Poor performance when cold

[Aaron]

I have an 86 GW that is 100% stock. It has a problem that I'd like to sort out as it is quite annoying. In the morning, I tap the gas, and the truck starts right up. If I tap the gas again, the idle settles down to a normal speed, and the truck seems to be running fine. However, when I start to drive it, it feels like its choked. At idle, its fine, and right off idle its fine, but over that it feels very restricted. It takes about 4 miles for it to run right. I replaced the thermostat (the old one was stuck open, and it got about 50% better, but its still a problem). I suspect the problem is the flappers in the air cleaner's snorkel. What moves them? Are they problematic? Once the truck totally warms up its fine.

[Stuka]

Thats called "Let the engine warm up".

Driving on a cold engine is NOT good for it. It causes excess wear as the block isnt expanded yet. 4 miles sounds about right for the engine to fully warm up if the roads are flat.

[Aaron]

No, its not just cold, something isn't right. It can sit and idle for 5-10 min beforehand and still do this for 4 or so miles. When its acting up, its very difficult to drive. It really won't go at all. 30 or so MPH max. It will still be doing this when the temp guage is above the blue section, and the heater is blowing hot air. I know this isn't how its supposed to be.

From what I understand, letting a car warm up (beyond 30 sec or so) is actually worse for it then just driving it. The oil will take much longer to heat up at idle then it will at operating speed.

[reddog]

Sounds like it is either the choke pull off ( the vacuum operated diaphram on the rear passinger side of the carb) that pulls the choke open some to improve drivability, the flapper as you suspect or just the choke adjustment. As I recall the hot air flapper is controlled through a TVS (theromstatic vacuum switch?) that is in the air filter. It controls the outer flapper in the snorkel of the air cleaner so air is pulled in either cold or from the heat riser. I don't think that the flapper would cause such a noticable drivablity problem though...

Kerry

[johnwom]

I agree with Kerry. I have had a similar issue and have found some likely culprits in the choke, vacuum and EGR systems. All 3 will need to function properly for best performance.

First, check your choke mechanisms and make sure that they are all moving freely. My '81 had some rust on the hinges and levers on the choke mechanisms that were inhibiting the free movement of the butterfly flap on the carb.

Next, do like Kerry said and check the vacuum lines (make sure they are even there, some of mine were missing). To me the best thing to do is to just replace them. Vacuum hose is cheap and you probably won't be able to see any tiny cracks or whatever that may be causing a leak so just replace the vacuum lines.

Lastly, check your EGR system. My EGR valve wasn't hooked up to anything at all. There should be a forward delay valve between the EGR valve and the CTO switch. This valve will keep the EGR system from draining the manifold pressure too quickly when you accelerate.

The heat riser valve in the snorkel of your air cleaner is operated by a thermal vacuum switch near the mouth of the carb inside the air cleaner cylinder. I like to make sure mine is hooked up at this time of year but I seriously doubt that that is what's causing your driveability problem.
smile.gif
Good Luck,
John

[letank]

How cold are we talking....

After a few miles how is your choke plate.... partially open or totally open. It could be running lean.

I had the same problem..... starts fine, accelerate fine with no load.... but as soon as i was in gear.... and on a steep climb... it was a hog.

Michel
74 wag

[Aaron]

reddog: It "feels" like the choke is staying on way too long. I'm gonna check this choke pull-off part out this weekend. It makes sense what you said about the flapper not really having much effect. I'm also gonna lubricate all of the carb pieces, includeing everything associated with the choke
johnwam: I checked all of the vacuum lines and replaced all of the suspect ones. Like you said, I'll take a closer look at the EGR valve. After reading these replies, I'd bet the problem lies somewhere in the EGR valve or choke take off.
Michel: Not real cold. Maybe 40 degrees. Never had a chance to look at choke plate, was in a hurry to get to work, and figured it had to do with the thermostat being stuck open. It really reels like the choke stays on too long. I'm gonna investigate more this weekend and tell you all what I come up with

Lastly, what do the vacuum lines on the thermostat housing do?
-Aaron

[johnwom]

Aaron,

I also did a TFI ignition upgrade when I replaced my vacuum lines so it would be difficult to say which action had more impact. I do know that The Chief starts and runs much better now.

Is the line from your thermostat housing a farily thick one? I'll check mine for you but if memory seves me correctly, that one goes to the carb just right in the front there.

John

[Aaron]

Last night I started the Jeep up and let it run for 30 sec or so. When I got underway, the performance was very bad. After about 6 miles, I finally pulled over and pulled the air cleaner off to look at the carb. Sure enough, the choke was still on. Keep in mind, the truck was totally warmed up according to the temp guage. I fiddled around with it for a minute, (nothing seemed frozen or stuck, it just felt like a spring was keeping the butterfly 90% or so closed.)and all of the sudden the choke was off, and the truck ran fine. This morning I let the truck warm up outside for 10 min. It still took like 10-15 miles for the truck to start running right.

There is a brake line type fitting on the choke. I imagine it carries coolent. Would the small coolent leak in my radiator have anything to do with this unit not working correctly? I thought maybe it works off pressure rather then temperature?

Can the choke be bought seperately at an auto parts store?

Lastly, I'm gonna tackle the SUPER LEAKY rear main seal tomarrow. on an '86 with a v8, do I need to move the y pipe?

-Aaron

[Panoscopic]

My Wag has been extremely cold blooded from the time it was new. It was less of a problem in LA, but its downright dangerous in a Chicago winter. I've looked at everthing and still have yet to find a solution....

[Aaron]

Thanks not what I wanted to hear :(

[Don S]

Originally posted by Aaron:
There is a brake line type fitting on the choke. I imagine it carries coolent. Would the small coolent leak in my radiator have anything to do with this unit not working correctly? I thought maybe it works off pressure rather then temperature?
-Aaron..
Aaron:...
I don’t have experience with that ‘late model’( MC-2150-?)carburetor. Your problem is probably the choke system needs setting and the heat riser may not be operating correctly. Read the link below…it will tell you about the choke…
http://www.ifsja.org/tech/fuel/2150.shtml

... Some choke setups have a heating system and if the system gets clogged-up the choke is not going to open back up soon enough. When cold, the heat riser in the exhaust header pipe forces some of the hot exhaust into the intake manifold. The carburetor sucks the exhaust through a metal tube and through the choke spring.
... This system also heats the carburetor for better combustion of the gasoline. Carbon can clog the passageways up….
Good Luck CUL ;) … ds..
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[Ernzo]

Originally posted by Aaron:

There is a brake line type fitting on the choke.
Can the choke be bought seperately at an auto parts store?

-AaronOn the passengers side of the carb, there is a metal tube. IF that is what you are referring to, it carries heat to the choke from a 'stove'. I believe there are actually 2 tubes.

I would warm it up and ensure that the choke is open. Ensure that the tac motors are functioning. Ensure that the fast idle is set correctly as well.
The flappers are vacuum operated. The outside one is closed by vacuum until the motor is warm. CLosed, it allows the motor to suck heated air through the pre-heater tube that attaches to the snorkle and the exaust manifild. You can see the holes. The inside one is closed until the motor is turned on, then it opens. It opens on straight manifild vacuum. It is closed to keep fumes in.

When warm, both doors ought to be open. IF the inside one is closed, it is choking the motor.

There are detailed diagrams here on this as well, really helped me. Luck!

[Lippy]

I have an '88 GW with the same exact problems. It has been a personal vendetta to find the reasons behind it! I actually have 2 '88 GWs. One of them will start stone cold and run like a champ in 0 degree weather. The other one will load up in 30 degree weather and can barely be driven with the choke flap "springing shut". The 88 that runs great in 0 degree weather is all stock but the heat riser is wired open and the heat riser tin on the passenger's side manifold is long gone so there is no hot air being pumped into the air cleaner when cold since there is no flexible tube in place. There goes that theory! This is what I've come up with. Make sure the choke pull off is working correctly. More importantly make sure there is 14 volts at the wire that plugs into the choke coil at the passenger's side of the carb. Also, make sure the choke coil is correctly grounded. I ran a small jumper wire from the negative battery side to the choke coil housing. Just did this today(friday) I will post after tomorrow mornings cold start with results. I'll let you know if I definatively find the problem!

[johnwom]

I'll be the first one to tell you I don't know much about carb tuning so take this with a grain of salt (the size of a meteor).

I hear about a lot of problems with electric chokes. I also hear a lot of resistance to going to a manual choke but I can't understand why. I've never had, (or even heard of), a problem with a manual choke. I know they sell manual choke kits for about $10, so why not try one? At least you'll be certain of its position.

Also, I think the TFI upgrade helped the cold performance of my FSJ a lot and it was too easy.

John

[Don S]

Originally posted by Lippy:
I have an '88 GW with the same exact problems. It has been a personal vendetta to find the reasons behind it! The other one will load up in 30 degree weather and can barely be driven with the choke flap "springing shut". The 88 that runs great in 0 degree weather is all stock but the heat riser is wired open and the heat riser tin on the passenger's side manifold is long gone so there is no hot air being pumped into the air cleaner when cold since there is no flexible tube in place. There goes that theory! I'll let you know if I definatively find the problem!..
Lippy:...
WOW!!! :confused: :confused: I that makes me wonder why all the manufactures wasted time and money installing those unneeded devices in the first place :rolleyes: … …DUH !!

… I removed my exhaust gas riser (not hot air riser) and installed a manual choke cable… :D
Good luck ;) … CUL… ds..
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76 406 QT TruTrac 2"lift 31x10.50s been over 261 Colorado MTN Passes since '85-BRC#30093 http://www.sharetrails.org/ –Join and save your Trail
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[Aaron]

Lippy:

Did your mod work?