Well fix one problem then move on to the next - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
Carbs and Fuel System
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post #1 of 5 (permalink) Old 07-17-2008, 11:39 PM Thread Starter
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Question Well fix one problem then move on to the next

I'm looking for some advice on next steps. I've found and fixed a variety of issues with the carbs/fuel system thanks to the help and support from the folks here. Now on to the next issue. The last problem I was having was that the bike would occasionally hesitate/skip somewhere around 4000-4500 RPM while running in 4th or 5th gear. A couple of days ago, I found a crack in the vacuum hose to the carb, replaced the hose, and no more hesitation/skipping. However, since I replaced the hose, I noticed that once I get the bike near that same range, 4000-4500, the tach starts to jump around a bit; not terrible, but it is definitely not as rock solid steady as it was. It smoothes out again at around 5000. This happens when I am running steady on the highway. Then tonight when I was almost home, I had essentially just come off of the highway after about 25 miles of steady 65-70 MPH riding, stopped at a red light, the idle dropped suddenly, and if I didn't work the throttle the bike would stall. Once the bike got moving all was well, but as soon as I had to stop, the idle would drop and the engine would cut out. The second behavior that has been going on, is that the bike sometimes will idle momentarily at around 2000 then very slowly drop to the normal 1100 or so. Sometimes I can get the idle to drop right away by rev'ing a little then letting it return to idle, but not always.

I'm not sure if these are symptoms of the same problem, or multiple problems occurring at the same time. Based on what I have read I was thinking that the carbs might be slightly out of sync (the jumpy tach), but I don't know if that could also be the problem with the idle. I am guessing that the new vacuum hose could effect the sync, but I am not sure. I initially thought that the slowly dropping idle, which was happening before I noticed the jumpy tach, could be the result of a sticky butterfly valve in the carb(s), or sticky or out of adjustment throttle cables. I was also thinking that I could still have some junk floating around in the system that is gunking up the pilot jets causing intermittent idle problems (the stalling).

I'm not sure how to move forward. I don't have carb stix or a sync pro tool to check the sync. (and would prefer not to spend the bux! but I will if I have to) I was going to move the boots and spray the butterfly valves with carb cleaner, move them by hand to make sure they move freely, and finish it up with a bit of WD40 before putting the boots back on. Mostly I have it running around in the back of my mind that I could be completely off with my thinking. I just don't have the experience to back any of this up, and I really don't want to waste time chasing ghosts in the machine. So after a painfully long post, I would, as usual, welcome any and all suggestions as to the steps I should take to get this resolved. THANKS!!!

Chris
Wayne, NJ
1989 VN750-A5
VROC #27781
-Replaced/Fused Stator & Replaced/Relocated R/R (15K mi.)
-MF Battery
-De-Goated/Re-goated
-Coastered
-Splines Lubed
-Stebel Nautilus Horn
-AutoMeter 2" VOM
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post #2 of 5 (permalink) Old 07-18-2008, 09:02 AM
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Chris, you can make your own manometer for a couple o' bucks and it'll work just fine: http://www.powerchutes.com/manometer.asp That's what I've used in the past. Definitely sync the carbs and see if that clears up the problem, but it still sounds like there might be a vacuum leak somewhere.

C
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post #3 of 5 (permalink) Old 07-18-2008, 10:51 AM Thread Starter
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Cindy, Thanks for the link. I'm going to put one of these together tonight if I can get the parts. This saves me the $100 for the Motion Pro Tool. I'll check the sync to rule it out (or fix it!), then I guess I'll go back to the drawing board and check all of the hoses and connections for another leak.

Chris
Wayne, NJ
1989 VN750-A5
VROC #27781
-Replaced/Fused Stator & Replaced/Relocated R/R (15K mi.)
-MF Battery
-De-Goated/Re-goated
-Coastered
-Splines Lubed
-Stebel Nautilus Horn
-AutoMeter 2" VOM
-Silverstar Headlight
-Refinished Gauge Rings and Mirrors(Flat Black)
-Refinished Swingarm/Lubed Pivots
-K&S Turn Signals Clear Cover/Amber Bulb
-Kenda Kruz 110/90-19 front 170/80-15 rear
-Clear Alternatives LED tail light
-Plexifairing III
-Willie & Max Saddlebags and SissyBar Bag
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post #4 of 5 (permalink) Old 07-19-2008, 06:32 AM
 
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Definitely check and fix the carb sync problem if there is one. I would suspect the issue may be some trash in the idle circuit of the carb. Run some Seafoam in your next fill up and see if that helps. Put in half the can and then fill the tank. Usuallly this will break up any junk in the carbs, but if not you can try spraying some carb cleaner in each of the carb boots while the bike is running. Keep us updated.
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post #5 of 5 (permalink) Old 07-19-2008, 08:48 AM
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Chris
You can sync the carbs at idle or at any rpm.
I found that syncing the carbs at 4000-4500rpm helped smooth out the engine at highway speeds. That's the rpm my bike spends most of it's time, not at idle.

Glenn

1985 VN700
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