79 Johnson 115 rpm

[papachaz]

what RPM should I be seeing when running wide open? I know prop matters but what rpm is this motor going to be comfortable at? thanks in advance, Chaz

 

[Rapio]

Re: 79 Johnson 115 rpm

Specs. indicate WOT @ 5000 RPM. Depending on motor condition, tune up, prop pitch and boat design and weight you might not get there. Also this wide open and I suggest 5000 is Max. not necessarily "engine comfortable" for too long.

 

[papachaz]

Re: 79 Johnson 115 rpm

thank you sir. I have seen it max to 4700 with me and the wife (she's tiny) not quite a full tank of gas. This is a 16 ft procraft bass boat that I think I've read weighs around 1100 lbs before adding anything else. I'm guessin around 225 for the engine, that much for me and probably another 150 for gas. It felt pretty smooth once it got there, but it started out cold, and bogging down. took it a bit to get to full speed.

I'm thinking it's time to start doing some ignition/firing tests. Had the son in law pump the gas line bulb while we were out yesterday and it didn't make any difference. Got to pick up a spark tester and a compression tester and we'll go from there. I haven't decarbed it, although I have rebuilt the carbs. I really get the feeling that the 'fire' is breaking down. that's just what it feels like. Probably going to put it in the lake monday and tie it up at the dock and start doing some testing. don't want to do it on the muffs

 

[Rapio]

Re: 79 Johnson 115 rpm

4700 RPM under load for a 30+ year old engine is not unreasonable if it is consistant and running smooth. Like the old saying, "if it ain't broke don't fix it". Take care....have fun

 

[papachaz]

Re: 79 Johnson 115 rpm

got out today and did a compression check and spark test. here's the description:
cylinders 1 and 3 each have 95, 2 and 4 each have 110. that's a 15 lb difference, which is just a bit over 10%. how much does that matter?

on the spark test......I started it up and it wasn't running good at all. I realized I'd left the #3 off, so I put it back on, and let it warm up. I took my welding gloves, and pulled the plug wires one at a time, which made an obvious difference each time. I laready knew the #3 would. But, when I set my newly acquired spark tester at 7/16 and checked each plug, the #1 is weak, like barely made a spark at all weak. There was NO doubt on the other 3, bright blue lightening bolt and loud pop.

The #1 coil has already been replaced at one point, I know this because it is different than the other three, and the plug wire has the boots on each end. the other three coils look like the plug wire is made into it. So obviously at some point this coil has been changed out. I have no idea when, or if it was new or used.......but the thing that confuses me is that it really made a difference when I pulled this wire while it was running. would it 'break down' at higher RPM? which could be what is causing my problems with not going wide open?

As always, I'm open to advice and suggestions. Ignition coils aren't that expensive, should I just go ahead and change it? I wonder if that wire is bad, maybe I should thrill the neighbors and wait until after dark and go start her up and see if it's jumping the wire?

 

[V153]

Re: 79 Johnson 115 rpm

Try swapping the coil with another one'n see what happens. If you get the same weak spark on a different cylinder the coil is probly going bad.

If you get the same weak spark on the #1 cylinder you likely have a problem with the powerpack.

 

[papachaz]

Re: 79 Johnson 115 rpm

thanks V153, I should have thought of that. the ignition part of engines is always what gives me trouble. I'm going to swap it with #2, that one had a great spark and being on the other bank would tell me if it's the pack or the coil. going out to do that now, will post results later.

 

[papachaz]

Re: 79 Johnson 115 rpm

ok here's what I've found. I swapped the coils between 1 and 2. the 1, is the newer style. it doesn't have a ground wire, it has the strap for the bottom bolt to hold it over tightly against the head. The paint wasn't removed for it to get a good ground. I made sure on #2 I removed the paint to ensure a good ground. Also, the orange wire going to #3 had a bare spot scraped in it. I sealed that up, gotta love that liquid tape in the spray can.

fired it up, now here's the thing. Since I've had this boat and put it in the water, even the first time out when it ran ok, I could never start it, even when warmed up, without pushing the key in to activate the choke, and raising the fast idle lever. This time, it fired up with no choke, and the idle lever down. shot a good strong blue lightening bolt on both, so I'm of the mind it wasn't grounded good, that would do it, right?

I do have another issue I would like some suggestions for. This thing will NOT go back to idle set screw against the block. I put it in gear to see what it was going to idle in gear at (I do know I really need to put it back in the water again to test that btw) and revved it to about 16-1800, and puttting it back in idle, it stayed around 1200, but the screw didn't go back to the stop. I shut it down, disconnected the cable end completely, pushed the screw back to the stop, adjusted the trunion knob to line the hole up with the stud, put it back together, tightened everything down. started it back up, revved it, back to idle, same thing. The idle screw will NOT go back against the block. not sure what else to do or check. is this spring loaded? any and all suggestions and advice greatly appreciated!

 

[V153]

Re: 79 Johnson 115 rpm

Relax. Running on muffs it's not uncommon. They do that.

Put it in the water'n see if it still happens ...?

Leave yer Trunion alone!

 

[papachaz]

Re: 79 Johnson 115 rpm

thanks again V153......as for 'leave teh trunion alone' I have it adjusted as per my manual, so that should be ok

but even in the water, the idle screw doesn't go all the way back against the stop

 

[Solittle]

Re: 79 Johnson 115 rpm

papa - Before you tear the poor thing completely apart what is the max rpms at WOT now? That is the place to start.

A good running V-4 of that era should run 5-5500 rpm WOT and 3800-4500 economical cruise depending on boat & load.

 

[papachaz]

Re: 79 Johnson 115 rpm

thanks solittle. today I took it out, and again, it just didn't seem to want to max out at first. it would surge like it was trying to, then all at once it caught up and away we went. I maxed it at 5000 on the tach, it was running good, smooth, I mean I was movin along great! then all at once, it bogged down again and wouldn't go over 3500. I figure a good comfy cruising to the fishing hole speed would be about what you mentioned, 3800 to 4500.

the most I'd seen before today was 4700. when it's bogged down, you can smell it, like it's running too rich. even a lady sitting at the dock when I came back in mentioned it smelled rich, her exact words. That makes me think it's not fuel related, but that it's electrical, I think? Oh something else to, I've noticed a backfire at idle. not noticed when running, even when it's bogging. but at idle, both in the yard on the muffs and in the lake, a backfire

I have a multimeter, and a spark tester I bought the other day, but that's the extent of my electrical testing equip. I keep saying I'm gonna get a timing light, but haven't done it yet

 

[emdsapmgr]

Re: 79 Johnson 115 rpm

That engine was spec'd by the factory to run between 4500 and 5500 rpm's. Current thinking is that it should turn in the upper end of the rpm range for max durability and fuel economy. (5500)