1977 Garelli NO1

ok so i cant figure this one out, my Garelli runs great when i first start it and ride for a little while but after it has been running for about 15 min or so and i go up a big hill or have it wide open for a few min it sounds like the piston starts "tinging" i recently switched to synthetic 2 cycle oil and that helps some.

the only thing i can think that is causing this is when it is running hard it is not getting enough gas or the gas cap is preventing enough suction, also i have had this ped for over a year and a half and the problem just started about a month ago. and yes i have cleaned everything and checked for good gas flow the works and my rings look fine and there is no scuffing in my cylinder.

but i wanted to see if anyone else had any ideas about what would cause this or has anyone else had this problem with a Garelli.

Re: 1977 Garelli NO1

Smitty Smith /

One thing that I do is remove the exhaust, and look up into the exhaust port of the cylinder. With the piston at bottom dead center (BDC), you can see the intake side of the cylinder wall, and look for scratches, discolorations, etc. Then, with the piston at top-dead-center (TDC), you can see the piston skirt surface of the exhaust side of the piston. While rotating the flywheel and moving the piston, you can also inspect the piston rings at their hottest point, and inspect for scratches and/or discoloration of the piston below the rings. You will also be able to note how much carbon is built-up in the exhaust port.

Hope this helps.

Smitty

Re: 1977 Garelli NO1

Smitty Smith /

Oh, and a question...where have you isolated this "tinging" noise to, what area of the engine / moped is the noise heard the loudest, and where can you feel a vibration to match the sound. I use a stethoscope sometimes to locate and isolate a strange noise. At least this will give you a more accurate pin-point on where/what the problem may be.

Re: 1977 Garelli NO1

well it only happens when the engine is under a load and at speed

it will not do it when on the kick stand or simply ideling

Re: 1977 Garelli NO1

Smitty Smith /

it's possible that you may be hearing a spark knock? Even some mopeds will spark-knock on low octane or old fuel. Ignition and timing problems or in need of resetting could also cause this condition. Is the noise coming from your exhaust, do you have a stock exhaust, or an expansion-chamber type?

I'm trying to troubleshoot and diagnose the engine/moped, without putting my own ear to it.

Re: 1977 Garelli NO1

Steamboat Aka J. R. Stevens /

First, drain your tank and refill with high test gas and the proper oil mix. If the pinging goes away you have a compression or timing problem. Jim.

Re: 1977 Garelli NO1

the "tinging" sound is defiantly coming from the piston area and from what i can tell it is near the head,

the exhaust is a stock exhaust the cylinder and piston is a 60 cc polini the carb is stock except the jet i went from a 52 to a 60 whats strange about this is i originally had this setup on this bike and it ran fine for over a year and a half then it started doing this about a month ago. i moved the engine, carb, exaust and tires same sprocket setup to a garelli step through frame. and it ran wonderfully for a month, but i only did this while i rebuilt my toptank which i just got done with and re mounted everything on the toptank and it started doing this again.

what i have done so far to troubleshoot cleaned carb, checked gas flow from tank, checked spark, changed spark plug, gaped spark plug, checked timing, checked chain to make sure it was not to tight and putting to much tension on the engine, checked that gas cap was letting air into the tank, put on new petcock, replaced float with new one, changed ND oil, removed cylinder and piston completely to check for ring and wear problems, drained gas and put in fresh remixed gas with synthetic 2 cycle.

all i am left with now that it could possibly be is i mounted the exhaust one hole closer because the other one was missing the rubber or it is an electric issue with the wiring of the bike itself not the flywheel

one electric issue with this bike i have never been able to solve is the break light i have to hardware the contacts on the handlebars together so it wont shut off when i put on the breaks and yes i have replaced the bulbs :) i have re wired the bike exactly like my other 2 garellis and still the same problem

also i did a plug-chop when it was doing this just to see what it would be and everything looked good

i guess tonight i will try completely replacing the taillight housing with one from another garelli i know works and clean and reconnect all grounds. clean the points, and put a new head on.

but hey this is one part of what makes mopeds fun.

Re: 1977 Garelli NO1

if it weren't for the fact the problem seems to have appeared out of nowhere i'd have no doubt that you are hearing the typical "ping" of preignition, especially since it's happening under high load..

but since the combustion chamber's volume is not packed with carbon, raising Compresion Ratio.. and since timing is on the mark, what could have changed that would cause it? A bad batch of gasoline? A wrong spark plug that extends into the combustion chamber (or has something wrong with it's tip causing a hot spot)?

Anyway, i'd try a little experiment.. Add some thickness to the head gaket and take it for a ride up that hill.. see if it makes a difference.

Re: 1977 Garelli NO1

good idea ill try that with the gasket

Re: 1977 Garelli NO1

i dunno what you meant by:

_i mounted the exhaust one hole closer because the other one was missing the rubber_

Something to do with exhaust could be part of it since greater backpressure gets things like the piston crown hotter.

This added heat promotes a faster burning mixture. If ignition timing is already borderline-too-advanced, some added heat in the combustion chamber could push it over the edge of pre-ignition.

Re: 1977 Garelli NO1

ok now i feel really stupid but i did not notice this last time i removed the head and I'm sure i looked right at it. I took off the head to ad an extra Gasket and notice that the original head gasket had slipped and was hitting the piston. good thing it did not damage the piston, but after pulling the gasket out it was nice and form fitted to the head, anyway i replaced it but could not test it out tonight but I'm sure that was the problem.

Re: 1977 Garelli NO1

Smitty Smith /

COOL...sometimes it's the simplest things that will baffle ya'.

Good to hear that it's nothing major.....you gotta let us know if that cures the noise though.

;^)

Smitty

Re: 1977 Garelli NO1

nah.. "stupid" is ignoring the problem.. so you wouldn't qualify.

Why wasn't it making noise all the time? Seems like noise from the piston hitting something would be even more obvious at idle than when flying up a hill..

But piston-to-head clearance does shrink at high engine temperatures.. or the gasket's sharp edge could have been getting red-hot and actually pre-igniting the mixture..

in any case, tomorrow will tell the story..

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