I see this, "the mixture and throttle adjust screw all the way backed out" and with a strong southern drawl I say, "Do What???" No wonder you can't keep it running.... You have the throttle screw all the way out! Turn that back in until you can keep it running and idling. Then adjust the mixutre screw until the idle speed is as high as possible. Then turn the throttle screw until the idle slows down, but still idles. Then back to the mixture screw and so on until you have the mixture set just right. If the mixture screw is all the way out and you still haven't gotten the idle to peak out, you need a bigger pilot jet. If the mixture screw is all the way in, you need a smaller pilot.

A properly tuned carb, once warm, will have its fastest idle speed at, say, 1 1/2 - 2 turns out on the mixture screw. If you turn the screw in or out, the idle will slow down. If you're up to 4 turns out on your quad and the idle has been getting faster n faster and never slowing down, you need a bigger pilot. Never turn more than 4 turns or the screw might fall out on the trail.

What does the spark plug look like? Black? White? Tan?

 

Well I can get as many jets as I want and shipping will be $6.99. I'd rather order it from DK over eBay because the jets will be there before I am this weekend if I do. I'm going to call a few dealers in a while to see what kind of selection they have. I'm worried they won't be open this weekend though with the holiday.

I think what'd I'd probably end up doing is ordering a bunch, and when I find the one that works, I'll see how many I can return.

 

Well we could get it idling once it was hot at one point, but its starting that's our problem. It just won't start! And we put a new plug in so it hasn't had a chance to get colored yet. The plug we took out of it was from back when the vehicle ran right and prior to the guy we bought it from rebuilding the carb.

So will upping the main jet size allow it to start easier? Why would it only start when it was being pulled?

 

Once you finally get the quad idling perfectly, you can move on to the needle. With it idling nicely, give it a bit of throttle.... Just as small amount as you can with your thumb throttle. Does the quad stumble a bit once the throttle opens a bit? If so, this indicates the cutout on the slide is wrong. You might be able to work around it by making needle clip adjustments. If the engine doesn't stumble on the smallest possible throttle openings, you're lucky. Now open it up more and listen for stumbles, backfires, or anything out of the ordinary. Take it for a ride and see if it takes throttle nicely and will take it fast enough to pull a wheelie. If something is wrong, move the needle clip around till the problem goes away. Don't be concerned with opening the throttle all the way at this point. Just concentrate on popping wheelies and puttin around the yard listening for anything amiss. Check the spark plug after a couple minutes of lugging it. If its black n sooty, your clip is too low on the needle. If you can't get the front end to pull up, the clip is too high on the needle. Once you get all that ironed out, move on to the wide open throttle tests (main jet). Also, changing the main jet will throw off everything you've just done for the needle, so you'll have to go back and do all those tests all over again. Carb tuning is an art.





http://www.mikuni.com/pdf/vmmanual.pdf

 

Fig 16 is an airscrew. You have a fuel screw. The curve should look the same, but the screw turns different ways. Turn an airscrew out to get more air and turn a fuel screw out to get more fuel.

 

The main jet has nothing to do with starting or idling.

You either have the idle circuit out of whack or you have a bad magneto coil like I did. Bad magneto coil will give you starting problems when its hot only. It will start fine cold.

 

What's the idle circuit? Its has starting problems no matter what the engine temp is.

 

Maybe I should just fly you up here for the weekend! lol

 

Idle circuit is just a fancy way of describing the idle parts in a carb.

It might be easier, like I said, to just tape the airbox lid back up. If you want to learn how to tune carbs, be prepared to put a lot of time and energy into it. Its not a very financialy rewarding endeavor, but satistfying along the lines of finishing a large jigsaw puzzle. So, you have to ask yourself how far you willing to take this... Are you THE atvman or just someone who likes to ride atv's every now n then? If its the latter, just put everything back to stock and cut your losses (except the exhaust pipe which doesn't affect idle - only the main jet).

This reminds me of something I read at dansmc a while back:

"I had a friend who put a monster Mikuni carb on a Honda 350cc single. It was like 40 mm or so. Maybe bigger. A real monster. It was supposed to be pre-jetted... yeah, right. He stayed with me for several weeks while he worked on it just like a regular job. Like 6-8 hours a day, every day. At night he poured over all my carb and carb parts books. Bought a bunch of very carefully selected main jets, idle jets, jet needles and needle jets. It would barely start when he started and I got to admit it ran almost perfect when he finished... almost ! Now, I don't think it had any more Horse Power than stock, but it did run pretty smooth. Over 100 hours of careful tuning, another $150 in parts (at wholesale prices, no less) and all we can say is that it runs smooth ? I don't think it was worth it. Who knows... maybe it will be worth it to you."

Been there, done that! Don't recommend it unless you're a puzzle freak. My buddy bought a carb, fmf pipe, kn filter for his warrior. He spent about as much for carb parts as he did for the carb and we're no closer to getting it running right as we were in the beginning. I am glad to have a somewhat extensive selection of needles and jets though.

Recommended reading:

http://www.dansmc.com/hopup.htm
http://www.dansmc.com/carbs2.htm
http://www.dansmc.com/mc_repaircourse.htm

 

lol, well I'm definitely not trying to get to some amazing level of perfection tuning it, I just want the four wheeler to start!

So I'll tape the airbox up and you think that will get it to start? Do you suppose it was just sucking too much air and the mix was too lean?

And for the pipe I'll only have to adjust the main jet size? That would make sense since we could get it to idle once it was hot.