Mikuni Carb Conversion - Steve Saunders Goldwing Forums

 
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post #1 of 9 (permalink) Old 03-29-2019, 07:24 AM Thread Starter
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Year: 1977
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Model: GL1000
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Question Mikuni Carb Conversion

Hi All,
Thanks in advance for your input. Last week I purchased a 1977 GL1000 with 32K miles on it. I am trying to decide if I should keep the carb conversion or switch back to stock carbs. Asking for your advice.

The bike has the Dyna Ignition upgrade and carb conversion "VM26 Mikuni Carbs with accelerator pump (4 Mikuni Carbs)". From with I can tell everything else seems stock. The bike is in above average condition. The bike idles well and accelerates great but awful with everything else induction wise. It surges and has a slight misfire during steady state riding, backfires on deceleration, plugs are wet and dark so I'm thinking it is running rich and takes 3-5 seconds to return to idle after letting go of the throttle. I think the last issue is because the linkage to the right bank of carbs has a lot of slop in it or misadjusted. One thing about the setup is it takes some effort to twist the throttle off idle but suddenly gets easy causing an overrev - no amount of throttle finesse seems to prevent me from doing jack rabbit starts.
In the last four years the bike has been through 3 owners - I am number 4. Only 50 miles has been put on the bike since early 2015. The previous two owners sold it because they could not sort out these problems. BTW - I'm assuming this is a carb tuning/repair issue not the Dyna upgrade or some other issue.
So should I put my resources into sorting out the Mikuni carbs or start searching for a stock assembly? I am OK with rebuilding carbs but not sure I can handle sorting out these problems. I searched online and have not found any info on this carb conversion. Has any of you heard of a Mikuni VM26 conversion?
One last question. If I swap out the Mikuni carbs is there a market for this upgrade - can I sell the kit online?
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post #2 of 9 (permalink) Old 03-29-2019, 09:40 AM
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That is something I never heard of. Mikunis are way simpler carbs than Kehins & usually work pretty well but tuning them to that engine may take some work.

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post #3 of 9 (permalink) Old 04-01-2019, 02:52 AM
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That is a new conversion to me and i think it would be wery hard to make this to work correct .
Imho the stock setup is the best .

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post #4 of 9 (permalink) Old 04-01-2019, 03:23 AM Thread Starter
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Thanks DavO430 & SMEDEN,
I am still sorting this out but I think I will source and install a stock carb assembly. This will allow me to determine if everything on the bike is in working order then I may reinstall this Mikuni carb assembly and have a go at tuning. I know very little about the history of this bike so I could be chasing my tail due to unknown problems. Also since the bike has sat idle for many years I will have to rebuild the Mikuni's regardless.
I wanted a quick fix so I can get this bike on the road again - just don't like it when machines are not in working order. But this is looking like a long term project which is not really a problem.


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post #5 of 9 (permalink) Old 04-01-2019, 06:10 AM
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GL1100 carbs work well on 1000s and are probably easier to find, and are a little simpler, if you are not trying to go back full original.

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post #6 of 9 (permalink) Old 04-01-2019, 08:34 PM
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Are they slides in the Mikuni carbs or throttle plates, vacuum dampened, or directly lifted? The OEM had throttle blades and the slides were opened by vacuum by a diaphragm. This kept the throttle opening smooth and made the take off less jack rabbit like. I had a cycle innovations conversion, an my 1100. It had an aluminum plenum that dropped into the space between those rubber sleeves in you image. Just had a single barrel Holley carb, much like one that would have been found on an early 60s Ford 170ci 6 cylinder. Cycle Innovations had them specially made with a spool for the throttle cable, and a 3 layered primary booster venturi, to give it a smooth transition from idle to high speed circuits. I gained 1mpg and lots of bottom end torque, would really scoot when you got after it. Only drawback was carb/intake icing on cool damp days, but once the cooling system got warm, it went away because all the heat from radiator was dumping on the intake and carb. The single carb was awesome, set it once, never adjusted again. I had it on there for 14 years, with no problems.

Finding an acceptable carb for a DYI conversion could be tough, gotta look for something pre-emision, maybe solex, Early Datsun pickup, something around 1800cc engine.
Maybe even a progressive 2bbl. with vacuum secondary. The intake plenum could be fairly easily made. Just a box with 4 runners, single plane.
I never cared for the 4 carb setup, I would OH the carbs, set it up with manometers, and next time I road it, everything was Fubar.

MGK
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post #7 of 9 (permalink) Old 04-01-2019, 11:18 PM
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Somebody went to a lot of trouble to set up that rack of carburetors. For my 2 I vote for the stock carburetors. Everything else being equal, these bikes are pretty simple. If the engine has proper compression, the timing is correct and the spark is hot, the only thing left is the carburetors. There is a reason Honda went with individual carburetors for each cylinder. Get a set of 1000/1100 carbs, rebuild them using the Randakk kits, make sure every passageway blows clear air, make them pass the straw test, and balance them with a manometer. You will be happy with the results. Or maybe you can make the Mikunis work.

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post #8 of 9 (permalink) Old 04-02-2019, 08:36 AM Thread Starter
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If I installed a GL1100 carb assembly on a 1977 GL1000 would I use the GL1100 stock jetting, etc? Would ignition timing stay stock GL1000?


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post #9 of 9 (permalink) Old 04-02-2019, 01:41 PM
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Quote:
Originally Posted by bweber111 View Post
If I installed a GL1100 carb assembly on a 1977 GL1000 would I use the GL1100 stock jetting, etc? Would ignition timing stay stock GL1000?
Yes & yes.

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