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Top 80 engine fuel supply system


steelmesh
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I am building a paramotor using the Top 80 with the WG8.  I have a universal frame that came with a gas tank ready for drilling.  After some deeper research into specifying what I need I have learned the black springs steel on the carb is for priming, "priming level".  Based on my knowledge of similar carbs the priming lever will manually open the needle valve.

Just clarifying my understanding here, by pressurizing the fuel tank and then hitting the priming level, that would squirt fuel into the carb throat.  Is this a correct statement?

If that is the case, I think I understand how the priming bulb will work with this carb...because before I was concerned that the primer bulb inline with the main fuel feed to the carb would need to exceed pop-off pressure to force fuel through the carb.  So it appears that you build a little pressure with the inline primer bulb and then hit the manual primer lever.  I was looking at putting in an independent primer system (it's own fuel pick up and a nozzle inside the carb or airbox); until I started finding Top 80 youtube videos trying to trace their fuel lines haha, that's when I saw the primer bulb inline.

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For the rest of the fuel system, I am running an 8mm pickup hose with a clunk filter, that will then be stepped down to 3mm for the carburetor inlet.  My concern is if the 8mm is too large of a diameter, as far as priming the fuel hoses or if it picks up air bubbles will it require a manual air purge.  

For the fuel tank vent, I'm looking at a 6mm dirt bike vent with a one-way check valve (air in, nothing out).

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I've just fitted a priming bulb to mine. No more caveman blow tube.  To prime i just hold down the carb lever and give the bulb a wee squeeze until the air in the line clears.

It doesn't have anything to do with pop off as you are manually opening the diaphragm by pressing the lever. The reason that lever is there is to stop you pressing too much and damaging the spring behind the diaphragm.  

One or two pulls and it starts.

I used a Polini priming bulb. (probably the only decent thing Polini make.)

As for your 8mm dia fuel line, is that internal diameter? Id say thats far too big. The diaphragm pump in the carburettor wont be able to pull the fuel up that, get some smaller tygon line on there, 4mm.

Edited by Vauxscott
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3 hours ago, Vauxscott said:

I've just fitted a priming bulb to mine. No more caveman blow tube.  To prime i just hold down the carb lever and give the bulb a wee squeeze until the air in the line clears.

It doesn't have anything to do with pop off as you are manually opening the diaphragm by pressing the lever. The reason that lever is there is to stop you pressing too much and damaging the spring behind the diaphragm.  

One or two pulls and it starts.

I used a Polini priming bulb. (probably the only decent thing Polini make.)

As for your 8mm dia fuel line, is that internal diameter? Id say thats far too big. The diaphragm pump in the carburettor wont be able to pull the fuel up that, get some smaller tygon line on there, 4mm.

Thank you for clarifying the priming procedure with this carb!

I'll save the 8mm (5/16") ID tygon for a bigger motor upgrade then. 

I have 3.175mm (1/8") ID tygon in stock...but, is the WG8 Top 80 fuel inlet supposed to work with 4mm ID fuel line?  When I measured the nipple on the carb I assumed it was for 1/8" or 3mm, I'll have to re-measure.  Looks like 4mm would be equivilent to 5/32" so at least I got that going for me if 4mm is the best practice with this engine.

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Ive had a look at whats on mine and its 6mm tygon from the tank to the filter, then the last bit is 4mm (helps stop the bubbles)

The smaller stuff is a nightmare to get over the filter barb but it does go eventually.

Scott.

Edited by Vauxscott
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