Hot Start Issue -

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post #1 of 13 Old 05-26-2010, 08:36 PM Thread Starter
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1979 CJ7 
Join Date: Sep 2009
Location: Cincinnati
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Hot Start Issue

Hi everybody, I searched for something similar but had no luck on similar issues. My Jeep is a '79 CJ7 with the AMC 304. It seems I have a pretty bad case of hot starting issues. On first start up and up to about 15 minutes of running it has no issues restarting. After that it hesitates and lately just won't budge until it cools down. I have new plugs, cap and wires. The coil looks to be original. The carb was rebuilt a couple months ago. Just about everything is stock.

My thought was the choke at first, but while trying to start it I had a buddy open the choke wide open and had no difference. Someone suggested my ignition coil might not be sparking when its hot, although it never gets rough or misses when running. Lastly it does get fuel, you can hear it squirting into the carb.

Anyone have any other ideas? Should I replace the coil just for good measure?

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post #2 of 13 Old 05-26-2010, 08:45 PM
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1986 CJ7 
Join Date: Mar 2007
Location: Danvers
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I know it sounds so simple but check the air filter and make sure it's not clogged up. Maybe when you are having the problem starting it.. remove the air filter and try again. If it starts.. you need a new filter.


1986 Jeep CJ7 (photos)
Remanufactured 258, ARB lockers front & rear, 4.10 Yukon gears, 35x12.5" Super Swamper SSR's, Motorcraft 2100, 4.5" Rubicon Express Extreme-Duty lift, York 210 OBA, Big Daddy steering, Tatton rear CV driveshaft, Herculined interior, TJ flares, lots of body & upholstery work
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post #3 of 13 Old 05-26-2010, 09:00 PM Thread Starter
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Did that, new filter and took it off to check the choke.
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post #4 of 13 Old 05-26-2010, 09:10 PM
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1986 CJ7 
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Do you have the original style fuel filter? One in and two out.

I am wondering if your having some type of vapor lock.

'86 CJ7, 258, Carter BBD, Nutter'ed, TeamRush'ed, T-18, Twin Sticked Dana 300, D30 Frt-Pwr Lok L/S-4.10, AMC 20 Rear-Mosers-Detroit Locker-4.10, 2.5 BDS Lift, 1" Body Lift, 33" Wild Country M/Ts, Black Spoke wheels

'45 CJ2A, L134 Go Devil, T-90 Tranny, Warn O/D, T-18 T-Case, Dana 25 Frt, Dana 41 Rear, 531st CJ made

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post #5 of 13 Old 05-27-2010, 05:46 AM
Mike Romain
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1986 CJ7 
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As mentioned, make sure the gas filter is in right side up so on a hot shutdown the vapors produced get blown out the return line off the top of the filter back to the gas tank rather than vaporlocking the gas line.

Another issue can be headers too close to the starter which overheats it.

86/00 CJ7 Laredo, 33x9.5 BFG AT's, 'glass nose to tail in '00, 'New' frame,wires and plumbing in '09. Carter BBD Carbed 4.0 HO in '10.
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post #6 of 13 Old 05-27-2010, 07:57 AM
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1974 CJ5 
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Check your timing. If your timing is too far advanced it will produce a hard start when hot. It will sound as if your battery is dead or dying, and the starter will drag. Either that or vapor lock. It's not the air filter, you can be sure of that.
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post #7 of 13 Old 05-27-2010, 08:11 AM
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1973 CJ5 
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There are two things I would look for right off the jump...

1. Modules heat soak when you stop,
They will get overheated and not work correctly, once they cool down, they will start working again.

2. Some carbs will heat soak and boil the fuel out of the carb and sometimes the fuel lines if they are too close to the exhaust for too far.
Headers in particular like to cook fuel lines which usually run inside or on top of the frame right next to the exhaust for quite a distance.

I'm always advocated putting the module up higher on the fender, or even in the passenger compartment to keep it safe.

I have a hot start problem in my dedicated off roader, and I'm sure it's fuel lines getting cooked when I shut down.
The exhaust is just about 2" from the lines, which I intended to run inside a boxed frame,
But forgot to put them in there when assembling the last time.

I can spray water on the fuel lines and the stupid thing will fire right up once the fuel reaches the carb again...
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post #8 of 13 Old 05-27-2010, 09:32 AM
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You says it hesitates... Describe what you mean by that. Does the engine spin at normal speed (as it would when cranking it cold) while cranking it hot? Or does it drag and barely turn over, kind of like a near dead battery?

If it's the latter, check the starter cable going to your starter motor. I ran into this same problem with a Ford 200 I-6. The heater hose was actually laying on the starter cable, causing high resistance. It caused the symptoms of a dying battery only when hot. Make sure your starter cable isn't touching or too close to any heater hoses or exhaust pipes.

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4.0 I-6 / T5 / D300 / D30 / D44
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post #9 of 13 Old 05-27-2010, 01:13 PM
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Before switching to Hooker Headers on my SBC years ago the unknown maker headers came in such close proximity to the starter I often had startup issues owing to the electrical impedence caused by this high heat. You might try a starter heat shield or wrap.

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)
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post #10 of 13 Old 05-27-2010, 01:30 PM
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Lets see, you checked for fuel getting to engine, air getting to engine, now make sure you are getting spark.

You stated that the coil is probably stock, so it could be weak after getting hot. Pull a plug wire and see if your getting fire when it won't start.
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post #11 of 13 Old 06-28-2010, 09:48 AM
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1982 CJ8 
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Did you ever resolve this? If so, what was it?

I'm getting the same issues on my scrambler and have been through similar steps. I'm beginning to wonder if it's a vapor lock. I've put a junkyard charcoal canister on it, and I'm wondering if the canister is operating correctly, or if it was infested with dirt dobbers. I'm having a hard time fueling the vehicle now, which says to me the tank isn't venting correctly. Thoughts?
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post #12 of 13 Old 06-28-2010, 10:21 AM
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1983 CJ8 
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Originally Posted by mtbtweety View Post
..... Thoughts?
You may want to open the filler cap a notch so that you're assured that the tank has a vent. Not suggested as a permanent fix but a simple way to either rule out or realize that a correction to the venting should be made.
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post #13 of 13 Old 06-29-2010, 10:43 PM Thread Starter
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My buddy had my Jeep for the summer so I don't get to tinker much. He put the filter in the right direction and that helped somewhat. I'll pass along the advice to open the filler cap since it seems vapor lock may be the issue as the filter suggests. We're going to try a new coil too to see if that helps since they're cheap.

Its no fun being 600 miles from your Jeep for 6 months
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