Hard cold start and backfiring during acceleration

[CaseyCJ5]

I just recently purchased a 74 CJ5 with a AMC 304 V8. Most of my mechanical experience is working on modern 4 cyl engines with MPFI so this is new to me. I am having a few issues with it right now, the main 2 being a cold start problem and backfiring when I'm accelerating.

The guy that I bought it from just put a Holley 2 bbl carb on it recently and I don;t think he made any adjustments out of the box. I'm assuming, like me, he did not know how to do it. The one thing I think he did adjust was the idle screw and cranked it up to try to keep it running when he started it. I dialed it down from 1300 rpm to about 700. When I initially start the engine I have to keep the engine at 1500- 2000 rpm until it warms up. Then I can finally drive it. Once I do start driving, the engine backfires when I accelerate. The harder I accelerate, the more it backfires. I am assuming this is a carb issue, but like I said, I don't know much.

Any advise is greatly appreciated.

 

[Purple77CJ7]

If you can find the model number on the carb, you can go to Holley's web sight and down load the install instructions. It will go through how to set it up, and make adjustments. I would also check the timing, it sounds like it is not set right.

 

[JR74CJ5]

If you can find the model number on the carb, you can go to Holley's web sight and down load the install instructions. It will go through how to set it up, and make adjustments. I would also check the timing, it sounds like it is not set right.

Backfiring during accelleration seems like:

Carb adjustment (mixture)
Fast idle / choke adjustment
Vac Leak for distributor advance
Timing

I think with all of those things checked, you may also make sure it has a fuel pressure regulator.

For the cold start, Same as one of the above. Just double check / go over the fast idle / choke system.

I do not have more details, since I am more familiar with the MC2100.

Timing wise on AMC 304 I'd have some pointers on though if needed... Do you still have the points distributor in there? Or has it been modified / swapped?


~ JR

 

[CaseyCJ5]

I couldn't find the carb model number when I looked the other day, but I will try again. I'm pretty sure it is about the most basic Holley you can find. It has manual choke if that helps. The manual choke isn't hooked up to anything though. I was thinking about putting a cable off of an older jeep on it. I've actually already ordered a cable from ebay thinking that may help. It does have the points distributer still. This is something I am even less familar with than the carb. The guy I bought it from said he just adjusted the points recently, but did it by eye and didn't use a feeler gage. I'm sure this is probably part of the problem. I was thinking about switching to an HEI distributer, is there anything else that has to be changed with that conversion or is it pretty much plug and play? This is the one I was looking at AMC JEEP CJ5 CJ7 304 360 401 V-8 HEI DISTRIBUTOR 6512-R | eBay. I will try to get the model number off of the carb this afternoon when I get off if it is no longer raining. Thanks for the help!

 

[DJ1980CJ5]

If you are not familiar with points, you not only have to set the gap (usually .020") and also the Dwell. You'll need a meter for that.

Backfiring and "sneezing" are two different things. I consider a backfire to be through the exhaust. A loud bang!

Sneezing is back through the carburetor. That is usually cuased by the above or the engine is just too cold to take the fuel.

You definetely need a working choke. The nice thing about a manual choke is that you can feather it to make the engine run.

Get the choke cable, hook it up and then attack your ignition system.

I think Petronix makes an electronic ignition changeover kit for that engine. Everything stays in place, except you eliminate the points. I've used them several times on Marine applications. They work great.

 

[JR74CJ5]

I think Petronix makes an electronic ignition changeover kit for that engine. Everything stays in place, except you eliminate the points. I've used them several times on Marine applications. They work great.

They do...

I only changed my distributor because the screw holes for the points or pertronix to tighten up on were stripped out so needed new distributor anyway...

IF you do change the distributor, read up on AMC dizzy gears vs cam shaft gears. You'll either want to change both of them, or re-use the old distributor gear on new distributor.

I'm not trying to turn you away from it, I love my DUI HEI distributor... BUT hated it when I was stranded a mile from the rubicon in the begining of a week long trip... Chewed distributor gear up...


~ JR

 

[CaseyCJ5]

I have ordered the choke cable and am just waiting for it to arrive now. If I put a HEI distributer, will I have to change anything else? I won't have to buy a ingnistion control unit or anything will I? I know most of them have the internal coil so I can remove the coil but I'm not sure how everything else converts.