99 XT600 Severe popping under acceleration

[pursang]

Last couple rides the bike has been popping severely through the carbs, starts around 3500 rpm and up and is getting worse, it pops five or six times each time I start getting on the gas and with each pop it momentarily kills the power, not like a fuel starvation bog but requires gearing down to get up hills, no popping on decelartion, bike starts and idles perfect, valve clearances are all up to spec, plug looks fine, compression is 159, fuel flow is good, I'm thinking it might be electrical since I dismantled/cleaned the carbs only 2500km ago when I installed a new top end. my question is if it's electrical which is the most likely part to cause this ? don't have a lot of cash so I'd really like to get it right, any suggestions are welcomed and appreciated !

[xtrock]

Have you checked the rubber intake? and there is a filter inside the carb did you clean this? sounds to me like the problem is when you need more fuel and its not getting the right mixture.

[Bandit127]

A very long shot but a sticky inlet valve could explain it -it might allow the mixture in the inlet/carb to ignite under certain circumstances. This would clear them of combustible air and account for the bog down.

Perhaps a cheap start would be some redex and an oil change?

Timing is electrical and very hard to get wrong. You are much more likely to get no spark than one at the wrong time/place.

[jjrider]

I agree with Bandit127, to get the popping through the carbs might require a stuck valve or timing way off. Slipped timing chain?? The cdi defaults to the early advance stage I believe or quit outright. Are you sure the poping was from the carbs?
I had a V8 car engine with high miles that the valve springs were getting weak and as the rpm hit 4500, the things would start to pop, crackle, flames out the side pipes, from floating valves. Broken spring a slight possibility, but definately check the "normal" stuff, like Mezo's suggestion, hate to overlook the simple

[pursang]

The link below shows how the carbs looked when I rebuilt the top end about a year ago. the only thing I didn't pull apart was this diaphragm valve cause it was pinched in place.

Motorsports Forum - Carb Inspection/Cleaning

Mezo do you mean the coasting enricher ? what should I be looking for ? I remember the diaphragm was in good shape last time I pulled it apart but I didn't remove the brass pin below it since it was pinched in place I wasn't sure if I should play with it.



Shouldn't be a sticking valve I just a did a valve job 2500km ago and the two exhaust valves are new.
extrock the rubber intake boots were starting to seperate from the aluminum but those have been cleaned up and resealed with silicone and are still looking good, when I had the carbs apart the only filter I remember is the course foam filter for the air coming into the secondary diaphragm (top of carb) otherwise the fuel tank has screen filters on both petcocks and an inline fuel filter between the tank and the carbs.
It does sound like it's coming from the carbs and sounds a lot like the pop you sometimes hear when first starting the bike, the one that blasts out the left side of the carb, I'm getting lazy I don't wanna pull the carbs out/apart again if it's not an obvious electrical part going bad but I guess I might have to.

[xtrock]

Yamaha XT600 1990 1992 Carburetor Rebuild Kit 00 082 | eBay

Dont know if you have same but as you see on pic there is a small filter, and i had same problem when this was full of dirt.