I don't think if you used a dyno or whatever this dial a jet would match the power of a properly jetted engine, if getting the most out of your engine and your expensive add-ons wasn't your goal I'm sure it would be fine. Carb jetting isn't rocket science but it's not for everybody either, I'm sure that is where the market for this device really is. Like I said earlier I know these things have been around for a long time so I'm sure they work well for their users, but Like I also said I got near spot-on jetting just following the instructions in the Dynojet kit.

 

To get more horse power, dump more fuel.

To fine tune an engine, precisely meter the fuel through out all the ranges of engine speed and load.

OK I'll shut up ,,,,,,

David

Still: Happy Holidays!

 

I've put the proper words in bold...

Go read how much power Motorcyclist wrung out of a GSXR1100 over stock. Not to mention they didn't have to tear down carbs six times to get there. That brings up the one weakness of your "proper jetting" which varies with temperature, humidity, and elevation.

That has been the one thing that the Dial-A-Jet has proven to deal with in the ATV use. They actually did use it in intentional extreme elevation changes with comparison to stock. That is also the point that many ATV riders point out in their testimonials - it compensates for air density.

I had the flat spot in both my bikes disappear with the Dial-A-Jet. Sure I could have bought a jet kit and done it spending an afternoon or two to get the thing jetted in perfect - for that day. But I learned enough about the DAJ to realize it could and would work both easier and better for street use. It would deal with riding summer and winter, low elevation and high for where I live. On a four stroke it just makes sense. And as was posted, one performace builder is using them in his modified carbs for MX bikes. My bet is if he's able to get the recognition he has, he probably has dyno tested it and proven it's worth.

But again, I've done hard jetting and know it can be done. I also know it isn't easy and will need to be modified if ranging over a 5000 foot elevation change to maintain good performance. I've also done the Dial-A-Jet and know it needs no modificaton in that same elevation change, not to mention changes in temperature and modifications that would require jetting changes.

Have you? "I think" doesn't cut it. Experience does.


By the way, the new Intellejet from Thunder Products using the very same science as the Dial-A-Jet, but a bit more trick with remote adjustability, does seem to work well based on the experience and the high performance carburetors put out by Dick's Racing. Go read the reviews... seems they like it.

 

Have you actually used mercury sticks or vacuum gages to balance carburetors? What happens when the throttle is opened rapidly, when the draw is leanest and jetting is working to fill the need for fuel? Seems the vacuum instantly goes up higher. Whenever the fuel/air mix catches up the vacuum will drop to a steady level. Roll the throttle on slowly and the vacuum does not jump as high. Sure there is almost always some vacuum, but not as high. Fact is there is some reversion in the intake as well, when the rush of the inlet is stopped when the valve closes. But the fact still remains that when the engine runs lean, inadequate fuel mixed in the air, it will start to draw a very heavy vacuum. It doesn't take much to realize it if one has ever experienced that situation.

You know, the situation where you open the throttle and the engine starts to draw hard (lean) through the intake, but won't seem to catch up so you close the throttle a bit (richening the mix due to air cut off) to let it kind of catch up. By doing this quickly over and over the engine may eventually bring up the revs. This is what happens when pilot jets get partially clogged, a rider can blip the throttle up enough to get over the lean spot onto the slide and needle circuit where the engine will run fine until it drops back to the idle circuit.

The only reason I mentioned listening for the sound is because it is something anyone can prove. Pull off the airbox lid and pull out the air filter - unrestricting the intake side - and crank open the throttle. You will hear the vacuum. As the mix gets leaner the vacuum will become greater. That simple. It is both audible and, with vacuum gages or sticks, visible.

As for the CV carb adjusting for altitude, no it does not. The slide does nothing to meter gas. The amount of fuel allowed in at any given slide opening for air volume is fixed by the needle jet, jet needle, and main jet. Air density has to do with molecules per volume, aka gallon of air to gallon of gas which is ideal at 15:1, but the common generality ends up at about 12:1). The number of oxygen molecules per gallon volume of air in Denver is less than the number of oxygen molecules per gallon of air at sea level. If the jetting lets in too much gas (high altitude less dense air) the performance will fall off and vacuum will drop, if they don't let in enough gas (lower altitude more dense air) the performance will fall off, but vacuum will increase. Hard jetting is only perfect for one narrow general condition, any extremes will vary the performance. The dynamics used by the Dial-A-Jet allow addition of fuel based on the draw of vacuum in the carb throat.

That variation is the reason many racers do jetting and keep notes for every track, temp, humidity, and other bit of information they can and then jet at the tracks?. Conditions change and performance falls off. Dick's Racing is using the Dial-A-Jet type Intellejet to take out the need for constant jetting changes. So clearly it must work for them - I know it has for me. And you are the one who pointed Dick's Racing out, using the Dial-A-Jet!

The facts contradict your opinion.

 

Air density and vacuum have a direct relationship.
You guys are talking about watching a vacuum guage and twisting screws and seeing change,, you will see a change absolutely becasue you have changed the RPM of the motor and changed your CONSTANT.
To prove vacuume changes, you need a flow bench with a magnahelic guage to see flow under specific barametric pressures.
Have any of you guys ever fooled around with small nitro engines like radio control??? I remember years ago when messing with RC boats runnig on 70% nitro, the needle setting was very critical to performance during the day. On the same day at the same elevation, a motor would run like crap if the temperature rose or fell or humidity rose or fell.
In order to find the perfect needle setting in the afternoon, we would FLOW the carb and write down the flow numbers for that elevation after a perfect setting. just minutes prior to a race we would flow the carb on shore and adjust to the number indicated prior. The boat would run perfectly every time regardless of the heat and humidity, as long as the altitude was maintained.
I guess what i am trying to say is that dense (HEAVY) air will flow less than dry air, hence, rich mixture will flow less than lean.
Does that make sense???
hope this helps you understand the flow characteristics.

 

Yes, I have worn out a couple of fuel pressure/vacuum gauges. I have a manometer at home for my twin cylinder BMWs. I have used mercury sticks on my bikes and others. A 650gx suzuki and a 750 honda. For the last 10 years I have been reading vacuum as MAP volts on the scanner.

The needle is attached to it.


David

 

I agree with Gary here. I understand what Mark,klx678, is trying to describe, but the issue of a CV carb having some advantage with extreme altitude change is a known factor. Air density, venturi velocity, and other issues come together to influence how the vacuum slide rises and falls on the carb and thus affect fuel delivery. I don't think I'm qualified to explain in detail the science of the exact differences. There are several good sites that explain the nuances between the cable pull slide carb and CV carb. Sure, both designs rely on engine vacuum and venturi velocity to pull fuel through the jets, but the vacuum slide is responding directly to the engine's ability to pull that fuel more precisely than the mechanically operated slide. Yes, that usually also results in some kind of a millisecond lag in response, but it's pretty darned small.

I'll add this real world experience too. I've been to the same trails in the Silverton/Ouray area of Colorado on both a cable pull slide carbed XR250R and various CV carbed KLRs and my KLX. All bikes were jetted perfectly for my home altitude of about 1700'. The XR would even chug fuel rich black smoke as I approached 10,000' and was downright nasty at over 13,000' on Imogene Pass. All my CV carbed bikes would pull very cleanly until right at the top of the pass, but even they would idle at the very top. I've ridden with other riders with cable pull slide carbed bikes and always noticed similar results. Obviously this is where the DAJ system would be greatly appreciated on a cable pull slide carb and would probably also improve the CV carb's performance.

 

But the CV will still lose more power just because the thinner air volume will be mixing with the same gas volume that you had at the lower altitude. No matter what altitude or temperature the engine is operating in, the CV will only flow as much air as the slide allows and the fuel metered at that setting is set by the needle and jet needle at the level of the slide. If the CV could adjust for altitude, why does everyone put shims to lift the needles? The reason is the CV does nothing to adjust fuel to air ratio, just how quickly the slide will open is all it does.

That is the point of the DAJ, if the jetting is leaned out to start with and using the the DAJ to add the extra fuel, the DAJ will cut back on adding to the point of doing virtually nothing. Allowing the higher fuel volume at lower altitude when needed. That is what it is all about. From what I read, the Dick's Racing carb set up uses the Intellejet set up to feed about 20% of the fuel requirement, giving that much range for the carb set up to adjust for temperature and altitude changes.

I also agree, there is vacuum at all times in an intake, unless it is supercharged, but the leaner an engine is running the higher the vacuum draw will become. That is what causes an enrichener to work when the standard hard jetting has hit its maximum flow at a given slide setting. That is what Dial-A-Jets and PowerJets do - add fuel flow when the higher vacuum of the lean engine draws it. That's what Dick's Racing is doing - jetting lean on the fixed jetting and using the DAJ to add fuel as needed, comping for atmospheric conditions that would affect hard jetting. Thus eliminating the need to jet for a given day.

Is it simply a lazy way to deal with jetting? I don't know, maybe. But if so, so is fuel injection. And you'd have to be nuts not to go that way if it works and isn't prohibitive in obtaining it.

 

Then why haven't you figured out that cracking a throttle open, creating a brief lean situation spikes the vacuum?

The needle is what meters the gas, the slide meters air. Air volume does not change as air density changes, that's one of the characteristics of a gas - it will expand to fit the container, molecule spacing increases and thus we have what is called thinner air. A gallon is still a gallon, just a lot less molecules. If the air is thinner at higher altitudes the slide still allows the same volume of air flow as it did at a given opening at lower altitudes with denser air as does the needle with the fuel. So the needle dictates the quantity of gas, the slide dictates the volume, but not the molecular density, of the air intake. The sheer volumes remain the same with the fixed jetting for the most part. And the engine gets too much fuel for the density of the air at higher altitudes. Granted it may not be as bad as a slide controlled intake, but it is still too rich. If a carb is tuned at higher altitudes and higher temperatures the opposite will occur. The slide will still let in the same volume, but the density requires more fuel. The needle will not meter more fuel. A fuel adder set up will.

There might be a bleeder circuit that might help a tad, but certainly no where near what automobile carbs have. And those bleeders work on the same principle as the enricheners - intake draw above a certain level sucks more fuel when needed... or not, which works in altitude change when a fuel adder is set up on a lean fixed jetting carburetor.

If you do have the background in fluid flow and accoustic wave patterns or whatever, read Lonn Peterson's written work at Thunder Products, it should make sense to you of all people. It made sense to me, even with my limited knowledge, partly due to learning about two stroke exhaust wave patterns from reading Gordon Jennings, and some fluid dynamics knowledge from college course work.

 

Opening the throttle makes the vacuum go down. Down as in less inches of mercury.

Increasing engine RPM makes vacuum go up.

The better tuned the engine the higher vacuum it will carry.

This is all I know.

I can tell you if you Look into a 4 barrel carb with improperly working accelerator pumps, and hit the throttle it can back fire, burn your hair, and make your face red.

I think what you are describing is the vacuum in the manifold moves out to in the carb. Fuel takes more time to get moving than air, so is the delay.

It does sound like the vacuum is changing. How can you tell if its going up or down with your ear? Do you associate a loud intake with more (higher) vacuum? A lower pitch as more vacuum? Higher pitch higher vacuum?

Once the engine gets proper mixture, it runs faster which increases vacuum. This is if the throttle has stayed the same.

A good carburetor should meter the proper amount of fuel for all conditions.

Fuel Injection does it far better.


We have temp in the teens, snow, and wind. All I can do is discuss carbs instead of ride.

David