A question concerning Robin 35 with walbro carb.
- Thread starter motorbikemike45
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loquin
Well-Known Member
The link in post #7, above. Walbro also makes carbs with the diaphram pumps built-in. The after market pumps I was talking about are separate, diaphram pumps that use the manifold vacuum or (in a 2-stroke) the crankcase pressure/vacuum.
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Its still off topic and Walbro should do real world testing.Those pumps are for larger engines than the EHO35 I never measured a lawn mower engine so it may be that low, but not in the mini four strokes.They don't take into account spit back which is caused by the intake valve shutting and the mixture flow stopping abruptly, causing a spike in the intake port presssure. These small engines are plagued by spit back. They also have a fairly high intake port vacuum because of the small port and short valve timing.
The question was about the internal pump in the carb used on the EHO35, all the WYL series carbs are internal pump carbs.
Honda used 6 different carbs on the GX31 alone, half of them had the return spring the other half didn't.The spring does not make it a four stroke carb.
98% of all pumping issues with the WYL are related diaphragm problems or clogged inlet screen or clunk.
The question was about the internal pump in the carb used on the EHO35, all the WYL series carbs are internal pump carbs.
Honda used 6 different carbs on the GX31 alone, half of them had the return spring the other half didn't.The spring does not make it a four stroke carb.
98% of all pumping issues with the WYL are related diaphragm problems or clogged inlet screen or clunk.
loquin
Well-Known Member
I agree that a 2 PSI (if it is or isn't valid for these motors) shouldn't a problem. After all, 2 PSI is equivalent to the pressure of over 4 feet of water column and over 5 feet of gasoline. If you assume that half of this head would allow the fuel pump to push/pull enough gas to keep the engine running, you're still looking at two and a half feet...
As far as some carbs having a spring, and some not, if the diaphram is 'springier' it could be act as it's own 'spring.' Or, if the carb was intended for use on a motor with an attached fuel tank, the diaphram could be springy enough to work just fine...
However, the physics of the design of a separate diaphram-style fuel pump are exactly the same as an attached fuel pump. The basic pump design is the same as well. (Specifics, of course, can be different.) So, in that regard, the information provided by Walbro describing how separate diaphram fuel pumps actually work is applicable.
As far as some carbs having a spring, and some not, if the diaphram is 'springier' it could be act as it's own 'spring.' Or, if the carb was intended for use on a motor with an attached fuel tank, the diaphram could be springy enough to work just fine...
However, the physics of the design of a separate diaphram-style fuel pump are exactly the same as an attached fuel pump. The basic pump design is the same as well. (Specifics, of course, can be different.) So, in that regard, the information provided by Walbro describing how separate diaphram fuel pumps actually work is applicable.
