FE400 gradual loss of power

[Ricks_club]

Originally Posted by Kudzupatch

Dang it! Almost there.

That tube was dirty and I cleaned it thoroughly. Heck, the whole card has been cleaned thoroughly (3 times now). It made a big difference, it doesn't stall off idle. There is still a slight hesitation but it is driveable.

But it is still got a misfire/stumble that has me stumped. At speed down the road you can fill the miss. Still acts like it is running lean but power is much better. A little choke will smooth it out and cause it to speed up on a hill.

I am going to replace the spark plug next. It looks great but I have seen it fix odd issues before. If that is not it I am really going to be stymied.

If after all the work you have put into the carb, here is my suggestion. 1. Make sure that there are no leaks in the intake manafold. Could be a cracked rubber part. 2. You say it is missing at high speed, time to disconnect the the RPM limiter, could be going bad.

[Kudzupatch]

Cables are fine.

I am still leaning toward fuel because the choke improves it. That tells me it is lean.

Every time I mess with it, it gets a little better. But it still low on power and stumbles when you step on the throttle. Not nearly as bad but still will stall out if you open it to fast.

At WOT (and yes it is opening fully) I feel it misfiring slightly. Just running rough. Again, a little bit of choke to richen the mixture and it picks up power.

The only thing on the carb I have not done was taken the idle mixture screw out because of the locking tab. But I just ground down the tab and took it out. Passage appears to be clean and the brass looks good.

But I put in the cleaner once again. Going to let it run for 3o minutes this time. Might run in for a full hour just because I am getting desperate.

[Kudzupatch]

FOLLOW UP

Found the idle circuit was clean. No dirt, not clogged, looked fine.

I ran all the part through the the cleaner for the 4th time. Put it together, set the idle screw back about where it was and it ran exactly the same. Pretty much disgusted at this point.

I decided since I had lot of lee way with the idle screw now to fatten up the idle mixture and see what happened. I back off 2 turns, idle dropped but didn't die so I drove it around and with some small adjustments I have it MUCH better. Not 100% and still lean on the top end but I can drive it now. I don't go around wide open except on steep hills.

Still not right. Wondering how you check a fuel pump? Anyone know any specs? Pressure or a volume test? Wondering if the pump is not pump enough fuel, cause it to run lean.

[Scooter Bob]

Is your float level set right? You say it's lean on the top end. Is it lean as soon as you get to top speed, or does it get lean after running high speed for a bit?

The engine runs on the fuel in the float bowl. The pump should pump more than enough fuel to keep the bowl full all the time.

If it slowly leans out after sustained high speed, then your pump may not be keeping up.

If it is lean right away when you step on it, then you probably still have a restriction in your main jet system, or are sucking extra air in somewhere (intake leak).

[Kudzupatch]

Originally Posted by Scooter Bob

Is your float level set right?

Great question. problem is it is not adjustable. At least I can't see any.

The float is plastic so you can't bend the arm to adjust the height. It appears to to have plenty of drop so that fuel can enter but the cut off point is fixed so I can't change that.

I agree with you thinking because I have leaned that way. Since you can't change the float that is why I was asking about pumps. Wondering if it running out of fuel. But as much effort as I have spent on the carb I am starting to think it must be something else I am missing.

[Fairtax4me]

These engines are not normally that picky. But if opening the idle jet makes a difference then you still have an obstruction in the main jet or pilot tube, or the passages that supply air through the tube.
If opening the idle jet up made a difference then I would make sure the main jet is not obstructed, and if everything there checks out then go up a size on the main jet.

[Kudzupatch]

Had the carb apart once again. 30 minutes in the ultrasonic cleaner. Spray cleaner on every port, hole, jet, tube etc. Had a buddy of mine double check my work and he too is convinced that carb is clean.

We are leaning toward lack of fuel supply. Just checked all the line and filter. No obstructions. They flow fine under gravity. Valve in the tank is open. Pick up tube is clear.

That leave the fuel pump. It appears to be pumping enough volume but doesn't seem to have an pressure to speak of. Not sure how much it should have but I can easily stop the flow with my thumb.

Really dreading bottom here trying to find this.

[CP241]

These pumps don’t make “pressure”. If you weren’t able to stop the flow with your thumb you would constantly be flooding the engine as it would bypass the float needle.

These fuel pumps (according to mikuni website) are capable of up to 14 liters per hour. Which if my math is correct, divide by 60 minutes is 230ml or 7.77 ounces per minute. This is a measurable value with a mason jar. However do note that this flow rate will vary based on RPM since each revolution of the motor creates a “pulse” that pumps one “spurt” of fuel. Obviously it will be much closer to that spec’d volume at 5,000 rpm than it will at 1,000 rpm. So while not a hard set pass/fail number you should be able to get a pretty good idea if it’s starving the carb or not. If you crank the engine with the starter for 60 seconds and get even half of that 7oz I’d say you’re perfectly fine.

If it’s working well enough to drive the cart and not run out of fuel in the bowl, I’m gonna guess “not”.

[Kudzupatch]

I am not one to 'throw parts at the problem' but I am running out of options. Engine is not getting enough fuel.

Going through the list you need fuel supply to carb and then the carb to deliver the proper amount of fuel and air.

Seeing as how we have about worn out the threads on the carb it leads to delivery side. So I ordered a pump for it. Not confident it will fix the problem but I getting desperate.

It could be something internal in the carb we can't see and I would replace it but they cost $550-600!

A pump and replacement fuel lines are cheap. When that doesn't work I am fresh out of ideas.

[Jeff McGuire]

"MOST" FE400 are hydraulic lifters, but there are some that are solid lifters with adjustable valves. Might pull your valve cover and check. Also check for intake and exhaust restrictions. I had an ATV I worked on for longer than I'd like to admit that I found mud dobbers in the intake tube.