Primer keeps running when trying to start

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Well-Known Member
Dec 12, 2020
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Merritt Island FL
Hey all, looking for some advice. When I went to start my bike tonight, the primer ran longer than normal, and when i hit the starter it started priming again, and the bike would not start.

It's an 86, and i've owned it since new, just under 20k miles on it.

any thoughts on what I should check first?

The starter does engage and the motor spins over perfectly, but the primer starts running again as soon as I hit the starter button. the motor turns over, but won't fire. So I assume it's not getting any gas.
The starter does engage and the motor spins over perfectly, but the primer starts running again as soon as I hit the starter button. the motor turns over, but won't fire. So I assume it's not getting any gas.

What you are hearing is the fuel pump.

If you suspect that there isn't any fuel in the carbs the open the drain screws and see what comes out.
By primer you mean the clicking sound from the fuel pump?

If the bike has been standing for even a short time, the fuel has dropped slightly in the float bowls so the fuel pump will run.

Once carbs are full, then the pump will not click.

So turn on ignition, hear the pump clicking is normal.

Press the starter, run engine for a short turn off, ignition on, no clicks from pump is normal.

1 if you turn ignition, does the pump stop?

2. When was the last time the engine ran?

3 when was the fuel filter changed? Is filter clear?

4 when engine is turned over, can you smell fuel?

If the filter is blocked, the pump isn't able to pull fuel so continue to runs.

The pump also continues to run if the carb bowls cannot be filed due to a leak, usually because the float valves are stuck, but you would see fuel pour out of the overflow pipes, if they are clear.
when I turn on the ignition, the pump kicks on and runs for probably 5 seconds or so, much longer than ever in the past, usually it would run for a second or two.
it's been 3-4 weeks since last started.
fuel filter was changed several months ago, maybe a year at most.
I am not smelling fuel when turning the engine over.

as soon as I hit the starter button, the pump kicks on again and runs the entire time I am trying to start, I have never noticed this happening before.

I think I will try the fuel filter first, as that would be the easiest thing to try.

If that doesn't do it, is it possible the fuel pump has an issue? it's original to the bike.
I think you're out of gas. I think it really is just that simple.

If you turn the bike on and the pump runs 5 seconds, that only happens when the fuel bowls on the carbs are completely empty. You turn the bike off and back on it should run another few seconds and shut off. If it runs another 5 seconds than there are only two possibilities:
  • Your fuel pump is shot.
  • You are out of gas.
It does not sound (sic) right but I'm surprised you can hear the pump as the engine turns over.

This it how it works.

There's a solenoid plunger within a spring. There are contacts that supply power to the solenoid and close by being pushed by the spring. Opposing this force is the pressure from the fuel.

When the pump needs to top up the carbs, there's no pressure so contacts close, solenoid is energised and moves pushing fuel to the carbs. Eventually the needle valves are closed by the carb floats producing sufficient force to overcome that of the spring so pump stops pumping.

It is possible that the pump has failed, there have been posts about it. I seem to remember it can be taken apart and overhauled.

I suggest to remove the hose at outlet of the pump and have it run into a container, say half a pint, and time how long it takes to fill it. You can calculate the flow rate and check vs the spec.

Second test is to place your finger over the outlet and see if the pump stops. Do this before you turn on the ignition to avoid squirting fuel everywhere, especially in your eye (wear goggles and not smoking when doing this)

If it does not stop, only reason for that is diaphragm is damaged. You would need to take it apart but I'm not sure if replacement spares are available - but it probably is a model used on other Japanese bikes.

Then your options are find company that overhauls fuel pumps, by new or used Vmax pump or another fuel pump with similar fuel delivery, bearing in mind it may be different size and shape so some modifications to mounting bracket may be needed.
thanks all, great suggestions and starting points.

it is weird for sure, like I said, the pump is running way longer than normal before shutting off, then immediately kicks back on and runs when I hit the starter and the engine is turning over.

Let me try the suggested troubleshooting on the pump and report back.

There is a safeguard built into the Vmax where it shuts off the fuel pump when there is no ignition. If you put the bike down, it would otherwise keep pumping in the event the fuel line ruptured. Once the engine dies, the fuel pump stops.

If the fuel pump is bad like Dorney mentions, the fuel pump will not pressurize and will continue to pump for about 5 seconds after which it shuts off. Normally the ticking becomes slower and slower until the carbs are full and the line is pressurized so you don't hear it shut off. If you try and start, the ignition is seen and the fuel pump once again starts pumping, trying to build up the pressure.

So normal behavior for a bad fuel pump.
sounds like that might be the case, it runs solid for about 5 seconds, then just shuts off. then when I hit the starter, it starts running again, then will shut off after about 5 seconds when I release the starter button.

I am in the process of removing the fuel pump, but wanted to ask if there is any special procedure for removing the braided line between the pump and the carbs? Never seen hose clamps like that before.

Undo the screw on the clamp and slide it back as far as you can, ideally off the hose. .

Then pull on the hose with a twisting motion. Chances are it won't budge so use a small screwdriver or a pick to get in between the hose and pipe to attempt to break the seal between them .

Repeat the pull and twist and use a flat bladed screwdriver to also push the hose off the pipe.
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I was able to get the fuel pump off and test it. It is not pumping any gas, so guess I need to replace. Any suggestions? I am thinking I will try to get the Yamaha replacement.
Would be worthwhile stripping to see what the issue is and depending on what you find looking at re-build kits.
There are much less-expensive fuel pumps than OEM. Advantages of OEM are it fits in the allotted space, the inlet/outlet are positioned properly, and they are durable. Be sure that you get a proper PSI rating in the fuel pump you choose, if you go aftermarket. Too-much PSI and your gas float needle valve won't control the flow of gas properly.
good point, I will pull it apart if I can, to see if I can tell my it quit working.

i think I might buy an OEM if I can't rebuild. Hell, the first one lasted 35 years.
Aftermarket pumps are 'way-cheaper, be sure what you choose fits in the space, and that you can run the inlet/outlet connections w/o restrictions from kinking flex tubing. Sean Morley has connectors you can use to make anything 'plug & play.' [email protected]