Xt600 Misfires, then cuts out... Help Needed
 

Hi Everybody!


I recently bought myself a poor running 1984 XT600 34L.
The original symptoms was:

Won't run at full throttle
Idles bad when hot.

Thinking that this would be a doddle to fix I bought the bike.
Well, not it has turned in to quite a headache. So I need some of your wisdom.


The symptoms are now the same.
Here are two videos, one is when the bike is just started. Then it will run with no problems, when it gets to operating temperatures, it misfires, cuts out etc.
When it does this, it can be hard to start it again.

http://youtu.be/HGipgiK3Xj0
http://youtu.be/_FgNRz8LKdk

Well I have done the following.

Cleaned out the carbs
Measured Pickup
Measured Source Coil
Measured Ignition Coil
New rubber intake boots incl. o-rings
New sparkplug
New CDI
Checked the ground-connections for CDI, Coils etc.
Checked Valve clearences

After all this the symptoms are exactly the same..!


I am thinking that this is Ignition related since it gets hard to start after cutting out because it sucks in fuel while stumpeling and therefore drowns.

Please let me know if you have any good ideas to what this might be...


thank you
jonas

Bad stator likely. Testing them does sometimes show them to be good but once hot they short out. Try doing the same tests, once cold, once hot and compare.

Hi -

I have done a test like that measuring the resistance in both pickup and stator both hot and cold.
And everything was within spec.

The ignition coil was within spec aswell

Just because you've cleaned and tested something doesn't mean you should necessarily cross it off your list.


Any chance of getting another carb off another bike and trying it out ?

Cold engines and hot engines have VERY different fuel/air requirements.

It could be running very rich and at high temperatures, trips it up.

How is the choke and pilot curcuit ?? Do you need choke to start it ??

What jet sizes are you using? What altitude are you at? Could be waaaay too rich.THUMPTHUMP

Hi Ted

It's true!
As it is right now it will start without choke. It did need it before.
The thing is, I havn't been able to adjust the air / fuel screw since I can't get it to idle.

Last time i cleaned out the carb I went through pilot / choke systems with a piece of piano wire and they were 100% clean.

I am thinking that this might be my ignition coil that is going wrong. It is afterall a momentary fault. So I guess I won't be able to measure it....

I sent this to a few mates who had XT or similar in the past.. one of them just emailed this..

Have you changed the air filter or is the one fitted a cheap after market one? Once had a Honda with a similar issue - as you ran towards full throttle the foam compressed making it run rich to the point of misfire and cutting out.

FYI, dragging steel wire through aluminium carbs isn't a great idea. You can do damage and make things worse. However, lets assume you were super careful and everything is okay.

Well, In my experience a big 600cc air-cooled single usually always needs a decent amount of choke to get it going. Even in hot countries. If it starts without any choke in a bleak, cold British winter then I think your jetting is out.

Take it all back to standard book settings with the jet sizes and pilot screw and see how it goes from there.

Do you know what your screw setting and jets are at the moment ??

I know that steel vs alu or brass is bad. So yes, I was super carefull.
As it is now the jetting is standard.
And the air/fuel screw is 1,5 - 2 turns out. I havn't felt a big difference when turning the A/F screw. But then again, it will not idle long enough to adjust proper.
I have tried turning in and out for 1/4 turns then starting.

Hi
it might be worth just taking the end off as on the older xt they quite oftern blicked the silencer up and this would xause the engine to run bur cut out soob after starting skip

There is a capped off nozzle on the left carb boot between the carb and motor. Take that cap off and see if it clears up. It'll let more air in and if it's running extremely rich there will be a very noticeable difference. I have one carb that is screwy and always ran overly rich, Till I had the time to make smaller jets I had that cap off(put a foam over it to somewhat filter the air). That carb needs several sizes smaller jets than all my other XT carbs. It would puff black though when I twisted the throttle, but idle like crap(had the mixture screw bottomed out even) and top end surged badly but would rev out.

I don't think it's carb related but you never know. I should need a choke to start definitely when properly jetted.

Jonas has posted the problem last week on my forum, have a READ.

Nothing wrong with posting on here as well Jonas, we post on all forums so more brains will hopefully fix the problem.

I think the clues are when the bike gets to operating temp, electrical components can fail when hot so its leading towards your coils breaking down.

Possibly your trigger coils are giving mixed signals to you CDI?

Mezo.

News..!

Hi Everybody.
Well, after being fed up with this bike i decided to try all over again. But this time focus was on fuel and carbs.

So I pulled the off yet again and cleaned them and put them in my small (read too small) ultrasonic bath.

Everything was clean.

On assembly I saw that the small disc that contains the piston for the Fuel Enricher maybe was the wrong way in.
I have not been able to find any info on the, but it will fit both way.
It has a high lip on one side, and a small rounded on the other side.

Can Anyone tell me if this picture is right?
http://s879.photobucket.com/user/Mot...x384x.jpg.html

Anyway, I turned it around.
But the carb on the bike and fired it up. Cold idle was perfect, as it was before.
But it didn't seem to misfire.. Rolled around the carpark and nothing, just a bit of adjustment to the A/F screw.

I was not able to do a test ride tonight, but will try tomorow.

Could all this be related to a bad Fuel Enricher / Air cut-off valve?

Hi.

I don't know how it's meant to look on the XT but yes this cut off valve can cause you problems if it's assembled incorrectly or is the air hose is damaged or kinked etc.

I pulled this off the net because I can't be bothered typing it ;)

It's for a YZF but it's the same principle.



"The Air Cut Valve lets extra air flow to the pilot jet during most running conditions, but not under deceleration. The carburetor has 2 air passages to the pilot jet and one (the ACV passage) closes of during deceleration. This richens the pilot circuit on deceleration to reduce popping. The Air Cut Valve "cuts" the air passage off by using vacuum to pull opposite the spring and diaphragm. When you back off the gas at high revs, the ACV richens the air/fuel mix to stop the bike from popping and banging through the exhaust. In the perfect world, the air cut valve would ONLY richen the circuit on high RPM deceleration (to prevent backfire).

How It Works:

The center hole with white plastic valve leads directly to the pilot jet air circuit, along with the pilot air jet. The diaphragm spring and pin normally hold the valve open.
The hole on the left leads straight into the intake manifold for vacuum. This pulls the diaphragm pin away from the center hole on deceleration, closing it.
The hole on the right leads to the airbox side of the slide. It allows atmospheric pressure air to flow thru the passage in the center when the vacuum is lower, and leans the pilot circuit. The WRF's have a bigger pilot jet(42-45) than the YZ's(40-42) to compensate for the added air.
The ACV simply cuts the air to the pilot jet in half when using engine braking.
Unfortunately, the spring tension against the vacuum at mid throttle position also richens the circuit and keeps changing. Some riders have suggested that it is hard to set the fuel screw by ear because the ACV constantly changes the mix. Others have indicated that reading the plug color and jetting the pilot circuit are also more difficult due to the ACV. Especially if you have YZF timing on your WRF, it's a good idea to modify the ACV, so jetting will remain more consistent."




Read more here...

http://www.thumperfaq.com/acv.htm

I had played around with the valve on one of mine when I didn't know which way was right, it didn't make any difference to how it ran. I think it still does the same thing either way except maybe have less/more spring tension. I would think something else was the main issue that changed from the cleaning.

Problem solved..!

After cleaning everything out yesterday and turning the washer for the coasting enricher around everything works..!

It starts great cold
Has nice throttle response when warm
and doesn't pop and bang.

I took it for a ride along a country road, it had a small issue at 80km/h when accellerating.

After that I took it through central Copenhagen. Classic city traffic and redlights. No issues.
But, it stalled for me at a red light. And then it was really hard to start.


Conclusion
I believe that all this is many small thing adding up to a bike that wouldn't run.
But I do believe that all this has been an carb issue, and truly fuel related.
I think the bike was starving from fuel all along.
I am even considering to remove the small filter within the carb itself.

Anyway, thank you all for your help..!!!

You are Awesome

If it starts good cold but not hot it is usually rich , not lean.THUMPTHUMP

You can plug the Air Cut off valve entirely... It's not strictly necessary.


But yeah. Older bikes can be a consortium of problems. Glad you're on the way to full motorcycle health :thumbup1:

My bike has been doing something similar. It's an '03 xt600e and on deceleration it pops and cracks like no other. I thought this could be from clogged jets ect., but cleaned and checked and they were spotless. When I checked over my carb, gasket #17 (5Y1-14536-00) was missing from the previous owner. (In the bowl there is a shaft that fills up from the bottom and has a tube that reaches the bottom.This tube goes into this shaft from the carb side of things and is located near the pilot jet. That gasket which sits right there. ALSO what is this for?????) Also the Rich \ lean screw was out 4.75 turns, which normally its 2.5 give or take. I have an aftermarket CRD pipe on it. ( I think that's the name. I wrapped it after I burnt myself) Anyway, I turned it to 3.5 turns out (little richer for pipe comp)and am running the #130 main jet (main carb) , and the #46 pilot jet, living 1 mile from the ocean but at times traveling to the mountains. SO, now it runs better but still pops back through the carb at times and is real poppy on decel... could this be caused by the same valve? Valve clearances are all good also. I checked those all. This carb pop at idle is driving me to drink!!!! jeigerbeerjeigerbeer:funmeterno:

If you are turning the screw on the main carb underneath and towards the front of the carb, this is a FUEL screw, not AIR screw. Further out is righer. Air screws are on the inlet side of the carb, fuel on the outlet side.

Hope this helps.

That popping on decel is from a lean condition. You should have the next size bigger pilot jet if your at 4.5 turns out with the fuel mixture screw. I believe #48 pilot is the biggest available with #46 as the "normal" one. If you have an adjustable needle in the primary carb maybe the clip should be moved down one groove (needle will be raised up for a richer mixture). Otherwise a washer can be added under the clip if not adjustable.

An air leak up at the head on the exhaust pipe will also cause a backfire, but usually just one or 2 big bangs, a steady crackle and popping as the motor slows down is from being lean. The coasting enrichment setup should also be checked for proper operation.

I dont know about 4,5 turns out. If i dont remember all wrong mine is 2,2-3 out with bigger size jet and never have any problems, sparkplug looks fine.

Thanks I will have to rip out the carb and do this with the needle. Ya the guy before me was kind of an idiot, so i think Im fixing his problems. The thing I cant understand is that when I bought the crazy thing it was running better and now its running like garbage. When it back fires under idle it kills itself. *** I did let it sit for 4 months while I was in the states *** But i drained the carbs (during that time) and have cleaned the jets ect. IS there something I missed while cleaning it? BTW been wrenching for 8 years so I'm not a newbie. Just trying to track down ghosts.

Check the enrisher valve on the side of the left carb for any cracks in the diaphragm, along with the spring and plunger there and working. Also make sure you have the o-ring around that pipe you were talking about in the bowl where it seal to the bottom of carb. There should also be an o-ring and small washer on the mixture screw to watch out for falling out if you had that out.

Check check and check.... Man alive still. Does this bike come normally with exhaust gaskets? :nono: (haha) There wernt any on it when I took off the exhaust. (thanks to the previous guy!) So I bought 2 close to the size i needed and put them in... Uff. Seemed to get worse, now the "puffing" back firing sound is now also a leak pop. So looks like EBay is in order to get the gaskets.

Someone told me that the Yamaha 660 Raptor had timing chain tensionr problems. This being said... xt600 and Raptor 660 are almost the same low end. Could it be the same cheap plastic tensionr going bad, causing all of these back firing "puffing" sounds and not wanting to run proper?? Uff....:funmeterno:

Xt600 Misfires, then cuts out... Help Needed
 

Is this thread still active? I'm trying to tune the carbs on my 1989 xt600 and I'm not sure what the stock main jet size is. Can someone please enlighten me?

Thanks!

Pk


Sent from my iPhone using Tapatalk

I think my stock ones are 120 main left carb, 125 right carb,
#46 pilot and 2 turns out on the mixture screw.

My 86 came with 130 in the left and 125 in the right. TTs had 135 in both. THUMPTHUMP