Well just when I thought I was on the downhill side of the rebuild..a fuel delivery issue has now popped up.

Over the weekend I hooked up my new square fuel pump along with all new lines, new filter, and new three way valve (which I checked for proper operation, its fine)

I used 3/16 reinforced line from the crank to the pump and then new reinforced 1/4 inch to everything else.

I can not get the pump to draw from the fuel tank.

I have no obstructions in the tank for the fuel shutoff or from the lines inside the tank. I blew through all connections with my compressor and air moves freely.

You can feel suction coming from the vacuum line when you put your finger over it.

I tested the pump also by just putting a small container of gas and running a line into it and it spits fuel out the other side.

But then you put it back into the regular setup hooked back into the stock tank and it will not pull fuel.

The fuel pump is not a true" Mikuni" but it looks just like one. Ordered from Odd ATV.

Do I need to use smaller lines or what?? I am really irritated now!

What If I increase my compression by removing two of the metal stock head gaskets and just use one thin one??

Do I need more compression to get better vacuum coming from the hose??

Right now after doing the topend rebuild and all the other work that Ive done my new stock compression is around 122-125.

That's with a 81MM new bore and piston.

Shouldn't it be a bit higher??

Or do I just have a "lemon" fuel pump??

One of the 350s I have is completely stock and when it sits for long periods of time it wont prime. I pull the fuel cap and blow air into the fuel tank. Just to prime the lines and then it will start right up. It will start fine until I let it sit for a bit again maybe a few weeks. I'd try that. I've started many things that same way

As jknarfal just mentioned, if an Ody has a completely dry fuel system, you will have to prime it to get it to pump fuel.

another method is to remove the spark plug and pour a little fuel down the spark plug hole to get the Engine to fire. This usually puts enough pulsing through the pump to get it to prime the system.

If all this doesn't work then you have a cheap Chinese POS fuel pump that's never going to work.

Rand

Its got to be this knock off fuel pump. I took off the line that feeds the carb and filled the carb full of gas thru the line then put it back onto the fuel pump.

The Engine fires right up and runs until the bowl is out of gas. It will not draw fuel from the pump.

I've got the Mikuni DF44 pump on my rig and it works great. Connections are obvious, so can't be that.

Can you blow/suck on the top connector of the pump and see if the diaphragm is moving? You can hear/feel the pump working if you blow/suck back & forth.

Please, no suck/blow jokes!!


What is your comp anyways?

My Compression with all three stock metal head gaskets installed is right around 125...

It fires right up and idles and accelerates fine.

I have not actually driven it...im still on jack stands at the moment.
The new top end is not even broken in yet.

DMoney..you using a "real" Mikuni branded pump?

Ive ordered a new real Mikuni pump just now..

Sending back the no name look alike.

When I here this story it scares the crap out of me. In the beginning I lost several engines due to a fuel pump that delivered just enough fuel to start and run to mid range and then at full throttle it runs out of fuel and poofkaboom. Tolarfl350 I think I mentioned earlier that you need to do a fuel flow test. You need to get 4 1/2oz approx. in ten seconds out of any pump. I think I also gave you the polaris number for the fuel pump we run. With regards to compression, I did a vacuum and pressure test on the fuel pump vacuum line on my two machines. My machine has 120psi compression after a new rebuild and when I hooked up the gauge to the vacuum line I got 8 inches of vacuum and 5 psi pressure. My brothers machine had 170psi compression (modified Engine) and gets 10 inches of vacuum and 5 psi pressure on the vacuum line. So higher compression don't make much difference. With regards to fuel not getting to a pump when the tank is empty --- you mean when I run out of gas in the bush I have to bring a compressor along to pump up my fuel tank so that the fuel pump is "primed" ?? Baahahahahahaha I don't think so, you got another issue then.

Install just one head gasket (thin) to get you compression back up.

Problem Fixed!!
I ordered an original Mikuni fuel pump.
Hooked it up and it runs now.
You can actually see fuel in the filter now.

So..lesson learned again..don't buy cheap crap!

Quote: "you can actually see fuel in the filter now" ----- buddy you have no idea how close you got to blowing that thing up.