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Unread 08-22-2015, 08:59 PM   #1
jahardway
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1977 CJ5 
 
Join Date: Aug 2015
Location: Palestine, West Virginia
Posts: 6
304 v8 carb problems

I recently bought a 77 jeep cj5 with a 304 v8 that had major motor problems. Well, I got the motor running again, buttoned up, and running pretty well. Engine bored .40 over, stock piston dish, larger than stock cam (dont know how much because it came in the jeep), stock heads, aluminum intake w/ edelbrock 1406 4bbl carb, 14* initial timing, and 16" manifold vacuum at 750 rpm idle. I took it for a few short drives just to make sure everything was working and it seemed pretty good. This evening I took it for its first major ride and discovered I am having problems with the carb at very light throttle application. With very little throttle application the engine has a major hesitation, even when just revving it with no load. If you barely rev the engine out of gear (to like 1100 rpm) it will bog and then rev up. If you tip in much more than that it will rev good with no hesitation or stumbles.

When I try to take off it is very evident and makes taking off a challenge, I have to use granny gear to take off or in 2nd take off at like half throttle. If I shift gears at a low rpm it also stumbles and occasionally backfires through the carb, but the backfiring goes away after it gets completely warmed up. Also, when i'm driving and get the rpms up a little and then drop back out of the throttle and cruise I get some significant pinging and sometimes it surges a little. If i give it more throttle the pinging stops and it runs just fine. Full throttle and part throttle power is great and no detonation, the problem only lies just off idle.

I thought about trying to play with the primary rods and jets a bit to richen up the mixture a little bit. I also had the initial timing bumped back to 8* at first and the hesitation was the same, so I don't believe the timing is causing a problem, but it may be. I didn't notice the detonation then, but I wasn't really listening for it either. Just wondering if any of you guys have had a similar problem or can offer suggestions.

Thanks,
Jerry

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Unread 08-23-2015, 07:11 AM   #2
Oldcraneguy
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1982 CJ7 
 
Join Date: Feb 2010
Location: FL.
Posts: 416
Had the same problem with my 360/600 Holley I jumped 4 sizes on primary jets and put a t-stat in to get my temp up and made a world of difference, course I was running 270H cam and barely had 11.5-12" vacuum. Id still say fatten it up and make sure your temp is close to 170* or better...luck...OCG
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Unread 08-23-2015, 12:58 PM   #3
davbytrace
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1979 CJ7 
 
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Location: clinton, MS
Posts: 481
Your carb is too big.

Edelbrock specifies a 1403 500 CFM for engines smaller than 305.
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Unread 08-23-2015, 01:41 PM   #4
RedNeckCorvette
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1979 CJ7 
 
Join Date: Mar 2013
Location: Oregon Coast, OR
Posts: 765
Yes you have 600 cfm carb and my 304 runs just right with 460 cfm.

May I suggest if you get it warmed up to do a compression test, back firing might involve a cam, or a burnt valve.
RN
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Unread 08-23-2015, 02:36 PM   #5
turbogus
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I'm running a 625 Carter AFB on 'BB' and with jet and needle changes it works well on my 360~until recently when I had a sunken/perforated brass float.
If it's backfiring through the carb throat it could be indicative of a lean condition like perhaps a vacuum leak of some kind. Check all of the vacuum lines and caps and make sure they are not abraded or otherwise leaking. Also the carburator base gasket.
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Unread 08-23-2015, 04:58 PM   #6
cjmike75
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ii used to run the same carb on my 304 and would have the same prob if I let jeep sit to long without running it. the gas would plug the idle jets and it wouldn't run right just off idle. just had to clean and blow carb out.
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Unread 08-23-2015, 05:26 PM   #7
Oldcraneguy
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I dont think its possible to say your carbs too big without knowing what cam your running, look at the original z28s 302" w/800 cfm holleys, I still think your lean, especially since your popping goes away as it builds heat...just my 2 cents...ocg
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Unread 08-23-2015, 08:04 PM   #8
jahardway
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1977 CJ5 
 
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Well, I'm fairly confident that there are no internal engine issues as I just had the thing torn all the way down to replace the rings and bearings. Everything checked out ok with a mic and dial bore gauge. The heads were done by a machine shop, and the cam checked out good, unless it has went flat on startup. The carb and intake came on it, so I didnt have any say as to what I got there. I was kind of leaning toward a carb or ignition issue causing the problem.

A vacuum leak is a possibility that I will check more thoroughly for. The carb is clean as I just had it apart and gave it a very thorough cleaning and rebuild to remove the mud from the previous owners abuse. I had a chevy 350 recently with a flat cam and this acts completely different, so i'm sort of ruling out that possibility but might look into that further if I have to. I would like to try keep from buying another carb if at all possible, so I purchased the eddy tuning kit to try and tune it out. It seemed to me like it was a lean stumble and backfire, but i'm not above other suggestions.

This weekend I will try and richen up the primaries and see if that takes care of it. Also, I will add that while it is warming up it stumbles and backfire between low rpm gearshifts, but after it is completely warm it only stumbles from a dead stop and the backfiring goes away completely and it only pings a little.

Thanks,
Jerry
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Unread 08-24-2015, 03:44 AM   #9
Oldcraneguy
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Just out of curiosity you didnt by chance advance your cam when you built the motor did you? (made that mistake myself recently)....ocg


meanwhile if you wiped out a cam lobe youd have a dead miss...
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Unread 08-24-2015, 08:52 AM   #10
jahardway
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Provided that my new timing set was accurate the cam was installed straight up. I never degreed it to find out how accurate it was though.
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Unread 08-28-2015, 07:34 PM   #11
jahardway
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1977 CJ5 
 
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Location: Palestine, West Virginia
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Okay, I want to thank everybody for there advice. I got a chance to tinker with it this evening and changed out the metering rods. I stepped it up one stage richer for the cruise mode, readjusted my idle, and all of my problems vanished. It runs great now with no pinging anywhere in the rpm range and plenty of power off idle as well as no stumble. Thanks again for your help.

Jerry
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Unread 08-29-2015, 07:18 AM   #12
turbogus
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Congrats! I knew you'd get to the bottom of this (no pun intended)
__________________
The parts shop that stocks part for Skylab II will not have parts for our year/model of Jeep
We cannot accurately judge the trajectory of a speeding critter (cat, dog, sasquatch)
Record heat waves and floods only occur when we visit that area
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