XT350 stumbles at 4,000 RPM

[scottieh]

Hey there, I'm trying to sort out an issue with a 1992 XT350 that cropped up after a top end rebuild. I took apart the valves and cylinder to lap and hone and reinstalled following the service manual instructions making sure the alignment marks were correct on the camshafts at TDC. The bike started up fine, though it would not idle without the choke but I rode it around anyways to begin the break in period. The first three or four rides were great. Very responsive throttle, good sounding engine all around with some small oil leaks here and there but nothing major. Then during the fourth or fifth ride as I start to go down the street and bring the RPM's up it stumbles and hesitates a lot. I can't hold the revs at 3,000-5,000 RPM. It will rev higher and hold that RPM but not in the middle there. I think it's just a carb rebuild so I did that and cleaned out all the jets and replaced whatever rubber I could get my hands on thinking it'll solve both the idle and the rev issue. Well, it may have solved the idle problem but I still can't hold the revs at 3,000-5,000 RPM.

A few forums suggest changing the needle height but that wasn't changed before the issue began. Another forum suggested a possibly bad CDI or ignition coil and recommended I check the ohms of the wires. Haven't done it yet but it's on the checklist. Anybody else have a suggestion they want to chip in? I'm trying to sell this thing and focus on my XT600's. Thanks!

[xtzrick]

Providing everything is clean & no air leaks I'd alter the needle height.

Ride it for as long as you can with it stumbling, pull in the clutch & hit the kill switch at the same time, when you stop check the plug colour.
If it's dark or wet drop the needle (raise the clip) 1 notch, vice versa if the plug is white.

Rick

[scottieh]

Providing everything is clean & no air leaks I'd alter the needle height.

If it's dark or wet drop the needle (raise the clip) 1 notch, vice versa if the plug is white.

Rick

Did some fiddling today and managed to get the bike to idle decently by turning out the fuel screw 5 whole turns. Then i rode up and down the street keeping the throttle at the point of stumble and killed the engine and pulled in the clutch like you said. The plug was a little white therefore lean. Now, these xt350 carbs are like the 600 carbs as they have a primary and secondary side. Which side should i raise the needle first? I may have to use the washer trick since i think most of these american bikes don't offer notches on needles in order to comply with the EPA.

[xtzrick]

5 turns out sounds like too many.

I think you need to look for any air leaks 1st.

If you're confident you have no air leaks then shim the primary needle.

Ha, just did a quick google for the carb settings & found THIS on Thumper
Looks like ya not alone.

Rick

[Mezo]

I would be checking the float needle valve filter (same as the 600`s) get clogged with shit from the the tank.



Mezo.

[scottieh]

I would be checking the float needle valve filter (same as the 600`s) get clogged with shit from the the tank.



Mezo.

Replaced the float valve and the filter already.

What confuses me about the stumble is that the bike ran pretty good before I did the top end rebuild, it just blew smoke and had low compression. And then it was only after a few rides that the stumble presented itself as an issue. I'll try shimming the needle and see where that gets me. I also saw some people have had issues with their 350's stumbling around 3500 RPM as well so I'm glad there's a community of people trying to figure it out. Onward and upward

[scottieh]

I should also note that I am at 4,500 feet above sea level here

[Mezo]

I should also note that I am at 4,500 feet above sea level here

Try removing the air filter & cover (just temporary) and see it makes any difference.

Mezo.

[xtrider]

3500-4000rpm is right where the cdi will max out and convert to steady advance , me thinks there is a connection if it will then rev past it and run normal . Or doesn't it run good up top either ?






.

[scottieh]

3500-4000rpm is right where the cdi will max out and convert to steady advance , me thinks there is a connection if it will then rev past it and run normal . Or doesn't it run good up top either ?

It does run okay above that rev. It's been a few weeks since i rode it and i was going to fiddle wih the carb today, but I'll ride it and give a better report in a few hours