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BoschZEV
01-23-2015, 11:01 AM
A good friend successfully competed in the most recent Cannonball using his 1923 JD, but now he would like to replace its carburetor with something that is more user friendly. Has anyone transplanted a Mikuni onto their JD and, if so, can you give me the details of what is involved?

Clearly a manifold has to be made, but what model Mikuni, choke size, jetting, etc. are required? He isn't interested in authenticity so he really does want a modern Mikuni rather than a replacement Schebler, Tillotson, Zenith, or whatever.

T. Cotten
01-23-2015, 11:29 AM
BoschZEV!

Please tell your friend that no modern carburetor is more friendly than a Schebler DLX or Linkert, if all is in order!
(Would you rather adjust with knobs going down the road, or stop and bleed everything to trial-and-error jets, needle settings, etc.?)

And he would need only to refurbish the original manifold, not "re-invent the wheel".

Please ask him if he really wants to paint a moustache on the Mona Lisa.

....Cotten
PS: If I already serviced his carb and manifold, reassure him that he won't pay twice if issues arise.

BoschZEV
01-23-2015, 11:45 AM
And he would need only to refurbish the original manifold, not "re-invent the wheel".He doesn't want to reinvent the wheel. He wants the specifications from someone else who already reinvented it.

Trust me, he really, truly, honestly wants the information on adapting a Mikuni, not adjusting an XYZ. A separate thread could be started giving all the reasons and opinions why someone should stick with XYZ, but here the question is, what does my friend need to know to switch to Mikuni.

Shaky Jake
01-23-2015, 12:22 PM
I've never invented that wheel, and it's probably not something I personally would do. But I will offer that I've used Mikuni carbs on various dirt bikes and a British twin from the sixties. My experience has been that, if you by a new Mikuni (set up for a four stroke engine) from Sudco and leave it jetted as it is out of the box, it will be pretty close no matter what bike you put it on, as long as it's about the right venturi size, and you avoid the temptation to go too large. Another thought would be a Keihin CV carb. James Mosher at performanceindian.com sells a Keihin CV kit for Indians, he might be someone to talk to. Good luck.


Kevin


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T. Cotten
01-23-2015, 12:55 PM
He doesn't want to reinvent the wheel. He wants the specifications from someone else who already reinvented it.

Trust me, he really, truly, honestly wants the information on adapting a Mikuni, not adjusting an XYZ. A separate thread could be started giving all the reasons and opinions why someone should stick with XYZ, but here the question is, what does my friend need to know to switch to Mikuni.

Well BoschZEV..

Everyone gets to play with their toys any way they wish.
And spend their money over and over as well.

But obviously some folks should ask themselves why they want a vintage vehicle in the first place.

....Cotten

BoschZEV
01-23-2015, 01:03 PM
My experience has been that, if you by a new Mikuni (set up for a four stroke engine) from Sudco and leave it jetted as it is out of the box, it will be pretty close no matter what bike you put it on, as long as it's about the right venturi size, and you avoid the temptation to go too large. Another thought would be a Keihin CV carb. James Mosher at performanceindian.com sells a Keihin CV kit for Indians, he might be someone to talk to. Thanks very much for your reply. My one experience with Sudco (for a British single) gave me a carburetor with the jetting quite far off. The slide cutaway was fine, but main jet, needle jet, and pilot jet all required changes. Be that as it may, the issue is what venturi size to buy, and here I'm hoping someone with experience with this conversion will find this thread and offer their experience.

I checked the Indian site and they do for Indian what my friend wants to do for his Harley. Of course, the manifold and linkages are "details" that would be different. Personally, I'm not a fan of CV carburetors, but that's a different issue.

Again, thanks very much for your post.

exeric
01-23-2015, 01:45 PM
I have to agree with Tom. The whole allure of vintage vehicles is interacting with the technology of the day, and immersing yourself in the nuances of riding the bike as it was originally designed, and intended. There's a lifetime of dedication required to understanding the world of 1930's and earlier motorcycle technology; let alone hybridizing. Of course it's his bike to do with as he pleases.

BoschZEV
01-23-2015, 02:03 PM
But obviously some folks should ask themselves why they want a vintage vehicle in the first place.
The whole allure of vintage vehicles is interacting with the technology of the day, and immersing yourself in the nuances of riding the bike as it was originally designed, and intended. I worded my original question to try to keep the answers focused on the Mikuni question, but I knew it was going to be futile...

All I'll say is that if "the whole allure" were only interacting with the technology of the day, no one would be be in business selling electronic voltage regulators, electric starter conversions for Gold Stars, LED taillights, CV carburetors for Indians, substitutes for clincher tires, electronic ignition systems, etc. etc. If an entire electric starter system is OK for a Vincent Black Shadow (and some people say it isn't; others say it is), than surely my friend's only choice shouldn't be to either keep it stock or buy a modern motorcycle instead.

exeric
01-23-2015, 02:29 PM
I'll always remember looking at a '37 Chief with the late Toney Watson. The Chief had a digital speedometer where the Corbin should have been. . . Toney's comment. . . Nerd cycle !

T. Cotten
01-23-2015, 02:51 PM
Golly BoschZEV,...

Folks who pioneered and made these machines legendary weren't 'Rocket Surgeons', so your friend shouldn't need to be either.
But if he thinks he won't have endless variables to deal with (and spend for..) by bolting on a piece of a flying saucer, by all means let him go for it.

Especially if he has a lathe, welding skills, and all the rest that makes it *fun* for many of us.
(NOT ME! I do it for a living dammit.)

But please, please encourage him to keep his DLX20 high and dry!

...Cotten
PS: Maybe you should ask on the Yucky Urinal: http://www.jockeyjournal.com/forum/forumdisplay.php?f=2
But don't mention my name: They barred me for punctuation.

Shaky Jake
01-23-2015, 03:36 PM
Whether it is better to augment or not to augment; on this men will never agree... ;)

Let's just hope that he didn't repaint it! :rolleyes:



Kevin


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Frankenstein
01-26-2015, 04:36 PM
Having had good results with Mikunis on a variety of flathead and OHV Harleys, I would suggest that the Mikuni marketed for 45's would be a good starting point, re: jets, choke size, etc. I suspect it would give reasonable results out of the box.
Just one man's opinion, "your results may vary"
DL

BoschZEV
01-26-2015, 09:08 PM
I would suggest that the Mikuni marketed for 45's would be a good starting point, re: jets, choke size, etc. Do you know who sells Mikunis for this purpose?

T. Cotten
01-26-2015, 09:50 PM
Do you know who sells Mikunis for this purpose?BoschZEV!

Try your local dirtbike boneyard for a bucket of them.
But beware that swapping various jets and needle settings for tuning is a "given", and new assemblies should come with an arsenal of sizes. Beware also that any rubber boot that you hang it on with will be subject to ever-changing modern fuels.

Yet you will be certain to save some investment in the long run, since anything new out of a box will depreciate as soon as you open the box;
The real thing would appreciate, even just sitting on the shelf.

.....Cotten

BoschZEV
01-26-2015, 10:36 PM
But beware that swapping various jets and needle settings for tuning is a "given", and new assemblies should come with an arsenal of sizes.Old carb or new, getting the jetting correct is part of the process. It's just faster if someone has gone through it before on the same motorcycle, determined the size carb that works best for a particular application, and the jets that work for them. That saves a lot of time. Once a Mikunki is jetted properly it will start, accelerate, idle and do everything well without headache for at least 10,000 miles. Even if the ~$100 for a Mikuni VM depreciated to $0 in that time my friend will have lost all of, um, $100 for having had a trouble-free 10,000 miles. That's why my friend wants one on his bike.

Eric
01-27-2015, 03:23 PM
Hi,

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

BoschZEV
01-27-2015, 07:59 PM
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
01-28-2015, 04:25 AM
Here's a link to 45 restoration's page on carbs, this should help.
http://www.45restoration.com/Departments/Carburetors/Carburetor-Kits.aspx
Reputable operation, in Albany, NY area. They fixed me up with a kit for my first UL conversion, years ago.
DL

BoschZEV
01-28-2015, 10:50 AM
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
01-28-2015, 07:16 PM
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
01-28-2015, 08:56 PM
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
02-22-2015, 02:31 PM
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
02-22-2015, 05:28 PM
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
02-23-2015, 05:58 PM
I read his comment to be it comes with a fixed vs adjustable main jet.
DL

BoschZEV
02-23-2015, 08:34 PM
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.