262xp R&D

[Mastermind]

Ahhh. OK. Didn't mean any harm at all. Just putting my foot in my mouth. Lol
All in good fun. [emoji106]

No harm done brother. At one time I drank a lot........just not anymore.

 

[RI Chevy]

I hear you. Keep up your good work sir.

 

[Chainsaw Jim]

You get to talking about the venturi's ability to pull more fuel with less or more air flow and that's when the light bulb should come on about pop off pressure. The pop off pressure specs are for stock applications and the pressure usually needs tuned to help whatever you did to the cylinder, intake, or carb so it'll work right.

 

[Keith Gandy]

You get to talking about the venturi's ability to pull more fuel with less or more air flow and that's when the light bulb should come on about pop off pressure. The pop off pressure specs are for stock applications and the pressure usually needs tuned to help whatever you did to the cylinder, intake, or carb so it'll work right.

Jim would u elaborate about necessary adjustments ? Carbs arent my thing at all. Thanks

 

[drf256]

I believe a lighter spring or a higher metering lever (viewed with metering surface towards you) would allow more main jet flow with less venturi vacuum.

Jim makes a great point. If we increase venturi size, metering adjustment should follow.

 

[paragonbuilder]

I believe a lighter spring or a higher metering lever (viewed with metering surface towards you) would allow more main jet flow with less venturi vacuum.

Jim makes a great point. If we increase venturi size, metering adjustment should follow.

So I thought the metering pop off pressure was more for idle??? Am I confused? It seems when it won't idle right we adjust this.

 

[Keith Gandy]

I believe a lighter spring or a higher metering lever (viewed with metering surface towards you) would allow more main jet flow with less venturi vacuum.

Jim makes a great point. If we increase venturi size, metering adjustment should follow.

So the lower the metering lever less flow and the higher the greater the flow? What makes the spring need to be less or more tension?

 

[smokey7]

Lower pop off will increase fuel flow across the board kinda a steeper ramp. On skis if we change flame arrestors we usually must lower pop off or increase a jet size or both. If bet porting would change popoff required also.

 

[Chainsaw Jim]

A lighter spring will allow fuel to flow through the carb with less vacuum but will cause flooding while the saw is sitting or when you pull start with the choke on. Or just straight flood out and never run.

Never leave the metering lever adjusted higher than spec because it will have no affect on how much fuel is delivered at wot and will only cause a very high idle. The only way to get more fuel is to enlarge that passage and I do not like to give advise on how to do that because it's way way too easy to ruin a carb. Not only is it important to have an idea of which bit size to use, it's even more important to polish the surface perfectly so the metering pin doesn't get damaged or leak.
This isn't something that I was taught and I'm not having an easy time trying to convey my understanding of it into understandable sentences.
A person could literally take a block of aluminium, a foredom, a drill press, and a threading tool for the jet screws and build a working carb body from scratch.

 

[paragonbuilder]

A lighter spring will allow fuel to flow through the carb with less vacuum but will cause flooding while the saw is sitting or when you pull start with the choke on. Or just straight flood out and never run.

Never leave the metering lever adjusted higher than spec because it will have no affect on how much fuel is delivered at wot and will only cause a very high idle. The only way to get more fuel is to enlarge that passage and I do not like to give advise on how to do that because it's way way too easy to ruin a carb. Not only is it important to have an idea of which bit size to use, it's even more important to polish the surface perfectly so the metering pin doesn't get damaged or leak.
This isn't something that I was taught and I'm not having an easy time trying to convey my understanding of it into understandable sentences.
A person could literally take a block of aluminium, a foredom, a drill press, and a threading tool for the jet screws and build a working carb body from scratch.

That would be really cool if someone were to build a carb from scratch. Show us how it's done Jim!

 

[drf256]

Interesting.

 

[jmssaws]

The most important thing to remember when messing with carbs in my humble opinion is not to lose the low pressure differential between the throttle plate and the venturi. Sure, a bigger carb might bring some engines to life.......but if it won't pull enough fuel to match the increased air flow you ain't getting anywhere.

I took a stock wj35 and stock boot off my 066 and put a 088 boot and 1" bore carb on and it didn't change at all.
Possibly stronger with the oem carb and boot.
Put the same setup on a 064/056 and made a big gain. Not really sure why but I tried it on another 064/056 and gained nothing. Carbs confuse me

 

[jmssaws]

The saws I port the only carb trouble is occasionally have is a touchy low jet and being lean after a cut and generally a few more lbs of pop off fixes both

 

[drf256]

It would be helpful if someone were to explain the function of the metering diaphragm and lever.

I was under the impression that any fuel pulled into the carb Venturi pulled up on the diaphragm and opened the needle valve which was under pressure from the pump side of the carb. Idle/transition or main jet.

Jetting should ultimately affect the overall flow of the high speed circuit, but wouldn't more resistance to the needle valve opening affect low end and mid range up to max jet flow?

I thought it was an overall curve that was changed by metering spring pressure and lever height and not just the idle circuit?

I'm likely way off here, but I'd like to know why.

@Terry Syd @Poleman

 

[paragonbuilder]

It would be helpful if someone were to explain the function of the metering diaphragm and lever.

I was under the impression that any fuel pulled into the carb Venturi pulled up on the diaphragm and opened the needle valve which was under pressure from the pump side of the carb. Idle/transition or main jet.

Jetting should ultimately affect the overall flow of the high speed circuit, but wouldn't more resistance to the needle valve opening affect low end and mid range up to max jet flow?

I thought it was an overall curve that was changed by metering spring pressure and lever height and not just the idle circuit?

I'm likely way off here, but I'd like to know why.

@Terry Syd @Poleman

 

[drf256]

A tip for any 262 build.

The meteor piston is .006 shorter in overall height than the OEM 262 slug.

My builder case has an OEM on it.

Works out that the skirt is .001 shorter and the crown is .005 shorter.

So when you're trying to nail a perfect .020 squish and your squish comes out at .025 on assembly, you can scratch your head a little less with this knowledge.

 

[paragonbuilder]

A tip for any 262 build.

The meteor piston is .006 shorter in overall height than the OEM 262 slug.

My builder case has an OEM on it.

Works out that the skirt is .001 shorter and the crown is .005 shorter.

So when you're trying to nail a perfect .020 squish and your squish comes out at .025 on assembly, you can scratch your head a little less with this knowledge.

Are the meteors consistent in their height?

 

[paragonbuilder]

I'm partway through reading this. So far it's pretty informative about carbs and the how's and whys.
http://www.wind-drifter.com/technical/WalbroServiceManual.pdf

 

[drf256]

Are the meteors consistent in their height?

Not sure Dan. My last 262 came in with a looser than expected squish as well. Both meteors. One an "A" and one a "B".

 

[exSW]

Both my 262's with factory pistons and a beer can base gasket run about .17 thousandths.