258 loosing prime after sitting for a few days.

[Halfmoon]

I've read through a ton of threads about this and now its time to ask for some help. Basically once my AMC 258 i6 / 4.2l sits for more than a day or two it seems to loose prime and takes a really long time to crank. Once it finally cranks it runs good and will crank again with no problem. I've checked the fuel filter just before the carb and the second fitting going back to the tank is directly above the center fitting. I've sprayed the outside of the carb while running to see if it has a leak.

The carb is a Carter 2 barrel 2378. I don't know when it was rebuilt last as I've only owned it for a month. I've heard of fuel evaporating from the bowl but I haven't had this issue with other carb motors I've owned that sat for a lot longer.

Can someone tell me what else to check that could cause this?

Are there things I can do before replacing the fuel pump? I dont want to start just throwing parts at it unless I can tell they're bad first. Would vac lines cause this?

Thanks for the help!

 

[cj7inthetwigs]

I ask for help regarding the same issue,but don't know how to paste my previous thread. Did you test the fuel pump and make sure it's working. That cured mine oh yeah and some rotten fuel hose near the tank. Same problem with our 4x4 yota. Its still on jackstands

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[Petescj]

http://www.jeep-cj.com/forums/f2/got-starter-fluid-15451/

 

[cj7inthetwigs]

And,there you go:thumbup:

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[Halfmoon]

It will start eventually, just takes a long time--30-45 seconds of constantly turning the engine over. How do I test the pump for leaks?

Could a bad vacuum line cause this?

 

[Kane]

Your issues actually lay within the carb. The fuel in the carb is evaporating out and when you go to start it the pump must refill the carb. If you only lost prime the engine would still start since the carb would have fuel in it. Since it doesn't then you have to crank it over until the carb is full enough to supply it to the motor. I am not sure how to solve this as i have seen it on most carbs including the qjet i just installed on my 350. I just deal with it since it doesn't hurt operation.

 

[Halfmoon]

Your issues actually lay within the carb. The fuel in the carb is evaporating out and when you go to start it the pump must refill the carb. If you only lost prime the engine would still start since the carb would have fuel in it. Since it doesn't then you have to crank it over until the carb is full enough to supply it to the motor. I am not sure how to solve this as i have seen it on most carbs including the qjet i just installed on my 350. I just deal with it since it doesn't hurt operation.

Just curious, how much fuel is stored in the carb? Can you look down into the top and see it?

If that's the case I'm not going to put any money into the Carter because I've been wanting to switch to a MC2100.

 

[thescot]

Either carb including a healthy 4bbl dosent hold that much fuel. Been a while since I had the pleasure of looking at a carter being Im running Howell FI but a few ounces in the 2bbl up to a cup+ or so in something like Thermoquad. GM Quadrajets are notorious for what you describe as a result of a leaky casting plug in the center of the bottom of the carb. Most rebuilders JB weld the plug to prevent it. On one case my old Chevy PU would not pass smog because of the constant dripping fuel while at idle. I cant recall if the Carter have any known issues like this.
Another possibility is a worn accelerator pump diaphram. You should be able to clearly see a nice stream of fuel shoot down the carb throat when you pump the gad pedal if the bowl if full of fuel. If the pump is shot it will be pretty hard to get it to fire just off venturi and choke.
This will sound like a PITA somewhat but you could always pull the carb,sit it on a work bench and gravity fill the bowl then watch if fuel leaks out, if so track the source and fix it.

 

[Petescj]

Just curious, how much fuel is stored in the carb? Can you look down into the top and see it?

If that's the case I'm not going to put any money into the Carter because I've been wanting to switch to a MC2100.

The Nutter Bypass and MC2100.

 

[Jimbos76cj]

The Nutter Bypass and MC2100.

X2 and while your at it change the fuel pump and soft lines.. Im sure its a little bit more work then you want to do but seems silly not to. My buddies jeep had the same type of issue and a new fuel pump fixed it.

 

[thescot]

The Nutter Bypass and MC2100.

Sure....long as you dont live in a smog state

 

[Halfmoon]

I've been looking for a 2100 to rebuild but its been surprisingly hard to find in the yards. Still on the hunt!

The computer has been removed. Does that mean nutter has already been done?

 

[Petescj]

I've been looking for a 2100 to rebuild but its been surprisingly hard to find in the yards. Still on the hunt!

The computer has been removed. Does that mean nutter has already been done?

Yeah it should. Can you take some pics? And do you know what 2100 your looking for?

 

[ThisGuyUKnow]

Just my 2 cents. I'd check all your hoses at the tank and in the engine compartment and then bypass the mechanical pump with an inline low pressure pump. I did that on my 88 GW and had really good results.

 

[Halfmoon]

Yeah it should. Can you take some pics? And do you know what 2100 your looking for?

I have some pics. Which part do you need to see?

I'm looking for the 1.08 MC2100. The salvage yards I've talked to aren't overly helpful.

 

[Petescj]

I have some pics. Which part do you need to see?

I'm looking for the 1.08 MC2100. The salvage yards I've talked to aren't overly helpful.

There should be some tell tale signs of the Nutter being done by looking at the wiring from the module on the fender and the wires leading back to the distributor. As for the Mc 2100 I was just making sure you knew what Veturi size to look for.

 

[johnnyreb]

I have the same problem with my mc2100. Look at it as a prelube for you bearings.

 

[S76]

Here is a simple test you all can do.

Take the top off a rattle can. Fill it half way with gas. Let it set on the work bench until the gas is 3/4 or so gone. Mark down how many days it took for this to happen. This is at the least how long your Jeep should be able to sit without having starting problems.

It has nothing to do with pumps and filters and lines. Once you shut the engine off, it has X amount of fuel sitting in the bowl. If the bowl is not leaking, even if it is vented, it takes a quite a while for the gas to evaporate. You should be able to shut your Jeep off, remove the fuel line, and it should still start up a week later without connecting the line. It should start on what is in the bowl. Granted it will only run briefly, but it will run.

If it doesn't, then your carburetor bowl is bleeding down. Or leaking down. As mentioned earlier in this thread, Quadrajets are famous for this. They have a welsh plug in the bottom of the bowl that does not seal off the fuel bowl very well and over time the fuel drips down into the intake manifold until the bow is empty.

The problem is most likely in the carburetor bowl.

 

[Doug27]

Interesting, I've had exactly the same issue. All stock, with the Carter carb. I've only had the Jeep a few months, but the carb was re-built less than a year ago by what is supposed to be a very reputable shop.

I replaced the fuel filter and moved it around a bit to make sure that it was higher than the carb. Interestingly enough, the lines coming out of the filter were reversed. Basically the filter had to fill up and overflow before gas would flow to the carb (correcting this surprisingly had zero effect).

I did replace the fuel pump (not even sure if the other one was bad, but it seemed worth trying for $16 and 10 minutes of my time). That had absolutely no impact.

I really don't want to go with an electric fuel pump, but that would solve the issue.

Certainly something that I could live with--just have to crank longer after it's been sitting for a few days, but it never fails to start (I'll just be working the starter harder than I should need to ).

 

[harleydragon]

carb probably has a very tiny leak internally as a few guys stated previously