Another post recommended these to simplifying tuning. I'm not a gear head. Any advice? http://www.thunderproducts.com/dial_a_jet.htm

 

I have experience with adjustable main jets back in the 60s and 70s. Now its all fixed jets. Its worth finding the proper one and leaving it alone. Sort of "Set it and forget it"

For your example, I have not.

David

 

Wondering the same thing??

 

OK, I read the web page. If you buy it let me know how it works.

Skeptical at least......

I see nothing wrong with jetting the carb properly the way it was designed to be used.

David

 

Absolutely, about 24 years worth, from selling them for street bikes to using one on my KLX.

Back in 1997 when I got the KLX650C it had a bit of a flat spot in the power and then I pulled the snorkle out of the air box lid for a bit freer breathing, which helped performance, but made the flat spot more noticable. Enter the Dial-A-Jet, which we had used on some streetbikes back in the 80s.

Some history. Motorcyclists are almost hardwired to change brass, that's what's always been done. The variable fuel adder that the DAJ is has gotten poor reception in motorcycles - in spite of the fact that it is the same general fluid dynamics used by the Mikuni PowerJet used by racers. The DAJ gets bad mouthed by people who've never tried it. Seems the ATV and Snowmobile community came about with a more open mind and the DAJ has great acceptance by them. Just read about it in the Thunder Products magazine reviews. Both DirtBike! and Motorcyclist had good results, yet the product still doesn't get recognized for what it does. It works.

Now for my comments and experience. I put a DAJ in my stock/snorkle removed KLX and picked up power. I did take off the float bowl to drill the bowl for a fitting since I didn't want to lose the bowl drain screw, otherwise I wouldn't have had to take the carb apart at all, the make float bowl drain fittings for the gas line they use. The impact was immediate - no flat spot and stronger power - at least from the seat of my pants and in run offs with my brother on his NX650 Honda. I didn't even change the adjustable mix screw, it ran fine.

Then I got a reverse cone megaphone exhaust and had the engine bored out to fit a Vulcan piston (678cc) when I had to rebuild the top end due to the poorly designed "automatic" cam chain tensioner (second one) that quit working. So now we have more open breathing at both intake and exhaust, plus a larger bore. The DAJ compensated for those changes again - no adjustment.

Now, I also rode the bike in temperatures ranging from about 18 degrees to 95 degrees with no noticable variation in power. I commuted to work in the winter so it wasn't just a quick ride, it was daily, and then of course there were the summers. The bike has also run in elevation from zero at Daytona BikeWeek to the 60s to 80s at about 5000 feet or so in West Virginia during the summer. Again - no changes. I have yet to ever move the mix setting from position 3. Just haven't needed to do so. Exhaust color hasn't changed, nice color and no puffs of overly rich white exhaust.

So in other words I've not had the carb off to change jetting since it was lean to start fitting Thunder Products' recommendation of having a lean jetting to allow the lean vacuum draw on the fuel mix from the Dial-A-Jet injector tube. If you know any thing about fluid dynamics and the siphoning effect of a vacuum over the end of a tube - the way the actual carburetor works with the main jet, needle jet, and jet needle in fixed flow you will realize how the DAJ adds a variable flow at the mouth of the carburetor to increase gas/air to the mix when the intake pulls a lean vacuum, yet will stop working when the vacuum grows weaker. Thus the variability and "fuel adder" label fit quite well.

I have several forum members at the Yahoo KLX650 group who will vouch for how well a Dial-A-Jet worked for them over a variety of modifications as well as myself. I also have a few friends who have installed them and have yet to have one want to remove it and go to hard jetting. I gave my one friend a guarantee when he wanted to jet his XT225. I told him if he didn't find adequate improvement I'd buy it from him for my up and coming SR500... I still need to get a kit for the SR. He was impressed.

If you want to know more right up front, call Thunder Products. I'm thinking the guy's name was Phil, but I'm not certain. We talked for a while when I bought a kit for a KLX member in Singapore. I told him my experience and he said he's never had a bad review from anyone who's used the part. I know why.

Save headaches and do the DAJ for similar money to a jet kit and less work to install and in the future. You won't regret it. They worked in my own Nighthawk S back in 1989 and one has been in my KLX since 1998 working for all the modifications, elevations, and temperature changes. No carb disassembly for rejetting again. And no, I get nothing from DAJ, I get to let you know about a good product that too many ignore due to old school hard jetting being ingrained into motorcycling.

 

As easy as it was to jet my old short tracker and TM125 motocrosser I'd now do a Dial-A-Jet in both if I had to do it now. Both the standard motorcycle carburetor and the Dial-A-Jet use the same fluid dynamics, but the DAJ only comes into play when the intake vacuum draw grows stronger due to leanness. Mikuni uses the technique with their PowerJet set up. Although Thunder Products' claim the DAJ is not simply a power jet it is clear the difference is in fuel/air mix versus raw fuel. The PowerJet uses a pilot jet in its circuit to meter fuel, where the DAJ uses the addition of air through ports.

There is nothing wrong with jetting with hard jets - if you want to alter jetting to maintain proper jetting for weather and elevation change. When I went to the Blackwater 100 for the first year in 1975 it was clear that riders from my area at 1300 feet had to drop in jet size and needle position to lean the bikes out for the approximately 3500-4000 foot elevations. If they didn't change it was very noticable in power drop, increased engine heat, engines loading up, and spark plug fouling. I know well, one friend got bad advice from a local off roader, in spite of good advice from another very good local off roader, and went UP two sizes in jetting. He never made a lap, constantly fouling plugs and loading up his 250 KTM two stroke, while the good rider got 9th overall on a more or less stock set up KX420 with a jet change.

At this point I've gone over a 5000 foot range without jet change on my KLX650 and with no loss of power noticable. Read the comments from riders on elevation changes at the Thunder Products testimonials and reviews pages. The 250s are even more susceptable to power loss with lean stock jetting, the smaller the worse they are affected.

If you read up on the reviews and such you will find the DAJ set up is credited with several thousand foot elevation changes without any other alterations. In fact they have an external adjustment that helps. And it is infinite real-time self adjustment in flow due to the siphoning effect used... less draw less siphoning and less flow, more draw more siphoning and more flow at any given instant. Just doesn't happen with fixed air inlet to gas inlet of the standard carburetor.

Break out the tools and rejet to maintain the performance or break out the tools once and put in a Dial-A-Jet to not have to tear down a carb again.

By the way googling a Dial-A-Jet review will come up with a number of experiences from others - mainly ATV, but one was on the little Ruckus 50 and 250 scooters. I mean after all, they all are IC engines now. Those people are open to new and different methods for tuning than motorcyclists. Even after experiencing positive differences neither DirtBike! nor Motorcyclist have since, to my knowledge, acknowledges anything other than hard parts change out. Clearly their review wasn't due to some advertising revenue thing. Doesn't make sense to me. Tearing down a GSXR carb set a few times to jet when they gained a bunch of horsepower on them with a Dial-A-Jet. Of course fuel injection now has made it unnecessary to do either jetting or adding fuel adders now on a lot of models. But where there are still carburetors, the Dial-A-Jet is a great device to avoid having to screw with a carburetor more than once.

Oh,... I have about 45,000 miles and about 12 years experience with the DAJ on my KLX650, so it's not just a shortie few miles review by any stretch.

 

So if I have already rejetted my pilot and main, would it still be a good idea to put the DAJ kit in?

 

The pilot will be fine, it isn't affected by the slide opening and vacuum in the front of the carb throat, it would have to be done anyway.

The main and any needle adjustments should be leaned out. The recommendation is to drop two jet sizes under on the main. I don't remember on the needle. Call Thunder Products and talk with them.

 

Cool, thanks

 

Let me say I've been through the jetting stuff with the old Sherpa S for flat track, the TM125 motocrosser for harescrambling, the Sherpa T when I put on a 24mm Mikuni (and never have got it quite right), playing with the Honda MB5, and doing the stuff with a 38mm Mikuni on one of the SR500s I've had. So it's not like I'm saying hard jets don't work, I'm saying hard jets are hard to do when you have to redo jetting several times, playing with the plug and stuff.

I am saying that jetting becomes a breeze when all you do it spend an afternoon fitting the Dial-A-Jet on a stock jetted engine, then riding. If need be, the fuel mix can be altered to five different levels and it works only when needed. Not a bad deal.

Maybe if I did some hard core racing I'd be doing jetting with the brass, but for my play bikes I'll stay with the personally tried and true Dial-A-Jet.

And when Mikuni does a simlar ploy with their PowerJet, you know the Dial-A-Jet isn't just smoke and mirrors. The only difference between how the two function is that the Mikuni adds raw gas metered by a pilot jet in the system with no air added and the Dial-A-Jet draws in some air to emulsify the gas. They both richen the mix when the intake is lean and draws a vacuum. The Mikuni is more applicable for racing conditions due to the raw gas being added.

I saw someone posting about guys messing with dials mid race. I'd venture to say they were working with Mikuni's variable main jet which was also mentioned in another post. I know flat trackers were always playing to run as close to perfect as possible. One guy I knew was told to run the engine wide open down the straight and at about the half way mark to pull on the enrichener lever - the bike was jetted that lean. Regardless, neither one is similar to the way the DAJ or PowerJet works.