1980 Yamaha 400xs special with straight pipes?

Message

nruzicka2006 · Wed Sep 19, 2007 12:17 pm

ok here is the deal i just got the yamaha and one of the mufflers fell off when i was riding and it had a short straight pipe after the muffler fell off, so i thought the sound was really good with the straight pipe so i had the muffler shop weld the rest of a straight pipe on it to both sides. My question is is this bad for the bike? Back pressure?

mgdavis · #2 Unread post by **mgdavis** » Wed Sep 19, 2007 12:33 pm

You're allowing the engine to flow more air, now you need to flow more fuel. If you don't you cause a lean mixture, which is bad. Bigger jets are needed to keep up. You might want to look into the laws about unmuffled exhaust in your area.

nruzicka2006 · Wed Sep 19, 2007 1:18 pm

how many sizes up in jetting would i have to go? any how bad is it for my engine? btw the idle is a little touchy with the straights on it, is that what you mean about it being lean?

nruzicka2006 · Wed Sep 19, 2007 1:45 pm

also do i have to re-jet or is there some sort of air mixture screw i could use to richen it up?

mgdavis · #5 Unread post by **mgdavis** » Wed Sep 19, 2007 1:59 pm

You'd need to do new jets. I have no idea how many sizes. A lean mixture = running hot. The mixture being lean is probably the root of your idle problem, if it ran well before.

nruzicka2006 · Thu Sep 20, 2007 7:27 am

i have one more question, if i am going to get 5 sizes up what kind would i have to order because as understand there are different "models" of main jets? thanks a lot