Anybody Running a Fuel Pump?

Ozpall

Ozpall

Member
Hey guys, so just finished building my ct70 with a 150cc and vm26, the issue im having is, i can't finish a tank of fuel, as soon as im low the fuel doesn't go down anymore since its too much on the same level.
so i was thinking about adding a snowmobile vacuum fuel pump, has it been done with good results?
thanks for any info.
found 1 bike online a dax but no info as if its working or not.

thank you!

Oscar.

Dax-fuel-pump-small.JPG
Resized_20190413_144832_2222.jpg
 
OLD CT

OLD CT

Well-Known Member
It's hard to see in your pic but, try repositioning the remote petcock so the sediment bowl is facing ''down''. Some close ups of that setup you have going on there, on the white bike will help. I take it that's the problem bike? Also a smaller fuel filter lower in the line wouldn't hurt, like a 4 inches from the tank nipples. Re route the lines. I just dump my sediment bowl every couple months on one bike.
Looks like a good bike to run a remote gas tank where the grab handle would be on a Dax.
 
Last edited:
Ozpall

Ozpall

Member
OLD CT said:
It's hard to see in your pic but, try repositioning the remote petcock so the sediment bowl is facing ''down''. Some close ups of that setup you have going on there, on the white bike will help. I take it that's the problem bike? Also a smaller fuel filter lower in the line wouldn't hurt, like a 4 inches from the tank nipples. Re route the lines. I just dump my sediment bowl every couple months on one bike.
Looks like a good bike to run a remote gas tank where the grab handle would be on a Dax.
Click to expand...

Thank you, I will get closer pics. I just added the fuel filter it was doing it even b4.
I'm not really crazy about the external fuel tanks.
 
Adam-NLV

Adam-NLV

Well-Known Member
Have you considered an electric fuel pump for your 12 volt 150cc? You could mount a small 12 volt pump somewhere (on the side) and you will always have reliable fuel pressure!
Btw That bike looks like it can move!:red70:
 
6

69ST

Well-Known Member
With some bikes, routing flexible fuel hose can be more difficult than seems possible. The primary issue is lack of cubic real estate. Even a 1/2" can be the difference between make & break. If you opt for a fuel pump, vacuum would likely be the better choice. Imho. An electric needs dc which is in short supply with these alternators. A pressure regulator may be needed to prevent flooding. These carbs aren't designed to handle much fuel pressure. Then there's the longevity to consider, for multiple reasons.

You're really close to success as the bike sits. I second OLD CT's idea to reposition the fuel lines. That matters. However, I'd suggest possibly using sections of metal fuel line, which can be precision-bent and retain the shape. Lowering the carb, by cutting & rewelding the intake manifold, could be enough to solve the fuel flow problem. A pro should be able to handle the TIG chore...which only has to be done once.

The tank outlets are roughly the same height as the lower edges of the sidebadges...fwiw.
 
Ozpall

Ozpall

Member
racerx said:
With some bikes, routing flexible fuel hose can be more difficult than seems possible. The primary issue is lack of cubic real estate. Even a 1/2" can be the difference between make & break. If you opt for a fuel pump, vacuum would likely be the better choice. Imho. An electric needs dc which is in short supply with these alternators. A pressure regulator may be needed to prevent flooding. These carbs aren't designed to handle much fuel pressure. Then there's the longevity to consider, for multiple reasons.

You're really close to success as the bike sits. I second OLD CT's idea to reposition the fuel lines. That matters. However, I'd suggest possibly using sections of metal fuel line, which can be precision-bent and retain the shape. Lowering the carb, by cutting & rewelding the intake manifold, could be enough to solve the fuel flow problem. A pro should be able to handle the TIG chore...which only has to be done once.

The tank outlets are roughly the same height as the lower edges of the sidebadges...fwiw.
Click to expand...

yeah i will try rerouting, i also like the idea of cutting the intake, i can get it weld it, my only concern with this is that the carb then might hit the head fins.
thanks
 
Ozpall

Ozpall

Member
Adam-NLV said:
Have you considered an electric fuel pump for your 12 volt 150cc? You could mount a small 12 volt pump somewhere (on the side) and you will always have reliable fuel pressure!
Btw That bike looks like it can move!:red70:
Click to expand...

for all the research that I've done, everybody recommended not doing electric, it might flood it. so that's why I'm searching vacuum.
she definitely moves, that kawasaki couldn't catch me at all, i know he is only a 125 but he was just way back and i wasn't even max out.
thank you!
 
6

69ST

Well-Known Member
Ozpall said:
yeah i will try rerouting, i also like the idea of cutting the intake, i can get it weld it, my only concern with this is that the carb then might hit the head fins.
thanks
Click to expand...

Yeah, it takes some time, care and a lot of dry-fitting to get a manifold fitted "perfectly". But, imho, it's well worthwhile. There are numerous possibilities with custom fab work...the tradeoff is dealing with all of those seemingly endless possibilities and committing in metal.

Obviously, interference cannot work. I'd start by placing the carb in what you judge to be the best possible location, then figuring out how to mod the intake accordingly. Generally speaking, ideal carb placement has the fuel inlets at least 1/2" below the bottom of the tank. That should keep the fuel flowing...and gravity has no electrical, or moving, parts to worry about.
 
OLD CT

OLD CT

Well-Known Member
What do you think about running a ATC125M intake, they sit low. I have one and might part with it for what I paid for it.
 
dirtbkr188

dirtbkr188

Active Member
Here's a pic of one I was experimenting with some years ago. In order for the aftermarket carb to clear the ignition cover, I had to use two heatstops to raise it up.

VKZL9W.jpg
 
6

69ST

Well-Known Member
dirtbkr188 said:
Here's a pic of one I was experimenting with some years ago. In order for the aftermarket carb to clear the ignition cover, I had to use two heatstops to raise it up.

View attachment 60575
Click to expand...
That's similar to how I have the intake (not this intake) mounted on my daily rider...only using one phenolic insulator for clearance. It's not optimal, believe me; but, it does work in ambient air temps above ~70F. Running a "hot" intake, i.e. nothing but a single gasket at the port, makes about a 1 main jet size difference. That is, one size smaller to get the same A:F ratio numbers, which means it's more efficient. I've left mine alone, it works and has been dialed-in for 16 years; but, there's no ignoring the fact that it's not really optimal. Seriously, I'd likely see a 10% improvement in mpg, the light-throttle transient lean spot could likely be minimized further (or eliminated) and it'd run better in cooler temps.

When choosing an intake, keep in mind that A.) it must be at least as big as the carb venturi and B.) no bigger than port ID, of you'll have reversion/unwanted turbulence problems that won't be "tunable".

If you've noticed, most aftermarket intakes have a LH "turnout", that's for float bowl clearance, nothing else. Having the carb further outboard is a tradeoff, just usually the smallest tradeoff/compromise possible, without investing a lot of resources.

For those engine/carb combos where the ATC intake will fit, it's pretty slick and inexpensive.
 
kirrbby

kirrbby

Well-Known Member
I've had similar problems. A couple suggestions...maybe for at least the short term.

Pull the fuel line right at the carb and prime everything with fuel...blead out ALL of the air in both/all lines, then reconnect to the carb. Do this before each ride.

Same as above, plus, ONLY use the reserve line, AND never turn the fuel off.

I believe these things will minimize air in the lines...causing a resistance from the tank.

If you never turn the fuel off and only use reserve, hopefully you won't need to bleed it each time.
 
Ozpall

Ozpall

Member
kirrbby said:
I've had similar problems. A couple suggestions...maybe for at least the short term.

Pull the fuel line right at the carb and prime everything with fuel...blead out ALL of the air in both/all lines, then reconnect to the carb. Do this before each ride.

Same as above, plus, ONLY use the reserve line, AND never turn the fuel off.

I believe these things will minimize air in the lines...causing a resistance from the tank.

If you never turn the fuel off and only use reserve, hopefully you won't need to bleed it each time.
Click to expand...


ok great, thanks!
 
6

69ST

Well-Known Member
Bleeding the lines is worth a try. Mine will fill completely, as soon as the fuel is switched "on". But, air pockets reappear soon. They don't seem to make any difference. Just pointing out the fact that gravity fuel flow is very different than pressure-fed. Fuel only flows until the float reaches full height and needle + seat assembly stops it. If everything is unrestricted, it takes very little head pressure to fill the float bowl, so little that air pockets will form. FYI, I run Tygon fuel hose and a clear fuel filter.
 
Ozpall

Ozpall

Member
OK thanks, yes i do see some air bubbles in my lines, but runs ok as long as i have enough fuel in the tank. what size line are you using?
i just ordered one from eBay and is a 4.5mm i believe.
 
6

69ST

Well-Known Member
Pretty sure I went with 3/16 Tygon. It's a bit of a bear to install but, no leaks and no clamps needed.

Seems restrictively small, in text, doesn't it? Now, consider the entire fuel circuit. The inlet needle & seat orifice is far smaller than any fuel line that could fit over any of the barbs (tank outlets, petcock, filters etc.), as is the bowl drain of a stock 16mm carburetor. There is a point to these ramblings...it is possible to guesstimate fuel flow requirements, based on a few crude numbers that are widely known.

A CT70 tank can be drained via the drain valve on an OEM Keihin carb in less than 5 minutes. Thus, by extension, it'd take less than 10 minutes to run a gallon of fuel through that tiny (~1mm) drain orifice in the bowl. That's far more fuel than one of these bikes could burn. At 90mph, a gross exaggeration...to illustrate...15 miles would be covered in 10 minutes. Even at 50mpg, another exaggerated number, that 3X the flow rate required.

My overall point is that sustained fuel flow rates, real world, are a small trickle. From that perspective it's easy to see why air pockets persist in the lines, why gravity feed should be more than adequate and why carb height & line routing(s) matter as much as they do. IMO, that's where the fuel delivery issues are to be found and resolved.
 
Top