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[pintheair]

hi there,  putting a chainsaw engine in a boat.  problem is , runs great with the original fuel tank in situ,
 but only runs for a few seconds with new tank from  pmb.   got new pipes for flow and return,    can anyone  help.

[gwa84]

is the original fuel tank designed to be seald as in no air vent if the carb is designd to be run from a vacumed tank then it wont run of a vented one

[50mm]

yes a breather hole is needed to allow the fule to move as trapped air will cause a vacuum!

best bet is off the tune pipe there should be a tube connector near the exit hole ( a little nipple) if not fit one! this tube is then connected to the breather hole,(also fitted with a nipple)  the force of the engines exhaust (back pressure) aids to pressurises the tank enough to push the fuel to the engine making it more efficient. This will solve your problem 

[HS93 (RIP)]

hi there,  putting a chainsaw engine in a boat.  problem is , runs great with the original fuel tank in situ,
 but only runs for a few seconds with new tank from  pmb.   got new pipes for flow and return,    can anyone  help.

Is there  a reason why you have posted this twice ?


Peter

[50mm]

yus cos the guys posted the same question twice!
http://www.modelboatmayhem.co.uk/forum/index.php?topic=27433.0

[pintheair]

posted twice cos i put it in the wrong place 1st time
where did i put those glasses!!

[HS93 (RIP)]

posted twice cos i put it in the wrong place 1st time
where did i put those glasses!!

 pintheair    Martin will sort it, it is not easy at times to find the correct section.

Peter

[glennb2006]

yes a breather hole is needed to allow the fule to move as trapped air will cause a vacuum!

best bet is off the tune pipe there should be a tube connector near the exit hole ( a little nipple) if not fit one! this tube is then connected to the breather hole,(also fitted with a nipple)  the force of the engines exhaust (back pressure) aids to pressurises the tank enough to push the fuel to the engine making it more efficient. This will solve your problem 

Don't try and pressurise the tank on a petrol engine. The carb has a fuel pump built into it which will draw the fuel from the tank for you, the tank does need to be vented.
Which PMB fuel tank did you use?
Have you a photo you can post of the installation to see if there is anything obvious that is creating your problem?

Glenn

[BJ]

For what this is worth....
It sounds as if the fuel is flowing BACK from the carb before you start the engine.
Has the carb got a primer button/pump? Is it above the carb body?
If so, try to prime the carb with the bulb/pump, immediately place thumb over venturi and pull the engine over twice THEN try to start and see if it will run properly.