250 cfmoto engine. i know this has been addressed

[mikeyscootin]

i read the article on stans page and i am still not sure what my problem is. after about 2 miles or so of higher speeds the bike acts like it wants to konk out.. starts going slow and major loss of power. does my mc 54 250 have an electric fuel pump? does it need one? do i just need to have hoses replaced? it rides just fine for prolonged periods at 5000 rpms or less. i would have never guessed there was a problem.
mike.

[12string]

You have a fuel pump problem. Your scoot should have a vacuum pump,at high RPM the engine will produce very little vacuum and the pump will not be able to keep up causing the engine to starve for fuel. The fix is to, replace the vacuum pump with an electric pump. I believe that Auto Zone carries a small electric pump that is low pressure that will work great.
Hope this solves your problem, good luck, and keep on scoot'n.

[scooterollie]

mikeyscootin;
Here is information Stan provided recently about another choice for vac. fuel pump replacement:

"For those of you with fuel pump models (tank below the carb), you can get the Mikuni vacuum fuel pumps from www.heeters.com and they are far superior to the JinBo (Chinese translation = crap) fuel pump. These are just a matter of swapping the lines, so you don't have to wire in an electric pump. The standard pump works just fine and is around $25. Stan"

[Jacine]

Ok what's the difference between the 35 LPH pumps. They all look the same, cost different?

[mikeyscootin]

scooterollie said:

mikeyscootin;
Here is information Stan provided recently about another choice for vac. fuel pump replacement:

"For those of you with fuel pump models (tank below the carb), you can get the Mikuni vacuum fuel pumps from www.heeters.com and they are far superior to the JinBo (Chinese translation = crap) fuel pump. These are just a matter of swapping the lines, so you don't have to wire in an electric pump. The standard pump works just fine and is around $25. Stan"

There are several models at heeters.com. do you know which model i need for my scooter?

[YellowScooter]

Ok my tank is under my footboard and my filler neck is in the front, that means I got one of these P.O.S. pumps too right?
If I do, it won't by this weekend!

[mikeyscootin]

does anyone know the particular Mikuni vacuum fuel pump that stan speaks of for my MC 54 250 which is the CF MOTO engine? there are 3 or 4 of the pumps listed on the heeters.com site and I haven't a clue as to which one I need to buy so that i can have my mechanic change it out for me. I dont' really know where my gas tank is but I put the fuel just under the glove compartment underneath the steering column. So i am assuming the fuel is below the carburator? Anyone know for sure. Obviously I am not a mechanic.. Sorry if I sound dumb as a rock. I did buy new mirrors from stans site and they seem to be far superior in that they are much stiffer and don't flop around.
mike any help would be appreciated.

[90GTVert]

The rectangular one will do just fine and it's the easiest to hook up since it's a single outlet type, just like the OEM. Stan

mikeyscootin said:

does anyone know the particular Mikuni vacuum fuel pump that stan speaks of for my MC 54 250 which is the CF MOTO engine? there are 3 or 4 of the pumps listed on the heeters.com site and I haven't a clue as to which one I need to buy so that i can have my mechanic change it out for me. I dont' really know where my gas tank is but I put the fuel just under the glove compartment underneath the steering column. So i am assuming the fuel is below the carburator? Anyone know for sure. Obviously I am not a mechanic.. Sorry if I sound dumb as a rock. I did buy new mirrors from stans site and they seem to be far superior in that they are much stiffer and don't flop around.
mike any help would be appreciated.

[mikeyscootin]

thank you, i have ordered the part and im sure all will be fine with higher speeds
mike

[roadster250]

I've had the same issue with the warmed CF-Moto engine konking out. I replaced the original vacuum powered pump with the universal electric fuel pump mentioned by 12string above. While that solved the high speed dying, it would not idle (too much pressure on the float stop, I suspect) and also drew too much juice so that I developed a charging problem as well.

OK, so i took the advice from Stan above and bought the Mikuni vacuum pump from Heeters for about $35. With some machining to the mounts on the new pump and some re-routing the vacuum pump hose, I installed that this weekend.

Took it for a drive and once it warmed up, its' back to the dying at any continuous run over 60. It won't restart without a 4 or 5 minute rest. Is there a vapor lock thing going on here that some insulation might help with?

[Jacine]

Which of the $35.00 pumps did you buy? There seem to be several that run at 35L vs the 14L. Obviously they must be different in some way due to price differences. They have two vacuum ports, but the bikes only require one. If one vacuum port is blocked, does that mean the flow may be decreased?, and then by how much?.

What I have discovered is that the carbs (carb float valves) seem to be too small and too flimsy to handle an electric pump pressure when they were designed for vacuum pumps.

It would seem that if the powered pump solved the high speed dying, then the problem was fuel starvation at high speed, the filling of bowl cannot keep up with the requirements and it could have been the vacuum pump. If the carb is drained, and the engine is hot it will create a vapor pressure lock.

If your tank is above the carb, then I would try to bypass the pump and directly connect to the carb and see if this helps.

[roadster250]

Thanks Jacine,
I bought the Mikuni DF-52-21-D. It has two outlets (for dual carbs, I suppose); I blocked one.
I may have inadvertantly added to the problem, on talking to a neighbor/mechanic, who suggested that the extra fuel filter I installed on the output side of the pump (as you suggested in another thread about electric fuel pumps) might also be adding to the problem as it's so close to the cylinder head.

[ By the bye: I appreciate all your suggestions; I also put an in-line fuse in when i originally installed the electric fuel pump and it did indeed protect the system as it popped during troubleshooting last week]

I'm going to attempt an insulating of the fuel line and the new filter and see if that solves the isssue. It's just so annoying that the little bugger is still trying to pull at 65 and then chokes and croaks.

Chris

[90GTVert]

Make sure you don't have a tank vent blockage, and if you haven't already, I'd bump the main jet up to about 115 or 120. Be sure the pump is mounted as low as possible so you can use all the fuel in the tank since it's basically gravity fed to the pump. Also, try to get the filter mounted vertically so air doesn't get trapped in it. Stan

roadster250 said:

Thanks Jacine,
I bought the Mikuni DF-52-21-D. It has two outlets (for dual carbs, I suppose); I blocked one.
I may have inadvertantly added to the problem, on talking to a neighbor/mechanic, who suggested that the extra fuel filter I installed on the output side of the pump (as you suggested in another thread about electric fuel pumps) might also be adding to the problem as it's so close to the cylinder head.

[ By the bye: I appreciate all your suggestions; I also put an in-line fuse in when i originally installed the electric fuel pump and it did indeed protect the system as it popped during troubleshooting last week]

I'm going to attempt an insulating of the fuel line and the new filter and see if that solves the isssue. It's just so annoying that the little bugger is still trying to pull at 65 and then chokes and croaks.

Chris

[stormy]

I have a question about the vacuum fuel pump. The fuel pump on my MC-54 would stop pumping gas on scooter at WOT on a long hill or mountain as I live in north central PA. So I switch it out for a electric pump. I notice that now after installing the 12v pump, ( which works real well ), I'll run the scooter in the garage and put it on the charger after a couple hour run, and it takes the charger over a half hour before the battery is charged back up. Now if I switch to the vacuum pump from Heeters, at WOT, won't it do the same thing, no vacuum to operate the pump? I thought that is why the vacuum pump quit working, was you lost vacuum at WOT for long periods at a time. Before I installed the 12v pump, after a couple hour run, my battery would be full charged in a couple minutes.

[maydog]

Hello,

I have been dealing with a fuel starvation problem on my RR250 (linhai) for a few weeks now. My first idea was to add a larger fuel filter, since the original was dinky. That actually casued more problems, since it flows worse than the OEM. I found this out after dealing with a lot of stalling. I will have to look for a better filter.

I also tried the fuel pump idea, I wired it to the headlight feed (directly off the regulator) that way it only runs when the engine is going. It was a purolator 04 model. This solved the sputtering at high speed, though the carb barfed a lot of gas and it hesitates at 1/4 throttle. Also, it seems the pump allows fuel to remain flowing when shut off

A bypass of the vacuum petcock seems to solve the problem, though I put it back in line for now. I believe the petcock shuts off the fuel supply at WOT due to the lack of vacuum.

I am considering one of several solutions (from the simple to most elaborate):

1. Straight bypass - works, but I would like to be able to shut off the fuel supply

2. Manual valve - should work, though I am not fond of the manual part.

3. Direct Acting Electronic solenoid valve - something like this www.dan-marcrvparts.com/12vomufushof.html, I think I can find something suitable at the hardware store, NOS also makes valves, but they are too expensive. This would ensure a constant valve opening at all throttle openings with no user intervention. I could also add a manual button to prime the system should the fuel lines run dry.

4. Fuel Pump with modifications - put the fuel pump back in line and add a tee down stream. From the tee, add a check valve and a line going back into the top of the fuel tank (involves drilling the tank and putting a fitting in, make sure the tank is empty and aired out.) The other feed from the tee goes to the carb. This would ensure that the fuel supply is always equal in pressure to that at the highest tank level. Though I would still have to figure out how to shut off the fuel supply to the carb (maybe from #3). This is overkill but fun to think about and I already have the pump.

I will keep experimenting and post back on the results.