'79 Johnson 150 NO GO!

[Thompy_04]

I have a '79 Johnny 150 model #150TL79C that just started to do this two days ago. Starts up great, idles great go to get on plane and does nothing but bog like fuel restriction or running on very few cylinders. I noticed this when I was coming home from a fishing trip a couple of weeks ago, we were coming back came off plane was running fine passed the ramp and tried to throttle up again wouldn't plane idled over put it on the trailor and went home. I thought I had spun a hub so switched props and did a test run the next day, planed fine, ran out good put it on the trailor and went home. Went fishing yesterday same thing, couldn't plane idled back put it on the trailor. I did notice a little steam coming from the exhaust relieve ports on the leg, but didn't get an overheat alarm.

I took out the plugs and got this, starbord side (drivers side) plugs look clean, espically the two on the bottom of the bank port side (passenger side) all three looked a little black. Both were NOT grey or burnt looking so I'm guessing it wasn't ran lean carbs were rebuilt late last season as well. I haven't done a compression test as of yet, but will when it stops raining, as of last November I had 120-115 on all cylinders and had no problems this is the real first problem I've had with it except a broken starter boss which I had welded back on.

I'm hoping for just a blown head gasket hince the "steam cleaned" plugs, but what other than water can cause plugs to look farely new? Also I could NOT find any signs of water intrusion such as dropletts or another indictaion water had gotten in the cylinders nor any metal shavings or flakes like the cylinders have been scored or rings have broke. I'll leave with this photo not the best one but I'm hoping you get the jist of the story. Plug on right came from port bank, plug on left came from starbord.

 

[boobie]

Re: '79 Johnson 150 NO GO!

First do a compression check on it and then a spark test. Need an open air gap tester and spark should jump a 7/16 " gap.

 

[emdsapmgr]

Re: '79 Johnson 150 NO GO!

Weak ignition components tend to fail when they heat up to normal operating temps. The engine may run fine when cold, but after it warms up you may have an ignition component breaking down. Next time out, run the engine till it starts to bog, then pull the cowling and put an inductive timing light on each plugwire. The flashes from the gun will tell you a lot about the spark to each plug.

 

[emdsapmgr]

Re: '79 Johnson 150 NO GO!

If you have no sign of water in the cyls, your head gaskets are probably ok. Your compression test will validate that. If some plugs are not firing, they could be washed by the incoming fuel/oil mix.

 

[andrewddrennon]

Re: '79 Johnson 150 NO GO!

If the plugs are not firing the clean plugs may have been gas washed.

 

[cdn-pk]

Re: '79 Johnson 150 NO GO!

Check fuel lines ensure no air leaks.... these may get worse after the lines warm up too. and of course dirty carbs.

 

[Thompy_04]

Re: '79 Johnson 150 NO GO!

Give me some good news fella's! Just ran my compression test and got 125 or just under on every cylinder except #2 or the top hole on the starbord bank she had just over 0, maybe 10# tops. I know this could be the end of my motor but I also noticed some unburnt fuel out of the exhaust relieve at the bottom of the leg, and also the top exhaust cover just under the rectifier and terminal block. I don't know if that has anything to do with low to no compression, just thought I'd throw that in as an observation. My real question is, if one hole is bad it still should show some sort of compression right? I'm hoping for just a blown head gasket, could these symptoms be spot on for a blown head gasket?

 

[Thompy_04]

Re: '79 Johnson 150 NO GO!

Just popped the starbord head off and the hole that with 10 psi had a broken ring, busted the piston and head up a pretty good one. Can I just replace the piston and rings or do I have to bore and go with an oversized piston, I'll try to get some pictures of the bore but I can feel some scratches with my fingernail. (I don't have a machine shop in my area that does machine work on outboards.) In addition, what am I going to need to purchase to replace to get it running again. Can I reuse bearings? Generally whats the cost to replace one hole? All work to be done myself, also would it be cheaper to replace the powerhead with a matching year 175 with great compression for $500?

 

[emdsapmgr]

Re: '79 Johnson 150 NO GO!

It is permissible to replace just one piston. It is also permissible to overbore just one cylinder. I'd replace all 6 ringsets, however. No point in doing just one ringset, then have the engine throw another ring a few months down the road. A 175 is a 150 block with big-throat carbs. You'll need to pull the block down to examine the bad cylinder. Have a machine shop tell you if the cylinder can be saved (just rehoned) or needs overboring.

 

[Thompy_04]

Re: '79 Johnson 150 NO GO!

Thanks, by the looks of it, the powerhead off the 175 looks to be my cheapest and easiest way to get back to fishin'. Will all the ignition parts bolt right up to the 175?

 

[Thompy_04]

Re: '79 Johnson 150 NO GO!

Also here are some images I snapped today of the jug on the intake side and the top of the piston. The head also has the same damage as the piston crown. The ring broke on the right half of the piston you can obviously see it in person maybe not so easy in the photo. So this doesn't happen again what could be the cause of the broken ring? Coking, overheating, lean fuel mix? I had an overheat one time but ran fine afterwards (sucked up some sand running in shallow water). I rebuilt carbs late last season with new fuel lines I just don't want this to happen again and learn from my mistakes, I just don't know how a motor can go from almost perfect compression and in good health to blowing up in a matter of seconds.... Just my luck, haha

http://www.flickr.com/photos/79657603@N03/

 

[emdsapmgr]

Re: '79 Johnson 150 NO GO!

The ring will crack when it overheats, probably due to lack of fuel/oil. Yes, it can be from coking or lean fuel mix. I'd check the water diverters in the block by the cylinder which failed. Make sure it is in the proper position and not blocking off water flow around that cyl. Then remove the carb off that feeds that cyl. Pull it apart, remove the main jet that feeds the barrel on the damaged cyl. Examine the main jet for debris in the orfice-will cause a lean condition. When you have the engine apart, examine the piston skirt and ring area for carbon buildup. The original 79 pistons were high ring pistons. Maybe you still have the original pistons in the engine. The rings were put close to the top of the cyls in order to make the most compression. The problem was that when the fuel went to no lead, or the engine got hot-many of the rings broke. If you buy a replacement piston you will see the ring grooves have been moved down somewhat for added reliability. For that reason, you might just opt for 6 new pistons/ringsets. The ignition systems are the same for all V6''s this year.

 

[Thompy_04]

Re: '79 Johnson 150 NO GO!

What carb barrel feeds the #2 cylinder which blew? Right or left looking down the carb throat?

 

[emdsapmgr]

Re: '79 Johnson 150 NO GO!

Top carb, port side.