Petrol question

[David perry 1]

My son is fitting a petrol engine to a model and inside the tank we find two clunks. One is a normal metal clunk but the other is a felt covered one. We assume the latter is a pickup clunk with a filter on it which leaves the former as a filler clunk or vent clunk. But why a clunk on either of those? I've never known a glow motor have two clunks. We have many theories but no fact. ..

Any ideas?

David

[Martin Harris - Moderator]

It's possibly to facilitate emptying after use. Was it petrol or glow originally?

[David perry 1]

Ah of course. Stupid me. That's exactly what it's for.

Thanks.

[bert baker]

If you have a felt clunk I would leave enough fuel to cover the felt,

If it is allowed to dry out the chances are you will get felt splinters getting into the carb and in turn it will eventually block the small mesh filter that is inside the carb

also it’s worth periodically running them just to keep the diaphragms and flap valves operating

When the oil fuel mix evaporates chances are the oil will remain and stick the flappy valves closed

I have been told that Aspen fuel doesn’t affect carbs,,, not tried it myself

[David perry 1]

Thanks for that advice. I'll pass it on.

Where works they fly a lot of large 1/4 and 1/2 scale models and all are petrol, but for him it's a new adventure . Because of lockdown he is not at the workshop as often so hasn't got easy picking of brains...

 

That tank is from a previous petrol model but not this one...a large Wot 4 . He got the lot, including a new Futaba 14channel tranny, all new and all gratis. Well sort of. They ask a lot of him of course. Where were these jobs when I was young???

 

Thanks guys.

Edited By David perry 1 on 19/04/2020 11:12:29

[Brian Cooper]

All of my tanks have two clunks in them. This is to facilitate emptying after a session. Whilst this is okay for glow fuel, DO NOT empty a petrol tank. If anything, fill it up at the end of a session.

If left empty, the felt clunk will dry out and go brittle. This will lead to bits falling off it which will end up in the carburettor. Also, the fuel tubing will harden so the clunk will not be able to follow the fuel around the tank.

Petrol is a very differed game compared to glow fuel.

[David perry 1]

Thanks for that tip. In fact the line with the drain has gone stiff and wont clunk! I've recommended a complete line change anyway. Thanks again

[Solly]

Replace the felt filter with a sintered type and you won't have the problem.

[David perry 1]

Thanks

He sort of got it running then said "blimey dad. With a lipo I'd have been out and back by now". Kids eh

[cymaz]

Aspen Fuel contains no ethanol...so I understand. The ethanol can degrade some rubbers and plastics in the fuel system.

Texaco Super Unleaded contains no ethanol

[Ronaldo]

Well you learn something everyday, been flying petrol 20 years and never even questioned the contents of petrol or it's effects. A club mate and I have had the odd 'petrol' bung degrade and break up, not many, but enough to leak into the fuz and cause more work in repairs and recovering, but could never figure out why. Also thanks for the link cymaz, ..... I think I'll be a bit more choosy where and what petrol I use from now on

[cymaz]

Luckily we have a Texaco garage where I live.

[Mike T]

Posted by cymaz on 19/04/2020 22:24:51:

Aspen Fuel contains no ethanol...so I understand. The ethanol can degrade some rubbers and plastics in the fuel system.

Texaco Super Unleaded contains no ethanol

Conversely: **LINK** - see 4th 'Q'. Best to check the pump carefully!

[Anthony Scott 2]

Aspen for me, even at a similar price to glow fuel!

[David perry 1]

Thanks all.

The motor starts okay now but he say (my son that is) that it throws the prop every time. He cant fit a lock nut for whatever reason (as I told him we do on glow fourstrokes) so hes at a bit of a loss. Im wondering if it is caused by effectively having advanced timing due to lean mixture...but I have zero experience of petrol.

Any tips?

[Martin Harris - Moderator]

A heavier prop might help if he's using a light wooden one.  2 strokes aren't normally prop throwers like 4 strokes can be and my only petrol [Zenoah 38] has never had any problem with its single bolt fixing.

Is the timing fixed on the engine? If not, he could try checking it's correct and if so, retarding it a couple of degrees.

Edited By Martin Harris on 20/04/2020 19:15:27

[cymaz]

Sounds like a timing issue. It sound be 28* before TDC.

There are plenty of good videos to help with this. CH Igntions ( US) do a good one.

[David perry 1]

Cheers. We tried timing to no avail.

 

The use of throttle has no effect at all when it is actually running. I suspect fuel starvation..

With the Walbro carb off I cannot blow through the fuel nipple...is that ad it should be? Removing the plate proves the pipe isnt blocked and it seems that when the side plate is in place the rubber seal or flapper valve actually seals the fuel inlet fast. That might be right, but to seal it so fast that I cant blow through it???

 

All channels and events are clear of debris and the mesh filter screen is clean.

 

We adjusted the slow running needle from 1/2 a turn out to about 3 out in 1/4 turn increments and got no real change.

 

D

Edited By David perry 1 on 20/04/2020 21:33:38

[cymaz]

Walbro carbs use a pulse from the engine cycle which is why you can’t blow through it. The one way check valves put paid to that.

Also check the fuel metering needle for the correct height. This is critical for good running.

This is a good video for the basics and explanation.....if a little corporate. The basic needle settings for Walbro carbs is 1 1/2 out from closed on both needles. The high speed needle is nearest the carb bitterly. The speed needle nearest the engine.

On tuning the LN is functional right up to about 3/4 throttle, so it’s very important. Tuning a gas engine is not like tuning a glow engine.

Also check for any leaking gaskets....air leaks from gaskets etc are your worst enemy. Also check the reeds and the cage are sealing properly. If not lapping the cage so the petals sit flush with the cage is very important.

Edited By cymaz on 20/04/2020 22:17:23

[Paul De Tourtoulon]

I Just found this about the membranes.