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XT350 carburetor woes.....

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First off, I'd like to say hello to ThumperTalk and all its members.

Ok, I am at my wits end with this carb set-up on this thing .. been trying to get the bike to run right since I bought the thing a year ago. I have went through the carb(s) several times, bought a used one for $90 here in town at a salvage store, and made one decent carb assembly out of the two, or at least I thought so.... the Yamy dealers say they cannot sell me a rebuild kit, and I am at thier mercy of spending $300 or more on a new one!! Cannot do that(poor college student with baby coming any day), I am convinced there is another way. I have read several posts but nothing is steering me in the right direction. There are NO external adjustments for air or fuel anywhere that I can tell....

Symptoms are:

~cannot get past about half throttle without it cutting out and tufts of black smoke (indicitive of a rich scenario, yes?)

~seems to idle relatively stable, choke works, starts up fairly easy

~secondary seems to be opening when it should...

I have:

~replaced petcock vavle assembly(there was rust present in the screen)

~drained tank several times

~replaced intake boots from carbs to engine

~cleaned the carbs countless times

Shall I:

~give up on this thing, I love everything about the bike except the CARBS

~save up for the overpriced new carb

~hope there is a rebuild kit out there....

PLEASE, if anyone can aid me in my plight to make this thing right, I would SO much appreciate it. ANY input is very valuble to me.

Mathias maximus0067@yahoo.com

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Mine would do that EVERYTIME it sat for more than one day. It did it for the entire 17 years I owned it. I absolutely had to remove the float bowl drain and let some gas run through every time I started it for the first time on any given day. Otherwise it would start OK on choke, but would not rev without coughing and shutting off. Don't know if that helps you, but it sure sounds familiar.

Another possible issue is that the float bowl is very, very hard to get set right. And it is very easy to bent the floats when removing the float bowl. You need to make or buy a special tool and have a manual to set the float height. And you need patience because it is checked with the float bowl on. So you have to keep taking it apart, adjusting, reassembling and checking until it is right. If you bent the float bowl arms that might be the problem.

The only other thing I can think of is that the air screw passages are clogged. For that you have to drill a brass plug out of the bottom of the carb to access it. I don't have my XT350 anymore, so I can't remember exactly where that plug is located. Make sure you count the turns out from seated before you unscrew it to clean the passages.

Once you are beyond those things you are into the land of mysterious carb workings where I would put it in the shop. I once mailed mine to a shop in SC where I knew they have an excellent mechanic. He did an R&R, rejetted it, readjusted everything and sent it back for $125. Also, I assume you have checked the ignition side of things, though a failure there is rare.

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....sigh.. I WISHED I would have copied those other helpful posts on my issue. If any of the previous posters could reply again, I would be more than tickled.

Thanks so much TT,

Mathias

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Ok... the strangest thing happened on my ride to work today. I was able to go past half throttle and it had gobs of power ( I remember it used to do this sort of thing.. ) and the goofy thing is, I had to switch it to reserve shortly after it was running right, and sure enough about 3/4 of the way there (about 5 mile ride) back to the cutting out scenerio. Go figure. Is it possible the temp wasnt fully brought up and that has something to do with it? It was around 44 degrees and should have been warmed up by then if that helps. Does this neccessarily eliminate valves, ignition, other? It certainly seems fuel related to me. I am still going after a Clymer manual this weekend and looking into valve adjustments and ignition check. Again, any input is SO much appreciated!

Thanks TT!

Mathias

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Please don't take offense, but have you taken the fuel tap apart since you replaced it? The screen inside the little bowl clogs easily and XT350 tanks are famous for rusting from the inside out. If you are getting rust, a Clarke is probably in your future because it will continue to cause trouble and eventually start to pinhole. While you are at it, pull the fuel tap out of the tank again and check the screens on the pickups.

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No offense taken at all grreatdog, your wisdom is more than appreciated. :) I am going to try to find time this weekend and the first thing I'm going to attack is that petcock valve! I did not think to check that again. :) I put the brand new petcock on last summer and drained/rinsed the tank, but I did not use a tank flush kit. The original one was packed with rust, I cleaned it and the screen to get buy. I cleaned the carbs multiple times thereafter of course too. So, we'll see. Thanks for the idea grreatdog.

Mathias

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Sorry to intrude, but lets focus on the part about the bike running right, you had to switch over to reserve shortly after... hmm. You also mentioned that it would spit out black smoke, correct? First hand I would guess something is up with your floats. Maybe the floats have a leak? Maybe you just bent something? If not that, then there is something else not right with the bike. Could be jetting.

Id help you more if i could, but being as I have my own problems i cant resolve, im obviously no motorcycle mechanic. Good luck!

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Well, it was running out of gas on the normal "On" setting. One thing I've noticed about this bike is it seems to rev fine until under a load. I tinkered around with it all afternoon today and It just plain doesn't run smooth at high rpms if I hold it there with light throttle; under a load makes it even worse. When you crack the throttle is when it starts to huff and tiny tufts of black smoke come out. :) And sure enough there is shit in the tank coming out in the fuel lines. :p Tiny specks of stuff... I couldn't verify if it was getting past the lil in-line filter, nor did I have time to pull the petcock valve out of the tank. But fuel is heartily flowing out of it. I wish I could explain the ultra rare times it has ran great. :) I have taken note of the idle being erratic as well.

Maybe its time to do a compression check and look into the other ABC's. I just don't wanna give up on this thing yet.

Thanks guys,

Mathias

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Now I remember what got deleted. You said you bent the float arms when I asked about the float height. Make sure the two floats are level and you could try raising the height a little. Once the float height is out of spec it is a PITA to fix. Setting the correct float height is very hard to do because it requires a Yamaha special tool. It is a graduated clear tube that attaches to either the float bowl drain or overflow.

XT350's are famous for the fuel tanks rotting from the inside out from corrosion. Pinhole leaks are probably in your future. Either a new Clarke or POR-15 fuel tank treatment fixes the problem. The same condensation that eats the tank also settles in the bottom of the float bowl and causes the symptoms you describe. Remove the float bowl drain screw on the bottom left side of the carb, open the petcock and let some gas flow out of the hole. Try this first if you haven't yet.

Also try loosening the gas cap when it isn't running right to check for venting problems. Mine had a carb TSB back in '86 and I think it was for a venting problem.

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Ahh, yes, that is what you posted... Ok yes, I tried the grreatdog drain method and same results. I got a Clymer this weekend and the valve assembly's look abit out of my skill range. I could take the thing apart no problem Im sure, but the servicing of the valves requires some specialty tools and such. :) The valve cover is leaking terribly now, so I'd venture that they have not been serviced in a long time. The head doesn't make any abnormal noises so that is why I didn't think to even bother with that. I certainly hope it isn't the valves, that is intimidating. :)

So we've definitley identified a problem with the tank. I am going to tear apart the carbs again as soon as I have time and try to get that Yamaha float bowl leveler too. Check the floats/level and toss some of that tank treatment in the tank. What a pain.

Thanks,

Mathias

'85 XT350

'89 CR250

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