifold vacuum and modify the distributor for more centrifugal advance. Either way works.

Also, watch the plug coloring with the 500. they are jetted a little on the rich side, so you may have to drop them a couple sizes.

Chris

here here Bill, Here here

+1

Bill Spiliot>As I said I don't have any experience on Holley carburators or CJ5s.

Well, duh, Bill...it's in my handle

-- Old Crow "Yol Bolsun!" '82 FLTC-P "Miss Pearl" '95 YJ Rio Grande BS#133, SENS, TOMKAT, MAMBM