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Old 03-01-2007, 10:45 PM   #1
potatoho OP
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Joined: Aug 2004
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LC4E, BST40, jet4power

Just starting my own thread. I'm bad about thread-jacking

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

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.
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Old 03-02-2007, 05:52 AM   #2
NICO
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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
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Old 03-02-2007, 09:29 AM   #3
potatoho OP
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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.
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Old 03-02-2007, 08:51 PM   #4
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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.
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Old 03-03-2007, 01:43 PM   #5
potatoho OP
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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.
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Old 03-09-2007, 07:58 PM   #6
potatoho OP
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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.
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