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Discussion Starter #1
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
 

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Premium Member
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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.
 

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Discussion Starter #3
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
 

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

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Discussion Starter #5
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
 

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Discussion Starter #6
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
 

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Premium Member
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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??
 

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and the Adventure Cycle
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Ya sure the clutch isn't slipping?
 

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Discussion Starter #9
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
 

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Old Truck Junkie
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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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Discussion Starter #11
he took it out on the road,it has no power after 4000 rpm,checked tonight for a spark issue ,nothing,the rear plugs look lean,and the back fire is coming from the rear cly pipe,the carbs been aprt twice and nothing found,cleaned anyway both times,and still the same thing
 

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My bike seems to have a similar issue.

In neutral it seems to rev up fine. Under load it can bog down.
It seems to me to be less about the RPMs and more about the percent of throttle. To further explain:

If you just keep the throttle open around 20% you can climb right up to 6500+ RPM just fine.

If you roll on the throttle, say more than 50%, it will bog down, miss, etc.

Seems like mine may be the difference between the primary and main jets.

I have not done anything to my bike yet. Time to go clean the carbs, and whatever else you guys say.

EDIT: I also am getting lower MPG.
 

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Discussion Starter #13
sorry ive been out of town guys.
had the carbs cleaned again for the 3rd time,bike is still running really lean on rear cly(plugs white),bike is getting plenty of fuel to the motor,also we tryed take the filters out and running it and it only revs to 4000.00,but if you take the boots at the carb off it runs and revs all the way up,but under load it runs like it has no power,and the bike gets hot very quickly,i had 2 techs look at it and neither one can fix it,anyone out there know whats going on with this thing,getting gas
got good plugs and spark
 

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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??
If you try the after dark trick use a spray bottle with water in it and spray a fine mist around the coils, plug wires, and plugs. the fine mist will give any "leak" an easyer path to ground.
 

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Discussion Starter #15
its getting spark to all,if it wasnt the plugs would be wet,they are lean,white in color
new plugs and it has good spark,its not grounding,its something else dumb
 

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The Professor
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its getting spark to all,if it wasnt the plugs would be wet,they are lean,white in color
new plugs and it has good spark,its not grounding,its something else dumb
Is the rear carb vacuum line attached to the carb and vacuum switch under the seat? If marbled or coastered Is the rear carb vacuum port capped?
 

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Premium Member
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Exactly! This is screaming air leak. If you are positive that the carbs are delivering fuel correctly, and your air filters are in good shape (very important) and your plugs are white, you are obviously running lean from something, vacuum leak or otherwise. Have your carbs been re-jetted in the past? Maybe your mains are too lean, or they have been screwed up by someone working on it. It's either starving for fuel in the mid to high range or getting way too much air...
 

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Discussion Starter #19
Yes rear vacume line is hooked up to the valve,the whole bike is stock with 9000 miles,even went through the carbs again,everything clean and synced again,everything is rite on,nothing leaking ,spary them down with carb clean and nothing,cant figure what its doing,the wiered part is if you pull the boots at the carbs,the slides are staying up and gas is spraying alot of gas,if you take the air cleaner covers off it wont rev past 4000,i dont understand that,its a ghost
 

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Old Truck Junkie
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If the bike set for some time you may have a bugs nest in the hose that goes to the carbs. The hose that goes to the right ear. Just make sure that it is clear of any obstructions.
 
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