Problem with the rear cylinder - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 21 (permalink) Old 06-04-2012, 07:07 PM Thread Starter
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Problem with the rear cylinder

Hey guys I finally got around to getting my vulcan running that I bought in March, but have an issue. The bike starts and idles good, but taking it for a ride I found it was low on power. Now I'm coming from a 07 gsrx600 so I'm used to something quick, but thats not it, I'd be surprised if I could get the bike up to 70mph right now. The other day I realized after running the bike for a couple minutes the rear cylinder's exhaust was barely a little warm so i grabbed the front exhaust and damn it was hot. I checked spark and have it at both plugs. Pulling the plugs showed me that I was getting fuel, they were cleanish but wet with fuel compared to the front plugs. I swapped both the rear plugs with the fronts, started it and still no change. I thought maybe I had a weak coil so I swapped it with the front... still no change. Then I got to thinking the worst and maybe compression, tested it and is right in check with the front cylinder. I am running out of ideas.

Another symptom I have that may or not be related is a "knocking" sound coming from the rear head. I tried the Gambo trick but it didnt change the sound or help the rear cylinder.

The bike has 16,000 miles on it and its an 88 if this makes a difference, also when I put the new carbs on I also de-eared and rejetted. When I removed the airbox and installed the coasters, one bolt broke off in the head on the rear... right now I just have one bolt holding on the rear coaster and it is not sealing completely, could this cause a problem? My understanding is that it pushes air out of the head and into the exhaust through the valve which I removed, so I am thinking that it is not that urgent right now to drill and tap.

Sorry for the long post I am just running out of ideas, the only other thing I can think of is a rocker maybe popped off the intake but it doesn't look like the valve cover wants to come off with the motor in the frame Anyway any help is appreciated thanks
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post #2 of 21 (permalink) Old 06-05-2012, 04:00 AM
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Check for spark on the rear plugs. If you don't have spark make sure the back coil is getting power. If you do have spark it must be a fuel problem, likely too much. Make sure the enrichment valve "choke" isn't suck open. If a rocker was off the intake valve I wouldn't expect wet plugs.
I'm also very new to motorcycle maintenance so anything I said may be wrong. Hopefully one of the experts will chime in.

4/12/12 1st bike ever! 95 VN 750 13k
New plug wires
Iridiums
Coil relay mod
MCCT mod
Marbled
EPA stuff removed
Rear signals shaved
Shinko 170-110 oversized tourmaster tires
Splines lubed
Front signals relocated.
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post #3 of 21 (permalink) Old 06-05-2012, 07:56 AM Thread Starter
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Yea your probably right about the if the rocker was off the plugs wouldnt be so wet I didnt think about that. I do have spark in the rear for sure, I just thought maybe the coil was "weak" or something so thats why I tried to swap it. I also checked the choke and everything its moving as it should, at least on the outside of the carb
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post #4 of 21 (permalink) Old 06-05-2012, 05:34 PM
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Disconnect the vaccuum line on the rear carb. Plug the nipple with your finger. Has the niose stopped? Sometimes it is the air valve under the seat that makes a knocking noise.

02 honda sabre 1100
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post #5 of 21 (permalink) Old 06-05-2012, 07:58 PM Thread Starter
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I have that vacuum line capped off since i deleted the airbox and reed valve, It seems like the rear cylinder isnt firing at all..
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post #6 of 21 (permalink) Old 06-05-2012, 08:06 PM
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Spray some carb cleaner into that capped openning and see if you get a hit off the cylinder.

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post #7 of 21 (permalink) Old 06-05-2012, 09:33 PM
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Have you changed the ACCT to the MCCT, if not I wonder if the chain slipped making the timing off ? I'm new to this too with a 96 and have been reading alot about the chain tensioners.
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post #8 of 21 (permalink) Old 06-05-2012, 10:47 PM Thread Starter
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Quote:
Originally Posted by niterider View Post
Spray some carb cleaner into that capped openning and see if you get a hit off the cylinder.
Ok I'll try that out


Quote:
Originally Posted by dirtdemon718 View Post
Have you changed the ACCT to the MCCT, if not I wonder if the chain slipped making the timing off ? I'm new to this too with a 96 and have been reading alot about the chain tensioners.
I was thinking that but if the chain slipped my compression should be showing it
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post #9 of 21 (permalink) Old 06-06-2012, 05:21 AM
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In the OP you said "new carbs". You think maybe the rear carb might have a sticking float? You might drain both carbs into identical containers and compare the amount of fuel, or since the ears are gone just see if you smell gas in the rear air filter. When I got my bike it had a stuck float along with black plugs in the back and the identical pathetic performance you describe. One you get the other half of your engine running you will be amazed at how peppy it is.

4/12/12 1st bike ever! 95 VN 750 13k
New plug wires
Iridiums
Coil relay mod
MCCT mod
Marbled
EPA stuff removed
Rear signals shaved
Shinko 170-110 oversized tourmaster tires
Splines lubed
Front signals relocated.
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post #10 of 21 (permalink) Old 06-06-2012, 08:43 AM
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I had similar problems with mine and after cleaning and di-electric greasing all the connections and installing iridium plugs the problem was solved.
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