I've lost all my Powers

[Boorune]

We own an old 4.8m runabout with a 1973 Evinrude 70hp 2 stroke.
We recently went out and I started to notice that the engine was losing a lot of bottom end torque and was really struggling to get onto a plane.
I asked my friend if he mixed the fuel correctly and he said he mixed it at 25:1. The mix should be 50:1 so we luckily had some spare fresh fuel onboard so we mixed a fresh batch of 50:1.

The engine performed better after we changed the fuel for a while but then the power almost died completly. We could not get the engine above idle with the throttle wide open.

I cleaned the plugs when we got home (they were a bit oily) and we took the boat out again to test a couple of days later. Again the boat started fine and got onto a plane fine but then the power started to die again untill it would barely get above idle.

Has anyone got any ideas why the power really drops off.
Would the fuel mix of 25:1 damage anything?
Would the carby be blocked by the wrong fuel mix?

Any sugestions would be apreciated.

 

[tashasdaddy]

Re: I've lost all my Powers

check your compression and spark with a spark tester, before, then when it starts to act bad, retest asap. see if there is any difference. could be loosing compression, or you could have a coil/coils heating up and failing. also is the motor running hot? good cooling water flow.

 

[achris]

Re: I've lost all my Powers

As long as the oil added to the fuel was for a water-cooled engine, then 25:1 will not do any harm. Make absolutely sure he did mix at 25:1 and not 100:1, it's easy to get the figures backward. 25:1 is double the correct amount of oil, not half. As for the power loss, run the engine on flushers until it's warm and then do a compression check.

Chris..............

 

[wilde1j]

Re: I've lost all my Powers

25:1 won't hurt a thing, but prolonged use will carbon up plugs. Your problem isn't related to the fuel mix. You may have a fuel starvation problem, tough. Make sure the tank is vented properly and the fuel line has no leaks, and the pickup screen in the tank doesn't have trash on it. And check the stuff Tash suggested.

 

[Boorune]

Re: I've lost all my Powers

It's good to know that the excess oil didn't cause any mechanical damage.
Assuming that the engine was running fine up untill the poor fuel went in would it be safe to assume that it wouldn't be a compression or spark issue and would more than likely be a fuel issue?

The plugs are not in the best shape so I should get some new ones either way. What plugs are recommended and what should the gap be set too?

Thanks for your promptness.

 

[tashasdaddy]

Re: I've lost all my Powers

the reason is said
"check your compression and spark with a spark tester, before, then when it starts to act bad, retest asap. see if there is any difference. could be loosing compression, or you could have a coil/coils heating up and failing. also is the motor running hot? good cooling water flow."

is the fuel mix 99% did not cause the problem, and the checking that the fuel tank vent was open is a good idea, the fuel pump can't suck from a vacuum.

 

[Texasmark]

Re: I've lost all my Powers

Don't overlook a clogged fuel filter. Checking the firmness of the squeeze bulb when the engine struggles will give you an indication of fuel availability.

Other thing is you may have a thermostat which is stuck shut. I had a '75 70 hp that had that problem....dunno if '73 had a stat....worth looking into. The slowing of the engine would be to internal binding of the pistons to the cylinder walls caused by excessive heat if that is the problem.

Mark

 

[Willyclay]

Re: I've lost all my Powers

I'm no expert like TD and Mark, but just went through a similar experience earlier this year with a Mercury 60HP 3-cylinder motor. Started fine, idled well but would not run above 3,000RPM at WOT when it normally turned 5,800RPM. With the help of the folks on this forum, I was able to isolate the problem as clogged high-speed carburetor jets before removing and/or replacing a lot of other stuff. The best procedure for determing this problem is to put your boat in the water and let it warm-up using a fresh supply of properly mixed fuel. Then make a WOT run and activate the choke/primer. If the motor runs normally with the extra shot of fuel, it means your jets are clogged/blocked. If not, additional troubleshooting is required. FYI, I was able to clean the jets without removing the carbs or jets on my problem motor by using a needle and Gumout spray. Good luck with yours!

 

[HighTrim]

Re: I've lost all my Powers

I dont think Evinrude made a 70 hp until 1974, which was the first year. What is the model number for the motor? Very likely though that you will need Champion plugs QL77JC4 gapped to .030, but lets figure out the year first. Also very possible Im wrong, havent had my coffee yet this morning

 

[carpenterken]

Re: I've lost all my Powers

I had his issue once when the check valve in my primer ball went bad.
The check valve was restricting gas flow.

 

[Boorune]

Re: I've lost all my Powers

Would you say it was just a coincedence that I lost power when the poor fuel went through and something else is casuing the fault?

 

[HighTrim]

Re: I've lost all my Powers

Did you locate the model number yet?

 

[Boorune]

Re: I've lost all my Powers

Just got the model number sent to me then.
It is 70773S
Serial No. A318028

 

[HighTrim]

Re: I've lost all my Powers

I didnt think they made a 70 hp until 74, your motor is in fact a 1977. Use the Champions QL77JC4's gapped to .030 . I would start with a spark and compression test, as advised by Tash, and go from there. Im sure a carb rebuild is probably in your future as well.

 

[Boorune]

Re: I've lost all my Powers

I didnt think they made a 70 hp until 74, your motor is in fact a 1977. Use the Champions QL77JC4's gapped to .030 . I would start with a spark and compression test, as advised by Tash, and go from there. Im sure a carb rebuild is probably in your future as well.

I hope it is as simple as that.
What is involved in a Carb rebuild? Is there a previous post anywhere that outlines the steps involved. I have done a search but can only find references too rebuilds but no instructions.
I'm quite mechanically minded and could probably figure it out by myself but it would be good to have some pointers before I rip them out.

 

[wilde1j]

Re: I've lost all my Powers

Get a shop manual (original OEM), if you don't have one. Parts list can be found on line at BRP's website.

 

[HighTrim]

Re: I've lost all my Powers

Might want to watch this video as well. But as stated, get a manual, you will thank us.

"http://www.meegsonline.com/tmd/TMDsVideoChronicle2.wmv"