89 GPZ1000RX stutter

[ojyamaha]

Some old school knowledge / commentary needed if you can.
Low km' s 20,000 recently from Japan. Starts and runs fine except about 3200 thru to 4000 rpm where it sounds like it is sucking not enough air or not enough fuel and feels under powered. Worse if under load. If you role through the rev range slowly seems fine. Below and above this range bike runs well.
Mechanic suggests all set up like this for emission testing. How ever I have owned a few big bikes from this era most recently last year a fzr1000 and it didn't behave like this.
Carbs have been synched and checked but not ultrasonic cleaned. Awaiting the shop to have their ultrasonic cleaner fixed.
Any opinions on what else to look at if ultrasonic doesn't work ? Plugs, leads , coils etc. Does the ignition change thru this rev range , spark get weaker / stronger ??
Cheers for help.


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[sidecar bob]

Does it have a factory air filter element installed? No air filter or K&N style would be a possible cause.

[FJRider]

Some old school knowledge / commentary needed if you can.
Low km' s 20,000 recently from Japan. Starts and runs fine except about 3200 thru to 4000 rpm where it sounds like it is sucking not enough air or not enough fuel and feels under powered. Worse if under load. If you role through the rev range slowly seems fine. Below and above this range bike runs well.
Mechanic suggests all set up like this for emission testing. How ever I have owned a few big bikes from this era most recently last year a fzr1000 and it didn't behave like this.
Carbs have been synched and checked but not ultrasonic cleaned. Awaiting the shop to have their ultrasonic cleaner fixed.
Any opinions on what else to look at if ultrasonic doesn't work ? Plugs, leads , coils etc. Does the ignition change thru this rev range , spark get weaker / stronger ??
Cheers for help.


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Quite a few years back I got my FJ (24,000 km's) ex Japan. Carbs had been "cleaned" but ran like shit (a still installed and almost blocked inline filter I found didn't help) but the diaphragms in the carbs had holes. Finding all this out over several months annoyed me a little. A low km bike of that age means it was stored and probably not prepared for (as such) so start looking closer at poor storage/age type issues. Degradation in all parts that contact with fuel could be expected. (fuel pumps, lines, filters, seals etc)

[ojyamaha]

Does it have a factory air filter element installed? No air filter or K&N style would be a possible cause.Cheers sidecar . Definitely has air filter. Standard type . Have it a clean recently . Looks ok .

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[ojyamaha]

Quite a few years back I got my FJ (24,000 km's) ex Japan. Carbs had been "cleaned" but ran like shit (a still installed and almost blocked inline filter I found didn't help) but the diaphragms in the carbs had holes. Finding all this out over several months annoyed me a little. A low km bike of that age means it was stored and probably not prepared for (as such) so start looking closer at poor storage/age type issues. Degradation in all parts that contact with fuel could be expected. (fuel pumps, lines, filters, seals etc)Thanks fj. As the shop I bought it off are looking at carbs as part of the deal my hope is that they will pick up diaphragm etc. I get the feeling tho that if the carbs aren't the problem then I will be left to find/ fix on my own. So other things you have mentioned will help. Cheers.

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[Grumph]

Find a manual for the export market - US or UK versions. Check the carb jetting in it against those specs.
Back when we got a lot of grey imports, there were often jetting differences.

The other big question - std pipes ? If it's got an aftermarket pipe on it, expect it to need rejetting as they simply weren't allowed to at home.

[F5 Dave]

The simple bodge for exhaust or filter mods used to be a thin shim (1.5mm washer) under each needle and see if it gets better.

[ojyamaha]

Find a manual for the export market - US or UK versions. Check the carb jetting in it against those specs.
Back when we got a lot of grey imports, there were often jetting differences.

The other big question - std pipes ? If it's got an aftermarket pipe on it, expect it to need rejetting as they simply weren't allowed to at home.Cheer for that. Stock standard pipes. I got a manual so will check settings if the shop doesn't resolve.

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[ojyamaha]

So as a follow up . I have the bike back from the shop and seems the carbs being cleaned and obviously retuned has resolved the issue . Cheers for now.

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