Full Yamamoto, runs like shi....

[gpz900]

Hi everyone,

I'm hoping someone can point me in the right direction here.

I recently acquired an NC30 race bike, it was a bit of state and needed some serious TLC, which it got.
Initially it ran OK, although it had a really nasty race exhaust that didn't seem to fit together properly it still pulled well. Smoked a bit though. It came with a nice looking Dyno graph peaking at 63bhp. It has:

138 main jets
top cut off the air box with a very thin air filter

I just fitted a second-hand full Yamamoto race system. The baffle was damaged so I took it apart and replaced the perforated tube (same size) and re-packed with glass fibre.

Now, it runs like a dog. It just wont pull at all. Idles well and will rev OK (but backfires occasionally) but under load it's got nothing.

Any ideas? I didn't think replacing one race system with another would make that much of a difference, but could it?

If I didn't pack enough glass fibre in the muffler could this have the effect of shortening the exhaust and messing up the fueling to this extent?


Thanks in advance.

Al

[Hadies]

It'll be a PITA trying to jet it right with that set up.
I would revert the airbox and jets to standard, rubber flaps present and go from there. Maybe start with 118 front 120 rear jets.

[Neosophist]

Yamamoto system was probably designed for standard jets and standard airbox.

Did you disturb any of the airbox settings etc?

Is your full system sealing properly and not blowing? (backfiring could be an airleak allowing fuel to ignite in the pipes)

Easiest way to verify is to switch systems again and make sure it is the exhaust that is causing the difference.

If so then your best bet if you want to use the Yamamoto system is to switch to standard airbox and standard jetting... should still make around 58-59hp.

[Cammo]

It has:

138 main jets
top cut off the air box with a very thin air filter

That's your problem, the exhaust will just be highlighting the jetting issues.

Fit a genuine honda filter (RB Imports in Sydney, google them), replace the hacked airbox with standard part/s (try RB again) and whack in some 118/120 jets it will have it fixed and running well in no time I suspect.

NC30's are very fussy when it comes to induction modifications and jetting as you've found.

[Neosophist]

It has:

138 main jets
top cut off the air box with a very thin air filter

That's your problem, the exhaust will just be highlighting the jetting issues.

Fit a genuine honda filter (RB Imports in Sydney, google them), replace the hacked airbox with standard part/s (try RB again) and whack in some 118/120 jets it will have it fixed and running well in no time I suspect.

NC30's are very fussy when it comes to induction modifications and jetting as you've found.

If it ran ok with the other system though it's quite odd that the exhaust would make that much difference unless the race one is really different?

[gpz900]

It has:

138 main jets
top cut off the air box with a very thin air filter

That's your problem, the exhaust will just be highlighting the jetting issues.

Fit a genuine honda filter (RB Imports in Sydney, google them), replace the hacked airbox with standard part/s (try RB again) and whack in some 118/120 jets it will have it fixed and running well in no time I suspect.

NC30's are very fussy when it comes to induction modifications and jetting as you've found.

If it ran ok with the other system though it's quite odd that the exhaust would make that much difference unless the race one is really different?

That's what I thought, but maybe it was a bit naive to think that because it was jetted for a full race system then
any race system would work ok.

Putting the old system back on isn't an option now as i hacked it apart to get a donor baffle and then threw the remains in the skip (it really was nasty).

Ideally I don't want to take it all the way back to standard as it is a race bike, and I'd like to think the full Yamamoto could accommodate bigger jets etc , but maybe thats where I have to start and then take it from there. Hmmmm...

[Neosophist]

Realistically without spending super money your open airbox won't make anymore power than the standard system.

[skinnydog0_0]

How is the battery? does the bike run total loss?
I would try a spare battery first (a known good one) and see if this solves the problem.