XJ 750 Seca with 850 big-bore kit

This isn't a plea for help so much as asking for opinions and advice. I bought my '81 Seca last fall that had an 850 big-bore kit installed by a previous owner, along with a K&N filter and 4-into-1 exhaust system. It started rough, wouldn't idle, ran too rich and had would fall on its face at about 5 grand. I ran some carb cleaner through it, and that helped a bit.

Over this last winter I had the carbs apart and to my horror found that three of the four carbs had been re-jetted with Mikuni jets (Hitachi carbs) several sizes larger than stock, while the fourth carb still had stock jetting. Per the recommendations of a friend who works on Yamahas, I purchased jets in the stock size (112 I think) for the mains and one size larger (41) for the pilots. Long story short, it still runs a bit too rich and won't idle, but the bog is all but gone and it doesn't spew half-burned fuel out the muffler any more. It's really strong in the upper revs and doesn't make any unusual noises, and uses very little oil. I think at this point I just need to sync the carbs and do some tuning and I'll be in business. What do you guys think?

 

I got my Seca back from the shop a few days ago. He managed to get the carbs fairly close to properly tuned, and the bike runs quite a bit better. The mechanic, however, warned me that my engine is about to go belly-up. Symptoms include:

#1 carburetor will _not_ synch with the other 3
#3 cylinder has an EGT about half of the other 3
Some valve noise/clatter at idle
Low compression (~95psi on 1-3, about 110 on #4)

This winter I'm going to get inside the motor and see what I can find out. I might end up doing a valve and ring job if it looks salvageable. In the meantime I'm keeping an eye out on Ebay for an XJ motor to either swap in or use for parts. I honestly have no idea what's inside my engine. I took the PO's word for it, but if he's the last one who worked on the carbs I'm not particularly impressed with his mechanical skills.

 

Wow! What a royal PITA! I hope you gave the P.O. a piece of your mind. I'm sorry no one got back to you on your initial post. Looks like a good idea to change out the motor or at least get one to have around incase of meltdown.