MF35 Petrol/TVO running very poorly

[Mitmah]

Hi folks, I’m looking for any advice on my early 60’s petrol tvo 35. I changed oil, filter plugs and points a few months ago and it was running ok afterwards. I Started it up last week (it only gets used about 3 times a year and only on petrol) it started ok but then within a half a minute it started to misfire, running on 2 cylinders, spitting back through the carb and dying. I checked fuel flow to the carb with fresh fuel, same thing each time i tried to start it. Checked plugs, leads etc. Took off the carb, cleaned it, and blew out jets etc. Fitted overhaul kit - new needle valve, new gasket and choke spindle, checked and set float/fuel height. Still same problem. It will run after a fashion at high revs but not well although adjusting the main jet needle or the idle jet needle all in or all out seems to have very little if any effect.
I backed it out of the shed in low with the high revs and started to reverse it down a slight incline and it immediately tried to die when on the slope. Kept it going with pumping choke and managed to get it back in the shed. I must have had the carb off half a dozen times now and the fact it tried to die when the front was slightly raised leads me back to fuel and the carb? Any thoughts or ideas would be very welcome. TIA

 

[Ericp351]

May be a carb clog- but I'd check the float + stuck open inlet needle first. Are the plugs crazy-wet when she stumbles? Also- after she quits verify you still have any spark. Want blue. "Just for fun"- can you run it- fuel bowl full- then shut fuel tap and have it run longer? Would almost prove sunk float without dismount carb. Best Luck,

 

[Mitmah]

May be a carb clog- but I'd check the float + stuck open inlet needle first. Are the plugs crazy-wet when she stumbles? Also- after she quits verify you still have any spark. Want blue. "Just for fun"- can you run it- fuel bowl full- then shut fuel tap and have it run longer? Would almost prove sunk float without dismount carb. Best Luck,

Thanks - good advice. I think I may have found the problem now and feel very stupid for not seeing it before. There is a blanking plug that fits in the orifice behind where the pilot jet hole emerges into the Venturi by the throttle butterfly, I guess it’s there to allow the pilot hole to be machined in after casting the carburettor top. This plug was missing it must have popped out perhaps when I tried to start it but no sign of it on the shed floor maybe it was corded. On pictures of some carbs I’ve looked at online this is not a plug but a spigot maybe for a vacuum feed. Anyway I’ve plugged it now and will refit carb and try it out tomorrow.

 

[Ericp351]

You probably got it- a 3/16 +- hole will make her Ritch!. If a Welch/ cup plug , and a worn casting, a bead of your favorite gas- resistant epoxies (Marine Tex, Devcon, Jb Weld+) gives piece of mind. When in doubt- test float the float then a shake of your floats (coffee can fuel, whatever) never hurts.