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Old 07-18-2012, 04:50 PM   #1
ejute OP
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Mikuni's Allens Performance

G’day All
I’m looking for some feedback regarding Allens Performance mikuni carb. Kits.
I’m looking at fitting them to my 82’ R100, currently fitted with 40mm stock Bings, Dual plugged heads, 9.5:1 comp. pistons, standard cam and Epco sports mufflers. I have researched as much as possible agonised over whether to fit 38mm Dellorto’s or go for the 34mm Mikuni kit from Rockypoint in the US or go for the kit offered by Allens Performance in the UK either in 36mm or 38mm VM Mikuni’s?
They don’t seem to provide much info on their site as to what the kit contains and they are painfully slow in responding to email queries.
I like the Airhead simplicity of the Mikuni’s and would welcome some more throttle response.
Most of my riding is touring but when I overtake or get excited in the twisties I want good throttle response
Cheers
Mark
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Old 07-18-2012, 05:32 PM   #2
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IMO 34mm is too small so that knocks them out of contention. I know from experience that 38mm works great on small port heads but you have big port heads. They MIGHT carb better with 36's for having the big ports if you are following my logic but I bet 38's work well too. I prefer Dellorto's because the stock airbox snorkels fit on them perfectly and SEAL perfectly. About every Mikuni airbox snorkel setup I have come across has been letting a least some dirt in. The airbox snorkels that come on 32mm Bings fit onto Dellorto's perfectly just like they do on the Bings with no additional R90S style hose clamps and radiator hose if you remove about 1/3 of the velocity stack threads on the Dell's for the cleanest installation I have ever seen.

What is going to matter ten more times over 36 versus 38mm is whether of not they are jetted correctly. Most Dellorto's are jetted for a R90S and that jetting is way too rich for any small port which R90S's were. It will work but . . . . With Mikuni's you still have to pick round slide versus flat slide. All the flat slides I have seen have very troublesome independent floats. Just like Bing's independent alcohol float kits, they are very problematic to the point that Bing no longer sells them although they never admitted they were a problem from what I know. If you get the Dell's or the Mikuni's jetted right you will get better mileage and a lot better performance than the Bings. Good luck!
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Old 07-19-2012, 01:25 AM   #3
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I'm about to put some VM34's on my G/S with 1000cc siebenrock jugs (and G/S heads).
I'm following the advice of a local 'guru' who has set these and and the VM32's (and the roundlsides, and the Dellorto's, etc, etc) up on dozens and dozens of bmw airheads, including on bikes with my exact specifications. He swears by the VM mikunis for decent performance, response, economy and rock-solid reliability.
When specifically discussing them I was told (from someone who tried both these setups on his 100GS) that the 32mm was great on the 1000cc airhead, but in comparison he preferred the 34mm. Not necessarily better, just preferred it. All up the two RTW-built airheads he has with the mikuni's he couldn't be happier with them compared to the Bings.

To be honest I am a bumbling amateur when it comes to fiddling with carbs, which is why I don't want to go out on my own on this issue, which is why I am following the precise advice given to me by someone who knows their stuff- he has spent countless hours trying endless combinations of jetting and settings over the last couple of decades.
The jetting I am going with should get me if not right where I need to be, then very close to it- for my set up. I wouldn't know enough to say how the set-up would want altering for your different heads.

In short I wouldn't write-off the 34's like Supershaft above- But I can only say so from second hand advice/experience, gotten from those who have made them work very very well.
Of course, just like Supershaft says, 32, 34, 36, 38- whatever, obviously, it will all come down how they are jetted/set up.



I looked at where to best buy them. Buying them local to me wasn't so cheap.
Sudco in the US can provide everything you need if you know what you want- but they are a tad difficult to deal with from a retail customer point of view (there is no way to 'backorder' missing parts- everytime I tried to order there was a part I needed missing, and I wanted to get it done in one order).
Instead I have gone through a nice US based small seller- like a lot of others, he orders wholesale (cheaper) from Sudco, which ends up costing ME the same. Parts cost for the carbs and jets and other extra's I am getting from him is exactly the same price as if I ordered it myself from Sudco, and he is charging me a little extra for the labour of setting up the carbs with the exact jetting and specs I have asked for.

But then after all that, Rocky Points prices (for what the kit includes) actually look pretty damn good- and they have a great reputation. If I didn't already have my own jetting specs I wanted fulfilled, I probably would have gone with them.

Hopefully you can get some advice from people who have bought from those retailers who sell 'kits' for our airheads. I know there are a couple of people here at least who have the Rocky Mountain kits and are happy with them.

Good luck,
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Old 07-19-2012, 04:03 PM   #4
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I'm using 38 mm dells on my Seibenrock 1070 kit equipped bike, the bike has various other changes as well, I run 165 mains and get 72 bhp and can get get 50 mpg. No other carb related problems , they seem to stay in tune and don't need fiddling with.

If you go for the Mikunis, just make damn sure that you have a setup spec that will fit your bike, some people have had real problems getting the right setup for Mikunis.

IMHO etc etc. charles
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Old 07-24-2012, 07:34 AM   #5
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Ontic, care to share your set up details ?

The one thing that has stopped me ordering a kit like the Rocky point is that they seem to have one setting for each capacity, irrespective of the state of tune, which is unlikely to work, and I dont really fancy paying for the dyno time and bits to set a new pair up.

PM me if they are a trade secret------
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Old 07-24-2012, 08:11 AM   #6
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Quote:
Originally Posted by Beemerboff View Post
The one thing that has stopped me ordering a kit like the Rocky point is that they seem to have one setting for each capacity, irrespective of the state of tune, which is unlikely to work, and I dont really fancy paying for the dyno time and bits to set a new pair up.
I wouldn't sweat it too much. Anyone selling you carbs jetted for "your" bike from thousands of miles away is really only guessing at best, and intentionally erring on the rich side to be safe. It's an educated guess, but still probably not "right."
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Old 07-24-2012, 11:19 AM   #7
supershaft
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Plus there's the fact that most all different BMW models ended up with almost the same jets. For instance, BMW ended up jetting R65's to R100's with 135 mains. Except for needle jets, all the different models ended up needing about the same jets. I always thought it was interesting that with opened up exhaust, modified airbox, cleaned up ports and a 336, my 32mm Bings jetted best with 135 mains. The exact size I jetted my 38mm Dellorto's down to until I dynoed it and saw that it was safe to run what my butt dyno had told me ran best: 130's for over yet another hp. I wouldn't be alarmed if they jet different models with the same jets. There's good reason for it.
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Old 07-24-2012, 03:25 PM   #8
Rob Farmer
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Allens performance are only 20 minutes or so away from me. If you're not getting a response let me know and I'll call by for you.

One of the local guys fitted their kit to his paralever.





My mate has their Kit on his Commando and is very pleased with it. Came with everything you could possibly need including new fuel line and clips.


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Old 07-25-2012, 05:28 AM   #9
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I called by Allens this morning. They wrote this list of parts that make up the kit. The throttle cable is a universal cable that you cut and fit to make up what you need. The kit doesn't include any adapters to mate the Mikunis to your airbox stubs but if you tell allens the sizes they will provide something for an extra cost.






Roger Chaterton (UKGSer) recently got rid of his Mikunis and went back to Bings because he wasn't happy with a few things. If you get in touch with him I'm sure he'll tell you why. However Roger did post this when there was a discussion about Mikunis:-


"Personally I'd avoid the Mikunis - various reasons, couple of which being-

much better fuel economy with the Bings - approx an extra 50+ miles per tankfull, (from 270 to a reliable 325 miles)

Mikunis were always difficult to line-up with the airbox air intake tubes, and backfired off a few times -very embarrassing,

Mikunis would allow water (rain !) in either via the throttle cable into the carbs, or via a badly fitting air intake ( see above),

choke levers were a bit of a faff-( ie no choke cables attached),

Bings seem smoother, and certainly no slower , (however, they have been "tweaked" by Richie Moore...say no more )

So - happy to have put carbs back to standard 40mm Bings.

The above is only MY experiences, so opinions might (will ) differ !! "

Rob Farmer screwed with this post 07-25-2012 at 05:36 AM
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Old 07-25-2012, 12:58 PM   #10
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SS. If BMW ended up jetting all their later bikes at 135 mains, is this what accounts for the general reduction in power in the later bikes versus the earlier engines?
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Old 07-25-2012, 01:15 PM   #11
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Quote:
Originally Posted by chasbmw View Post
SS. If BMW ended up jetting all their later bikes at 135 mains, is this what accounts for the general reduction in power in the later bikes versus the earlier engines?
No, it was the reduction in compression ratio.
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Old 07-25-2012, 02:59 PM   #12
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AW is right. Lower compression is MOSTLY what lowered peak HP output. That and advancing the cam timing. Smaller intake valves and so on contributed too but . . . . Reducing the main jet sizes got them the most out of what they had but that can be done with the earlier higher CR and straight up timed cam models too! The more they chocked the engines, the less room they had to throw away power with conservative jetting.
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