2005 RX1 MCX rear mount

[Helgy]

Are you sure the electric pump is even turning on? Or that it's flowing correctly?
I wouldn't trust the power light alone to tell you the pump is operating correctly. You need to jumper power to the electric pump to check and then set the regulator with it to ensure it's pressurizing.
If the float needles and seats in the carbs are in good shape, then they shouldn't leak or overflow with the electric pump 100% of the time as long as the regulator base fuel pressure is not set any higher then 4.5 lbs. If you install a manual shut-off valve to replace the check valve, then put it AFTER the stock pump (on outlet line) so you can block it off from the high fuel pressure keeping it from getting pressurized so you don;t worry about blowing out a diaphram.
IMO that i'd run the electric pump all the time, run it off a relay that powers up with the head light. That way it only kicks on when the engine is running, and not during cranking / starting.
The sled should start with the fuel that is sitting in the full float bowls from when you shut it off last.
If it happens to run dry on fuel during extended cranking, etc , you can manually open the valve so the stock pump fills the carbs during cranking.

Cool, I have a little project to do now, maybe I already have a blown diaphragm and that is whats causing the probs. Thank you for the great info!

 

[rxrider]

What kind of Fuel Pressure Regulator do you run?
The Malpassi on my RX-1 comes from MCXpress.
It has one fuel inlet, two fuel outlet to carbs, and one fuel Return going back to the tank.
There is no way the carbs will overflow if they are set up correctly.
Get rid of the Stock fuel pumps and run the Electric pump only.
The Electric fuel pump is supposed to run as long as the ignition in on.
If you turn on the ignition but do not start the engine, all that happens is that fuel is pumped past the FPR and back to the tank.
The carb float bowls will be pressurized to the idle fuel pressure Level, approx.
MCX kit came With a big Y-pipe to T together the two Stock fuel lines feeding fuel directly to the Bosch Electric fuel pump.
The Stock fuel pumps are limiting the fuel pressure you get to the carbs, get rid of them.
If you read through my early postings on rxrider's turbogarage (link in my signature) you will find Pictures and writing from my MCXpress days.

 

[Helgy]

What kind of Fuel Pressure Regulator do you run?
The Malpassi on my RX-1 comes from MCXpress.
It has one fuel inlet, two fuel outlet to carbs, and one fuel Return going back to the tank.
There is no way the carbs will overflow if they are set up correctly.
Get rid of the Stock fuel pumps and run the Electric pump only.
The Electric fuel pump is supposed to run as long as the ignition in on.
If you turn on the ignition but do not start the engine, all that happens is that fuel is pumped past the FPR and back to the tank.
The carb float bowls will be pressurized to the idle fuel pressure Level, approx.
MCX kit came With a big Y-pipe to T together the two Stock fuel lines feeding fuel directly to the Bosch Electric fuel pump.
The Stock fuel pumps are limiting the fuel pressure you get to the carbs, get rid of them.
If you read through my early postings on rxrider's turbogarage (link in my signature) you will find Pictures and writing from my MCXpress days.

That makes a lot of sense, I wondered why I couldn't get 4.5lb at idle. I think I have the same regulator as yours, it was from MCX. I think I can just remove the pressure solenoid and hook the wires together, set the idle fuel pressure, add a shut off valve after the stock pump, and try it.

 

[rxrider]

Please remove the Stock fuel pumps.
Why would you need a shut off valve?
I have never flooded the carbs even running the pump all the time from igniton to shutdown.
Remove the solenoid.
Get hold of a Y-pipe to T together the two Stock fuel lines into a larger single fuel line going into the fuel pump.
Use a hose With the same inner diameter (going into the fuel pump) as the the inner diameter of the fuel pump inlet to get good flow.

 

[mbarryracing]

X2 on the feed line size to the pump. You can cause pump cavitaion if you have too much restriction in the supply line, reason rxrider mentioned they use both feedlines Y'd together to feed the electric pump so it isn't starving itself. I killed 2 Bosch 044 pumps in 2 seasons because the stock fuel pickup in the tank was too restrictive for that 300LPH pump I was trying to use.

 

[rxrider]

Mbarryracing - exactly what you said

 

[Helgy]

The Bosch is fed with its own 1/2 inch supply line, I look forward to trying it this weekend. I will let you know how it works out. Thanks guys!

 

[mbarryracing]

Helgy,
Be cautious, because the gas tank fittings aren't 1/2 inch, probably more like 5/16, so your flow will only be as good as the smallest restriction.
Your feed line might be 1/2 O.D. but that isn't what matters, it's the I.D.

I ended up running 3/8 inch line and using dual 5/16 inch pickups in the tank to ensure low restriction. But that was necessary for a 255 LPH pump for my EFI Apex. I should take some time and do a thread on my new fuel system to share the learnings I had.

Not sure what size pump is on your MCX but carbs systems typcially don't need huge pumps because they operate at significantly lower pressures than EFI's. Their smaller pumps needs less feed flow obviously.

 

[rxrider]

Half inch Works With the Stock lines.
It will flow enough fuel as the carbs do not need as high pressure as the EFI engines.
It will work.
Let us know what AFRs you run.

 

[Helgy]

It has a completely separate fuel line plumbed into the tank in a different place that is 1/2 inch feeding the Bosch pump. The stock fuel fittings and hoses still feed the stock fuel pump, which I plan to remove. AFR was 12.6 to 12.8 under boost and at midrange, 15 at idle. I will watch and see if it changes.

 

[rxrider]

How much boost?
My AFR rule of thumb on adjusting carbs
Idle: 14.0-14.7
Engagement: 13.5
0 lbs 13.0
5 lbs 12.5
10 lbs and up 11.8-12.0
Jetted to these AFRs your carbed engine will run at its best.
You may adjust Your pilot screws out 1/8 to 1/4
I have mine set at 2 turns out from lightly seated.
Needle Clips in the Stock #3 postition With one plastic shim on each side of the C-clip