Currently having big issue with fuel delivery on the death machine.
Here is the problem: Only getting 2 oz in 10 sec. Has new fuel filter as of yesterday.

This is what I have tried:
1) tried 2 brand new pumps straight out of the plastic plus the pump on the machine -- no change
2) blew back through the pick up line with air to verify clear -- no change
3) pulled fuel from a jerry can -- no change
4) pinched off the return line to tank to make sure there is no bypass -- no change
5) hooked a vacuum/pressure gauge to the pulse line from the Engine and getting 5 psi -- it's good
6) This is the one with the R401 experimental Engine but it has 135 lbs compression
7) took a spare Engine from the shelf and hooked the pulse line to a new pump -- no change
8) removed the lines to the fuel filter to verify that I did not pinch off the nipple on the filter because clamp to tight

WTF ??
Anybody got any ideas ??

Is your pulse line breaking down or worn out? Maybe its got enough flex to give a weak pulse?

Pulse line in good shape?

When I used the spare Engine to test the pump I had a separate pulse line from that to the pump.

Take a line and pump off of running oddy and check again.

Can you get gas to freely flow out of supply line from tank?

It is the tank that I built and has a 1/4" copper line in it.
It is all new and did blow back through it to verify it is clear.
Also I tried pulling from a jerry can with a line and it made no difference.
In fact I got less fuel pulling from a jerry can. These are all new pumps and the one on the death machine has very little hrs.

Id of new lines too big, not enough pull and it looses pull? . Was the jerry can line the same id or bigger?

Just came in from the shop. Beer poacher was over.
He noticed that the return line to tank on this one was much shorter than the other two machines.
On my other two machines I run the return line to the top of the roll bar and then down to tank.
I do this to create a small amount of head pressure.
Then I remembered that I had the jerry can on the floor which meant that the pump had to pull even more head to get fuel and that's why I only got 1 - 1.5 oz on that test instead of the usual 2 - 2.5 oz I got on other tests. So just for giggles I put the jerry can on the table. Presto. 4.5 oz.
So your comment on the larger ID of the fuel pick up line has some merit. It is larger than stock.
Also of note is that the other two machines pick up fuel from the bottom of the tank because I tapped into the drain plug on those machines. On this unit I have the 1/4" copper line going through the top of the tank and then to the bottom. Not sure if this would make any difference though because this Engine ran well for several rides already so it is all just a mystery to me right now.
So my current plan is to run the return to tank like the other two and if that don't work then use a smaller pick up line like your suggestion. Will keep you posted.
Thanks for the suggestions all.
CO

Quick side note,


I feel that the idea of running the return line higher to simulate a check valve is about as useless as it can get. Sure you have head pressure till it reaches its peak, then it becomes a siphon pulling back into the fuel tank... just how I think of it at least. What makes this any different than someone siphoning your gas tank or a simple fish tank cleaner hose. Hope I'm wrong but I cringe when I see people set up like that.

I still have a check valve inline.
It's one of my homemade ones -- the same as on my other two machines.

I'm more so venting than criticizing your setup specifically. I genuinely think that's the case, and I've seen many setups like that and have seen many people advising others to go that route.

I just had to go out into the shop one more time before bed time.
I thought that pick up line was 1/4" copper but it's not. It's 5/16".
So now the more I think about your comment the more I think you nailed it.
That's a lot of fuel for that little pump to pull.
Will find out next week sometime.



It's still a valid comment.
CO

Put some clear lines on. See if its pulling in air from anywhere.

Update:
Still having a fuel flow issue on the death machine. This is the R401 Engine.
Basically what I have done now is pulled all three "new" pumps out of the plastic n box and tried them all.
So that's a total of 3 new pumps and 1 almost new pump (just one season) all from the same manufacture. I ran straight out of a jerry can with clear line on the pick up (as suggested by zero) and straight into a measuring container (no bypass line). Then I hooked up the vacuum line to one of my spare engines and also to one of my running machines. All pumps put out 2 -2.5 oz in 10 sec regardless of which Engine I tried them on. I checked the pulse on the vacuum lines as well and they were the same so all engines are good. It's a pump issue for sure.

So now I look a bit closer. All of my spare pumps are Chinese and the two running machines have Japanese. Well you guys can shoot at me now because I know I have said many times that I have no issue with Chinese, and that was true until today.
Why did I buy these ?? ----- I'm cheap. The Polaris Japan ones are almost $100 here.

How do you know if they are Chinese ?? Look at the pics below.
Japanese ones have writing on the top and the Chinese ones don't.

So at the moment I have given up until I get time to see if I can "fix" these or if I have to buy Japanese.
I have given up because my brothers machine developed a real bad vibration. New post coming for that.

Well I played around with this a bit today.
I took a spare Honda "T" that I had in a box and put a rubber cap on one end. Then checked to see which way this check valve worked. I hooked this T check into the pickup line on one of the pumps. It didn't draw any fuel. Then I hooked it into the outlet line and got 2oz flow. I did this to see if the check valves in these pumps could be faulty. They are not.
This tells me that the vacuum part of these pumps is no good.
When I took the pump apart that was on the death machine I noticed that the vacuum diaphragm on these Chinese pumps is made of some kind of clear see through plastic similar to what you would find on something like a display box that a toy is in or your wallet, but slightly stiffer.
My thinking is that these Chinese pumps are not getting a good stroke. I find it difficult to believe this plastic would flex or stroke enough to draw a large amount of fuel. I don't know what is in a Japanese pump and I am not about to strip a good one to find out. What I might do is cut a piece of inner tube and see if I can make a diaphragm. Then test it again. Stay tuned.
CO

Pics of the Chinese pump internals.

Nope making my own diaphragm didn't work.