1976 Johnson 115 hp no take off power.

[flech01]

I have a 1976 115hp Johnson on a 17ft Sunbird.<br />It takes forever to get on a plain. It like I just have no take off power. During take off I am at WOT and I have about 3000 RPM it eventually<br />get on a plain and tops out at 4900 RPM. I have tried 3 diffrent props a 16, 19, 21 pitch I get the most rpms with the 19 and the most top end speed. But if I get to much weight in the boat it will not get on a plain or get over about 3000 RPM. I have checked the compression and they are 115 on three and about 95 on one. <br /><br />Do you think I am droping a cylinder? Can That be tested and if so how do I do it?<br /><br />Thanks guys If you need pics of the motor placement or anything else I will post them.

 

[Silvertip]

Re: 1976 Johnson 115 hp no take off power.

Yes -- its very possible its losing or lost a cylinder. Generally an engine with a dead cylinder will shudder and shake during hole shot. Buy or make a spark tester. Do a search on Checking Spark. If the engine tops out at 4900 its no wonder it doesn't get on plane. That engine should run a minimum of 5500 RPM. But with a 19P prop it should not struggle on a 17 foot boat unless it weighs a ton.

 

[flech01]

Re: 1976 Johnson 115 hp no take off power.

Is there a way to test if I am loseing compression in that cylinder? I don't recall any shuddering or shakeing on hole shot. Its just like the motor has no get up and go.

 

[flech01]

Re: 1976 Johnson 115 hp no take off power.

Should the motor reach 5000 rpm on take off or after I get on a plain and if not what should the rpm be? <br /><br />Do you want me to test the jump of the spark at the spark plugs?

 

[flech01]

Re: 1976 Johnson 115 hp no take off power.

I know someone out there knows.

 

[emdsapmgr]

Re: 1976 Johnson 115 hp no take off power.

The low compression cylinder may be the problem. While it may make compression, it may not have much suction on the upstroke. If it can't create vacuum, it won't pull in enough new fuel charge-won't make horsepower.

 

[flech01]

Re: 1976 Johnson 115 hp no take off power.

Is there a way to test this? I will do another compression test soon and give the updated numbers.

 

[flech01]

Re: 1976 Johnson 115 hp no take off power.

Well by the amount of post,help I have receved on this I guess I will just scrap it.

 

[wilde1j]

Re: 1976 Johnson 115 hp no take off power.

Engine will not wind up until you're on plane and it won't instantly go to the WOT value ... probably 15 to 20 seconds after planing, depending on the prop and setup. You said you've tried 16, 19, 21 pitches. The 16" should clearly give the highest WOT RPM; you should shoot for 5800 @ WOT. Get the setup right first. (i.e how high is the cav plate relative to the keel?)

 

[flech01]

Re: 1976 Johnson 115 hp no take off power.

The plate is just above the keel. I think the set up is right and with the 16 pitch it will not get over about 3000 rpm and if I have more than two people in the boat it will not get on a plane.

 

[Tom Scully]

Re: 1976 Johnson 115 hp no take off power.

With those numbers it sounds like you are running on 3 cylinders. I would pull the head on the bank with the low compression and see what it looks like inside, before you cause more damage.

 

[ezeke]

Re: 1976 Johnson 115 hp no take off power.

If all conditions are otherwise equal, there is no logical reason whatsoever for a 19 pitch prop to exceed a 16 pitch prop in RPM, or for speed in getting on plane. <br /><br />What kind of prop is the 16 pitch? None were listed for the motor.