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Having trouble with Mikuni VM29 Smoothbores 02 Aug 2016 16:41 #737143

  • zukdave
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Smooth bore's don't have a ood idle system plus running them on a small motor you will get a weak idle signal
and will need a pilot jet way bigger then you think. Sudco list's a 25 pilot and a 125 main as a starting point for a 750 cc motor.

Mine on my 810cc GPz750 motor I'm at a 22.5 pilot and 125 main clip in the middle slot and I get some poping on decell
if I pull the baffle.
1980 KZ650 F1
ZX750A1 motor.
Wiseco 810cc kit.
Zukiworks racing ported head.
VM 29 smooth bore's.
Dyna 2000 Ign. w/Dyna mini coil's
APE cylinder stud's and nut's.
APE valve spring's.
APE Track King clutch.
V/H KZ1000 sidewinder.
3.5x18 laced to a KZ1000 disk hub.
150/60/18 Shinko 006 Podium.
63" wheel base.
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Last edit: by zukdave.

Having trouble with Mikuni VM29 Smoothbores 03 Aug 2016 22:49 #737356

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I finally figured out what was going on with my float levels and I'm kind of embarrassed it took me as long as it did. Almost all the sidewalls on the brass floats were collapsed in and concave. I'm not sure how this happened but it's how I received them from the P.O. and I thought it was just how they looked until now.After I bought all new float valves /needles and was still getting too much fuel in some of the carbs (even with the tangs maxed out) I too a closer look at the floats themselves

Once I figured out that the floats were crushed I set out to try and fix em. I used a soldering gun to melt off the little plug on the inner wall and I shot some air at the opening with my air compressor. Sure enough they plumped up and after soldering the plugs back look good as new. After I checked them for any leaks I installed them, bench set them to 23mm and tested the fuel levels with the clear tube method. They're all at about 4mm below the gasket surface now. Here are some pictures of before and after the surgery.

Attachment IMG_1215.JPG not found



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1977 KZ650B
KZ750H Motor Installed
gpz750 Intake cams Kz750 Exhaust Cams
VM28SS Mikuni Pumper Carbs
Elecrosport Stator and Regulator Rectifier
Dyna 3ohm coils
Derale Oil Cooler
4into1 delkevic Pipes
Pod Airfilters
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Having trouble with Mikuni VM29 Smoothbores 03 Aug 2016 23:37 #737357

  • Dirtyhands
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Thank you Zukdave I switched over to a 125 main and 25 pilot. I'll see how it goes tomorrow before work
1977 KZ650B
KZ750H Motor Installed
gpz750 Intake cams Kz750 Exhaust Cams
VM28SS Mikuni Pumper Carbs
Elecrosport Stator and Regulator Rectifier
Dyna 3ohm coils
Derale Oil Cooler
4into1 delkevic Pipes
Pod Airfilters

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Having trouble with Mikuni VM29 Smoothbores 04 Aug 2016 06:05 #737378

  • Patton
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Dirtyhands wrote: . . . tested the fuel levels with the clear tube method. They're all at about 4mm below the gasket surface now . . . .


Well Done! :cheer:

Good Fortune! :)
1973 Z1
KZ900 LTD
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Having trouble with Mikuni VM29 Smoothbores 04 Aug 2016 17:24 #737442

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Alway's better to start fat on the jetting and take fuel away then
start lean and burn it up chasing the right jetting.
1980 KZ650 F1
ZX750A1 motor.
Wiseco 810cc kit.
Zukiworks racing ported head.
VM 29 smooth bore's.
Dyna 2000 Ign. w/Dyna mini coil's
APE cylinder stud's and nut's.
APE valve spring's.
APE Track King clutch.
V/H KZ1000 sidewinder.
3.5x18 laced to a KZ1000 disk hub.
150/60/18 Shinko 006 Podium.
63" wheel base.

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Having trouble with Mikuni VM29 Smoothbores 06 Aug 2016 22:18 #737686

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Whelp, I took the bike for a quick 5 mile ride this morning before work and took a peek at the plugs when I got home. Same deal 1 and 2 look lighter and 3 and 4 are sooty black. I'm about ready to throw in the towel on the VM29s or at least buy a set of used stock carbs to see if the problem persists when I switch carbs. I may switch the components over from 1 to 4 to see if the problem moves then. What else could it be? This problem has been with me since I got the bike and I've Bought new coils, updated the entire electrical system, rebuilt the entire top end (including using a new head and cam set up) Cleaned, bench synched and set float heights on the carbs multiple times. I feel like the problem has got to be in the carbs some where but I'm just stumped. If I buy some used carbs are kz650, kz650, gpz750 and others pretty interchangeable? If so what are some of the best kind to look for ?
1977 KZ650B
KZ750H Motor Installed
gpz750 Intake cams Kz750 Exhaust Cams
VM28SS Mikuni Pumper Carbs
Elecrosport Stator and Regulator Rectifier
Dyna 3ohm coils
Derale Oil Cooler
4into1 delkevic Pipes
Pod Airfilters

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Last edit: by Dirtyhands.

Having trouble with Mikuni VM29 Smoothbores 07 Aug 2016 07:25 #737695

  • SWest
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Try adjusting the float level with the bike on the centerstand.
Steve

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Having trouble with Mikuni VM29 Smoothbores 07 Aug 2016 08:05 #737698

  • Patton
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Compression test results (especially cylinders #3 and #4)?


Is choke circuit malfunctioning whereby enrichment circuit fails to fully close when supposed to be fully closed?

Is choke required to start cold engine?

Have carb float repairs failed (especially carbs #3 and #4)?

Are carbs properly bench-synced?


Using brand new B8ES plugs,is there healthy fat blue spark on plugs #3 and #4?

Could experiment by test running with hotter running B7ES plugs in cylinders #3 and #4.

Possibility of broken oil ring (perhaps when installed) could allow crankcase oil into the combustion chamber while the engine is running.
Is smoke visible from the exhaust:
• When cold engine first cranked?
• During initial riding pullaway after starting a cold engine?
• On acceleration with warm engine?
• On deceleration with warm engine?

Good Fortune! :)
1973 Z1
KZ900 LTD

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Having trouble with Mikuni VM29 Smoothbores 07 Aug 2016 08:08 #737699

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Would also check the BS30-97 jets.



Good Fortune! :)
1973 Z1
KZ900 LTD
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Having trouble with Mikuni VM29 Smoothbores 07 Aug 2016 08:27 #737701

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After I get mine going again I'm gonna try 22.5 pilots and 122.5 mains.
1978 KZ650 b-2
700cc Wiseco kit 10 to 1.
1980 KZ750 cam, ape springs, stock clutch/ Barnett springs.
Vance and Hines Header w/ comp baffle and Ape pods, Dyna S and green coils, copper wires.
29MM smooth bores W/ 17.5 pilots, 0-6s and 117.5 main
16/42 gearing X ring chain and alum rear JT sprocket.

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Having trouble with Mikuni VM29 Smoothbores 07 Aug 2016 10:27 #737713

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Yes Swest I set the float levels with the centerstand. I even put a wood block under the front wheel and checked the carbs with a little level.


Patton- I will try to get some compression numbers in the next couple days , after that I will be away for a few weeks. I would be surprised if those cylinders are off since this is a problem that existed before the top end rebuild I did where I replaced the rings and honed.
I'm going to look closer at the choke mechanism. I installed new orings in all the choke plungers but maybe something else is going on. I use the choke to start the cold engine but turn it off almost immediately
I have quadruple checked the float levels. They all sit at 4mm below the gasket surface
I bench synced the carbs using the wire method on the forum. They were a bit off before I did this but I believe are squared away now. I will double check next time the carbs are off.
The spark is healthy and blue in all cylinders. This issue has actually followed me after putting new coils and wires on the bike. I've switched back and forth between B7ES and B8ES plugs as well
'I have not noticed any smoke. I
1977 KZ650B
KZ750H Motor Installed
gpz750 Intake cams Kz750 Exhaust Cams
VM28SS Mikuni Pumper Carbs
Elecrosport Stator and Regulator Rectifier
Dyna 3ohm coils
Derale Oil Cooler
4into1 delkevic Pipes
Pod Airfilters

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Having trouble with Mikuni VM29 Smoothbores 07 Aug 2016 11:25 #737716

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I'm toying with the idea of just getting another rack of carbs while I'm away so they're waiting for me when I get back. If not only to see if the problem persists. How are the pumper carbs?
1977 KZ650B
KZ750H Motor Installed
gpz750 Intake cams Kz750 Exhaust Cams
VM28SS Mikuni Pumper Carbs
Elecrosport Stator and Regulator Rectifier
Dyna 3ohm coils
Derale Oil Cooler
4into1 delkevic Pipes
Pod Airfilters

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