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Discussion Starter #1
Just bought my 1995 VN750 about 130 miles ago and I have a problem already. After riding for about 20 minutes the engine seems to stick in high rev mode (about 4K). Whenever I let off the gas to shift gears, the throttle seems to snap back but the bike keeps revving at about 4K. When I shift into neutral the high revs keep up. Any ideas? Thanks.
 

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..have a vulcan good day!
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Have u messed with/ turned the Black Idle adjust knob, possibly having the idle set too high ? That was my first thought, but i now doubt it... sounds like a throttle cable problem.
keep in touch
WilliamTech
 

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If only it had 6th gear..
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Sounds like a problem with the decelerator cable. Check my post#4 here
http://www.vn750.com/forum/showthread.php?t=19761
Could be that, but also you might want to look at your intake boots and check for cracks. A crack might be closed when the bike is cool but after it warms up It could open a little letting some air in. Also if you start your bike with choke maybe one of the enricher (choke) plungers isn't returning to it's seated position. That could make it rev without dying out if it's up or on just a little.

If you're still having the prob, give more detail if you can. how high does it rev and when it does is it smooth or choppy and popping, stuff like that helps.:smiley_th
 

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Discussion Starter #5
Thanks JM2001 for your tip on the decelerator cable.
I followed your thread and did my best to adjust both throttle and decelerator cables per instructions, but sadly no luck. Everything started off well, but after driving about 15 minutes the engine locked into its 4K rev mode. I have learned to drive home with a tricky combination of break and clutch, but it doesn’t seem too safe.

DavesVulster, as soon as I figure out where the intake boots are, I plan to give them an inspection for cracks. Will I have to remove the gas tank to perform this inspection? Will I be able to see the choke plungers with the gas tank on? It revs around 4K and builds to about 5K. By then I turn the bike off. The revs are smooth with no popping.

Thanks guys.
 

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Giggity!
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Silly question I know but you don't have the choke on do you? Also, check your vacum lines, you could have one pinched or loose.

An easy way to check for cracks or bad seam on your carb boots is to spray some carb cleaner around the connections. If the idle drops, you found a leak.

Another check, Do you have a propane torch? You can run an unlit propane torch with the valve cracked open over the suspected hoses/connection while your engine idles. If you pass it over a hose and it idles up and take the torch away and it idles down - then you found your leak. The propane going in the system will cause it to idle up.
 

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Thanks JM2001 for your tip on the decelerator cable.
I followed your thread and did my best to adjust both throttle and decelerator cables per instructions, but sadly no luck. Everything started off well, but after driving about 15 minutes the engine locked into its 4K rev mode. I have learned to drive home with a tricky combination of break and clutch, but it doesn’t seem too safe.

DavesVulster, as soon as I figure out where the intake boots are, I plan to give them an inspection for cracks. Will I have to remove the gas tank to perform this inspection? Will I be able to see the choke plungers with the gas tank on? It revs around 4K and builds to about 5K. By then I turn the bike off. The revs are smooth with no popping.

Thanks guys.
You stated everything started off well. I would asume that means the bike started ok, idled well, and ran well for 14 minutes. This leads me to believe the cables are ok, the choke plungers are ok, and no air leaks. If you run the bike to 4000 rpm and then the reving condition happens I would suspect the throttle valve ( carb slide) in one or both carbs is sticking open.
 

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I had a similar issue and it was nothing more than adjusting the idle setting. The idle setting was set to 1100rpm when the choke was turned off, but the bike was not completely warmed up yet. After a few miles of riding the idle would creep up to about 3500rpm and stay there.

Re-adjust the idle knob on the left side of the bike once the engine is hot. It may be a little tricky because when the bike is cold it will tend to idle a bit low until it completely warms up again.
 

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If only it had 6th gear..
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Wow I answered you yesterday but I don't see it here. Musta not clicked reply. Anyway, the boots I was talking about connect the carbs to the engine heads. They are thick rubber tubes, about 2 inches in length. That's where you would spray to check for a leak. The suggestions are good but what JM2001 said about a slide sticking sort of floats to the top of them. To check the slides you'll have to take off the airbox boots <opposite side of the carb from the intake boot :drool:, and both airbox boots go from the carbs and turn up under the tank.

This is just a guess - never tried it, but you might be able to test for sticking mechanics inside the carbs this way; when the bike is stuck in high idle, take a screwdriver and with the handle side rap on the side of each carb to see if it frees up and the idle drops. If it does, remove an air cleaner and spray some lightweight top cylinder oil or "fogging " oil in there while the bike is running. It'll smoke out the exhaust some so don't be concerned, just spray a little wait for the smoke to let up, spray some more and wait, not too much oil, just a little at a time. This may or may not help depending on where it's getting hung up, and if it actually is the problem, but it's worth a try. :blah::blah: You can use the fogging oil to check for leaks on those boots and to protect your engine's top end if you put it away for off season so either way it won't be wasted. Most hardware stores have the stuff. Good luck.
 

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Discussion Starter #11
Wow! so many great ideas. I'll try them all this weekend and let you know what happened.
 

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If only it had 6th gear..
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Maybe this picture will help you
 

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Agree with the above, the one thing that i did not see was the condition of your plugs. It may be of benefit to know what the tip of your spark plugs look like. They should be that nice tan color at the tip, if they are black (fouled) then we know you are running rick (too much fuel) or lean (not enought fuel/too much air). This does not apply to my current 02 Vulcan, but had a similar issue with my old 82 Maxim. It turned out to be a float being stuck open, which plug condition helped me diagnose. Just a thought.

Kevin
 

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Crap, I WAS in 5th gear.
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Check your coasting enrichener diaphragms- this can be done with the carbs on the bike. Depending on the fuel formulations in your area, the life of these can be shorter than 10 years (mine lasted 10 years in CA with alcohol and MTBE fuels.) If the diapragms look OK, your carbs are going to have to come off and be cleaned, I think. It is sounding like you have clogged slow jets, causing the bike to run lean. Don't take the carbs off until you are absolutely sure it is an internal carb problem. You might be able to spray cleaner up through the carb drains until it runs out of the vent lines, some guys have had success with that. I wouln't do much with fuel additives, but some guys here swear by Sea Foam which is a Naptha/Alcohol cleaner- worth a shot I guess. If you do pull the carbs, go ahead and change the slow jet to the next higher size. I would also add one or two washers to the needle.
 

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Hmmm

Check your coasting enrichener diaphragms- this can be done with the carbs on the bike.
I think my front may be bad...may need to check soon...Ive read this a number of times, so sounds logical...but if I replace 1, may as well do both...
Thanks for the original post, and thanks for confirming my suspicions Kelly. :smiley_th
 

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Crap, I WAS in 5th gear.
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They are expensive, Wolfie. Make sure they're bad before you replace them, and you just don't need a carb cleaning.
 

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Yep...

An '85 bike which sat for 5 yrs in a barn. Wouldnt doubt old gas was left in it. But rear carb works great, and Ive cleaned em both (quick method) before...if I remove the diaphragm, will damage be visible ? (seems like its dumping fuel)...my eyes aint too good close up anymore (I can still tell the gender of a hawk 1/2 mi away tho, lol)...there GOTTA be aftermarket replacements...these carbs were used on so many diff bikes, even some Harleys....I think I wanna keep er awhile, and ride thru winter, so a diaphragm would be a quickie...gotta link to the replacement thread ?...or is it in the general carb rebuild one ? (aint been there yet, but will soon I guess).
Wanna get some sheet Alum and make my own coaster covers too...hoses goin nowhere are butt-ugly...
 

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Discussion Starter #18
The garage where I keep the Vulcan is in a different location from the house where I do my computing. I printed everyones comments along with DavesVulster's great photo and will bring them to the garage tomorrow.
 

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I had a similar issue and it was nothing more than adjusting the idle setting. The idle setting was set to 1100rpm when the choke was turned off, but the bike was not completely warmed up yet. After a few miles of riding the idle would creep up to about 3500rpm and stay there.

Re-adjust the idle knob on the left side of the bike once the engine is hot. It may be a little tricky because when the bike is cold it will tend to idle a bit low until it completely warms up again.
Excellent suggestion here. Idle should be set to 1100 after the engine is completely warmed up. Having the idle set too high could cause the exact symptoms described.
 

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Just for all's info...

Just found out that Arctic Cat snomos use CVK34 carbs too, and prices there are WAY low for carb parts !
 
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