Remove the inline fuel filter.

Its a larger sized paper filter with 1/4in fuel lines. but I replaced it with a new filter and same thing. Also, the petcock outlet is smaller than a 1/4in so it's hard to go any larger than what I have.  I'll try with no filter and see what happens.

seve321 wrote on 04/06/18 at 14:16:40:


The problem with the 1/4 inline filters is the hole in the nipples are too small.  The plastic housing is thick, so the actual hole in the end of the filter is very small.....and air bubbles get stuck in them and cause an air embolism, and it won't allow the fuel to flow down to the carb.

And......when you reduce the diameter, the change in flow area decreases dramatically as show below:

Stock fuel line is 8mm, and the area is 0.0778 square inches.

Most hardware and auto supply stores don't carry 8mm - so we buy 5/16" hose which has an area of 0.0766", which is a flow area of 98% of the stock fuel line.

When you buy the Chinese copy or other petcocks with 1/4" fuel line, the flow area is now 0.0491 square inches - which provides 63% of the stock fuel line area.

I measured the inlet hole in a 1/4" plastic fuel filter, and I found the hole size to be 5/32", which has an area of 0.0191 square inches - and provides only 24.6% of the original flow area.

So....how well would you perform if I cut your food supply down to 24.6%?

OK....I screwed up - the stock fuel size is 6.5mm on the parts list - not 8mm.  No wonder we can't locate the stock size anywhere.

When I go to a cycle shop and buy new tubing.....I use 8mm as it is something the local bike shop stocks in bulk and they just cut off 2-3 feet for me when I stock up again.  The 8mm fits snugly on the petcock and carb, and I do secure it with a couple spring clamps on each end.

The 6.5mm fuel line has an area of 0.0514074 square inches.

The 1/4" fuel line is similarly small at 0.04906 square inches, which is 95% of the stock size.  If you buy reinforced fuel line from an auto store that is used on carbs with fuel pumps - it will be difficult to push this small tubing onto the diaphragm and carb (the 5/16" reinforced fuel hose is much easier to get on the fittings).

The 1/4" plastic fuel filter has 37% of the flow area of the 6.5mm stock fuel tubing.  (Which is a 63% reduction in flow).  


Gary_in_NJ wrote on 04/07/18 at 05:21:22:


Gary - They are only getting 24.6% of the food, which is a 75.4% reduction in food!  Enough of a reduction to make anyone anemic.

Removing the filter helped. I am only able to use a 1/4in hose because of the outlet on the petcock. It is enough to get everything flowing again though. Thanks for all the input.

  Having looked at the Mojave tanks again  it seems the two stock petcocks are only 1/8 inch , which is confirmed by the fact that your using 1/4 inch fuel line. I think your in trouble as even 2 petcocks of this size should only feed about 28% of the fuel normally supplied to our 40mm carb. You may need to customize the tank to except one(5/16) or two(1/4) inch petcocks.