Hybrid Build

[Mastermind]

The best threads are the ones that meander around. If they are too dry.....I get bored of em.

Plus GFYs.

 

[Derf]

Show me/us please. I aint never been that far into a carb. How the heck do you do that?

Look up Poleman's threads on modifying a Zama for a 7900 I think.

Basically you buy a set of micro drill bits that fit on the end of a pencil-type holder, and you ream out the hole in the carb body throat. This allows more fuel to enter the airstream. That means that you don't need to turn the screw out as much to flow the proper amount of fuel to match the amount of air being sucked through the carb. But this is only really necessary on engines that have been modified to flow better (muff mod, larger exhaust, larger intake, longer intake durations, etc).

 

[redfin]

A lot of these walbro have a removable jet. Carb screwdriver will unscrew it.

I took a tilly from a 2100 apart after you wrote this Mike. This one didnt have the removable jet like you said but i believe I know what you mean in the Walbro. Thanks

 

[redfin]

Plus GFYs.

Im fairly certain if we could do that we wouldnt be hangin at a chainsaw site. Id be makin bank on some other site. Good evening Mr Randy.

 

[tree monkey]

View attachment 466782

that is not the venturi

 

[tree monkey]

Plus GFYs.

no

 

[tree monkey]

I took a tilly from a 2100 apart after you wrote this Mike. This one didnt have the removable jet like you said but i believe I know what you mean in the Walbro. Thanks

on older carbs, all the fuel went past the adjustment needle

 

[tree monkey]

Look up Poleman's threads on modifying a Zama for a 7900 I think.

Basically you buy a set of micro drill bits that fit on the end of a pencil-type holder, and you ream out the hole in the carb body throat. This allows more fuel to enter the airstream. That means that you don't need to turn the screw out as much to flow the proper amount of fuel to match the amount of air being sucked through the carb. But this is only really necessary on engines that have been modified to flow better (muff mod, larger exhaust, larger intake, longer intake durations, etc).

I think this pertains to the low side, under the welch plug

 

[KG441c]

that is not the venturi

Oh ok. Ill admit I dont know too much about carbs. Just trying to learn alil though

 

[huskihl]

Oh ok. Ill admit I dont know too much about carbs. Just trying to learn alil though

The venturi is the smaller diameter hole near the middle of the carb

 

[KG441c]

The venturi is the smaller diameter hole near the middle of the carb

Okay thanks. I just downloaded the walbro manual for their diaphragm carbs and see that. The pressure differential made at that point draws fuel from the main nozzle?

 

[KG441c]

Someone may be interested in this
http://www.arboristsite.com/communi...7/?temp_hash=4230a3d51eae6f883b426df4d0cd9388

 

[huskihl]

Okay thanks. I just downloaded the walbro manual for their diaphragm carbs and see that. The pressure differential made at that point draws fuel from the main nozzle?

Correct. Every carb on every internal combustion engine has some sort of a venturi to accelerate the air and grab fuel on the way by

 

[KG441c]

The venturi is the smaller diameter hole near the middle of the carb

Is it the small hole or the bottleneck in the middle of the carb throat or the combination of both?

 

[huskihl]

Is it the small hole or the bottleneck in the middle of the carb throat or the combination of both?

The venturi is the bottle neck. The larger jet coming up into it is for fuel metered by your h jet

 

[KG441c]

The venturi is the bottle neck. The larger jet coming up into it is for fuel metered by your h jet

Ok sounds good. So when the motor reciprocates and draws air through the carb throat and hits the venturi causes a pressure drop and pulls fuel in through the main nozzle? What happens if the check valve is bad ? Reverse flow? Is there a way to check the check valve in the main nozzle?

 

[KG441c]

Wonder if polishing before and after a venturi will increase flow?

 

[huskihl]

Wonder if polishing before and after a venturi will increase flow?

Not sure. Above my pay grade. Usually it's more beneficial to just upgrade to a larger carb. Or drill it out. I've never done it, but others here have

 

[huskihl]

Ok sounds good. So when the motor reciprocates and draws air through the carb throat and hits the venturi causes a pressure drop and pulls fuel in through the main nozzle? What happens if the check valve is bad ? Reverse flow? Is there a way to check the check valve in the main nozzle?

1. Yes
2. Idk
3. Idk
4. Yes, but idk how lol

 

[DexterDay]

Wonder if polishing before and after a venturi will increase flow?

The intake/venturi you don't want to polish. All the dirt bike motors I've seen built, the intake side was rougher so the air/fuel mixture could mix/atomize better... After the intake is where polishing helped to exhaust the gases faster.