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Old 03-10-2007, 01:44 AM   #8
potatoho OP
Cheese and Rice!
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Joined: Aug 2004
Location: Sea-level
Oddometer: 4,704
Basically as it sits now, it is a nearly stock bike. When I was actively riding it, I ventured into the Mikuni pumper carbs and farkles, gained a little power, but ultimately I lost a lot of mileage and it became finicky. When I picked up the bike after a while I found it leaked, ran poorly, and needed things to be cleaned up.

Since I had great success with my AFR meter on the two stroke, I wanted to re-purpose the LC4 as an efficient, quiet four stroke. I mulled over trying to tune the pumper carb better, but then I found that the float setup was toast and the a/p needed cleaning and reaiming. So I went back to the BST which I had begun to rebuild.

Ideally I would start with a CV carb, get a baseline AFR to where I want it, then match the slide metrics (holes & springs). That's where I am right now, except my needle is toast. I can set the AFR to where I like but I haven't yet decided which ratio I like better. I've gotten a little side tracked because there is an anomoly in the combustion beyond around 55mph and I need to determine if it is an exhaust seal or the funky needle.

I think that with the ideal carb metering I will be stuck probably at 50mpg. I'm not quite there yet but that is because I have left it stuck slightly rich at the cruising speeds because I hate pulling it apart. My worn needle has left me unable to lean the mixture to where I want, plus I had the wrong pilot jets and had to drill one of them out. So I am left waiting on a package containing pilot jets and a needle.

From working with one of the yost performance kits, I recognized that this motor really gets a charge with improved atomization. The yost kit was a small piece which fit into the HSR42 emulsion tube. It gave a sweet sweet rush to the acceleration. There is no yost kit available for the BST40, so it would have to be made by hand. There is however, a yost kit available for the Harley Davidson Keihin CV carb. I was temped to buy one of these carbs, as it's quite a decent kit, a CV carb with an accelerator pump! But I didn't feel like making cables or fitting a spigot to the intake flange.

So my only purpose at this time is to see what the 1999 LC4 will do with a BST40 at the proper AFR and with a matched slide rate. It has surprised me so far, in that it exhibits strong performance. The exhaust tone is also interesting. At the times where the meter shows solid combustion, the tone is muted. When I see the combustion artifacts, there is vibration and also white noise introduced into the exhaust tone. I'm going to work on it to get rid of the combustion defects. I believe it will really improve the driveability.

Does fuel injection work well? I've always thought the fuel was rather clumpy.

My ideal *thing* would be to add ultrasonics to the carb bore. It would be crazy good, I expect. In lieu of that I hope to use the dial-a-jet, if I can figure out a good install. It should provide a nice wift of air-fuel vapor. The purpose of this would be to jet my baseline more towards combustion stoich and just exploit the dial-a-jet under higher vaccuum conditions. Similar to an a/p except that it should be more seamless.

That's going to be some amount of trial & error. The way the dial-a-jet works is that you put the dial in one of 5 places and this controls its AFR. Then you have a tube, which there are actually several different sizes available, and you mount it at a particular location and a particular depth. So when it sees a vaccuum signal, it just delivers its tailored AFR to the bore. The claim is that it will only enrichen, but I swear I got it to displace my carb's AFR when I set the d-a-j's AFR to one of the leaner settings, and the overall mixture became leaner.

Anyhoo, the d-a-j is like a mini-me carburetor. It's just a little cheap & funky to work with. I may not even get to that stage though. My first attempt sucked and the bike is running pretty good anyways. But I really want to improve the mileage.
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