dragging at top speeds

Hi Everyone,

My Sparta is up and running but acting a little funny. It runs well until I hit top speed. After a while of cruising along at top speed the engine kind of stutters or drags a bit. It feels like a little loss of power or a pulling. I don't know any better way to explain it. Any thoughts?


Re: dragging at top speeds

ಠ_ಠ Jon Folks ಠ_ಠ /

Yup, it sounds like you might be running an incorrect fuel/air mixture. You should probably check to see if your carb and airfilter are clean. If they are, you can try down jetting a size or 2, because it sounds like you are running rich.

Re: dragging at top speeds

Sachs motors are naturally detuned. Instead of downjetting, carefully drill some holes into the airbox until it smooths out.(make sure you don't crack it though)

Re: dragging at top speeds

clean the points and ignition timing.. and get a new spark plug.. Check the carb for dirt.. check float level. Check head bolts for tightness. Check for compression leaks on the cylinder top and bottom..

A bike should run smooth and steady at top speed no matter how the factory set it up, using all original, stock parts.

I think it just needs a tuneup.

Re: dragging at top speeds

No it shouldn't, and you have obviously never owned a stock Sachs. If the motor was built with components to restrict it's speed, then it will only perform to the restricted maximum. Trust me, Sachs motors run naturally rich, thus detuned.

Re: dragging at top speeds

we're not talking about a restricted maximum.. all mopeds are restricted.. detuned in some ways or others to limit top speed.

_After a while of cruising along at top speed the engine kind of stutters or drags a bit_

No factory does things like that, partly because there's no reason to do it. .. there's definately a tuning problem.

Modifying a sick bike is begging for more trouble.

Re: dragging at top speeds

If you have ever ridden a stock Sachs bike, like the 4 I have plus the other 12 in Seattle, then you will notice that when you are riding at full throttle, the pitch of the pipe changes significantly, and the motor begins to '4-stroke,' when it feel like it should still be going faster. What I'm telling you, Joew, is that this is the problem, that the motor is naturally 4-stroking because it is restriced by the stock airbox.

Re: dragging at top speeds

thanks angry brendan! maybe we should just make our own forum called "Brendan Answers Questions about Craig's Moped"

Re: dragging at top speeds

What you're also trying to tell me is thousands of people bought brand new Sachs, and got them to up top speed whereupon they started to run like crap..

Upon mentioning this to the dealer, the dealer referenced the factory.. The factory says "We built them that way. They are supposed to choke and stutter at top speed"

And the customers said OK while recommending the bike to friends..

I find this very hard to believe..

The idea it's running rich at WOT is believable.. And I don't find it hard to believe something like an air filter element is clogged or has deteriorated over time .. or that stock factory settings of various sorts do not apply to old bikes with lots of miles on them. From your experience it seems to me that, whatever it is, it's a universal _problem_

There is NO reason to restrict top speed by flooding the engine with fuel and more than a few reasons why it's a very bad idea... A hundred other manufacturers have successfully restricted top speed while maintaining smooth operation throughout the range. Why should Sachs be different.

Re: dragging at top speeds

That is EXACTLY what I'm trying to tell you!

Look, Joe, they start to '4-stroke' at about 27mph, and the top speed is 29mph. Note that they go exactly under 30mph, so they would meet the requirements of the LAW. They aren't flooding the motor, running an entire jet size too rich, or fouling out plugs, or hindering it's ability to run in any way what.so.ever! They'll run for thousands of miles without modification. But as soon I open up the NOS air boxes and NOS air filters, they gain a couple mph, as well as stop 4-stroking, and the resonance of the pipe no longer exists, which is exactly what Craig was describing. TRUST ME, Joe.

They were restricted from the factory. All mopeds were, in too many different ways to count!

Some old Sachs in Germany have an IDENTICAL motor; the exact same 47cc top end and exact same crankcase, stroke, etc., yet they were restricted to go only 25Kmh (thats about 18mph!). They have a smaller carb, even more restrictive air filter, smaller jets, and a tiny header, to make them _just slow enough_ to meet the speed restrictions in the Law.

Re: dragging at top speeds

I'm perfectly aware that you're trying to tell me that :)

Now think about what i'm trying to tell you..

If my factory manager came to me (I'm the Sachs CEO) and said "Sorry boss.. the only way I know to limit top speed makes them run crappy at top speed", I would quote Donald Trump and say "You're FIRED!".

Re: dragging at top speeds

You're going to have to accept it.

Re: dragging at top speeds

And they by no means "run crappy at top speed." It is simply an audible resonance in the pipe, and a slight hesitation. Versus a stock Puch stops at 30mph without that transistion.

Re: dragging at top speeds

so I'm going to go with brendan on this one because I kinda love him, but anyways, how small of a hole are we talking here good buddy? Like a tad bit smaller than the air intake hole or small like a pinhead.

Re: dragging at top speeds

Perfect timing, I was just about to ask about the same question (as the original one). I just made some adjustments to one of my two sachs bikes and now it seems to do this at the top end. I went up to a 56 jet from a 52 and it really made no difference. I figured it would add more to the top end so I went back to the 52. I am game to drill the air box, but it seems to me if it was to little air, there would be more of a difference (negatively) on the 56 jet. I am new to the game and have only several months with this stuff though, so I don't really know. If it is starving for air, should the ped run better without any airbox and filter coompared to with the stock airbox and filter? Would this be an acceptable check before drilling the airbox? Also, how big should these holes idealy be, how many, and on what side of the box? Thanks. If it makes a difference, I have a 505/1A, 12mm bing stock carb, 52 jet, Gianelli Pipe, stock front sprocket, and 34 rear tooth..... Nothing special, no kit or anything. Thanks.


Re: dragging at top speeds

Running your machine up and down the street a couple of times without an airbox on is a good idea. This minimal time without a filter should not hurt the bike at all. If youre mahcine runs great without a filter, then you know to make more large holes in the air box. If its too lean... then you know to make a slight ammount of change in the air box. It seems to me that most machines run better without any air filter or air box restrictions at all, but if you want your rings to last you better have a filter on there.

Run some tests, see how it goes, then adjust.

Re: dragging at top speeds

I usually start with 4 holes and add more if needed. You can always put tape over a hole if there are too many. I usually drill holes that are slightly smaller than a 1/4" on the side and near/under the original hole. But be really careful because those airboxes get brittle. It's best to use a hand-bit, instead of in a drill.

Puzzling to me all these holes

Ben Van Zoest /

So the airbox intake hole is the very same size as were it connects to the carb would you not have to ream out the carburator intake tube for more air? Why not buy a bigger Delorto? Ok, my Sach Columbia was tuned to the max, brand new in 1976 it never would go over 27 without protesting by behaving badly, 27 WAS the acceptable top speed to me, it's only a moped! I have to agree with Joew that you are barking up the wrong tree, sorry

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