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diaphragm fuel pump not working - KT100 2 cycle #4439741
06/23/17 06:25 PM
06/23/17 06:25 PM
Joined: Jun 2009
Posts: 3,820
Chicago, IL
tomcat27 Offline OP
tomcat27  Offline OP

Joined: Jun 2009
Posts: 3,820
Chicago, IL
after assembling a very sorry Yamaha KT100 2 cycle kart engine - it is not pumping fuel. I was a little surprised that the line from the engine to the crankcase actually seems to be pushing air - I was expecting suction. is that correct?


2019 Cherokee, 2018 Jetta, 2014 Sentra, 1995 Escort, 1970 Cougar, 2013 XT250, 2010 Vstar, 2014 CTX1300
Re: diaphragm fuel pump not working - KT100 2 cycle [Re: tomcat27] #4439836
06/23/17 07:36 PM
06/23/17 07:36 PM
Joined: Mar 2017
Posts: 146
northwest pa
justintendo Offline
justintendo  Offline

Joined: Mar 2017
Posts: 146
northwest pa
yes a two stroke builds pressure in the crankcase, totally different design than a 4 stroke. the pulses will operate the external pump if you are fitted for one


2013 escape 2.0 awd mobil 1 10w30ep
2008 fusion 2.3 mtx redline 0w20
1996 f150 4.9 2wd mtx mobil 1 10w30hm
1999 kaw zrx 1100 redline 10w40
many husqvarnas
Re: diaphragm fuel pump not working - KT100 2 cycle [Re: tomcat27] #4439842
06/23/17 07:41 PM
06/23/17 07:41 PM
Joined: Jun 2009
Posts: 3,820
Chicago, IL
tomcat27 Offline OP
tomcat27  Offline OP

Joined: Jun 2009
Posts: 3,820
Chicago, IL
thanks. sigh.....


2019 Cherokee, 2018 Jetta, 2014 Sentra, 1995 Escort, 1970 Cougar, 2013 XT250, 2010 Vstar, 2014 CTX1300
Re: diaphragm fuel pump not working - KT100 2 cycle [Re: tomcat27] #4439929
06/23/17 10:03 PM
06/23/17 10:03 PM
Joined: Dec 2016
Posts: 8,006
Waco, TX
Linctex Offline
Linctex  Offline

Joined: Dec 2016
Posts: 8,006
Waco, TX
When the piston goes DOWN, it pressurizes the crankcase - that's how the air fuel mix gets from the crankcase -> up through the transfer ports -> into the combustion chamber.

When the piston goes UP, it makes a vacuum in the crankcase.
That is how the air/fuel mix gets sucked through the carb.

Get it?


"The evidence demands a verdict".
(Re:VOA)"it's nearly impossible to actually know the particular additives that are in there at what concentrations."
Re: diaphragm fuel pump not working - KT100 2 cycle [Re: tomcat27] #4440115
06/24/17 08:04 AM
06/24/17 08:04 AM
Joined: Oct 2004
Posts: 3,277
Midwest, Illinois
beanoil Offline
beanoil  Offline

Joined: Oct 2004
Posts: 3,277
Midwest, Illinois
https://en.wikipedia.org/wiki/Two-stroke_engine

Simple design, not much power down low, but as it builds revs, it's a powerhouse.


beanoil: Tough under heat, real dirty afterwards.
Re: diaphragm fuel pump not working - KT100 2 cycle [Re: beanoil] #4455730
07/10/17 09:37 PM
07/10/17 09:37 PM
Joined: Mar 2017
Posts: 146
northwest pa
justintendo Offline
justintendo  Offline

Joined: Mar 2017
Posts: 146
northwest pa
get a big enough piston, and the power will be down low too!


2013 escape 2.0 awd mobil 1 10w30ep
2008 fusion 2.3 mtx redline 0w20
1996 f150 4.9 2wd mtx mobil 1 10w30hm
1999 kaw zrx 1100 redline 10w40
many husqvarnas
Re: diaphragm fuel pump not working - KT100 2 cycle [Re: tomcat27] #4456363
07/11/17 02:32 PM
07/11/17 02:32 PM
Joined: Apr 2014
Posts: 637
MN
ironman_gq Offline
ironman_gq  Offline

Joined: Apr 2014
Posts: 637
MN
diaphragm pulse pumps are dirt cheap for an externally mounted one, should be able to track one down on ebay or amazon for under $20.

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