mrd injection on 750sx

[BigTex]

hey guys! wandered over here from the other site as its getting somewhat 'dramatic' lately, and im wondering why i never bothered posting here until now...

anyway, just bought a fuel injected 750, doesnt like anything near WOT or it will just surge badly and sometimes even stall. ive notice while riding with the hood off air bubbles will form on the carb side of the inline filter of the feed line, as if its not flowing sufficiently. could something so simple be the culprit? this never happened on my carbed skis but i know nothing about these injection systems....

i wouldve just replaced it by now but i cant seem to find a good stainless element-style filter anywhere. only cheap paper filters at auto parts stores...

 

['Crockett]

Most paper filters will not flow enough fuel for the MRD to run properly. It flows a high rate of fuel constantly through the throttle body and then bypasses back to the tank. The engine only uses fuel when the metering valve is opened to the injectors.

Try some motorcycle shops for the screen type filters. They are what you need to be running.

If this doesn't fix the surging, remove and inspect the two check valves for bad o-rings or debris that is keeping them from seating properly. One is in the return line and the other is screwed into the throttle body where the pressure line comes in from the pump.

Most MRD malfunctions are related to these check valves . . . . . .

 

[BigTex]

thanks! ill stop by a speed shop this week for a filter and hopefully test again this weekend. ill let y'all know....

 

[Prem1x]

There's a good thread on MRD in the FAQ here.

 

[BigTex]

thanks for the help so far guys, the faq was helpful too. new problem though: never made it on the water last weekend because ever since replacing the filter it will only run off the primer. i figured it just lost its prime but even after purging out all the air it will only run if i pressurize the fuel tank. i took apart both check valves and both are clean and working, o-rings look good. how would i know if the fuel pump went out? i could tee in a pressure guage on the fuel line, what psi should i see? are there any other ways to make sure the pumps working??? thanks again

 

[Jr.]

Both the fuel pressure problem & the air in fuel lines will be the fuel pump. early models used plastic gears in the pumps, those will need to be changed out with metal gears. off the top of my head, I don't rember what the part number is, but they are off a paint sprayer & avail thru mcMaster carr.

 

[BigTex]

thanks a TON, i didnt see that anywhere in either forum.

 

[Prem1x]

I've been using the same plastic gear for years and never had it go bad. You can get plastic gears too. I believe it is intended to be the sacrifical gear in case something bad happends. I wouldn't want the one pressed onto the fuel pump shaft to go bad.

Two things to check:
1) Did the relief (pop-off) valve come off or have something caught in it? What pressure is it set to release at? If the system can't build up pressure, it will start up but eventually run out of gas like you describe. The relief valve is usually mounted inside the fuel tank and I have mine at @12 p.s.i. There is a diagram in one of the other threads.

2) If that is not the culprit, is the inside of the cover of the fuel pump damaged with grooves, or the plastic gear's teeth damaged? Either one would cause the pump to not push enough fuel.