New top end?

Matt /
Jun 14, 2001 09:56PM

Well ive been riding and working on mopeds for about a year now, my 78 puch maxi(2hp) has a biturbo and is in great shape.The only problem is it is slow as hell for some reason. the accel. is extremly bad and it tops out at about 25-30, the regular 2 horse maxi should go 35 and have good accel and mine only does 30 on a GOOD day and it has a biturbo! ive cleaned the carb,cylender,exhaust, the timing is right on, clutch is good. ive been riding motocross for a while now and these symptoms sound like worn rings and/or piston. How much is a new top end kit and a gasket kit? also what is this i hear about honing the cylender? will i achieve any better performence after i get the new top end and gaskets?(my head gasket is bad because when i hold the decompression lever in and put pressure on the pedals i can hear pressure coming out of the cylender) thanks ahead of time.

Matt

Swarm and destory.................... no, just destroy

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Re: New top end?

don-ohio /
Jun 15, 2001 02:37AM

Hi,Matt! Go to Fred's post on `HOW TO FIX YOUR MOPED' and start troubleshooting.You definitely have a jet restriction or air leak or something wrong with the points,plug,or spark plug wire.Make a copy of that post and do what it says because it covers just about everything.BYE!

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Re: New top end?

miguel /
Jun 15, 2001 03:18AM

it is very possible that your piston or rings are worn. if you've already done all the troubleshooting (exhaust, points, etc.) then it might be. i've been told that rings can get worn down and produce "ring slap" which has a pinging sound when you idle. if so, then you're loosing compression (and, hence, performance).

so if everything else is just as it should be ... you may want a new head. but you might just need new rings. don't take anything i say as gospel, though.

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Simple things first.

Reeperette /
Jun 15, 2001 09:52AM

While there's nothing wrong with havin fresh rings in there...and it's cheap at the price...it's nice to have a positive ID on the problem first.

Do a couple of "plug chops" and check your air/fuel mixture, cause if that goes south on you - it can mimic the signs of poor compression.

Or just do both, check and reset the mixture, AND get new rings.

Either way, one of those two will likely solve the problem, and if it don't, let us know.

-Ree

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Re: New top end?

daveb /
Jun 15, 2001 12:37PM

How many miles have you put on this thing? If it

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Re: New top end?

Ron Brown /
Jun 15, 2001 01:39PM

Matt,

I don't understand. You are telling us that the head gasket is leaking and no one is telling you to fix that first. Go ahead and pull the cylinder, clean it out and especially the ring grooves. If the rings and cylinder look good, keep them, the piston went up and down a lot to achieve that perfect fit. Solve your head gasket leak and make sure your decompressor valve seals.

If you have a leaky base gasket, crank seals or crankase leaks of any kind, you will see gas/oil come out while you are running. A little seepage is ok, a lot is not.

Then work on jetting the carb, trying no air cleaner etc.

Ron

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Re: New top end?

don-ohio /
Jun 15, 2001 10:34PM

Note to Ron: The reason I didn't address the head gasket `problem' is I rejected that notion out of hand because you will hear leakage when decompressing some engines and without seeing oily residues, I wasn't too sure he had a leaky gasket.I think you and daveb are right on though,and I didn't even think to ask how many miles were on that engine. Note to Matt:When Ron says see if your cylinder and rings look good,he's assuming you know that it's not just visual but within tolerances listed in the manual,I think.And you should know that the rings should still have a good amount of outward pressure when you fit them into the cylinder.But there is no substitute for a good shop manual.BYE!

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Re: New top end?

Reeperette /
Jun 16, 2001 01:36PM

Yeah, that was my take on it too...that funky sound when the decompression lever is pressed is supposed to be there...and is not, in fact, the sign of a bad head gasket.

Won't do ya no harm to replace it, however.

-Ree

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Re: New top end?

Nick /
Jun 17, 2001 09:20AM

When I first put the Bi-Turbo on my Puch I had to re-jet the Bing Carb. The Bi-Turbo scavenges so good that it made the motor run lean. I went from a 66 to an 82 for a jet. The 82 is too big but I don't care. (it 4 cycles at times at full throttle). The new kit is coming soon.

Nick

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Re: New top end?

Duane /
Jun 26, 2001 10:17PM

Heythere! I had a problem too! BUT they are ( steve's Moped in NewJersey ) making an upgrade kit to make 50 cc - 65-70cc . does that sound like you would be interested in? I am doing just that as soon as they come out with it. Depends on the bike though. I have a 78 Cimatti city bike.

Anyway, if you need anything or questions anwsered give me a hollar.

semmelvon@yahoo.com my name is Duane

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