Rear Cylinder Problems? - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 6 (permalink) Old 08-22-2011, 10:02 PM Thread Starter
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Rear Cylinder Problems?

I just bought a VN750 that I knew had an issue, but I couldn't pass it up because it was almost free. The bike runs and I can ride it. I have risen it about 15 miles since I bought it yesterday. I am planning to take it to the Kawasaki dealer nearby to have them check it out, but decided to do some basic troubleshooting until I take it to them. Also bear in mind, this is my first bike and I have no experience working on them.

So here is the problem. When I am riding and it is below 2200 rpm it seems to stutter, once I get it up above 2200 it rides just fine. Also when you cross the 2200 mark there is a sudden increase in power. Other than this issue, the bike runs great. Once above 2200 rpm this bike has a ton of power!

I decided to pull the plug wires to make sure I was getting a spark on each of them. This checked out fine as they all are generating a spark. However, when I pull the plugs on the rear cylinder there is no change in the engine. In other words, its as if the rear cylinder isn't working. Keep in mind this is at idle. This could explain the sudden increase in power at 2200 rpm, as I am guessing this is when the second cylinder kicks in and starts working. When I pull a plug wire from the front cylinder, you can here the difference just as you should.

Earlier today, I thought it may be a carb issue so I put some Sea Foam in the tank when I filled it up. I did notice a mild improvement, but I checked the plug wires after I had ran that through.

Anyone have any ideas on what may be the problem or any further troubleshooting steps to take?

Thanks,
browngd
'93 VN750
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Last edited by browngd; 08-22-2011 at 10:06 PM.
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post #2 of 6 (permalink) Old 08-23-2011, 01:37 AM
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Your rear carb is flooding the rear cylinder. I had the same exact issue with mine, idled rough, but when I got on the throttle and got it above 2500 rpm's it would take off.
I drained the bowl on mine, and it went away. Had a little bit of crud in there.
On the bottom of each carb bowl, there is a screw, you turn it counter clockwise slowly until gas starts coming out, and let it drain good.
Gas is flammable as you know, so please don't do it on a hot engine.
Another thing to do is change the spark plugs to a set of Irridiums. They are more expensive, but well worth it. I don't remember the part number of the plugs, but someone on here will chime in and let you know.
This forum is full of good mechanics and knowledgeable people who will help out all they can.
Welcome to the forum.
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post #3 of 6 (permalink) Old 08-23-2011, 04:26 PM Thread Starter
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Thank you. I decided to try this but am running into some difficulty. The only screw I can find near the bottom of the bowl is some sort of allen screw or something. I can't seem to find anything that will fit. Is this the right screw and if so what do I use to open it up?
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post #4 of 6 (permalink) Old 08-23-2011, 04:39 PM Thread Starter
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Well, I found the drain nipple and the screw I am looking at is the correct one. I got the front carb drained and it came out clear with nothing in it. However, the one for the rear is a different story. Loks like the PO tried to do this and he stripped out the drain screw. Anyone have any ideas on how to get this screw out easily? The screw is an allen type screw so at this point it's pretty rounded off. I can't think of anything that is going to get this out. Looks like I may be looking at a major expense for a mechanic to get this screw out. This is the carb that is giving me the problems as well. Thanks!
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post #5 of 6 (permalink) Old 08-24-2011, 10:39 AM
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A screw extractor the correct size might work. Can you reach it with Vice Grips? Be sure to hit it with penetrating fluid and let it soak overnight. I'd also give it a good rap with a hammer before trying to remove it.

I'm keepin' all the left over parts. I'm gonna use 'em to build another bike!
_____________________________________________
"Black Beauty"
1989 VN750 acquired December, 2008, 6,711 miles
Currently 23,298 miles

Old Blue
2001 Honda CMX250 Rebel acquired July, 2008

1987 VN750 project bike, acquired August, 2009, 33,000 miles and balancer sticking out of the case, currently awaiting attention and parts
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post #6 of 6 (permalink) Old 08-24-2011, 05:01 PM
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Quote:
Originally Posted by flitecontrol View Post
A screw extractor the correct size might work. Can you reach it with Vice Grips? Be sure to hit it with penetrating fluid and let it soak overnight. I'd also give it a good rap with a hammer before trying to remove it.
Vise grips won't reach; the internal hex drain screw is recessed. A screw extractor may work. If the two screws holding that bottom plate (jet chamber cover) that the drain is in are hex head, it's a 7mm wrench and a bit of patience to get it off; clamp it gently between some thick rags in a vise, and work on the drain screw off the bike. If those screws are round Phillips head, it's a bit more involved, and a lot more patience; right angle screwdriver, or a box end 1/4" wrench and a screwdriver bit will get those out. If they're the round ones, and too tight, you may need to persuade 'em with a pair of small needlenose vise grips.

Jim

J.D.
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