1987 Yamaha 70 hp power loss

[mdegood]

This weekend, while out fishing, I encountered total power loss on my 70 hp yamaha. Ran the boat for about an hour without any problems. Stopped to read maps. When I tried to start back up, hard to start (kept dying), once I finally got it started and advanced power, boat powered up as bow was starting to plane out, lost pretty much all power. Was able to make it back to the landing running at full throtle with a speed @ 1.5-2 mph's. Once back at the landing,<br />1)Pulled plugs - a little wet but not bad<br />2)Checked fuel filter/bowl - no water or trash<br />3)Checked all fuel lines and carb mountings - no defects noted.<br />4)Drained fuel bowls - no water<br />After letting engine sit for a while, could go out and power up again, same thing, start to plane out and engine rpm would drop and no power. If you brought it back to idle it would die. When you restart, wouldn't develope any power at all. Shut it off for 30-45 minutes then try again, just a momentary burst of power. After scrubbing a good day of fishing and got boat to the house, did a compression test. All cly's running @125 psi. Anyone got any ideas?

 

[rickdb1boat]

Re: 1987 Yamaha 70 hp power loss

Mdegood,<br />Did you check for spark on all cylinders?

 

[ob]

Re: 1987 Yamaha 70 hp power loss

There are a number of things that could be problematic in your symptom . Here are a few things to consider. When motor doesn't repond to incereased throttle application try pumping primer bulb to see if it picks up.If so it would be indicative of failing fuel pump or air leak on suction side of pump.Is fuel tank venting properly?If not,negative pressure on tank will restrict free flow.Check anti syphon valve on fuel tank and insure it is not sticking or simply remove it.Fuel filter?Possible restriction in carb bowl pickup tubes or fixed orifices.<br /> Next you need to verify whether you have sufficient spark energy to all plugs.Sparkplug leads should jump 1/2" gap to engine block while cranking.Check individually or ground the other two leads while cranking.

 

[butlp]

Re: 1987 Yamaha 70 hp power loss

If spark at all plugs it could be fuel starvation, did you try squeezing the bulb? You may want to try the JB patented gas filled spray bottle, take the air box off and with someone at the helm spray gas into each carb mouth and see if she wants to pick up and go.

 

[mdegood]

Re: 1987 Yamaha 70 hp power loss

Okay folks, Thanks to all for the fast response. Here is an update. Yes I did try to pump the primer bulb. The first couple of pumps seemed to make a difference 9only for a split second or two). After that it made know difference. I just checked all 3 plugs and coils. Great spark on all. I checked my compression agian this time with my screw in and not hold over the hole. Results as follows:<br />#1 cyl - 125 psi, #2 cyl - 122 psi, #3 cyl - 112 psi.<br />I know that the #3 is showing low, but does'nt the 10% rule apply? I can understand that I will probably see a litle performance drop, but this!<br />Also checked the anti-siphon valve in the tank - no problem there, also the vent line from tank to hull overboard is clear. Took the fuel pump apart, diaphrams look good and no crud in it. Once again any help please!!!

 

[bonitoman]

Re: 1987 Yamaha 70 hp power loss

Do you have a water fuel separator on that boat?

 

[ob]

Re: 1987 Yamaha 70 hp power loss

Mdegood, Sounds like a carbureator issue.If you pumped the primer bulb a couple of times with some response to motor operation there is a fuel delivery problem. Does primer get firm when initially priming?If so , I feel that there is a restriction or gummy deposits in either pickup tubes or fixed jets or your fuel pump is getting tired.

 

[macojoe]

Re: 1987 Yamaha 70 hp power loss

I am not an expert but my owners manual for my 1989 Yamaha say that when the oil injection isn't working or the motor runs low on oil the motor will not advance past 2000 rpm to protect the motor. Is the oil pumping?

 

[Capt Ken]

Re: 1987 Yamaha 70 hp power loss

I would first check to be sure the engine isn't overheating and trying to sieze up. Then remove the carbs for a good cleaning. The only reason I mention the heating problem is the fact that waiting 30-45 minutes for the engine to run again without stalling.

 

[mdegood]

Re: 1987 Yamaha 70 hp power loss

It's not that it won't run. But after the first burst of power that is the only one you get. Just loads up and runs lousy. But it will always run. The water pump is new (entire pump, not just impeller) also has new thermostat. After it first started doing the power loss, I thought I had a crab trap rope around prop or had badly damaged it. When I first got this boat a few months ago. It did pretty much the same thing, would start to power up and pale out then lose all power. That turned out to be the guy that owned it before me had taken the carbs apart and didn't put the o-rings back in around the high speed tube. I really don't think that will be the problem this time, considering that the orings are in a non-moving area. Just really baffling, one minute running like a spring chicken, next turn of the key and runs like an old man. ??

 

[ob]

Re: 1987 Yamaha 70 hp power loss

mdegood, If you don't feel you have a carburetor issue,And you have possitively ruled out spark to all three ,compression looks good,then the only thing left is the possible overheat mentioned by Capt.Ken.You'll have to obtain a 163 degree temp stik and mark on several locations around block and heads.Bare in mind that many overheat situations ,if not colling system related, are due to leaning of cylinder or cylinders from restricted carburetors.<br /> The only other scenario is if you have an intermittent failure of powerpack or ignition coil.

 

[butlp]

Re: 1987 Yamaha 70 hp power loss

OB might be on to something!<br /><br />It could be a power pack or coil that is breaking down when it gets hot. What happens when you run with the cover off? <br /><br />Did you try the spray bottle with gas? That would eliminate the carbs.

 

[mdegood]

Re: 1987 Yamaha 70 hp power loss

I am going to pull the carbs off this afternoon and double check everything. When I got the boat I put temp labels on 6 different locations. The highest the labels have read is 150 f. But I am going to double check those numbers again when I get home. I haven't tried the spray bottle approach just yet, weather has been kind of cold and rainy. Hopefully this weekend I can get out and try again. The 12 year old still hasn't forgave me for the lost speckled trout and red fish trip. Is there any reliable way to test coils/power pack that will show that it is breaking down? (other than a restitance test)

 

[bonitoman]

Re: 1987 Yamaha 70 hp power loss

When you are running, choke the engine and keep choking it. If rpm's shoot up it is your carbs.

 

[mdegood]

Re: 1987 Yamaha 70 hp power loss

Unfortunately I was not able to get a close look at the carbs last night as planned, (12" cast iron skillet and mommas disire to try to get me into the xmas spirt by going xmas shopping overrode my plans). Anyway when I was stuck this weekend, I did try choking while runing, it only made the problem worse, if I would have kept it choked, it would die. I still haven't ruled out the fuel pump, but am leaning more towards the coil or powerpack. I looked at my temp labels, none of the 6 locations has the engine exceeded 150 f. I have been trying to put the outside temp that morning into the equation (it was @ 33 f, water temp @ 65). But would think that my problem would have been on the first leg, not after running for a while.

 

[mdegood]

Re: 1987 Yamaha 70 hp power loss

Ok, here is what I found. I was fixing to remove the carbs, and decided to look under fly wheel. I found the lighting coil totally destroyed. I mean swelled up and burnt to a crisp. Of course none of the boat shops around here stock one, so it's on order and will be here Tuesday. My question now is, if the lighting coil (goes from coil to rectifier)is bad, will this cause the peoblem I am encountering, or is just another problem that needed to be fixed? Unfortunately my yamaha book is loaned out and the guy won't be back in town untill Mon or Tues, so I have to wait so I can get the numbers so I can ohm out the rectifier and cdi.