I had the oportunity to ride the 48MM Mikuni for the first time over Labor Day weekend. Having not had any time to "dial it in" is set it up like the 45MM and went with it. I prefer to run without an accelorator pump because my bike is often in other riders hands and most prefer the easy throttle pull without the pump.

Right off the bat, I was happy with the "seat of the pants" feel of it. I thought it might be a pain to dial in since I had not "base line", but was pleased that it ran well. It felt as though I pulled stronger up top, but I had done some other changes at the same time and didn't know the results of those. Over the corse of the weekend, I was impressed with how little fuel was used and the carb needed no attention at all. Considering I jetted it in Vegas [1800 feet] and Sand Mountain is at 4000 feet, it ran eaqually well in each location, with no jetting change. I came home happy with it, but didn't have any #'s to support the added price.

A couple of days ago, I got the bike on the dyno for some R&D on that carb. I started with the 45MM that I had previously "dialed in" to get base line #'s. This took the extra changes that I made to the motor out of the equation. I changed to the 48MM as I had it set up when riding at Sand Mountain, and was imidiatly happy with the #'s. Thinking that I may lose some bottom end with such a large single carb, turned out to be no problem at all. From 5000 RPM down, the charts looked identicle. From 5000 up, the extra flow started to shine. With a steady gain in power to a gain at peak RPM of over 3 HP. It also let the HP fall off less quickly after peak, effectively increasing the usable "power band". I then tuned and tweeked on the carb to get the maximum out of it. Trying both direction [leaner and richer] to find the "sweet spot" showed me something I was sort of expecting, but still was happy to see. Ten main jet sizes in each direction only showed a variance of 1 HP. That made the total gain from this carb, 4HP. It also lets people that don't want to have to re-jet for every change know that "close" is "close enough" for most.

With great throttle responce, easy throttle pull [without the pump], ease of installation, almost fool proof jetting [once properly set up, initially], and HP increases on the big end without losses on the bottom end, I can't see a down side to this carb. It is somewhat expencive, with a retail price of $499, but seams well worth it to me.

Having had the chance to compare the 44MM Lectron to the 45MM Mikuni over Labor Day weekend as well [with the Mikuni being the clear winner], I'm not going to try the 48MM Lectron unless one is handed to me. If nothing else, the "rudder" needed to work the Lectron makes it less convienient than the Mikuni.

I just thought I would share my findings with all of you. This may be a pretty good alternative to dual carbs, at alot better price and much less hassle to install. The 48MM HSR Mikuni is now the standard carb for the 760 motors.

Last year I was 10 bikes behind Jeffinrivercity, this year only 5 [on his good runs, without nitrous]. Considering I'm still running the same Scat-Trac Edge's as last year, and they are rather worn out, I'm pleased to think that I'm catching up. The "Adaptor" is in the works Jeff, prints are done and the shop is prototyping them. That may be all I need to catch you. As I get faster, so do any cutomers that are willing to give me a chance when I re-open. I offer this info to all though. You'll be able to get these carbs any were. Consider it "good faith" info for all of you that have offered their support as I work through my business troubles. As well as those that have been victoms of my troubles and not "trashed" me as badly as you had the right to. Thanks!

 

I'd just like to say that I appreciate reading your posts. It's really good to hear a contribution from someone that is willing to spend time and money to improve these bikes and let others know the results.
These forums are a great way to share information but in reality there aren't alot of hard facts to be found.
I know that you have come across stock bikes that run stronger than normal. Have you ever found anything you could atribute that to? higher comp or cam or ignition timing? Also, what is this adaptor you are making, any other projects in the works that you can tell us about?

 

Great Info!!

Thanks Knutz.



Biggerisbetter.

 

I'm assuming you need a larger intake manifold than stock? Will just the 48mm carb give any performance gains without any internal mods? cams? higher comp pitons?

 

what was the total HP of your motor? thats a big gain.(4HP) thats 1 more than i got with the 2 39mm. would i gain a extra HP being getting 1 48mm? how much power increase do you get on the 2 carb set up?


a stage one kit from ron woods gives a bike about 5HP. thats pipe, carb, intake rev box.

 

I ported my stock intake out to give the flow for the 48MM. It requires removing A LOT of material to get near the throat size of the carb. I went to 47.5MM on the intake, because going all the way to 48MM only leaves 1MM of material at the groove of the carb mounting flange.

I haven't been able to test the carb on a stock bike since the stock bike I used to use was sold. I then built the motor, slightly, and it's currently a desert race bike.

The adaptor is a little something a group of us were looking at up at Sand Mountain. It should allow us to use a part that is claimed to give a 5 bike length advantage. I'm not sure I want to let the cat out of the bag yet; 4-stroke wars is coming and I want my customers to have that advantage.

I haven't had the oportunity to compare it to duals either. I'm currently testing on my personal bike that is using stock size valves, so the larger valves are another part I haven't been able to throw into the equation. With no help from Bombardier [like they gave RWR], I count on my bike and customers bikes to do R&D. Combine that with money for dyno time being tight, I can't test all the combinations.

As for the peak #'s for the bikes I test, I can't say much any more. My personal bike has been on several different dyno's and gotten such a wide range of #'s, it's not funny. The dyno I used to use was consistent with Bombardier's dyno and with Trinity's old dyno. It was also consistent with Dynojet Research's dyno here in town. That dyno has recently been sold, and replaced with a motorcycle dyno with one drum. I obviously can't use that one any more. The dyno I have easiest access to now, is EXTREMELY conservative. Not to mention, the owner is much less generous with time on it than the previous shop. The last shop charged me $60 for an hour and a half, now I'm paying $60 for 35 minutes, and had to wait an hour in the middle of my testing. With the same motor, in the same bike, I've had charts ranging from 54HP to 72HP, depending on the dyno I'm on and conditions for that day. Now, I'll just compair runs done on the same day, on the same dyno to each other.