1980 Jeep CJ7 Carburator Problem

I have been driving a blue 1980 CJ7 for the past 20 years. After blowing a head gasket at 140,000 miles I had the engine rebuilt in yr 2000. I also had a rebuilt Holley carburator installed in yr 2003. The last carburator adjustment was performed in Feb 2009 at 171,000 miles. Current mileage is 183,000 and the car has an annoying hesitation problem when driving up hills at any RPM level, and often when lugged down in 3rd or 4th gear. The problem really manifests itself into a jerking, bucking bronco when refueled with an 87 octane gas with 10% alcohol mixture. I have to add a $10 gas additive to get it back to a driveable condition which then returns to the occasional annoying hesitation problem. Any advice? I’m willing to have a new carburator installed if that’s what it takes to get Ol’ Blue purring like she’s never purred before!

You might check the timing and both timing advance mechanisms.

You might want to take the carb apart and look at the condition of the accelerator pump. If the diaphram/plunger is stiff or hardened that’s what the ethanol is doing to the rest of the fuel system.

I had a 79 Mercury when Minnesota mandated that E10 be the mandatory motor fuel in the state in 1992. Once that happened, I had to rebuild the carburator in that car every 8-12 months from the damage the ethanol caused to the rubber/plastic/brass components. I got so good at it, I could have the carb off, rebuilt, and reinstalled in less than an hour.


This thread raises an interesting question: a 2003 car should be able to use 10% ethanol without problems, but will a carburator rebuilt in 2003? Will the parts used be compliant with the new formulations? I wonder.

The first thing I’d check would probably be the fuel line pressure.

I then might want to look at the carb float bowl. If the float is hanging up and not allowing sufficent fuel to keep the bowl full when the engine is drawing lots of fuel, when it’s under load, the engine will starve and chug.

You also might want to chack the spark advance. If the spark timing isn’t advancing you’ll also get chugging.

bruce, an 80 Jeep could have any of several possible ignition systems and used either a Holley or Carter carburetor as original equipment. Over the years many switches often get made among the possible choices. Your problems could be the symptoms of several different problems. If you warm the engine fully, remove the air filter and confirm that the choke plate is standing up and QUICKLY snap the throttle wide open and release several times to see just what happens. If it seems to bog down snap it open and hold it momentarily (don’t sling a rod) and see if it back fires. If there is no severe bogging down or back fire move the vacuum advance hose from the carburetor base to a connection on the manifold and watch for the engine to increase the RPM significantly, if yes OK if not the vacuum advance is not working. Look at the fuel filter and if it has 3 outlets pinch the one on the side tightly and test drive. Then post back. A couple of old timers here are better than me on those old Jeeps, Maybe they’ll show up. Well I guess they have already been around it seems but maybe they’ll get back.

Holly carbs are marginal at best when used as you use your jeep…They require periodic rebuilding…The “metering block” sandwich design is prone to leaks and blockages…I would try to find the far more common Carter carburetor.

One of the unique things about Jeeps was trying to figure out the assortment of parts suppliers they used when building the vehicles…Ignition systems and carbs and alternators were strictly whatever they could find at the time…Some of it worked and some of it didn’t…Good Luck…

All this information is great news. It confirms what I was just told by a local mechanic, that is, the Holly is a troublesome carb. I do not know what type of carb was originally on the car. What ever it was, it worked poorly, that is why I had a new carb put on. My guess is the mechanic just replace the old one with the same type. That’s probably why this one is a Holly. The local mechanic suggested two alternates that would be better, Carter was one of them. I can’t remember the other. He cleaned the carb, adjusted it and reset the mixture yesterday. I immediately drove it accross town then up a 3000’ mountain road over 16 miles. The same hesitation and coughing/missing occurred all the way up, although it did seem to run a little bit better, but not to the level I was hoping for. Atleast I now know it’s just a Holly carb characteristic and it’s not just going to blow-up and leave me stranded.

I really want to get this car running smooth again. It is in great shape, I enjoy driving it both summer without the top and winter with the 4WD. I’m going to check into the price of a Carter.

Will I run into linkage, accelerator cable, and other hidden issues if I change to a Carter?

Thanks for your information!

Post the model number of your carburetor. That might give some insight into what will interchange with it. It should be visible when the air filter housing is removed.

Embossed vertically on the passenger side of carb:

Embossed on the back corner of the passenger side:
6251 5A

Attached to the front drivers side of the carb is something round with an electical wire going to it. (electronic choke?) It says: Varaiet II Rochester. If I buy a new (or rebuilt) Carter carb, does this item also come with the carb or can I re-use this one or should I replace it also with the Carter equivalent?

As you can see, I’m in over my head.

I appreciate your comments

Thanks for all the advice.

The Jeep Took a turn for the worst. As explained below:

Matt & Brett,

I want to give you a heads up on the condition of the jeep and my experience on the commute to work this morning.

As you both know Old Blue has not been at her best since I returned from my Skibatical in March. By adding fuel treatment and carburetor cleaners to the fuel system she has remained running but very reluctantly as we have all experienced on any trip up the hill this year.

I?ve spent over $1,400 this year in repairs and this has been expenses on items unrelated to making her run better, but just to keep her running in her less than stellar manner. I spent $400 last week to replace the water pump and headlights last week. While she was in, I had them look at the carburetor, adjust it, and do whatever they could to cure the jerking/missing/hesitating that we have been putting up with. I filled her up with premium gas, drove her to Bogus last Wednesday for her last trip and she coughed all the way. But she purred coming down. On Friday I noticed a worsening in her performance. The engine sounded and felt like it was running on 3 cylinders rather than 4.

This leads me to this morning. She continued to worsen as I came down the hill. When I pulled out onto Warm Springs, I was not sure I was going to get to Walnut. We did make it to the street by the parking garage where I was forced out because of the smoke and foul smell coming from the front end. My guess is the engine blew a head gasket. How do I know? It smells just like it did in 2000 when she blew the last head gasket.

The resulting rebuilt engine cost over $4000 in 2000. In 2001 I invested $1,400 and in 2002 I invested another $2000 to have a new carburetor installed along with other minor fixes. Since then she has been fairly reasonable until this year when we are at $1,400 so far.

Based on the above, are either of you willing to pay for her towing charge, re-built engine, new carburetor, continued repairs, tires, insurance, et.al.? Let me know by 5:00 this afternoon!

I plan to remember her for all the fun we have had in her over the past 18 years. I am not going to sore those memories by making her into the Brett Farve of our memorable fleet.

Much Love,