Hesitation/bog on throttle tip in until warmed up

[kingmatt16]

89 Wag, 100k miles, cold New England winter now. Carb is brand new 2 barrel 2150, tuned to spec. Starts excellent, high idle and 2nd cam settings are correct rpms to spec on cold start. Car will stall out unless you let it idle for over 5 minutes. Also the real problem is that when you apply the thottle it starts to bog real bad for about an 1/8" of travel, if you can feather it past that point, you can take off as fast as you want beyond that initial hesitation. It will do this for several lights for at least 15 minutes or FULLY warmed up. When warm the tip-in hesitation is gone and it runs and drives 100%. Also cold starts later in the same day do not elicit the same hesitation problems as a 1st morning start. Any ideas?

ps it has been to the jeep dealership 3 times for tuning this december to try to catch this problem. no vacuum leaks, timing is corect, carb has been disassembled many times, new float & spring, new choke pull off...plugs wires, tfi, fuel pump, all done within last year as well as more stuff im forgetting

[Lippy]

Check the EGR temperature solenoid in the air cleaner-it is the blue one mounted on the side of the air cleaner housing. Sounds like the vacuum is being applied to the EGR before the engine is at correct temp. Also check the CTO at the back of the engine. It is right near the firewall.

Good luck.

Lippy

[reddog]

I have little experiance with cold weather tuning but I do get up into the mountains during winter and my 87 runs fine.

I would first check the accelerator pump linkage and make sure the spring that drives the accelerator pump (it is coiled around the drivers side butterfly shaft) is well lubed and opererating smoothly. You might also try setting the accelerator pump one step richer.

The 2150 is a pretty simple carb to rebuild and tune. 3 trips to the dealer?? :( I would consider doing it yourself or finding a new mechanic.

Kerry

[FrankenJeep]

Might be your accelerator pump (though that should be an issue with a new carb). This seems to be common with Motorcraft 2 bbl carbs. Mine does it too, but I hope to solve it with a Edelbrock Performer and Q-Jet. :cool:

[Ernzo]

well, if your choke unloader is set wrong, that would do it. when cold, take off the air cleaner, pump the gas once. do not start. go out and look at the choke plate. is it closed? is it all the way closed with no tiny gap at all? it ought to be closed with a tiny, matchstick sized gap or maybe a little wider depending on how cold. now start the truck, wait about 20 seconds, rev it a little and go look. any changes? the egr idea is good also. timing. the 360 like some advance, especially with all the smog stuff. carefully check the specs on timing advance. i use 18 degrees here at 5280 feet! sea level is less, but it varies from jeep to jeep due to the condition of the cto's etc.

[ClarkGriswald]

These things never run right unless they are warmed up.. you can improve on it a bit but its still gonna suck until its warm.. Ive been drivin around on like 4 cyl's lately until it gets hot.. then mabye I get 6 or 7 hahah.

[olin18]

I would assume that if the carb has been rebuilt it has a new power valve. But the problem you speek of sounds like maybe it is running rich, and that can be the result of a bad power valve. Take off the air cleaner and pull the vac hose that goes into the front of the carb on the passangers side on the bottom. This is the vac like that feeds the power valve. When you pull this line check to see if gas comes out. If any gas at all comes out of this tube, or if there is gas in the tube... you have a bad power valve. Even if the carb is brand new rebuilt it could be bad. They seem to poop out at the drop of a hat.

[Coley]

I had very similar problems that had been bugging me ever since I bought the dern thing. I replaced the choke pull off and it cleared it up. Turns out the choke pull off was halfway working, it had a hole in the diaphram, so when i tapped the throttle to back the idle down after starting it, it would pull off some, but not enough. While fiddling with the choke pull off while it was still on the carb, I broke it completely and then it really started to run like you describe. Bucking and snorting, black smoke, ran fine after about 15 minutes of warming up.

You can test the choke pull off by removing it (easy) and seeing if it will hold a vacuum.

Good luck!

[ December 17, 2002, 08:31 AM: Message edited by: Coley ]

[CLS]

I have the same problem with my engine. The carb was completly rebuilt and still if you try to drive it without warming it up, it really bogs down. But after it warms up it seems to drive fine most of the day. From what everyone is saying this is mostly normal.

Maybe finding the right combination of timing, idle settings and fuel mixture settings is the key. Or just live with the way it is.

Chris

[letank]

Check the choke plate operation.... about a matchstick or 1/8 is good... use a drill bit to check the measurement, i would say more like too lean, this is why when you feather the throttle it gives a little gas.... and prevent stalling, this is why the accelerator pump is also mentioned.... gives same symptoms but it would do it cold or warm.

Been there done it.

Bonne chance

Michel
74 wag

[JINGA]

Do you have a heat riser?

That bogging can indicate clogged exhaust. COuld be the result of a heat riser that's a bit slow to open.

As it finally heats up, it'll open and then be okay. Sounds a bit like what you're describing.

HTH
JINGA

[james1414d]

if you warm it up completely in the morning and it dosent bog, its your choke. might also check to see if your vacuum advance is hooked up properly and working.