You need a Dynojet kit he said.

[BikeJake]

A mate of mine is certain I need a Dynojet kit. 

What can they do that the right jetting can't? 

[wraith]

That all depends on who you ask 

[Gixer1460]

In simplistic terms - you can change all the 'removable' jets but will always be stuck with OEM needle and needle jet / emulsion tube! This assembly covers fuelling from about 1/8th throttle to 3/4 throttle in rough terms so if the induction isn't as designed to work with that arrangement & in that range, you'll get poor running! The best example is removing the airbox from CV carbs - they generally won't rev out past 4.5 - 5k rpm which is smack in the middle or needle range. DJ kits mostly have different needles and emulsion tubes to combat that very problem.

Dynojet have been around since the late 80's and developed kits for thousands of applications and for the most part they just work on modified induction systems short of swapping to slide carb alternatives. I've found they work - following the included instructions - out of the box with minor fine tuning on a dyno to get perfect.

You may be able to fool yourself that changing OEM this and that, blasting up and down roads, taking carbs on and off, rinse and repeat LOADS of times is worth saving £££ - but is it really? I'd rather spend an hour, fit something that works and then just ride!

[wraith]

I've got a Dyna jet kit in a set of gsxr750 38mm carbs that are fitted to a gsx1100f motor etc etc when I ordered the jet kit I spoke to Dyna and they put in jets etc for the set up I've got on my bike, worked first time very happy, all I had to do is replaced the needles and emulsion tubes (Dyna will send new needs free of charge but you have to buy the tubes) but this kit has been fitted for well over 6 years.

Where as on a other bike I've got, same 38mm carbs but in a b12 ISH motor didn't put a Dyna jet kit in just bort the Dyna jets but the bike has a small but there stutter around 3-4 rpm that I can't get rid of, so a jet kit will be got for that.

Some people don't like Dyna stuff some do, I do like there gear, each to there own.

 

[Shill]

Yeah my understanding is it's partly the specific non-standard taper on the needles? If you only swap jets that assumes the rest of the setup is in some way still sensible/appropriate in a given running condition... if you've made a more radical change like ditching the airbox as mentioned above, you can't rejet your way out of the really significant change you've made to the airflow and fuel metering requirements through the rev range by just changing one part (considering that on CV carbs the needle movement is a function of specific pressure differences that are probably affected by removing the airbox). So basically, what they said above

I have a kit on my B12 and it works great - it has a *slight* stumble sometimes moving away from standing at low revs+throttle, but not enough to inspire me to try and fix after 2 years so can't really complain.

Edited November 3, 2022 by Shill

[BikeJake]

Thanks all... Bloody informative that. 

I built an XS Tracker and the carbs were murder with pods until I got the exact right pods. 

Never thought of DJ kit.. 

Will get one ASAP as I am removing air box and getting new headers before Xmas. The new barrels are hear and going off for blast cleaning 

[XXXSpro]

I have a 1991 GSX1100g  essentially same engine as the B12 with the  1127cc Oil Boiler

Went with a kit from Factory Pro but was way lean up top and didn’t hit power until 1/2 throttle or so after mods

Now have it pulling like a train without any stumbling in the Rev range.

Took a few try’s and a few weekends but better than paying to get it jetted ($600) 

Mods:
Full Hindle 4-2-1 Exhaust 
GP Style Muffle w/Baffle
Dual Pod Foam Filters 
+5 Timing Advance 

Tuning:

Main Jets: 140 1-4 Cyl 145 2-3 Cyl
Pilot Jets: 35 All 4
Needle: 2 Up w/Metal Shim 
Idle Jet: 2 Turns Out On 1-4 2.5 Turns 2-3