XR600 acceleration backfires

I've been messing with my carb for a month or so now and its running better than it has before from idle on up to 3/4 throttle but from 3/4 to full not so good. Right now I'm running a 65 pilot, and a 168 main (stock for my 88 XR600 is 60 pilot, 165 main).

If I'm going "slow" (1st gear) rolling the throttle on it starts to die and backfires constantly when I hit 3/4 throttle until I let off. I tried putting the choke on 1/2 position and rolled the throttle on up to full and never got any backfires and it ran OK all the way on up to and at full throttle but not great.

If I get up to speed in 3rd gear and roll the throttle on when I get up past 3/4 throttle it will continue to run but does backfire occasionally on up to full throttle. At the same time the power feels much, much better (when it isn't backfiring) between 3/4 to full throttle.:banghead:

Am I running a little lean still because turning the choke on 1/2 way helps? Does the backfiring on acceleration from 3/4 to full also mean that its lean on the main?:worthy:

One strange thing I noticed was that whenever I changed a jet and got the beast started again (takes a while) the bike would run awesome for 20 seconds or so then it would settle down and start to do whatever it was going to do. Does that mean anything?:lol:

are you SURE your float level is correct?

any mods? muffler, non-stock air cleaner, etc?

I had a 88 XR600.... put a 660cc kit in it.

the float level was so low, that it would run AWSOME for 30 seconds, {sound familiar? } then warm up / lean out and make the header pipe glow in the dark like flourescent bulbs. ( not good. ) it also ran better with the choke on.

And I learned from my Corvette disaster, if you "punch it", and it pops through the carb, you are really lean. ( that was another expensive lesson )

Hurry up & figure it out. I've got an old XR185 that does the exact same thing..

2 weeks ago I let the carb sit in dip overnight and set the float level to 14.5 mm when putting it back together. My wife had surgery right after that and I haven't been able to touch my bike until just yesterday so I'm fairly confident that the float level is still good.

I have a supertrap exhaust, Moose air filter, hotcam, and air box opened up.

I don't know much about jetting so can't advise. Best I can say is it sounds like a coil problem or a Spark plug gap that is to small..If you haven't touched either and it was working ok before I suppose it must be the carb..

I just put in a new spark plug yesterday afternoon and gapped it before putting it in.

I put in a 175 main with the 65 pilot and would get it started long enough to cough 3 or 4 times out the carb then die. So I swapped out the main for a 160 main and tried again and it was still trying to die at full throttle and would backfire when I reached 3/4 throttle while rolling it on. To summarize so far, from 160 to 168 on the main its doing the same backfiring as before at 3/4 throttle.

I rode it up the road once I got it running and 4 blocks away it just lost all power and died. I couldn't get it started again so i pushed it home. I think I'm fighting more than one problem at once, one being the jetting/carb, and another being possibly electrical. I have a buddy who had an 88 XR600 years ago where his stator would work fine for a bit then when it got hot (mile away from home) it would stop working, and I'm wondering if this could be my problem as well. An inconsistent spark that may be loosing contact at certain times.:lol:

Yep..It could be electrical. Lots of people on this site seem to have jetting issues when changing pipes etc. Being at sea-level here in NZ we don't get anywhere near these problems. Heck, I whack pipes and things from different models of bikes on my machines and never bother re-jetting at all..Must be the altitude you people deal with. Maybe check the lead running from the Stator up to the under the seat connection point and make sure it hasn't got a break or bad connection somewhere. You may need to remove the Stator cover to check the wires down by where it exits the Stator cover and also the wires below the rubber grommet thing..Might need to unwrap a bit of the insulating around the wires to have a proper look at them..I'd also be looking to borrow a coil from somewhere just to test thats not the issue..I don't know if other types from another model of Honda will work,,someone may..then just get a secondhand one as a test unit. I'll just add..If the bikes got an inline fuel filter then try it without it..they do get blocked and can starve the carb/motor of gas..

Well I swapped things around one more time and now have the stock 165 main back in and it was the same ole - same ole. It ran great for the first 20 seconds, then started to die and backfire at 3/4 throttle. So I pulled the float bowl and it was barely dripping any gas when I let the float drop so I pulled the float needle and flushed the orifices by turning on the gas and let it rush out. I don't have a fuel filter on and I saw some small brown stuff floating in the gas so I may get a new one and put it on, as well as check the petcock screen in the tank. I think part of my problem could be the gas being drained from the float bowl and starving the bike and the other is definitely my stator.

I checked the spark and I could just barely see the spark at all it was so weak. The bike does run but fighting multiple problems will make it impossible to get my jetting correct.:lol:

I know the 83-87 XL600R are well-known for stators going bad....

I guess your 88 might have the same part. my 87 XL600 did the same "loose spark 1 miles from home" trick... a new rickystator was $108 on ebay, a new cdi was under $120 here at TT.

I changed both at the same time, it was worth it because "no more worries".

then the bike could be started without my butt leaving the seat.

If you can, get her warmed up, and rip it down the road at full throttle.

as it's breaking up, coughing, etc., hit the clutch and kill switch at the same time.

push it back to your garage and pull your spark plug.

This will give you the best clue to what is really wrong.

one more thing... is you head light BRIGHT, like on a car, or kinda yellow when the bikes running? my headlight went from 'yellow' to really bright when I changed stators. ( std, not high output. )

Huge changes in jetting hasn't had an effect, so jetting isn't the problem. Make sure that the slide needle is moving up and down with the slide. If it isn't, then the clip on the end is missing and the needle is blocking the main jet circuit. It's a rare problem, but I have heard of it before. Also, what notch is/was the clip on?

I would also start checking electrical connections.

I overlooked a really dusty weekend one time. After 3/4 throttle it liked to pop and die out sometimes the 3rd day of riding. It drove me nuts looking for problems. Finally I looked at the new K&N with a precharger. Both were dusty looking. I pulled the gas line off and cleaned them both well and let it dry trailside. Ran mint after that. I ended up switching to a foam Uni after that when riding really dusty conditions. Hope yours is this easy.

You could roll on the throttle ok, but you couldn't hammer it without problems. Top speed was also not possible.

may sound a bit :ride: but seriously...CHECK THE KILL SWITCH!

There are three sixhundos in my garage at the time, to 86's and both had a ton of money thrown at the ignition (cdi, stator, coil) not to mention carb rebuilds. Until one day my roommates wised up and disconnected the kill switch and all of a sudden...:p

don't over look the simple things

When I pulled and dipped the carb 2 weeks ago I checked the slide needle and the clip was in the 3rd position (stock) and I worked it up and down after reinstalling it to verify it worked correctly.

I also remember reading about someone having problems at higher speeds with their bike and it was a loose ignition coil wire connection vibrating at those higher speeds making intermittent contact, so I checked mine and found one was a little loose and re-crimped it tighter to make sure it wasn't the problem. That didn't sole my problem though. I also had tried disconnecting the kill switch completely and it didn't change anything either.

Right now I'm pretty convinced its my stator because when I kicked it over multiple times I couldn't even see a spark in daylight for 8 or 9 kicks then I could just barely. But the resistance levels check out for the stator within speck when its cold (I haven't checked it again after I ride it for a bit and its warmed up) so apparently that doesn't guarantee a good stator. I think at 3/4 to full throttle the weak spark is being drowned out by all the fuel coming into the combustion chamber and keeping it from running. I may try rewinding my ignition coil on my stator to save some coin.

Thanks for the suggestions.

I had the same problem and the stator was the ticket. I am running a bit lean from the pilot adjustment with an older supertrapp (95?) spark arrestor and modified pipe (3in longer than stock) and get a little backfire if i lay off the throttle quickly.

Have you checked the RFI resistor in the spark plug boot? I have seen them fail and cause the problem you are experiencing. If in doubt, replace the resistor with a length of brass or copper rod. Toss the spring and make sure the rod is long enough to be held tightly by the retaining screw.

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