I ride between 5000-6500 ft with some trips to 8000-8300 ft. Most of the time it's between 20f and 45f for temps. I ran it with 135 main jets when I first got it l. This is a stock 93 750 and the plugs were black. I then looked up the jetting chart and swapped to 132.5 main jets and the plugs still are totally black. It seems like it's taking more throttle to keep 55-60 mph than it did all those years ago when I first got it even though it's jetted down. The mid range is strong but now it doesn't to do more than 7900-8000 rpm and doesn't really want to pull past 80 mph when it used to pull past 100 on the speedo no problem. I just put in a set of 130 main jets and routed the carb vents to the foot area. I'm wondering if I'm leaning it out too much. Is there any other reason for the plugs being black? I just don't want to burn this thing down. I also noticed it runs way stronger for the first few minutes after sitting for a while then it's sluggish after warming back up with the 132.5 jets.
Do I just keep jetting it down?
- Thread starter Reeve
- Start date
Big Bore 904
Member
What drive belt are you running? What kind of shape is it in?
The belt is a Carlisle ultimax3 138-5232U3. With probably 1000 miles on it. It looks to be in good condition but I'm no expert. When installed it I changed the shims in the secondary for a new belt and checked that it was riding within spec. It looks like It might need a shim because it's riding about even with the outer clutch diameter now. My backup belt is a new Dayco HPX5016
I checked the needle seat O rings and they were intact but looked very suspect so I ordered new ones as well as new fuel screw o rings because they were flat. I also found the Yamaha part number for the 131.3 main jets so I'll start with them and then go down to 130 if it's still too rich.
I checked the needle seat O rings and they were intact but looked very suspect so I ordered new ones as well as new fuel screw o rings because they were flat. I also found the Yamaha part number for the 131.3 main jets so I'll start with them and then go down to 130 if it's still too rich.
Thanks for the offer. I didn't spend too much for them from Ebay and also picked up new bowl gaskets and combined shipping. The old O rings just snapped in half when I went to take them off so I figure I'll save their price in fuel in no time.
The one thing I didn't dig into is the needle position and part number. From what I've seen this sled was jetted all stock when I got it. I assume the needle has multiple grooves like the TM38 carbs on my MachZ. What do you have to take off to check the needles part number and clip position? I'm into this thing far enough might as well check everything while I'm in there but it looks like a job to pull all the linkage from the slides.
The one thing I didn't dig into is the needle position and part number. From what I've seen this sled was jetted all stock when I got it. I assume the needle has multiple grooves like the TM38 carbs on my MachZ. What do you have to take off to check the needles part number and clip position? I'm into this thing far enough might as well check everything while I'm in there but it looks like a job to pull all the linkage from the slides.
Big Bore 904
Member
Between the carb work and a good belt you should be on track. A lot of people try alternatives but the genuine Yamaha 8BU belt is best. Good luck.
I'm feeling pretty good about this last round of maintenance. I replaced the reeds which were in prefect condition with boyesen super stock reeds. Probably made no difference. The carbs have now been completely gone through with every possible problem area checked parts replaced and reset to spec. It's now jetted another step down with the 131.3 jets and the vent lines will be routed out of the engine bay. I'm going to try to pull the secondary and shim it for belt wear before the next ride. If it doesn't run any better I know I have a clutch /ignition or compression issue.
Well I finally got it out with the latest updates. New O rings on the seats. 131.3 jets and the vents routed to out of the engine compartment. It's running a ton better and pulls to 8300 rpm now. The top end is a lot better but trail conditions limited me to just north of 90mph but it wasn't nearly done. The bottom end is still pretty soft. It engages at 3000-3200 rpm so I'm
assuming my primary spring is warn out and I need a new one. Fuel mileage seems better but I'm not sure because I had to tow a 93 a storm 750 a couple miles and that took a lot of throttle and rpm.
assuming my primary spring is warn out and I need a new one. Fuel mileage seems better but I'm not sure because I had to tow a 93 a storm 750 a couple miles and that took a lot of throttle and rpm.