Kawi2strokes.com Forum

I had an issue with my S2 sputtering and popping and losing power when it gets hot. Tried new plugs, then replaced all the points and condensors. I went for a test ride again today, and had exactly the same symptoms. It ran fine for about a mile, and then when it got a bit hotter, it started popping, sort of like a backfire. (losing power also)...as long as I kept the throttle down, it made it back home. The more I tried to give it, the worse it ran.

Lets also say that I found some oil under the points cover, but I dont think its coming from the seal. It does sit for long periods of time on its side stand, and I think the gas is leaking down there. (I run premix) Im just wondering if the igniton coils, or rather, whats behind the points plate could be going bad....(Not the coils up under the tank)..the generator coils I guess you would say. Ive had problems with an old Yamaha dirt bike, and it turned out to be one of the coils behind the magneto.

It probably doesnt help that the coils get all that gas drip all in there as well.

I dont know. What else could it be?

Thanks in advance!

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1972 S2 350, 1972 F9 350 Bighorn, 1975 KX400, 1981 YZ465, 1980 XT500 (Built for MX) , 1987 KD80, 1995 MZ Skorpion, TTR 125, 1994 KDX200 , 1978 Mobylette, 1985 KX350R-F91m (Frankenstein) and a Doodle Bug

The coils in the stater are for charging only and have nothing to do with ignition except for keeping the battery charged.

If you have a gasket or sealer on the points cover there is no way for the points area to get oil/gas in there except for a bad seal. If so, the points set that is at the bottom will become contaminated and get intermittent firing of the plug. However, I wouldn't think it would be related to whether or not the engine was hot.

An bad ignition coil (under the tank) would offer the symptoms described (missing after hot). If you could determine which cylinder is at fault, you could swap coils and see if the problem migrates to a different cylinder.

Most carb problems would not be a "when hot only" problem.

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Answers are here: http://kawatriple.com/

Excellent info, thanks!
Good to know about the generator coils. No gasket or sealer on the cover. Shame on me. LOL....

In any case, I will check the ignition coils next!

Thanks again,
Neil

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1972 S2 350, 1972 F9 350 Bighorn, 1975 KX400, 1981 YZ465, 1980 XT500 (Built for MX) , 1987 KD80, 1995 MZ Skorpion, TTR 125, 1994 KDX200 , 1978 Mobylette, 1985 KX350R-F91m (Frankenstein) and a Doodle Bug

Another thought.... not related to heat, but to time.

It is possible that you are running out of fuel to one or more carbs. If the float level is not set properly, float leaking or there is a problem with petcock or lines you could be running out of fuel in the float bowl and after setting it fills back up. Less fuel would be required at small throttle opening.

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Answers are here: http://kawatriple.com/

As MRAXL said about the fuel. I had a similar problem on a Kaw ZR-7. turned out to be a small piece of trash in the fuel line to the number 2 cylinder. After cleaning, problem gone.

have you checked bowl in petcock ? also are cut outs on carb slides facing airfilter ?

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downwind of three mile island

My S3 did that a while, back in the summer, pop and crack and carry on. Only do it when I'd get on it hard in a high gear. It was also noticeable when you held it down hard, the center cylinder would drop out and the bike would slow down. I went though a lot of chasing that bug down, seems it was a slight lean condition on the center carb.

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74 H2B with reeds and 34mm carbs
75 S3A Ram Air with reeds and 30mm carbs
73 S2A (wife's bike)
71 Yammi RT1B
83 HD Sportster
03 Yammi R1
06 Kaw 750 Vulcan (wife’s bike)
12 Yammi vstar 250 (wife’s bike)

check your battery is charging

Gary T

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Wine for my men we ride at dawn

Absolutely my thoughts

Wow,.
Thanks everyone for all the suggestions. I pulled the coils and tested them. Im reading from 5.1 to 5.4 ohms across the screw terminals, and 8.1K to 8.4K from the + lead to the center prong. May seem nuts, but I put the coils in the oven for a while to heat them up to see what they read while a bit hot.
Resistance rose across all of them a bit, 6.0 to 6.5 ohms lead to lead, and 10.1K to 10.6K from positive lead to plug wire prong.
They read the same as my original readings when they cooled down.

So.....theres not one that jumps out at me.

The grounds to all of them were a bit loose, I swear EVERYTHING vibrates loose on those things. The wires are a bit crappy as well....when I was in there soldering the condensors in, one of the ignition wires was kind of dark.... I am going to rewire all the grounds and Ive got half a mind to re wire all the ignition wires as well down into the stator. I dunno...I rewired the entire accessory system, all the lights, horn, blinkers, etc way back when I got the bike but the ignition wires are all still 40 years old.

The carb idea sounds very possible. I can see one of them not filling quick enough when Im getting on it and boom, a big lean on one cylinder....

My rear tire has a nasty split in it anyway and I am in dire need of a rear sprocket. Ive got to get all that squared away before I start riding it again. While juggling in getting my boat ready and my vintage MX stuff ready....I swear winter is not long enough sometimes. Of course we have NOT had any winter to speak of here in Maryland. Thats whats really driving me nuts, I need to be RIDING!

thanks again!
I will let you all know what I find

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1972 S2 350, 1972 F9 350 Bighorn, 1975 KX400, 1981 YZ465, 1980 XT500 (Built for MX) , 1987 KD80, 1995 MZ Skorpion, TTR 125, 1994 KDX200 , 1978 Mobylette, 1985 KX350R-F91m (Frankenstein) and a Doodle Bug