carbs cleaned and replaced, engine bogs, won't go faster than 70km/h - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
Carbs and Fuel System
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post #1 of 10 (permalink) Old 06-08-2015, 01:47 PM Thread Starter
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carbs cleaned and replaced, engine bogs, won't go faster than 70km/h

Please help, I'm at the end of my rope. I had a stuck float valve so with the help of a friend, a former GM engineer, we pulled and cleaned the carbs. That was not a fun job! Once replaced, the bike idles fine (is still tough to cold start) but once driving is powerless and has terrible throttle response. I drove it home and could get no faster than 70 km/h at full throttle.
My engineer friend thinks that the float levels need to be adjusted as the fuel supply isn't keeping up with the demand however I called a local shop, feeling a bit overwhelmed, and they insist that its internal to the carbs and say that they must be pulled again...at $85/hour. The bike while driving will rev to about 5000, but will spike higher while sitting but only in short bursts.
Any thoughts on this? I'm about ready to set fire to this bike; nothing but problems....

86 VN750
Completed mods:
Custom solo seat
side mirrors
Windsheild
Bars, grips and end caps
side-mounted tail light with plate bracket
Reshaping, shortening rear fender
Paint
V&H exhaust

Projected mods:
rear indicator lights
shifter arm

Lots of polishing!
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post #2 of 10 (permalink) Old 06-08-2015, 02:36 PM
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Question

Does sound like weak fuel delivery.

Chance it could be float level, that can be checked with the carbs on the bike (different procedure than most carbs). Do you have a repair manual? Can download one if you need it.

Could still be dirt in the carb(s) or a petcock flow problem (check for flow from tank and each carb supply hose). Either could contribute to cold start trouble, as would clogged enrichers (choke), since we don't have a butterfly choke.

How are the slides and diaphragms, were they tested? Lift slide by hand, drop, listen for the air/vacuum sound. The slide shouldn't slam shut, but close with slight resistance from the diaphragm. (can test this on the engine) If the diaphragms are leaking they won't correctly lift the slide needle, which meters in more fuel as the throttle opens. The rubber can crack inside the grooves where they flex, sometimes hard to see. Also, if they don't fit right on the top plate, the diah. can leak pretty easy too.

Were the carb bodies soaked at all or just sprayed?

Make sure the carb vent hoses are open and in dead air space.

2003-21k mi
Shaved w/UniPK92+Stock Jets-TPE/MOSFET-Shinko Tires-AGM batt-bags-chrome-LEDs...more
__________________________________________________ ____________
Repair Manual: http://www.mediafire.com/file/mj7z81..._Catalogue.pdf

Owner's Manual: http://www.mediafire.com/file/nscb5f...ers+Manual.pdf
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post #3 of 10 (permalink) Old 06-08-2015, 03:00 PM Thread Starter
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The carbs were soaked for two weeks while I was busy with other things. The fuel lines and vent hoses from the petcock and T are all new as are the ring seals to the float chambers and the float valves themselves. We finished cleaning the float chambers and valve tubes with 00 steel wool and q-tips but didn't take them any further apart. At dissasembly one of the float valves was siezed open so we thought that was the culprit. No leaks now.
As for the diaphram, I'll check that later as with the vent hoses to ensure no pinches (we cut them from bulk stock and may be longer than OEM). I have the manual and will take a look at the float levels once I figure out how to do that.
Thanks for the help, really, much appreciated.

86 VN750
Completed mods:
Custom solo seat
side mirrors
Windsheild
Bars, grips and end caps
side-mounted tail light with plate bracket
Reshaping, shortening rear fender
Paint
V&H exhaust

Projected mods:
rear indicator lights
shifter arm

Lots of polishing!

Last edited by north115; 06-08-2015 at 03:02 PM.
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post #4 of 10 (permalink) Old 06-08-2015, 06:21 PM
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Not sure, but it sounds like the jets maybe were not removed for cleaning?

Also verify good flow from both petcock outlets.

2003-21k mi
Shaved w/UniPK92+Stock Jets-TPE/MOSFET-Shinko Tires-AGM batt-bags-chrome-LEDs...more
__________________________________________________ ____________
Repair Manual: http://www.mediafire.com/file/mj7z81..._Catalogue.pdf

Owner's Manual: http://www.mediafire.com/file/nscb5f...ers+Manual.pdf
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post #5 of 10 (permalink) Old 06-08-2015, 07:37 PM
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If you ear shave it getting your carbs out will be way easier... What did you soak them in for two weeks? My carb cleaner will evaporate over night unless you close the container... I would try taking the vent off at least for now and pulling the petcock to make sure it's not clogged up then double check fuel and vacuum hose, the vacuum on the right side should be plugged
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post #6 of 10 (permalink) Old 06-08-2015, 08:13 PM Thread Starter
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Spockster, correct the jets weren't removed for cleaning. I knew nothing about carbs when I started out on this job which is why I had the friend helping. Following his lead, I didn't know enough to do the jets as well.
I read up on checking the float levels...right up to the part where you have to pull the carbs out again to bend the float arm in order to change it.
Looks like I have no choice but to pay a pro to sort out the mess for me :-(

86 VN750
Completed mods:
Custom solo seat
side mirrors
Windsheild
Bars, grips and end caps
side-mounted tail light with plate bracket
Reshaping, shortening rear fender
Paint
V&H exhaust

Projected mods:
rear indicator lights
shifter arm

Lots of polishing!
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post #7 of 10 (permalink) Old 06-08-2015, 08:27 PM
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You don't need a pro for carb work look up mrmaxstory on YouTube to learn about carbs and then read up a little with a service manual, plenty of ppl on the forums will help you but don't be afraid to take it apart and find out what it all looks like only thing you need to be careful with is the diaphragms and the floats but you already know float work so your good the rest is cheap to fix
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post #8 of 10 (permalink) Old 06-08-2015, 09:55 PM
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I soaked my jets and the jets still were clogged. I used a welding tip cleaner and literally had to drill like action to get the low jet unclogged. They were so bad that I thought I was going to have to replaced them. Finally got them cleaned and resoaked them;. Ran great when I put it back together.

Grace and Peace to you!
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post #9 of 10 (permalink) Old 06-09-2015, 10:33 AM
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Word of warning - brass Jets and aluminum passage ways are soft, and it is not recommended to clean these places with anything abrasive. Doing so could remove material from the Jets or passageways, causing a different flow profile.
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post #10 of 10 (permalink) Old 06-09-2015, 06:53 PM
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Quote:
Originally Posted by mrseedsower View Post
I soaked my jets and the jets still were clogged.
I'd bet it's your jets too, if you didn't pull them out and clean them.

"Show me a man who makes no mistakes, and I'll show you a man who doesn't do things." Theodore Roosevelt."

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