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Chris
Chris, Motorcycle Mechanic
Category: Motorcycle
Satisfied Customers: 6658
Experience:  20 yrs. experience as motorcycle, dirt bike, ATV, UTV and watercraft technician.
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Hi There I have a 1995 Kawasaki VN800 that is running very

Customer Question

Hi There

I have a 1995 Kawasaki VN800 that is running very rich at idle. It blows black smoke out of the exhaust, and on part throttle it stumbles and misfires.

Heavy acceleration and full throttle is ok and it runs well during these throttle settings. I have had the carb apart and there was not too much crud in there, but I fully cleaned out all jets etc anyway. I also found a hole in the air cut off valve diaphragm and replaced it.

It still runs very rich at idle. When I had the carb apart I looked for numbers on the main and pilot jet but couldnt spot anything.

If I screw the pilot fuel screw all the way in (which should be lean if I am right), the bike still runs. I can also see fuel coming up the main jet at idle, even with the inlet butter fly closed and the throttle closed.

Where to go from here?
Submitted: 2 years ago.
Category: Motorcycle
Expert:  Chris replied 2 years ago.

Chris :

Hello how are you

Chris :

Has the bike been in storage for some time?

Chris :

It sounds like you have a faulty float valve, its job is to shut off the flow of fuel into the carb when the bowl fills up, over time the rubber tip shrinks up and cracks. The link below will take you to a breakdown for the carb, part # XXXXX shows the float and valve assembly

Chris :

If you have any further questions or problems post them here. Please remember to rate your experience, my goal is excellent service. Thanks and good luck

JACUSTOMER-gravod4m- :

HI There, yes it was sitting for some time, but was recently put back into service.

JACUSTOMER-gravod4m- :

I have checked the rubber tip already and the needle valve seat and they are both in good condition and sealing. I checked this by hodling the carb upsidedown and blowing into the fuel inlet pipe, with the valve closed it let no air through.

Chris :

Is this bike new to you? Has it ever ran well with the current set up? exhaust air filter etc?

Chris :

sorry for the delay in my reply, the site is experiencing issues today

Chris :

Is the oil level ok, does the oil smell like gas?

JACUSTOMER-gravod4m- :

It is new to me yes, the previous owner was the owner of a motorbike shop and had rebuilt the engine. He said he hadnt had time to tune the carb as well, he seemed pretty clued up. Oil level is good and doesnt smell like gas, but its only 50 miles old, I am due to change it in 300 miles anyway as the engine has been rebuilt.

Chris :

Do you feel the engine is burning gas or oil?

JACUSTOMER-gravod4m- :

Definitely gas, no blue smoke.

Chris :

are both spark plugs fouling?

JACUSTOMER-gravod4m- :

yes, heavy with black soot

JACUSTOMER-gravod4m- :

as are the exhaust tips

Chris :

The only thing both cylinders have in common is the carb, I really feel your issue is the float valve

JACUSTOMER-gravod4m- :

OK, Just on a side note, if I had blocked passages in the carb, ie pilot air passages, would this cause fuel to be forced up the main jet during idle, or would the bike die?

Chris :

no the engine sucks the needed fuel into the intake, unless the valve is not sealing, then gravity takes over and pushes the fuel up and in

Chris :

I find it hard to believe the jetting would be that far off

JACUSTOMER-gravod4m- :

OK so the only thing causing the flooding up the main jet has to be valve sealing or float height issues?

JACUSTOMER-gravod4m- :

as do I

Chris :

correct

JACUSTOMER-gravod4m- :

OK, so as the float height seems to be right from the outside, whats the easiest way to check and adjust with the carb off the bik?

Chris :

Give me a moment to post some additional info for you

JACUSTOMER-gravod4m- :

Thanks

Chris :

Take a clear plastic tube and stick it on the carb bowl drain nipple, open the drain and hold the tube next to the carb (end being higher then the bowl) the fuel level will be the same in the tube and the bowl

Chris :

understand that?

JACUSTOMER-gravod4m- :

Yes, thats what I have already done. I followed the service manual and the level matches up with the top of the float bowl. See this link for the instructions I followed:

Chris :

didn't know you had the manual, that bike has a vacuum petcock right?

JACUSTOMER-gravod4m- :

http://fotifixes.com/imagehosting/Nr

JACUSTOMER-gravod4m- :

Yes it does

Chris :

Did you test in the PRI position?

JACUSTOMER-gravod4m- :

Same thing

Chris :

? was the petcock in the prime position for testing?

JACUSTOMER-gravod4m- :

Yes, I have done testing in the prime and on and res position

JACUSTOMER-gravod4m- :

The petcock only flows when vaccum is applied so all good on that front

Chris :

Does the fuel overflow the carb and into the intake that you can see

JACUSTOMER-gravod4m- :

With the engine running ?

Chris :

engine off petcock in the pri position

JACUSTOMER-gravod4m- :

I havent checked that, I will check

JACUSTOMER-gravod4m- :

give me 30 minutes

Chris :

it does not take much to load the cylinders up, given the age of the bike I would replace the float valve either way

Chris :

I have to run out for about 30 min so that will work out good,

Chris :

talk to you soon

JACUSTOMER-gravod4m- :

Great. I have just checked and yes fuel does slowly flow out of the needle when on prime. Thats a pretty good indication its the float height isnt it?

Chris : More likely the float valve is faulty. Float level shouldn't ever need to be changed.
Chris : Unless your compensating for other worn components. I.e the float valve. Replace it and you should be fine.
Chris : As I mentioned previously rubber shrinks up over time. Now the float does not have the travel to close off the flow of fuel.
JACUSTOMER-gravod4m- :

Aha ok. New one on its way, will have it replaced and let you know how it goes. Thanks

Chris : You are welcome. Please remember to rate my assistance Thanks
Customer: replied 2 years ago.

Hi There


 


New needle valve arrived today, still had fuel coming up the main jet, so I adjusted the float level which has sorted the main issue. I no longer have fuel coming up the main jet at idle.


 


I do however have a misfire on part throttle still, which is the main reason I was looking at the mixture. Its ok on full throttle, but If you ride on part throttle at a constant speed (ie 30 mph) it stumbles and misses. Not sure if its a lean or rich condition but im guessing rich considering my last problems.


 


My only guess is that the needle or the main jet are worn or have been changed for the wrong ones at some point?


 


Any thoughts?

Expert:  Chris replied 2 years ago.
Does the condition improve when the choke is applied? Worsen? Jetting I a trial and error kinda thing. What add ons does the bike have? Exhaust, slip ons, baffles, air filter, any other mods?
Customer: replied 2 years ago.

The condition worsens when the choke is applied. Just checked it on a ride around.


 


It has open pipes and a k and n air filter. Apart from that it appears to be stock (lol).


 


I have no idea at what time these modifications where done to the bike and if anything has been changed since then.

Customer: replied 2 years ago.

I have just checked, I have a 135 main jet (which is stock) and a 47 pilot jet, which is also stock.

Expert:  Chris replied 2 years ago.
Get yourself a jet kit. It will make life a lot easier and takes most of the guess work out. It will also include a more progressive needle and the needed shims.

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