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potatoho 03-01-2007 10:45 PM

LC4E, BST40, jet4power
Just starting my own thread. I'm bad about thread-jacking :wink:

I was just making another round of changes and took some pictures.

Here is an extra dial-a-jet I had. I installed it onto the boot and used the filter kit as a little stubby air source rather than routing it up the frame. Not sure how well this is working at this point, but I had it, and it was an easy install. The fuel source is a replacement bleed screw with a spigot on the end. So all in all, I just had to punch a hole in the rubber boot, replace the bleed screw, and then run some plumbing. Like I said though, I'm not sure how well it is doing yet. I think they do work as advertised, except that my implementation may not be 100% because I put it in a pretty large venturi.

I didn't realize at the time I did this that the area was so vaccuous. May not be getting any dial-a-jet action at all. It can be a somewhat subtle effect. The little box acts as a mini carburetor which supplies a vaporious air-fuel mixture to supplement the normal carb circuits. Poor install notwithstanding, it makes sense to me that something like this could work well in a CV application. At some point I'll probably disable it just to check its function, though that will involve plugging both fuel and air sources so it's kind of a pain.

Here is an oversized main jet drain nut I got from yostperformance. I drained the BST40 bowl and it only contained 40mL of fuel. And that's with a 45 degree bike drip angle. This is very low capacity in my opinion.

Blurry in the background you can see the location where I installed a Bosch #11027 lambda sensor onto the front portion of my midpipe.

Here is my jet4power meter tied onto my dash. I really use this a lot because it is such a simple system. You only have a ground wire w/ eyelet to screw into your frame somewhere, and then a wire to connect to the lambda sensor. A 9V transistor battery connector is also present and you just stick that onto your bars or something. Then you just warm up the bike, and tune all of your ranges to the rightmost green light. Done.

The meter is nice because it helps to figure out issues. You can watch the AFR as you ride and see what is going on. For example, tonight I was able to diagnose that I had fuel starvation, and also that I have some uneven combustion at higher rpms. Dialing in the idle mixture is very easy, you just turn the fuel screw until the light you want is lit. If you change air filter, air box, pilot, or other settings this can be pretty handy because it all sounds pretty much the same even though the mixture can be anywhere from 14:1 to 12:1.

The one thing I haven't done yet is to get the bike running well :rofl

I threw a few things at it tonight so hopefully I have fixed one or more of the outstanding issues. I've got the AFR where I want, but the carb is flaking out on me a bit. Hopefully will have it sorted out by the weekend.

I put on a new spring-reinforced (to avoid kinks) fuel line, changed pilot air jet back to 1.2, installed a deep bowl nut. Not sure why I went back to 1.2 from 1.1. I just was never impressed with the change. If I can fix the fuel starvation and get the AFR to read without fluctuations at mid rpms then it will be pretty good. Those are my main issues right now.

NICO 03-02-2007 05:52 AM

OK, I am a bit feeble minded and n00bish with the world of carb's, but can you enlighten me a little on how this dial-a-jet works? Is this a new product or something that has been around for some time and proven to be effective?

Thanks, Nico

potatoho 03-02-2007 09:29 AM

It's been around for a while. To explain what it does, I'll explain what it is. It is a hollow tube which you mount in your carb bore. On the outside there is a small box into which the tube mounts. The box is a little carburetor. It has a tube where you supply fuel, and it has a series of holes where you put an air filter. The 5-position dial adjusts which air hole is active, and this controls what ratio of air-fuel it delivers.

What it is supposed to do is provide an atomized air-fuel mixture which supplements your normal jetting. I think the numbers they give out are "up to 15%" replacement for your normal mixture, so you need to jet down a little bit to compensate. The concept behind it is that it provides a level of atomized fuel which is more immediately available, lighter and quicker to react than the normal carburetor circuits, so it tends to help acceleration and fill in the transition areas of the carburetor.

My desire with the CV carburetor application is to use it as a pseudo acceleration pump. If placed correctly, where it will react directly to an increase in signal, it should supply an air-fuel mixture as a stop-gap while the slide is equalizing. I don't believe I have placed it in the optimal location yet. I didn't feel like drilling holes in my carb.

In my pictured install, I'm assuming that it is just supplying a general whift of highly atomized fuel in the vacinity of the carb intake. It would be interesting to experiment with different nozzle locations to see the affect. I installed one on my two stroke before but I wasn't so impressed with the results. Yes it supplemented (and in fact I could get it to detract in the lower settings) the air-fuel ratio, but my two stroke didn't give a squat about atomization levels.

The dial-a-jet differs from a powerjet in that a powerjet will supply only fuel. And a powerjet requires a significant vaccuum signal in order to siphon. The dial-a-jet has a small chamber in the box where air & fuel are mixed, so what gets drawn through the tube is a lighter mixture and requires less signal to siphon. When I hooked up a powerjet to my two stroke, it only became active at near full throttle. The dial-a-jet hooked on the same bike, same hole in fact, was active everywhere and in fact I had to lower the needle.

The dial-a-jet is a really simple device. I find the construction a little cheezy but I got some cheap ones off rockymountatv that were returns. If you were to make one yourself, you should make the chamber accept some standardized main jet rather than trying to make a funky dial. Also there may have been something mentioned in the instructions about maximum fuel line length. I imagine that having the chamber too high above the float level is probably not a good idea.

potatoho 03-02-2007 08:51 PM

It's running quite a bit smoother at all rpm so I think I've got that issue somewhat taken care of. I sorta threw everything at it.. new plug, 1.1 pilot air jet, 47.5 pilot, extended bowl nut. I suppose it could still be some wacky electrical issue. I've got my eye on the regulator since that is common between the lighting and ignition and last year I was having some lighting blank-outs which made me remove my HID.

I think I've got most of the issues worked out. I still had one fuel starvation burble episode today but on my next run I am going to determine if float height is an issue. I had it set a bit low and now I've just set it back to stock horizontal. I also suspect a possible sticky slide. So anyways for my next run it will be with stock float level, slicker slide, 1/2 clip richer needle.

I just need to run the needle up to a level which removes the 1/8 throttle artifact. When I went up on the pilot, it didn't even touch this 1/8 area. There's something freaky about that position on this carb. I didn't start seeing it until I went down to clip #2 so I'll see if it goes away at 2.5 or 3. My best guess is that there's not enough air velocity to work the slide until past 1/8.

potatoho 03-03-2007 01:43 PM

Today I rode on/off road to test things out. The strange AFR dips are occuring only on the street and I finally found a correlation. It only happens beyond a certain speed and when I'm on windy streets. Noting the location of my O2 sensor, I'm thinking that what I'm seeing is a seal leak in my exhaust. Either the joint directly before the sensor or the header/cylinder joint.

As a side note, I removed the dial-a-jet and I haven't noticed any change in readings. It appears that my install location is poor, because I know that these things do affect the mixture quite a lot when installed directly on the carb. Not sure when/if I will reinstall. I actually do believe it was supplying some mix, but it felt like it was only doing it during extreme vaccuum, such as when decelerating. I notice more AFR dip / popping during deceleration than before. That could also be an indication of my exhaust seal deteriorating.

So now, I'm running a stock BST40 (47.5 pilot, 155 main, 2.5 clip position, stock float level). I have an ids2 quiet core w/ 10 discs. Stock airbox side cover, snorkel removed and opening enlarged towards the front. I think it's pretty darn quiet. 2.5 clip is evidently the lowest you can sit this needle in this carb. At clip 2 I was getting an extreme 1/8 throttle lean dip.

It runs well. I can quickly twist the throttle wide open from a low idle and it revs. My idle is extremely low, just for giggles. I don't have the auto-decomp on my cam so I was able to set it to like putt putt putt. Off-idle torque is good, power is electric. No bogs so far on the whoops. Power is not super good, but it's the most this bike has had so far.

The exhaust leak, or whatever it is, is causing a noticeable artifact in the running. When the AFR reads solid, the bike is running smoothly, but when it starts jumping around then it has some vibes and an audible distortion to the exhaust tone. At first I thought it was some airbox vortex due to my removal of the snorkel, and it still could be, but now I think it is the exhaust.

My mileage is currently 45mpg.

potatoho 03-09-2007 07:58 PM

Anxious to get back to working on this, but I am awaiting my order of a new stock 6G5 needle. My current needle has some asymmetric wear and I need to remove that from my testing. I'm also curious as to whether it is contributing to some jumpy AFR readings at certain throttle positions, so I can't change anything (reseal etc) until I do a test run with a fresh needle.

I have thought about the dial-a-jet a bit more. Seems to me that on a CV carb the ideal location would be on the motor side. It certainly needs to be located downstream of the slide system for best effect. When the butterfly opens, a low pressure area forms in this area which would be the perfect place to add some highly atomized accellerant. I have also considered a mount which would introduce air-fuel into the slide itself. This would be drawn into the venturi via the bleed holes during the equalization process.

Anyways there are a lot of things to play with besides a dial-a-jet. Bleed hole matching (to reduce AFR deflection under acceleration) and slide spring rate (to achieve proper taper). I am intrigued by its newly acquired stealth and smoothness, which as near as I can tell is an attribute of improved fuel metering over my pumper carbs.

Max Kool 03-09-2007 11:49 PM

This is a "because you can" excersize, isn't it?

For if you would get real, you would use the info on the A/F ratio bar to tune the carb on the bike itself, not to correct it with a bypass fuel injection system.

Or ditch the carb altogether and fit a decent injection throttle boby. (ever thought of fitting a BMW oilhead throttle body & injector?).

Anyway, nice work and a great way to pass the time!

potatoho 03-10-2007 01:44 AM

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.

potatoho 03-17-2007 09:47 PM

Finally got my replacement stock BST40 needle today. Wow, I had to move it from clip 2.5 to clip 4 to get similar AFR readings. My old needle was very worn, both in a central area and also near the tip. I have gone up 7.5 on the main so far but I'm still testing it out.

Since I ran through a few clip positions today I was able to see a bit more about the strange AFR readings. It seems pretty stable when I keep the mixture towards the rich side, and at certain rpms it is not very tolerant of a lean-ish mixture. Seems that once it gets to a certain lean-ness it begins to falter more, so it looks like I may just need to avoid going lean when it is on the cam.

I think from the first day I put in the G1 cam it has acted a bit more finicky regarding jetting. My first ride with the G1, and with stock cam appropriate jetting was filled with pops and bogs. I'll have to go dig up my notes to see what I did as a jetting correction. So far I've just been running the same AFR across the whole throttle.

This weekend I've been setting it up for a stable AFR in a richer zone. I should be pretty close. My last ride was with #4 and a 160 main and it was just about where I want the AFR to read. I've upped another 1/2 clip and gone to 162.5 main for tomorrow's ride.

My last mileage check yielded only 40mpg.

bmwktmbill 03-17-2007 10:33 PM

Neat stuff,
It mirrors the process we all go thriugh without instruments.
Of course we guess, looking at plugs and evaluating roll on and acceleration.
Nice to put a little science in the process.

potatoho 03-18-2007 09:30 AM


Originally Posted by bmwktmbill
Neat stuff,
It mirrors the process we all go thriugh without instruments.
Of course we guess, looking at plugs and evaluating roll on and acceleration.
Nice to put a little science in the process.

There's still the ride testing to get the best feel, but your right, the AFR lets you see what air-fuel mixture is associated with each throttle position and then you can make changes from there. As a baseline it is good to have a constant AFR, but we know that is a compromise because the motor needs more fuel at some times.

I'm a bit disappointed that a lean-ish mixture isn't doing it for me. Seems to work at the lower throttle positions without too much of an issue, but when it gets on the cam it really falls apart unless you go a bit richer.

The thing that makes me mad is if you google on the use of lambda sensors for tuning, you'll find that virtually everyone says that narrowband sensors are useless. Well, that is 100% B.S.. There is plenty of resolution on the Bosch narrowband sensor to tune between 12:1 and 14:1 (all we care about on a motorcycle). However the voltage isn't linear. You just have to build a calibrated gauge to display the non-linear voltage.

Anyways, having some type of air-fuel meter is useful for cases like mine, where I had some worn components which placed my settings far from the norm. Easy to see on the meter, so it saves time in the long run. The other benefit is that you can take virtually any weird carb and get it dialed in to a motor.

trond 03-18-2007 09:47 AM

I have a question about the location of the Lambda sensor; do you think it might be too far away from the exhaust port ? I have mine in the exact same position (also Jet4Power) and it seems to be varying too much with temperature, so I am thinking it might be a bit too far away, and that maybe exhaust tape would be an idea to make th temperature more stable. Also I have a comment about you aiming for green LEDs. I seem to be getting more power with 1st and maybe even 2nd yellow lit up. I have jetted for green at cruising speeds, for economy and smoothness, and to get top end 1-2 yellows.

Surly 03-18-2007 10:04 AM


Originally Posted by trond
I have a question about the location of the Lambda sensor; do you think it might be too far away from the exhaust port ? I have mine in the exact same position (also Jet4Power) and it seems to be varying too much with temperature, so I am thinking it might be a bit too far away, and that maybe exhaust tape would be an idea to make th temperature more stable. Also I have a comment about you aiming for green LEDs. I seem to be getting more power with 1st and maybe even 2nd yellow lit up. I have jetted for green at cruising speeds, for economy and smoothness, and to get top end 1-2 yellows.

I think that that particular location would make little difference in the EGT
But I am also a fan of wide bands over the (from my understanding) lean/stoic indications you get from narrow band sensors.

Is that sensor heated?

I have an LM1 I want to use to tune my 640. I either need to weld on a bung or try an exhaust adapter. Id be interested in others opinions on the sensor position.

BTW: Nice work guys

potatoho 03-18-2007 10:10 AM


Originally Posted by trond
I have a question about the location of the Lambda sensor; do you think it might be too far away from the exhaust port ? I have mine in the exact same position (also Jet4Power) and it seems to be varying too much with temperature, so I am thinking it might be a bit too far away, and that maybe exhaust tape would be an idea to make th temperature more stable. Also I have a comment about you aiming for green LEDs. I seem to be getting more power with 1st and maybe even 2nd yellow lit up. I have jetted for green at cruising speeds, for economy and smoothness, and to get top end 1-2 yellows.

That's where I'm leaning too. I now have it set up in the first yellow light full time so I want to see how much it affects the economy. When I put the BST back on, it was clip 4 on my worn needle. I felt it had pretty crisp rollon but it fell apart when I pressed it later in the ride. I was running the stock main at the time which was too small. I only did a couple of rides after that because I needed to wait for parts.

You mean weather outside temperature is changing your readings? I've not seen that on this bike. I think the sensor location is good. I feel that it is hot enough to work consistently. I had it on the two stroke near the cylinder and that is still not even as hot as the location on the four stroke. I have had ultra copper silicone bake off of that header-midpipe joint. Though I do see others who install sensors a bit closer to the cylinder, I just didn't want to mess up my headers.

You can get another sensor if you suspect it. I've killed one by rock, one I think was silicone contaminated, and then I believe I've bought two others for various reasons. The location on the two stroke is like right down in front on the first turn of the pipe, so it gets messed up. I'm down to one now :-) They are like $16 or $18 at my auto parts store, Bosch #11027 and then put a bullet connector on it.

trond 03-19-2007 07:27 AM

The readings from a 'primitive' narrow band A/F sensor as the Jet4Power, and I believe possibly any A/F sensor must be correlated to power output (max speed/seat-of-the-pants-dyno) and spark plug readings. So jet for max power/top speed without worrying too much about the LEDS. Keep changing main jets until max power/top speed. I have the luxury of endless sand sheets where I can load the engine properly for many kilometres

After this you know what LEDs to aim for to get max power.

At cruising speed you don't need max power. Economy, sound of the engine and smoothness is more important. Change needle setting and other until it runs really nice in one RPM range. Now you know what LEDs to aim for in the cruising range AND when wringing the throttle.

Only after this excercise is the A/F sensor is really useful. And the Jet4Power is a great instrument ! I'll use it next for setting up the carbs on my old Ducati. No need for more expensive wide-band logging types although they probably work well too

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