70 hp going slower than a 25

[LukeBRoberson]

My buddies and I just took our boats out for the first time, mine a 1974 evinrude 70 hp, his a 1972 20(ish) hp.

After a tune-up and getting it to run as good as I've had it, we took it out. It seem to Idle well, and wasnt having problems.

Then, while I was going full throttle to catch up to him on the lake, he was going faster than me! I couldnt have been going faster than 15 and couldn't get past plane, and he was taking off losing me! I checked the weight to hp rating chart and it said I should be able to go 40 mph, why can I top 20? I have a 13.75x15 prop on it, is this a bad sized for this motor? Could it be "spun" ?

Any ideas from you guys would be great.

 

[NYGiants]

Re: 70 hp going slower than a 25

you might have bad compression

 

[Triton II]

Re: 70 hp going slower than a 25

For an average runabout/cc up to 2000lbs in weight, the prop's about right for a 70, so it must have either spun its hub or the engine isn't developing its rated power. More information on symptoms will help iboaters help you.

Boat weight, type and RPMs being achieved will be a good start.

Or, on the other hand, maybe take it off the trailer before speed testing it? LOL

 

[steelespike]

Re: 70 hp going slower than a 25

Welcome,
Check that is running on all cylinders. I think you may find one plug running wet and perhaps fouled.Not unusual to not realize a 2 stroke is not on all cylinders except for the performance.Wouldn't hurt to confirm throttle is opening all the way.Let us know what you find.

 

[Silvertip]

Re: 70 hp going slower than a 25

You might also have a boat load of water soaked foam thus adding a bunch of weight. But since you have trouble getting on plane I too suspect you have an engine that is seriously down on power -- as in one dead cylinder. An engine with one dead cylinder will seem to idle just fine to someone that does not have a keen ear for engines.

 

[LukeBRoberson]

Re: 70 hp going slower than a 25

Welcome,
Check that is running on all cylinders. I think you may find one plug running wet and perhaps fouled.Not unusual to not realize a 2 stroke is not on all cylinders except for the performance.Wouldn't hurt to confirm throttle is opening all the way.Let us know what you find.

Thanks, I checked the throttle opening, and its all good. Ill pull the plugs today to check them out. Should I just check for spark, or if it is just wet/fouled should I go ahead and check compression?

Thanks for the help guys, Ill check things out today and give more info as discovered.

 

[LukeBRoberson]

Re: 70 hp going slower than a 25

Also, if I run it a little bit for compression test, etc, will it hurt my motor more if its not running on all cylinders?

 

[steelespike]

Re: 70 hp going slower than a 25

Yes you can check for spark. A spark tester is the best way.If you mean to run it to warm it for a compression test it really isn't necessary.Assuming it is simply no spark
on a cylinder running isn't a problem.If its a carb issue a lean condition could cause damage if operated any longer than a brief test.If you run it briefly *about a minute
then carefully feel the plugs you may be able to tell if one is cooler than the others.
Let us know what you find.

 

[Silvertip]

Re: 70 hp going slower than a 25

The engine does not run for a compression test because you have the plugs out. What you find determines what you do next. The engine needs spark, fuel, air, and it all needs to happen at the right time (ignition timing). Miss any one or more of these and the engine will be drastically down on power. A comression test is advised regardless. For all you know one piston may have a hole in it (as in zero compression).

 

[LukeBRoberson]

Re: 70 hp going slower than a 25

Woo Hoo!!! I'm just not getting spark to my #2 Cylinder (knock on wood thats all it is). So what now? What needs replacing or further tested?

I cant thank you guys enough. Thanks alot, keep the help coming!

 

[wildspeed]

Re: 70 hp going slower than a 25

Time to check plugs wires and coils and hopefully nothing wrong with the power pack

 

[QC]

Re: 70 hp going slower than a 25

Moved this to the JohnnyRude forum, sorry we didn't get this over here sooner . . . Good luck!

 

[LukeBRoberson]

Re: 70 hp going slower than a 25

When I check the coil, I read online one way of checking it is to remove the coil not getting spark and plug it up to a meter and see its resistance in ohms, is this one way of doing it?

If not, any direction is appreciated

 

[bktheking]

Re: 70 hp going slower than a 25

Exchange the suspect coil for a working one on another cylinder, if it starts firing you'll know it's not the coil.

 

[LukeBRoberson]

Re: 70 hp going slower than a 25

Exchange the suspect coil for a working one on another cylinder, if it starts firing you'll know it's not the coil.

Will try that out in the morning and report back, thanks again.

 

[LukeBRoberson]

Re: 70 hp going slower than a 25

Update

Swapped coils out and the coils are all good.

When I started it up this morning I had all 3 sparks jumping for about a minute and it idled very well, then after swapping things around it went back to not firing on cylinder 2. Could it be grounded somewhere or is this just the sign of the power pack going out? Everyone keeps sounding like the power pack going out is a terrible thing... is it because the money or the time to change everything out?

Thanks for the help

Im a new "cadet"

 

[bktheking]

Re: 70 hp going slower than a 25

Powerpack change is a quick change, it's the cost of the powerpack and not knowing if it's the problem that's the gotcha.

Read the troubleshooting from CDI

http://www.cdielectronics.com/downl...er 1971-1978 (Screw Terminal Power Packs).pdf

Could be rectifier, timer base, powerpack- test everything before dropping $$$ on something you may not need, darts are expensive

 

[ezeke]

Re: 70 hp going slower than a 25

It's quite common for ignition coils to test OK and fail when heated up. Bad ignition coils can kill a good powerpack.

 

[LukeBRoberson]

Re: 70 hp going slower than a 25

It's quite common for ignition coils to test OK and fail when heated up. Bad ignition coils can kill a good powerpack.

But I swapped coils and the suspect coil worked well?

 

[bktheking]

Re: 70 hp going slower than a 25

Yup, agreed, I don't think it's a coil, if that same coil had of failed then yes , but it dropped on the #2 after the swap- timer base , rectifier or powerpack.