rich bogging at rpm and 4 stroking throughout

brad peterson /

in short- how do i know what size bing carb i have and given that, should i go for a larger one or just lean out jetting?

the long version:

the last owner of my Puch put a 70cc kit on- and I believe either changed the carb to a 15mm bing or kept it the stock size. point is even without an air filter and with a jet that should be too lean for this kit (72) its still 4 stroking throughout the rev range and then full on bogging at top end.

i have good strong spark and ignition timing set to 15 degrees advance (slightly retarded to stop knock, plug gapped to spec, et cetera. does not even start on choke and needs throttle stop screw all the way in. i swear it must be my carb just not being quite big enough to move the air required. from what i hear the OD on the outlet and inlet ports on the 12, 14, and 15mm bings are the same (mine was 20mm). i digress.

Re: rich bogging at rpm and 4 stroking throughout

Wesley Ambrosini /

Bings have the size printed on the side

http://myronsmopeds.com/category/carburetor/bing/

Stock intakes usually have the size stamped on the side as well, but you can measure the ID of the intake and just know in a few seconds.

Clogged / cracked exhaust can cause four stroking symptoms. I had this happen on a biturbo and a puch treats pipe.

Start with that.

It's a good idea to rip into a new (to you) bike, at least I think so. Go ahead and make or buy a new gasket set and spark plugs and rip that top end off and see what you're working with

Re: rich bogging at rpm and 4 stroking throughout

Wesley Ambrosini /

Oh and a 15 bing is plenty of carb for that setup, something else is wrong.

Re: rich bogging at rpm and 4 stroking throughout

Check float level and float seal. That can increase fuel flow through the jet and have a lean jet act rich.

If you are rich, you shouldn’t have to retard ignition to 15*. But that’s me speculating; not speaking from experience.

Re: rich bogging at rpm and 4 stroking throughout

♣Slew Foot♣ /

If the horn bypass was done it can still arc at above 1/2 throttle if there's wonkiness in the wiring. The horn might buzz a little...

Rev in dark with covers off look for arc near horn or at wiring loom before you buy a carb.

Re: rich bogging at rpm and 4 stroking throughout

have you tried dropping down a size on the jet to see what happens (edited)

Re: rich bogging at rpm and 4 stroking throughout

Overpriced Parts /

Pull top end and inspect it could have piston/ring damage

Pull the magneto and service it like in this :

https://www.mopedarmy.com/wiki/Puch_timing

Re: rich bogging at rpm and 4 stroking throughout

brad peterson /

yeah i think im gonna play around with the timing. probably going to pull the flywheel because its a pain in the ass trying to do it with the flywheel on. if i remember correctly, the timing was set at 15 degrees BTDC which i checked with a light

Re: rich bogging at rpm and 4 stroking throughout

brad peterson /

it also ended up being a 14mm carb. gonna set the timing a little more advanced and get a 15 or 17mm carb later on.

Re: rich bogging at rpm and 4 stroking throughout

might just need a new plug.

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