T250 Rebuild

[TripleKing]

As part of my T250 project, I am forced to rebuild my engine (which is a 74 GT250). Since the engine will be bored out 1mm (effectively making it a 260), the exhaust ports will be cleaned up and I have to run pod filters due to a missing air box, I am planning on installing Mikuni VM26-8074 carbs. The problem is, I need base line jetting so I don't blow up the engine while I am tuning. I am looking for suggestions.

Also, although the engine is a 74 GT250, the timing plate, etc., is from a T250. Will I be able to time the engine properly with T250 timing gear on a GT250 engine?

 

[Kanticoy]

As far as timing, yes you'll be able to time them just fine as long as the plates are the same diameter. They are both 180° motors so no issue there. The T250 came with 26mm Mikunis from the factory, when I get home I can tell you what the stock jetting and other settings are.

 

[TripleKing]

My manual says they are VM24s and the T350s got VM30s. The other probalem I am having with my oem carbs (two sets of rebuilt carbs) is that when I tighten them down to the engine, the slides bind. Wish they were spigot mounted. DK what jets I would run as a baseline. Manual says that #97.5 main jets were stock.

 

[TripleKing]

oops, sorry, my main is an 87. Might be a moot point anyway. By oem carbs have a vacuum port for the petcock and the aftermarket carbs do not. Not sure of what aftermarket petcock would work with my tank.

 

[joeschuit]

Check the mounting surface on the cylinder and carburetor for flatness. Make sure you're not using too thick of an oring on the carb or else it'll pull the flanges warping the carb. If you want to, get some gasket material and hondabond and use a paper gasket instead of the oring. Stock jetting for a 74-75 gt250 using a 26mm mikuni is a 113 mainjet and 25 pilot. I highly suggest foam unifilters over pods. the hard backing on the pods don't pay well with the blowback of the pistonport cylinders. I'd bump the main up to 117.5-120 and the pilot to 30 when using open filters. Play with the needle for best midrange. I found the bike to have better torque with the stock airbox, which I've got if you would like it. My bike now has 350 cylinders(bored to 336cc with wiseco pistons) and 32mm carbs but I drove the bike stock for 1 1/2 years. Thanks, Joe