MA3SPA Carb

[davism]

My Franklin 150 hp on take off roll stumbled at about 2000 rpm causing me to abort. Checked electrical and fuel found nothing that would cause that problem. My carburator accelerator pump has a ball valve that keeps gas from flowing back into reservoir. Marvel website says to blow into the pump to check if air passes the valve. My valve lets air pass. The ball is located in a small hollow bolt that appears crushed on the threaded end. I don't know if that is designed to keep the ball in place or if it is damage. I sent an email similar to this one to Marvel. So I have 2 questions for the group. Could the accelerator pump be the problem? can I replace the ball valve without a $600 re-build? AS sells kits but they don't include that valve. I fly a Stinson with that carb not sure if it is used in your franklins.

 

[N427]

When did it stumble? Were you advancing the throttle and at 2000rpm it stumble? was it a hesitation or a burble, too much fuel? Primer locked ? Did the rpm raise above 2000 RPM to your static take RPM after the stumble? If so, did it run as smooth at static RPM? 2000 RPM is pretty much at the end of or passed the pump cycle. Meaning that the accelerator pump circuit is no longer in use and has no effect on fuel enrichment.

Try the simple stuff first, https://msacarbs.com/carburetor-troubleshooting/

https://msacarbs.com/pdf/A5-67.pdf

The bolt you mention is the check valve for the pump. Some are sealed by crimping depending on the age of the carburetor, you can test it with the carb body opened in half, using alcohol to fill the pump body with the carb bowl empty, and check to see if fluid flows or seeps back into the bowl. if so, the value is bad. some are held in place by gravity and some with a small spring. I use these kits

https://www.mcfarlaneaviation.com/products/product/10/

https://www.mcfarlaneaviation.com/products/product/286-04/

You will need to select the correct kit for your carburetor Part Number / Serial Number,

Mike.