39mm FCR question

[Barnapkin]

My '93 900ss has the 39mm FCRs. They were on when I bought them. I know ... Why wouldn't the previous owner put on 41s.

My question is this:

I get quite a bit of backfiring when I roll off of the throttle. This doesn't happen on my other ducs. What are things that I could check?? If the needle is in the middle, would raising or lowering help?


The bike runs OK on the top end. (Still not as strong as my FE). It's quite stubborn to start. I typically have to raise the idle, and then lower it once it's warmed up.

Thanks.

[sideways]

Originally Posted by Barnapkin

My '93 900ss has the 39mm FCRs. They were on when I bought them. I know ... Why wouldn't the previous owner put on 41s.

My question is this:

I get quite a bit of backfiring when I roll off of the throttle. This doesn't happen on my other ducs. What are things that I could check?? If the needle is in the middle, would raising or lowering help?


The bike runs OK on the top end. (Still not as strong as my FE). It's quite stubborn to start. I typically have to raise the idle, and then lower it once it's warmed up.

Thanks.

The 39mm's offer a more low-mid range torque than the 41mm's. Theoretically the 41mm's will offer more top end if the cam/piston/valve combo will allow it. What the previous owner was thinking is your guess as good as mine but the 39mm's are still a good addition.

You might want to increase your pilot jet one size and fine tune the needle.

It is also a good time to check for any exhaust leaks which will cause a good deal of popping on decel. I hope this info helps. Keep us posted.

[fraz]

My bike too has 39mm FCRs from the previous owner. He chose them intentionally for low to mid range improvement. I know everybody and their brother gets 41s for top end but to be honest I don't know why. This bike is plenty fast on the top end and any more would only be usable on the track anyways.

Mine pop like mad but its largely because I am jetted for race gas and I have slipons that aren't so tight.

[Barnapkin]

I know that the beater cans that I have on the bike have a small hole from Grattan's busstop. I was considering having a friend see if he can weld the spot. Anyone know if staintunes can be welded??

Sideways - At some point before spring, I was thinking of dropping the bike off for a good once over @ sec8 at some point this winter. I figured that a carb sync/eval would be included.

[DesmoBob]

A hole in the exhaust will indeed cause backfiring; unless you have other problems w/ the mixture, I wouldn't change anything yet. And being flatslides, your carbs don't synchronize according to the vacuum each one "sees"; they are sync'd mechanically. Once set, it's pretty hard for them to "go" out of sync.

[Norm]

I believe all Staintunes are stainless steel - weld away.