Novice carb kit question

[JonCraig]

So forgive me for asking what are probably stupid questions, but here goes.

Whenver I put a carb kit into a 2cycle carb, I obviously match up the old diaphragms, etc. with the new ones from the kit, and there are always leftover parts that fit some other carb. I have two questions:

1) Sometimes there's are multiple "options" for the fuel pump diaphragm. That is, multiples that are exactly the same shape, but made of different materials. Sometimes it's black rubber vs. a kind of purple plastic. Other kits (I believe) have black rubber vs. a kind of striped brownish-clear-ish. I think I remember reading that one is perhaps better at dealing with Ethanol fuel but the performance was not as good as the black rubbery one.

2) Sometimes there are two pump diaphragms that look identical, except one doesn't have the little "flappers" that (presumably) act as one-way check valves. I don't understand why/when you wouldn't want these little "flappers" to cover the holes… isn't that the whole reason there are little chambers and passages machined into the carb?

I always just use whatever matches what's in the carb already, but I've wondered if there are intelligent decisions to be made when selecting those diaphragms, etc. Figured I'd ask people smarter than me for the real scoop. Thanks in advance!

--JC

[bgsengine]

So forgive me for asking what are probably stupid questions, but here goes.

Whenver I put a carb kit into a 2cycle carb, I obviously match up the old diaphragms, etc. with the new ones from the kit, and there are always leftover parts that fit some other carb. I have two questions:

1) Sometimes there's are multiple "options" for the fuel pump diaphragm. That is, multiples that are exactly the same shape, but made of different materials. Sometimes it's black rubber vs. a kind of purple plastic. Other kits (I believe) have black rubber vs. a kind of striped brownish-clear-ish. I think I remember reading that one is perhaps better at dealing with Ethanol fuel but the performance was not as good as the black rubbery one.

that is pretty much it - the "fiberglass" (brownish striped) or the lexan (purplish plastic) is much more resistant to ethanol but not as flexible for older carbs or worn engines that may not have enough "oomph" to flex the pump part of the diahpragm but either can work - personally I will always use the ethanol resiatant ones before the rubber ones.

2) Sometimes there are two pump diaphragms that look identical, except one doesn't have the little "flappers" that (presumably) act as one-way check valves. I don't understand why/when you wouldn't want these little "flappers" to cover the holes… isn't that the whole reason there are little chambers and passages machined into the carb?

Actually they are meant to work together - the one without the flappers is actually more of a spacer to add a little more room for movement in particular carburetor designs - very rarely ever seen - but I have seen them set up that way a couple of times - so in those carburetors there's actually 3 pieces - the diaphragm, then the spacer, then the gasket..

I always just use whatever matches what's in the carb already, but I've wondered if there are intelligent decisions to be made when selecting those diaphragms, etc. Figured I'd ask people smarter than me for the real scoop. Thanks in advance!

--JC

Good job - better to always match what was there before - but in some cases where you have a choice of material it's a judgement call on which to use - the rubber ones perform better but the non-rubber ones last longer in various fuel types. Keep in mind that most (especially Walbro) kits will be designed to fit many different models, to minimize the number of SKU's that distributors and dealers need to stock (Which is why I really kinda hate Zama - in some cases, there's one kit that fits only ONE carburetor.. ) so there'll almost always be extra un-used parts that you may or may not have ever seen before or have any idea what they do.. but I think I have probably seen enough different carbs that I've seen just about every diaphragm/gasket/check valve configuration... then again.. probably not...

[JonCraig]

Makes perfect sense. Thanks as always for being so willing to teach a noob like me!

--JC