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TOPIC: Gas Hog?

Gas Hog? 1 year 4 months ago #147472

  • ed-mc
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Man, that seems really hot. Normally these shouldn't ever develop a surface temperature on the block of more than 140F. And normally the top cylinder would run hotter than the bottom. Of course if there wasn't good combustion in the top cylinder, it would have cooler temps.

Did you attached the sensors to the spark plugs' body or actually on the head itself? I can see where maybe the spark plug runs a bit hotter than the rest of the engine.

There is a way to affect the timing of an individual set of points on a 2-cylinder engine; you vary the gap. Closing the gap gives more dwell; and opening the gap more decreases dwell.

So what you want to do is have a timing scale, and set it up so #1 cylinder is firing (i.e. points are opening) right at the Zero mark; then adjust the points on #2 cylinder so that it fires right at the 180-deg mark. Regardless of the point gap. This is the only way to get them in sync with each other.

I've attached a file for an old Mercury Twin Synch Plate. You may be able to size it so you can print it out on heavy stock and use that for your timing scale.

That is pretty wild, though, to see such a variance in timing between top and bottom cylinder. I'm assuming points gaps are the same?
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Gas Hog? 1 year 4 months ago #147473

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BTW does the block get really hot when the engine is running? Most of the parts on the block and also the exhaust manifold cover should not be so hot that you can't comfortably put your hand on them. That threshold is around 140F. 180F is so hot that you can't even touch it for a second and no 2-stroke should ever be that warm.
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Gas Hog? 1 year 4 months ago #147474

ed-mc wrote: Man, that seems really hot. Normally these shouldn't ever develop a surface temperature on the block of more than 140F. And normally the top cylinder would run hotter than the bottom. Of course if there wasn't good combustion in the top cylinder, it would have cooler temps.

Did you attached the sensors to the spark plugs' body or actually on the head itself? I can see where maybe the spark plug runs a bit hotter than the rest of the engine.

There is a way to affect the timing of an individual set of points on a 2-cylinder engine; you vary the gap. Closing the gap gives more dwell; and opening the gap more decreases dwell.

So what you want to do is have a timing scale, and set it up so #1 cylinder is firing (i.e. points are opening) right at the Zero mark; then adjust the points on #2 cylinder so that it fires right at the 180-deg mark. Regardless of the point gap. This is the only way to get them in sync with each other.

I've attached a file for an old Mercury Twin Synch Plate. You may be able to size it so you can print it out on heavy stock and use that for your timing scale.

That is pretty wild, though, to see such a variance in timing between top and bottom cylinder. I'm assuming points gaps are the same?


The gauge attaches between the spark plug and the head. It looks like a copper washer with a wire attached. I can put my hand on it for a couple of seconds before it gets too hot. Seems about the same as a car radiator. The points gaps are both set to factory spec of .020. I used a degree wheel similar to the twin synch plate, only it has hash marks every degree.
Most old school cars that I have worked on have an idle timing around 6-8 degrees BTDC. My manual on gives specs at full advance timing of 32 degrees.
Any idea what the timing should be at idle?

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Gas Hog? 1 year 4 months ago #147475

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OK, so that explains the temps. But the difference in temps is indicative of whatever issue it's having. So #1 isn't having as good of combustion as #2 or is making less power. Maybe because of the difference in spark timing? IDK but you're gonna have to correct that before pressing on.

Most outboards are probably gonna be happy at 0-to-5 deg BTDC at idle. Each one is particular about where it wants to run at.

So whatever yours is when you're getting a "happy" idle out of it. There is usually a synchronization mark on the throttle linkage, such that timing is advanced so many degrees and then the carb will start to open. Typically you'd want the carb butterfly fully shut or whatever small opening is necessary to get it idling well, before timing kicks in.

At any rate, you need to set up the degree wheel for #1 set of points opening, then adjust the gap on the 2nd set of points so that it opens exactly 180 deg after the 1st set. Then adjust the maximum spark advance stop based on points set #1.

Then you should have consistent timing between the 2 cylinders and it should run better just as a consequence of that. You can use a test light to tell when the points open/close. A "Buzz Box" is ideal, but they are rather expensive.

Here's some good info on how you'd use a Buzz Box to set points, and handy instructions on a D-I-Y model:

dansmc.com/buzzbox.htm
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Gas Hog? 1 year 4 months ago #147477

ed-mc wrote: OK, so that explains the temps. But the difference in temps is indicative of whatever issue it's having. So #1 isn't having as good of combustion as #2 or is making less power. Maybe because of the difference in spark timing? IDK but you're gonna have to correct that before pressing on.

Most outboards are probably gonna be happy at 0-to-5 deg BTDC at idle. Each one is particular about where it wants to run at.

So whatever yours is when you're getting a "happy" idle out of it. There is usually a synchronization mark on the throttle linkage, such that timing is advanced so many degrees and then the carb will start to open. Typically you'd want the carb butterfly fully shut or whatever small opening is necessary to get it idling well, before timing kicks in.

At any rate, you need to set up the degree wheel for #1 set of points opening, then adjust the gap on the 2nd set of points so that it opens exactly 180 deg after the 1st set. Then adjust the maximum spark advance stop based on points set #1.

Then you should have consistent timing between the 2 cylinders and it should run better just as a consequence of that. You can use a test light to tell when the points open/close. A "Buzz Box" is ideal, but they are rather expensive.

Here's some good info on how you'd use a Buzz Box to set points, and handy instructions on a D-I-Y model:

dansmc.com/buzzbox.htm


I agree that the timing problem should be sorted first. It maybe the cause of the fouled plugs anyway.
I will work on it in a few weeks when I make it back to the lake.

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Gas Hog? 1 year 4 months ago #147480

sounds like maybe your points should be adjusted. the below link I know is not your motor but should be similar. check your specs on point gap. if the gap is not set correctly on both, they will crack open at the wrong time.

https://www.youtube.com/watch?v=CmfGuHUy1Rs&t=2s&ab_channel=chrysleroutboarddude

Well I see that others have already posted. disregard my suggestion. Im at a loss. But, if your cooling system is not clogged somewhere, I would think you shouldn't have this much of a heat difference. I'm suspecting a clog in a port somewhere in the cooling system, and or not pumping enough water in the mid RPM ranges.
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Gas Hog? 1 year 2 months ago #147596

I finally had suitable weather to dig into the timing issue. I rechecked the points gap and found that the number one points was not where I set them last time. I set them again and checked them with my degree wheel. Each cylinder is now set to 32 degrees at full advance. As soon as the weather permits I will take it out for another test run.

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Gas Hog? 1 year 1 month ago #147704

Update...I took the boat out this past weekend and still have the same problem. I will remove the reed valves and replace them with new valves next time I get a chance.

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Gas Hog? 1 year 1 month ago #147707

any chance your points adjustments moved on you again? This is one hell of a gremlin you got in there.
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Gas Hog? 1 year 1 month ago #147708

I would say anything is possible at this point. I will check them next time I work on it. Thanks for the input.

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Gas Hog? 1 year 1 month ago #147748

I checked the timing and both cylinders were spot on. I checked the drain reeds and all was clear and clean. I was unable to replace the intake reeds because the new gasket is torn. I ordered a new one and will tackle it next time.

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Gas Hog? 1 year 1 month ago #147765

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Very vexing, ain't it! Sure is a contrary engine. Especially for a 2-cylinder. Grrrrr!
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Gas Hog? 1 year 1 month ago #147769

No doubt...but I will keep plugging away at it.

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Gas Hog? 1 year 1 week ago #147864

I was planning on replacing the reed valves a couple of weeks ago but before I pulled the intake off, I noticed that the gasket wasn't correct. I also noticed other minor differences from the 1970 parts catalog diagram. After countless hours of research, I discovered that it doesn't have the original powerhead. It has a 1973-76 powerhead. I ordered the correct gaskets for the intake so I can replace the reed valves.
I checked the crankcase and cylinder drains yesterday to make sure they were working properly. I also tested the check valve on the crankcase drain. Everything is working properly with no obstructions. I checked the cylinder drain reeds a few weeks ago and all was clean and clear.
I removed the exhaust cover to get a look at the pistons and buildup of carbon as well as any other clues. Everything looked really good with very little carbon buildup and the pistons look like new with the lathe grooves still prominent.
I will change the reeds next time, hopefully!

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Gas Hog? 11 months 3 weeks ago #147892

I was finally able to remove the reed valves this past weekend and I am pleased to report that the reed valves look like brand new. They lie flat with no gaps, so I didn't replace them. There is a small drain in the bottom corner of the top intake port that seems clear. See pics. At least I think it is a drain. I tried to blow air through it but the hole is so small I couldn't tell if it was blowing through. There was no oil in the intake.
In another twist, I know the powerhead cases are 1973-76 based on the design, but while I had the reeds out I noted the crankshaft part number on the counterweight. It matches the part number from the 1970 engine but not the 1973-76. I can't find any numbers on the cases to determine the exact year of the engine. It has nothing to do with the problem that I am chasing but still puzzles me.
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Gas Hog? 10 months 3 weeks ago #147956

After exhausting all conventional avenues to solve my plug fouling problem, I started thinking outside the box. I took an extra set of reed pedals and cut three of them off. I removed the reed stop on the top reed pedal set and mounted this on on top of the existing set of reeds and reinstalled the reed stop. So I now have one extra reed pedal that applies extra tension and restricts a small amount of fuel and air to the top cylinder.
I ran it this weekend and am happy to report that after checking numerous times the top cylinder plug looks like it should and did not offer to foul. The bottom cylinder plug looks great as always. Maybe it will hold up!

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Gas Hog? 9 months 2 weeks ago #148065

I am still tinkering with this engine and stumbled upon a way to fine tune the air/fuel ratio to each cylinder independently. I found the spec for setting the reed stops. This setting is to limit how far the reed pedals are allowed to open. The factory recommendation is 9/32". So I removed the extra reed pedal, mentioned in an earlier post, to conduct this new test. I left the bottom cylinder reed stops set at factory spec and closed the top cylinder reed stops by about 1/32". I ran it with this setting and it doesn't foul the plug. Although at mid throttle it is still slightly rich according to the plug reading. Plug readings at idle and wide open throttle are still fine. The temperature reading between both cylinders are now closer together, which I would expect since the top cylinder is now a bit leaner.

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Gas Hog? 9 months 2 weeks ago #148091

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Well, that's a Heck of a way to have to tune it, but it sounds like you've got 'er licked!
Good On Ya for persevering!
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Gas Hog? 9 months 1 week ago #148109

ed-mc wrote: Well, that's a Heck of a way to have to tune it, but it sounds like you've got 'er licked!
Good On Ya for persevering!

No doubt...and thank you for all of your advice!
By the way, I pulled the plugs today and both looked perfect.

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