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Weber Carb problem???

Weber Carb problem???

GOPDiesel

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I'm a new Jeep owner. It's a AMC 258 i6 / 4.2l V6 with a Weber carb on it. I have a bad driveability problem when accelerating. The rig runs good at idle, around town and on the freeway. BUT, when I press the accelerator 3/4 to all the way down, and put the rig under load, the engine basically stops and I lose all power. I can usually back off the gas and it stays running. This mainly happens while going up inclines. It can happen in any gear. I've recently had the carb checked by a mechanic so it could pass emissions. I did pass. The driveability problem occurred before the mechanic worked on it and his work seemed to improve it. It was worse before. I have fresh gas and have replaced the fuel filter.

Any ideas on what my next step should be? I'm a weekend mechanic and don't know much about carbs. What I do know from my experince with cars, trucks and motorcycles is that it sounds like it's starved for gas. The fuel pump looks pretty old. I don't know much about the past history of the Jeep.

What would cause this issue while under load and going up hills under hard acceleration? Any ideas?
 
First off, welcome to the site GOPDiesel and to the world of CJ's welcome.webp.

Just FYI your AMC 258 i6 / 4.2l is a straight six, not a V. It sounds like you aren't getting enough fuel not getting to much. If you were flooding the carb, it wouldn't idle well. Webers require a certian (I think 7psi) amount of fuel pressure. If I remember correctly most Weber guys say that Weber suggests an electric fuel pump vs. the stock mechanical one that the AMC 258 i6 / 4.2l uses. You could have a bad fuel pump, or if you're still using the mechanical one, you aren't getting enough fuel to the carb. The sending unit in your tank could have gunk in it too, but that's a stretch. That's all I've got for ideas, but I'm sure there will be other people with more.
 
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first of all, Look at that puny square air cleaner they use and make 100% sure that it is clean and free flowing. If you are clogged then you cannot get enough air for combustion.
Second, check your float level. If it is set to low then you are running the bowl dry on acceleration.
Third, pull apart and clean the carb thoroughly while it is apart.
The carb has 3 circuits for running. It has the idle circuit which sounds like it works fine. that is adjustable with your air mixture screws. and also has pilot jets. If the pilot jets are clogged you will not idle at all.
The second circuit is the cruise circuit. It has the needles and it controls part throttle operation. These are what you adjust when you have surging at a stready throttle or bogging under load. The accel pump helps with this also and usually has a diapragm and a pump arm that is pushed by the throttle linkage. It gives an extra shot of gas to allow the carb to not choke when transistioning from the idle circuit to the cruise and drive circuit.
the third circuit is the drive. It is the main jets and needles repsonsible for everything from partial to wide open throttle. This is the main control of overall fuel mixture. If these are clogged then you will have bigtime bogging and the carbs will just die out like you described. These jets need cleaning and are usually the problem, escpecially if your fuel is bad because they get :dung: in them and varnish first.

So check your air filter, pull your carb and clean it, check your float level and then if it doesn't run after that go to the fuel pump and pressure issues.

My opinion of Weber carbs are not very good. I had one and I hated the thing. they are a bitch to get set up perfectly and keep running. I had much better luck with small Holley 2 barrels and even the factory Carter 2bbl carbs. the factory carb runs great if you just pull it once a year and clean it out.
 
Kane, thanks. I'm not a car guy at all. How would I check the float level? I know I can pull the carb off but am hesitant on tearing it apart. Would any bad vacume line cause this? The cat has been temporarily removed and I'm not sure what other emission stuff is even working. I don't have to take it in again for emission testing or inspection.
 
The vaccum will cause issues at idle and part throttle cruising only. You do not have any vacuum when the throttle is wide open so this could not be an issue. You vacuum is created by the throttle butterflies being almost fully closed. Try to find a Weber manual online and it talks about the float level setting but if yo uare not sure find a friend who can do this. I would bet almost 100% that a good cleaning will fix your issues.
 
I recently put a weber on my 85 and it had issues similar to yours except it seemed to be running richer instead of leaner. A guy in a local jeep club i belong to suggested putting a fuel pressure regulator on and setting it at about 3 psi. He said the factory pump will run at about 6.5 or 7 lbs and it is too much pressure for the float bowl seat and will continually bypass. It sounded ridiculous to me but I reluctantly installed one and I am here to tell you it made all the difference in the world. Its like a totally different motor, idles better, runs out with no problems, no more smoke, much more power. He told me he talked to weber directly and thats what they told him to do. I dont know if this will help you but it certainly made a world of difference on mine.
 
CJ:

I had one, and played around with it on all settings. No difference. I have now taken it off and still no different results. I will put it back on and set it to 3.5 That is what the Weber site says it should be at. I guess I might pay to have it rebuilt ($195) and go from there.

Thanks, Pat
 
Just found this thread. I had fuel trouble with the Weber I installed and could for the life of me not get it running properly. One day on a whim I turned my fuel pressure up to 4.5 lbs and now she runs like a champ.
 
I have found it easy to get irritated with carbs when I fail to step back and remember what functions they perform. They really only meter the amount of fuel to give to the motor during different functions. When they evolved to satisfy the changing environment and introduction of computers to monitor thousands of variables in a micro-second manufacturers added all sorts of parts to make it more difficult to pinpoint problems. But underneath it all the carb still does the same thing. Fuel to air ratios is always critical, and following simple science the best way to set it up. Too much air, the fuel is spread to thin to burn hot enough to make sometimes enough power to just keep the motor running. Too little air, such as higher elevations means too much fuel. Try sticking a lit match into a cup of gas. On a stick of course....dummy, without letting it linger in the fumes above the cup and it won't burn. If you do light the cup of fuel, you just throw a lid on it and it goes out. That's the only variable here, lack of air.
 

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