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Discussion Starter · #1 ·
I believe this is a fuel issue, but what do you think?

2005 vn750
I bought it a month ago, ran for a couple weeks, then wouldn't start.
What I've done/tried so far:

I've had the tank off a couple times, drained the gas and added fresh gas. (Have not done seafoam)
Pulled apart and cleaned the petcock (was carb cleaner ok?)
Pulled out the carbs (twice...) and thoroughly cleaned. The jets are clear, floats seem to work great
Replaced spark plugs (all 4 are getting spark)
cleaned the ignition switch (I think, the puck thing under the key right?)
replaced the whole kill switch/start button setup
New battery. Testing at 12.6v when off. currently on trickle

OK, that's all I know, and all I've tried. I'm still super mechanically new, learning a lot from you guys.

I'm wondering how to test to see if the carb is getting fuel. I believe my petcock is a vacuum deal, when I took the tank off, fuel would not drip in ON / RES / OFF (I don't have a "PRIME" setting. So wondering how to test if it's a bad petcock since apparently it's not supposed to work if the bike is off...

What should I look at / try next? Questions? Suggestions?

Thanks!!!
 

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Apply vacuum to the center hose on the petcock and fuel should flow from the other two ports.

There's a drain screw at the bottom of each carb, open and see if fuel drains.
 

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Discussion Starter · #3 ·
Apply vacuum to the center hose on the petcock and fuel should flow from the other two ports.

There's a drain screw at the bottom of each carb, open and see if fuel drains.
Thanks! Well, apply suction and fuel does flow freely. I also sucked and then clamped the hose and it continued to flow. I guess good news it’s not the peacock...

I also drained both carbs as they had fuel in them. When I cleaned the carbs the floats both seemed good and not sticking.

I guess I’ll try seafoam in the gas tank, see if there’s anything else there.

Anything else to try next?
 

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Discussion Starter · #5 ·
I know there are already some technical threads on this, but I wonder I if didn’t adjust the carb jets correctly when I put it back together... I think they may be closed, or tightened too much.

I’ll check the spark plugs too
 

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I know there are already some technical threads on this, but I wonder I if didn’t adjust the carb jets correctly when I put it back together... I think they may be closed, or tightened too much.

I’ll check the spark plugs too
It should start on the choke, the mixture screws would affect the idle after warmup.
 

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Discussion Starter · #7 ·
UPDATE:

It Starts and runs!!
So, it appears the major problem was me being a dumb ass. While I was taking out and cleaning the carbs, I also switched to K&N Air filters, and didn't oil them. So there's that... I took them off completely and tried to start, started right up. I sprayed them with filter oil and put them back on, still starts and runs.

NEW PROBLEM 🤬

Now after a min or 2 running it begins burning black smoke. Can't tell exactly where, but it's coming up from under the tank, smells bad. I know that would suggest excess fuel, but not sure where to look first. It also backfires a bit after a full throttle now, didn't use to do that.

Here's what I've done at this point, wondering which of the things I've tried to do right may not have been right...


Checking compression, it looks like of the 4 plugs, both rear are at 90, and both front are at 110.

I flushed and changed the coolant. I used a mixture of distilled water and cleaner, ran the bike for 5 min. Cooled down, then drained and filled with straight distilled water. ran it, cooled down, then filled with a 50/50 mix. Again, the smoke is black, and definitely doesn't smell good ;-)

New battery, I checked a couple wires between battery and engine, and a ratchet strap had melted! I ziptied a couple wires further out of the way.

When I cleaned the carbs, I tightened down both jets completely, I did not back off 1 5/8 turns (I know that mistake now...)

Lastly, I filled the tank with 92 and half a can of seafoam. Not sure if that would cause this or not. It ran on high octane before OK, but I've been reading that our bikes perform better with 87. I'll refill with that.

Any ideas???
 

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Black smoke from the melted strap? Was there ever any black smoke from the tailpipes?

When checking compression on this engine, you only need to do one plug on each cylinder. 10% difference between all cylinders is acceptable on any engine, but yours is only down slightly on one cylinder.

Adjusting the air screws out to 2 1/2 might help with the backfire. Don't crank the screws tight, that can bend the tip of the screw. Just touch bottom and back off.

87 octane is best, 93 will only hinder it.
 

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Discussion Starter · #9 ·
Black smoke from the melted strap? Was there ever any black smoke from the tailpipes?

When checking compression on this engine, you only need to do one plug on each cylinder. 10% difference between all cylinders is acceptable on any engine, but yours is only down slightly on one cylinder.

Adjusting the air screws out to 2 1/2 might help with the backfire. Don't crank the screws tight, that can bend the tip of the screw. Just touch bottom and back off.

87 octane is best, 93 will only hinder it.
Thanks Sprockster, will do. But the pilot screws couldn't be causing the smoke right? If it's running rich. I think I'll take the gas tank back off and see if I inadvertently pushed a hose or wire to close to the engine. Maybe?

No smoke from the tailpipes, only under the tank
 

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When I do a compression test I pull both plugs for each cylinder I get 165 and 170 . If you do it with only one cylinder plug pulled I think that’s why your getting the low compression
 

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When I do a compression test I pull both plugs for each cylinder I get 165 and 170 . If you do it with only one cylinder plug pulled I think that’s why your getting the low compression
I don't understand the benefit of pulling both plugs on the same cylinder. ??
 

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Discussion Starter · #13 ·
FINAL UPDATE:

I just love diagnosing... LOL

I found the stator 3 wires routed real close to the engine, the rachet ziptie was melted, and the couplers were starting to melt. Moved the wires away and black smoke is gone.

Of course, then the smoke magically turned into white steam, lol (It was there all along but couldn't see it or smell it past the burning plastic! Also coolant was leaking a bit from the top.

I pulled the tank off this morning and found one radiator hose had a loose hose clamp. I never tinkered with the hoses, but nonetheless tightened it back up and leak and steam is gone. Running pretty well (other than my needed carb adjustments for later.)

I'll close this thread now, as my other issues are of a R/R and Stator nature...

Thank you for you help!
 

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I don't understand the benefit of pulling both plugs on the same cylinder. ??
I did my compression check a long time ago when i just pulled one plug i got 90 lbs when i pulled both plugs i got 160 lbs the specs call for 165 to 170 lbs i just followed the instructions in the factory manual. I will look up again and see mif what ia nmtelling you is correct
 

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I did my compression check a long time ago when i just pulled one plug i got 90 lbs when i pulled both plugs i got 160 lbs the specs call for 165 to 170 lbs i just followed the instructions in the factory manual. I will look up again and see mif what ia nmtelling you is correct
Thanks. I'll also take a look in the manual, but it seems like if you pull both plugs, all the pressure will escape from the empty hole. Unless you use two gauges.
 

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I drilled a hole through my piston head and it doubled my compression.
Thanks. I'll also take a look in the manual, but it seems like if you pull both plugs, all the pressure will escape from the empty hole. Unless you use two gauges.
 

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Ok, got a PM from Buddy, then also had a look at the manual.

First, the manual gives a range of 129-199 psi for compression.

Second, you're supposed to hold the throttle wide open when taking a reading.

And third, they want you to remove both plugs from the cylinder not being tested. This will allow the starter to turn faster.
 
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