Electric choke in sub freezing temperatures

[MrPaco]

This is a question for anyone who lives in a cold area, where winter temperatures are often in the teens and 20's, AND still has the mikuni carburetor.

I'd like to hear about how your choke operates under cold conditions so I can compare it to mine.
When it's below freezing it seems like the choke in my truck takes some time to "engage". Here's what happens:

I hit the ignition and the engine starts right up, but if I don't keep my foot on the gas the engine runs really rough for a few seconds (rpms hovering between 400-800) and then it stalls. If i keep my foot on the gas for 30-45 seconds then eventually I feel that the choke kicks in and maintains the rpms at around 1,000 and slowly goes up to 1,300 ,without having the foot on the gas. After a few minutes running at the higher rpm, when the engine is starting to warm up, it will drop to the normal operating rpm, around 900.

So it seems like the choke it's doing its thing, it's just that it takes a minute to get going when it's really cold. In 40 degree temps the choke kicks in right away, it seems.

I've removed the air intake to see if the choke is stuck, but it seems to be moving fine. With the engine off, if I pull on the throttle the butterfly closes right up.

I'm wondering if this how all of them work, or if it's something off with mine, and it should kick in from the get go.

Any thoughts welcomed. Thanks.

[geezer101]

I have had a Mikuni auto choke reactivate from freezing temperatures. Did it to me on highway cruising speeds a few times - it would just lose all power and die. I'd be forced to pull over and let the engine idle for 5 or so minutes before the choke disengages. What I can recommend is a little sketchy but I was out of good options. I used an offcut of core flute (the plastic version of corrugated carboard) and cut a square of the stuff big enough to restrict air flow one one side of the radiator from the front vertically. Abut 1/3 of the surface area should be enough. I drove it to work first up before sunrise and when I got to my destination, I pulled the restrictor out as the afternoon temps weren't cold enough to mess with the choke. Your other option is to take the thermostat out and swap it for a winter rated unit.

Your choke is working perfectly by the way, it's just freaking cold... ;)

[StarquestMan]

Mine seems to be acting kinda strange sometimes too. it used to fire right up in the cold by doing the method the manual states which is to press the gas pedal down once and release it then turn the key and start it but mine seems a little starved for fuel at first which may be something clogged in the carb or the filter. when you checked the choke plate operation was the engine completely cold from sitting overnight? im wondering if maybe there is some hardened grease or something gumming things up? I remember when mine was running right it would start like it was fuel injection in the cold. as it idled and warmed up it would start to run fast and i would have to tap the throttle to kick the choke down a notch, this may be due to a bad vacuum choke opener though. Im going to take a bit of an educated guess but I think either the choke linkage is a bit sticky or it may be starving a bit for fuel somehow?

[MrPaco]

Your choke is working perfectly by the way, it's just freaking cold... ;)

I figured this could be the case, that's why I'm interested in other's experience with it.

Wait, are you saying that your choke closed on you while you were driving? Were you driving in Antarctica?

[MrPaco]

Mine seems to be acting kinda strange sometimes too. it used to fire right up in the cold by doing the method the manual states which is to press the gas pedal down once and release it then turn the key and start it but mine seems a little starved for fuel at first which may be something clogged in the carb or the filter. when you checked the choke plate operation was the engine completely cold from sitting overnight? im wondering if maybe there is some hardened grease or something gumming things up? I remember when mine was running right it would start like it was fuel injection in the cold. as it idled and warmed up it would start to run fast and i would have to tap the throttle to kick the choke down a notch, this may be due to a bad vacuum choke opener though. Im going to take a bit of an educated guess but I think either the choke linkage is a bit sticky or it may be starving a bit for fuel somehow?

Sounds like it's doing the same thing as mine.
Yes, when I checked the choke plate the engine is stone cold from sitting overnight. While I was there I sprayed some carb cleaner just in case.
Your description of how your's was running before is exactly how mine would run. Start right up, and eventually stat to get really high on the rpms and a little tap on the gas would make it come down, I assume that the tap was disengaging the choke.

If the linkage was sticky it wouldn't easily close when I pull on the throttle cable, right? How do I tell if it's staved for fuel? Could it be that the filter is clogged and fuel is moving too slowly?

[geezer101]

Nope, Adelaide (South Australia). I was leaving to go to work @ 4.30-5.00 a.m. and morning temps were 1-5 C. Once you get to highway speeds, the the chill factor drops below that quickly. I was driving a modified Mitsubishi Colt hatch and the radiator for those was a 3 core from factory so it was crazy efficient as far as engine cooling was concerned. The first time it did it, I was thinking the worst case scenario. I was going to be stranded out in the boonies with a broken down car miles away from a work site. What struck me as weird was the temp gauge - it bottomed out. I got it to start, thought "I'd better get my ass to work before it happens again" and took off. Not even 5 minutes later - stalled. Took a breath "right, it runs but not for long. I've got a new T-Coil and it's not running hot. I've got fuel. I'll let it sit for a few minutes idling". It started and idled perfectly so I got back onto the road, kept my road speed down and an eye on the temp gauge. It ran a lot cooler but it didn't die on me so I came up with my McGuyver fix for those really cold morning starts.

*how cold was it that year? - we would lay our hoses out on site (I was operating a concrete pump) and they would freeze stiff within half an hour. Concrete lines, water hose, everything...

[MrPaco]

Nope, Adelaide (South Australia). I was leaving to go to work @ 4.30-5.00 a.m. and morning temps were 1-5 C. Once you get to highway speeds, the the chill factor drops below that quickly. I was driving a modified Mitsubishi Colt hatch and the radiator for those was a 3 core from factory so it was crazy efficient as far as engine cooling was concerned. The first time it did it, I was thinking the worst case scenario. I was going to be stranded out in the boonies with a broken down car miles away from a work site. What struck me as weird was the temp gauge - it bottomed out. I got it to start, thought "I'd better get my ass to work before it happens again" and took off. Not even 5 minutes later - stalled. Took a breath "right, it runs but not for long. I've got a new T-Coil and it's not running hot. I've got fuel. I'll let it sit for a few minutes idling". It started and idled perfectly so I got back onto the road, kept my road speed down and an eye on the temp gauge. It ran a lot cooler but it didn't die on me so I came up with my McGuyver fix for those really cold morning starts.

*how cold was it that year? - we would lay our hoses out on site (I was operating a concrete pump) and they would freeze stiff within half an hour. Concrete lines, water hose, everything...

That's really interesting, and counter intuitive, hadn't though about the wind chill. Makes sense though, that's probably why big rigs have those apron covers on the grills in the wintertime, to reduce the amount of cold air into the engine.

[StarquestMan]

after reading the first post and replying I decided to get off my but and go change out my fuel filter finally. I put a piece of hose on the old filter and blew through it and it felt a bit plugged but not much, it did have lots of sediment in it though that i could see since it was a clear type filter. I replaced it with a new filter that was not clear so it will be a bit hard to check in the future for sediment but i always carry a spare since it seems to clog fairly regularly. anyway after cranking it a bit to prime the new filter it started and stumbled like it has been doing but it smoothed out pretty quickly. I quickly shut the truck off so it wouldn't warm up and tried it again, fired right up! granted the system was somewhat primed and ready but the choke still closed and it ran without the initial stumbling for a minute or so that I had before. If you haven't changed out the filter before its probably due for a replacement since they are easily overlooked in the location that they are mounted in. this may or may not be your problem though. im going to let my truck sit a while out in the cold and try it again. my dad has a scout that he has to put a piece of cardboard in front of the radiator much like the mentioned covers on semi's that they use

[StarquestMan]

geezer is right about the wind chill too, it can affect the way something runs even when the cooling system is in tip top shape. my old boss told me about working in montana where it got so cold that they would have a work van in a warm garage to get everything up to operating temp then they would drive off only to have the thing not run right due to how cold it got. I forgot how cold it got down to where I was at maybe -20 or -30 and I went to open the van door and the metal handle just broke right off. it would even get so cold that the coaxial cable we would run out doors would just snap when bent!

[MrPaco]

after reading the first post and replying I decided to get off my but and go change out my fuel filter finally. I put a piece of hose on the old filter and blew through it and it felt a bit plugged but not much, it did have lots of sediment in it though that i could see since it was a clear type filter. I replaced it with a new filter that was not clear so it will be a bit hard to check in the future for sediment but i always carry a spare since it seems to clog fairly regularly. anyway after cranking it a bit to prime the new filter it started and stumbled like it has been doing but it smoothed out pretty quickly. I quickly shut the truck off so it wouldn't warm up and tried it again, fired right up! granted the system was somewhat primed and ready but the choke still closed and it ran without the initial stumbling for a minute or so that I had before. If you haven't changed out the filter before its probably due for a replacement since they are easily overlooked in the location that they are mounted in. this may or may not be your problem though. im going to let my truck sit a while out in the cold and try it again. my dad has a scout that he has to put a piece of cardboard in front of the radiator much like the mentioned covers on semi's that they use

Nice job!
If the filter is clogged, how would it manifest during regular running of the engine, after its nice and warm? Any tell signs?

[StarquestMan]

Im not entirely sure but it may have to do with that a cold or choked engine using a bit more fuel and not quite having the flow to keep the bowl filled when initially started. mine has plugged a few times with the warning symptom of being difficult to start and eventually it starts to starve the engine when driving. of course my fuel tank has some sediment in it that I couldn't quite get out when I cleaned it so I have had to replace filters more frequently than usually needed.

[Salteen]

I like a manual choke for this. When the water is cold it will choke, when it gets hot it wont, so as soon as you crank it up, say after a long commute and 30 min park, it won't I instantly choke. Manual choke is good for this too.

[StarquestMan]

I tried my truck now that it has sat overnight, seems like the fuel filter helped a lot but not 100% it still shakes a bit on start up but when I give it throttle it doesn't bog down and stall. the vacuum choke opener seems to be doing its job by opening the choke once it starts up and closes again with the engine off and tapping the throttle. so this might be part of your problem MrPaco. does yours bog down when you give it some throttle when it starts up and runs poorly?

[pennyman1]

you need to adjust the fast idle speed if it is stumbling when cold off idle. It is the screw that rides the cam on the choke linkage.

[MrPaco]

you need to adjust the fast idle speed if it is stumbling when cold off idle. It is the screw that rides the cam on the choke linkage.

A friend suggested the same thing, was hopeful this would be the issue. It might be related to this, but not as straight forward as I was hopping.

I followed the service manual steps to test and adjust the fast idle, the results are a little confusing.
I disconnected the vacuum hose from the choke opener and manually set the lever on the fast idle cam. Turned the ignition on, and engine went to 2,200 rpm, adjusted the screw to 2,300 which is what the manual recommended fast idle speed for my truck configuration, and then reconnected the vacuum hose like the manual says to do, which made the rpms go down to curb idle, 900. I think this is supposed to tell me that the fast idle is adjusted correctly, and the vacuum is working.

I let it sit overnight to start it from stone cold next morning, and the start was still rough, no change.
What's weird is that after about a minute of stepping slightly on the gas so it doesn't stall, the choke seems to engage at that point and keep the rpms slightly raised, but it only goes up to 1,300 and it stayed there for few minutes until the temperature needle reached the second notch on the gauge. Then, when the engine is nice and warm, the rpms dropped to curb idle, 900.
So even though the fast idle is correctly set to 2,300, it never went past 1,300...

Should I try adjusting the idle speed screw while it's warming up (and stuck at 1,300)?

[geezer101]

Don't adjust the idle speed screw as all it will do is ramp your overall base/curb idle rpm. Is there any play in the choke butterfly? There should be a little play when the choke is dead cold. If it snaps shut like a mouse trap when you tap it with your finger, it might need adjusting.

*I'd better add this as it may very well affect diagnosis. The Mikuni I was using was the water choked type. Should've paid more attention to the thread...

[xboxrox]

MrPaco, my truck runs like crap (over choked black exhaust smoke) lately when the engine is cold upon first startup... Warmed up it runs good; I don't think stepping on the gas does much to the RPM when the engine is cold & choked (seems the choke is automatic somehow)... Blasting the choke plate with carburetor & choke cleaner in the Mikuni seems to help and cures the problem for a good while... At least it did before; time to do it again... Temps here in Hawaii go as low as 59F once in a great while at 6AM but back to 70s & 80s in an hour... It does not seem to matter what the outside air temperature is coz starting my truck with 80F weather it still chokes itself and runs like it's very rich... The engine RPM does rise with a cold engine then once warmed it goes back to idle, all by itself; tapping the gas pedal don't do a whole lot... When I first bought the truck it was even worse; cold engine = black smoke = super rich = pumping the gas pedal to keep it running... No telling how long (in years?) my truck just sat waiting to be auctioned off by Uncle Sam... To get it started the first time it needed BooKoo starting fluid & cranking galore & more cranking & more cranking and some more; fuel lines musta been bone dry... This was in Barstow, California a rather dry desert area...

Anyway, without reading the FSM -- maybe try cleaning the carb & choke plate hinges with da spray... Moral of the story; moving to a warm climate will not cure the problemo..!
:cookiemonster:

[Salteen]

i had this problem with my weber 38 38, idk why but it does this. I also have a loud popping. I got to tuning the jets and it fixed the problem and it stopped popping on idle. I used 110 jets, though you may want to use a 105 or lower because my butterfly are 38mm and yours are 32/36

[FMS88]

Before you start it, open the throttle about 50% and release it. Check that the fast idle cam has rotated enough that the throttle lever contacts the cam near the end of the cam as circled in this picture:

24287

If it's not at the third notch or beyond as in the pic, thoroughly clean the cam linkage and lube it with a light oil.

24288

The spring for the cam is quite fine, so dirt and grime can cause it to unwind slowly. When operating properly the cam, its linkage and the choke valve should move freely and snap into position when the throttle is opened quickly.

If the lever-cam contact is correct and the linkage fine, check the delay valve and its vacuum hose on the valve cover side of the carb. With a hand pump, the vacuum should leak down slowly - about 1" Hg per second.

[MrPaco]

Before you start it, open the throttle about 50% and release it. Check that the fast idle cam has rotated enough that the throttle lever contacts the cam near the end of the cam as circled in this picture:

24287

If it's not at the third notch or beyond as in the pic, thoroughly clean the cam linkage and lube it with a light oil.

24288

The spring for the cam is quite fine, so dirt and grime can cause it to unwind slowly. When operating properly the cam, its linkage and the choke valve should move freely and snap into position when the throttle is opened quickly.

If the lever-cam contact is correct and the linkage fine, check the delay valve and its vacuum hose on the valve cover side of the carb. With a hand pump, the vacuum should leak down slowly - about 1" Hg per second.

Thanks, will try this in the morning. Dumb question, but what is the best way to get good access to this area to do all of this? I had a hard time getting my hands in there while doing the fast idle test, and didn't have a direct view of what these pictures show, even with the air filter housing removed. Do I need to remove the carb? (hope not...)

[FMS88]

Don't remove the carb. It's a real hassle and shouldn't be necessary for this problem. Best access is afforded by removing the air cleaner, but you're correct, things are still cozy. Removing the throttle lever end of the dash-pot-to-throttle-arm spring will make it easier to see the cam/lever contact points. (I removed the spring to get the above pics.) Other than that, a small mirror and flashlight are the only other things to recommend that will help your evaluation.

[xboxrox]

FMS88 & MrPaco thank you both for this thread & posts... Yesterday was rare, starting my truck it acted OK not choked but it was about 5pm and it was 80F temps all day

[geezer101]

Hmm, I wonder if your carb just needs a good blasting with carb cleaner inside and out, then a hit with WD40 or some other light spray lube. The butterflies and linkages might be gummed up a bit and the cold won't help. The weirdo 34 DATA carb I picked up from a JY was really clogged. The choke butterfly returned to closed position with glacier-like velocity from all of the crap it had collected. After completely stripping it down and removing every last granule of gunk out of it, everything moves fast and free.

[Salteen]

Yeah, my buddy's 2.4 had a stuck throttle. He sprayed it with carb cleaner and cleaned it with a shop towel where the butterfly sits. It's a MPI motor, but still it has a butterfly and fuel flows through it.

[MrPaco]

I believe that I got to the bottom of the issue with the choke, with the help from my friends here in the forum.
FMS88 walked me through a long and detailed troubleshooting and diagnostics process to make sure all components of the system were working as designed, which they seem to be. A breakthrough came when StarquestMan's eagle eye noticed on a picture I shared that two vacuum hoses (one of them connected to the choke delay valve) were connected to the wrong ports, after reversing them the system started to respond as it should. After that, some adjusting of the fast idle screw, as pennyman1 suggested, got it back to where it needs to be. Now it starts right up, no stalling, and the choke it's doing its job to warm it up without hesitation.

So case closed, I hope. Thank you to all that shared your time and knowledge, much appreciated.

[StarquestMan]

Nice! I was about to ask you how it all worked out, then I saw this post. glad you got it all working!