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Air in fuel line


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Ive got a Zenith with a moster185 and ive been having problems with my carb set up. Bad starting and a mixture that is either too rich or too lean and now ive got air in my fuel line. The air might actually be the reason for the varied mixture settings. Ive just replaced the fuel line inside the tank, and the quick release connector (bloody expensive) but no change. Going to replace the rest of the fuel line tomorrow but just wondered if anyone else had any issues setting up the carb. Ive spent years building competition bike engines and the carbs on them are much easier to set up. It seems the range of adjustment is really tiny on these carbs and just the slightest turn of the screws makes a huge difference. 

Any input would be welcome and ill see how i get on tomorrow after i change the other bits. 

ps, do the primer bubbles play up on these very often. Mines only done about 14hours.

Thanks

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Personal experience with primer bulbs , yes they can play up , my Miniplane has had one for a couple years waiting for it to fail but still good condition, fitted one to my AC eos , it lasted half dozen flights , valve inside started to randomly stick closed stopping carb sucking fuel or restricted fuel flow , 

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UPDATE, for some reason Parajet use a type of silicone sealer in the fuel fitting on the top of the tank on a Zenith,(not sure if its the same on other models) and on mine this sealer has turned to a messy jelly. It has then passed through the fuel line and primer bubble to the carb. Im hoping that this is the root of my carb set up problems. Also while trying to fit new fuel line to the primer bubble i quite easily pushed the fitting straight through into the inside of the bubble! The rubber on the bubble has also gone a bit soft. 

So ive ordered a new carb kit, primer bubble and fuel filter and im going to replace the lot. Ive also used a small o ring on the tank fuel connector instead of sealer. 

I will let you know how it goes later in the week.  

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Wonder if that's one of the reasons more motors are being fitted with simple blow/breather pipes - less to go wrong ?

why you'd put silicone anywhere near petrol is certainly a mystery - it just dissolves as you say.

assuming yer carb's a walbro type it'll have a mesh at least to stop most of the crap, but I imagine you've already had that to bits and cleaned it/carb kitted it.

I agree about the carbs though - YES folk will go on about how simple 2 strokes are, etc - and when they work, they seem rock solid - till they don't and it seems like all you need to do is look the the carb funny and the bloody thing never seems to be able to be set up right again.. 😫😫

I've lost count of the number of times I've had some weird issue with a paramotor 2 stroke, took it all apart, found nothing wrong, put it all back together and again.. and it works.. does yer head in. I swear somehow it is conscious and just wanted the attention. 😖

 

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UPDATE!!

Well £150 later, new fuel line from top to bottom, new filter in tank, new quick release fuel connector, new primer bubble and a carb kit all fitted (yes the mesh seemed to catch all those little bits) and no bloody difference!!   Fast tick over and the fuel line just starts to fill with air. Little bubbles coming up right from the tank. Its almost as if the vibration is causing it.  Not sure where to look next? 

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2 hours ago, cas_whitmore said:

If it’s air from below the new pipe that goes in your tank , you’ve only got the barbed brass / ally joint , could you run a length of tube from carb in to tank filler , with no joints anywhere, then start  adding your clunk /pipe / tank joint, / filter / then primer  , 

Yeah thats my plan later. Seems strange when everything is brand new. Ill let you know how i get on.

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On 30/01/2020 at 08:43, cas_whitmore said:

If it’s air from below the new pipe that goes in your tank , you’ve only got the barbed brass / ally joint , could you run a length of tube from carb in to tank filler , with no joints anywhere, then start  adding your clunk /pipe / tank joint, / filter / then primer  , 

Yeah thats my plan later. Seems strange when everything is brand new. Ill let you know how i get on.

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Well im going backwards at the moment.    I took the pick up pipe out of the tank this evening just to check everything was ok in there. Oh dear!! The brand new fuel pipe from parajet has only been in there a couple of days and it has expanded and gone soft and was about to drop off the connector at the top of the tank. There is a bit of a problem here. Because of the way the fuel fittings go into the top of these tanks there is no way of putting any kind of clamp around the pipe because it simply would not fit through the hole ( unless im just being thick) . Hence it is just a push fit. Im glad i didnt go flying with this new pipe because with the vibration the pick up pipe would of simply fallen off into the bottom of the tank!! I will give them a call monday to see what is going on with that pipe. It is supposed to be the correct stuff for the job. obviously not as its turning to jelly already.. 

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8 hours ago, cas_whitmore said:

Strange , wonder if they’ve used the same tube on the units being put together 😬

I get my tubing from kart supplies on ebay . Forget the make , but it’s clear with a red line running along its length.

https://www.ebay.co.uk/itm/Freeline-Kart-Racing-Fuel-Pipe-Hose-Line-6mm-Bore-1-Metre-Length/372515446668?hash=item56bba69f8c:g:EFEAAOSwFINdzQuQ

Is this the stuff?

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3 hours ago, cas_whitmore said:

Yep that’s it , Tygon tube is the go to make , but seems most of it on sale is fake crap , I’ve had no issues with freeline tube .

The tube i have from Parajet says Tygon on it but is is obviously no good.  Im going up to london thursday so im going to pop into them on the way and show them. Could be a problem if they have a dodgy batch

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On 02/02/2020 at 16:39, cas_whitmore said:

There probably  all over it , if they see your post 

Taking my tank in to show them at parajet tomorrow to see what they think. Its quite interesting that the tygon pipe  is known to be the right stuff for the job but i actually wonder. My old pipe out of my tank has gone really hard and brittle and the new stuff is going really soft straight away.

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On 05/02/2020 at 13:49, toploader said:

Taking my tank in to show them at parajet tomorrow to see what they think. Its quite interesting that the tygon pipe  is known to be the right stuff for the job but i actually wonder. My old pipe out of my tank has gone really hard and brittle and the new stuff is going really soft straight away.

Any update on your problem and/or answers from Parajet?

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On 08/02/2020 at 08:31, Pete S said:

Any update on your problem and/or answers from Parajet?

Hi Pete, Parajet said that it is normal for the pipe to go soft when it comes into contact with petrol. The reason mine was falling off the tank fitting was because they sent me the wrong diameter pipe. The pipe in the tank is smaller. They put a new piece in so fingers crossed. 

 

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  • 11 months later...

I have been fighting with air in the fuel line and have rebuilt warboro carb , changed primer bulb. wraped wire around clamps on primer bulb, changed fuel filter on the line from the tank to the primer bulb , changed fuel line from fuel tank to  to the filter below the primer bulb and still did'nt work. The air in the fuel line was visibly building just before the carb and under full throttle would stall the engine until you dropped the rpm. The Problem after all this was a plugged fuel line filter in the gas tank. The carb was sucking air from anywhere there was a connection even though there was  no visible leak anywhere. The polini filter is made of a changeable cotton fuzzy type material that I cant find . There was a gummy residue in the tank that plugged it. My own fault maybe as I have been leaving some mixed av gas in the tank  and it sits for 6 months while I am not able to fly. Replaced the tank filter and it runs and idles perfectly

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