1977 70 hp evinrude slow on take off

[muledeer]

I have a 1977 70 Evinrude on a 16-foot Sylvan- she starts great / idles good but when I give her full throttle, it does not rev up instantly - the revs start off slow then gradually the revs start to come up-takes about 10 secs for her to get to top speed-any clues?
carbs are rebuilt-new plugs-compression is ok-it fires on all 3
Thanks

 

[billy4hp]

Re: 1977 70 hp evinrude slow on take off

I have a 1977 70 Evinrude on a 16-foot Sylvan- she starts great / idles good but when I give her full throttle, it does not rev up instantly - the revs start off slow then gradually the revs start to come up-takes about 10 secs for her to get to top speed-any clues?
carbs are rebuilt-new plugs-compression is ok-it fires on all 3
Thanks

Was a Link-N-Sync performed when the carbs were rebuilt? If not, it's possible the carbs are not opening in unison and could be off on ignition timing as well... Everything needs to work together in order for the engine to accelerate properly...

 

[muledeer]

Re: 1977 70 hp evinrude slow on take off

No a Link-N-Sync was not done- I'm still waiting for my manual to come in.There is a new prop on the motor just wondering if that could be it.I think she tops out around 28-32 mph

 

[billy4hp]

Re: 1977 70 hp evinrude slow on take off

No a Link-N-Sync was not done- I'm still waiting for my manual to come in.There is a new prop on the motor just wondering if that could be it.I think she tops out around 28-32 mph

Most props are stamped with diameter and pitch.... The basic OEM prop for the 70HP Johnson's are in the 13 1/4 dia X 17 pitch range...

With my 1978 70HP Johnson mounted to a 16' deep V fiberglass Glasply boat I turn a 13 1/4 X 17 pitch 3 blade prop 5400 rpm and some change and run about 36 - 38 mph depending on water conditions per my GPS... My hull weighs 1000 lb without gear, motor, fuel, rigging, etc...

HTH

 

[tashasdaddy]

Re: 1977 70 hp evinrude slow on take off

being over propped will slow out of the hole, to increase top end speed. you need to prop the motor so that your WOT RPMS are in the 5500 range. this will give you a decent hole shot and top end.

 

[muledeer]

Re: 1977 70 hp evinrude slow on take off

I will check the prop tonight, this is a pic of the boat
Thanks

 

[muledeer]

Re: 1977 70 hp evinrude slow on take off

I think I found the problem ... prop on the boat was a 13 x 19 -going to buy a 13 1\4 x 17 prop -boating at 4500 ft elevation i'm being told that the 19 would be good for sea level? Too bad it is in mint condition

Thanks

 

[countvlad]

Re: 1977 70 hp evinrude slow on take off

I think I found the problem ... prop on the boat was a 13 x 19 -going to buy a 13 1\4 x 17 prop -boating at 4500 ft elevation i'm being told that the 19 would be good for sea level? Too bad it is in mint condition

Thanks

before you buy a prop what are your current rpms at WOT???

 

[muledeer]

Re: 1977 70 hp evinrude slow on take off

I do not have a tach on the boat - but the RPM's are not high at WOT- it purrs like a 4 stroke at WOT

 

[billy4hp]

Re: 1977 70 hp evinrude slow on take off

I do not have a tach on the boat - but the RPM's are not high at WOT- it purrs like a 4 stroke at WOT

You really need a tach, even a temporary one, to determine what prop you need. Tiny Tach's work great and are reasonably priced... They only require two wires to hook up and have a built in power source (5 year battery)...

http://www.tinytach.com/tinytach/index.php

Although the 17p would surely help, it might not be enough @ your altitude and combination...

HTH

 

[muledeer]

Re: 1977 70 hp evinrude slow on take off

I will borrow a tach from work and try it out this week
Thanks

 

[muledeer]

Re: 1977 70 hp evinrude slow on take off

Finally received my manual and did a lync and sync-ordered a tach for it (tiny tach),
and I put a 13 1\4 x 17 prop on and wow what a difference. without pushing the motor I can get it up to 29 mph(GPS) and it is alot faster out of the hole.


Thanks for the help

 

[billy4hp]

Re: 1977 70 hp evinrude slow on take off

Finally received my manual and did a lync and sync-ordered a tach for it (tiny tach),
and I put a 13 1\4 x 17 prop on and wow what a difference. without pushing the motor I can get it up to 29 mph(GPS) and it is alot faster out of the hole.


Thanks for the help

Glad you figured it out...