03 SX viper centre miss on idle

P

P Herauf

New member
Joined
Dec 27, 2018
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3
Location
Odessa Sk.
Hi guys. I am working on a 2003 Sx Viper that I bought used.
This sled has had SLP Triple pipes installed on it. I seem to have a weak centre cylinder on idle. The pipe coming off the centre cylinder does not get even warm while idling. I have cleaned the carbs, and checked the reeds. I have swapped the plug, plug wire cap, and coil to another cylinder, but the problem stays with centre cylinder. While idling,I can pull the centre plug wire off, and there is hardly any drop in Rpm. Pull the wire off pro or mag and it drops way down. I have tried spraying fuel into the carb with no change. Pulled off pipe and fuel dumped out.
It does seem to clear up when you get it revved up on the stand.
Compression testing at 95 pto, 110 centre, 105 mag. These sound low to me, but it could be my old compression tester.

I plan to check the fuel pump and pulse line next, to see if the pump is loading up the centre cylinder via pulse line. I also plan to ohm test my stator using numbers I found on here in another post.

Any thoughts on where else to look? I was not able to find another post with issues similar to mine.

Thanks - Peter
 

I had some time this morning so I checked the spark. With the plugs out siting on the head, pull it over and all 3 are the same blue colour spark. Then I fired it up, let it idle for a while at about 1700 rpm. Same centre cold pipe. Pulled plugs and I was surprised to see that the outer plugs were black and wet, centre plug was also black but not nearly as wet. Finished warming up the sled and went out for some plug chops. On light riding mid throttle, all 3 are dark brown but not wet. Then I did a 3/4 - full throttle pull, all three plugs came out medium brown, maybe a little light brown, with the Mag side plug being lightest of the three.
It pulls crazy hard on WOT. Mid range seems to slobber a bit, doesn't sound quite right in the mid range.

When I had the carbs apart, All the main jets were 162.5. The chokes all seem to move freely. When I cleaned the carbs I did lower the floats so they were parallel to the bowl base. The medium/light brown plug colour on WOT makes me think I wanna raise them up a bit.

Still not sure on the cold centre pipe on Idle, but I do know that once riding all three wake up and it goes good.

Is it possible that the needles and needle jets are worn out causing the mid range stumble? This machine does have 8000kms on it.

Thanks! - Peter
 
Thank You! I went through the post you linked me too, and I watched the video on float level adjustment. I had done the float level with carbs upside down, and the dampener compressed on the needle. That is likely causing a lean condition. I will remove the carbs and adjust the floats properly.
Might be a few days till I can get it done. Once back together I will re-check plugs and post results. - Peter
 
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