Jeep dies when braking - JeepForum.com
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post #1 of 42 Old 10-27-2019, 01:13 PM Thread Starter
Zuccus
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Cj Jeep dies when braking

Looking for some help here. Done a lot of research and want to see if anyone has any suggestions to try.

Jeep CJ7
258
Weber 34/34 Carb (About 8 years old)

Got some strange gremlins here. The jeep wants to die when I push on the brakes. The harder I push, the quicker the rpms go down. Yet here is the strange part. It doesn't do this when I am idling and doesn't do it when I am reverse. Only when I am moving forward. I checked and checked for a vacuum leak. I have messed with the float valve on the carb. I cleaned the carb up pretty good several times. Really got the needle valve good this last time, but none of that seemed to help. It also Doesn't matter if I am going slow or fast.

A few questions:
Would the brake booster only effect it when I am moving forward?

Nuclear option: Is it time for a new carb?

Any other options I can try?

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post #2 of 42 Old 10-27-2019, 01:50 PM
only in a jeep cj
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When mine did this, I could press the pedal lightly and no rpm drop......press down more/harder, rpm drop.

Small rip in diaphragm and the movement exposed that section.

Dont know about reverse, but my guess is the booster

Ed
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post #3 of 42 Old 10-27-2019, 02:03 PM
JFM626
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Quote:
Originally Posted by only in a jeep cj View Post
When mine did this, I could press the pedal lightly and no rpm drop......press down more/harder, rpm drop.

Small rip in diaphragm and the movement exposed that section.

Dont know about reverse, but my guess is the booster

Remove vacuum hose from booster and plug vacuum line. you still will have brakes just no vacuum assist. Apply brakes, if no drop in rpm--- booster is BO.
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post #4 of 42 Old 10-27-2019, 02:16 PM
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^^^ This

If you cannot fix it with a hammer then it has to be an electrical problem.
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post #5 of 42 Old 10-27-2019, 02:37 PM
KevinCJ7Jeep
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I had similar issue, turned out to be stuck rear float on my 4 barrel carb. Cleaned and adjusted floats bowls
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post #6 of 42 Old 10-27-2019, 02:44 PM Thread Starter
Zuccus
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Originally Posted by JFM626 View Post
Remove vacuum hose from booster and plug vacuum line. you still will have brakes just no vacuum assist. Apply brakes, if no drop in rpm--- booster is BO.
I tried this and it didn't change anything.
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post #7 of 42 Old 10-27-2019, 02:45 PM Thread Starter
Zuccus
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Quote:
Originally Posted by KevinCJ7Jeep View Post
I had similar issue, turned out to be stuck rear float on my 4 barrel carb. Cleaned and adjusted floats bowls
This is what I am suspecting it was. However, I have played with the float a few times and it doesn't seem to change anything. Tried the float normal, high and low. That doesn't seem to do anything.
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post #8 of 42 Old 10-27-2019, 03:12 PM
KevinCJ7Jeep
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I would clean the carb. Not sure on webers, but it could be a stuck needle/seat. Maybe try the old hit the carb trick with a 2x4 to free it up. Mine acted the same way, fine sitting still or in reverse.
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post #9 of 42 Old 02-02-2020, 01:10 PM Thread Starter
Zuccus
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I wanted to follow up on this thread in case anyone else has a similar issue. I suspected that I had a really small vacuum leak on the bottom gasket of my carb. When I would spray it with cleaner, the rpms would bog down. I finally found a rebuild kit for this carb and took it apart, cleaned it and put all new gaskets in. That seemed to have solved the problem.

Thanks for the suggestions all who offered them.
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post #10 of 42 Old 03-19-2020, 11:35 AM
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glad to hear your issue is cleared up/fixed. but, I'm hoping to glean some Intel from you.

I have a follow-up question about your "engine stalling/dying" symptoms because they all appear similar to mine; however, one symptom you describe is missing as far as my experience goes.

I'm assuming this happened only when the engine was cold?? however, did the "engine stalling/dying" last for only a few (3 or 4 stops) then kinda clear up where the jeep would idle better after running a few minutes and thereafter??

mine does this getting outta my neighborhood. 3 or 4 stop signs (the jeep stalls/ dies) until I'm out, then drive a couple, few miles then the jeep more or less idles properly.

did this exact situation apply to you? stalled/died first few stop signs/lights until engine warmed up?

thx, I appreciate your help.

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post #11 of 42 Old 03-19-2020, 03:07 PM
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Originally Posted by 0hcanada View Post
glad to hear your issue is cleared up/fixed. but, I'm hoping to glean some Intel from you.

I have a follow-up question about your "engine stalling/dying" symptoms because they all appear similar to mine; however, one symptom you describe is missing as far as my experience goes.

I'm assuming this happened only when the engine was cold?? however, did the "engine stalling/dying" last for only a few (3 or 4 stops) then kinda clear up where the jeep would idle better after running a few minutes and thereafter??

mine does this getting outta my neighborhood. 3 or 4 stop signs (the jeep stalls/ dies) until I'm out, then drive a couple, few miles then the jeep more or less idles properly.

did this exact situation apply to you? stalled/died first few stop signs/lights until engine warmed up?

thx, I appreciate your help.

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What kind of choke do you have? This sounds more like a choke or fast idle issue to me. My mechanical choke takes forever to open up (I think because the stove pipe is cracked) and will stall if I let off the gas until the choke fully opens. Itís also impacted by the fast idle which should be kicking up your rpms until the choke is fully opened. Again mine isnít currently set right (I had it right once, but then I rebuilt my carb and havenít had the time to get it set right again - itís either way too fast or not enough). But my Jeep does this every time I run it right now. I just let it warm up until if I kick it down it doesnít stall. Iím installing a Tach this week to make setting my idle and fast idle on the fly easier.


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post #12 of 42 Old 03-20-2020, 09:27 AM
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One question I have to the OP is "did the RPMs drop when you were moving and coming to a stop, or would it do this sitting still and just pressing on the brakes?"


Moving and coming to a stop, the momentum on the fuel in the fuel bowls could show a float issue.



Being it was a leaking gasket on the carb, the demand of the diaphragm just exacerbated the vacuum leak.

Rick

1978 CJ5 5.0HO/T177/D300, '86 D30/D44 WT axles, 'glass body, 31x10.5 BFG A/T, TDK galv'd frame - DD and weekend toy


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post #13 of 42 Old 03-22-2020, 12:09 PM
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Quote:
Originally Posted by Cutlass327 View Post
One question I have to the OP is "did the RPMs drop when you were moving and coming to a stop, or would it do this sitting still and just pressing on the brakes?"


Moving and coming to a stop, the momentum on the fuel in the fuel bowls could show a float issue.



Being it was a leaking gasket on the carb, the demand of the diaphragm just exacerbated the vacuum leak.
ok, so to try and be as specific as possible, just took the jeep out. cold start, needed to start a few times (pumped the gas, started jeep, stalled maybe 2-3 times) but once started appeared to idle (sitting still) at or about 700-750; steady.

took off (moving) RPM's increased properly/steadily, but this time when applying the brakes at a stop, no stall (kept idling fairly evenly) . normally, at the stop it would stall, and by number of times this would happen; about the first 2 or 3 stops. after this, usually maintains an idle, and keeps running.

you mention "do the RPM's drop when I'm moving, or coming to a stop ". not sure if it is related, but many times when sitting at a stop the RPM's drop erratically almost to the point where it wants to stall, but picks right back up again (I have a short video off the Tach doing this, but can't seem to attach it to the post).

so, these are the two classic things that happen fairly regularly or 99% of my starts, whether or not they're related.

be happy to trouble-shoot more if needed, as well as sending that video clip if helpful.

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post #14 of 42 Old 03-22-2020, 03:52 PM
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[QUOTE=PottsyCJ5;40907395]What kind of choke do you have? This sounds more like a choke or fast idle issue to me. My mechanical choke takes forever to open up (I think because the stove pipe is cracked) and will stall if I let off the gas until the choke fully opens./QUOTE]

how do you tell which kind of choke it is?

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post #15 of 42 Old 03-23-2020, 06:36 PM
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[quote=0hcanada;40909727]
Quote:
Originally Posted by PottsyCJ5 View Post
What kind of choke do you have? This sounds more like a choke or fast idle issue to me. My mechanical choke takes forever to open up (I think because the stove pipe is cracked) and will stall if I let off the gas until the choke fully opens./QUOTE]

how do you tell which kind of choke it is?

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Videos seem to be a pain to upload these days. You can take a picture and post it though, so take a picture of your carb. Take it before you start it up. Remove the air cleaner so we can see the choke plate. Take the picture from the passenger side, angled down. Doing this will allow us to see what kind of choke you are running and also see how open/closed the choke is.

Rick

1978 CJ5 5.0HO/T177/D300, '86 D30/D44 WT axles, 'glass body, 31x10.5 BFG A/T, TDK galv'd frame - DD and weekend toy


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