Losing RPM

[Three]

Also check your fuel primer bulbs have a check valve in them. If they fail that could be a cause. Also possibly replace your fuel lines. Sometimes the begin to fail on the in side and when the suction/flow increases the failed part of the hose causes restrictions.

 

[dbiscayne]

I've had the exact problem posted above happen to me, fuel line is collapsing on the inside. Most fuel lines are double walled and can look fine on the outside, while the inner liner is getting soft & sucked on hard enough by the fuel pump it's collapsing.
Also not sure if you mentioned it but did you try running it with the fuel cap off to make sure the tank was venting? A clogged vent could do something similar but sounds like you're problem is isolated to one side so thats probably not it.

 

[kdneuzil]

HI everyone. Thank you for all your valuable input. To date...I have previously replace all fuel line, primer bulbs, both fuel/water separator filters, took out back flow preventers (reinstalled today) filtered old gas and then pumped out to use in my truck( there was about 25 gallons of gas ran at 9 gal per minute inline with a particulate filter and goldenrod water separator...all looked clean), replaced with premium gas at 50:1 ratio oil (premium synthetic). today we blew out all gas lines today, blew dip tubes into tank, tested gas flow from tank to motor connector (removed connectors to visually see gas flow) everything checks out......took "her" out for test drive and has a very smooth ride getting up to 3800 RPM. 10-12 minutes and then headed for harbor.....at 2700 RPM she started to have an issue in the port motor (previously was the SB motor). lost 3-400 RPM and squeezing primer bulb it would reev back up to 2700. went for another 12-15 minute spin. Performed well at higher RPM. where as previously at 3100 RPM it would loose RPM as much as does to 1200 and act like it wanted to stall. Now the port just looses a few 100 RPM. I plan to spend Friday fishing and making a long run to deep water. My brother in law will be tailing me so I feel comfortable running a fairly long run to "test further" the performance. )I also have towing ins)
so I am going to live with the issue for now. I don't think it is the fuel pump my experience with fuel pumps is that wen a fuel pump goes it goes it doesn't start to go bad. And the fact that it is the port motor and not the starboard tells me that the dip tubes were an issue and perhaps whatever was in there is still in the tank. Well I will be pricing a new tank to install after the first week of August. I will continue to post anything I do to resolve this issue and will continue to look at posts to try to solve the problem.

For everyone posting I should have been clear on the year of these motors. They are two stroke 150's vintage 1988.
I mix my own oil when I fuel up as the injectors leaked too much in the past. I have no problem with mixing my fuel/oil when fueling up.


once again thank you for your help...

Ken

"I Chase Her"

 

[SkunkBoat]

You could have a fuel line collapsing on you.
Or some wierd thing you would never think of...

Years ago I installed a brand new primer bulb/hose....troubles
Long story short... the clear lining of the new hose pushed back and blocked the line when it was on the barb fitting...but pulled open when I removed the hose from the fitting
I thought I was crazy...pump the bulb with hose off, plenty of gas...hose on barb to fuel filter, bulb collapses when running engine...

 

[kdneuzil]

I don't have any lining on the new hose. it is a double walled marine gas line installed new just two weeks ago.

 

[Sparkdog118]

Oem Omc fuel hose is like insurance that your hose will give you no problems for 10 years plus. Even exposed to south Florida sun. It is about 8 bucks a foot but it will outlast all other hose. I buy it by the 25 ft roll for customers that don’t want future problems with their fuel lines.

 

[Sparkdog118]

You could have a fuel line collapsing on you.
Or some wierd thing you would never think of...

Years ago I installed a brand new primer bulb/hose....troubles
Long story short... the clear lining of the new hose pushed back and blocked the line when it was on the barb fitting...but pulled open when I removed the hose from the fitting
I thought I was crazy...pump the bulb with hose off, plenty of gas...hose on barb to fuel filter, bulb collapses when running engine...

I’ve seen that at least a hundred times. Lol. It’s like you plugged your hose with Saran Wrap. I’ve also seen the hose pinched where the cowling cable clamp clamps. The grey Yamaha hose turns to jelly and collapses under suction from the fuel pump. Then it expands again when you pump the ball.

 

[seasick]

There are two types of fuel pumps on that motor, the high pressure and the low pressure. The low pressure pumps wear out and can get to a point where they just can't get enough gas to the high pressure pump. Since you replaced just about everything in the fuel plumbing and if you don't know when the lp pumps were last serviced (replaced) you may want to replace them. I think that motor has two lp pumps, replace both, they aren't that expensive

 

[kdneuzil]

Okie dokie. I will most likely do it on both motors. I have no records of Service swork done previous to my purchase of the boat. It's not like I can't afford it. I want it in top notch condition. Thanks. Ken

 

[Sparkdog118]

One clue to the cause could be the primer balls collapsing at high speed or not expanding right away when pumping. Yamaha had a problem with the lp pumps with clear tabs coming out the top. If it is black, they are the replacements. I would still replace them.
another thought, how is the compression? The back side of the compression is the suction that drives the pumps.

 

[DennisG01]

If I read correctly, you ran on a portable tank and never had an issue? That eliminates anything on the engine side.

Seasick mentioned above about running with the fuel cap off. If you didn't try that already, try that if you have another issue while running the engine. If a clogged vent line/fitting/thru-hull fitting is the issue, taking the fuel cap off should correct the problem quickly. I know it would seem that if venting was the issue that both engines should be having problems all the time - but there may be some combination of "kind of" blocked and fuel demand relationship going on. It may not be the problem, but it's a variable to check into.

Concerning the dip tube - which as I was reading was your thread, was sounding like your issue. You blew air through - good. But maybe it's still clogged. Try this - remove the fuel line from the tank and stick THAT into the portable tank (use a barb fitting and extra fuel line if needed). This will further clarify where the problem is.

 

[kdneuzil]

We blew out the vent line. Ran both motors off of a 6 gallon remote tank.(ran good) we took the fuel cap off. The one thing we couldn't do was clean the dip tubes but we blew them out and they sounded wide open. About the only thing we didn't do was rotor router out the lines.

I think I am leaning to replacing the tank. The question is Aluminum or Poly? Same tank custom built or same size (or near same size) from tank company made to order or off the shelf? I want to stay with a single tank. Personally I have spent so much time on this over the last three weeks I am exhausted. I haven't had "Her" out fishing in weeks. I am spent and ready to have someone install the tank when I can get one or take it to the GW dealer in Huron (1-1/2 hours away and 4 weeks behind) to get one in and install it. I would be very disappointed if it is not the tank dip tubes but I am really done. Perhaps a few days not working on it and seeing how it runs Fri and Sat will settle me down and give me a rejuvenated spirit.

We are going to fish tomorrow and Saturday so I will see how she performs

Thanks

Ken

 

[seasick]

If I read correctly, you ran on a portable tank and never had an issue? That eliminates anything on the engine side.

Seasick mentioned above about running with the fuel cap off. If you didn't try that already, try that if you have another issue while running the engine. If a clogged vent line/fitting/thru-hull fitting is the issue, taking the fuel cap off should correct the problem quickly. I know it would seem that if venting was the issue that both engines should be having problems all the time - but there may be some combination of "kind of" blocked and fuel demand relationship going on. It may not be the problem, but it's a variable to check into.

Concerning the dip tube - which as I was reading was your thread, was sounding like your issue. You blew air through - good. But maybe it's still clogged. Try this - remove the fuel line from the tank and stick THAT into the portable tank (use a barb fitting and extra fuel line if needed). This will further clarify where the problem is.

Running on a portable tank eliminates a lot on the motor but not everything. Since the portable tank is sitting on the deck, the fuel level is higher than the level in the tank. That can ean that it takes less 'suction' to get the gas into the motor. Therefore, weak low pressure pumps may work OK on a portable but not on the main. The gas level on the portable in theory could be higher than the fuel level in the fuel bowl and the motor is getting gas by gravity feed.
There are still other possibilities like air leaks as vent blocks that have to be eliminated form the usual suspects.

 

[kdneuzil]

Well I guess I can still replace the pumps. I think they were like $45 each and the gaskets were $4. so $200 for all the pumps.

I think I can install them myself.

Ken

 

[seasick]

Well I guess I can still replace the pumps. I think they were like $45 each and the gaskets were $4. so $200 for all the pumps.

I think I can install them myself.

Ken

The install is easier on some motors because they don't have a lot of other stuff in the way.Usually the motors with two pumps are easier to replace as opposed to the ones with three. Check the hose connections to see if they are clamps or tie wraps and if tie wraps, make sure you buy new ones that are made for fuel lines. The regular ones you find in the box store can leak. Fuel line tie wraps have a different curved spot on the end so that it site tight all around the hose.

 

[seasick]

Here is an example of the difference between fuel hose tie wraps and the standard tie wraps

Fuel Hose Zip Tie

Buy the 8 inch ones and cut as needed. The 4 inch may sound like a better fit but they are intended for smaller hoses like the oil lines.

 

[dbiscayne]

another guess - when you're running and the problem shows up, is the ride getting a little bumpy? could be a fuel fitting, filter housing, or something like that is cracked but only enough to suck air when the ride gets rough.

 

[kdneuzil]

Well I wanted to thank all of those with advice on the issue I was having. It has been a hectic couple weeks and we worked to the boat about a week ago. we blew out all the lines and fittings from the dip tubes to the motor connections. We blew to the vent lines again. all of this done with 100 psi. After all this we took her for a spin and the boat performed rather well. I did notice that the port throttle is a bit forward of the starboard throttle ....it was never like this. Is the throttle cable adjustment on the throttle? I have to look. as I hav e been pretty busy. I was fishing a walleye derby and now working on a rental house project. So we have had our hands full. Anyway she ran really well after all the blow outs and I am pretty happy right now. But I just learned that my main mechanic is retiring Sept 30th. so I need to find another. I have a marine dealer one mile from my house but I am not liking them too much. Anyways I'll be fishing more when our house is done.
So. Thank you very much.

Ken

 

[Ling king]

Hi have two Yamaha 200 2 stroke. Same issues. As mentioned earlier. It's the VST filter. Losing RPM's at higher RPM's. The motors are starving for gas. Replace the Racor filter, the gas filter and the
VST internal filter. Some models have 2 filters inside.

Yamaha outboards have a Vapor Separator Tank (VST) attached to the electric fuel pump. The VST filters gas again just before it's pressurized into the fuel injection rail(s).

What is VST filter?
Vapor Separator Tank (VST) Filter.
The VST is a prime spot in your fuel system where deposits and gum can form, particularly if fuel is untreated, and the VST filter is the most difficult to access and usually the most expensive to replace.

*It really isn't that difficult to install. Just make sure you keep track where all fuel and electrical the lines go. You also have the other motor to reference

 

[seasick]

Well I wanted to thank all of those with advice on the issue I was having. It has been a hectic couple weeks and we worked to the boat about a week ago. we blew out all the lines and fittings from the dip tubes to the motor connections. We blew to the vent lines again. all of this done with 100 psi. After all this we took her for a spin and the boat performed rather well. I did notice that the port throttle is a bit forward of the starboard throttle ....it was never like this. Is the throttle cable adjustment on the throttle? I have to look. as I hav e been pretty busy. I was fishing a walleye derby and now working on a rental house project. So we have had our hands full. Anyway she ran really well after all the blow outs and I am pretty happy right now. But I just learned that my main mechanic is retiring Sept 30th. so I need to find another. I have a marine dealer one mile from my house but I am not liking them too much. Anyways I'll be fishing more when our house is done.
So. Thank you very much.

Ken

Did you happen to notice if anything blew out or did you blow towards and into the tank.
100 psi is an extremely high pressure for those fuel lines but I doubt the actual pressure in the hoses was anywhere near that number.
Fuel tanks get pressure tested at 3 psi. Anymore and you stand a decent chance of distorting the tank. The pressure in the fuel lines is just about zero since fuel is usually running at a vacuum. Pressure after the low pressure pumps is a few PSI

I don't see how your throttle alignment issues is related to the line cleaning. The adjustment usually is done at the motor end, not at the control. Common causes are cable stretch, cable break, loose or broken clevis connection hold down clamp. I suppose something at the control couls be an issue but that would be a rare event. Binding is more common