Rough Idling and dies when weather gets cold

I just registered (newbee) I'm having problems with my first 1989 mitsubishi mightmax and also my first time ever working on a carburetor vehicle. I seafoam it, marvel mystery the gas tank, put Rislone in the engine to keep the infamous ticking low, Set the timing,new cap,rotor, intake manifold gasket, fuel pump spacer, wires,sparkplugs, and oil change. The truck still idle rough and dies when it gets cold in the afternoon. I also check for vacuum leaks but can't seem to find any.
Does anybody know the stock setting on the fast idle screw,SAS(all 3), air/fuel mixture screw and the throttle opener screw? I want to set it back to normal factory setting then start tunning it from there. The truck came with no air filter and a modified fuel pump that's wired to the fuse box.
When I installed the Intake manifold gasket i broke one of the nipple off of the thermovalve, which is the very top one off of the 3 that lines up together, but i glued it back. I check the pvc and it's sucking air to the intake manifold. I cleaned the egr and check the vaccum suction on it ; everything is working.
I'm really trying to avoid a carb rebuild. Any help or suggestion will be appreciate it. Thanks for your time in advance.

Welcome to the site.
You might want to root around in the manual section for the stock settings. I just finished locating about 100 factory manuals for darn near every engine I could find. There not organized yet but I'll get that done in soon. So you will need to literally look through the server for the right one. Look for the 811-4D55-4G63-4G64 colt and a crap load of others. It's in there. Your rough idle can be the PCV valve sticking. You might also consider swapping out the carb with a smog legal after market one. I thing there is a post on witch one is the correct one.

Thanks camoit, I will try replacing the pcv, I checked it and it has vacuum. The manual doesn't have any info on how to adjust the carburetor screws to stock setting. I really hate to put more money into it by getting a new carb.

I would say setting the screws from a closed butterfly is the best starting point.
If you know where the screws are you can look and see how she works.
One screw controls the speed of the engine when hot. the other one when it's cold and the choke is closed. The throttle opening adjusting screw works with the secondary or choke. It will determine at what vacuum the secondary or choke move. I can't remember of the top of my head. But if you look at it's fairly straight forward on how it does it's thing. You just fallow the vacuum bore holes and linkage.

As for the PCV it works as a regulated vacuum leek and has caused many strange idle problems. After that comes the EGR valve stuck. It can be checked by disconnecting and plugging the hoses from it. Then connect a hose on the diaphram of the EGR and pull a vacuum. Confirm movement of the shaft. Engine will run like crap.
Let off the vacuum engine runs better. EGR, OK..

NOTE: Early years,, Some carburetors came with a slide ding-A-ling in it. It would need to be pulled at the same time you are sucking on a vacuum hose of the EGR.

Thats because exhaust gas, is also controlled by the carb as well.
Of course back then we had to show the smog guy how to properly check the EGR. They swore it was broken. But they could fix in a day, or so they would tell you.
Now you would proceed to hold there hand and show them how the carb worked. The light would come on in the projector of a brain they had. And low and behold like some magic trick they had never seen before it worked, just the way they were taught in state smog school.

Thanks for the quick reply camoit, I still haven't replace the pcv for a new one yet. I checked the vacuum on the pcv and it's sucking air to the carburetor so do i still need to buy a new one? I have checked the EGR without a vacuum pump, by lifting the diaphram up and pluggin the nipple to see if it hold suction. It does hold suction and when i let my finger off the nipple it release the diaphram back down. So im thinking it's in working order, right ? I don't think my EGR has a ding-a-Ling thing, haha

I don't understand why it dies out right when it gets cold outside? I then have to hop out of the truck and screw the SAS 1 in about half to one full turn or more to keep the idle high to keep it from dying at stop lights at night. The thing it is it runs fine in the day time without adjustmenting the idle it's still a loping/erratic idle, but it doesn't die. I Think i can't get away from doing a rebuild on this carb, but not before i try everything i can to fix it first.

You wouldn't happen to know the part nbr for the Thermovalve for the 1989 Mighty max SOHC 2.0 motor would you ? One of the nipple is cracked that i glued but coming a apart. The one that is connected to the EGR system.

Also i do hear a large amount of vacuum suction coming from the secondary valve on the carb. Let me know if you need any photo's to identify some parts im refering to .

Thanks for your time camoit

Have you tried turning out the mix screw 1/4 turn? That makes a big difference. As for the speed screw does it stay at a high idle when it gets warm? If so then you might be turning the main idle speed screw and not the choke speed screw.

hey, sup camoit , Today i did the cold choke adjustment you said, adjusted the fast idle cam lever to the second step from the manual and screwed the fast idle screw to tighten it down. Then I screwed the SAS 1,2,3 down and backed off 3.5 turns. I read some where that those are stock setting for the carb. I plugged the air hose going to the distributor to to check if the timing is off , then started the motor up and the truck ran with a high idle. Which is normal on a cold start, I waited to for the idle to go down and it never did. The truck warmed up and i adjusted the idle a/f mixture screw by screwing it it 8/16 at a time and waited 10 seconds on every adjustment. I ended up screw the screw almost all the way in, I found that out when i took count to see how many more turns i can get it all the way in(1.5 turn). Guess i had the a/f screw out too much.

After that i adjust the SAS 1(idle control) by backing off until the engine idle lower. Did the timing and found out the crank pulley only has one(white) marking. Can i use this for setting the timing ? Well i hooked up the light and it was way off, so Turn the distributor clockwise towards the motor and the white mark on the crank went to 12degree BTDC (guesstimation). I'm starting to think it's timing now , guess im going to have to buy that equus timing light with the digital rpm display.

The truck idle better but not smooth. It sounds like it has that aftermarket camshaft sound that lopes erratically. I drove it to kragen and picked up the PCV and radiator cap(old cap sounds like it's leaking). I forgot to unplug the vacuum hose that i plugged up to do the timing adjustment, so i parked to the side of the road and pop my hood, then unplugged the screw and plugged the hose back into the distributor and the truck dies. I closed the hood and started the truck back up. While coming to a stop the truck keep dying so i ended up plugging back the vacuum hose. After 30min of driving, it idle high, so i backed off the SAS 1 bout 2.5 turn to get it to idle lower. The truck is still idling a lil high but i can't risk to adjust it lower cause it might die. Everything went cool until it hit 5 o'clock pm. The truck continues dying at 30-45mph. came home and adjust the idle screw a couple turns and left the truck for another day to work on.

35 to 45. Does it surge like it's running out of gas, or some one is turning the key on and off? Swap out the fuel filter if it's never been done that you know of. It's on the frame, drivers side frame rail, under the bed. That will reduce 1 possible problem.
Next how many mile are on it, has the timing belt ever been changed? You might want to look at the cam to crank timing. It also sounds like the choke system might not be working correctly. Does the choke flap open when hot? If it is then there is somthing keeping it at a high idle. 1200 is normal for cold start. 8 to 10 deg BTDC. There is somthing strange going on. It will just take a little time to nail it down, but don't give up. You will win.

sup camoit, The motor is a rebuild motor and i don't know the miles on it. The bottom block is a 92 lancer bottom and the head is off the mighty max. Everything is pretty new far as tune up wise. The miles on the odometer is 230k
When it dies at 30-45mph, it's more like turning the keys off. I think the problem is when it gets cold the engine keeps wanting to shut off. To fix the problem i just screw the SAS 1 in more to get the idle higher. The truck runs really good on the freeway, it's just the rough idling and dying at stop lights when it gets cold outside.

Out of no where my starter came loose and the car wouldn't crank.(headache)

I pulled the sparkplug out today and it was black (exhaust carbon pipe black) I think you might be right about the choke

I had a lil talk with the PO and I was telling him the timing is a lil off(12degree btdc, he told me to pull the distributor back out and rotate the distributor rotor so the timing mark on the crank pulley can move to the correct timing 8btdc. This is what i did to day. I had to pull the distributer rotor off and rotate it counter clockwise to have it set barely at 8degree BTDC .
I also adjusted the af mixture screw again, backed off the SAS 1 again also, and backed off the Fast Idle Screw. The primary intake valve throttle is not fulley open now, but you said it's a good thing. Should i adjust it where the plate is barely open when the truck is hot? I wonder if i screwed the Fast Idle Screw too far in. I'm thinking of screw it back out some more, because in the manul it says when you unscrew the fast idle screw; the choke will close the throttle more.

The truck is running better now, Just need a lil more tinkering and i'll be back to saving some gas. Right now it's doing 17mpg.

Any other advises or suggestion is appreciated, Thanks for your time and helping me trouble shoot camoit.

It sounds like you are on the right track. You are getting closer. You also might want to check ground wires for a good contact. I'm not sure what else I can tell you. It's just a matter of tweaking things to get it to run the way you want it to. Also make sure to check all vacuum lines and make sure there hooked to the correct place.

Honestly, you need to look into a 32/36 weber if you want to have it running right. The stock mikuni carbs are crap.....

I agree tintedram, but i just don't have the fund for one. Well, I end up going to a local pickNpull and got me a carb for $40. I found out my depression chamber was clogged and i was running on barrel. Now it's running on 2 and riding smooth on the freeway. (SAS1)9 turns out(SAS2)6 turns out Fast I forgot the (SAS2) Idle 2 throttle opener .25

The truck now idles at 1,000, but the idle shakes when at a stop , say between 1000-700 and then some times lower. The pickNpull carburetor ended up having a leak through the gasket by the vent bowl. It didn't hold idle so i swap back my old carb with the pickNpull depression chamber. That's when i found out my depression chamber was clogged. It's running good now , just the idle wont stay still@1000rpm.

I'm also planning to replace the pickNpull carb gasket, I just got to figure out how many bolts is holding the top piece off.

I hope this help some one that went through the same dilema i did with my solex mikuni carbuertor . Happy driving to all !!

He is in Cali-somg-ya. Is got to be stock or a carb certified.

Back again with more plms. I ended up buying a Carb rebuild kit($24@KRAGEN) for the pickNPull carb. I unscrewed the 5 screws on the top piece of the carburetor to install the gasket. In order to remove the top part of the carburetor i need to detach the electric choke. After that i put in the two new gasket and screwed everything back together. I tighten the screws as hard as i can, before and after i tighten the 4 carburetor bolts to the manifold.
i FOUND out there was a leak in my intake manifold(top stud on the right port towards the firewall). Found this out when i sprayed some starter fluid for the hell of it to see if it was the manifold that was leaking like everyone was saying about the truck. Ended up finding out the stud is stripped. I unscrew that stud out and place a bolt in the thread instead of the stud. Then i bought a new IM gasket with some gasket silcon to keep it seal. (torque 14ftlbs) It worked and the truck idles steady now. :))

I installed the pickNpull Carburetor on the IM and plugged everything back up . started the truck and it idle really high. It was going from 3k rpm to 4k rpm and i was worried so i shut the motor off. I think when i took the electric choke arm off I might of messed up the cold idle adjustment. I just mess with the idle cam to lower the rpm and drove it around. I test drove it around town and on the hwy for about 30min. Everything seems to be working in order, Until the next day. :shakehead:

I'm thinking the truck is running good now, Idling reaaaaaal smooth, right? (NOT) I'm going to take this baby fishing. Loaded all my fishing equipment and the cooler in the truck bed. Started the truck up and the battery is dead.:bang: I still haven't fix that short yet. haha I got a jump start from dad and it started idling high again. I just play with the idle cam and lower the rpm to where i can drive it. While driving i notice the rpm going to 1500, I kept driving and almost ran a stop a light so i slammed on the brake real hard to stop. The truck just shut off and wouldn't start back up, but it cranks. I push the truck to the side and let it cool down. Looking around the motor i notice the carburetor gasket has leak around the 4 screw area. DARN!:shakehead: Will i be able to make it back home? I did, Now im here typing on the laptop to help a future mighty max member with any similar plms they might run into that i have encounter today or through the whole time of owning a mighty max(carburetor)

So now the question is , What can i do to seat the top carburetor part to now leak. Could it be warp, did i forget to install something, what's going on with the electric choke, and can i adjust it ?:shrug: I still have the other carburetor , but the middle stud is broken off it for the air cleaner to screw onto .

What a day!

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Get a Toyota and be done with this minuki BS, nahh just messing with you. I ran for the longest time on the stock minuki, i had issues like you had and it would run so rich it would foul my number 3 plug if I floored it. I switched to a weber and it solved alot of issues, when I threw a rod in my Mighty Max I was loaned a 1984 Toyota (About to me mine in a few months) and I had the same issues, so i slapped the weber from the Max on there and it is awesome now. I got a second Weber for $20 from the scrapyard, you just got to look around on vehicles besides a mighty max, granted you will need an adapter ($40 on ebay). But since you are working with stock why don't you try some gasket sealer on the base gasket, I had a little vacuum leak with my weber and that fixed it (Its actually recommended to do that)

you probably over tightened the carb top screws. They aren't that tight to begin with. 10 inch pounds. s for the choke it is adjustable I think. Like a weber you can loosen the screws and rotate it so the spring doesn't push as hard and it comes off high idle faster.

abeemanator, I put permatex grey on the gasket that adapts the manifold to carb base. I realy don't want to gum it up with too much permatex. The truck runs good, it's just the leak that's stopping it from starting when it dies. I think the leak is from the carburetor float fuel over flowing. I'm prob going to take it apart (again) and check the float to see if it's cracked,leaked or the pin is stuck.

camoit, when you say carb top screw, do you mean the 5 phillips screw? It's too late to loosen the screws now, huh ? haha Should i put a thin coat of permatex in between the gasket that seals the top bowl to the carb ? The electric choke is adjustable on the carb.

Thanks for the replies, yall keep trucking now yah hear.

Never, ever, ever, use a silicone on a carb. It will turn into a runny gelatinous goo that will run into the carb or engine. A trick I learned a real long time ago is if you ever plan to remove a gasket later on in life you use a very tiny amount of anti seize AKA Never seize on it. Just a film is all I'm talking about. This way when you take it apart it stays in one peace and never sticks where you need to scrape it off the parts. I can't tell you how many times I pulled the weber base gasket, intake, and exhaust off and just reused it over and over. Hell Mopar_JA is running on them now. Water pump is OK, carb base to manifold is OK, Carb top gasket is OK, Head gasket A BIG NO NO, Exhaust a BIG YES. Intake OK, Oil areas like the pan or valve cover is silicone. There are differences between silicones. Not just the color, heat, or resistance. One big thing people overlook is how thick of a seal it makes. The package will tell you the gap it will seal. 1mm to 100mm or so. One of my favorite is LocTite 518 gasket eliminator. I use it around the timing chain cover. Great for areas of good metal to metal contact that does not move.
You might get away with loosing the 5 screws and re-torquing them. You just need to remember what they felt like when removing them. You can check the top with a straight edge.

Haha, I have to admit I have had tried to seal a briggs and stratton float bowl that way, and I couldnt figure out why the carb kept getting gummed up. I have to admit, carbs are my weak point, I understand the basics and the use of a venturi, main jet, a float and bowl, but anything more I start to get confused. See if you can snag a Weber from the scrap or salvage yard, hell the scrap yard is my second home, I snagged some good parts there for cheap, I got a clutch, sport cluster, dash clock, bed light, marker light, tail light, flasher and headlight control, window regulator and a sliding rear window for 35 or 40 bucks all together, now salvage yards are a little more spendy, I got a drivers side window for $30 after talking the guy at the counter down from $45. But remember not to limit your search to only Mitsubishi pickups, look at rangers, vw's bronco II's, small ford chevy or dodge cars and trucks, Isuzus, or anything with a 4 or a small 6 cylinder.

camoit, when you say a thin flim on the gasket to save it from sticking to metal, do you mean a thin flim all over the gasket or just in certain area's ?
I end up taking the carburetor apart to check the float and the pin. Everything looks okay to me, so now im thinking i shd just run double gasket since there's two gasket that came in the rebuild kit. what do you think, either that or im going put on a thin flim of permatex gray on the gasket around the float to try to stop the leak.
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abeemanator, I will keep an eye on a webber if i ever go to the junkyard. For now i will have to try to eliminate every little problem that this mikuni carburetor throws at me. I'm not doing so good, i tell you that. I tried to do some adjustments on the electric choke and got confuse on how to set the cam follower to adjust ? I'm thinking i have to have it in the truck and running to adjust the idle. So i put a double gasket on the carburetor top bowl piece and while tighting the 12mm bolts down i snap one clean off. Damn! :thumbdown: So now i have to run to the store and look for a extractor that will take this broke piece out. Attachment 2724 Attachment 2725 Attachment 2726 Attachment 2727 Attachment 2728 Attachment 2729Attachment 2730 Attachment 2731 Attachment 2732 Attachment 2733 Attachment 2734

Choke is easy to set, loosen the 3 screws,Flick the carb to wide open throttle (not running and when cold), turn the choke so it just closes, then fire up the truck with the choke closed. quickly do a rough set on the high idle screw. Turn truck off, let cool and try it again till you have it run at 1200-1300 rpm when if first fires up.then flick the excelarator to drop it out of high idle and adjust to low idle speed

2 gaskets are ok. You coat it on both side of the gasket, the hole thing.

Attachment 2743Thanks for the tip Fordubishi, I will give it a try once i fix this broke thread in the intake manifold. So i went to harborfreight and bought a thread extractor to remove the m8x1.25 thread. With my lucky this is what happen. haha Attachment 2741






Camoit, When you say anti-seize, do you mean this right here Attachment 2742

Yep thats the stuff. 1 can will last a life time. Just don't over do it. You'll see.
The next time you pull it apart you will save lots of time and say Holey crap it worked. Then you will look at it and say,,,, I can use that again, if I want to. Makes for a life saving road repair = :)

Chapstick also works on the carb gaskets and is imho better than nickel anti-seize inside of a carb. Another anti seize that isn't well known is Phillips milk of magnesia - works great on exhaust manifold studs.

You broke off the extractor. Thats bad. Now you need to find a machine shop that can remove it. Nothing we have will drill it.

Hey penny, I think im going to have to try the chapstick trick cause i don't have anti seize with me. Also kragen(orielly's give you a 1 year warranty on fel-pro gaskets) I just exchanged a IM/Carb gasket and refund the other one i purchased a week ago.

Camoit, The harbor freight tool did not do it for me this time, haha. I think i might had used it incorrectly by not drilling deep/center enough so the extractor can settle down in more to catch. I just used a hammer and a flat head screw driver to remove the extractor. Once the extractor was removed, I then started to drill deeper, to only realize that a helicoil/time-sert kit will only cost as much as a intake manifold that i remove the carburetor from. Went back to PickNpull and it was still there in the engine bay. $25.99($4 core charge)


When removing the manifold , I accidently broke the brake booster check valve. The stealership wants $25.19 for it, damn!
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I removed the intake manifold and notice the starter was missing a bolt. 14mm(don't know the lenght) also my starter wire keeps coming off.
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I broke one of the same vacuum tube on both of these switches, Does anyone know what they are called ? Vacuum(ported) Switch ? I also need a pricing, called the dealer and they told me i would have to come in to verify the part on the computer. I'm thinking of just expoxy the tube back.

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Broke a piece off of the thermo valve also, haha I will be back visiting pickNpull soon. I need a beer now. CHeers!


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Dam dude, you fricking brutal to that thing aren't you :) Or it's all bad luck... Sorry to here it.

camoit, I like to think of it as bad luck. It's one thing after anothe with this truck. I ended up swapping the old carb back cause the the picknpull one is still leaking fuel around the carb bowl. I tried taking the old carb top piece off by unscrewing the 5 screws, but it won't even budge. I really don't know what's causing the picknpull carb to leak fuel from around the carb bowl. The picknpull carb runs so much better too. darn it! *headache*

Back at it again. haha

So PicknPull is having a half off sale for members only. I end up buying another carburetor from a overheated 88 truck in the yard. Brought it home and slapped it on my truck only to find out the jets are clogged, so it won't rev pass 2000 rpm. I disassemble the carb to check to see if the jets are clogged and they were. When i removed the float i notice that it has a float over flow ball. I then took a quick look at the other carb i bought and that's what it was missing. Attachment 3115
Maybe that's why the float bowl gasket is leaking.

I also end up breaking the thermo valve sensor again after i have perfectly silicon the nipples. Attachment 3116

I took the over flow ball and retainer from the overheat carb and installed it in the first carb bought from PicknPull. Feeling good about this plm being solved. After installing the carb on the truck it still shows a minimal leak around the float bowl gasket where the fuel inlet area. Damn! :shakehead:What to do? Guess im going to use the over heat carb float bowl but not needle valve to try to cure the leak.

The truck idles at 1000 rpm steady with the hybrid carb , I still haven't adjust the choke yet. Im more focus on the leak right now.
I got my temporary tags to drive till July to get the vehicle to pass smog. The muffler shop wants $235 to weld on a cataylic converter. :thumbdown:

Try the top of the over heat carb on your first carb - the top may be warped, not the base. Magnaflow 2" universal cats are 65 on ebay all day.

sup pennyman1,
I figured out the problem and im pretty embrassed to say it was the wrong gasket the whole time. The thing is, the first carburetor i bought from pickNpull had the same leaking gasket plm. I pulled out that gasket and traced it with the new rebuild gasket i bought and it looked the same. Did he buy the wrong rebuild gasket kit from kragen like i did, maybe?

After swapping out parts from 3 carburetors to try to figure out the leaking float bowl gasket problem, it was the wrong gasket and missing over flow ball.
Lucky i saved one of the old float bowl gasket from the pickNpull carb.

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The black gasket is the right float bowl gasket shape. So i went to harborfreight and bout a leather hole puncher , then to kragen to buy a gasket paper.

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It was a pita to cut out the gasket into the shape of the float bowl, but with a lot of patience and time it came out alright.

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I also bought a UltraSonic Cleaner at HF to clean the old dirty carb parts. After taking 3 carbs apart so many times, I think i can actually rebuild one good carb to run on or sell.



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I would like to thank everyone that helped me through my trouble shooting and hope this will help someone in the future with the same plm. Don't stop trying and keep on trucking.

I like the leather punch tool for making gaskets. I never thought of that so ill have to go get one. :thumbup:

I saw an article in a mag that suggested using brass shell casings for punches; the various sizes are perfect for standard holes.

Quote:

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Originally Posted by TintedRam50

Honestly, you need to look into a 32/36 weber if you want to have it running right. The stock mikuni carbs are crap.....

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Do you think this is the solution that will solve my issue ? I had my carb rebuilt 2 year ago..

Most of the generic off the shelf carb rebuild kits are sketchy at best. You get overhang into the internal galleries partially blocking them, overhang into the venturi throats slowing air flow and messing with fuel atomisation and add to that someone who grabs the wrong top gasket and installs it (some kits have 2 or even 3 different gasket configurations). I hand prep every gasket during assembly and it's a PITA but I rarely have issues with a carby that's choking on itself. Said it plenty of times, the Mikuni is not a carb for noobs. Some guys who've rebuilt Rochesters, Holleys and Hitachis pull fails on Mikunis...