Running rough at cruising speed - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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View Poll Results: What area should I focus on for problem of running rough at cruising speeds?
Carbs - Venting, possilble more cleaning 3 75.00%
Electrical - plugs, wires, R/R 1 25.00%
Other????? 0 0%
Voters: 4. You may not vote on this poll

 
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post #1 of 8 (permalink) Old 07-12-2010, 12:37 PM Thread Starter
'93 VN 750
 
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Unhappy Running rough at cruising speed

Background:
Recent carb cleaning, lots of Seafoam, removed the 2 small red diaphrams in the gas cap and cleared vent lines (after reading about POOGS)...

I have easy cold start in the mornings (with Choke ON), smooth idle, smooth and fast acceleration, easy warm start after a drive, but when reach cruising speed 45+ mph it feels like its struggling for enough gas (or air?) not sure, but doesn't matter if I open the gas cap and close it again while going down the road (I've read that on the POOGS post). I've also tried switching between ON and RESERVE on my petcock (has OFF/ON/RESERVE on it). No improvement. I kept riding and it didn't seem to get any worse (or better) after a 2 hour ride like that yesterday. (FYI - I'm getting about 38 mpg like this.) Just had me worried with it sputtering all the way.

I'm thinking I should try syncing the carbs. I did not do it after the rebuild because it idles and accelerates so well. Also thinking of replacing all spark plugs. I recently replaced the cap on the plug under the throttle cables because it was arcing.

Speaking of plugs, all are either greyish or light brown/tan. Seems like I remember the #1 cylinder were more greyish and #2 cylinder were more brownish/tan.

I'm really stumped as to what to try next. Need HELP please?!?

Last edited by CDUB; 07-12-2010 at 12:42 PM.
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post #2 of 8 (permalink) Old 07-12-2010, 05:25 PM
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For as what you describe from the plugs apparently they are fairly ok so electrical can almost be ruled out. If you want to be completely sure you may want to measure the voltage getting to the coils on the low voltage side. With the engine off and the ignition key turn on you should be measuring about the same voltage of the battery (12.6-12.8V)
Too low voltage means the wiring is defective, there is a post here somewhere where it details a way to wire around the original wiring.
From what you describe I think the diaphragms on top of the carburetors is leaking air so may want to do a carburetor dis assembly a see what they look like. Rooted rubber should be replaced. If you don't have any acceleration or idle problems either cold of hot the jets must likely be clean.
Hope this helps.

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post #3 of 8 (permalink) Old 07-12-2010, 05:30 PM
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I go with the carb cleaning. Your gas mileage is way too low.

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post #4 of 8 (permalink) Old 07-12-2010, 05:32 PM
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I presume you have good clean filters in the ears. How about the vent tube that goes to back of the right filter is that cut at an angle so it does not bottom out when stuck in the hole. This can cause what you are sort of explaining.

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post #5 of 8 (permalink) Old 07-12-2010, 06:50 PM
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Quote:
Originally Posted by CDUB View Post
Background:
Recent carb cleaning, lots of Seafoam, removed the 2 small red diaphrams in the gas cap and cleared vent lines (after reading about POOGS)...

I have easy cold start in the mornings (with Choke ON), smooth idle, smooth and fast acceleration, easy warm start after a drive, but when reach cruising speed 45+ mph it feels like its struggling for enough gas (or air?) not sure, but doesn't matter if I open the gas cap and close it again while going down the road (I've read that on the POOGS post). I've also tried switching between ON and RESERVE on my petcock (has OFF/ON/RESERVE on it). No improvement. I kept riding and it didn't seem to get any worse (or better) after a 2 hour ride like that yesterday. (FYI - I'm getting about 38 mpg like this.) Just had me worried with it sputtering all the way.

I'm thinking I should try syncing the carbs. I did not do it after the rebuild because it idles and accelerates so well. Also thinking of replacing all spark plugs. I recently replaced the cap on the plug under the throttle cables because it was arcing.

Speaking of plugs, all are either greyish or light brown/tan. Seems like I remember the #1 cylinder were more greyish and #2 cylinder were more brownish/tan.

I'm really stumped as to what to try next. Need HELP please?!?
after reading all these posts and your history of what you have done the poor mileage and stuttering leads me to think you have more plug wire or coil problems.Let the bike Idle and take some 409 or water in a squirt bottle and wett your ignition wires down ,if you hear the engine start to stumble you can pobably figure on wires being bad,if not take the neck cover off on the left side and squirt the coil and remove the side cover and do the same to the back one it doesn't cost anything and it is usually definitive,X2 on checking carb vent hose also.




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post #6 of 8 (permalink) Old 07-12-2010, 09:13 PM Thread Starter
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My bike does not have a vent hose going to the ear. The bike has been coastered and the vent tube on the right is plugged with a small bearing. I tried removing it but bike ran poorly and almost stalled.
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post #7 of 8 (permalink) Old 07-12-2010, 09:14 PM
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The carb vent hose "T"s off of the carbs, and needs to be tucked up under the fuel tank away from wind drafts.

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post #8 of 8 (permalink) Old 07-18-2010, 10:44 AM Thread Starter
'93 VN 750
 
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Quote:
Originally Posted by niterider View Post
The carb vent hose "T"s off of the carbs, and needs to be tucked up under the fuel tank away from wind drafts.
I had the hose tucked under the seat, so I moved it back under the tank and hooked it to the plastic vent underneath. Problem went away. Next I synced the carbs using a manometer (powerchutes version). Hoping for improved gas mileage.
Thanks for the suggestion.
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