Jaymichael
XS650 Addict
Greetings all. Ive got a 74 tx650 with bs38 carbs. Carbs were overhauled by rick at oldschool carbs. Engine is freshly rebuilt with a heiden 750 kit. I have not been inside my carbs to see what jets are currently installed and when Rick did the overhaul I had told him the engine was going to be stock configuration (I had not decided on the 750 kit at that time) so I suspect I will require some rejetting. Off the top I have to give thanks for the wonderful carb tuning guide supplied by this community, its already helped a ton in getting me up to speed on how my carbs function.
Now for my current situation. Bike fired and ran decent right from first kick. My idle mixture screws were set to 1 full turn out on both. I used a monometer to balance contribution between both cylinders and set my idle to around 1000 rpm. Engine starts nice everytime, idles real nice but I did notice a bit of black smoke from the pipes at idle. Pulling the plugs confirmed they have quite a bit of black soot forming on both indicating a rich idle.
Today I followed the dead cylinder method in the carb guide. I disabled 1 cylinder, adjusted the running cylinder down to the lowest stable idle with the idle screw and started adjusting the mixture screw. Right away I found the more I turned it out (counter clock wise) the lower my idle would go, and it would start to stumble or stall. I then tried screwing it in (clockwise) and the idle improved. Eventually I found that highest idle came with the mixture screw turned all the way in until it stopped. I tried turning the screw out again but came to the same conclusion, the highest idle was found with the screw turned all the way in. I repeated the process on the other cylinder to the same result.
After adjusting both mixture screws to fully turned in I again synchronized both cylinders using the monometer. Engine seems real smooth at idle, snappy throttle and I am not seeing the same black smoke from the pipes, indicating that I have leaned it out more than it was originally.
Now, I have to say I am a bit perplexed. I wasn't expecting the result of having to screw the mixture screws in that far, and If I have closed them completely I am wondering I may be well served to drop a size on my pilot jets. Considering I have increased my displacement 100 cc's this isn't making a whole lotta sense to me?
I think in the morning I'm going to swap in a pair of clean plugs and run it a few times and see if they are sooting up as bad as before.
What do you guys think? Am I missing something here or on the right track?
Any thoughts super appreciated.
Now for my current situation. Bike fired and ran decent right from first kick. My idle mixture screws were set to 1 full turn out on both. I used a monometer to balance contribution between both cylinders and set my idle to around 1000 rpm. Engine starts nice everytime, idles real nice but I did notice a bit of black smoke from the pipes at idle. Pulling the plugs confirmed they have quite a bit of black soot forming on both indicating a rich idle.
Today I followed the dead cylinder method in the carb guide. I disabled 1 cylinder, adjusted the running cylinder down to the lowest stable idle with the idle screw and started adjusting the mixture screw. Right away I found the more I turned it out (counter clock wise) the lower my idle would go, and it would start to stumble or stall. I then tried screwing it in (clockwise) and the idle improved. Eventually I found that highest idle came with the mixture screw turned all the way in until it stopped. I tried turning the screw out again but came to the same conclusion, the highest idle was found with the screw turned all the way in. I repeated the process on the other cylinder to the same result.
After adjusting both mixture screws to fully turned in I again synchronized both cylinders using the monometer. Engine seems real smooth at idle, snappy throttle and I am not seeing the same black smoke from the pipes, indicating that I have leaned it out more than it was originally.
Now, I have to say I am a bit perplexed. I wasn't expecting the result of having to screw the mixture screws in that far, and If I have closed them completely I am wondering I may be well served to drop a size on my pilot jets. Considering I have increased my displacement 100 cc's this isn't making a whole lotta sense to me?
I think in the morning I'm going to swap in a pair of clean plugs and run it a few times and see if they are sooting up as bad as before.
What do you guys think? Am I missing something here or on the right track?
Any thoughts super appreciated.
