Cylinder Compression Question - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 7 (permalink) Old 08-30-2016, 09:17 PM Thread Starter
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Cylinder Compression Question

Hi All,

I just bought a 95, 750 V-Twin. 11,461 original miles. No leaks, ran great for a couple weeks. Coming back from a ride I noted a power loss and a little bogging. I've been reading through the forums and have eliminated;

Timing
Battery
Rectifier & Stator
Plugs & Wires...

I am convinced at this point it is a carb/fuel supply issue (namely to the rear cylinder). But before going all the way and tearing it down (which I know I'm going to anyway, but can't at this time) I did a compression test on each cylinder. Throttle open, wires removed from all four plugs and cranked it over and tested front and rear.

Spec in the book says 122 to 199 psi. I got 110 on both front and back. She still runs fine on the one cylinder (for running one one cylinder) so I don't believe compression is a major player in the problem here and am still leaning towards the carbs. However, my question is - how bad is 110 (particularly since both cylinders read identically)? I'll eventually do the leak-down test, but in your opinions, is it safe to go with the carbs for now and then do what will probably be an overhaul come winter and still put mild commuter miles on it for now? If all were perfect circumstances I'd probably just tear it down, but I need the wheels for a short time longer before I can do that.

Thoughts please?

Thanks in advance!
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post #2 of 7 (permalink) Old 08-30-2016, 10:28 PM
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You're fine on compression. Consistent readings on all cylinders is more important than specific numbers, within reason. I've seen many stock engines running fine with compression readings close to 100 psi.

Good bet that it's the carbs. Tried seafoam yet? Not a cure for all problems but it can help as long as fuel is flowing.

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post #3 of 7 (permalink) Old 08-30-2016, 11:04 PM
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Is rear cylinder flooding? Are plugs wet?could be dirty float needles
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post #4 of 7 (permalink) Old 08-31-2016, 10:03 AM Thread Starter
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I have not tried the Seafoam yet - but am willing to give it a shot. - Thx!

The rear plugs are (were) burning a bit hot I think - carbon build-up on the metal post, clean element, tan color with a little darker brown on the ceramic but not major. Btw - thanks for the welcome msg!
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post #5 of 7 (permalink) Old 08-31-2016, 10:46 AM
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Tan/Brown means it's burning fine.white is lean.how's the front cylinder?re-read post.the ceramic is brown?the element on the very bottom of the plug(where the spark jumps from)should be tan,not black or white

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post #6 of 7 (permalink) Old 09-02-2016, 04:16 PM Thread Starter
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Front cylinder plugs both in good condition. I'm tearing the carbs apart this weekend for a rebuild, then I'll sync them and make a run. Hoping the problem will be cured. Btw - I'm replacing all four plugs with NGK's. Can't decide if I want to go with the Iridium ones or not.
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post #7 of 7 (permalink) Old 09-03-2016, 08:23 PM Thread Starter
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Okay! So, it turns out I have a "California Model" with all that wonderfully useless crap in the way. Even with the Clymer manual and videos for reference, it took me 3 solid hours to get the carb out. I'm worn out at the moment and am going to wait till tomorrow to tear down the carb, clean and rebuild. I did decide to go with the Iridium plugs since everything I read, and a friend who is a master mechanic, basically all said you can't go wrong with them.
Once I've got the carbs cleaned and rebuilt/installed, I'll sync them with the standard NGK's I'd already bought - then install the iridiums and do some math. I'm curious to see what happens and plan to post the results when all is said and done.
Thanks everybody for the help so far! Much appreciated!!!
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