Have you tried to fatten up your pilot jet?

 

Pilot jet covers from idle to 1/8 - 1/4 throttle. Probably why all the needle tapers look the same to that point. Don't really know where your problems lies though. Good luck with it.

 

I would highly recommend installing an EGT gauge so you can monitor exhaust temps, you will easily know if there are lean conditions at any throttle setting. You will also know which circuits of the carb that need attention. I have modified my needles as needed to correct lean spots. I run a 38 TMX which I found out is not a good choice for a mod motor. It took a lot of internal mods to get enough fuel but it works well now. My stock carb didn't run clean either at low throttle settings, the TMX is very clean throughout once it's setup properly. I use shims on the needle when needed.

Is your piston dome melted at the exhaust port seizing the rings? I had the last Weisco that I installed in my Scrambler coated with a thermal barrier on the dome at Swaintech. .004 is plenty of clearance, I make sure my cylinder is hot to the touch when warming a cold engine before I ride.

When premixing oil in the gas remember the oil displaces gas so you should increase the carb settings to offset this or your effectively leaning it out.

 

Thanks again for feedback. Changing the pilot jet had no effect on the part throttle operation at all. May have changed cold start choke sensitivity with a fatter jet and begin to load up if I let it sit and idle too long. Powerslider the wiseco dome is not melted or deformed. I was able to pry the stuck rings out of the piston with a small pick. It was clear that the ends of the rings had collided and started to roll into the piston - like there was insufficient end gap clearance. This evidence is why I have asking if others have experienced "cold seizure". When it went together initially at 0.004 piston to cylinder clearance it had 0.020 ring end gap. I would like to know what you guys with experience with these set the clearances at so when I put this thing back together it will be "right" this time. Vig may also have a good point concerning the annealing of the sleeve from the initial meltdown. The previous owner did not realize the oil injector had failed and literally ran it until it locked up. That having been said I don't know if it is worth the risk to bore this thing as it is already at 0.060 over. Anyone have experience with sleeving these things? I have the old style cylinder on this thing and have considered updating to the "new" type cylinder. The way it is looking this may be the ideal time. I have a 1999 400 scrambler with a dynoport pipe that has the newer cylinder on it but I have not had both cylinders off at the same time for comparison. Anyone know if there are advantages are outside of a straighter reed cage entry with a straighter path into the rear boosters? It appears the newer cylinder may have a potential power advantage over the old one. Would this be the case? I have been so frustrated with tuning the stock carb for drivability issues ( I have way too many tuning components for the stock carb and the damn thing still defies me) I have considered installing a bigger carb such as the 38 tmx or the 39 pwk but with the amount of miles we ride up in the adirondacks I have to retain the oil injector. I know the factory throttle and cable does not have sufficient travel for this but it appears the oil pump does have sufficient travel to allow the extra pull with the right cable and throttle components. Has anyone ever done this and if so what parts were used? Last but not least if I put this thing back together with the newer cylinder and a new wiseco piston does anyone have any suggestions on porting dimensions for maximum power with the Hot Seat trail pipe (runs at 6500 rpm) or suggestions for better trail pipe that will fit this chassis if there is one out there?
Thanks,

 

you can run the hot seat pipe at 6700-6800 rpm on a good setup no problem,,you need to a better carb to cover the whole rpm range of the engine now with the performances gains,,tmx 38 for trial pwk for max out put or race mods,,i found the wiseco .020 over to run best in that motor so far,,yes,the 96 and newer 400 cylinder have improved performances from the original motor.

 

Got a 400L already taken apart don't know where mark is suppose to be can not see any more , could some one tell me how many teeth from key way it would be ?