Dynojet kit Tuning

[Anonymous]

I decided to go the air pod jet kit route mostly because trying to get the airbox on and off was more than I could take. So I took Keiths advice and got new O rings from Robert (Great service by the way) and new O rings for the intake boots. I have a Vance and Hines pipe, K & N air pods and a Dynojet stage 3. The floats are set and as soon as I put the exhaust pipe and battery back on I should be ready to start it. I bought a motion Pro carb synch tool and thats where the questions start. Is the tool used just for adjusting the slides? Or is it also useful for determining correct jetting. I am pretty familiar with the different circuits in the carbs and what jets affect what circuit and at what throttle position. Except I don't know much about the screw on the bottom of the float bowl. You have air screws on the sides which I believe mostly affects idle mixture. but I don't know about the adjustment on the bottom.

 

[lhanscom]

The carb sync tool is only useful for synciing the carbs. The screw on the bottom is the fuel screw, same idea as the air screw, but deals with fuel, and is more sensitive to adjustment. It will primarily effect the idle, and small throttle opening mixtures.

 

[KEITH KRAUSE]

The carb vacuum tool is for synchronizing the slides.
You need to set the levels as close as possible to avoid mixture problems that make jetting more difficult. Don't bother to test and take plug reads unless the levels are set closely.
I set mine so the difference is no more than about 1/2" from the highest to the lowest level. I set mine at around 3,00 rpm's. USE A FAN OR TWO to keep the motor cooler while you make adjustments. Don't over-tighten the throttle valve adjusting nuts/screws either. 3 ft/lb is good. A good synch by eye before installing the carbs makes the final vacuum synch much easier.
The pilot fuel screws underneath are sensitive. I hope you kept a record of where each was set? This would give you a better starting point in re-jetting. Your mods will generally require about 3/4 turn more out from the original settings. The pilot screws have an overlap effect with the jet needle and will effect performance/plug color up to about 1/5 throttle.
If you didn't keep records, I would set yours at about 1 1/4 to start and go from there. After setting these and the vacuum synch, be sure the side air screws are adjusted for highest idle. Remove the two floatbowl vent lines also so the bowls can breath better.
My jetting experience with the DJ kits and your model/mod's:
138 main, needle e-clip in the 4th position from the top. The leanest needle setting I've seen give good results was with the clip in the 4th position with a jetting spacer on top the e-clip. My bike has the clip in the 4th position, but I also have the 1085 pistons. The pilot circuit to me is the most trouble to get right.
Just be sure to re-synch with the vacuum tool if you make any needle adjustments or disturb the needles/throttle shaft.
I have a lot of experience with the VM carbs if you need help.

 

[marcovandevelde]

Hi Kev,
Keith is correct in saying that you need to adjust the float levels FIRST of all. Also, don't touch anything on the carbs before knowing what it does.

I use an A/F meter in the exhaust to optimise settings, it makes a HUGE difference in power, economy and driveablilty.

Look at http://www.markvanderkwaak.com/dbbp/tech-tips/mm.html to see how you can simply construct this A/F meter. You can also buy one ready on ebay. Weld a socket for the sensor in the exhaust just after the collector. Let the sensor just stick its full nose inside the pipe.

Basically:
-The air screw controls idling and rev pickup, set these to DJ values, it hardly makes a difference if you set them different. Be careful not to srew them in too tight, it will break the small tips off of the needles
-The needle height controls mid rev fuelling, set these on DJ settings and alter after you have determined the main jet size.
-main jet size controls mainly fuelling at top range revs but also affects midrange.

Start by putting an oxygen sensor in the exhaust with the A/F meter on the dash. Check at wide open throttle and good load of the bike wether this is set OK. In my expirience, DJ over-jet because too rich is better than too lean. IF THE METER SHOWS A LEAN MIXTURE STOP IMMEDEATELY. Change the main jet accordingly.
Then check the A/F in mid revs, lowering the needle will lean the mixture, raising will enrichen.

Good luck.

Greetings, Marco.

 

[KEITH KRAUSE]

Hi Kev,
Keith is correct in saying that you need to adjust the float levels FIRST of all.

No, I was advising him to adjust the VACUUM levels closely first.
He said he set his float heights already.

 

[Anonymous]

Somewhere I read that jetting is directly related to throttle position but not to engin RPMs... I see you're talking about idle, mid and hig rpm ranges for tunning... Can somebody tell me if what I thaugh was true?

Thanks!

 

[KEITH KRAUSE]

Somewhere I read that jetting is directly related to throttle position but not to engin RPMs... I see you're talking about idle, mid and hig rpm ranges for tunning... Can somebody tell me if what I thaugh was true?

Thanks!

Absolutely. The three jetting circuits... pilot, needle and main, operate at specific throttle positions, though there is some overlap.
People do tend to use rpm's to describe their problems. But if related to jetting, I always try to ask at what throttle position are they having a problem.
Carb synching however, I like to do at a certain rpm. I like to balance the vacuum levels at something closer to a cruising speed, where I'll be spending time riding, not idle.

 

[Anonymous]

Thank you very much Keith!! That makes things clear...