ET3 misfiring at low RPMs or throttle in heat
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Moderibbit
1980 P200E - "Old Rusty", 1976 ET3 Primavera
Joined: 12 Jun 2008
Posts: 8128
Location: Atlanta, GA
Tue May 28, 2019 3:08 pm quote
I'm assuming this is a mixture problem, because I've only noticed it since moving to GA and only when it's hot/humid as hell out, but... Something about that seems too easy.

The bike: 76 ET3 with 135 kit but otherwise stock

The symptoms: seems to be ok at speed, and *usually* idles fine. But in low throttle ranges (takeoff or gradual decel) it will suddenly and severely splutter, sputter, and occasionally vocally misfire (not a "bang" but a big "puff").

Since it doesn't do this at all Fall/Winter/Spring I'm inclined to say something is off with my mixture at the low throttle range with regard to hot dense air. However, what's fishy is 1) it only does this maybe 1/3 of the time (e.g. takeoffs), and cranking the throttle certainly helps but it isn't a magic bullet - sometimes it just keeps it alive while spluttering at higher RPMs for a bit (10s?) before it ACTUALLY clears up.

These caveats have me worried it could be some weird electrical gremlin (CDI going out, etc)

Any thoughts?
Enthusiast
79p200e 66smallstate 85pk50xl 84p125ets
Joined: 24 Nov 2016
Posts: 92
Location: Flatness, Tx
Wed May 29, 2019 3:17 am quote
I've had something similar happen to me twice and both times, it was simpler than I originally thought the problem was.

First time turned out to be a plug that just started to foul up. Very simillar symptoms to yours and a new plug solved it.

Second time was water in the fuel. Modern gas with ethanol is hydrophilic and will pull the moisture out of the air and into your tank, especially in a humid area like Atlanta. The moisture eventually collected in the bottom and made it to the carb which then needed to be burned out through the engine before the engine would run normal again. I drained the tank and put in fresh gas, and problem solved.

Hope your issue is this simple, and hope this helps.
Moderibbit
1980 P200E - "Old Rusty", 1976 ET3 Primavera
Joined: 12 Jun 2008
Posts: 8128
Location: Atlanta, GA
Wed May 29, 2019 5:03 am quote
Thanks for the reply! I'll give that a try before tearing my hair out
Member
Stella
Joined: 28 Jan 2012
Posts: 33
Location: USA
Wed May 29, 2019 10:47 am quote
I bet it is ignition.
Enthusiast
79p200e 66smallstate 85pk50xl 84p125ets
Joined: 24 Nov 2016
Posts: 92
Location: Flatness, Tx
Thu May 30, 2019 3:02 am quote
If it is ignition related, the green kill wire is the easiest to isolate and diagnose.

Hope this helps.
Moderibbit
1980 P200E - "Old Rusty", 1976 ET3 Primavera
Joined: 12 Jun 2008
Posts: 8128
Location: Atlanta, GA
Sun Aug 11, 2019 12:26 pm quote
realized I never followed up on this - although my conclusion is only more valid with more time/testing:

big thanks to poidog on the gas separation idea, because it turns out that flushing the gas and starting afresh completely turned things around. Not a sputter since...

Really quite striking. On a related note I took a gander in my jerry can around the same time I did the tank flush, and a half gallon of spare gas I had in there from about a month prior was a mess! A white powder had separated out of it and lined the surfaces of the canister the gas had been in contact with.
Veni, Vidi, Posti
74 50s x2 78 P200 84 Cosa 58 AllState 68 Sprint 80 50special + projects
Joined: 22 Nov 2010
Posts: 6996
Location: seattle/athens
Sun Aug 11, 2019 1:48 pm quote
Thanks for the follow up. Have you tried ethanol free gas?

After your post I feel better about driving 5 miles with my 2 five gallon cans to get ethanol free premium. Even premixed I've had it sit in bikes for a year through summer and winter but then it fires up & runs fine.
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