YICS

[YamahaRider]

I have a 1982 400 seca I put a different head on it and now the thing starts really hard.
If I put a little mm oil in the cylinders it seems to start ok.
Once I get it going down the road it seems to lack power
It is also backfiring a little.
I tried syncing the carbs and it was very difficult to get them to balance.
I am wondering if maybe it has something to do with the YICS?

 

[16VGTIDave]

No, it won't. And even if it did, there is nothing one can do to remove the system. Though it could be disabled.

On the DOHC 400's it is a chamber in the head connected to the intake port that builds pressure and releases it to create turbulence in the port and cylinder. This helps the mixture to be more consistent and burn better, which provides more power and therefore more efficiency.

If you want to pull the head off, you could have the passages welded. But that would be costly to have done and will reduce power and economy.

 

[16VGTIDave]

And it sounds like your engine has low compression. Test it and find out.

 

[YamahaRider]

And it sounds like your engine has low compression. Test it and find out.

Thanks for the reply. I have an adapter coming so I can do a compression test on it.