1979 Johnson 85-HP Seahorse: No Power At Full Throttle.

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Author Topic:   1979 Johnson 85-HP Seahorse: No Power At Full Throttle.

opetous posted 08-07-2010 02:03 AM ET (US)
[A 1979 Johnson 85-HP Seahorse] starts great and idles great, and its take off seems alright until about quarter-throttle; then [there is no power] after that. [A 1979 Johnson 85-HP Seahorse] just [runs at a very narrow band of engine speed of 1,500-RPM to 1,550-RPM], fast enough to create a tiny wake behind us. [I] took [the 1979 Johnson 85-HP Seahorse] home and changed spark plugs and tested them all. [The spark plugs during the test] all have blue spark. [The results of a] compression tests [were] 122-PSI to 125-PSI [unclear, perhaps meant among all cylinders]. [The fuel is] new gasoline with synthetic two-cycle oil mixed at 50:1. [The 1979 Johnson 85-HP Seahorse] started in garage with ear muffs on and at 4,600-RPM almost [wide-open-throttle] it sounds like an Indy car with tonnes of power with no load on [a propeller with 17-inch pitch]. [A]gain went back to the lake and same results of great start and idle. But take off,then no power after 1,600-RPM. Please help [diagnose the problem],
jimh posted 08-07-2010 07:20 AM ET (US)
Check the spark ignition timing.
Tohsgib posted 08-07-2010 10:38 AM ET (US)
Clean your carbs...timing never goes south unless something breaks or somebody messes with it.
Tohsgib posted 08-07-2010 10:39 AM ET (US)
Ps...just because you have spark does not mean it is enough spark but I would check fuel first. Also if you want the engine to last, do NOT rev it over 2500 on muffs.
opetous posted 08-07-2010 10:58 AM ET (US)
[Thanks] for [replies.] [I] have fixed many cars but [am] new to boat [engines]. [T]he spark looks good from what [I] can tell. [A]lso they are new [spark] plugs. [N]ow [I] am wondering if one or more cylinders isn't dying out under load. [The Johnson 85-HP Seahorse] runs and idles [too] nice, until [I] just have no power. ]I] think today [I] will try to [go to] the lake and try pulling off plug wires, seeing if it affects anything, that is, indicating which cylinders are not firing under load.
Sal DiMercurio posted 08-07-2010 11:33 AM ET (US)
4600 rpms in neutral is a recipie for one blown engine for sure.
As Nick said, do ...."NOT".... run your 2 stroke engine over 2500 rpms in neutral.
Those engines are engineered to run under a load [ in gear ] & when run in neutral with no load, you can & will scatter that engine all over the lawn if over reved passed 2000 rpms.
Sal
opetous posted 08-07-2010 11:47 AM ET (US)
[T]hanks for the [replies.] [I] will not rev [the Johnson 85-HP Seahorse] that high again. [D]o you have any [ideas] about what the actual problem is? [The Johnson 85-HP Seahorse] starts good[,] idles good[,] takes off [okay]. then gutless. [I]t is only running on either half [of the carburetors]--which were just rebuilt--or half cylinders.
Tohsgib posted 08-07-2010 12:13 PM ET (US)
Could be electrical or it could be carbs. Those carbs do not have idle circuits, they use the butterflies to meter low speed operation. Once you get to a certain load the high speed jets kick in....or....you are running on half bank of spark after a certain rpm which could be anything. Do me one small flavor...take off the cowl and run it at night. After a certain RPM you might have a grounding on 1 or 2 coils due to cracks from old age. Those older coils are known for cracking. At night you should see a light show if they are bad. Usually they will crack on the bottom facing the block where they get the heat. Temporary fix is a bunch of silicone to seal them up to double check.
opetous posted 08-07-2010 12:45 PM ET (US)
[T]hanks Tohsgib for reply. [T]his motor is almost still new. [I] will post a few [images] shortly. [A]ll components from what [I] can see are like new including all electrical and such. [I] opened the [carburetors] today and verified that all butterflies are opening. [The problem] could still be the high speed jets, as you had mentioned, because, again it seems to have good power out of the pocket then it is just gutless. [B]ut [I] had [carburetors] re-built last week and looking inside they sure are clean everywhere. [C]an [I] do damage if [I] [go] back to the lake and run it [until] there is no power at 10 KM/Hour, then try to remove one plug wire at a time to isolate maybe which cylinders aren't firing?. [I] can[']t get this thing to have any problems at idle or in gear at 2,500-RPM with muffs on in garage. Thanks again.
[A]lso [I] have the [carburetors] off now. [Tell] me which of the jets are the high speed jets. [T]here are two facing directly front, then there is one behind them facing up or vertical. [W]hat can [I] do to adjust the high speed jets to see if any adjustments helps? [T]hanks again.
Tohsgib posted 08-08-2010 11:23 AM ET (US)
Nothing to adjust, just make sure they are clean. I use torch files from an autoparts store to clean. Be carefull because they can "rejet" you jets if you clean them too aggressively. Again try running it at night. Yes you can do damage if you are running out of fuel, you won't do damage if spark. Easy thing to also test is to squeeze the bulb when this happens or spray some fuel into the carbs. If either works it is fuel, if not electrical. Again looks or anything else does not matter on that engine, it is age. The powerpack is another common problem. Also look and make sure your timing is moving. If something broke there it might not be advancing your timing. That you can check without running it.
jimh posted 08-08-2010 03:33 PM ET (US)
The high speed jet has a fixed size orifice. If you want to make an adjustment to the size of the orifice on the jet you have to remove the orifice and replace it with one that has a different size. I do not recommend you undertake changing the size of the high speed jet orifice as a method of diagnosis of the running problem at higher throttle settings.
Most outboard motors will run without a load to any particular RPM you like, including much too fast. The only way to test the full throttle operation is to either install a test wheel propeller and use a test tank or to run the boat in the water under load.
The Meddler posted 08-16-2010 05:20 PM ET (US)
Just had the same problem with my 1982 70HP Johnson. My engine has three carbs which looked clean as the day they were put in. When my brother and I cracked the nut on the bowl of the carbs, top and bottom flowed gas out, the middle bowl was dry though. Ended up that the needle was stuck and not letting gas through. Sprayed a dab of carb cleaner on the needle, it started moving again, gas flowed into the bowl and the engine now runs like a top. Hope that helps.
Ron
opetous posted 08-21-2010 04:45 PM ET (US)
I tried everything i can think of, and no results. I have since removed my newly rebuilt carbs and verified they are spotless, also set the floats. Last run on the lake was alright but i am still getting a dead spot from 3/4 throttle to wide open throttle. Any ideas would be greatly appreciated.
adlert posted 08-23-2010 08:46 AM ET (US)
I suggest you remove the air silencer cover, grab a timing light and a friend, and head back to the water again. Though I agree with Nick regarding timing rarely going south unless someone fools with it, it can still go south via the timing base and associated linkage getting gummed up to the point that it is not advancing as it should. Timing advance on that motor is not through "hard" linkages. The final advance occurs via a spring-actuated mechanism. It is certainly not unheard of for a 31 year old engine to have problems in this area. The large arm bushing (the arm that the throttle cable connects to) gets gummed up as does the timing base under the flywheel.
So head to the lake. Do as Jim suggests and check maximum timing advance while your friend is driving. Compare to the appropriate specifications. Also while you're back there at the engine running wide open visually check each throttle venturi for fuel delivery occuring up the main nozzles in the bottom, center of the carb throats. You won't know if the volume being delivered is correct, but it ought to look about the same in all 4 carbs and be a healthy spray. Each of the carb throttle butterflies should be flat. All 4 choke butterflies should be flat.
Finally, make 4 more full speed runs moving the timing light pickup between each of the 4 ignition leads. Check for spark during these high speed runs by shining the light at yourself. If it is flashing your plug is most likely firing (unless you have a short to ground somewhere along the ignition lead).

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Author	Topic: 1979 Johnson 85-HP Seahorse: No Power At Full Throttle.
opetous	posted 08-07-2010 02:03 AM ET (US) [A 1979 Johnson 85-HP Seahorse] starts great and idles great, and its take off seems alright until about quarter-throttle; then [there is no power] after that. [A 1979 Johnson 85-HP Seahorse] just [runs at a very narrow band of engine speed of 1,500-RPM to 1,550-RPM], fast enough to create a tiny wake behind us. [I] took [the 1979 Johnson 85-HP Seahorse] home and changed spark plugs and tested them all. [The spark plugs during the test] all have blue spark. [The results of a] compression tests [were] 122-PSI to 125-PSI [unclear, perhaps meant among all cylinders]. [The fuel is] new gasoline with synthetic two-cycle oil mixed at 50:1. [The 1979 Johnson 85-HP Seahorse] started in garage with ear muffs on and at 4,600-RPM almost [wide-open-throttle] it sounds like an Indy car with tonnes of power with no load on [a propeller with 17-inch pitch]. [A]gain went back to the lake and same results of great start and idle. But take off,then no power after 1,600-RPM. Please help [diagnose the problem],
jimh	posted 08-07-2010 07:20 AM ET (US) Check the spark ignition timing.
Tohsgib	posted 08-07-2010 10:38 AM ET (US) Clean your carbs...timing never goes south unless something breaks or somebody messes with it.
Tohsgib	posted 08-07-2010 10:39 AM ET (US) Ps...just because you have spark does not mean it is enough spark but I would check fuel first. Also if you want the engine to last, do NOT rev it over 2500 on muffs.
opetous	posted 08-07-2010 10:58 AM ET (US) [Thanks] for [replies.] [I] have fixed many cars but [am] new to boat [engines]. [T]he spark looks good from what [I] can tell. [A]lso they are new [spark] plugs. [N]ow [I] am wondering if one or more cylinders isn't dying out under load. [The Johnson 85-HP Seahorse] runs and idles [too] nice, until [I] just have no power. ]I] think today [I] will try to [go to] the lake and try pulling off plug wires, seeing if it affects anything, that is, indicating which cylinders are not firing under load.
Sal DiMercurio	posted 08-07-2010 11:33 AM ET (US) 4600 rpms in neutral is a recipie for one blown engine for sure. As Nick said, do ...."NOT".... run your 2 stroke engine over 2500 rpms in neutral. Those engines are engineered to run under a load [ in gear ] & when run in neutral with no load, you can & will scatter that engine all over the lawn if over reved passed 2000 rpms. Sal
opetous	posted 08-07-2010 11:47 AM ET (US) [T]hanks for the [replies.] [I] will not rev [the Johnson 85-HP Seahorse] that high again. [D]o you have any [ideas] about what the actual problem is? [The Johnson 85-HP Seahorse] starts good[,] idles good[,] takes off [okay]. then gutless. [I]t is only running on either half [of the carburetors]--which were just rebuilt--or half cylinders.
Tohsgib	posted 08-07-2010 12:13 PM ET (US) Could be electrical or it could be carbs. Those carbs do not have idle circuits, they use the butterflies to meter low speed operation. Once you get to a certain load the high speed jets kick in....or....you are running on half bank of spark after a certain rpm which could be anything. Do me one small flavor...take off the cowl and run it at night. After a certain RPM you might have a grounding on 1 or 2 coils due to cracks from old age. Those older coils are known for cracking. At night you should see a light show if they are bad. Usually they will crack on the bottom facing the block where they get the heat. Temporary fix is a bunch of silicone to seal them up to double check.
opetous	posted 08-07-2010 12:45 PM ET (US) [T]hanks Tohsgib for reply. [T]his motor is almost still new. [I] will post a few [images] shortly. [A]ll components from what [I] can see are like new including all electrical and such. [I] opened the [carburetors] today and verified that all butterflies are opening. [The problem] could still be the high speed jets, as you had mentioned, because, again it seems to have good power out of the pocket then it is just gutless. [B]ut [I] had [carburetors] re-built last week and looking inside they sure are clean everywhere. [C]an [I] do damage if [I] [go] back to the lake and run it [until] there is no power at 10 KM/Hour, then try to remove one plug wire at a time to isolate maybe which cylinders aren't firing?. [I] can[']t get this thing to have any problems at idle or in gear at 2,500-RPM with muffs on in garage. Thanks again. [A]lso [I] have the [carburetors] off now. [Tell] me which of the jets are the high speed jets. [T]here are two facing directly front, then there is one behind them facing up or vertical. [W]hat can [I] do to adjust the high speed jets to see if any adjustments helps? [T]hanks again.
Tohsgib	posted 08-08-2010 11:23 AM ET (US) Nothing to adjust, just make sure they are clean. I use torch files from an autoparts store to clean. Be carefull because they can "rejet" you jets if you clean them too aggressively. Again try running it at night. Yes you can do damage if you are running out of fuel, you won't do damage if spark. Easy thing to also test is to squeeze the bulb when this happens or spray some fuel into the carbs. If either works it is fuel, if not electrical. Again looks or anything else does not matter on that engine, it is age. The powerpack is another common problem. Also look and make sure your timing is moving. If something broke there it might not be advancing your timing. That you can check without running it.
jimh	posted 08-08-2010 03:33 PM ET (US) The high speed jet has a fixed size orifice. If you want to make an adjustment to the size of the orifice on the jet you have to remove the orifice and replace it with one that has a different size. I do not recommend you undertake changing the size of the high speed jet orifice as a method of diagnosis of the running problem at higher throttle settings. Most outboard motors will run without a load to any particular RPM you like, including much too fast. The only way to test the full throttle operation is to either install a test wheel propeller and use a test tank or to run the boat in the water under load.
The Meddler	posted 08-16-2010 05:20 PM ET (US) Just had the same problem with my 1982 70HP Johnson. My engine has three carbs which looked clean as the day they were put in. When my brother and I cracked the nut on the bowl of the carbs, top and bottom flowed gas out, the middle bowl was dry though. Ended up that the needle was stuck and not letting gas through. Sprayed a dab of carb cleaner on the needle, it started moving again, gas flowed into the bowl and the engine now runs like a top. Hope that helps. Ron
opetous	posted 08-21-2010 04:45 PM ET (US) I tried everything i can think of, and no results. I have since removed my newly rebuilt carbs and verified they are spotless, also set the floats. Last run on the lake was alright but i am still getting a dead spot from 3/4 throttle to wide open throttle. Any ideas would be greatly appreciated.
adlert	posted 08-23-2010 08:46 AM ET (US) I suggest you remove the air silencer cover, grab a timing light and a friend, and head back to the water again. Though I agree with Nick regarding timing rarely going south unless someone fools with it, it can still go south via the timing base and associated linkage getting gummed up to the point that it is not advancing as it should. Timing advance on that motor is not through "hard" linkages. The final advance occurs via a spring-actuated mechanism. It is certainly not unheard of for a 31 year old engine to have problems in this area. The large arm bushing (the arm that the throttle cable connects to) gets gummed up as does the timing base under the flywheel. So head to the lake. Do as Jim suggests and check maximum timing advance while your friend is driving. Compare to the appropriate specifications. Also while you're back there at the engine running wide open visually check each throttle venturi for fuel delivery occuring up the main nozzles in the bottom, center of the carb throats. You won't know if the volume being delivered is correct, but it ought to look about the same in all 4 carbs and be a healthy spray. Each of the carb throttle butterflies should be flat. All 4 choke butterflies should be flat. Finally, make 4 more full speed runs moving the timing light pickup between each of the 4 ignition leads. Check for spark during these high speed runs by shining the light at yourself. If it is flashing your plug is most likely firing (unless you have a short to ground somewhere along the ignition lead).