Kawasaki VN750 Forum banner

1 - 20 of 44 Posts

·
Registered
Joined
·
51 Posts
Discussion Starter · #1 ·
So my vulcan has like an oily build up on the carbs bike rums fine then when it gets warm it starts idling sporadically like 1800 up to 4000 im lost any ideas on what is causing this? I rode for an hr earlier today and it was fine then i went for a second and bam 5 mins in and it stuck at 4000 while i was rolling with the clutch pulled so i hit the kill switch restarted it and it was at 1800 i limped it home. You can see the build up at the base of the carb intake boot and all over the carb
 

Attachments

·
Registered
Joined
·
8,819 Posts
Possibly an air leak on the engine-carb boots, gets worse after warmup.
 

·
Registered
Joined
·
51 Posts
Discussion Starter · #3 ·
Possibly an air leak on the engine-carb boots, gets worse after warmup.
Ok thanks ik honna order new boots also i started it and ut almost feels like a backfire through the carburetor every once in a while like a pop that i xan feel in my leg while sitting on it.
 

·
Registered
Joined
·
641 Posts
Check the boot clamps for tightness.
You can spray the boots to check for leaks. I don't recall what to use. Starting fluid maybe? Someone else should be able to chime in.
 

·
Registered
Joined
·
51 Posts
Discussion Starter · #5 ·
Thank you anyone know why only the right carb has oil on it and theirs like black burnt oil around the intake boots too?
 

·
Premium Member
Joined
·
1,024 Posts
Check the boot clamps for tightness.
You can spray the boots to check for leaks. I don't recall what to use. Starting fluid maybe? Someone else should be able to chime in.
I read to spray them with WD40, if that gets sucked into a crack or loose boot it’ll make the idle drop and it’ll help you pinpoint the leak.
My bike does this when it starts to get warm out, not so much in the winter, what you need to do to calm it down is just use the clutch and rear break together, if you’re in 1st and it revs up, shift up to 2nd and apply the back break a little and give it just enough throttle to not lug or stall it and the idle should settle down and then shift back down.
The carbs are a part of the bike that I haven’t felt brave enough to try and mess with so I just learned to deal with the occasional erratic idle for now.
 

·
Registered
Joined
·
51 Posts
Discussion Starter · #7 ·
I read to spray them with WD40, if that gets sucked into a crack or loose boot it’ll make the idle drop and it’ll help you pinpoint the leak.
My bike does this when it starts to get warm out, not so much in the winter, what you need to do to calm it down is just use the clutch and rear break together, if you’re in 1st and it revs up, shift up to 2nd and apply the back break a little and give it just enough throttle to not lug or stall it and the idle should settle down and then shift back down.
The carbs are a part of the bike that I haven’t felt brave enough to try and mess with so I just learned to deal with the occasional erratic idle for now.
May i ask what in the carbs causes this problem? I ordered carb rebuild kits, new air cut off valves and new intake boots from partzilla.com in case these would fix the problem
 

·
Premium Member
Joined
·
1,024 Posts
One time the idle was jumping around it was simply because the clamp on the carb boot was loose and the vibration of the engine was enough to to shimmy it off. That I was able to fix on the street by just tightening the clamp. The high rev I see from time to time is probably just something not reseating properly either because something is wearing out or gunked up. I’m not really sure and I’m in no hurry to pull my carbs because it’s too sporadic. If you’re going to rebuild the carbs there’s a good chance you’ll correct whatever is wrong but I’m sure the more seasoned folks will weigh in on what exactly is happening.
 

·
Registered
Joined
·
8,819 Posts
If the idle just hangs a bit before finally dropping, that's usually an air leak.

If the engine revs higher and holds, that can be an air leak combined with additional fuel coming from somewhere it shouldn't be, such as the petcock vacuum, float set too high or stuck, internal leak, or clogged air bleeds. Sticky slides or cables can do it also, so that needs ruled out before chasing other problems.
 

·
Registered
Joined
·
641 Posts
May i ask what in the carbs causes this problem? I ordered carb rebuild kits, new air cut off valves and new intake boots from partzilla.com in case these would fix the problem
To clarify, you bought the boots that sit between the carbs and the engine, correct? Leaks in the boots above the carbs won't cause any problems.

It could also be the slide diaphragms causing issues. When you pull your carbs, check the slide mivement for smoothness. It should have some resistance and you should hear pumping air as you push on them, but it should feel like a spring and air pump, with no catching.

Take off the slide diaphragm covers and diaphragms and check the diaphragms for leaks by putting a strong light behind them and look for pinholes. When you put them back, make sure they are properly seated.
 

·
Registered
Joined
·
8,819 Posts
This video talks about the woosh test and diaphragms.

 

·
Registered
Joined
·
51 Posts
Discussion Starter · #12 ·
To clarify, you bought the boots that sit between the carbs and the engine, correct? Leaks in the boots above the carbs won't cause any problems.

It could also be the slide diaphragms causing issues. When you pull your carbs, check the slide mivement for smoothness. It should have some resistance and you should hear pumping air as you push on them, but it should feel like a spring and air pump, with no catching.

Take off the slide diaphragm covers and diaphragms and check the diaphragms for leaks by putting a strong light behind them and look for pinholes. When you put them back, make sure they are properly seated.
Yes i bought the carb holder boots and i will check the diaphrams what i dont understand is it will eun great until it warms all the way up and then the issues start.
 

·
Registered
Joined
·
8,819 Posts
Yes i bought the carb holder boots and i will check the diaphrams what i dont understand is it will eun great until it warms all the way up and then the issues start.
The cracks in the boots can open up after it warms up.
 

·
Registered
Joined
·
51 Posts
Discussion Starter · #14 ·
The cracks in the boots can open up after it warms up.
Thank you my all balls carb kits came in today and my k&l air cut off valves with springs. Im still waiting on the new carb holders i appreciate all the help everyone. Ill let everyone know how it goes and what the problem was.
 

·
Registered
Joined
·
51 Posts
Discussion Starter · #15 ·
These are the rebuild kits that i bought for my carbs. They say closed corse racing? Can i use these kits for my bike? Also looks like ill be doing a top end rebuild my rear cylinder has oil on the plugs and also a little bit of white smoke when i start it only for a min. Could the case being contaminated and a little over full cause the plug to get wet with oil?
 

Attachments

·
Registered
Joined
·
8,819 Posts
You can use the kit, that's just a disclaimer to keep the EPA off their back.

Overfull on oil can cause what you're seeing. Fix the carbs, make sure the oil is right, then see how it goes.
 

·
Registered
Joined
·
51 Posts
Discussion Starter · #18 ·
Ok i have found that I need to do a top end rebuild looks like oil has been getting on these plugs since before I owned it. What is all needed to do a complete top end rebuild? and also about how long it will take? The ends of the plugs looked ok but the threads had oil on them and the plug holes had oil in them maybe im wrong and its not this bad? I know sprockster said maybe its from oil too full do to gas leaking in. Where do I get the tool fomr a leak down test?
 

Attachments

·
Premium Member
Joined
·
1,024 Posts
I’m not sure if you’re getting ahead of yourself or not yet. I’d finish the carb rebuild and make sure your petcock is not leaking. I too had the gas leak into the cylinders and I ran it like that because I didn’t know. Oil found its way into wherever it could. Remove and clean the plugs and get the right amount of oil in the bike and start it up. You can recheck the plugs after that before you tear into the motor.
 

·
Registered
Joined
·
51 Posts
Discussion Starter · #20 ·
Alright after some more investigation the plugs were only gunky on the threads the ends were dry i am thinking because of the vaccuum leak on the petcock gas had built up and turned amber color on the plug threads due to being dry fouled and not combusting all the fuel (thats my guess) it doesnt smell or really seem like its oil. I have been busy at work so im going to pull the carbs tomorrow while looking at them it seems that the boots are on kinda crooked their not even all the way around the carbs both the ducts and intake boots look crooked on the carbs. My question is could them being improperly mounted cause a vaccuum leak?
 
1 - 20 of 44 Posts
Top