Possible carb vacuum leak

C

cameron.rw

Member
Joined
Jul 20, 2020
Messages
31
Location
Bridgeport, OH
So here is the story on my weber 32/36 for my 4.2. When I got it I could tell a slight sputter in performance at low speeds. I could hear an almost hissing sound when putting it into Drive and Reverse. In park and neutral I really didn't hear much. So I decided to make sure the Idle and mixture screw where in the correct place. I was noticing the Mixture wasn't really making any affect at the two turns out. Only when it was turned in completely was I able to to really feel the engine to run rougher. I then just put the idle and mixture screw in the recommended position. (1.5 turns and 2 turns).

Today I went back to jeep and it was basically refusing to start. I noticed I left the choke on all night (this weber has the manual choke) but I do not think that would cause this. I can get it to start and run as good as I did before by putting the idle screw all the way turned in. Now the mixture screw has basically zero affect. But it did not do much before this.

I am thinking this is a vacuum leak because of the hiss I can here when I put it in drive.

I am a beginner so I am not really sure how to start here.
 
By chance did you do anything with the timing, perhaps a vacuum line? No start could be a timing issue but I have zero experience with that engine but lots of troubleshooting with older engines.

On my 92 the timing cannot be manually adjusted
 
The only thing I touched was the idle and mixture screw. This is my first jeep and a car with a carb so a lot of this is new to me. Any help on what to do is a help. I am seeing some tricks online to search for a vacuum leak but just checking for help. Some of the lines seem pretty dried out. so I am assuming maybe a rubber tube is leaking or the leak is directly on the carb. The hissing sound appears to be becoming right on or maybe near the carb.

but the only time I can really hear it is in that video when I rev it quickly and when I put it in drive.
 
I am wondering if the vacuum leak is just from the brake booster. I noticed that the brake hisses when you press the brake so I know that was bad. But could it now cause the engine to barley idle and has lowered the slug performance?
 
cameron.rw said:
I am wondering if the vacuum leak is just from the brake booster. I noticed that the brake hisses when you press the brake so I know that was bad. But could it now cause the engine to barley idle and has lowered the slug performance?
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That may be the connection to when you put it in gear because you're on the brake?

With the engine off press on the brake pedal and hold it down then start the engine. If the booster is working you will feel the brake pedal go further down.
 
The booster is definitely leaking and it has since I got it. When the brake is pressed you can hear a hiss from it. Maybe the reason from putting it in gear because I am on the brake. But could the brake booster leak be so bad now to cause this rough to almost no idle, along with the leak sound with the throttle. As of now to get it to idle I put the idle screw all the way in. then it cranks up to similar performance it was yesterday. But as you can hear in the video when i hit the gas quickly you can hear a vacuum leak and i'm not touching the brake. The slugish feel of the engine and at low speeds was there before it now becoming more rough
 
Flyer58 said:
That may be the connection to when you put it in gear because you're on the brake?

With the engine off press on the brake pedal and hold it down then start the engine. If the booster is working you will feel the brake pedal go further down.
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it sounds like it’s coming Directly from the carb. I’m thinking maybe it’s leaking around the base or many a manifold leak. The mixture screw appears to not really affecting anything expect in the extreme. This was taking with the Jeep in R
 
Get a piece of garden hose or PVC to use like a mechanics stethoscope. You can really pinpoint where the sound is from. It's hard to tell the sounds on my phone. Does the brake vacuum line go in right at the carb or far away on the manifold?
 
Well when I pump the brakes with the engine on I can hear a hiss coming from the brakes. I’m not sure if that’s normal. But I did the test to see if the brake goes down when I turn the Jeep on and it does. So idk if that means it’s still working or maybe it has a slight leak. The hiss noise from the carb sounds like it’s coming from directly inside of it. Not around it but inside. I’m thinking since I have to have the throttle open more and the mixture screw does nothing that the carb is definitely getting or has air leaking. That noise in the video sounds like it’s coming directly inside it.
 
That hissing may be a normal sound from the 2 barrel carb. The hesitation could be because it needs a tune up. How to the spark plugs look? I would start with a a Sea Foam treatment where you slowly pour or siphon a can into the carb, let it sit for 20 minutes or so then go for a drive. Look for a YouTube video about it. I've had it work wonders for cleaning out the intake and valves. It will make lots of smoke as you pour it in.
 
I wasn't sure if that sound is normal or not. I am fairly sure the idle was much better yesterday than before. I don't think I had the idle to the extreme last time. But i know the engine is running rough to barley at all at the stock settings on the carb. So something is up
 
After thinking what is happening here the solution may be simple. I was reading that the 32/36 carb needed to be run at 1.5 turns for the idle screw and 2 turns for the mixture. But I’m thinking those are for another engine. Listings for this carb for the 4.2 say turn them to your vehicles specs. I’m pretty sure both these screws were not in the 1.5 and 2 turn positions when I looked at them so maybe the 4.2 has different settings and I’ve just been getting caught up on those numbers? So I think I need to actually settings for those screws. Unless it’s best to just do it by ear
 
From messing with it today this is the best I could have gotten it. The idle screw is basically turned completely in and the mixture screw really doesn’t seem to affect it much.


I got the idle a bit higher and it seems to get rid of the sluggish performance at lower rpm. But the engine seems to be running rough and causes the dash and wheel to shake
 
You really need to pull out the spark plugs and check for color or oil and then clean and re gap them. They tell a lot about the mixture and engine condition. Look online for a plug comparison chart to see if it's running lean or rich or some other condition. Then drive it around for a while as you normally would and check them again. Sometimes letting it idle for 15 minutes will give them a false color with high carbon that's not accurate.

Here's a chart:

1a.png
 
New plugs will help a lot. That looks like dry black carbon which would mean it's ruining rich unless it looks wet from oil to you. The gap looks too big also but it's hard to tell.
 
Flyer58 said:
New plugs will help a lot. That looks like dry black carbon which would mean it's ruining rich unless it looks wet from oil to you. The gap looks too big also but it's hard to tell.
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I took a wire brush to the plugs and it sounds so much better. I’m assuming some seafoam and new plugs would help a lot. The mixture screw is definitely making a difference now.
most plugs were like the dry carbon but some seemed a bit wet possibly. But the other plugs had a lot more build up than that plug.

 
Possibly wet from unburned fuel or residual oil. If there's that much on the plug the Seafoam will help clean the intake and valve area too because it will be covered with carbon and oil too.
 
The last owner had it serviced only two years ago so I really wasn't figuring them to be that bad. But I think its been since that service the plugs or any other work has been done. Ill try the seafoam when I get back to working on it. I would hope something isn't horribly wrong that caused this. Thanks for the help so far!
 
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