Yamaha 225 2 stroke - Weak fuel pump output

networker

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'96 Yamaha 225 2 stroke. Model L225TXRU
Problem: Engine stalls if idled for very long. Fuel pumps won't deliver adequate fuel at idle. Good fuel flow at higher rpms. Engine runs rough and has knocking noise when trolling at idle speeds. Runs great at all other speeds.

I've changed out all 3 fuel pumps. I have replaced primer bulb, and fuel line from tank to bulb. I have bypassed fuel line altogether and run from separate portable tank.

I used clear tubing at the output of each fuel pump. Noticed lots of bubbles on the top two pumps but the bottom one looked pretty good. Switched top and bottom pumps and the bubbles still existed on top pump so it doesn't look like it's a pump problem. Also, all 3 pumps work well at any speed higher than idle.

Is there a way to test vacuum level? I wonder if there just isn't enough vacuum (or a leak somewhere) to adequately drive the pumps. If there is a way to test vacuum, what should the vacuum level be at idle?

Any other ideas of what could cause this problem?
 

networker

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Re: Yamaha 225 2 stroke - Weak fuel pump output

After further reading, I understand that the pumps are driven by a combination of vacuum and pressure pulses that are generated in the crankcase. Is there any way to test the strength of these pulses? On this engine, are all these pulses the same for each pump or are they coming from separate chambers in the crankcase? Can a crankcase seal or leaking reed valve cause weak pulses.
Am I barking up the wrong tree?
 

micel

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Re: Yamaha 225 2 stroke - Weak fuel pump output

Bad spark plug wires ? Take a look at spark plugs also.I always troubleshoot easiest to fix things first.
 
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networker

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Re: Yamaha 225 2 stroke - Weak fuel pump output

I have already bypassed filter and went directly to the pumps. Didn't use clear tubing at the input of pumps, just the output. Will try that next. Pumping the primer bulb will keep it running. I'm beginning to think that the problem is a reed valve or crank seal causing low pressure in the crank. Do you know if there is anyway to check for leaks or low compression in the crankcase? Conventional compression at the plug is 105-110 all cylinders.
 

99yam40

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Re: Yamaha 225 2 stroke - Weak fuel pump output

check for air leaks before going farther would be my thoughts.
I have no idea for checking that suction you are speaking about
 

clanton

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Re: Yamaha 225 2 stroke - Weak fuel pump output

You need gauges with a damper on the gauge. The pulse goes from 6lbs vacuum to 6 lbs pressure. The back and forth movement of the gauge needle will ruin the gauge without damping the pulse. I would check the pulse fittings, hoses, passage in block. You may find one of the gauges at a Kawasaki motorcycle shop. That's where my gauges came from.
 

networker

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Re: Yamaha 225 2 stroke - Weak fuel pump output

Thanks for the advice. I'll see if I can find one of those gages.
 

lawcki

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Re: Yamaha 225 2 stroke - Weak fuel pump output

It sounds like the hose connecting bottom pump to the other two pumps has a leak in it.
 

13' Whaler

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Re: Yamaha 225 2 stroke - Weak fuel pump output

First off that's a great engine. I have serious doubts its a reed valve. I have worked on marine engines for about 20 years and never had to replace them unless there was some obvious internal damage.

You are sucking air somewhere, your good move of using the clear line determined that. Try the clear tubing on the input side as was previously suggested. I have a feeling you will find the problem at the fuel line joints.

Once you have confirmation I would replace all the engine fuel lines anyway. They are relatively cheap and still available for that model. Plus who knows what sort of effect todays fuel is having on their insides.

Some other thoughts come to mind before going out and buying guages.

Make sure the fuel pump gaskets and the pump housing itself are seated properly. (Get new gaskets if any doubt)

Are the pumps new or remanufactured? I have had more run ins with remans and self-rebuilds than I'd care to mention. I'd always install new OEM fuel pumps on my customer's engines.

I think I read between the lines that you bypassed the fuel filter. If that is the case, connect it back to the filter. I had a customer do that and he filled his fuel pumps with trash from his fuel tank.

I have a feeling you'll find where there is a pinhole leak in one of your engine fuel lines or a fuel line clamp at one of the joints that is a little loose.

Good luck.
 

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networker

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Re: Yamaha 225 2 stroke - Weak fuel pump output

Well, thought I would share the solution in case someone has similar problem. I took the thing to a Yamaha master mechanic about 90 miles from home and this is what he discovered:
  • Aftermarket Mallory fuel pumps I bought weren't strong enough to bring fuel from tank. Replaced with OEM pumps.
  • Removed anti-syphon fitting at tank. He tells me Yamaha indicates they are not needed.
  • Replaced fuel inlet valves at floats. He says several were flooding carbs. Floats were also misadjusted by mechanic who cleaned carbs earlier in the year.
  • Carb #1 enrichment valve was stuck open, replaced. That one took a while to figure out.
  • Knocking noise was due to missing bushings in water pump assembly. Previous mechanic replaced pump assembly and didn't install correctly.

He had the thing for 5 weeks but it's finally running great. I don't feel so bad about not being able to figure it out myself.
 

rsmith22222

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Re: Yamaha 225 2 stroke - Weak fuel pump output

First off that's a great engine. I have serious doubts its a reed valve. I have worked on marine engines for about 20 years and never had to replace them unless there was some obvious internal damage.

You are sucking air somewhere, your good move of using the clear line determined that. Try the clear tubing on the input side as was previously suggested. I have a feeling you will find the problem at the fuel line joints.

Once you have confirmation I would replace all the engine fuel lines anyway. They are relatively cheap and still available for that model. Plus who knows what sort of effect todays fuel is having on their insides.

Some other thoughts come to mind before going out and buying guages.

Make sure the fuel pump gaskets and the pump housing itself are seated properly. (Get new gaskets if any doubt)

Are the pumps new or remanufactured? I have had more run ins with remans and self-rebuilds than I'd care to mention. I'd always install new OEM fuel pumps on my customer's engines.

I think I read between the lines that you bypassed the fuel filter. If that is the case, connect it back to the filter. I had a customer do that and he filled his fuel pumps with trash from his fuel tank.

I have a feeling you'll find where there is a pinhole leak in one of your engine fuel lines or a fuel line clamp at one of the joints that is a little loose.

Good luck.

I have a 250 HDPI and it also seems to be having the same issue with poor idle. I actually toolk it to an outboard mechanic and he indicated that the reeds were ruined by dirt dobber debree from a few dirt dobber nest inside the engine compartment cover. He adjusted something that dropped my speed by 10mph and seem to increase my fuel consumption. It has now started to randomly die while idling (not in gear) and will not start. It seems to be starving for fuel through an air leak as the bulb is not tight and I can't seem to pump it up where it will remain tight.

I also smell fuel during those times. After the motor cools off, it cranks up like nothing is wrong and then with in 15 minutes of several starts and stops it wants to die again and if it does it has the same problem of not starting.
 

rsmith22222

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Re: Yamaha 225 2 stroke - Weak fuel pump output

I have a 250 HDPI and it also seems to be having the same issue with poor idle. I actually toolk it to an outboard mechanic and he indicated that the reeds were ruined by dirt dobber debree from a few dirt dobber nest inside the engine compartment cover. He adjusted something that dropped my speed by 10mph and seem to increase my fuel consumption. It has now started to randomly die while idling (not in gear) and will not start. It seems to be starving for fuel through an air leak as the bulb is not tight and I can't seem to pump it up where it will remain tight.

I also smell fuel during those times. After the motor cools off, it cranks up like nothing is wrong and then with in 15 minutes of several starts and stops it wants to die again and if it does it has the same problem of not starting.
 
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