94 Yamaha YZF750R engine problems

[Mark2107]

I have a 94 Yamaha YZF750R
I have a problem with the engine when driving
when the engine hits around 4000 rpm i lose power almost like a rev limiter kicking in this happens in every gear although when bike is in neutral it revs freely right up to red line
i have replaced spark plugs air and oil filters i have checked all fuel lines i and the problem still persists
Does anybody have any ideas it has been mentioned it could be the coils breaking down or the fuel pump playing up but i don't want to just keep replacing parts and then still have the problem there

[Kickstart]

Hi

If you ride it at just below the rpm the problem occurs at does it still happen but take longer to happen?

Does it occur at exactly the same rpm in all gears / at all temperatures?

Did this problem occur suddenly?

Most bikes ignitions are pretty simple without any mechanical advance / retard. As it gets to the red line without any load I would suspect the ignition is fine.

Coils are possible, but I would expect them to get worse with heat. Best to check the resistances over them.

Failing fuel pump would likely mean that the bike would progressively get less fuel than it needed, and the problem would probably get worse if you tried sitting just under the rpm it occurs. You could probably exclude it by removing the pump from the system and running a pipe directly from the carbs to the tank, and trying it with a VERY full tank of petrol (carbs are positioned at a height about half way up the tank, so with a full tank it should gravity feed OK).

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Mark2107]

Hi Thanks for the info
I have only had the bike for a couple of months it had been sat in a shed for a couple of years previously so have been working on it to get road worthy
it gets worse the hotter the engine gets but it does not seem to happen at all below 4000 rpm
it seems to be the around the same in every gear

[Kickstart]

Hi

Coils do suffer from heat, but to a large extent generate their own heat rather than soak it from the engine. Definatly worth checking though.

However that it has sat for a while is a bit concerning. Have you stripped and cleaned the carbs? Have you checked the diaphragms haven't split?

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[tatters]

Had the same problem with my YZF750R, turn out to be the coils
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