Thor 80 fuel drip from air filter box

[chris scammell]

Hello. I am new here so before I explain the issue let me say hi. I am a pilot from Cumbria with 30yrs paragliding and hang gliding experience. I've dabbled with ppg for years but have more recently been committing more time to it and particularly enjoy long low XCs in the mountains in nil wind.
Now then, I hope someone can shed some light on a niggling problem with my motor, a Polini Thor 80 (Polini CP carb) fitted to  Pap 1400. 80hrs use.
After a flight I notice that there is a lot of oil (amber, so unburned) splattered around the unit. After a lot of head scratching I think it is due to a fuel drip from the air intake silencer box. The visible oil splattered about is what is left after the fuel has evaporated. A bit of research led me to try changing the float needle valve in the carb, which I have just done. A quick bench test after the change and there is still fuel collecting in the air intake box, which gradually accrues over a flight then drips out getting sprayed all over the shop by the airflow. It makes a right mess and is also a fire hazard.
My last resort will be to customise the air intake box so that I can rotate it and let gravity take the fuel back into the carb, but surely there is a way of tackling this at source. Why is fuel being blown the wrong way into the airbox?
Otherwise the motor seems to run well and I generally burn around 2l/hr with my free flight wing.

Any thoughts much appreciated.
Chris

[alan_k]

I had a similar thing with my Solo 210 2 stroke paramotor. With a 2 stroke not all the fuel is burnt, a necessity to keep the engine lubricated.

The return pulse from the tuned exhaust pushes some of this unburnt fuel back into the air intake.

The Solo used a needle/plunger type of carburettor, rather than a membrane carb. Don't know if this helps. 

[Mitch130]

It may be worth checking your reed valves .They  should stop the fuel coming out of the carb and back into the air box  . They act as a non return valve. Also when priming the carb you will probably have some fuel enter the air box as well as the carb.

[Mark Morgan]

Hi Chris..  Your using the Polini PWK 24mm carb for the Thor80? It may not be just when your flying... Sometimes with this heat the pressure in the tank can overcome the low jet in the carb causing either flooding of the motor or fuel getting into the Air box or both, Also depending how you get up of the floor can cause fuel to poor into the Airbox.. Both of these issues are the same back in the day when i used to fly Bailey engines with the CVK carbs..  Also over priming can cause this. The fuel evaporates but and leaves the oil in the Airbox..  Nothing to really worry about..

The pulse pipe on the Thor 80 doesn't go back to the carb but to the pump and comes from the Crank not Exhaust so that will not be the issue..  This just makes the pump, Pump... 

Have you changed your fuel pump set up? Bin the metal pump fitted as standard to the Thor 80 and fit a 130-190-200-250 pump with external primer bulb. The membrane in the metal pump fails..   

You may just find your running rich jetting if your motor is still new and running on the run in settings, Also Hot weather will make your motor run richer add the High pressure we have even richer, same goes for running at high altitude the higher you go the richer your motor becomes.. 

Hope this helps, you have my number but best to call your PAP dealer to confirm jet settings etc  Also make sure you have a good Temp gauge on your motor!!!!!! 

Regards

Mark  

[chris scammell]

Thanks for the useful info folks, much appreciated. I will report back if I manage to solve it.

[adamjedgar]

One solution is to buy a 4 stroke.

 

What you are experiencing is common among 2 strokes.

 

I would look at jet adjustment on carby first, exhaust port and pipe, and reed valves.

 

 

 

[Dariuszk24]

yeaa the best 4 stroke V8 5l

try what Mitch 130 sugest

if your reed valve its worn,crack or no sealing properly then fuel its thrown back to airbox

Edited July 29, 2018 by Dariuszk24