Kawasaki VN750 Forum banner

81 - 100 of 136 Posts

·
Registered
Joined
·
117 Posts
Discussion Starter #81
Ok started the bike fine. Idles fine. Still wont rev. This time past 3k. I will post a video. Also i noticed that when i put the bike on its side stand while running it dies. If i lean it to the side while running and then put it back up straight it will run fine. #stumped.
 

·
Registered
Joined
·
7,685 Posts
Is it popping out of the exhaust?

Will it rev higher with the choke on? edit: If it runs better with the choke on, it's not getting enough fuel. I'd guess clogged main jet first. But it could be a diaphragm problem.

No goat belly right?

I'm undecided between ignition, fuel, or something else.
 

·
Registered
Joined
·
117 Posts
Discussion Starter #84 (Edited)
Is it popping out of the exhaust?

Will it rev higher with the choke on? edit: If it runs better with the choke on, it's not getting enough fuel. I'd guess clogged main jet first. But it could be a diaphragm problem.

No goat belly right?

I'm undecided between ignition, fuel, or something else.
Yes it pops out of the exhaust. Also if i hold it at full gas it will bog down,hesitate, pop from exhaust and shoot odd flames out of the both exhaust. It dies when i give it choke. Yup no goats belly. I undid the ear shave and put surge tank back on because i didnt want to rejet with the ear shave and belly removed. Im thinking fuel problem because when i leave the bike rest on the kickstand it starves for fuel and dies. On the plus side i managed to take it for a quick test ride around my house. Starts first pick without choke, idles perfect. Drives great but wont go past 3k. Gotts be fuel right?
 

·
Registered
Joined
·
7,685 Posts
Part of it seems like too much fuel, and stalling when on the sidestand might be fuel level on the right carb, but get it running right and that might go away. Are the fuel lines level or running downward to the carbs?

Have you had the diaphragms out or checked the slides? Any carb work yet?

What color are the plugs?

Any black smoke ever?

I'd be real curious about the slides and diaphragms. Try to watch them while it's running, check the action when you lift and drop the slide (engine off). Seems like the slides could be bouncing up and down instead of opening smoothly.

Went out on a limb there, I could be wrong! :)
 

·
Registered
Joined
·
117 Posts
Discussion Starter #86
Carbs have been pulled more times than i care to say lol. Slides and diaphragms work perfeclty. Iv cleaned the carbs more times than i clean myself. Checked the plugs last night and the front are black and the rear are turning whiteish which means its running rich on the front and lean on the back. Never seen that happen before. No black smoke at all from either exhaust. I will check the fuel level of each carb today as per the manual. You might be right with to much fuel in the front. Definatly to little in the rear so im thinking my floats are adjusted wrong. I doubt they are sticking as the carb has been rebulit with all new float valves, gaskets and jets. If the fuel level shows ok i honestly dont know where to go from there.
 

·
Registered
Joined
·
117 Posts
Discussion Starter #88
Fuel line routing make sure you have good flow to carbs.. no upward loops or bends once it leaves petcock.
MTB i will re route the lines just to rule it out. Would this cause fuel starvation ? I personaly cant imagine it would with a vacuum operated petcock. Please correct me if i am wrong.
 

·
Registered
Joined
·
472 Posts
MTB i will re route the lines just to rule it out. Would this cause fuel starvation ? I personaly cant imagine it would with a vacuum operated petcock. Please correct me if i am wrong.
The petcock is opened by vacuum, but the fuel still flows by gravity.

Edit: That can be read multiple ways. It is vacuum that opens the petcock, but it is gravity that causes the fuel to flow. Therefore, uphill runs will prevent fuel from flowing.
 

·
Registered
Joined
·
7,685 Posts
Yes, uphill fuel lines limit flow. Asked about that earlier.
 

·
Registered
Joined
·
7,685 Posts
Which cylinder was rich, which was lean?

I've never really believed a whole carb can just be 'bad', there has to be something that can be corrected.

Can you check to see if the diaphragms are seated? Should be able to do it by just taking the tank off.

An easy check that should be done regularly..... Make sure the petcock vacuum hose is dry after a run.

This is the third or fourth 750 I've seen running like this, don't think I've ever seen a conclusion.
 

·
Registered
Joined
·
117 Posts
Discussion Starter #93
Which cylinder was rich, which was lean?

I've never really believed a whole carb can just be 'bad', there has to be something that can be corrected.

Can you check to see if the diaphragms are seated? Should be able to do it by just taking the tank off.

An easy check that should be done regularly..... Make sure the petcock vacuum hose is dry after a run.

This is the third or fourth 750 I've seen running like this, don't think I've ever seen a conclusion.
The front is rich and rear is lean. Petcock has been rebuilt so there is no issues there. diaphragms are seated. However i checked the slides while it was running and they are vibrating pretty rapidly. Also shot blue flame out thru the front carb. Lots of white smoke from the front exhaust also. Doesnt smell gassy tho. Everything i can think of i tried. I am running out of options at this stage. However i would like to get to the bottom of it. Iv searched for hours online with different bikes with the same problem but there is no definate answer to any of them.
 

·
Registered
Joined
·
7,685 Posts
The front is rich and rear is lean. Petcock has been rebuilt so there is no issues there. diaphragms are seated. However i checked the slides while it was running and they are vibrating pretty rapidly. Also shot blue flame out thru the front carb. Lots of white smoke from the front exhaust also. Doesnt smell gassy tho. Everything i can think of i tried. I am running out of options at this stage. However i would like to get to the bottom of it. Iv searched for hours online with different bikes with the same problem but there is no definate answer to any of them.
So the slides are bouncing.

Do you have a vacuum gauge? I'm wondering if the gauge needle bounces like the slides? Check both carbs.
 

·
Registered
Joined
·
117 Posts
Discussion Starter #95
I can grab the gauge tomorrow from work and have a check. This would mean a vacuum leak right?
 

·
Registered
Joined
·
7,685 Posts
I can grab the gauge tomorrow from work and have a check. This would mean a vacuum leak right?
I'm thinking diaphragm problem, or leaky valves. There could be two problems with fuel delivery.

We're both slides bouncing about the same or was there a visible difference?

I think when you check vacuum on the left/front carb, it should run long enough to read without having the petcock hooked up.

Front is rich, rear is lean? Right? Just reminding myself.

I'm afraid we might need compression, and most important, leakdown test.

Seems like if the diaphragms are good, then maybe the valves are leaking.

But need to see what the vacuum is doing. A number from the gauge, but mostly the action of the needle.
 

·
Super Moderator
Joined
·
2,569 Posts
Slides bouncing is normal. They pull every intake stroke, and since the carbs feed one cylinder each with no cross connection they will bounce in time with the intake stroke of the cylinder they feed
 

·
Registered
Joined
·
7,685 Posts
Slides bouncing is normal. They pull every intake stroke, and since the carbs feed one cylinder each with no cross connection they will bounce in time with the intake stroke of the cylinder they feed
It's all happening so fast, I don't think you should see them popping up and down after it's running, above idle at least. They should rise and fall with the throttle changes.
 

·
Registered
Joined
·
7,685 Posts

·
Registered
Joined
·
7,685 Posts
It's not normal for the slides to be bouncing. I think either the rubber is blown or kinked under the plate, or leaky valves are creating a bad pulse in the air stream.

At the beginning you can see a pic on his laptop of a diaphragm installed wrong.


Here's the lift test, woosh test, and a neat little air test for the diaphragms.

 
81 - 100 of 136 Posts
Top