mistergrumpy
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| posted on 18/7/08 at 05:41 PM |
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Dynojet
Can someone help me with my latest problem and explain something to me. I've just sorted a mis fire by replacing a plug that seemed a bit wet
and black so now engines running sweet. Hurray!
However when it gets up to temperature and I rev it, when it tries to settle at idle it stalls.
Now prior to revving its idling fine at about 1100-1200 rpm. I've a feeling its down to the dynojet and stuff needing set up properly but
I'm just trying to get my head around summat.
Whats the effect of moving the circlip on the needle and what's the effect on altering jets? I think its something to effect rich/lean mixture?
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smart51
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| posted on 18/7/08 at 05:55 PM |
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The clip settings are specific to your engine. My R1 has the clip set on the second groove from the blunt end.
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worX
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| posted on 18/7/08 at 05:56 PM |
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You could try altering your mixture screws for now to see if it has an effect? (sorry if that should be Affect - I wasn't allowed in
english/math/science lessons at school!)
ATB
Steve
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mistergrumpy
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| posted on 18/7/08 at 06:00 PM |
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Yes my clip is on 2nd groove from top too. I'm aware that the mixture needs leaning out a bit but would this possibly be the cause of the engine
stalling at temperature?
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mackei23b
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| posted on 18/7/08 at 08:55 PM |
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Here is my set up
ZX9R C1 1998 Engine
TTS Foam Filter
MK 4-2-1 Exhaust, CAT and R1 Can
Carb set up:
Dynojet Stage 1 kit
138 Main Jets fitted
Main Air Jet Blocked
Dynojet Needles installed on fourth groove from the top
Fuel Mixture Screw 2.5 turns out
I also drilled an extra hole out on the slides as per the Dynojet Instructions.
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David Jenkins
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| posted on 18/7/08 at 09:04 PM |
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Although I don't have a BEC, I do have bike carbs on a x-flow. Mine was running far too rich, and I didn't have a clue on how to sort
it.
I was pointed towards a book from the library: "Motorcycle Fuel Systems Handbook" by John Robinson - publ. Haynes, ISBN 1 85960 514 1.
It's written for students so gets a bit techy in places, but the practical bits are very useful, especially how Mikuni and Keihin CV carbs work,
and how they're tuned.
I borrowed a copy from the library...
[Edited on 18/7/08 by David Jenkins]
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mistergrumpy
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| posted on 18/7/08 at 09:06 PM |
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Cheers all. I have the same set up as you Ian. I'll try dropping onto the 4th needle groove too and drilling the slide, didn't notice I
had to do this.
I will have a look for that carb book too sounds really good. Cheers again.
[Edited on 18/7/08 by mistergrumpy]
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simoto
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| posted on 19/7/08 at 12:48 AM |
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Hi, I wrote this all once and deleted it by accident.
Its not too bad to work with these carbs when you understand them a little.
As you will have noticed the needle is tapered and when installed and at rest it sits through and almost totally blocks the main jet.
The needle is attached to the throttle slide and as you depress the pedal it lifts up through the main jet. Due to the needles tapered shape it begins
to allow fuel to be sucked up from the float below the main jet, by the airstream rushing through the venturis. The quantity being sucked past
increases at the desired rate depending on the rate of the taper.
There are as many tapers as swear words in the world and some clever tuners design their own to suit different engines and pipe set
ups'/circuits.
By the time three quarter throttle is reached the needle is entirely clear of the main jet and fuel is sucked through impeded only by the main jet
size itself.
So the carbs work in stages dictated by the throttle position as follows.
The first quarter is governed by the pilot screw(i think your problem relates to this being a little too far out-try 2-2 1/4) this screw partially
obscure a gallery in the carb allowing a set quantity of fuel to be pulled past at low engine speeds and while the main jet is closed by the
needle.
As the throttle is depressed beyond a quarter and up to approx three quarters the needle taper governs the fuel flow in an increasing rate as it lifts
up through the main jet as previously explained.
Then as 3/4 throttle and beyond are achieved simply the increasing air flow through the venturis governs the mixture as it drags petrol up out of the
float bowl through the fully open main jet. It does this because a partial vacuum is created above the jet by the speed of the airflow and this is
enough to draw fuel from the float at a rat set by the size of the said hole. This size is what the jet number refers too.
With this info and some imagination its easy to trial and error your way through and you will soon be very good at taking carbs out.
The needle goes leaner as the clip progresses up the grooves because the taper is being lowered in the hole and obscuring it more.As a clue to start
you off a needle tapers suitability is usually checked by observing the bikes/cars behaviour from corner apex to exit.
A lean needle will usually result in a lively car that wants to run quickly up the revs and spin up but actually lacks real grunt/drive, a rich car
will bog a little anf feel reluctant to get on with driving out.
Be careful and systematic while working with your carbs and it will be fine, only go one clip pos at a time though as you cant hurt anything that way
and simply decide better/worse. Same with jet sizes only one or two either way will not cause any catastrophe but improvements can be easilly noted
and an optimum can be found with patience/trial and error.
A good dyno operator will sort things out in a jiffy for you with a mixture trace, a couple of runs being sufficient for an experienced guy to
observe/adjust/check result.
Well done to anyone still reading and sorry to the many that already know this, hope it helps someone cos you struggle to find a car dyno with an
operator that understands these carbs properly.
Given some experience and and the info above its easilly possible to get within 10% of optimum in the garage without turning a wheel then check on the
road.
Sorry for open university epic, blush
Si
[Edited on 19/7/08 by simoto]
[Edited on 19/7/08 by simoto]
[Edited on 19/7/08 by simoto]
striker/blade now complete, thanks to all on this site.
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andrew.carwithen
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| posted on 19/7/08 at 10:47 AM |
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I would heed a little caution before drilling out the holes in the throttle slides.
I know the dynojet instructions tell you to do so, but remember, these are presuming that the vehicle is a motorcycle and not a BEC!
I remember talking to Andy Bates (AB Performance) about setting up my Dynojet kit when it arrived and he said under no circumstances should I enlarge
the holes in the throttle slides with the drill included with the kit! (I seem to recall him saying that because of the extra weight of the car
compared to the original bike, it affects the throttle response and opening said holes can ruin the running or something to that effect.)
Admittedly, the above is with reference to fitting a dynojet kit to 'blade carbs, but I'd have thought the same principles would apply to
other engines/carbs?
Might be worth giving him a call to confirm?
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mistergrumpy
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| posted on 19/7/08 at 03:37 PM |
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Si that's fantastic, just what I was after, thanks a lot.
Andrew, unfortunately I've been and drilled the slides earlier and guess what, it's all gone to sh1t Struggling to start, struggling to
idle and hunting a little. Admittedly I did alter the mixture screw as per the instructions but playing with it in 1/4 turns has just about got it
starting and it's only on 1 turn now. I think I might try to get some undrilled slides and try again.
Thanks again Si 
Ooh edited to add. When I rolled the sodding thing back into the garage I could hear the carbs gurgling. I removed the air filter and there was fuel
intermittently dribbling from the jet and the throttle valves were opening by themselves  What's going on? I checked for any ghosts pressing
the accelerator but none there
[Edited on 19/7/08 by mistergrumpy]
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simoto
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| posted on 19/7/08 at 05:30 PM |
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Could be seals blown by the pump pressure, hard without seeing it mate. Does the symptom appear as the pump is activated and dissapear when power is
cut?
The drilled slide thing is a non starter as its designed to improve throttle response in lightweight bikes. As the other poster remarked this is
innapropriate in a bec as more time is taken to gain momentum on depressing the throttle.
Sure it would be worth at least trying standard slides. If your suitably equiped its possible you could epoxy and redrill maybe cos the slides are
dear as you would expect. Prob got this to come with mine too, not even been in the carbs yet as so much other stuff i cant do distracting me.
Good luck again.
Si
striker/blade now complete, thanks to all on this site.
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mistergrumpy
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| posted on 19/7/08 at 07:16 PM |
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Wahey! Getting somewhere, well at least back to where I was before this morning. I've stripped the carbs again and noticed that the 138 jets
from the Dynojet kit are actually 140's! So i've put in some 136's that I have and that's helped loads. Just a bit of a
bogging down after a few seconds if I keep the revs at 2000 eventually leading to a stall. I'll work on that though.
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simoto
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| posted on 19/7/08 at 10:20 PM |
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Ok that could be a pilot circuit issue try half a turn either way and note changes to under 2000 rpm steady throttle. Also worth checking plugs after
stall.
New plugs are a revelation sometimes too.
If your unsure of yours then treat it to a new set now your getting near and unlikely to do any harm.
If the pilot screw has little affect set it at one and three quarters and alter the needle a clip either way and observe.
striker/blade now complete, thanks to all on this site.
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mistergrumpy
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| posted on 19/7/08 at 11:19 PM |
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cheers for this si. By pilot screw do you mean the pilot jet alongside the main jet when the float bowl is removed?
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locosaki
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| posted on 21/7/08 at 08:34 PM |
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Hi mate,
How are you getting on with setting your car up,alot of your symptoms I have been having too !!!
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simoto
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| posted on 21/7/08 at 08:42 PM |
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Sorry mate been away for a couple of days, by pilot i actually mean the pilot screw. The one some refer to as mixture screw i think.
Sorry again to have taken so long to spot this.
striker/blade now complete, thanks to all on this site.
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mistergrumpy
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| posted on 21/7/08 at 08:43 PM |
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TBH mate. I've not had time to tinker yesterday as I was putting a new roof on the conservatory. I'm too knackered tonight so it'll
probably end up being Thursday before I can play again. Ideally I'd like to get it running summat close then somehow get it to a rolling road,
not sure how yet though. I'll deffo kep you updated though. I take it you're having that bogging down/stalling thing too then?
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mistergrumpy
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| posted on 21/7/08 at 08:48 PM |
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Si, no worries mate. Yes I've been playing with the mixture screws. They're very fine adjustments needed there eh? I can tell when it gets
too rich now like you suggest. I'm just waiting on delivery of some carb balancers then I'm going to have a play with them too and a
little more tweaking.
Thanks for getting back though.
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locosaki
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| posted on 21/7/08 at 09:10 PM |
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Yeah,I think I have the pilot setup quite close as I get to around 3500/4000 rpm and it starts to misfire so I assume this could be down to clip
position,I noticed when going down hill tonight the problem didn't seem as bad though,I'm currently running 170 main jets and have my e
clip on the 3rd notch from the top,If I've read the info on this thread correctly I think It's a problem with being to rich,That was
certainly the problem with the pilot screw as I had it set at 2.5 turns and ended up backing it off too 1.5 turns out,That made a big difference to
how the car pulled.
Good luck all the same mate.
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simoto
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| posted on 21/7/08 at 09:40 PM |
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Process of elimination once you understand the stages of operation. Really glad someone has found it useful
I'll check this more frequently now, good luck. si
striker/blade now complete, thanks to all on this site.
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locosaki
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| posted on 21/7/08 at 09:58 PM |
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Hi,
Yeah cheers Si,Excellent info here.
You got any opinions in 170 mains,Maybe a bad starting point (too large)
Sorry to hi-jack the thread !!!
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simoto
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| posted on 22/7/08 at 10:04 AM |
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No worries, do seem a tad large but my experience is related to race bikes not becs sadly.
Are we talking about the same (roughly) mid to late noughties blade carbs?
Do you have a ramair box fitted or bare trumpets?
Sometimes they run much larger jets.
Cpould be your running issue is down to that, try holding a steady throttle at 3/4 thou and at 6/7 thou rpm.
If the engine needs coaxing to stay at selected rppm's like your chasing the dial up its prob rich in that sector.
If on the other hand it seems as if you are holding the revs down, like it wants to run up the dial without more throttle then it will be lean.
The rpm bands suggested are in order for you to decide weather it is needle to main transition or purely an overich main jet and may need tweaking for
best result to be obtained.
Sometimes tuners prop up a lean needle with a rich main(by accident usually) can in some circumstances give seemingly better running condition when a
lean needle was actually the prob.
The resultant overlarge main jet symptoms are not as obvious as an innapro' needle on the road.
Hope this helps, good luck.
Si
striker/blade now complete, thanks to all on this site.
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locosaki
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| posted on 22/7/08 at 03:52 PM |
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Its on an older zx10 motor I've been refering too !
The setup just now is bare trumpets,I've had a read through a few other posts regarding bike carbs and have not come across anyone running such
a large main jet,I'm now begging to think my self that this could be a little large.
I will go for a test run later doing what you suggest,I will also raise the needle 1 position without touching main jet to see what difference that
brings.
Cheers Mike
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simoto
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| posted on 22/7/08 at 03:58 PM |
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You can easily do the procedure on the driveway and make instant adjustment. then drive for overall effect. Actually easier static i think its about
feeling weather the revs"want to" rise or fall asyou attempt to hold them level with a steady throttle
[Edited on 22/7/08 by simoto]
[Edited on 22/7/08 by simoto]
striker/blade now complete, thanks to all on this site.
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locosaki
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| posted on 22/7/08 at 07:26 PM |
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Ok I tried raising the needle 1 notch and the same problems are still there so I assume now my main jet is too big !!
I also noticed when changing gear the revs don't drop back to idle right away they seem to rise on there own accord.I.E If i dip the clutch
while in 3rd gear at 1500 revs they will brielfy rise to 2000/2500 revs ...
Any ideas ??
Cheers
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