Using a "saw carb"

[2speedboi]

https://www.amazon.com/SeekPro-Replacement-Carburetor-Chainsaw-Rebuild/dp/B07D2YWRQS/ref=mp_s_a_1_13?crid=2V9RH4JZCDE4I&keywords=stihl+ms+270+carburetor&qid=1664729905&qu=eyJxc2MiOiIwLjAwIiwicXNhIjoiMC4wMCIsInFzcCI6IjAuMDAifQ%3D%3D&sprefix=ms+270+%2Caps%2C264&sr=8-13

So I have converted to a single line 1 gallon fuel tank for my friction drive that uses a feed and return line system.

1. I tried to block to return, the engine eventually floods as a result.

2. I made a 3 way copper split, works.. for a minute longer than blocked off return but still floods.


Is the carb above what people are using? I need to keep it at 15mm intake for my 25cc engine. I noticed this one listed uses no vacuum.

Ideally I would like to run 1 fuel line.
Or my freshly painted fuel tank may just get a hole tapped. I have tried to find my answer in other threads but I am not seeing results I am looking for.
Thanks guys.

 

[Karl Snarl]

https://www.amazon.com/SeekPro-Replacement-Carburetor-Chainsaw-Rebuild/dp/B07D2YWRQS/ref=mp_s_a_1_13?crid=2V9RH4JZCDE4I&keywords=stihl+ms+270+carburetor&qid=1664729905&qu=eyJxc2MiOiIwLjAwIiwicXNhIjoiMC4wMCIsInFzcCI6IjAuMDAifQ%3D%3D&sprefix=ms+270+%2Caps%2C264&sr=8-13

So I have converted to a single line 1 gallon fuel tank for my friction drive that uses a feed and return line system.

1. I tried to block to return, the engine eventually floods as a result.

2. I made a 3 way copper split, works.. for a minute longer than blocked off return but still floods.


Is the carb above what people are using? I need to keep it at 15mm intake for my 25cc engine. I noticed this one listed uses no vacuum.

Ideally I would like to run 1 fuel line.
Or my freshly painted fuel tank may just get a hole tapped. I have tried to find my answer in other threads but I am not seeing results I am looking for.
Thanks guys.

You can buy saw carbs without, or with returns. Most carbs will accept a conversion kit, making it a return or vice versa. I use saw carbs a lot, more power, better mileage, easier to tune. My advice to you is, if you plan on building more of these bikes and using saw carbs, just stock up on them and parts, never hurts to have a few extra's.

 

[Cannonball3]

If there is no pulse what pumps the fuel? must have a port in the bore? Most have either a nipple or a port in the mounting flange. I see neither.

 

[2speedboi]

Interesting enough, I had a air bubble trapped in the return before the 3 way I made. took it out for a spin for couple miles with no problems, air bubbles gone, then 6 miles to and back from the grocery store.

It seems that using a 3 way split to return the fuel works fine.

 

[Chainlube]

If there is no pulse what pumps the fuel? must have a port in the bore? Most have either a nipple or a port in the mounting flange. I see neither.

If you look at the last pic in @2speedboi link, bottom center right is the pulse hole.

 

[Cannonball3]

I see, just didnt look bored thru in the pic.

 

[Chainlube]

I see, just didnt look bored thru in the pic.

Little 25-40cc engines don't really need a big pulse to move the gas through them. When the need for fuel is greater, that's when a pipe is needed.

 

[2speedboi]

All my pump carbs for 23cc plus are full bore

Little 25-40cc engines don't really need a big pulse to move the gas through them. When the need for fuel is greater, that's when a pipe is needed.

Even the 12mm non adjustable. Wondering if it doesn't use a diaphragm pump.

 

[Chainlube]

All my pump carbs for 23cc plus are full bore


Even the 12mm non adjustable. Wondering if it doesn't use a diaphragm pump.

I was talking about a hose from the case to the carb for the pulse on bigger saws. They all need a pulse from the intake, as air gets drawn through the diaphragm move up and down.