Help needed with my IT400

[okkarner]

OK. I bought a 77 Yamaha IT400 that a guy had "tried" to turn into a cafe/street tracker bike for $200. He said it would start on starting fluid. After a major makeover and a carb cleaning along with a float adjustment, it is running and I have been riding it back and forth to work for about a week. The problem is that it feels like I'm riding on a yz80(it's slow). I am no mechanical genius and I'm not real great with carbs, but I know my way around a tool box and have been riding motorcycles for 15+ yrs. I just need some help with this one.

It feels like it doesn't rev up all the way. It doesnt have a tach so I dont know what its actually turning. Also, I dont know if it has a powerband like a more modern 2 stroke, but if it does, I cant tell because its not hitting it. It revs up to my best guess of around 4000 rpms, then starts cutting out like it has a rev limiter. But it doesnt. All the drivetrain/gearing is factory. The only things changed from stock is the pipe was cut up/modified to run under the motor and it has an after market cone type filter.

It is very disappointing to ride when you know its a 400cc two stroke and it performs like a moped. Everything I have read says the IT400s are fast as hell but this one is not. I have read other threads and it seems like it could be 10 different things.

SOMEONE PLEASE POINT ME IN THE RIGHT DIRECTION!!!!!!!

 

[okkarner]

Oh, and compression is 140

 

[okkarner]

Did some tuning/testing today. 1st I repacked the muffler because the packing was soaked and moist. I did a spark plug check and it was black and wet so I set the needle to the leanest (top) setting and adjusted the air mixture scew to the highest idle (3.5 turns out) and it revex a little higher. The air filter is a cheapo cone filter off eBay I think. I took it off and the bike was a whole different machine. Not quite right though. By taking the air filter off I leaned the mixture. Right? So I'm thinking time for a smaller main jet. It has a 350 right now. With the filter on it won't rev up no matter what the mixture screw is set at.

 

[Pantaz]

When I picked up my 1980 RM400 a few years ago, it too would not run with the old, clogged up filter. Cleaned the carb, installed a fresh filter, and it HAULS! I imagine your Yamaha should make comparable power.
The pipe can have significant effect if it's been severely modified.
Do you know original (factory) jet sizes and needle setting?
Any idea if the cylinder has been ported?

 

[okkarner]

The cure:

32:1 premix, K&N open air filter, 320 main jet, 40 primary jet, needle clip in slot 3 (middle slot), air/fuel mixture screw 2 1/2 turns out.

Spark plug reads nice and light brown color. Runs like a champ. It's a beast.

 

[cujet]

Ahh, very good. The IT's had very mild exhaust port tuning. If you want a bit more top end, (and you have a stock cylinder), you can raise the exhaust port 2 to 3mm and widen it 5mm (at the top only if you want good piston support). The transfer port timing is enough. What ever you do, don't go over 193 degrees exh port duration.

In any case, glad to hear you have it running well.

 

[okkarner]

Sorry but all that is a little above my head. Not that experienced of a mechanic.