371xp Carb Kit. Black or fiber diaphragm?

[barton174]

So I'm putting a carb kit in this 371xp, and what came out of it was the gasket and the fiber diaphragm. The kit came with the black one too. What's the black one for?

Thanks
Mike

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[hotshot]

Black one, as far as I can tell from your pic, is reinforced nitrile for non-ethanol gas, which is what you need to be burning.

Fiber is for ethanol laced gas, supposed to take longer to dry out/deform it versus the black. I’ll never know, because they get thrown out.

 

[barton174]

Black one, as far as I can tell from your pic, is reinforced nitrile for non-ethanol gas, which is what you need to be burning.

Fiber is for ethanol laced gas, supposed to take longer to dry out/deform it versus the black. I’ll never know, because they get thrown out.

Oh, I guess it is like a rubber coated fiber. Yeah, I only run either canned fuel or 91 E0 mix with synthetic oil from my local co-op.

Thanks,
Mike

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[Chainsaw Jim]

 

[barton174]

View attachment 678621

Ok, so since this is a ported saw, o should probably run the Teflon one, because it flows better, and that's what came out of it.

Thanks
Mike

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[homemade]

I was just thinking this same thing the other day. I put the black one in cause that’s what came out. I have to open it up again, I’ll put the Teflon one on next.

 

[hotshot]

View attachment 678621

Where did that come from?

Whoever created that is wrong, but it is the internet....

The nitrile diaphragms gave the highest flow rate.

 

[Chainsaw Jim]

Where did that come from?

Whoever created that is wrong, but it is the internet....

The nitrile diaphragms gave the highest flow rate.

It's about the action of the material or function. Either will flow, but one will respond better to the impulse over the others.

 

[hotshot]

Where did that come from?

Teflon or PTFE does not flex, and has to have a backer material. It was chosen by Walbro for chemical compatibility, not performance.

Notice that Tillotson doesn’t offer it.

I’ll find the diaphragm selection white paper for pump performance, maybe it was Ingersoll-Rand, Wilden, or ARO. I can’t remember.

 

[Chainsaw Jim]

Where did that come from?

Teflon or PTFE does not flex, and has to have a backer material. It was chosen by Walbro for chemical compatibility, not performance.

Notice that Tillotson doesn’t offer it.

I’ll find the diaphragm selection white paper for pump performance, maybe it was Ingersoll-Rand, Wilden, or ARO. I can’t remember.

That may be so in the RC world, but chainsaws are a different beast.

And yes.. Tillotson does offer it. A few examples are the RK-28HS, HL, and HR kits.

 

[barton174]

Where did that come from?

Teflon or PTFE does not flex, and has to have a backer material. It was chosen by Walbro for chemical compatibility, not performance.

Notice that Tillotson doesn’t offer it.

I’ll find the diaphragm selection white paper for pump performance, maybe it was Ingersoll-Rand, Wilden, or ARO. I can’t remember.

Fwiw, I tried both and the max rpm was 400rpm higher with the black one vs the fiber looking one. 14,4k vs 13,9-14k. Joe said to tune it back to 13,5 and roll with it, so I put the fiber one back in, richened it up a hair to 13,5 and it's happy.

Thanks,
Mike

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[flyinfinn]

Fwiw, I tried both and the max rpm was 400rpm higher with the black one vs the fiber looking one. 14,4k vs 13,9-14k. Joe said to tune it back to 13,5 and roll with it, so I put the fiber one back in, richened it up a hair to 13,5 and it's happy.

It will live a longer life at 13,5 anyways.

 

[barton174]

It will live a longer life at 13,5 anyways.

Yeah, that's where he originally set it when he ported it. It just went up a bit when I did the carb kit, so had to be brought back down

Mike

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[Derf]

This might be a little late to the party, but what Walbro says is that the tan teflon reinforced fiber gasket is for if your carb has a machined surface to sit on. The black is a Buna rubber gasket if your carb does NOT have a machined surface to sit on. Both have ethanol resistant properties.

How much each resists ethanol I don't know. But I would suggest planning on doing a carb kit once per year if you use ethanol gas. Also important is the float meter spring and valve. The spring wears out over time, regardless of ethanol. The valve wears out with use.