compression ?

cowboy_36618

Cadet
Joined
Mar 11, 2009
Messages
20
I got a 78 70 hp evinrude.... I got 110 lbs on #1 ,90 lbs on #2, and 100 lbs on #3. my question is , will those numbers on compression make the motor run bad at WOT and idle ? will it have a real affect on how the engine performs in all. Will it cause the engine to not want to go anywhere when you give it WOT. thanks
 

lindy46

Captain
Joined
Nov 27, 2008
Messages
3,886
Re: compression ?

More than 10 percent variation between cylinders. I'd try spraying some Seafoam into the cylinders and let sit overnight. Then try compression test again and see if it helps. #2 cylinder might have sticking ring.
 

BoatBuoy

Rear Admiral
Joined
May 29, 2004
Messages
4,856
Re: compression ?

Do as lindy says. Even if it doesn't help, you'll never know the difference. It'll run fine. It may not be the fastes 70 on the water, but it won't be the slowest either. I sure wouldn't consider a tear-down and rebuild for possible increase in compression.
 

Rick.

Captain
Joined
Jul 30, 2006
Messages
3,740
Re: compression ?

I agree with above. Go to "Top Secret File" at the top of this forum and see "decarbing motor". It might make a real difference to your numbers. Best of luck. Rick.
 

cowboy_36618

Cadet
Joined
Mar 11, 2009
Messages
20
Re: compression ?

about three weeks ago, i ran 2 cans of the evinrude engine tuner through the motor, one can through the carbs then the other trhough the spark plug holes , and let it set for two and half days. it didnt seem to help the compression. the guy at the shop has pulled the head off to replace the head gasket . havent heard back from him since then, im just looking for answers, just to see if what they are doin is goin to really do anything.
 

tashasdaddy

Honorary Moderator Emeritus
Joined
Nov 11, 2005
Messages
51,019
Re: compression ?

read cleaning carbs in TOP SECRET FILE. COMPRESSION will effect the way them motor runs. you have to have proper compression, fuel/air mixture (carbs), spark. all has to be properly cooridinated, by link n sinc.
 

cowboy_36618

Cadet
Joined
Mar 11, 2009
Messages
20
Re: compression ?

ok ,hello and yes I got another question . Recently I had asked about the compression on that 78 70 hp rude, now I have another ?. I took that 70 hp to a respectable boat shop here in town and it was there almost 4 weeks, I got it back yesterday, all they could tell me was that it was low on compression, they said it had 100 on #1, and 75 on #'s 2 and 3. That told me the engine was junk. So instead of paying $1200 to $1400 to get it rebuilt, Ive looked around and found a 1989 or 90 75 hp Evinrude for $1500 that another respectable mechanic has been thru and redone the lower end,such as water pump ,seals, thermostat. he said the power head had 132 to 135 across all 3 cylinders on compression ,so he didnt do alot to the top end. So I guess my question would be, comparing the 1978 70 hp to the 1989 or 90 75 hp , what kinda hp diffrence is there, if any?
I say 1989 or 90 because it was dark last night and I couldnt read the model number to determine the actuall year, Im going on what the mechanic told me.
One more thing is , is $1500 a good price for that 75 hp Evinrude wether if its a 89 or 90. what do you all think on that ?
Thanks for yalls input in the past.:cool:
 
Top