cuts out over 5000RPM????

[ausie]

HI Guys
Peter from down under with a problem on my sons bike. it is an 88 FZR250 runs ok then when I give it a hand full it cuts out completely between 4000 and 6000 rpm with no load standing still, it wont get over 50 mph or 80 klm on the road,it just dies then you drop it back to low throttle and it will pick up again any ideas?????
I hope you can help as I am lost when you get more than 2 carbies on anything under 30 years old
Thanks and happy new year
Peter

[shredex]

there is a feature like that...I remember reading about it somewhere.
its like that on some cars I believe.
someone explained it to me awhile ago but I dont remember it worth crap.

but it wouldnt be as low as 4k-6k when it does it...
and I dont think it would be on a motorcycle and one that old either..I believe that feature can only be on FI vehicals...

could be the wrong jet size.
you should talk to moey and ask how his bike runs...
we all dont know s**t about the 250's ...they are so rare...

[yamaha_george]

HI Guys
Peter from down under with a problem on my sons bike. it is an 88 FZR250 runs ok then when I give it a hand full it cuts out completely between 4000 and 6000 rpm with no load standing still, it wont get over 50 mph or 80 klm on the road,it just dies then you drop it back to low throttle and it will pick up again any ideas?????
I hope you can help as I am lost when you get more than 2 carbies on anything under 30 years old
Thanks and happy new year
Peter

Peter,
Has the bike been standing un used ? I would bet that you need to thoroughly clean the carbs, set the float heights (check your manual) as Shred said 250's are very rare.

I would also clean the tank out of old gas and put totally fresh in as old gas will hold water & crap and that fouls plugs & gas filters (check that while you are going thro the fuel system )

Put in fresh plugs properly gapped and make sure the caps are properly seated.

Carb tech & having more cylinders does not alter your basic knowledge just have to apply it more often :-}

Hope this solves the problem and you get to have a happy riding new year

[reelrazor]

All of what George said.

It's a 250 4pot so the jets are small, and air passages too! And proper mix will be critical for it to run right.

And inspect the slide diaphragms in the carbs well. In fact, before removing them I would check for smooth operation by pushing each up to the roof and letting them close on their own. If they are sticky at all, you probably have found the problem. If they aren't responding to vacuum when the butterflies are opened, you effectively choke the engine.

[ausie]

Thanks guys, I have done all of the above. the bike was standing for a year before my son purchased it so I pulled the head checked the bore, valves, reshimed the valves, fixed two air leaks in manifold gaskets, cleaned carbies, checked diaphragms and slide operation. The only bit of joy I have had was lifting the needle by 1 grove to enrich the high speed to the second last grove this allowed it to rev to 7,000 freely with no load then it cut out but dropped to a rough idle while the throttle was still open.
when it cuts out the slides drop and you can see a mist of fuel around each carb it is like the key was turned off it dosnt splutter just stopes running till it slowes to a rough idle
My next move is to take my T120RV Bonneville for a nice ride along the Queensland coast and soak up a few rays and try to forget about high revving jap bikes for a couple of hours, then try to work out what is wrong with the FZR this evening it will be something small but elusive.
any more suggestions would be very much appreciated

Thanks guys,
Peter

[ausie]

I even just rechecked the valve timing in case I got it wrong, but it is ok

[yamaha_george]

I even just rechecked the valve timing in case I got it wrong, but it is ok

Peter,
compression tested each bore & within 10% of each other, double checked air leaks when you re-seated the carbs? Vaccum checked the carbs 1 &2 balanced them then balanced 3 against 4 the finally 2 against 3.

pulled the carbs after it faltered and found wet plugs ? dry plugs ? a mixture of wet & dry?

Run the motor open with no air box is beter than with it on ? air filter is clean K&N type freshly washed and oiled ?

VR running hot and causing the firing system to fail by dragging the sparks ?

will she idle smoothly ever? will it run smooth anywhere else before the 5k limit ????



Just had flash of remeberence about a hondo that did this trick an old wasp nest in the exhaust pipe was choking the pipe after standing in an out building so she choked on her one fumes.

Start taking note religiously on all these then take cylinder 1 jets and using them in clyinder 2 TEST same for 3 & 4

any changes
Are the fuel level correct in each carb THIS IS CRITICAL WITH FZR's

[ausie]

Thanks George,
yes have checked all you mentioned the plugs are dry, disconnected VR and ran on battery still the same am going to try to borrow a set of carbies from a local wrecker and see if that helps

[ausie]

Check this out we did a video on You tube the throttle is held full open and it just revs and dies continual http://au.youtube.com/watch?v=S2ZnBvVSoIw

[yamaha_george]

Check this out we did a video on You tube the throttle is held full open and it just revs and dies continual http://au.youtube.com/watch?v=S2ZnBvVSoIw

Peter
AhAh, that is fuel / air starvation, I have only seen that twice before in nearly 50 years of biking on a Norton and a100 cc yamaha.

The clip does not show how the carbs are ie was the air box on ? if it was then take it off and see if it pulls the same stunt.

If no air box then your fuel pump aint delivering sufficient fuel for all 4 carbs .
That could be:
pump

fuel filter with shit closing it,, the as revs die the shit drops and it gets fuel

Tank same as above but in the petcock hole / tank filter

the main supply line that feeds the base of all carbs (on the carbs them selves NOT neccessarily the rubber hose )

all the floats are way off and starving the engine of fuel.

[reelrazor]

The airbox isn't there.

It looks and sounds like, to me, that the slides/diaphragms are responding to the vacumm change when the butterflies are opened...the vacuum stabilises...they drop and the revs fall. Vacuum catches up again-slides lift revs up.....and cycle repeats.

I think the cyclic nature of this precludes flat out fuel starvation. I think it would fall to low revs and stall...or at least not pull up to revs again so quickly. Full bowls should let this little engine run for 20 or more seconds all by themselves.

It sounds like the exhaust is pretty free flowing


I think it: a) needs the airbox b) needs the needles lifted another notch(at least). c) more fuel at the mixture screws (another turn 'out' )

[yamaha_george]

The airbox isn't there.

It looks and sounds like, to me, that the slides/diaphragms are responding to the vacumm change when the butterflies are opened...the vacuum stabilises...they drop and the revs fall. Vacuum catches up again-slides lift revs up.....and cycle repeats.

I think the cyclic nature of this precludes flat out fuel starvation. I think it would fall to low revs and stall...or at least not pull up to revs again so quickly. Full bowls should let this little engine run for 20 or more seconds all by themselves.

It sounds like the exhaust is pretty free flowing


I think it: a) needs the airbox b) needs the needles lifted another notch(at least). c) more fuel at the mixture screws (another turn 'out' )

RR,
I would agree except the fast pick up was exactly why the other two bikes pointed me to :-
the momentary closure of fuel OR air.

One was a piece of cloth from a tool kit right by the air intake of its box was flapping into the air intake , another that came to mind was a cracked seat base allowing the heavy rider to close the air intake , when he moved in.
frustration as the bike stalled it would start back.

The last one was paint flakes & a sizable rust flake blocking the internal gas tank filter as the engine demanded fuel as that demand fell the gas would flow again kicking the bike back to life it was real cyclic as per the clip.

[ausie]

my son picked up a set of late model flat slide carbs on ebay dropped them on and it runs like new thanks for all the help

[yamaha_george]

my son picked up a set of late model flat slide carbs on ebay dropped them on and it runs like new thanks for all the help

AMEN, now you can RIDE, glad to have helped.

[moey]

hiiiiiiiiii i had the same problem i cleaned my carbies and now i have to balnce them and there is your awnser good luck