i dont know what jet kit i need,im looking at dynojet kits...do i need regular kit # 8121 or thunderslide 8131...i have 01 fxdl,,with samson pipes,,and soon going to good aftermarket air cleaner,,,just curious whats the diffrence between regular kit and thunderslide ? i do need to rejet gas milaege is too damn good and plugs awfull white,bike coughs..hell im getting 52 miles to gallon...lol

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Generally all you need is a larger jet on the bottom end, usually a #46 that is available on line through JP cycles and an adjustment to the idle circuitand it's good as it gets. The kits as well as the sporty needle will drop your MPG and not give you much in return over the low speed jet change. Drilling the slide can cause some drivability issues in colder weather at lower RPM's with a cough back because the slide opens too fast and leans things out.

Save your money on the kits and spend the $3 on the jet.

 

Forget the Dynojet kit. It will work fine but cost to much and kills gas mileage. If all you have is pipes and air filter change a 48 slow and 185 main jet should get you close. That is what I ran for over 30k before I built my sig. Got 48 to 50 mpg 2 up loaded for trip 70 mph with it. Running 48/200 now and get 50-52 mpg. Air/fuel mix spot on on dyno. Jets cost less than 15 bucks total.

 

I agree with these guys. I have freinds who have bought these kits and all have said they are a waste of money. I was going to put a thunder slide on my bike, buddy said the throttle responcewas not worth134.00 dollars. You can find somebody to tune your carb properly for a better price than that.

 

Don't mess with a DynoJet kit. If you are going to jet it, do it right. Drag Specialties sells a Keihin No Hassle jet kit. It's about $30. This is the kit you want. Jetting has more to do than just changing a jet. The kit will have an emultion tube and a new needle. These are the most important parts of the kit. Also us a 48 pilot and a 190 main. Drill out the plug for the air/fuel mixture and set it 2 1/2 turns out. I have installed hundreds of these kits on the dyno. This is the BEST kit available.

Jason

 

One exception here, warm the bike completely and adjust the idle mixture to the highest and steadiest setting, not a pre determined amount.

 

Your tachometer nor your ear are calibrated to detect a change fast enough. By the time the motor reacts your past the point. Unless you have a dyno with a sniffer at your disposal 2 1/2 will be best.

Jason

 

Different size slow jets will throw that theory out the window. A larger slow jet will take less gas in the idle circuit for the same motor and the21/2would be much too rich for proper mixture.
I've been setting them with a tach and also by ear for years and had good luck doing it too. The 2 1/2 is only a ball park at best and most need more or less to get it where it belongs from there.

 

I have spent 100's of hours in a dyno. I know what results are most common. Hell why did we spend 15 grand on a dyno? We could have just used our ears???

Jason

 

You need to put your bike on a dyno to adjust the idle mixture now? I wishI had known that when I tried a 48 slow jet inmy '03 Dyna, anything over 1 turn out resulted in black smoke. The stock 45 and 190 jets with a Sporty needle worked for me, and I had no problem getting 50 mpg. Carburetor tuning over the internet is futile, too many opinions and too much bad advice.