After spending the last two evenings stripping and rebuilding carbs, it's now time to ask on here.. (not to say i didn't enjoy it)

Had my 893 carbs Dyno jetted - 132 main, needle clip 2nd from top, heavy duty springs, blanked air corrector ports and K&N filter.

Ever since, it lurches/hesitant at 5.5 - 6.5k rpm when at constant speed. Definitely not just a flat spot.
Coils, plugs, leads, standard air filter swapped/tried.

I stripped and re built to carbs to check there wasn't anything obviously wrong, and they were ok. (apart from getting a face full of carb cleaner when the air corrector plug blew out when i squirted it up the main jet)


So..... i had a spare set of carbs which i stripped and cleaned, and setup with standard 120 jets. Stuck these on tonight and it runs great. So it's safe to say its to do with this Dynojet.

Questions i have -

What exactly happens at 5.5-6.5k rpm? Is that on main jet at that point or going to be affected by lowering the needle?
Should i start messing about with this tried and tested Dynojet setup - like changing needle heights etc?

Suppose i could go to a rolling road, but from what i read here, this is pretty much bang on when done correctly.

Any suggestion would be great..

[Edited on 9/5/17 by Banana]

It's either a case of trial and error fiddling yourself ,or put it on a rolling road with AFR reading equipment and they will know straight away what the issue is.

Does it pop or bang etc when you have the issue?

Or feel like it's bogging down?

First and easiest thing I would try would be standard springs.

Thanks for that chart Snapper, really useful

Re pops and bangs, yes a few on overrun.
Not really bogging down, just stuttering - you can feel the vibration/lurching.

I'm convinced its running too rich, so looking at that chart i will try lowering the needle a notch.

Just a bit concerned with why mine should be different from all the others than run this setup, and don't want to damage anything running too lean.

[Edited on 10/5/17 by Banana]

Running too rich at part throttle is as damaging on a bike eng as lean!

Are you the guy who was at Andy Bate's race truck at Stoneleigh on the Monday? Nice car.

That does remind me, I dropped my carbs off to him for a fettle and haven't heard back yet. Better chase him.

Good luck with finding the problem.

Steve

Yep i was there at one point.

Andy can't really see anything wrong, and its only really noticeable when your driving and trying to cruise at 6K rpm.

So it made for a pretty unpleasant trip there and back from Suffolk...

Going to bunk off work early and go play with the carbs again.

[Edited on 10/5/17 by Banana]

Could you try the dynojet kit in those other carbs and see how it runs?

I know you tried the other carbs on stock and it seemed to run OK. Did you try driving with these carbs or just run the engine?

Dyno time or time at Andy's place is an option. Not particulaly cheap but you'll soon forget the cost if the car is running right and you're having a good time.

Best of luck

Steve

You read my mind - however, i know this set that has been Dyno'd was running ok before hand. So I've no reason to believe there is an underlying fault with the carbs.
It may come to that though...

Yes i did drive last night with the 120 jet carbs on, as that's the only real way to test. (Having a second set of carbs is damn handy)

I will lower the needle tonight, and see how that goes. (Even if that cures it - there will still be a niggle as to why mine is different from the majority who run that setup..)

What are you having done to yours?

At the moment I'm just having mine cleaned and setup.
Could've done it myself but finding the time is difficult at the moment with just moving house.
It appears that my idea of 'it'll do for the minute' decor are different to the other halfs.
I thought it meant we could live with it for months, it appears she meant days......

Andy did say the standard setup will be no good above 5-6K rpm but once IVA is out of the way I'll be dynojetting them to what you have I guess.

Steve

Standard setup is fine above 6k rpm...
You may just get a smoother power curve with the dynojet kit. Although not in my case..

Cleaning and rejetting is really easy to do yourself, and in hindsight i wish i had.

I had problems with my carbs a few years ago, would idle fine, full throttle fine but in between it would cough and splutter. Tried cleaning the carbs, change jet size etc to no avail.

In the end I took out all the jets, filled a glass with carb cleaner (don't use a plastic cup) and left them soaking in there for 24hrs. Put them back in and everything was perfect! I can only assume that there was a veneer of petrol gunk inside the pilots that spraying carb cleaner up did not get out. Only soaking them dissolved them. You could actually see the gunk floating in the cleaner!

from one of Andy's previous posts-

"jets -132
needles - FLTV50 - set e clips on 2nd groove from top
DJ half shim spacers not used
Pilots 2 3/4 turns out from full in
Heavy duty lift springs installed
Air correctors blocked
This assumes standard blade fuel pump and half decent pipe"

Mine ran spot on using this with a K&N filter ion the standard housing turned upside down.

Q, are you using the original bike fuel pump ?


Roger

Yep, all as per those settings. Correct Blade pump and Ackrapovic can.

So has anyone fitted a DynoJet as per the instructions – drilling the slides and not blocking the air corrector?

Looking at the Dyno Jet Stage 1 instructions, its says to use the 116 main jet.. Going from this I’d have thought 132 would be way too big!

Andy's reason for not drilling the slides was to prevent a faster rpm rate rise (i.e. throttle response), might be worth a call to the guru himself.

Suspect he could point you in the right direction.

Roger

[Edited on 10/5/2017 by rgrs]

So tonight i tried the DynoJet kit in the other set of carbs i have... and............................ its exactly the same.
Hesitant/jerky/rough when held at 6k rpm area.

So its either something else on the engine/car causing this or this jetting/needle arrangement is not liked by my engine. (Bare in mind the 120 jets didn't do this)

I paid closer attention to the throttle position when i was driving, and its probably only 1/4 throttle to hold 6K rpm (ish) which going by the chart above would be the straight section of the needle..
Not sure that really helps me though.

Will try lowering the needle tomorrow, as apparently there is more to life than playing with a car in the evening..