Maybe I posted this in the wrong place under vintage.
IT400 blues
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Hi all! New here, but have done a little pre-register perusing.
Maybe someone can help me out a little. I just got back into riding last year after a twenty-something year sabatical. I bought a '77 IT400. I grew up on 125's, and the 400 was a bit much for me at first. It was powerful and fast, and didn't stop that well besides. After a bit of riding, I started learning to handle it and was having a lot of fun. Then the rod threw through the piston skirt, cylinder skirt and both case halves.
I bought another IT400 a couple of weeks ago. It's a '78, and I thought --- hey! I've already got a parts bike! Well, the second one is NO WHERE near as quick! It also has a loud piston rattle type sound at high RPM. I bought a Clymers and turned some wrenches and since figured out that the '77 actually had a 400 enduro bottom end (injector pump--inactive) with an IT400C top end (compression release). The pipe is also almost certainly not stock IT, as it has a separate head pipe. The '78 is an IT 400E.
I'm thinking that the IT400E should not be any tamer than the 400C, but thought I'd ask here. The power difference is so marked that I don't think cleaning and dialing in the fuel system will make up the difference. I also hoped someone might have a hint for me about the high RPM rattle. The intake manifold of the '78 is cracked looking, and I'm wondering about an air leak. The other one ran so strong that I thought I'd swap over the intake and reeds when I go through the carb because it couldn't hurt, even if it isn't the actual problem. Thought I'd swap the CDI for the same reason. I wanted to check the compression before pulling the top end, but the Clymers doesn't give me any compression numbers. I'm also wondering what a primary compression leak would act like.
Any suggestions?
Thanks in advance.
Steve
IT400 blues
--------------------------------------------------------------------------------
Hi all! New here, but have done a little pre-register perusing.
Maybe someone can help me out a little. I just got back into riding last year after a twenty-something year sabatical. I bought a '77 IT400. I grew up on 125's, and the 400 was a bit much for me at first. It was powerful and fast, and didn't stop that well besides. After a bit of riding, I started learning to handle it and was having a lot of fun. Then the rod threw through the piston skirt, cylinder skirt and both case halves.
I bought another IT400 a couple of weeks ago. It's a '78, and I thought --- hey! I've already got a parts bike! Well, the second one is NO WHERE near as quick! It also has a loud piston rattle type sound at high RPM. I bought a Clymers and turned some wrenches and since figured out that the '77 actually had a 400 enduro bottom end (injector pump--inactive) with an IT400C top end (compression release). The pipe is also almost certainly not stock IT, as it has a separate head pipe. The '78 is an IT 400E.
I'm thinking that the IT400E should not be any tamer than the 400C, but thought I'd ask here. The power difference is so marked that I don't think cleaning and dialing in the fuel system will make up the difference. I also hoped someone might have a hint for me about the high RPM rattle. The intake manifold of the '78 is cracked looking, and I'm wondering about an air leak. The other one ran so strong that I thought I'd swap over the intake and reeds when I go through the carb because it couldn't hurt, even if it isn't the actual problem. Thought I'd swap the CDI for the same reason. I wanted to check the compression before pulling the top end, but the Clymers doesn't give me any compression numbers. I'm also wondering what a primary compression leak would act like.
Any suggestions?
Thanks in advance.
Steve
