CR125 Shifter Dual Sided Fuel Pump Issues

[Quinnduden]

Ive got a cr125 shifter with a round dual sided Mikuni fuel pump. Currently the pump is supplying WAY too much fuel to the carb. The pump is set up to be a pump around and bypass the carb floats. Engine, carb, and fuel pump have all been rebuilt. Everything worked before the rebuilds. The carb is jetted to 165/52 with stock turns on the screws. Clip position has been set to the leanest to try and reduce the amount of fuel going through. The kart will start up after being cold and then will flood itself after about 20 seconds. Any questions or comments would really help. I cannot figure out for the life of me why this thing is flooding so much.

 

[Joe-405]

my Shifter kart had a return fuel line to relieve pressure.

 

[Quinnduden]

my Shifter kart had a return fuel line to relieve pressure.

That is the dual sided part. It means it has an inlet and a return. It seems like it’s pumping more fuel than it is returning. But that doesn’t make sense because both side run the same pressure so they should be pushing the exact same amount of fuel.

 

[Flyinhillbilly]

I’d pull the carb and clean the needle and seat for good measure.
Seeing as how you have the return hooked up, I can’t imagine that it’s making too much pressure. It only take the tiniest pieces of debris to make the needle not seal.

 

[JTSpeedDemon]

It may also simply have too much output for that engine. There are high and low output Mikuni fuel pumps(I've got one of the single output ones designed for Briggs engines).

---------- Post added at 08:51 AM ---------- Previous post was at 08:49 AM ----------

Low output one: https://www.bmikarts.com/product.asp?itemid=923
High output one: https://www.bmikarts.com/product.asp?itemid=924

 

[Quinnduden]

I’d pull the carb and clean the needle and seat for good measure.
Seeing as how you have the return hooked up, I can’t imagine that it’s making too much pressure. It only take the tiniest pieces of debris to make the needle not seal.

I’ve already cleaned and completely rebuilt the carb.

---------- Post added at 09:39 AM ---------- Previous post was at 09:38 AM ----------

It may also simply have too much output for that engine. There are high and low output Mikuni fuel pumps(I've got one of the single output ones designed for Briggs engines).

---------- Post added at 08:51 AM ---------- Previous post was at 08:49 AM ----------

Low output one: https://www.bmikarts.com/product.asp?itemid=923
High output one: https://www.bmikarts.com/product.asp?itemid=924

It ran with this pump before the rebuild.

 

[Flyinhillbilly]

I’ve rebuilt carbs before and had to go back in and clean the needle and seat, it's worth a try. I’m running the same fuel pump as you on a 28mm flat slide and have the return blocked so that it gets full pressure and I’m not having any problems.
Something else worth checking is that no fuel is getting in through the pulse line. A leaky diaphragm could flood the crap out of one.

 

[JTSpeedDemon]

It ran with this pump before the rebuild.

The low or high output one? Did you have any problems?
I've had issues with carburetor flooding myself, it came down to the needle and seat, along with carburetor body warping, but that was on a totally different carburetor.
Check the needle, make sure it doesn't have a groove in it and is the correct taper.

On my carburetor I installed an aftermarket float needle and clip, and when I couldn't figure out the leaking problem, I compared it to a new OEM needle and clip, and the aftermarket ones were different. The needle had a different taper, and the clip was different.
Make sure you used the right parts!

 

[Joe-405]

That is the dual sided part. It means it has an inlet and a return. It seems like it’s pumping more fuel than it is returning. But that doesn’t make sense because both side run the same pressure so they should be pushing the exact same amount of fuel.

So the fuel pump has 4 ports on it ???? Mine had 3. A vacuum , a in , and a out. No return line port ! My return was a tee in the line between the pump and carburetor inlet.

 

[Flyinhillbilly]

So the fuel pump has 4 ports on it ???? Mine had 3. A vacuum , a in , and a out. No return line port ! My return was a tee in the line between the pump and carburetor inlet.

Yes, the round Mikuni like I’m using has two outputs