New exhaust, what now?

[Jukka Häyrinen]

Maybe one of u guys instantly knew what’s going on with my FZ and where’s the fix?
The bike:
I have a stock 1FN engine with: K&N in airbox, iridium sparks and 117,5 main jets (105 is the stock size.) It’s been like this from last summer, and it’s been working really well. Now, yesterday the stock exhaust (rotten..) was finally replaced into this; Sebring 4-1 stainless steel exhaust + Leo Vince SBK alu end can. The Sebring has a mid pipe of 75 mm diameter with a tad of silencing in it. The Leo Vince is of a honda (yak!) cbr900 of about 2002 model. Reason for this: is it has a connection hole of right size (76 mm) and I got it cheap.

So the little problem I found today: if I ride ~60 km/h in 6th gear so @ 3000 rpm and twist the gas handle; nothing much happens, only it sounds like the the engine is drowning in too much gasoline or smth (which probably is the truth), then at 4000 rpm; twist of the gas handle leads to rapid acceleration (after a little ~0,4 seconds thinking first), at higher revs there’s no thinking anymore and I kind of noticed a real charge at about 8000 revs..

I cannot say yet, if there’s really more power now (or just noise..), ‘cos I couldn’t properly compare it to anything yet. Possibly tomorrow I can drag race with my friends TDM 900 -04 to see if something has really happened (can I leave it sooner now 😉

But this lack of anything happening at 3k to 4k is the only real problem now. What could it be? :-/

[arch.1970]

I have a similar problem and have given up solving it. My FZ, which is equipped with a 4-1 one-off exhaust system, doesn’t go forward smoothly under 3500rpm when I turn the accelerator. The bike is okay over 3500rpm and runs at gathering speed over 6000rpm. I tried another 4-1 exhaust system (Over Racing) but in vain. The FZ had the same kind of problem. Though I thought a 4-1 system was not good for the FZ, I realized my mistake when I rode the 2MG equipped with an original 4-1 system. The bike accelerated smoothly even when I turn the accelerator at 2000rpm.

[Jukka Häyrinen]

Yea, I found from FZ750.com archive that 3k rpm problem being a common problem with 4-1 systems in FZ.. There also read that with different pilot jets and dyno time it may be possible to solve.. Oh well, Arch, what have u tried so far..? 😉 Yea, I would think a FZ from -87 onwards with 4-1 originally, don’t have this problem. Maybe should try find out what’s inside their carburetors. Anyway, I’ve changed this most sweetly carbureted bike into a monster! 😀

edit: and I’m not planning to give it any dyno time.. So I guess cleaning carbs, messing with pilot jets and jet needle is about all one can try, and probably try in vain too..

[Jukka Häyrinen]

OK, got tonight confirmation to my feeling of more power; TDM 900 was left behind a lot faster now in a drag race 😉 The cause was also helped by the lost weight during the drag race; side stand parted ways with the rest of the bike at about 200 km/h 😀 My friend stopped to search it (he saw the departure), and I joined into the search, but we couldn’t find it. I wonder if it would be possible to make the side stand out of aluminium.. This friend of mine works in a welding company, so he maybe could help in the making.. Anyway, found also that I have 122,5 & 125 & 130 & 142,5 main jets in the kitchen closet, I’ll try those too starting from the smallest ones.

Addendum to the 3k problem: if going 3k @ 3rd or 4th gear, twisting gas makes the bike accelerate somewhat ok, unlike @ 6th when nothing happens.

[Jukka Häyrinen]

OK, now I’m in a deeper trouble with the carbs.. Please Arch, can u tell what all u’ve tried with the 3k-4k problem? So I wouldn’t need to try the same things again and in vain. Thanx..

Edit: Lowered the needles one step back -> to the original hight, now it works again like in the beginning.. Maybe a bit better even, the butterflies were far out of sync originally, quick adjusted them with naked eye, now they r much closer at least. Should try the 122,5’s now again while the needles r back to normal.. *sigh

[Jukka Häyrinen]

I wonder if anybody has built an EXUP to an FZ.. That FZ11s (or smth) guy in those pics from Japan would be my 1st suspect if so 😉

[arch.1970]

Jukka, sorry late for reply.
I just tried another exhaust as I mentioned. I tried to adjust the air screw of the carburetor, but I couldn’t find the appropriate tuning.

[Jukka Häyrinen]

No prob. 🙂 I haven’t touched the air screws yet, and won’t do so until I’ve build that manometer to do it properly or smth.. (live 2 c that.)

[Author]

Posts