engine not revving past 6k but only when in gear

[Robbie8666]

Hi need help
my 2002 fzs600 has gone into what I can only describe as limp home mode!

I was riding along M40 when over taking and engine just refuses to pull in gear past 6000 rpm

I have had it with my mechanic and he has changed ecu
checked plugs
air filter
carbs
ht leads
coils
fuel & pump
he has bought the manual from Yamaha as well as using my Haynes. he thinks its electrical rather than mechanical as it runs smooth as upto 5500 around town speeds in all gears but just won't pull past that
revs freely not in gear and will red line!

anyone any ideas or had this themselves? how did you fix it?

[BBROWN1664]

What about when it is in gear with the clutch in?

[clayt74]

Sounds like a compression problem to me if the engine can't rev under strain??

[Fazerider]

There aren't many things left that can stop it revving under load yet not affect it off load.
Partial blockage of the fuel or air supply may still be possibilities.
Poor compression often makes starting difficult, but is worth checking.
The only electrical thing I can think of and may not have been changed is the TPS, though I don't know if that can fail in such a way as to limit the revs that severely.

[darrsi]

There aren't many things left that can stop it revving under load yet not affect it off load.
Partial blockage of the fuel or air supply may still be possibilities.
Poor compression often makes starting difficult, but is worth checking.
The only electrical thing I can think of and may not have been changed is the TPS, though I don't know if that can fail in such a way as to limit the revs that severely.

TPS tends to affect low end running, when I knew for sure mine was knackered it never really played up if I gave it a bit of welly.
Always worth ruling out though by giving it a quick check.

[stevie-g1968]

Breather on the tank isnt blocked is it?

[darrsi]

http://www.therevcounter.co.uk/threads/21097-Engine-won-t-rev-over-6000-rpm-First-thoughts

[wthorpy]

I had the same problem once while on a track day. But mine was due to a small era on my part.
While on track i got a fault on the rev counter to indicate EXUP problem.  So i stripped, cleaned and re fitted, then went back on track. Only to find that it would only rev to about 6k (i think). I returned back to the pits and found that i had put the cables on the wrong way round. ( Schoolboy era.).
Have you/anyone done any work recently.   

 Ps. When it was out of gear and on the stand it would rev freely.

[BBROWN1664]

A weak spark will stop it reving under load poor carburation.

[Dead Eye]

I had the same problem once while on a track day. But mine was due to a small era on my part.
While on track i got a fault on the rev counter to indicate EXUP problem.  So i stripped, cleaned and re fitted, then went back on track. Only to find that it would only rev to about 6k (i think). I returned back to the pits and found that i had put the cables on the wrong way round. ( Schoolboy era.).
Have you/anyone done any work recently.   

 Ps. When it was out of gear and on the stand it would rev freely.

This applies only to the Gen1 1000, not the 600

Testing the bike with the clutch in or in neutral is probably a good start. When you say it won't rev past 6k rpm - do you just lose power or do does the bike begin to stutter / cough / stall? If it just loses power than I would assume there is some problem with the fuel / air. Is it possible that the bike has been restricted (to 33hp etc)? I would have thought the mechanic would have picked up on that, but you never know...

[Robbie8666]

many thanks for all the advice

with clutch in in gear bike revs to red line

by not going past 6k I mean you can hear the engine trying to rev past 6 k but needle sticks @ 6 and speed limited to bout 55/60 mph all gears

bike not restricted as been riding it for 3 years and had been riding it long distance & higher speeds

have changed fuel stripped fuel filter & pump and air filter
 

[Dead Eye]

This is certainly a bit of a mystery...

I would agree with clayt74 - it's worth doing a compression check as obviously the bike is affected when it is under load and it is worth assuming spark, fuel and air are all ok given you seem to have gone over these thoroughly

The only other thing I can think of is exhaust / valves. Not sure, but can anyone confirm if valve float could be a culprit?

[pilninggas]

many thanks for all the advice

with clutch in in gear bike revs to red line

by not going past 6k I mean you can hear the engine trying to rev past 6 k but needle sticks @ 6 and speed limited to bout 55/60 mph all gears

bike not restricted as been riding it for 3 years and had been riding it long distance & higher speeds

have changed fuel stripped fuel filter & pump and air filter

With everything else explored it almost sounds like crank position sensor; the symptoms that you describe sound just like it and being electromagnetic (hall effect) they do have a finite life before the signal they output becomes too noisy for the ECU to interpret.

I'm not a great fan of buying sensors on the off chance, is there anyone who could lend you a known good one to try?

[hairnet]

reg rec

old mans cb400 did the same thing would only rev to 5-6k cos it was failing - and cut out at a stop

until it just finally died and the bike didnt start

new onw and away fine again

worth a check

[unfazed]

Change the regulator/rectifier

[Billy Balthorpe]

I had a similar problem with a blade, the bike would not rev past 8K, although it would in neutral. It spent 4 days strapped to a dyno and we changed all sorts, carbs, ecu, tps, crank sensor, cable tied the side stand switch, changed the loom (twice) etc. It was carburating perfectly up to 8K (100BHP) but then rev no higher. I rode it like this for two years, eventually I got fed up and linked out everything that could stop it running at the connectors closest to the loom, clutch switch, neutral switch, side stand switch, rode it and it was perfect, by a process of elimination I figured out that the cable which went from the connector to the side stand switch was faulty and would short out at 8K. Weird but true.

So before you start swapping big stuff like crank sensors and stuff, just try linking out all the stuff that could stop the engine at the closest connector to the loom, its worth a try and at least you will be able to discount the simple stuff cheaply and quickly, unlike me. 

[Lum]

Carb diaphragm split?

[Pickle]

by a process of elimination I figured out that the cable which went from the connector to the side stand switch was faulty and would short out at 8K. Weird but true.

So before you start swapping big stuff like crank sensors and stuff, just try linking out all the stuff that could stop the engine at the closest connector to the loom, its worth a try and at least you will be able to discount the simple stuff cheaply and quickly, unlike me.

Billy has got me thinking that isn't it around 6-6,500 rpm that the 600 engine gets "the vibes"?
Could this be causing a switch to flutter between open and closed?