Help with an XR350

[KTM wood spike]

I need a little remote diagnostic help here please. I have a ’84 XR350. I got it in boxes about a month ago. It had dropped a valve and destroyed the topend. I rebuilt it and it ran great for about two weeks. Saturday I was out trail riding with a couple friends and ran it out of gas. It just stalled--I turned the petcock to reserve and kicked and kicked. It still has not restarted. We got the truck and took it home.
Here are the troubleshooting steps I have taken so far.
Filled it up with gas, checked the spark plug, big and blue. Cleaned the carbs, the pilot was clogged so I thought I had found the problem, it still won’t start. I double-checked the valve tolerances and the manual decompression settings, they were all spot on. The auto decompression has been removed so that should not be the problem.
This is my first real problem with a 4 stroke so I am a little stumped. I have good compression, a big blue spark and gas is getting at least as far as the carbs. But it still won’t start.
Next I am going to pull the valve cover off and double check the cam and chain and make sure it is still set correctly. Can the cam chain actually slip on the cam sprocket?
It could be electronic problems but that would be a real coincidence since it happened after running out of gas.
What am I missing? Any suggestions will be greatly appreciated.

Scott

 

[84XRGuy]

Is the spark plug wet after kicking the engine over trying to start it??

 

[Highbeam]

The reserve setting on the petcock pulls fuel from the bottom of the tank where the "on" setting takes it from a few inches up. My guess is you switched to reserve and pulled a big slug of mud into the carbs.

Are your carbs overflowing? Is fuel making it to the engine? Can you see/smell it coming out of the exhaust?

At least drain the carbs using the release screw and try to get a good flush. The fact that your pilot jet was clogged is a pretty good clue that the rest may be at risk of clogature.

If my guess is right, a 99 cent fuel filter in line to the carbs would have prevented this.

Keep the old XR alive, it's worth it.

 

[84XRGuy]

Official old XR term?

clogature

:cool:

 

[KTM wood spike]

Part of my rebuild included cleaning the inside of the gastank and inspecting the petcock. It is in good condition, the screens of the petcock were good-no tears or dirt on the inside. With that said I agree that it must be the carbs. I kicked it about 10 times this afternoon and the plug was completly dry. Where would the main blockage be? I know gas is getting to the carbs because I can open the drain screw and gas pours out. I guess I will clean it again and see what happens.
I wish it wasn't such a PITA to get the carbs out of the frame...

You guys are right this thing is a blast to ride in the woods, real nimble for a big 4 stroke.

Thanks for pointing me in the right direction,
Scott

 

[jdbrusch]

A qiuck check to see if the eletrical system is ok is to remove the spark plug and spray something like WD40 into the cumbustion chamber(spark plug hole).Install a new plug just in case ,the engine should fire briefly on the WD40,if it does not try this again.If it fires you now know that it must be in the fuel system .Install the spark plug in the cap and ground it to the block to see if the is a good spark.Also check the small resister in the spark plug cap, these are common problems on the XR's replace it with a length of wire(coat hanger will work ).Hope this helps some I road one for 6 years they are a great bike.:)

 

[Highbeam]

"clogature" a very official term used to describe the occurence of clogature.

 

[KTM wood spike]

Okay, I had a chance to work on the XR today and this is what I found. After kicking on it repeatedly both with and without the choke there does not seem to be any gas getting to the cylinder. No gas smell and the plug is dry. Carb problem, right...so I removed the carbs again and everything looks good. The jets are still clear from the last cleaning. I cleaned it all again and reassembled. Still no luck. So I sprayed starter fluid directly down the plug hole, after 8-10 kicks it starts up but only runs for a second. I did this 3-4 times just to hear it sorta run. You know its the simple things that make me happy.
I held my hand across the carb boot and pushed the kickstarter through and there was suction so it should be pulling the gas through but I guess it's not. So what's next? Is there a specific part of the carb to suspect? I sprayed cleaner everywhere, all the little holes and passageways seem clear.
Thanks,
Scott

Also if someone would like to tell me more about the resistor I would appreciate it. I have not actually looked in the cap because I have a big blue spark and bigger problems, but that could be next.

 

[jdbrusch]

resister in cap

The resister in the spark plug cap can be accessed by removing the brass fitting inside the boot.Pull the boot off the spark plug and look inside the boot end use a slotted screw driver and unscrew the brass fitting counter-clockwise,turn the boot upside dowm in your hand and the resister and a small spring will fall out.The resister can be replaced with either a piece of coat hanger or welding rod if you have it.In regards to the carb problem only one carb is use at low throttle,I cannot remember which one, I would check this one before taking them both apart, must be a jet or fuel passage blocked somewere. :think

 

[84XRGuy]

Spraying carb cleaner into the carbs will not do a good enough job. Go to your local Yamaha dealer and purchase Yamaha's carb cleaner. Dissasemble the carbs compleatly and let all the non-rubber parts soak overnight. Blow all the carb cleaner out of the carbs with either compressed air or spray carb cleaner.

You will be supprised at how much junk will be in the carb cleaner from your already "clean carb":scream:

Good luck and keep us posted!

 

[Highbeam]

I'm pretty darn sure the left carb is the primary. My thought here is don't mess with anything but getting gas to the engine. Your sparkalation is fine since you can get it to run on ether. That primary carb is not working. Are you sure there is gas in the bowl of that carb? Open it's drain for a second, heck a minute, to make sure. No gas on the plug is something major. Not just a dirty jet. By the way, when you cleaned your pilot did you screw down the mixture screw and forget to back it out?

For grins, push the kill switch and open the throttle all the way with the choke on. Kick it through a few times, if your plug is still dry then look ahead of the carbs. Even pull off the gas line from the tank and make sure you have flow.

 

[KTM wood spike]

Great news, I found the clogature and removed it. The 350 runs again. Now the carbs are very clean, I have a fuel filter in place and a much improved remove/install time on the dual carbs.

Thanks to everbody that responded to my cry for help,

Scott

 

[Highbeam]

So where was the clog? What was it?

Good job finding it, doing your own work can be very rewarding.

 

[MikeOK]

ounds like you have it fixed, but I had an '83 and had a similar problem. One day it quit on me, and after going through every thing I could possibly think of to fix it I finally found that the carbs had slipped just slightly out of their boots and it was sucking too much air into the cylinder. Was hard to see until I got it all dismantled... I have a book on the bike so email if you need any more info.

 

[MikeOK]

One more thing, I was pretty sure the '83 was the only model with dual carbs, are you sure yours is an '84?

 

[penguin]

the 84 still had the dual carbs, the 85 had the single carb and was a big upgrade. I never did understand why Honda quit making the bike after 1985. there would not be a better mass produced 4 stroke dirtbike until the YZ400 showed up 13 years later.

 

[KTM wood spike]

Mike, it has 1984 right on the tag on the frame. And you are right about the fit of the carbs and the airbox/cylinder. It is a real PITA to get the carbs in and out, but once they are in place you have to be real careful about final placement. It is too easy to slide them out of either the airbox or away from the cylinder. When I am finished adjusting them it loooks like they are only half way in on all four connections. A rubber sleeve about 1 inch long to cover the airbox/carb junction would be nice, I wonder what could be used?

It still runs...
Scott

 

[Kramer]

You may want to just replace the boots. They shrink and get hard with age. Makes airleaks a recourring nightmare and can let dirt through.

With rubber that's in good condition you shouldn't have any trouble fitting things together.