Losing a cylinder intermittently ‘86 50hp

[Oldnbold]

I’ve a 50 hp johnson for 2 1/2 yrs and have run about 35 gallons of 10%ethanol fuel through in this time. I’ve replaced the fuel pump and spark plugs and cleaned the carbs initially . Boat was inactive from 9/15/20 - 1/5/21 when it started acting up.
Symptoms: engine starts easily with choke but within a minute the idle starts surging ( hi-low-hi) . It will usually take an advancing throttle at 1st, and will run WFO indefinitely. The problem starts when you throttle down to 5 mph or so and it drops a cylinder. Attempts to throttle up again and engine stalls. Restarts on 1 cylinder and usually takes a bit of sustained hi idle lever to get cylinder to reignite and once in gear and cylinders both firing , engine will perform as expected.
Ive replaced spark plugs ( 35 gallons of use) which looked rich and added new ones. Same results.
Ive cleaned the top carb again and saw zero reason for concern so I got lazy and didn’t clean bottom carb.
I noticed after the new plugs and carb cleaning and while testing on muffs for 10 minutes, my cylinder temps ( both) checked with my IR gun, were 86degF +/- 5degF.
I was thinking at this point this 2T engine is running way too cold and cold water was the only thing that changed since the engine ran properly. I took the water jacket cover off and saw engine had no T-stat nor the poppet valve installed. I installed a new T-stat but no poppet valve ( lead times too long) . Engine still runs the same since the install of plugs and T-stat. Water temps 55degF. Engine runs Ok at WFO but is inconsistent at idle speeds.
Any ideas?

 

[racerone]

Some will argue but , ----The trouble shooting always starts with a compression test.--Post your numbers.----Then see if spark will jump a gap of 3/8" ( 1 cm ) on a testing device.-----And the reason for the compression test is to establish motor condition.----No point in adjusting / tuning a motor that has cylinder issues.

 

[ct1762@gmail.com]

i'm guessing idle circuit/s have some gunk going on. only takes 15min to have your answer! as racer said, compression 1st.

 

[ct1762@gmail.com]

oh makes sense... simply allows the air pressure to flow one way, and not the other. like a backflow preventer in plumbing. i stand corrected!

 

[oldboat1]

Since you say the problem started after the boat was unused last fall/winter, it sounds like a routine carb issue -- depends on how it was stored. Pull off plug boots one at a time and see if there is a change in rpm at idle. If no change, that cylinder is probably not firing up. Do a spark test on that cylinder.

If no solution there, I would guess you have some fuel varnish in an idle circuit, requiring cleaning the relevant carb.

 

[Oldnbold]

My compression results were both cylinders were 140 psi. I’m about to go burn some gas through it and see if anything has changed since it’s warmer now.

 

[Crosbyman]

have you done anything electricaly ( clean plug wire ends , measure coil resistances to compare etc..)

what about the carbs..... any work done on the LS circuit jets and drip chambers

some don't like it but try simple stuff like a good shot of seafoam it did wonders on my snowblower carb.. try some before digging into the carbs again.

 

[oldboat1]

Think you need to check the idle with some back pressure (not on muffs). Also, the temps you cite after 10 minutes running are too low, imo, as you suggest. That also could relate to use of muffs.

 

[racerone]

Smooth surging is usually a fuel issue.--Water in the fuel ?--Try running with a different fuel tank and hose.------Run with a timing light to see if perhaps spark has issues.

 

[Oldnbold]

After 1 hr run time @4500 rpm in 75degF weather and 55degF water temps, the engine runs much better. Coming out of the hole both cylinders firing now, but the engine certainly has a sweet spot in Rpms before it sounds and feels happy.
IMO, my jetting is suspect for lower temps in the Low Speed circuit. For whatever reason, this Canadian Johnson has a fixed air jet, not a spring loaded, adjustable air screw.
Thoughts anyone?

 

[racerone]

What number is on your fixed air jet in your carburetors ?----What elevation are you running at ?

 

[Oldnbold]

After 1 hr run time @4500 rpm in 75degF weather and 55degF water temps, the engine runs much better. Coming out of the hole both cylinders firing now, but the engine certainly has a sweet spot in Rpms before it sounds and feels happy.
IMO, my jetting is suspect for lower temps in the Low Speed circuit. For whatever reason, this Canadian Johnson has a fixed air jet, not a spring loaded, adjustable air screw.
Thoughts anyone?

 

[juno pierrat]

yap for a couple /three years the air jet were fixed, my engine idles great with CCMS reeds at sea level. Note: at 1600 to 2000 rpm's my engine heats up 10 degrees or more, always wondered if getting a smaller air jet would help by making it run richer at lower rpm's

 

[webbd]

These are just my thoughts...

Surging - my lawnmower surges if I run it with ethanol gas because the needle and seat gets clogged with this amber cake whenever I let the carburetor sit for any time with fuel in it. The caked crystal deposits on the needle block fuel flow until the float drops far enough and then it gushes in. You mentioned ethanol gas, so it's a possibility.

Good on putting a thermostat in.

Cylinder drop-out at low engine speeds - My 1997 50HP Johnson ran with the same type of dropping-out-one-cylinder behavior from the time I bought the boat from a friend until a few months ago. When I throttled the engine up off of idle, it would run smoothly for a few seconds and then drop one cylinder. My engine just wouldn't run properly on both cylinders between about 1500 RPM and 2300 RPM, and it would idle down to a stop if left to idle for too long.

Here are some possible culprits for the low-speed running issue:

Link and synch. I don't know why, but on my engine one cylinder drops out while the other keeps running...

1. There is a follower roller inside the curved timing slot for the throttle lever plate on the starboard side of the motor on my 1997 model. The roller adjusts the position of the spark lever cam. This roller has a clear outer sleeve that makes the roller the same diameter as the slot is wide. When the sleeve wears down and falls off, the roller is too narrow and you just can't get your timing right.
2. The throttle cam follower roller also has a clear outer sleeve, and the shape of the throttle cam opens the carburetors correctly relative to timing when that sleeve is in-place.

If either of these rollers don't have their follower sleeves, get new rollers and see if replacing them solves the problem. If you're like me and tried to get the timing right without the rollers, then you probably need to redo your link and synch.

If you don't have an inductive timing light, you might need one. Follow the instructions in the manual to the letter (page 2-65 in the Seloc manual). You may need to back off the idle speed and timing advance stops while you make the adjustments. I have a bit of a background with tuning cars and tended to think that just a bit more advance without detonation means more power. In this case, more timing advance might mean that your engine doesn't like to run at idle until it warms up, so try for the middle of the recommended adjustment range.

One difference between your engine's behavior and mine was your engine stalling when you added throttle. The only times I've seen this behavior, I was able to resolve it by testing and then replacing the coil (power pack) with an OEM replacement. I bought a Sierra the first time and it lasted a few months. I also replaced the ignition module, spark plug wires, and spark plugs.

Primer fuel hoses. On my engine, these hoses route fuel from the Fuel Pump/VRO on the port side, between the intake horns to the primer valve on the starboard side, then when the primer is engaged, back between the intake horns to little barbs on the tops of the carburetors where the idle and low-speed mixture circuit is. Ethanol fuel over time makes them brittle and they might impact your mixture at low RPMs.

- DW

 

[oldboat1]

Run some soft wire through the idle (top) and high speed jets, then follow by some carb spray using the plastic wand. I believe the top jet is open on your motor, and the bottom one has a hex bolt in front of it (front of carb bowl).

 

[juno pierrat]

an often over looked part of idle circuit is two very small holes under the core plug on top of the carb, those holes are just behind the throttle plate and can be wired out without removing core plug if carbs off engine, if you think its the top cylinder not firing at idle, plug can be removed without carb removal, a welders torch cleaning tool has a wide selection of fine wires for wiring out small holes, a good tool to have for any carb work, Note: reference to core plugs on top of carb is for, in general, 80's carbs, early 90's carbs design changed

 

[ct1762@gmail.com]

i would highly recomment NOT running any wire through the tinly idle circuit holes. if you think they are dirty, just flip the carb over and spray some cleaner over the holes and watch to see if the fluid dissapears. if it doesnt, remove the core plug and blow it out. also, DO NOT use the Seloc manual. those are garbage. Use the factory manual. makes no sense to tune an engine without the manual that the actual engineers published IMO.

 

[Crosbyman]

agree with #17.... pushing the obstruction (crud) back into the idle chamber with a wire would only cause it to plug up the crab....... downriver :-(

 

[ct1762@gmail.com]

agree with #17.... pushing the obstruction (crud) back into the idle chamber with a wire would only cause it to plug up the crab....... downriver :-(

I was actually referring to how a stiff wire can easily change the profile of the holes, but your objection makes sense too!

 

[oldboat1]

Try a plastic bristle from a broom if you need a prod.