74 evinrude

[Cavalier]

Well we got our fine day on saturday and went to the lake and had a great day in the sun.However motor when first started ran ok but under load missed on one cyl for five minutes or so under load then was ok for the<br />day until I wanted to put it on the trailer at the end of the day,went out on a cyl again. With the new thermostat seems to get to a better temp. makes me wonder if I have a head gasket problem? I am using Champion L77jc4 plugs which my Clymer service manual recomends for low speed running. These replaced near new NGK BUHXW-1 Suface gap type plugs which were in the motor when i got it. any ideas?

 

[JB]

Re: 74 evinrude

Ahoy, Pest. You don't say what year or model your engine is, but I will assume that it is a 3 cyl looper.<br /><br />You may have some gunk or trash in one carb, or you may have an intermittent connection somewhere in your ignition system.<br /><br />Good luck.<br /><br />Red sky at night. . .<br />JB

 

[CAPTBLACKSMARINE]

Re: 74 evinrude

I WOULD ALSO DOULBLE CHECK THE SPARK PLUGS I HAVE SEEN IN SEVERAL AFTER MARKET MANUALS WHERE THE SPARK PLUG INFORMATION WAS NOT ACCURATE ACCORDING TO OMC/BOMB THE ONLY RELIABLE SOURCE OF PLUG INFO IS THEIR PARTS AND ACCESORIES CATALOG I HAVE BEEN AN EVIN/JOHN TECH FOR SOME TIME NOW AND HAVE FOUND THIS TO BE TRUE IF I KNEW THE H.P. AND YEAR OF YOUR MOTOR I COULD TELL YOU THE RIGHT ONES .BYE THE WAY YOU COULD ALSO HAVE EITHER TRASH OR WATER IN YOUR CARBS/FUEL SYSTEM WHICH CAN CAUSE A SIMILAR PROBLEM ALSO SINCE YOU DID NOT SAY HOW YOU KNEW IT DROPPED A CYL DID IT DROP FROM LACK OF FIRE OR LACK OF FUEL.

 

[Cavalier]

Re: 74 evinrude

OK ,The motor is a 70hp 1974 3cyl Evinrude.The spark plug recomendation I got from our Champion sparkplug catalogue at work. I have recently had the carbs off and blown them out.How did I know it dropped a cyl? Well after leaving the ramp and applying full throttle I could not get the boat to plane for about 7-8 minutes then all of a sudden we were away. I had better come clean, I am an automotive engineer with some 30 years experience but have had no experience with big water cooled two strokes, so any help i receive here is very much appreciated.<br />Cheers Pest

 

[CAPTBLACKSMARINE]

Re: 74 evinrude

ACCORDING TO OMC/BOMB BOOKS YOUR MOTOR TAKES A UL-77V CHAMPION SPARK PLUG LIKE I HAD SAID EARLIER YOU COULD HAVE A FUEL PROBLEM THAT CAN GIVE YOU THE SAME SYMPTOMS YOU NEED TO START BY CHECKING THE FIRE WITH A SPARK CHECKER AT CRANKING SPEED WITH THE SPARK PLUGS IN THE MOTOR THE SPARK SHOULD JUMP A 1/2" GAP IF NOT YOU HAVE AN IGNITION PROBLEM IF IT DOES YOU MORE THAN LIKELY HAVE A FUEL PROBLEM

 

[CAPTBLACKSMARINE]

Re: 74 evinrude

BY THE WAY THERE WERE OR HAVE BEEN SOME OVER SEAS MOTORS THAT WERE BUILT WITH DIFFERENT SPECS THAN THE AMERICAN COUNTER PARTS SO YOU MAY WANT TO BE CAREFUL ABOUT WHERE YOU GET SPECS FROM IF YOU GET ME THE MODEL AND SERIAL # I COULD LET YOU KNOW FOR SURE WHEATHER OR NOT YOURS IS ANY DIFFERENT

 

[Jaybird_94]

Re: 74 evinrude

I am sure not a tech but here is a thought that happened to me. My Johnson would fire right up then lose the top cyl. for about 5 mins. then it would kick in and go for the day. I had it checked and found that the voltage output was way down on the coil for that cyl. Seems that there must have been a internal breakdown that was OK when completly cold, but then expopsed its self until after complete warm up. I put a new coil on then it was fine. Have a voltage output check on all the coils and power supply to be sure.

 

[Cavalier]

Re: 74 evinrude

Hi Guys The serial no off the frost plug on the motor is A0099830. Captblacksmarine, I intend to ,next time I go out take a neon indicator my boss has and test every cylinder to see if we have spark before the plug at least. I still suspect water putting the fire out ie head gasket or water in cylinder but thanks for your replys will let you know what happens. Won't get out this weekend as I have my nieces wedding in Christcurch but will get back there as soon as I can.<br />Cheers Pest