MSefi.com read only forum (Jan.15,2018)

I'm not sure this is the correct section for this post so forgive me if I've misplaced it. The background is I'm running a fuel only setup on a 170cc Yamaha two stroke motorcycle engine using a MicroSquirt V2.0. I am having an issue with getting enough fuel into the engine. It will start up on the priming pulse then die. I started small but ended up maxing out the Req_Fuel, VE, fuel enrichement etc and it still won't idle due to lack of fuel. I decided to pull the injector to see what the fuel spray looked liked. The injector BTW is 260cc being run @ 60psi. Here is where my question comes in- What should the spray volume coming out of the injector look like? The priming pulse sends out a big solid spray of fuel for a fraction of a second. In my opinion that seems correct. When it goes to starting the engine visually I can't see any fuel being sprayed. I stuck my finger in front of it and I can feel a tiny bit of fuel being sprayed for a few cycles and then it stops. It's not even enough to make my finger tip wet. I this what I should be seeing? It seems like an awfully small amount of fuel coming out for how high I have everything set. if this isn't right where should I start looking for the problem? I should note I have a fuel pressure gauge and it is reading a solid 60psi. I thought maybe after the pump primed I maybe dropping pressure but that doesn't seem to be the case.

bz7,

Make sure you have set the PWM parameters correctly for your injectors. Setting this too high or too low will cause problems. There is more ion the manual here: http://www.megamanual.com/ms2/tune.htm#pwm And make sure your open time is sufficient (use at least 1.0 if you aren't sure).

Lance.

I'm running a high impedance injector which should make things easier. only setting I had a bit off was the PWM limit. It was set to 90%. I changed it to 100% but it didn't seem make any difference.

I looked into the fuel pressure again and there might be something going on. I made the pump run continuously and I look to be getting more flow out of the injector when cranking. Still nothing close to what comes out with the priming pulse. I'm thinking I may have some air trapped in the regulator. The fuel routing is a bit weird since there is only one feed off the tank. The fuel pump is in a smaller housing external of the tank and the pressure reg. return goes to that, There's really no where for the air to go in the system and the reg. is the highest point. I usually have to pull a line to bleed enough air to get the pump to prime. I may have to add another fitting to the tank or a manual air bleed at the highest point.

your routing of the fuel lines basically won't work. You need to make the return line return to the tank. If you don't do that, the regulator can't do its job of setting fuel pressure, you will have huge vapor lock issues, and you car will die every time you suck a little air into the fuel inlet.

I've got another fitting on it's way for the tank.

You can return fuel back to the fuel pump enclosure or the inlet of the pump, lots of guys reportedly do that on cars/trucks with some success. The drawback is that the pump always sees hot fuel, which can overheat it, but a motorcycle has a small tank anyway so there’s less benefit to that heatsink.

If a pump has fluid on its inlet, it will prime, and it will merely push fluid and compress the air on the outlet side. This is no different than a mechanical oil pressure gauge – those don’t need to be bled, yet they read pressure very quickly after the air in the line is compressed. This suggests to me that, in addition to having the regulator as the highest point, the return fitting on it is highest also, and that allows the trapped air to be pushed back to the pump enclosure. Otherwise, the air would stay trapped in the regulator and eventually get pushed to the injector along with some fuel.

Can you re-orient the regulator so that the line to the injector is higher than the return? If so, the air should get purged out.