Carburetor mods and mod theories

[Chainsaw Jim]

I have this little theory of piggybacking two carbs on my 064 hybrid using the longer 046 carb mount studs. Kind of like a velocity stack, only instead of just a tube and a carb it'll be two carbs as a stack.

Any ideas on this? Has it been done?

 

[drf256]

Will likely be worse.

Poiseuille's theory of laminar flow. You'll be adding restriction. Way better off with a bigger diameter carb or a Vstack.

I see where you're going with this and it sounds interesting. I think you need more air and not more fuel though. Creating a mainfold where 2 smaller carbs fit side by side would be interesting.

My 260 picked up torque with an intake elbow and Vstack of 75mm length, but the up diameter was much larger than the carb Venturi.

 

[Deets066]

I have this little theory of piggybacking two carbs on my 064 hybrid using the longer 046 carb mount studs. Kind of like a velocity stack, only instead of just a tube and a carb it'll be two carbs as a stack.

Any ideas on this? Has it been done?

Your goin to send fuel from both carbs or are you wanting to use one just as a spacer?

 

[Deets066]

If you took the butterflies out of the first carb and ground it out. Then used the piggybacked carb for the fuel supply it might work like reed spacers on a snowmobile. More atomized fuel/air volume.

This didn't seem to help much with torque but throttle response was instant

 

[Chainsaw Jim]

I'd run both for fuel. One would have the throttle in place while the other will be stripped of both throttle and choke levers and would basically be for supplemental fuel at wot. Stiffening the metering lever spring on the secondary so it doesn't open at idle. One thought is that it'll flood out and act like a governor, so I may need to restrict flow.

 

[Redfin]

Impulse?

 

[David Young]

One hole will have more area and flow more. The circumference is at the square of the radius.

Also for intake tract tuning. Shorter of bolsters a higher rpm.

This is some good talk. Glad to see the out of the box thinking is coming back.

 

[Chainsaw Jim]

Impulse?

I actually thought being an 066 jug on an early 064 case that the impulse would be strong enough to handle it, but as I thought about your question I realized that I'm not so sure it will actually matter as the air velocity will pull the fuel at high rpm's. The throttled carb will be taking care of idling.

 

[paragonbuilder]

I like the thinking! What gives you the thought that the saw needs more fuel? Seems usually they need more air?


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[Chainsaw Jim]

I like the thinking! What gives you the thought that the saw needs more fuel? Seems usually they need more air?


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It wasn't a thought based on that. It's just basically experimental. I suppose I may get more air velocity if I were to use an intake boot from an 880 and then build a V to attach to it. But then I'll want to build a twin throttle linkage bracket and that'll be a pain. The original idea with one carb in control may still work with the v since both carbs may not be necessary for idling if a spring loaded choke that opens under 3/4 to full throttle is used on the other carb.

 

[paragonbuilder]

It wasn't a thought based on that. It's just basically experimental. I suppose I may get more air velocity if I were to use an intake boot from an 880 and then build a V to attach to it. But then I'll want to build a twin throttle linkage bracket and that'll be a pain. The original idea with one carb in control may still work with the v since both carbs won't be necessary for idling.

Awesome! Experimenting like this breeds growth for all of us!


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[jmssaws]

As long as there is fuel to the second carb remove the butterflies and it will work off the front carb,no need for a linkage.

 

[paragonbuilder]

As long as there is fuel to the second carb remove the butterflies and it will work off the front carb,no need for a linkage.

Have you done this before Jason?


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[angelo c]

@Terry Syd

 

[idiotwithasaw]

I could see the benefit. Be hard as hell to tune, but use two smaller carbs off of an 026 or the like. Don't try and double your total area just add half or a quarter more and I bet there would be gains.
I would make an intake and stack them one on top of the other for easier tuning and linkage modifications.

 

[idiotwithasaw]

@David Young

 

[jmssaws]

Have you done this before Jason?


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The carb feeds from flow not the butterflies.
It will work off the front carb.

 

[czar800]

Not sure if this is the right thread or not, but I,ll post my thoughts anyway.
I picked up a poulan throw away saw the other day it play with. I was thinking of pressuring the carb with a leaf blower... I think of either building brackets to mount it above the saw or feeding it with something like a sum pump hose And leave the leaf blower on the ground... I know that this is totally not practical! But seems like it would be fun.

 

[paragonbuilder]

The carb feeds from flow not the butterflies.
It will work off the front carb.

Right. Just wondering if you ever tried anything like this?


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[paragonbuilder]

The carb feeds from flow not the butterflies.
It will work off the front carb.

Right. Just wondering if you ever tried anything like this?


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