crispinchurch

from ebay got ths veco 61 it has a nipple on crank case been blanked off i use the muffler for tank feed
the engine surges
do i try the crank case nipple ?

earlwb

it looks like someone drilled and tapped the crankcase for a pressure fitting to use with a pulse pump.
Normally everyone just puts the pressure fitting in the center of the backplate.

To use it for pressurizing the fuel tank, you would have to install a special fitting that has a rocket nozzle shape to it with a fairly small hole in the center. The nozzle end faces the engine and the flat square part faces outward so that it provides resistance to the pressure coming back from the fuel tank as the engine is running. a regular muffler pressure fitting won't work correctly. But these can develop a fair amount of pressure though, make sure the fuel tank is good and strong as it can rupture them. Also using a rocket nozzle type of fitting generally means you will have to use an electric starter to get the engine to run. You will also very likely need to use a pump carb because of the extra pressure forcing fuel into the carb and a more fine adjustment capability on the needle valves.

Now one could use a timed pressure fitting, in this case the pressure fitting is located under the carb on the right side of the crankcase, so that it is timed to the crankcase rotations to provide fuel tank pressure. A typical location is where they placed the little plastic fitting on the Cox Tee Dee engines.

crispinchurch

thank you very much i now know a lot more why its there and i think i leave it well alone
any idea on the surging when running

earlwb

Well, if the engine is a little on the rich side, they tend to surge some as the RPMs will vary. So it may be normal.
Now if you see some large RPM swings, then it could be some air bubbles getting into the fuel line from a pin hole or something farther back. A fuel tank that is vibrating and foaming a lot can cause this too. Usually with the semitransparent fuel lines you can look to see if there are air bubbles in the fuel line or not.

my first thought was that the engine might have a pump carb on it to match the fuel pump that would have been plugged into that crankcase vent someone made for the fuel pump. They sold pump carbs to go with the fuel pump in the past. I think they still sell them today too.
But I don't know if they tried a pump with the regular carb or they replaced the carb with a pump carb or not. You might measure the inside bore and the outside diameter of the stem to see what carb at Perry Pumps matches it or not. it might shed light on which carb you have on the engine.
http://www.perrypumps.com

crispinchurch

the rpm dont change a lot and yer i was rich
thank you for your answers i have learnt a lot from you

many thanks

Crispin