Mikuni for a JD?

[Eric]

Hi,

You can ask to Valand who used modern carb on JD.
The link : http://thepowerslidingsidecar.blogspot.fr

[BoschZEV]

You can ask to Valand who used modern carb on JD.

Thanks for the link. I see you are in France. I was there on a short trip last week. The police were more visible than normal, especially at CDG airport.

[Frankenstein]

Here's a link to 45 restoration's page on carbs, this should help.
http://www.45restoration.com/Departm...etor-Kits.aspx
Reputable operation, in Albany, NY area. They fixed me up with a kit for my first UL conversion, years ago.
DL

[BoschZEV]

Here's a link to 45 restoration's page on carbs, this should help.

Thanks very much for that. I've forwarded the link to my friend. Even though it's for a different model it help identify the required size of a Mikuni VM.

[Frankenstein]

Just judging by engine parameters such as working power range and output power, I think the carb offered for the 45 solo would be a very good starting point. The main jet might need adjustment, but I'd bet that if one bolted that carb on a JD, it would start, idle, run reasonably well with no more than a twist of the idle mixture. High speed running could be checked to adjust the main jet, and maybe an adjustment to the mid range needle might tweek performance a little.
I should warn you and your friend that I'm quite biased towards these carbs because of their ease of tuning and reliability. I converted 15 years ago on my fleet, ('37ULH, 47OHV, 65FL, and '61conglomerate). I traded up from the DC Linkert series, which are a good carb. I get equivalent performance and better mileage, which says to me that fuel utilization is superior.
Also, that ancient ritual of "priming kicks", a ceremony that kowtows to the shortcomings of the carburetion system, is eliminated, due to the effective enrichening circuitry for starting the Mikuni employs.
Well, I've said my piece, choose as you will :-)
DL

[BoschZEV]

Just judging by engine parameters such as working power range and output power, I think the carb offered for the 45 solo would be a very good starting point.

Thanks very much for your input on this. I wouldn't say I've analyzed it in sufficient depth as yet, but it appears to me that the 34 mm Mikuni that site sells for the 45 is a bit too large for the task, which would mean it isn't as responsive as it could be at low rpm. And, since the 45 is a flathead, there is not such thing as high rpm where larger would help (albeit, only a little).

The 45 has 737 cc, i.e. 385 cc per cylinder. Since the two pistons are almost out of phase it's almost as if they are separate single-cylinder engines so two carburetors of the same size on that engine would be nearly the same as one. For comparison, the flathead, single-cylinder BSA M20 used only a 1" (25 mm) carburetor for its 500 cc, and the 600 cc M21 only increased that to 1-1/16" (27 mm).

As another comparison, for the first 5 years the 350cc Road model 350cc BSA Gold Star used 1-1/16" (27 mm) and throughout its production the higher performance Clubman version of the 350 cc used 1-3/16" (30mm). Those OHV bikes would have much better breathing than either a flathead 45 or ioe JD.

Anyway, as I said, I wouldn't say I've done anything like a complete analysis yet but it seems to me a 30mm Mikuni, or even a 28 mm, would be best for a 1000 cc JD. Faster air flow results in a bigger signal to the jets and thus better response. The tradeoff of slightly restricted performance at 6000 rpm wouldn't be relevant for any engine that only sees beyond 4000 rpm in its dreams.

I well could be wrong, and I hope someone corrects me if I am. But my real hope is someone steps forward who has committed this Mikuni atrocity on his ioe Harley and spent the time to sort out the jetting. It would save lots of time and knee-replacement surgeries to know what jets they arrived at.

[NUMO]

Mikuni for a Harley JD

OK, we put a Mikuni on a JD chopper that we built last year. It was bought from V-Twin. It is a 32mm, suited for a 45". Fixed jet with the needle set on the center slot. Note: The chopper starts easy and runs great. With a 4 speed transmission it cruises at 70mph. Hope this helps. http://youtu.be/nC5q5EU-clI http://youtu.be/Gz0Lsxvem5U

[BoschZEV]

It was bought from V-Twin. It is a 32mm, suited for a 45". Fixed jet with the needle set on the center slot.

Thanks very much for this information. Did you happen to note the main jet you ended up with vs. the one it was supplied with? Also, was everything else inside left the same as they supplied?

[Frankenstein]

I read his comment to be it comes with a fixed vs adjustable main jet.
DL

[BoschZEV]

I read his comment to be it comes with a fixed vs adjustable main jet.

Surely Mikuni doesn't sell any of their carburetors with adjustable main jets. That would be inviting warranty disaster. The aftermarket supplies them, but just because someone sells them doesn't make their use a good idea.