The two stroke / four stroke carb question..??

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wilga12
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The two stroke / four stroke carb question..??

#1 Unread post by wilga12 » Wed Jul 06, 2016 2:47 am

I'd like someone to give me the best two reasons that two stroke carbs cannot be used on a four stroke bike,...?? OR,... can they be used interchangeably..???


Thanks guys/ gals ............Dave / wilga

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Gummiente
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Re: The two stroke / four stroke carb question..??

#2 Unread post by Gummiente » Wed Jul 06, 2016 5:47 am

2-stroke carbs can be used on a 4-stroke motor if they are up-jetted, but the question is why would anyone want to do that? Modern 4-stroke bike motors utilise a CV carb design for better performance, response and fuel economy. 2-stroke motors use a more basic slide carb design and are usually a smaller bore than what is used on a 4-stroke motor of the same size.
:canada: Mike :gummiente:
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It's THAT you ride

wilga12
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Re: The two stroke / four stroke carb question..??

#3 Unread post by wilga12 » Wed Jul 06, 2016 3:30 pm

Mike,.......... thanks so much for the come back.. Much appreciated..

Because I was trying NOT to be verbose,... I didn't give you all the facts of my situation.. The carbs that I'm referring to,... were not to go on another motorcycle at all,...dirt/off road or Highway. In fact,... they were to go on a (Four Stroke) seven cylinder WW II Radial aircraft engine of 915 cu. in.,...YES,... I did/do mean cu.in. not the lil cu. cent. This large power plant is to create a significant "Breeze" for operations of harvest, in a hazel nut (Filbert) orchard.. My preference for the two stroke carbs is two fold.. One,... they might be a lil more tolerant of the less than smooth travel and motions of the equipment, and may also be more tolerant of the unusual positioning, dirt bikes see routinely.. And two,... the overall simplicity of not employing the vacuum system to lift the slide/needle combination,...leaving that duty to the single cable running to each carb.. ...............Comprende..???

Side note, here.. If anyone reading this,... has a mildly educated,...not just a guess or hunch, idea as to the size of the venturies of these carbs I'm in search of,... I'd certainly be glad to hear of your thoughts... Some situation specs: Idle speed = 700 to 950 RPM. Normal working speed = 1800 to 2000 RPM. WOT. = 2100 to 2300 RPM. Individual cylinder displacements = 131 cu. in. Intake valve face size 1.85 in. to 2.00 in. approx.( I can be more specific on this measurement, later. After I pull one of the cylinder assemblies apart) Comp ratio = 7.4 to 1

Thanks very much to any and all who may become involved with this question.. Wilga..

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Re: The two stroke / four stroke carb question..??

#4 Unread post by GS_in_CO » Wed Jul 06, 2016 6:40 pm

That sounds like a really fun project.

I think at that level of simplicity a carb is a carb is a carb so long as you have the means to discover if the mixture is correct.
If the engine had its original carb that would be adjustable.

My father tells the story of getting the Model T that was in the back yard up on blocks intended to be the motive power for a belt driven wood saw running. It had no carb at all. So he had a buddy crank it over while he used a hand pump insecticide sprayer with gasoline in it to shoot some gas down the intake tract to get it to (sort of) run so long as he could control the pumping.

For stationary use the CV business is unnecessary. And a little internet searching should reveal that the very earliest stationary gasoline engine for farm pumps were basically wicks wetted with gas in the intake airflow.
Your biggest issue might be debris going into the carbs & engine followed closely by cooling concerns.
Ron

Current: 1988 BMW R100GS (the 'numberplate' model)

Past: 1987 Yamaha XT350
1983 Honda CB900F
1980 Honda XL185S
1979 Suzuki GS425E

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