MZ/MuZ Riders

Hi all, enjoying the weather are we?

Quick question please, what is the standard groove position for the slide needle on a bog standard skorpion sport? Fitted new standard exhaust and now have stumble between 5-6000 when on full throttle. Smooth as they come either side of that so presume it wants needle raising a notch but wanted to check the normal position. Before anyone asks, fuel flow is good, carb is as clean as a very clean thing (and the filter).........diaphragm looks fine too.

Also Is there a definitive carb crib sheet/thread anywhere that I haven't been able to find please? Have copy MZ service manual but doesn't seem to give that info. Thanks

you may be just shy of fuel at that point,then it catches up when stumbling....seen it before,try it at 3/4 throttle and see what happens

Thanks for the reply basser. Yes, if I go through the revs on lower throttle setting it is smooth all the way through. I've checked tank breather is absolutely clear, tap runs through well, tried various routes and lengths of fuel pipe. Carb drain when opened gives good constant flow with tap on too. Carb well cleaned, hidden filter clear as a bell, float height good.

The bike had been fitted with aftermarket exhaust when I got it and ran better than it does with the standard. Checked for evidence of carb mods but seemed quite unmolested. Wondered if they dropped the needle when they fitted the end can? hence my question. Will try raising needle tomorrow and see what happens, would just like to know where it normally lives just for comparison.

Forgot to mention, seemed a little better when I richened the idle mixture screw Tank is clean and new fuel too so no water or gunge in it. It's not a heavy misfire to be honest, it's just there some of the time but not always

try mixture screw out 5 turns. Now this really only affects mixture at idle and deceleration though. Having said that it is well known that the fuel petcock does not really flow enough due to its smallish diameter. Acerbis makes one that is larger and fits the tank. Think its a universal type. I have one I'm planning to install sometime........

Funnily enough that's about where it ended up. One thing the standard exhaust has cured is there is now no backfiring on deceleration at all there was plenty with the aftermarket job.

Thinking I'll also recheck float height when I move the needle and maybe raise the level a little, I just checked the float height measurement and didn't do a fuel level check.

I'm pretty sure that stock needle setting is the middle groove on both needles. You can also experiment with the screw that determines when the secondary carb opens. I like mine to open with minimal delay. You should just barely be able to feel the primary open before the extra load of the secondary carb spring kicks in. The stock petcock is crap. Mine couldn't keep up with 6 to 7 second full throttle stepped runs on the dyno starting around 6000rpms. The Acerbis universal works but the valve faces forward.

they do three types?

http://www.acerbis.com/fuel-tanks.php?i ... ategoria=4

That'll be next then........cheap enough? wonder if there's a supplier over here?

Well, needle was on middle groove-3 from top or bottom as you prefer. Have raised needle one notch and brought second carb delay down to 4mm, book says 6mm. No discernable difference run stationary, holds 5-6000 easily but it's not under load. Quick cuppa and then out for a spin.........fingers crossed.

no appreciable difference to the misfire, if anything it's slightly worse. Seems to pull better though when it's not missing. Might bear out fuel delivery issue Right - tap off who mentioned something about reaming it out?

fuel taps are always a problem --- they seem like they're off even when there in the open position
unless your float sticks !!

Too true David. Have had tap off and completely stripped, no gunk in there but noticed ports are rather small Cleaned it thoroughly but surprise surprise no difference. Just had carb off again and raised float level as high as I dared, it's back on runs well and doesn't flood - so will get plastics back on and see if it still does it........... There is a chap on ebay selling those Acerbis taps so that may well be the next job

Phew.......... 25 miles no misfire. Think it's cured .

Anyone care to comment on float level? I have copy of both MZ and SZR Service manuals, both say turn carb upside down and measure float height. Now I was always taught that when dealing with a spring type float needle, it should be measured @ roughly 45% so that the spring was not compressed? That is what I did this last time which raised the level and it seems to have cured the problem. Can't think the manuals are wrong but? maybe that level is correct when you have a pump delivering the fuel which of course I haven't since PO disconnected it?

Why the problem would occur after fitting a standard exhaust is beyond me......