Engine running lean

[sweetpeet]

I have a 1975 Amc 360 with a 4bbl carb. My issue is that it is running extremely lean.



It will run for a bit, like 1-2 min, then it dies out. I have tried to turn up the choke, make it less lean, before it died out. The only way it stays running is if I stay on the throttle.

Anyone know what's wrong?

 

[superj]

Your sure its lean? How are you getting that info?

 

[sweetpeet]

Your sure its lean? How are you getting that info?

Hmm I may be wrong, look at that pic above. Is that not lean? The flap in the carb is wide open.

 

[greg92jeepxj]

I once had a AMC 360 in a 78' cherokee with a motorcraft 2 bbl. with the same problem. I checked fuel pump pressure , was minimal so I replaced it thinking the float bowl was running dry . Did not help very much . Still lost power . Tried adjusting choke to compensate to no avail.
I pulled the air horn off to,see the float , found the float needle hanging up and not opening completely . Rebuilt it with a new needle and seat and float . Was good for a while. Ended up,replacing the carburetor . Was better , but was never satisfied with it. I do not recognize the carb on your engine , maybe someone had the same problem I once did and changed it ?
Could the float bowl be dirty from dirt gaining entry through the vent ? Causing a restriction in the jets and idle passages ? Has carb cleaner worked clearing passages ? I'm sure you tried this already , but just trying to figure out where your lean spot is coming from . What do the spark plugs look like ? If they have the white appearance like the wrong heat range , yes that would be an indication of lean condition . Check choke adjustment , but I think more proof is needed to be sure the engine is in fact running lean and not just " choking out " . Any vacuum leaks ? Lines and gaskets ? PVC , power booster , etc. ? Heat riser valve sticking ? So many things to check .
But all these items must be checked before we condem the carburetor .

 

[sweetpeet]

I once had a AMC 360 in a 78' cherokee with a motorcraft 2 bbl. with the same problem. I checked fuel pump pressure , was minimal so I replaced it thinking the float bowl was running dry . Did not help very much . Still lost power . Tried adjusting choke to compensate to no avail.
I pulled the air horn off to,see the float , found the float needle hanging up and not opening completely . Rebuilt it with a new needle and seat and float . Was good for a while. Ended up,replacing the carburetor . Was better , but was never satisfied with it. I do not recognize the carb on your engine , maybe someone had the same problem I once did and changed it ?
Could the float bowl be dirty from dirt gaining entry through the vent ? Causing a restriction in the jets and idle passages ? Has carb cleaner worked clearing passages ? I'm sure you tried this already , but just trying to figure out where your lean spot is coming from . What do the spark plugs look like ? If they have the white appearance like the wrong heat range , yes that would be an indication of lean condition . Check choke adjustment , but I think more proof is needed to be sure the engine is in fact running lean and not just " choking out " . Any vacuum leaks ? Lines and gaskets ? PVC , power booster , etc. ? Heat riser valve sticking ? So many things to check .
But all these items must be checked before we condem the carburetor .

Its an eledebrock. I'm gonna try to swap it for a Holley that I got and see if there's any change.

 

[69jeepcj]

Did you do anything to the jeep before this or did this just start to happen out of nowhere?? As I understand it, when you close the choke, that makes a leaner condition, not when its open, so if you choke flap is wide open then the choke isnt leaning it out. have you adjusted the idle screws any to see if it will richen up? VAC LEAK somewhere??? Almost sounds like a big vac port on the carb is unpluged somewhere. I would start by sprying carb cleaner in every passage you can get to, and check good for vac leaks. Can you post a pic of the choke side of your carb?

 

[Gennybro]

I was thinking of it being a vacume problem, or something not working properly due to being dirty.

 

[sweetpeet]

I think I may have found a solution. I came to the conclusion that my fuel reg was malfunctioning so I removed it and then swapped in the fuel filter with one that had a fume return.

Haven't really driven it yet but ill post the update tomorrow when I do the drive test.

 

[69jeepcj]

I would put a presure gauge on your fuel line to see what your fuel presure is, most vac gauges can be used as a presure gauge too. Your engine needs between 5-7 psi to run right, any more and it can push fuel past your needle and seats, power valves ect.. and can drip fuel into the carb when enginge is off, any less presure and it just wont run right. If you had a fuel regulator on the engine, I would suspect someone put it on there for a reason, so I would verify by checking fuel presure...
Hope thats all it was. Good luck

 

[sweetpeet]

I would put a presure gauge on your fuel line to see what your fuel presure is, most vac gauges can be used as a presure gauge too. Your engine needs between 5-7 psi to run right, any more and it can push fuel past your needle and seats, power valves ect.. and can drip fuel into the carb when enginge is off, any less presure and it just wont run right. If you had a fuel regulator on the engine, I would suspect someone put it on there for a reason, so I would verify by checking fuel presure...
Hope thats all it was. Good luck

Yah I put it on there. I was concerned about the pressure before but it never got over 4 psi.

 

[superj]

that is a weber carb in the picture. that is what the w and the magneti marelli is from. weber made that for another manufacturer. have you popped the top o nthe carb and looked inside? if its dieing out slowly, i would imagine you are running out of fuel in the bowl or something like that. does it run warmer then normal or cooler then normal?

no vacuum leaks though?

 

[69jeepcj]

4 psi is low, and as said above would think it is starving for fuel. I would check you carb GOOD to rule it out, then buy a new pump. Check the psi of the pump before you buy it. you may have the proper psi pump now but it may be on its way out and getting weak. There was a regulator on it which tells me at some point it pumped more than 7psi and needed to be turned down. Fuel regulators werent factory stock on your engine, so someone put it there for some reason.

 

[greg92jeepxj]

Yes , 4 to 7 psi is the standard mechanical fuel pump pressure for a single two or four barrel carburetor. Usually , in a carburetor application , a regulator is used with a high volume fuel pump , but only when a high volume of fuel is in demand such as a dual quad setup with large jets for high rpm and a high idle speed . I.E. , racing application . When I read there was a regulator in line , I was scratching my head , but felt it does not belong there. I agree that whatever carb is mounted , make certain the fuel pump carries adequate supply . 4 - 7 p.s.i. Is the normal application . Yes , application . Any vapor return lines ? The pump should have a fitting for it if it was factory OEM . Hope there are no issues with adequate engine vacuum (17-21 psi) , a healthy engine should pull fuel without any need of a pressure regulator. Now I wonder , what reason would someone put on a regulator in line with a single four barrel ? I don't think your running a high rpm top fuel high cube multi carburetored engine ? It's just that I was taught that these regulators are used in a high demand application and I don't think we run that kind of rig in this club , do we ? Well , I agree , the right carb for the engine with the proper fuel pump and some healthy engine vacuum should get the job done .