Fast Idling After Riding! - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 6 (permalink) Old 02-12-2019, 12:00 AM Thread Starter
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Fast Idling After Riding!

I have an interesting problem. The idle speed goes up to about 4000 rpm after it has warmed up and you ride it, it won't do it if you just let it run idling for up to 30 minutes and just rev the engine occasionally, you have to ride it! It doesn't take long after it is good and warm, a mile getting up to 30-35 mph and the idle speed will go up.
I have checked and lubed the throttle cables, they are not sticking.
When I first bought the bike the idle was set at about 2000rpm. I adjusted the Idle Adjusting Screw and set it at about 1100rpm. I rode it a few times and she ran great. Then...
How it all started: My Vulcan 750 is a 2006 with about 14900 miles and according to the last owner had only been ridden a few times in last couple of years, so I was concerned about varnish build up in the carburetors, I had read here about the wonders of Seafoam, I added 8ozs then filled up the tank and started off on a 30 mile ride. The first 13 miles is nonstop and she seem to be running fine, Until I came to the stop sign, it was idling at about 4000rpm, I tried flipping the throttle a few times, nothing changed. I was now holding up traffic so I put it in gear and took off, she ran okay. The next stop was 4 miles and as I came to a stop again the idle was at 4000rpm. This time I pulled into a parking lot and adjusted the idle down to about 1100rpm, it took quite a few turns, then off I went. I got caught at a stop light about a mile later and again the idle was at 4000rpm, I pulled off and again adjusted the idle down to 1100rpm. 8 miles farther I stopped to turn in traffic and again 4000rpm, I only had about 4miles to go so I kept riding. When I got home I am so convinced Seafoam is the culprit that I throw away the can (yah I know, ID10T). I have tried every hairbrained thing I can find from friends, the internet, and of course "carburetor experts" short of cleaning, rebuilding and synchronizing the carburetors.
So I am finally here humbly seeking your collective wisdom. What is wrong with my Vulcan? Also twice after a ride I had to wait till it cooled down before it would restart, but isn't that something else entirely? Please Help I haven't dealt with anything besides lawnmowers with carburetors since 2004 when I rebuilt and synced my Yamaha's 4 carburetors, that was tedious but not hard.

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post #2 of 6 (permalink) Old 02-12-2019, 07:49 AM
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Carb Boots are loose and or split. Mine did very similar, pulled carbs to solve another problem and found carb boot clamps not tight at all. Is a pain in the rear to get to them so i can see how easy it is to not do them up properly.

'99 Vulcan "Victoria"
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post #3 of 6 (permalink) Old 02-12-2019, 09:47 AM
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Quote:
Originally Posted by TonyO View Post
Carb Boots are loose and or split. Mine did very similar, pulled carbs to solve another problem and found carb boot clamps not tight at all. Is a pain in the rear to get to them so i can see how easy it is to not do them up properly.
Ditto, I have the problem of mine loosening after a couple miles hard ride. Maybe I should try thread locker?
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post #4 of 6 (permalink) Old 02-13-2019, 07:30 PM Thread Starter
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Thanks, to the both of you TonyO and Birga, I will check them out

How do you ruin a rotten egg?.....You can't!
as quoted by Mack Via (My Friend & "touched" Vietnam Vet)

Current Motorcycle
2006 VN750A
Past Motorcycles
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1980 Yamaha Maxim XJ650G
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post #5 of 6 (permalink) Old 02-23-2019, 11:41 AM
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i experienced the same thing with 4k RPMs. Before you tear stuff apart, check for vacuum leaks. I had a vacuum leak and the problems only made themselves apparent when i rode. Guess where my vacuum leak was...yup, carb boots. Get it running and idling at a normal RPM and spray come carb cleaner at the joints of the boots (carb and cylinder side).

There are other posts that talk about carb boot positioning, so while tearing stuff apart, i took a pic for everyone to see and have been scouting out posts to share my pic (can't attach here cuz i already did in another post). The cylinder and boot have alignment marks (didn't know about it until i had the same prob as the OP).

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post #6 of 6 (permalink) Old 03-30-2019, 10:54 AM
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I have vacuum leaks in the carb boots too! I was planning on buying new ones to fix it. Before I drop $70, is there anything I am missing?

Both boots are aligned (rear is off slightly by the width of the mark). Clamps are tightened. No visible cracking or damage. If it were not for the leaks, I would not replace them as they look and feel functional. Is there a way to seal them? I'd hate to replace them if I don't need to.


'89 Vulcan 750 Purchased 4/12/18 @ 17805.9 miles $800
Purchased stock except for K&N Filters. Wrecked once
20969.2 miles & counting

Completed modifications:
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Repainted Metallic Blue w/ new tank bages

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