MZ/MuZ Riders

I've just put a Dynojet kit on my Mastiff (the kit I bought was the stage 2 for a Scorpion).

I used the 1.8mm drill, as my bike has a road legal BSM Future exhaust.

It takes off like a scalded cat once the secondary carb kicks in, and pulls harder to the redline.

However, the idle is a bit hit and miss (I've increased it to about 1100 rpm to stop it stalling), and i reckon the bottom to midrange could be improved.

Have any of you guys fitted this kit, and if so, what settings are you using?

You had the BSM exhaust before. Are you saying the low to midrange is not as good with the Dynojet kit?

The idle at 1100rpm should be fine. (What's the stock rpm specified? 1100 sounds right for a big single. They're better off with a slightly high idle - it reduces the jerking and stalling - which is what the dual carbs do anyway.)

Have you adjusted the linkage so the secondary carb opens earlier than the stock setting?

Yes, I had the BSM before. I'm not sure the midrange is worse, it just feels like there is more of a step when the second card comes in (I assume that's what the step is...).
I adjusted the linkage to bring the second carb on earlier, and the mixture screw is set at 2.5 turns out.

I just wondered if anyone had any set-up tips before I have to spend some cash on a dyno session...

Try geting the bike run up on a dyno. This will show up any problems with the carb settings.

Keith

Fil wrote:Yes, I had the BSM before. I'm not sure the midrange is worse, it just feels like there is more of a step when the second card comes in (I assume that's what the step is...).
I adjusted the linkage to bring the second carb on earlier, and the mixture screw is set at 2.5 turns out.

I just wondered if anyone had any set-up tips before I have to spend some cash on a dyno session...

Keep on trying with the idle adjustment - the pilot screw and idle adjuster. Find the threads on advrider about setting it up on the LC4 Mikuni BST (it's a similar situation - big thumper with CV carb) ...probably start with the LC4 Index Thread. I think it's very useful to get a better understanding of what goes on with these idle settings - like what it means when adjusting the screw makes no difference, the effect on low end to midrange transition and so on.

The step - maybe dip - in the torque curve to where you feel it get stronger than before........it sounds like it's just something not right ..with the off-idle and low-end to midrange transition, then once it's past that you get the power coming in properly.

Does the kit provide a main jet for the primary carb? (There's that recommendation that you go from 130 to 135 there.) Given that it's the primary carb, I think that could affect the off-idle to midrange a lot.

The advrider BST articles will help you figure out if it's too lean or too rich there. Then you can try adjusting the needle - that new Dynojet needle.

Do you have the seal on the front of the airbox? Take it off and see if it improves or not. If it improves, you need more air. Needle too rich or modify the airbox first before changing the needle setting.

It's a pain to do it, I know, but what else? You want to avoid the dyno /bux, and that's no good unless there's someone there that can tune ...it could take half the day, at least. ...? expensive and no guarantee.

Fil, how did you drill the jet? Do the instructions just say "drill the jet" ?

Why I'm asking: I think they don't, I think they just say "drill the jet" ...and those recommendations (by ...I always forget the name, that were posted here a couple years ago) said you can do it by hand, twisting the drill bit by hand, but a friend of mine who is a perfectionist/etc fabricator/welder/etc say=is the only way to do it right is in a lathe. - to be sure the hole is smooth and concentric and perpendicular.

I think I should get a trip to the dyno booked. I went for a blast yesterday, and it stumbles a bit on part throttle aswell.

I have a problem with the 'pop..pop,pop' backfiring on closed throttle, although it did that before I fitted the kit. It's so bad even my wife asked if it ok, and she knows nothing whatsovere about engines!!

As far as the kit goes, it only modifies the CV carb. You get a new needle, a new needle spacer & E clip, a new, softer spring for the slide return and a couple of drills (1.8 & 1.9mm - to suit baffled or straight through pipes).
I just twisted the drill in the jet to drill it out. It's only brass, so was very easy to do. I would think it would be very hard not to get the jet drilled perpendicular, as the drills supplied are only slightly larger than the original hole.

I haven't removed the seal from the airbox, but I have made 4 x 20mm dia holes in the side, up under the side panels.

Try raising the needle one notch.

On the primary or the secondary carb?

I didnt see in your post at what level you adjusted your secondary carb to come "on". It should be set at 5mm of primary carb travel, if the secondary carb comes on too late it will not overlap enough with the primary (posibly causing a "dip"). Also, I went back to the stock jetting on the secondary and left the primary jetted. Also, make sure your air filter is clean. As for the backfiring, ensure your set-up is tight by spraying some wd-40 or carb spray on and around your manifolds/carb area during idle, if there is a leak the idle will change dramaticaly during this excersize... hope to help.

Thanks for the tip with the WD40 - I was wondering where the hell to start looking for air leaks!!

I have tried raising the primary needle 1 notch, but it now hesitates even worse between about 3000 & 4000 rpm. If you stay above 4000 rpm it pulls really well.

I have adjusted the secondary carb to come in sooner (don't know if it's after 5mm of movement of the primary - I'll check).

The Dynojet kit only alters the secondary carb, so the primary is exactly as it was apart from the needle up one notch.

Try to source a 132 size main jet and try to set the air screw at around
5<5.5 turns out. Also, what does the plug look like? Ride at full steam in 2 gear (redline and flip off the ignition (with the thumb switch, not the key *saftey first)) come to a stop and pull the plug. As far as the needle goes, remember you could be possibly adding too much fuel (bogging)... good luck.

Keep the tips coming!!

By 'main jet' do you mean the one in the primary carb or the secondary carb?

I'll try a plug chop when I'm feeling brave...

Main jet = primary carb