Dynojet

[billwest]

Those of you who have installed a dynojet kit, did you retain the original slide springs, or put the dynojet ones in?  I'm asking because I find driveability at low rpm a bit rough with the dynojet ones.

Bill.

[andyb]

Define drivability being rough, and define low rpm.  At real low rpm/throttle openings, the slides don't move much if at all, so they don't factor in to the equation.  Have you experimented with swapping them in and out?  It's probably easier than fiddling with the fuel height and pilots, but depending on what it's doing it may not be the source of the problem.

[Marsh White]

I use the stock slide springs.  I didn't make this decision myself, the previous owner did.  But he was very fastidious with multiple dyno runs while he was fine tuning the settings (this was in 1997 before owners groups like this one).  I have a specific entry in my records from him where he took the time to go back and take out the dynojet springs and put back in the OEM....so there must have been a reason.  Hope that helps a little bit anyway.

[Harvy]

Those of you who have installed a dynojet kit, did you retain the original slide springs, or put the dynojet ones in?  I'm asking because I find driveability at low rpm a bit rough with the dynojet ones.

Bill.

Bill, seems there are at least 2 different kits for the FJ from DynoJet.
My kit did not have springs, but it did have the slide drill bit which opens up the hole just a smick.

SO to answer your question.....I still have the OEM springs, with the slides drilled.
But since then I have installed FP needles and emulsion tubes.

My current setup is 108 mains, 45 pilots, 3rd clip position, 3.5 turns out, drilled slides, OEM springs.

Driveability is fine.

Harvy

[SlowOldGuy]

I use the stock slide springs.  I didn't make this decision myself, the previous owner did.  But he was very fastidious with multiple dyno runs while he was fine tuning the settings (this was in 1997 before owners groups like this one).  I have a specific entry in my records from him where he took the time to go back and take out the dynojet springs and put back in the OEM....so there must have been a reason.  Hope that helps a little bit anyway.

Hey Marsh, you might want to experiment a little some day.  The ultimate dyno setup for peak HP may not "necessarily" be the best street "driveability" setup, unless you ride your bike just like a dyno.  Street riding is hard to reproduce on a dyno.

Kevin Cameron wrote a Superbike Tuning (I forget the real title) book back in the day that had a chapter on CV carbs.  One of the things he mentions is the "weak factory springs" can over-react to the throttle demand and produce a stumble.

The DJ kit in my '85 was "designed" to re-use the stock springs with drilled slides.  The kit in the '93 came with stiffer springs.  I've tried the stiffer springs in the '85 once and don't remember detecting any noticeable difference.

I'm not saying your dyno setup is bad, but just that the dyno may not be the ultimate.

DavidR.

[billwest]

I will swap the springs back.  Driveability is less at the moment at low rpm, ie in city traffic, anything under 50kph.  Anything else is excellent.
Idle is good, low speed travel is rough.  Once you open it up, there are no problems.

I recently put a dynojet kit in my ZRX1200, and the instructions suggest retaining the original springs - according to them, the dynojet springs reduce driveability at low speeds for this bike, and are useful only for hard street riding, or the track.  That got me thinking about the FJ ('92).

I will swap them out one of these days, and report back.

Bill.

[Marsh White]

Very valid point David.  I just went through his specifics again and it turned out he only ran the dyno before and after the whole shebang of jet kit, removal of airbox, etc.  So his 3 changes of jets and parts and settings were done via seat time it looks like.  This is what he settled on:

   Jet needles:   3rd groove   
   Pilot air screws:   Open 3 turns   
   Main jets:   DJ118   
   Pilot jets:   DJ144   
   Slide springs:   Stock   

I have fiddled around several times over the years and now have the Pilot screws at 2 1/2 turns out (though I have not tried putting the Dynojet springs back in).  I have also lowered the needles one groove.  I honestly think my FJ runs fantastic - though I am thinking it might be time to put in some of Randy's carb rebuild kits now.  I now have over 68,000 miles on it and (with the exception of one of your bolt kits) none of the internal parts have been changed.  The Dynojet kit was put on at 18,000 miles - so I'm guessing my tubes may be ovaled out a bit and I'm sure I could use new rubber bits.

[RichBaker]

I will swap the springs back.  Driveability is less at the moment at low rpm, ie in city traffic, anything under 50kph.  Anything else is excellent.
Idle is good, low speed travel is rough.  Once you open it up, there are no problems.

I recently put a dynojet kit in my ZRX1200, and the instructions suggest retaining the original springs - according to them, the dynojet springs reduce driveability at low speeds for this bike, and are useful only for hard street riding, or the track.  That got me thinking about the FJ ('92).

I will swap them out one of these days, and report back.

Bill.

Are you sure it isn't an off-idle lean surge you're feeling? I had that (5th gear, 40 or so MPH) and it was gone after I installed the DJ kit air corrector jets. Didn't replace them when I did the initial install, then put them in after I had the rest of kit in and fine-tuned.... ~16 or so years ago. The big-bore bikes (in the 80s and early 90s) were jetted from the factory with fairly lean pilots because that is the circuit in use for the EPA emissions certification...
I also played around between the stock slide springs and the DJ springs, I have had the DJ springs in for the last 15 or so years...

[racerman_27410]

if the bike has a 4/1 header then i would definitely look at the air correction jets like Rich said..... definitely cleans up that midrange stumble on the pipe.


KOokaloo!

[RichBaker]

Frank, I still had the stock system with Yosh Zyclone slip-ons when I did that.... the air correctors made a huge difference.

[billwest]

Thanks Rich, I will try your idea first.

BTW, it has an aftermarket advancer fitted (Factory Pro).


Bill.