What to do?

Need some advice... (Puch Magnum MKII)

What do you do when you need a jet that is "in between" sizes? My stock jet is a #60. It will do 30mph and then "4-stroke." If I put a #58 jet in, I can hit 34, but you can tell it is running lean as there is a slight bog at full throttle. There was a small hole drilled in the air cleaner and I imagine it was done at the factory. I plugged it, and the speed dropped to 25mph with the stock 60 jet. I re-opened it and drilled another small hole right next to it. The speed is back to 30.

The guys at the moped warehouse correctly diagnosed another problem...

I have a replacement Bing 15mm carb on it. They said the nozzle and needle are different on those carbs and I need to run it with the stock parts. <very smart, those guys at the warehouse> I did that, then experimented a little. If I run the stock nozzle with the new needle, it will lean out slightly right before full throttle. I am running it this way as I can run up to 30 with it "floored" then back it off just a bit to hit 34. Is this a logical fix for an in-between jet?

Re: What to do?

Steeltoad /

Just guessing here (still learning) but could you stick with the 60 jet and just use a little more oil ?

Still too rich

You are making an assumption that it is now lean because it bogs a little at full throttle with a 58 at 34mph when it used to 4 stroke and only go 30mph with a 60 ??

And it will go a little faster when you back off the throttle ?

Then you are still too rich.

You are not "in between".

There is no way a 60 would cause 4 stroking... and then a 58 would be too lean.

Buy a 56 and try it... (it'll get faster yet)... then do a plug chop and evaluate the plug color.

You should do a plug chop with the 58 first... also.

Then switch to the 56 and test and check.

ALWAYS do a plug chop when trying different main jets.

And........ All this info is already in the "How to fix your Moped" guide.

Re: Still too rich


Believe me, it's lean at 58. Anything less than a 58 and I can't make it out of the driveway. It's a real touchy beast. I've gone down to a 54. The bigger the jet, the slower she goes. The peak speed is at #58, but the acceleration is off. The bike will accelerate OK with the 58 if I don't floor it, but if I do, you can definately feel the bike bog out. I have to overcompensate with a richer needle setting, but it is no longer smoothe throughout the throttle range. It's all over the place.

I've done the plug chop thing. It's slightly dark with a 60 and a bit pale with the 58.

One thing I seem to remember that someone told me years ago...maybe there is some truth in it, maybe it's BS. I've been told that the reason that BING jets skip to only even numbers is because the tolerance was a bit "lax" on them. You could have a "lean" 60 a normal 60 and a "rich" 60. They couldn't get them close enough to call them a 57 58 59 60 61so they jumped to every other one. In other words a rich 60 was closer to a 61. Maybe I have a rich 60 or it's been tampered with.

They all skip numbers.

They all skip numbers.... Mikuni...Keihin.

None of them go 1 by 1.

Doesn't matter though.

And I still think something is fishy with the situation.

Describe exactly what happens with a 56 in it.



top end

what do all those do?.

I am thinking there is a problem with your switched 'nozzle and needle' situation.

There is no way an engine goes from 4 stroking.. to too lean.. with a jump of 1 size.

Something else has to be wrong.

Re: They all skip numbers.

If I run matching nozzles and needles (ie. stock)...

#60...it accelerates strong right up to 30. It will 4-stroke if I go any faster such as downhill.

#58...The acceleration is down some. If I don't richen the needle, I have to feather the throttle a bit to get it to reach it's top end...which is now 34. If I raise the needle up, I can get my acceleration back if I don't floor it. 3/4 throttle is it's happiest position until I'm up to 30, then I can open it up all the way and hit 34.

#56...Crappy all the way around. Poor acceleration and it won't climb past 24mph.

#54...Beyond crappy and almost unridable. It's hard to get into 2nd gear.

If I switch the needle to the newer one but keep the nozzle, nothing really changes accept there is a slight lean spot just before full throttle. I can nail it up to 30 and then cut back the throttle just a bit to hit 34 with the 60 jet. It's a bit too lean all the way around with the 58.

Re: They all skip numbers.

I don't really know what to tell you... except that something is not right... the engineers who design things would never make it so that one step in the main jet size goes from too rich to too lean.

So something is goofy with that nozzle/needle situation... maybe try mixing them up?

Re: They all skip numbers.

I don't really know what to tell you... except that something is not right... the engineers who design things would never make it so that one step in the main jet size goes from too rich to too lean.

So something is goofy with that nozzle/needle situation... maybe try mixing them up?

Re: What to do?


I put the original slide in (along with the original needle and nozzle) and I am able to run the #58 now without it going lean. There must be some small change in the slide. A #56 jet provide no increase or decrease in speed, but the acceleration never can be adjusted out with the needle. It's always a bit sluggish. I guess the problem is solved?!


Re: What to do?

4-stroking? are you sure its not the revlimiter kicking in? mine goes up to 32 and then thats what happens, it sounds like its missing everyother stroke,, but in your search for jets are you switching octane cause higher octane often only leads to higher temperature and no better performance..

Re: What to do?

It has points, so I don't believe that there is a rev limiter.

Re: What to do?

You might not believe this,but on my Minarelli that did a similar thing,it was the points set too wide,.024",AND it wasn't getting enough air.Seems like she'd go up to about 32mph and then die back to 27 or so.NOW I remember that I fixed the main problem with the points setting and it ran 100% better,and then I found out it needed a couple more holes in the airbox.On the other hand,I just added power today to my Motomarina with Franco-Morini engine by filing and opening the points to .018" Also,is your exhaust clear?

Re: What to do?

The points are brand new and set to .018. I might try a different brand plug in it just to see how it runs.



In the service manual, it seems to say that the timing is affected by the point gap, but I've been told that the timing is affected by moving the stator plates. Which is it? It seems to make more sense to adjust the plates as you can actually move them clock-wise or counter...

Re: t-t-t-t-timing

Just trying to think logically here, but the longer the points are open (larger gap) the smaller the charge in the coil. So the points can control the power of the spark. The strator plates would control when, according to where the crank is, the plug sparks. This should be a specific measurement before top dead center.

Depending on how the points gap is set, it can cause the spark later, and the strator plates should be advanced to keep the spark at the correct timing with relation to the crank poosition, if you want to stay with factory specs.

Is this right, or should I get more coffee?

Re: t-t-t-t-timing

Ron Brown /

I think you have it close enough. On some peds, you can move the stator plate, on these, set the point gap to spec and adjust timing with the stator plate.

Some peds do not have an adjustable stator plate, on these, check the timing and adjust the points to set it correctly. If this varies the gap by more than .005" you should look for another problem such as a worn crank key or mis-installed cam if it is a non-keyed press fit.

Dwell, (open to closed ratio), is not much of a problem on a ped as it has a whole revolution to produce one spark.

On the carb problem, a few rules:

Make sure the carb is not too large for the application.

Set the timing and make sure the exhaust and carburetor are clean.

If you can, remove any potential intake restrictions like the air cleaner and or air box.

Do a wide open throttle plug chop to select the correct main jet.

Adjust the idle speed and mikture and select a good idle jet if you have to.

Test ride, opening the throttle wider as revs pick up. If you have a problem just off idle, it could be the slide cutaway (less = richer, more = leaner) and or the needle. If the power is ok from !/3 throttle up, the needle is most likely good, change the slide, or the reverse is true. You can also try making the idle a little richer or leaner to compensate.

Remember that plug chops work at any throttle opening and are the best way to determine mixture.

After setting up acceptably, install the air box and filter and see if it makes a difference, if it does, figure out how to get more air flow to the carb.

Hope this helps,


Re: t-t-t-t-timing

Good info. Ron! Also,I would say for anybody to use a timing light to set the final time AFTER ascertaining that the timing marks are CORRECT.Which they were 20 degrees OFF on my Franco-Morini the other day.If your timing marks are off as mine were,you will have to find TDC and measure accordingly or mark the magneto-flywheel at EXACTLY the distance listed in your manual before piston hits TDC.If I hadn't found Franco-Morini's mistake I'd have been timed 20 degrees slow forever.I NOW check the marks every time before hooking up the timing light.

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