puch newport quit mid-ride

Hi!

I'm looking for some help getting my '78 puch newport back up and running. My wife was out riding it when it died unexpectedly. I can't get it back up and running nor for the life of me can I figure out what the issue is. She said she was at partial throttle riding downhill when the engine "revved for a moment then died".

Here are some things I've checked:

-Fuel flow to the carb (15 bing) is there (brand new fuel as well),

-Jet is clean,

-Air filter is new this year, doesn't seem like that would cause this problem anyway,

-Big fat blue spark is there,

-Compression pushes my thumb off spark plug hole with ease, and

-I wouldn't expect it to be an exhaust problem as I replaced the whole pipe earlier this season.

When I try to start it, I am getting very little if any ignition in the cylinder.

Any thoughts on what would cause such a problem with the above conditions?

Thank you for you help!

-Tyler

Re: puch newport quit mid-ride

Did you put the bing 15 on? What's your jetting?

It would be odd for such a mild build to slip timing but it is possible.

Re: puch newport quit mid-ride

I’m stumped. Only time I’ve had everything needed to run, but the engine refused, it was float adjustment on a brand new carb.

The conditions sound like it could have lost some kind of seal or gasket. Sucked in air causing the rev and then opened enough to upset the air/fuel balance to not run.

Re: puch newport quit mid-ride

Moped Lar (OFMC) /

I would do a proper compression test. The finger test is bs. I have a feeling she soft seized it going down the hill.

Re: puch newport quit mid-ride

^ that would be my guess as well. if you don't have a proper compression tester then pop the cylinder and check the rings and piston.

Re: puch newport quit mid-ride

Thanks all!

To answer a couple questions:

-yes, I put the 15 bing this spring on along with an estoril pipe (over built these components because I knew I'd like to kit someday). It has run just fine until the incident last night!

-I don't have a proper compression test, so sounds like I'll need to take it apart. Probably a good exercise as I haven't taken the time to do it yet.

One additional clue I thought of- I did get it to start just for no more than a 4-5 seconds. The rpms were unstable, revving up and down near idle and eventually just died.

Thanks again for the help, folks.

Re: puch newport quit mid-ride

Gonna ask the silly question.... does it have fuel still? When a bike runs out of gas it will rev up just as it runs out due to the more lean mix from running out of gas.

If your tank has fuel I would inspect the float on the carb. The needle could be getting stuck. Clean out the float inlet and make sure the float needle point isnt misshapen.

Re: puch newport quit mid-ride

Overpriced Parts /

Not timed, tuned, Jetted correctly, not protected with a head temperature gauge, magneto not serviced , fuel flow compromised, wrong mix etc.

Basically you didn’t blueprint the whole build, Probably never changed the original seals and left every thing to chance so could’ve seized/so many things you could’ve done wrong,

Take everything apart and inspect it put everything back together with new gaskets,

Do a compression test, crank case leak down test, service the magneto, Point gap, time correctly, jet correctly, tune correctly,

Re: puch newport quit mid-ride

squirt some premix down the plug hole, if it fires its fuel related if not its compression or spark.

Re: puch newport quit mid-ride

bjaockx, that happened a few weeks ago, but was fortunately not the problem this time! Appreciate you asking though. Turns out I needed a new spark plug.

roffman, wouldn't it be nice to have all the time to do that! Hope to do that eventually. Thanks for the wisdom.

ggspeed, great idea! I'll have to remember that one.

Took the cylinder head off and found a rather crusty piston. I'm guessing it should not have this much carbon build up. The spark plug that fowled was an ngk b7hs, the new one I put in is a b6hs.

One one side of the spectrum, there is a carbon-y, oily b7hs and (in doing a plug chop) a much lighter colored b6hs. The ped felt faster today with the new plug. Perhaps because it is a "hotter" one. It looks as if I'll have to up-jet though because of the white-ish color. Can someone confirm I'm on the right track here for avoiding further plug fowling?

b7hs (old plug, after trying to clean it with a cloth)

IMG_1852.JPG

b6hs (new plug after plug chop)

IMG_1851.JPG

piston head during diagnosis, before installation of new plug

IMG_1842.JPG

Re: puch newport quit mid-ride

I'd be happy with that B6 . That color is just about as right as it gets and the base ring looks pretty clean to me .

Re: puch newport quit mid-ride

Yeah that b6 is a good color. Have fun!

Re: puch newport quit mid-ride

Thanks all!

Re: puch newport quit mid-ride

Just my lame two cents worth, but I'm going with an ignition/wiring problem. If you can, replace all the ignition stuff so you can rule those things out, like your points and condenser, maybe even the coil and spark plug wire and cap. Keep the old ones, but until you know for sure about all that, the rest of any diagnosis is pretty difficult. Make sure your magneto coils are looking clean and no issues with wires grounding that shouldn't as they wind around and through all sorts of possible places for shorts to happen when wire insulation fails. Heat does a lot of weird things to ignition parts as well as induction, so double check that you have a good o-ring in your carb jammed up against the intake since heat can open up air leaks. All basic stuff, but good for all of us to say these things for the sake of others hopefully doing their research here and who have similar problems.

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