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-   Carbs and Fuel System (https://www.vn750.com/forum/22-carbs-fuel-system/)
-   -   help needed poor power after 4000rpm (https://www.vn750.com/forum/22-carbs-fuel-system/12631-help-needed-poor-power-after-4000rpm.html)

gregr 09-11-2009 05:37 PM

help needed poor power after 4000rpm
i have a 1995 vn750 that runs great at idle and then when you try to ride it,it like loses power or running on 1 cly after 4000 rpm and starts back firing
had the carbs cleaned and synced,new plugs ,checked pet cock and the hose going to the right airbox
The bike sat for a year,then i had the work done above,
someone please give me a idea whats going on,iam going crazy with this thing,it only has 9000 miles on it

flitecontrol 09-11-2009 05:53 PM

Sounds to me like you may be losing spark on one cylinder and the unburned gas from that cylinder is igniting in the exhaust system. I'll let those with far more knowledge of the electrical system tell you how many ways that might be happening.

gregr 09-11-2009 06:22 PM

thanks ,this thing is driving me crazy,took it to the shop and they went through the carbs and sycned again and said everything is ok,runs perfect at ide,as soon as it gets a load onit at 4000rpm and up,no power,seams like its running on one cly
hope someone can point me in the right way to go with this

shark88 09-11-2009 06:31 PM

So it only does it under load? If you rev it up above 4,000 in neutral does it run fine?

gregr 09-11-2009 06:40 PM

its hard to tell but it seems to rev fine in netural,when you ride it you can tell,it starts to pull and then it has no power

gregr 09-11-2009 06:51 PM

just checked revs fine in netraul,i even rode it down the road,under load it looses power,pull in the clutch and it revs great
only does it in gear under load

Crobins365 09-11-2009 10:16 PM

Sometimes if you're only firing on one cylinder, you can be fine at a standstill and then the bike will bog down on the road. Any idea which cylinder seems to be the probelm? Backfire coming from the left or the right? At any rate, check your plugs to make sure you're getting spark; also, check the spark plug wires for any cracks or problems there - any current that doesn't make it to the plugs will create the problem you're describing. You might also run the bike (in your driveway) after dark and look at the ignition coils and wires to see if you have a short somewhere - can also cause the same performance issues you're describing.

On a related note....how come your mechanic hasn't taken the bike OUTSIDE to see what you're talking about??

hyperbuzzin 09-12-2009 12:31 AM

Ya sure the clutch isn't slipping?

gregr 09-12-2009 08:02 PM

checked spark getting spark at all plugs,even replaced the new plugs again,still does it,now today when i was messing with it,now it revs to 4000 then drops down to 2000 and back to 4000 holding the throttle open,even in netural
clutch is not slipping

niterider 09-12-2009 08:26 PM

Have the machenic take it out on the road. Just cause he has it idling good, but the bike does not run. He has not fixed it yet. To me the problem is that you are not getting enough feul to the carbs or from the carbs to the cylinders. Check the vaccuum hose to the carbs.
Tap carbs with a screw driver handle to free the floats if they are sticking.

Also remove the air filters and check for air abstuctions.

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