My Jeep runs better choked

[thistle3585]

My CJ5 has a AMC 304 V8 with manual choke and stock MC2150 Carb and it runs better when it is choked than when it is not. I usually let it warm up in the morning for about ten minutes and the temp gauge is at the 1/3 point. If I take the choke off then it gasps as I accelerate from a stop, but when it is on it runs without issue. I live in a small town, so a trip to anywhere is ten minutes or less, so I doubt it ever truly comes up to temperature. Is this a function of cold weather and/or such short drives or could there be something else at work? I've only had it two months, so I can't say how it runs in warm weather however we have had a mild fall/winter. It isn't a big deal but I am just wondering if I'm not getting the full "choke" effect.

 

[CJ]

Well... AMC Jeep never really sold a vehicle that needed to sit for ten minutes before you could drive it. . You should be able to set the choke by pressing the gas pedal to the floor once, start and then drive away.

So, tell us about your setup. Do you have the factory emissions? The factory manifold exaust heat? What about the air filter? Is it stock? What about the ignition and charging system? If you can, take as many pictures as possible and post them.

 

[thistle3585]

Everything is original and there doesn't seem to be any sort of special emissions setup like I've seen on CA models. The PO installed a manual choke. I've wondered if my idle is set too low just by sound, the tach doesn't work, but it hasn't been a problem. It does run better if I let the engine warm up instead of jumping in it and taking off cold, but I'm warming it up to warm up the interior cabin more than the engine itself.

I recently rebuilt the carb. It just pauses when I accelerate from a stop and it seems to be worse on colder days and it goes away altogether when I pull on the manual choke.

I'm not sure what other info to supply.

 

[Posi]

If your engine runs better with the choke on then your running lean. It could be a simple adjustment or a vacuum leak.

What is your vacuum reading?

How many turns out are the two adjustment screws?

 

[thistle3585]

If your engine runs better with the choke on then your running lean. It could be a simple adjustment or a vacuum leak.

What is your vacuum reading?

How many turns out are the two adjustment screws?

I don't know how to take a vacuum reading but I can do a bit of research and figure that out. I believe the adjustment screws are three full turns maybe three and a half.

 

[Posi]

There's plenty of info on using a vacuum gauge a quick search will do. Three full turns seems a bit much, when I tune my 2100 I start at two full turn and work in from there. It's possible you have a vacuum leak.

 

[jeffgtoman]

It's possible that your idle circuits in the carb are clogged. This happens often when the vehicle sits long enough for the gas to go bad. The gas turns hard and clogs the passageway that the gas travels thru at idle. I see this all the time on motorcycles when people don't store them thru the winter properly.

You could try a gas additive but it usually requires a carb soak and rebuild to get the passages cleaned out.

 

[7D8CJ]

Sounds like you need to advance the timing a bit.

 

[Torxhead]

I thinking of carb floats being too low causing a lean condition. Sometimes they get that way from vibration and bouncing around in off road conditions. Spark plug deposits can indicate a lot.

 

[Posi]

It's possible that your idle circuits in the carb are clogged. This happens often when the vehicle sits long enough for the gas to go bad. The gas turns hard and clogs the passageway that the gas travels thru at idle. I see this all the time on motorcycles when people don't store them thru the winter properly.

You could try a gas additive but it usually requires a carb soak and rebuild to get the passages cleaned out.

I recently rebuilt the carb.

Could be the float setting as torxhead mentioned as well.

 

[thistle3585]

Thanks guys. I rebuilt the carb in November and paid careful attention to the float height based on the instructions I got on the rebuild. I also replaced the fuel filters and used a can of Seafoam in the gas for good measure. I did have some problems with on jet, so I disassembled it and cleaned it and it was working well. I replaced the air filter, installed a filter for the carb float and replaced the filter material in the oil cap. I've also replaced the spark plugs. Oh yeah, and I haven't driven it off road at all and average about 50 miles per week.

So, I'll get a vacuum gauge and check that. What should the reading be at? I'll also adjust the idle screws in one turn and see if that helps.

 

[Posi]

I like to see 19 or 20 psi I believe the range is 16-21. If nothing changed then turning the screws in at this point would only lean it out more. A vacuum gauge will tell you if there's a leak then you have to find it.

I would focus on a vacuum leak first before moving on to something else if need be. Air should enter the carb to mix with fuel and that allows the engine to run like it’s supposed too. Occasionally you will end up with a leak where air enters where it shouldn’t and when that happen it doesn’t pick up fuel and the engine runs poorly. In your case you add fuel to a lean mixture by using the choke.

A typical way to check for leaks would be to use an aerosol spray i.e. carb cleaner or starter fluid. While the engine’s at idle spray the suspected areas if there were a leak the engine would ingest the spray and the RPM would change and you would have found the spot. Something that does work good and what I use is propane for a cleaner and faster job just do the same procedure as I already mentioned replacing the aerosol with propane (do not light).


Hope this helps

 

[jeffgtoman]

All of this advice is true. Any one or all of the ideas are possible. It is hard to help you with this problem because there are so many variables involved. You should try to get some help that involves a timing light, a fuel pressure gauge, and a vacuum gauge. A competent older mechanic familiar with carbs is likely to find several things wrong. I just thought of another possibility. Is your accelerator pump working properly? We'd all like to help you but this may be something you need to get onsite help with. Let us know how it goes.