Superchief Engine Trouble

[mikesnyder]

Hi everyone new to the forum. I have a 500 superchief. I have had it since I was eight and I am thirtyfour now. It has sat in my garage for the last twenty years. Last week I pulled it out cleaned the Carb cleaned and set the points new plugs new fuel line and filter and new synthetic 40:1. It runs great till it warms up then it starts to backfire and run like crap the needle on the Carb is set 3/4 s out from closed. last night it was only running on one cylinder changed the plug on that side it ran fine for about 5 minutes then acted up again not sure what to do thanks. Mike

[bucketobolts]

Welcome to the site. Sounds like maybe vapor lock or leaning out from sucking air from somewhere? maybe want to try a leak down test if all the simple stuff is eliminated. Possible crank seals??

[6X6]

What did the plug look like when you pulled it out? You say the needle is set 3/4 out from closed, but I don't know what carb you have. (I don't have a stock superchief so I don't know what carb they came with). To start, if your plugs are blackened and sooty, you are running too rich, if they're white or damaged, too lean. Start it up, and when it warms up and starts running lousy, choke it a bit, if it gets better look for an air leak. Start at the carb base gasket and intake manifold gaskets, their easiest. If not next place is crank seals. EASY CHECK - Spray carb cleaner, even wd-40 at the seal/gasket, one at a time, listen for an RPM change, if you get a change, wherever you just sprayed is sucking in air, and the fluid you just sprayed, and that seal/gasket must be changed. But so you know bad fuel will do what you're describing too, so try fresh fuel, if you can, plumb up a small temp tank, you may have water in the fuel tank too, if so you'll see the problem go away (Drain the carb bowl, it'll hold enough water to keep the problem going even after you're running good fuel), then you just have to clean out the tank. .
Good luck, and remember, when you get that machine going, it's gonna MOVE

[mikesnyder]

I checked for air leaks tonight there is a small one around the carb. I also had my buddy check the compression it was around 135. The stock carb is mikuni vm30-159. I let it idle on my truck tonight for an hour when I was at my buddies sounded good the whole time I reved it about every 15 minutes or so just to blow it out when i got it home and off the truck it was a sluggish on the low end once I got it moving it took off then when I would stop and start out again it would do the same thing. I turned the mixture screw out bit and then it got worst then I turned it in and it is some what better still sluggish though at this point the screw is set the whole way in. When I cleaned the carb I turn the screw out as per the manual but when we ran it when we were kids it was turned in. At this point I don't know what to do. thanks for all the help so far. Mike

[Frymechanic]

I have a similar problem with my KX100 dirt bike and I finally found it to be that the whole carb was just plum wore out. Its cheaper to replace the carb than the internals in some cases (like mine), but it sounds as if the low end needle and jet set are worn. When its cold the engine needs more fuel but when it warms up it needs to lean out but because of the excessive size of the low end it can't. Altitude plays a major effect too. 2strokes are super sinsitive to it.

[gus marrone]

check the crank seals by spraying 2+2 where it comes out of the case on the clutch side, also around the carb and manifold. make sure you clean every air port in the carb by running a fine wire thru it and spray 2+2 and make sure it exits on the other end . good luck

[jerbear]

Sounds like the same problem I had with my SC. Runs great, gets warm, runs terrible. Only fires on one cylinder. Boggs down, backfires. My problem was with the ign system. The coils get too hot where they are mounted on the motor. I scrapped the whole ign system, got parts from an ss model xenoah with CDI and converted the g50b to CDI. You need the stator plate and flywheel from a SS model xenoah. They come up on ebay. Aftermarket cdi box and coil. George posted a video about the conversion. My guess would be that's your problem, seems to be fairly common with this motor. Good luck.

[mikesnyder]

I have checked all the seals and boots no leaks cleaned carb again. I took the cover off the coils so they can get more air turned the mixture screw out to 1.5 turns runs good for about 5 minutes just putting around. Every now and then I will rip on it for a little bit top end seams slow. It will take off and then it seams like it has topped out around 30mph It dose not seem right but maybe it is. It is still sluggish on the bottom once it warms up it starts off like it barley wants to gun then it takes off. I am thinking about putting it back in the garage for another 20 years.

[Frymechanic]

When it bogs in the bottom end accel., does it smoke a bunch?

[mikesnyder]

I think not sure it dose in the garage when revving after i pull it in when it acts up

[Frymechanic]

Well, 2 things I can suggest because I have gone though similar issues. First, check the plugs carefully. Use a magnifing glass if you have to. Look at the insulators between the tip and base. Your looking for a black line running down them. If so replace. Then wipe them off nice and clean and look again. You might see a hair line crack. If unsure replace the plugs. Sometimes they are broken internally and make themselves apparent when they get warm. Second, try adding some more gas to the fuel mixture. For more exact mixing take the fuel out of the tank and put it into a gas can. That way you can see how much fuel you have and therefore add gas accordingly taking it to 50:1. This probably won't fix your problem but it will tell you if its loading up. If after doing this it still bogs in the low/accel end and has less smoke, then I can assure you its the low end jets/needles in the carb.

[techfx]

Try swapping another mikuni fuel pump - my dad's was causing issues on his superchief not allowing it to get enough fuel. Not sure if that is your exact issue or now.

[mikesnyder]

Well I worked on it for the most part of the day reset the points bought two new plugs again this time they were b8es set the gap on them to .014. Everything seams to be ok so far it runs great and isn't acting up at all rode it for about half hour tonight with no real big issues the only issue I am having is I had to turn the idle screw the whole way in to get it to idle. Not sure why but if that is all I have to deal with I think I can get used to it. thanks for all the help guys. Mike

[mikesnyder]

electric fuel pump

Well tried to put an electric fuel pump on the 484 today that was a waste of time and money should have just put another diaphragm pump on. Wired it in and it just wants to flood out the engine bought a 1 to 4 psi pump and put a 1 to 4 regulator on it set it at one and everywhere in between some times your better off with the original. I have been trying to eliminate all the cranking it takes to start this thing it is fine when it is warm but when the engine is cold it takes about 30 sec to start letting off about every 5 sec. I think my starter is going bad too.