YZF750 Clutch

[matty8887]

Hi guys,having trouble with what i think is the clutch.

First off, all gear changes are smooth and go into gear everytime, no gears pop out, clutch doesnt slip or drive, i replaced the master cylinder seal as they were f***d and bled as needed so theres no air in the system now.
The problem now is when i pull away its gets going then bogs down then i have to give it more revs to keep it going but then its fine, i have no flat spots anyway higher in the rev range,so could this be a flatspot around 2k revs, could it be someting to do with the chain or could it be plates or springs on the clutch?

any help before i delve into it further much appreciated.

Thanks, matt
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Test passed october 2005
Cadburys boost yamaha yzf 750r

[Kickstart]

Hi

Sounds like the effects of a flat spot. Stock exhaust? Worn atomiser tubes (common problem especially if fitted with a Dynojet kit).

All the best

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

[matty8887]

Its not a stock exhaust, i have a scorpian with the link pipe, dont think it has a dyno kit on it, exhaust was already on when i bought it. Would the atomiser tubes cause a flat spot? How can i get to these?

cheers, Matt
____________________
Test passed october 2005
Cadburys boost yamaha yzf 750r

[Kickstart]

Hi

Does it still have the EXUP valve? If that has been removed then all sorts of rubbish power delivery will result.

If it has got an aftermarket can then I would say that is the cause, and you might be able to solve it getting someone to set it up properly.

The attomiser tubes could cause a flat spot as they will result in a rich mixture. Problem with them on the FZ750 based engines with downdraft carbs is that the needles wear the attomiser tubes oval slightly (the dynojet needles reputedly have a rougher finish hence cause the same problem more quickly).

Don't think they are expensive.

All the best

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

[matty8887]

Still has the exup valve, not looked to see if it is stuck or owt.
____________________
Test passed october 2005
Cadburys boost yamaha yzf 750r

[owdamer]

If you just rev the engine in neutral does it rev freely or does the problem just happen under load?

[matty8887]

Revs freely, will even pull from the same spot it dies down at in all gears but 1, if i give it more revs on pull off and not let it get down to 2k revs it wont happen,only bogs down at 1.5 or 2k revs.

Just got back from a ride out, put £10 to start with and ive done 63 miles and the reserve light has come on so that would mean its only gettin 25 miles per gallon? I should at least get 100 miles for £10.

Any coincidences?

cheers, Matt
____________________
Test passed october 2005
Cadburys boost yamaha yzf 750r

[Kickstart]

Hi

Sounds more like the attomiser tubes to me.

All the best

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

[owdamer]

[matty8887]

Thanks all, i shall strip the carbs down the weekend, how will i tell if the emulsion tubes are knackered?
____________________
Test passed october 2005
Cadburys boost yamaha yzf 750r

[Kickstart]

Hi

Look at the closely (just take the carbs off, caps off and slides out and look down). Look where the needle on the slide goes into the carb body. The hole should be round but has likely worn oval (it will be elongated in the direction of air flow).

All the best

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

[matty8887]

OK will try and get round to it on saturday. Are they easy to change? Total strip down of the carbs or not?

cheers, Matt
____________________
Test passed october 2005
Cadburys boost yamaha yzf 750r

[Kickstart]

Hi

Fair strip down. Don't think they are that difficult to change.

All thebest

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

[instigator]

The emulsion tubes on the YZF750 are quite easy to change, I have done it before. The tubes themselves cost about £65 and that was sent from America.

You'd be hoping for 100 miles from £10 of fuel but in all reality, the bike is a thirsty bugger and will bleed you dry. I was barely getting 40mpg once the tubes were in ffs (if memory serves me correctly).

[owdamer]

I've owned mine from new & I think the best i've ever managed is 43mpg.

[bish777]

Those carbies are famour for ovalling their emulsion tubes (or fuel atomiser if you want to be clever..).

Factory pro do replacements far superior to the original.
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GSXR1100J

[matty8887]

Ive heard of the factory pro ones but they have to come from the usa.

Ive been quoted £17 each for the tubes(standard yamaha ones)

Id be happy if i got 40 mpg but 25 is rediculous.

Thanks all
____________________
Test passed october 2005
Cadburys boost yamaha yzf 750r