HELP!! 1974 Johnson 6hp issues

[blackhawkdc]

Hey all, I desperately need some help. I have a 1974 Johnson 6hp motor (6R74C) that seems to only be running on one cylinder. Now I know that this is a common problem and has been covered many times over. But I've tried everything and still nothing. Here's the history, it was my grandpa's motor and probably hadn't been ran in 25 years when I got a hold of it, but he took meticulous care of it. It had a misfire on the upper cylinder originally and found it to be ignition related, so I put a new coil in it and then put it back in to storage. Went to use it and it had a misfire on the lower cylinder, "appeared" to be ignition again, put a new coil in it and put it away till I needed it again. been able to use my dad's 9.9 as needed, so this 6hp hasn't been a priority, until now. Pulled it back out to put on a jon boat for pike fishing. Still misfiring, appears to be lower cylinder. So I rebuilt the carb, made certain the fuel supply was good. Still misfires. I spent quite a bit of time on it yesterday. I did a compression check on it, but cylinders came out at 55psi with a known accurate, quality compression gauge. Low, but even, so I put that in the back of my mind. Speak is good with strong blue spark at the plugs, but not quite 1/4" gap jumping. Pulled the flywheel and readjusted the points. Spark now jumps 1/4" gap, but engine still misfires.

Here's where it gets interesting. While it was running, I pulled plug wires off. At low RPM, its the bottom cylinder that's not doing anything, and I mean nothing at all. But I have good, strong spark. At part throttle, it seems to clear up and feel like both cylinders are now firing. Keep opening the throttle and she gains no more RPM's. Throttle wide open and she's only running on one cylinder again, except the majority of the time, she's swapped over to misfiring on the top cylinder. Ocassionally, and very seldomly, it'll pick up on the other cylinder and take off at full power.

All of my recent testing has been done with the motor in a barrel with water. In neutral, it'll rev up ok, but very slowly. In gear, it'll rev to part throttle slow, and then not rev any further. I removed the cylinder head and checked the gasket for any leaking and couldn't really see anything. But the gasket didn't come off cleanly either, as it had never been removed since new. I'm starting to lean towards a rebuild. Installing new rings and reed valves and going from there. The cylinders look clean and smooth, no scoring.

Thoughts???

Thanks,

Seth
Cedar, MN

 

[Tim Frank]

Re: HELP!! 1974 Johnson 6hp issues

Are the plug wires original?

 

[AlTn]

Re: HELP!! 1974 Johnson 6hp issues

was the compression test before or after the head gasket replacement?..did you surface the head using the sandpaper on glass using figure 8 pattern?...has the motor ever been decarbed ?...did you check or replace the condensors?...check or replace the sparkplug wires and boots?...link&sync the roller with the timing cam?..orfice plug removed and cleaned when you cleaned the carb?

 

[blackhawkdc]

Re: HELP!! 1974 Johnson 6hp issues

compression test was done before the head was removed. Head is currently removed. Points have been replaced, condensers have been replaced. Spark Plug wires were replaced with the coils, all passages/orifices were replaced/cleaned when the carb was rebuilt. As far as performing a link and sync, I am unable to find that procedure in my manual. It refers to a certain page for that procedure, but it was either omitted from the manual, or the page reference is incorrect and I have yet to be able to find it in the manual. I would venture to believe that, since nothing has ever been done to this engine before I got it, that things should be close enough to at least run ok.

 

[AlTn]

Re: HELP!! 1974 Johnson 6hp issues

the link%sync is easy enough to check...does the carb roller center on the timing mark on the timing cam when the the throttle plate is just begining to open?....does the throttle plate become perfectly horizontal when the twist grip is advanced to wot?..does the armature plate move freely?

 

[Monte1961]

Re: HELP!! 1974 Johnson 6hp issues

Is the the float in carb plastic or cork? If cork float will drive you nuts! Replace with known good or new one! 55psi is low, happy boating!

 

[blackhawkdc]

Re: HELP!! 1974 Johnson 6hp issues

Everything appears to line up correctly. The carb also does achieve full throttle.

Its just very odd, because, when one cylinder is pretty much completely dead, the other is running with no problems. And then they'll switch. What are the chances that the reed valves could be causing this issue? Turning it over by hand, with the head removed, the two cylinders do sound different as far as the air movement getting sucked through the carb and the expelled through the scavenging ports.

 

[jimmacl]

Re: HELP!! 1974 Johnson 6hp issues

Have you tried new plugs? Twice I have been tricked with a plug that seemed fine out of the cylinder but turned out to be bad.

 

[Daviet]

Re: HELP!! 1974 Johnson 6hp issues

Your engine uses a pulse type fuel pump attached to the block and pulsed off of the lower cylinder I beleave. If the diaphram in the pump is cracked, it will allow fuel to be sucked into the cylinder flooding it. It could clean up with high RPM if the pump can supply enough fuel to get the RPM up. Remove the pump and see if gas will run out of the hole on the back side that matches the pulse hole.

 

[blackhawkdc]

Re: HELP!! 1974 Johnson 6hp issues

Well, the carb float was already suspect with it being cork, but it doesn't seem to be acting like that is the issue. I've tried a couple different sets of spark plugs, and they are Champion J6C's. I plan on replacing the fuel pump, but don't feel like paying for an OEM one, and Sierra only lists the 18-7350 for '83-'92 motors. Is that Sierra pump correct for a '74 vintage motor?

Also, back to the compression, should I just plain plan on putting new rings in at a minimum? Or is there something else I should be checking? I know that 75-80 PSI is normal on these motors, and that 110 PSI is typical of a new 6 horse. So one would think that at 55 PSI, I'm at half of what would be ideal.

Thoughts?

Thanks!

Seth
Cedar, MN

 

[Monte1961]

Re: HELP!! 1974 Johnson 6hp issues

Seth 1st question. Did it have cork float? 2nd. compression test wet or dry? I have seen this engine run with a bit lower compression. The cork float causes, especially with ethanol fuels. It might run fine in tank, but as soon as you are out in the water with everything rocking, the carb will pick up some of the coating witch is clear and reak havoc on the low idle circuit. By the time you get it back home, the fuel will have dissolved the coating and you don't see anything making you think theirs something else wrong. What the heck, overhaul carb and reinstall it. Even if the motor is weak on compression and you have to re ring it, at least the carb will be fresh. And something else comes to mind, check low idle jet and see if the tip is broke or worn, pull the welch before you soak it in carb cleaner only real way to make sure its clean and clear!

 

[jrs_diesel]

Re: HELP!! 1974 Johnson 6hp issues

Since you say the dead cylinder moves at different RPMs, that leads me to believe you have a wiring issue with your ignition system. The timing plate moves with the throttle to advance the timing with increased throttle. That means your plug wires move around a lot.

Go through your ignition and look at everything, and clean all of your connections. If the plug wires are old, replace them.

 

[blackhawkdc]

Re: HELP!! 1974 Johnson 6hp issues

Monte and Jrs_Diesel,

Yes, as stated, it does have the cork float, which I will be ordering when I order parts for this motor. Compression test was done dry, and immediately after having run it for a while to get it up to operating temp and everything well lubed. No change. As stated too, the carb has a fresh rebuild, just didn't expect a cork float when I rebuilt it. If I had known, I've have put a new float in it then also. As for fuel, I am running ethanol free "pure premium" So there is no ethanol to cause issues. Also, the plug wires are NEW. They were replaced at the same time as the coils. All wiring connections appear tight and properly routed.

I am thinking that I will just plan on doing a re-ring job and replace the reed valves while I'm in there. In the mean time, I thankfully have access to a 9.9 Evinrude that I can run with until I get my 6hp fixed.

Thanks,

Seth
cedar, MN

 

[jrs_diesel]

Re: HELP!! 1974 Johnson 6hp issues

The compression is low indeed, but compression has nothing to do with the ignition system.

You are losing spark to both cylinders at different times with different throttle settings. This means your timing plate is in a different position when it happens to either cylinder. You have loose or dirty wires wires somewhere in your ignition system.

You should do a thorough clean and inspect of your ignition system and wiring. Tedious as it may seem, it is nessessary. I am a USCG Electronics Tech, and the hardest problems I troubleshoot and fix are loose and/or corroded wires. This system is far more simpler than chasing problems in a RADAR or antenna systems exposed in a salt water environment.

 

[blackhawkdc]

Re: HELP!! 1974 Johnson 6hp issues

Thanks JRS_diesel. I'm thinking right now, due to lack of funding, I am going to get a bottle of seafoam and let the pistons/rings soak for a few days. Then put the head back on, and proceed from there. Pull the flywheel off and go through the ignition system with a fine tooth come.

but here's a question, when the engine is misfiring, and I pull the plug wire off of the dead cylinder, i still get a consistent, strong spark that will jump a 1/4" gap. One would think that the ignition system would be kosher in that regard. Can't see how the timing would be far enough off between the two cylinders to cause the swapping of cylinders. Nothing seems to make sense on this engine right now.

 

[Daviet]

Re: HELP!! 1974 Johnson 6hp issues

If you are running on the top cylinder, and you pull the bottom plug wire and you have good spark, the only other items that can affect it is fuel (not enough or flooding) and compression.
If you swap plugs from top to bottom, and it stills runs on just the top cylinder that proves that both plugs are good.
Do you have good compression on the bottom cylinder, if so it only leaves fuel.
Is the bottom plug gas fouled, or is it clean?

 

[blackhawkdc]

Re: HELP!! 1974 Johnson 6hp issues

both plugs come out about the same, bottom one probably a little more fouled up though. Compression, as stated above, is even on both cylinders, but low at 55psi with a known, accurate gauge.

 

[AlTn]

Re: HELP!! 1974 Johnson 6hp issues

before reinstalling the head, surface it using the emory cloth on a flat surface while moving the head in a figure 8 pattern. If you use a flat edge and examine the head, you'll probably see high and low spots before you surface it. It's cheap and easy to do..sorta time consuming though.

 

[Tim Frank]

Re: HELP!! 1974 Johnson 6hp issues

EDIT:found the info...

 

[raczekp1]

Re: HELP!! 1974 Johnson 6hp issues

i had 6hp made in 73'
compresion in last year was 90psi in both cylinders after 3 starter puls.
i think compresion is the problem.
when head is of, pur some sea foam in cylinder holes and wait day or so.
take the head and go to repair shop to do the head flatening.
after sea foam tretment put new head gasket and torq the head back