Two problems, and theories about them.. - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
Carbs and Fuel System
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post #1 of 10 (permalink) Old 07-30-2013, 10:18 PM Thread Starter
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Two problems, and theories about them..

Ok, this is a bit of a long post. But I have two problems, and here is what I have done in terms of mods and purchases:

The ear shave (rejetted, and shimmed the needle). New AGM battery, and new iridium plugs. Deleted emissions stuff, plugged red/right side hose on gas tank, blue/left side is open to breathe. I have also done the pickup coil mod.

The problem is that the bike will idle when cold, and rev up well. But once it warms up, it will stumble to get to 2k rpm, and even dies at idle! If I rev slowly past 2k, it can rev up no problems. Sounds like a clogged jet, but wait, there's more! This only happens after it's warmed up.

After reading a few posts around here, I am led to believe it's the carb vent hose, which I don't think I placed in a proper position. After an ear shave, where is the best spot to put it? I'm still waiting for the breather filters in the mail.

The rear cylinder is not firing. I checked for spark on both of the plugs, they for sure have spark. But the plugs are not wet at all, and pulling both plugs with the bike running makes absolutely no change. Have not yet checked compression. Anything else I can check before I check compression?

I guess because I have been starting it so much, the battery quickly dies, and I have to recharge it. That shouldn't happen, right?

(Back to breather filters. One filter goes to the crankcase vent, and the other to the carb Tee vent, yes?)

Sorry for the long post, and thanks!
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post #2 of 10 (permalink) Old 07-30-2013, 10:43 PM
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Post ear shave hose routing is to the center frame tube under the tank. but a carb venting issue is usually only at speed... it sound more like you are having problems with a leaking carb intake boot.
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post #3 of 10 (permalink) Old 07-30-2013, 10:56 PM Thread Starter
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Thank you for responding. Are the carb boots finicky? I had a problem with idle not returning quickly, and I put on some new clamps, and seriously clamped them down good. They shouldn't be leaking, possible but unlikely.

I don't understand what you mean by the "center frame tube under the tank". Right now the vent is just breathing in air, and sitting under the fuel tank.
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post #4 of 10 (permalink) Old 07-30-2013, 11:10 PM
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Quote:
Originally Posted by AlienBacon View Post
Thank you for responding. Are the carb boots finicky? I had a problem with idle not returning quickly, and I put on some new clamps, and seriously clamped them down good. They shouldn't be leaking, possible but unlikely.

I don't understand what you mean by the "center frame tube under the tank". Right now the vent is just breathing in air, and sitting under the fuel tank.
Under the gas tank, you should have a plastic cap with a nipple. This covers the underside of the fuel sender. Plug the carb vent tube into that to. It normally sits with the nipple facing to the rear of bike, it can be removed and turned 180 degrees to face forward.

Another thing to check is the response of the slides. I had an issue where the slide boot was not sealing and causing the bike to flat line at around 5K RPMs. I noticed one slide or both would not respond well to opening the throttle. Took several careful tries to rectify them.

On the cylinder wall behind the carb boots is a notch in which the boot tab aligns to. If you noticed, the boots them selves are round with a small nub protruding. That nub aligns to the notch on the cylinder. The front carb boot should not have been removed and thus should have remained aligned. However, the rear boot removes with the carb. Check this boot for proper alignment.

Hope this helps

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post #5 of 10 (permalink) Old 07-30-2013, 11:56 PM
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What kind of clamps? The clamps on the carb to manifold connections should be oem. Worm drive hose clamps are to wide, and can distort the rubber, causing a leak, especially if you overtighten them. The crankcase vent needs a filter. The carb float bowl vent does not.

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post #6 of 10 (permalink) Old 07-31-2013, 03:19 AM Thread Starter
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Ok, so I realigned the boots, to where the notches line up. The bike idles much better now. I am using the worm clamps, yes. It's snug, but I don't think it's over tightened.

I rerouted the carb vent hose to a better spot, and it seems to have helps the stalling out issue.

The crankcase breather hose is in open air for now, until I get the breather filters in the mail. Does this make a difference?

I took the carburetor off and I cleaned the hell out of it with carb cleaner, being careful not to attack the rubber diaphragm. Cleaned all the jets, too. The slides seem to be fine as well.

The bigger issue is that the rear cylinder is not firing. It definitely has spark. I think it has compression, but I'm not sure if it's sufficient. I took a spark plug out, and cranked the bike, but not letting it start. I could see the valve move, and I felt a gush of air out of the hole.

I am pretty sure the problem is the cylinder is not receiving fuel. The plugs are clean as can be, and they are not wet. When I drain the carburetor bowl, no fuel comes out. It is not the petcock, because I have switched the fuel lines, and it runs the exact same. I'm at a loss of what to check next...

Thanks for the responses
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post #7 of 10 (permalink) Old 07-31-2013, 06:21 AM
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If no fuel comes out of the drain, and that cylinder is not firing although it has compression and sparks, I would say there is no fuel getting to that carb. Check:- Fuel flow out of petrol tap that feeds that carb. float needle, float needle seat, float. Check they all move as they should and that there is absolutely no dirt. It does mean removing the carbs and taking the three screws out hold the float bowl together, but I think you will find the problem. You can also take the opportunity to check/adjust the float hight.

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post #8 of 10 (permalink) Old 07-31-2013, 05:27 PM Thread Starter
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Yay! I took apart the carburetors again, and I took apart the bowls, and alas the rear carb float needle was stuck. put everything back, and WOW what a difference when it's two cylinders!

Now I'm going to sync the carbs. I'll touch base again soon. Thanks everyone for the help!

UPDATE: The carburetors are synced now. She runs really good now! Thanks again for your help, everyone.

Last edited by AlienBacon; 07-31-2013 at 10:37 PM.
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post #9 of 10 (permalink) Old 08-21-2013, 12:57 PM
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Quote:
Originally Posted by AlienBacon View Post
Yay! I took apart the carburetors again, and I took apart the bowls, and alas the rear carb float needle was stuck. put everything back, and WOW what a difference when it's two cylinders!

Now I'm going to sync the carbs. I'll touch base again soon. Thanks everyone for the help!

UPDATE: The carburetors are synced now. She runs really good now! Thanks again for your help, everyone.
OK so you synched the carbs and?

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post #10 of 10 (permalink) Old 08-23-2013, 06:59 PM
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