Sachs slow acceleration, great top end

5051a sahcs eagle. Replaced stock head with 50cc athena kit, mlm pipe, and 15 dellorta sha. Runs great can hit 35mph- But getting there is FOREVER. Almost even boggs down when I accelerate, and have to pedal to get it going. Do you think this could be solved with a front sprocket change, or bigger jet? or maybe timing needs to be reset since this kit is slightly different size than stock? Idk... Im lost, I just want to be able to accelerate faster than I can walk... The plug looks greyish light tan almost, it could be running a little hot/lean. This kit has less the 15 miles on it...


Re: Sachs slow acceleration, great top end

Will the bike idle? check for leaks. spray ether or carb cleaner on all your gaskets when you are running. if there is a leak, your engine will bogg down or die.

Timing maybe.

Up jet. greyish light tan is not rich, run rich or die trying.

Re: Sachs slow acceleration, great top end

Probably has a little to do with the fact that you're using a short conrod. Not sure if those cyls are setup for D or ABC cranks.... but you'd have more compression with a long rod D crank - chikabowow ;)

You should have a chocolate brown color to the plug... my money is on jetting... but you should check your timing and compression too. Buy a jet range and get it over with... there is no magic jet calculator... JUST BUY SOME JETS BRAH.

Also, I love you already because you got rid of the POS bing carb... so you're on the right track.

What's your compression?

What's your timing?

If you don't know what those are, go search for "compression" and "timing" in the wiki, do it and post the results.

Both of those are important - don't say the timing is stock - that means nothing.

You shouldn't need to change gearing... the 11x44-45 gearing on those bikes is pretty low for a pipe and carb (the athena 50 cylinder is basically a little better than the D cylinder) you should be gearing up - AFTER you figure out what's up.

I did 38 on an A with gearing pipe and carb once, but the take off sucked... Keep at it... you should see at least 42 out of that setup with a 13t up front... probably more if you're getting to 35 and the tuning sucks. (edited)

Re: Sachs slow acceleration, great top end

I appreciate the responses. Got a set of jets coming in the mail. Compression, timing... I'll get there, Im new to some of this so I'm learning as I go.I've read some wiki stuff on timing etc but still don't have it to where i'd feel confident in what I was doing. There needs to be more video tutoriols this subject.

Gearing I will get at most a 12t so I dont have to grind the case.

Will the sachs race crank work on the 5051a? Dont really want to spend the money, doubt it be worth it..

Re: Sachs slow acceleration, great top end

It'll raise your compression noticeably and yah... that's what you'd want. I'm not really sure what you're wanting out of your setup...

I would continue tuning... I don't think you have all the performance out of that setup yet.

If you do decide to go the D route, I suggest buying a whole other bottom end, because unlike Puch, all sachs cranks already have a small end needle bearing. However, it wouldn't hurt either. For $135 though I'd imagine you could get yourself a whole other engine.

Re: Sachs slow acceleration, great top end

ryan killin it.

Re: Sachs slow acceleration, great top end

What do I need to take into consideration when installing a D crank in the 5051a? With the slightest of slope my bike will not accelerate. It'll run 5-10mph until I pedal the hell out of it... Im guessing its a compression issue...

Re: Sachs slow acceleration, great top end

Maybe it's the porting on the kit and big pipe combo - maybe it's your jetting or timing.

I really hope it isn't a compression issue on your brand new $220 kit (and probably isn't).

Time and tune. A new crank won't fix poor tuning.

Don't guess it's a compression issue, don't guess it's a timing issue. Determine what it is through inspection.

Compression Gauge (finger test even)

Voltmeter for timing ($5 from harbor freight)

Tuning (just look at the plug and buy some jets)

D crank installation is reverse of A/B/C crank removal.

Re: Sachs slow acceleration, great top end

Luke “Funkenet” Hosfield /

We have the opposite problems. I wish I had your problem though. Also get a timing light instead of the volt meter trick its much easier see your timing. Well worth the $40 if you have a lot of mopeds.

Re: Sachs slow acceleration, great top end

Yah... timing light is best (what I use now) but I'm assuming you just have one ped. You can get a timing light for $20 from harbor freight if ya need something to get by... night and day difference. It's poor quality, but totally functions.

You can time bikes pretty accurately with a voltmeter too... Just a little more work and not as awesome. (edited)

Re: Sachs slow acceleration, great top end

ah... so I thought the slow acceleration was from compression on the bottom end, but at higher rpm was good. I guess if compression was bad the bike would run poor in both ends of the spectrum.

So timing light, and some tuning... Hope I can figure out that timing light.

thanks for the responses

Re: Sachs slow acceleration, great top end

You seem smart. I'm sure you'll figure it out in a jiff. Just don't give up - that's doing it wrong.

Re: Sachs slow acceleration, great top end

Ok so I tried setting the timing, or points rather and Im stumped. I have TDC, and fire point, but i cant get the stator plate to budge. took out the three screws....this maybe a "duh" question, but am i suppose to take the flywheel off?


Re: Sachs slow acceleration, great top end

Probably Fred /

No just loosen the stator screws that are in the slots a little

Re: Sachs slow acceleration, great top end

I did. But I really cant get it to rotate, is there a trick? am I trying to rotate the wrong thing? (im putting pressure on the the metal that the screw comes into contact with on the stator plate). maybe its just so old its need some extra force. it looks to be in great shape though.

Re: Sachs slow acceleration, great top end

Sometimes they get stuck - what I usually do (and is risky) is to take a small screw driver and hit on the HEADS of the screws that hold the coils on trying to rotate the plate - NOT the screws that hold the stator down, the screws that go through the coils. You must be VERY VERY careful... if you break one of the windings on your coil, it's ruined. One foul slip and you're done!

If you have a flywheel puller, some fingers under there might also do the trick... if not, just keep trying. They're a little sticky sometimes.

Re: Sachs slow acceleration, great top end

Update...still no acceleration. I really haven't done anything new besides timing. in fact I had to advance my timing to the point where the stator plate could not rotate anymore without covering up the three screw holes. so Im still off some degrees. Maybe the 15mm SHA is too rich on idle/ acceleration? though the plug chop is where it needs to be. Any thoughts on a 70cc kit giving more bottom end power vs a 50cc athena?

Does everyone else with a 5051a have crap acceleration like me??

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