73 50hp Johnson not firing top cylinder

[RKeller]

I posted some questions about this engine earlier. The engine was sitting for a few years. before I got it. This is what's going on.<br /><br />Top cylinder not firing. (running on bottom only)<br />Removed plugs, both sparks look strong.<br />Swapped plugs, no change.<br />Swapped Coils, no change.<br />Checked compression, 120 both cylinders.<br />Rebuilt carbs, no change.<br /><br />When running, when I put my hand in front of the carbs the suction feels the same on both.<br /><br />After runnin the top plug is clean and wet and the bottom plug is black and wet. if you swap them the black plug is cleaned when in the top cylinder.<br /><br />Could it be timing? <br />Is there a way to check the power pack with out buying a new one?

 

[fireman57]

Re: 73 50hp Johnson not firing top cylinder

You did a good job with your testing sequence. I believe that in '73 you had points. You probably need to pull the flywheel and check/clean/reset/replace points and condenser. If I remember correctly they should be set at .020.

 

[RKeller]

Re: 73 50hp Johnson not firing top cylinder

I thought about that but it looks like there are no points in the diagram.

 

[rickdb1boat]

Re: 73 50hp Johnson not firing top cylinder

Top cylinder not firing. (running on bottom only)<br />Removed plugs, both sparks look strong.<br />

Do you mean it is firing on the top cylinder or not? "Both sparks look strong" sounds like it's firing to me. Or is that from doing a spark test? How clean is the top plug? May be getting water into the cylinder and cleaning the plug. That would account for the loss of power in the cylinder...

 

[reeldutch]

Re: 73 50hp Johnson not firing top cylinder

no points on the 73.<br /><br />its cdi and has a powerpack.<br /><br />swap the wires that lead from your ppack to the ignition coils and check for spark.<br /><br />dont run the engine this way because it will crosfire.<br /><br />im shure your ppack is the cause.<br /><br />if you replace the ppack i would also get new ignition coils .<br /><br />good luck

 

[RKeller]

Re: 73 50hp Johnson not firing top cylinder

I'm getting spark on the top plug during spark test but if you remove the plug wire while running at high idle it makes no difference. The top plug is very clean. I thought about water but would there be good compression if water was leaking into the cylinder?

 

[Xcusme]

Re: 73 50hp Johnson not firing top cylinder

It's easy enough to pull the head and replace the heat gasket. Check the deck and head for flatness with a straightedge. You can inspect the cylinder walls etc. at the same time. The tip off here is that the once black lower plug is cleaned when you did the plug swap, which points to possible water intrusion. A head gasket is way cheaper than replacing the powerpack. BTW, try to keep your questions in only one post, kinnda hard to follow between 2 different posts. Anyway,you did reconnect the upper carb linkage, right?? I would think so after the carb rebuilds.

 

[RKeller]

Re: 73 50hp Johnson not firing top cylinder

could I have a bad headgasket and still get good compression?

 

[rickdb1boat]

Re: 73 50hp Johnson not firing top cylinder

I'm getting spark on the top plug during spark test but if you remove the plug wire while running at high idle it makes no difference. The top plug is very clean.

Classic symptom of water getting into the cylinder. I would do as Xcusme recommends before you have bigger problems. It won't hurt a thing to take a look....And it may save you some big $$$$

 

[RKeller]

Re: 73 50hp Johnson not firing top cylinder

I'll check the head gasket. could there be another seal allowing water into the cylinder? anyhting in the crank case or anywhere else?

 

[Xcusme]

Re: 73 50hp Johnson not firing top cylinder

c/p:<br />Water can gain access to the cylinders via the head gasket area, the exhaust baffle plate area, and as Mikey states, the powerhead base gasket area. It could also gain access via the bottom main bearing area but that's unlikely.

 

[RKeller]

Re: 73 50hp Johnson not firing top cylinder

anybody know the torque spec on the head bolts?

 

[RKeller]

Re: 73 50hp Johnson not firing top cylinder

nevermind, I found it. before I pull the head off I'll check the timing with a light just to make sure it isn't someting funky with that.

 

[DJ]

Re: 73 50hp Johnson not firing top cylinder

Head removal has nothing to do with timing.

 

[RKeller]

Re: 73 50hp Johnson not firing top cylinder

I know, I'm just not convinced it's the headgasket. I have a friend who had a 70 hp shear the key in the flywheel and it had similar results. just thought I should check the timing. it's easy enough. <br /><br />although now that I think about it that won't tell me if the flywheel spun. only if my timing is correct to the flywheel.

 

[tashasdaddy]

Re: 73 50hp Johnson not firing top cylinder

had 73 50 rude, same problem change head gasket, exhaust gasket, coils, end up being powerpack.

 

[DJ]

Re: 73 50hp Johnson not firing top cylinder

I, recently bought a '1975' 50 HP. It ran fine, but I pulled the head to check the bores and I replaced the thermostat while I was at it, since it was a salt water engine. I'm glad I did.<br /><br />It was worth the $25.00 in parts to know.

 

[RKeller]

Re: 73 50hp Johnson not firing top cylinder

had 73 50 rude, same problem change head gasket, exhaust gasket, coils, end up being powerpack.<br />

thank you for your reply. I've been wondering if that is the route I'll be taking. trying to avoid the expensive part can really cost a lot! at least it's a good tune up!

 

[RKeller]

Re: 73 50hp Johnson not firing top cylinder

well I replaced the head gasket. cylinders look ok, no scoring or galling. I carefully cleaned the sealing surfaces and bolted it all back together. Didn't fix it. Timing light looks good on that top cylinder. Not sure if I should order a power pack or try the exhaust gasket. Man I wish I had a PP I could just try! ugh.

 

[RKeller]

Re: 73 50hp Johnson not firing top cylinder

here's a question for ya, the PP has two sensor inputs and two coil outputs. does each sensor wire represent a cylinder? could I switch the inputs and the outputs on the PP and still run? that would tell me if the problem follows the PP.