Dynajet stage 1 1997 M900

Hello all,
I've recently been off the road with my Monster. It started with one of the ignition pick up coils failing which I replaced, while I was at it I removed the çarbs, checked valve clearances, ultrasonically cleaned the carbs and rebuilt them using a dynajet stage 1 kit. I'm not shooting for the stars with performance, just something suitable for running K&N filter along with straight through (marving) baffles. The bike wasn't shabby with its performance before starting the work.

Anyway, took it for its maiden voyage this morning and it was absolutely plop!!

I set the carbs up as per the instructions, pilot screws out by 3.5 turns, were originally 4.5, but it ran like a dog. I left the floiat heights at 10mm as the bike ran fine with previously, in saying that, I did adjust them to 14mm but they didn't seem right, they were almost locked in position (very limited travel) at that height.

Anyway, while running it, at town speeds, part throttle the bike ran very rough, this improved by adding a touch on the choke lever. at WOT it seemed to pull OK but once in a while the acceleration completely died under heavy throttle.
Idle was completely cocked up too, really high then eventually dropping to the point where it would stall.
I haven't balanced the carbs yet which I will do, it's almost like I have a massive air leak but I was very careful putting it all back together.
Any one else suffered similar problems?

Any help appreciated.

Thanks

Gino.

You should have taken the American approach

If it ain't broke don't fix it

The way I figured, running a high flow air filter (that came with the bike) and open exhaust, I may have been fixing something more serious at some point �� Saying that, maybe should have left it alone, although I think the carbs deserved ultrasonic cleaning after almost 20 years.

sounds like she s running way too rich what groove did you set the circlip on the needles?

[SteveM900]

For your mods you need a Dynojet stage 2 kit. Have a look on their website.

[Flip]

Are you running it with an open or closed air box lid?

100% certain the diaphragms are okay?

If you suspect it running rich try it without the filter in and see how it goes but remember at town speeds it's only partly running on the needle (clip position) and unless you're going mental definitely not on the main jet.

Once it's running properly and revving freely do an old fashioned plug chop.

Also check the state of the o-rings under the diaphragm cover.

Thanks for the ideas chaps.
The set up is exactly as per the Dynajet instructions, needle clip 3rd groove from the top. I was pretty meticulous rebuilding the carbs, the O rings under the lids are their, diaphragms not ripped or holed at all.
What puzzles me is that the pilot screw setting when I stripped the carbs was 4.5 turns out on both, yet the dynajet kit calls for 3.5 turns which is weaker??
The high idle that settles after a while & surging seems like weak mixture or air leak.
I wasn't after sparkling acceleration or wild performance & stage 1 kit seemed to fit the bill -
from the Moorespeed website " Stage 1 kits are fully adjustable to allow the use of a well designed aftermarket pipes and stock replacement air filters like K&N", the airbox hasn't been modified.
As far as the air filter and exhaust I ran the bike exactly as it was before the mod, even with DB Killers still in and it was far from right.
Low speed roughness I think may be pilot screws, for the rest, maybe the jets are smaller than the originals?? Original main was Mikuni 142.5, Dynajet replacement is YJ144, does anyone know how these compare.
Thanks for your help & comments.
ps, I know they are bit old fashioned but has anyone had any success with colortune on a bike?

Thanks for the ideas chaps.
The set up is exactly as per the Dynajet instructions, needle clip 3rd groove from the top. I was pretty meticulous rebuilding the carbs, the O rings under the lids are their, diaphragms not ripped or holed at all.
What puzzles me is that the pilot screw setting when I stripped the carbs was 4.5 turns out on both, yet the dynajet kit calls for 3.5 turns which is weaker??
The high idle that settles after a while & surging seems like weak mixture or air leak.
I wasn't after sparkling acceleration or wild performance & stage 1 kit seemed to fit the bill -
from the Moorespeed website " Stage 1 kits are fully adjustable to allow the use of a well designed aftermarket pipes and stock replacement air filters like K&N", the airbox hasn't been modified.
As far as the air filter and exhaust I ran the bike exactly as it was before the mod, even with DB Killers still in and it was far from right.
Low speed roughness I think may be pilot screws, for the rest, maybe the jets are smaller than the originals?? Original main was Mikuni 142.5, Dynajet replacement is YJ144, does anyone know how these compare.
Thanks for your help & comments.
ps, I know they are bit old fashioned but has anyone had any success with colortune on a bike?

I used to use colortune all the time on my two-strokes. They are gone now.
If I rebuild carbs I use it to check what I got there before road test and plug chop.
Done it on all my carb'd vehicles.

Hi DrD,

think I may have cleared one of the problems up.
I found some charts on t'internet giving comparisons of Dynajet, Mikuni & Keihin mains.
Apparently the Dynajet YJ144 is equivalent to Mikuni 135, the jet that came out of the was a Mikuni 142.5

I'm sure the jets flow in different ways, maybe the YJ144 flows higher but surely not that much. According to the cross reference a Mikuni 142.5 is equivalent to Dynajet YJ152.
While this won't cure the lower throttle setting problems I'm sure it won't help with the dying acceleration I experienced under WOT.
Looks like that was £100.00 wasted....Definitely should have left it alone.

I've got a stage 2 kit on its ebay to me from eBay

If you want I could let you know all the jet sizes etc when it arrives?

If so remind me

[SteveM900]

As I said Dynojet Stage 2. You are flowing more air in and out, hence you need the extra fuel.
With the Stage 2 you can mod the airbox lid for more performance and noise! My 900 has a stage 2.
The jet sizes are listed in the fitting instructions on the Dynojet.com website, click on the Pdf icon for your bike.

[SteveM900]

Had a look and the only difference between Stage 1 and 2 is the size of the main jet, so your kit isn't worthless, all you need is two bigger main jets from a Dynojet dealer.
My 94 900 with modded air box lid has DJ 175 mains.

Thanks guys,
175 main, wow, thats a lot bigger than 144! Apparently that equates to a mikuni jet size of about 162.5, more like what I would expect to see!!
I'll keep you posted how I go on.
Thanks again.