Hello, I have a 1990 XT350 Yamaha dual sport( remember those?), the bike is mint and is bone stock.when I ride the bike it starts right up, any time any weather, after about 45 min. of riding it gets really hot and revs at about 3000 rpms, which gets a little scary in tight traffic on the street, also pushes me into trees in the woods. I've tryed new oil, i've tryed extra oil, I even sanded the paint off the cooling fins to help it cool better. I replaced the head gasket but that didn't help, bike also has NO air leaks at or around carb, carb intake boots, nor does it have any exhaust leaks. It starts and runs perfectly for 45 minutes so it can't be carb related, anyone got any idea's?? I'd like to here from some old timers like myself, if one more teenager tells me to upgrade my exhaust, rejet every weather change, or uses the word mods, i'll scream. I rode 32 enduros on my 1974 husky 250 and never even seen the inside of my carb, or (mod) anything), jeez, I probably changed the old champion spark plugs twice a year, now they tell you to change it twice a week. Any of you old timers got an old husky for sale! ha... please help with the XT. mike- age 45 and missing old bikes

here's some "could be's" for ya...
Could be running lean, you may have to rejet of adjust the fuel and/or air screw, I dont know that bike or carb specifically.

Could be that you, like me, are slow, and dont get much air over the fins. Nothing personal!! Let's blame it on the tight technical trails!

I cured that problem by installing artificial air speed!!

Actually, ceramic fiber header wrap... got it in 1 inch width from my local auto parts store, along with hose clamps.

Think of it like this; the hottest part of you motor is the exhaust pipe. The pipe runs close to the cylinder and carburetor. With a motor running hot due to whatever cause, the pipe radiates more heat into the engine. By wrapping the header, the heat is release further away from the motor, allowing it to run cooler.

There are purported performance gains, I dont know about that, but I do feel a cooler motor runs stronger. Do not use header wrap on a titanium header!!! Some say dont run it at all, makes steel brittle too. I have had it on 3 bikes for more than three years with no problem.

But it does have a definite cooling factor on the bike. I can touch my wrapped pipe with a bare hand immediately after a hard ride, and not need skin grafts.

Looks pretty cool too!

Robert

Could be a base gasket leaking. Start it up and let it get to operating temp where it starts to act up. Take some starting fluid and spray it around the base of the cylinder while the engine is running. If it revs up really quick then you know it's leaking. Check the same way around the head to be sure that it doesn't have a slight warp. Although I kinda doubt it. It sounds like the engine is running lean at temp. I am wondering if as the temp comes up something warping a little causing an air leak. Hope that can be of some help.

It sounds like the bike is jetted lean. And I might try a semi or full synthetic oil especially for motorcycles.

The cermaic wrap is a good idea, but I'd do the oil swap and check out your spark plug. What color is it?

I have had this sort of problem, see if the timing is ok

Ok, I guess I should mention one important thing about this xt350, the beast has 2 carbs, should there be two fuel screws or one?

I owned an 85 XT350. The rubber tubes between the cylinder head and the carbs got brittle on mine and then cracked. When that happened the bike first ran lean when the crack was small, and then they broke completely off and the bike wouldn't run.

I had to replace them when the bike was 2 years old and had 2000 miles on it. They failed again when the bike was 8-9 years old and had 6000 miles.

I had an 86 which backfired like crazy when I bought it used, and real cheap. As somebody already said, the rubber intake manifold was cracked. With this replaced it ran great, but I still had to clean the 2 carbs (1 normal, 1 CV)every year as it became hard to start in the spring. Problem was it was just too lean and those teeny jets didn't take much to plug up. For the hot running prob, mine had a tendancy to vapor lock after stopping when it was hot and when riding in tight stuff. After changing to a slightly richer main, lowering the clip 1 notch and switching to a semi-synth oil, its was way better, but I thought it still needed an oil cooler. Its only holds just over a litre of oil and this is not enough for an air cooled engine.

Make sure your pilot jet isn't clogged, as you might be idling on the needle jet. Sometimes the pilot can be blocked, and the bike will still seem to idle ok if the idle speed screw is turned in far enough. But, you will have an erratic idle speed when engine temp changes. Also check the cold start plunger. The rubber tip might be bad.
More things to check would be valve adjustment & ignition timing (CDI may be on full advance. I've seen this happen a couple times). Hope this helps.

I agree about the carb boots. That was the problem on mine. I couldn't tell that they were cracked by spraying carb cleaner around them. But I replaced them on the advice of a good Yamaha mechanic and it solved the problem.

I've got a quick question about my XT350. I have trouble with it dying once i put it into gear. I will let it warm up with the choke out for about a minute, then let it run for maybe one or two more minutes with the choke in. When I put the bike in gear, it dies. It doesn't lurch forward. It won't start up in gear but it will start up in neutral first kick. After I get it started if I let it run for maybe a minute or two with the choke out it will go into gear fine and as I'm riding away I push the choke back in. Then I have no problems with it dying taking it in/out of gear.

Anyone got any idea on what it's doing?

Sounds to me like an air leak. There maybe a defect in the aluminum head, along the intake or maybe the exhaust. When the head heats up the casting defect opens up.
Next time you have the head off, have it ZYGLO. ZYGLO is a fluorescent penetrant testing method used for the detection of defects. If there is a small crack in the casting ZYGLO will find it.

Mine used to get condensation in the float bowl that made it do that. I pretty much had to drain the float bowl before riding any time it had been sitting for awhile. I doubt that is your problem, but it will only take 30 seconds to try.

Could the oil cooler have a clog perhaps?

steven1955 said:

I found an old radiator hose I had saved. Cut to the proper length with hose clamps it worked great.