TOPIC: Gas Hog?

That's an extreme amount of fuel at idle. This engine, at Wide Open Throttle, will only burn 5.5 gallons per hour (GPH).

So either the carb needle/seat is leaking profusely, or the fuel pump diaphragm is ruptured, passing copious amounts of raw fuel thru the powerhead and out the exhaust.

Are you getting a huge sheen on the water in your barrel? Assuming you're running in a barrel. A pretty good sign of issues like that is a very think, grey "milkshake" on top of the water. Not just a bit of gas/oil mix, a ton being heavily agitated.

Maybe the float is sunk? I can't recall but if these have a brass float, full of air; if it's leaking and fills with fuel, it'll just sink and let all the fuel thru.

A cork float can become saturated with fuel, and if you're on Gasohol, it'll dissolve the old varnish sealer on the float. You can bake the float at low temps to get all the fuel out, then seal with fuel-proof model airplane dope or epoxy-based sealer.

If you pull the carb, turn it upside-down and blow into the fuel inlet line. It should pass no air. Turn the carb upright, and you should get flow. I always do this when working on a carb, to make sure the float moves properly when things are all together, and it will pass fuel when it's supposed to & shut off too.

Anyway, just a few things to think about. A good way to test the fuel diaphragm or other leak points is to pump up the primer bulb. It should get hard and fuel flow should stop. If you hear fuel gushing somewhere, there's your leak. The side of the fuel pump where crankcase vacuum/pressure hits the pump diaphragm should be dry. If it's wet, fuel is leaking thru a failing or ruptured diaphragm.

HTH.......ed

I rebuilt the carb with new a needle and seat and did the blow test and it works perfectly. Yes, lots of raw fuel and oil in my barrel. It has the fiber(?) float that floats well on top of water. It sounds like a ruptured diaphragm to me. I don't see how an engine can fire with that much fuel being pumped into the cylinders. I tested again today with a measured 1 quart of gas/oil and it only idled for a timed 3 minutes and 4 seconds! Thank you for the great advise ed-mc!! I will rebuild the pump this weekend and let you know what I find.

It's probably only running on one cylinder, the one that's feeding the fuel pump would be so rich that it wouldn't run.

Good Luck with the repairs, let us know how it turns out.........ed

I rebuilt the pump and it was just as you said, Ed, the diaphragm was ruptured. I ran it afterwards and it runs smooth and doesn't suck down the fuel anymore. Thanks for your help! Next on the list is to replace the thermostat.

Glad it worked out! Thermostat shouldn't be too difficult as long as the cover screws come right out.

If any of the fasteners don't want to move, apply heat from a torch around the screw area, it should help loosen it up.

While waiting for the thermostat, I replaced the impeller yesterday and opened the drains for the foot oil. I will refill the foot oil today and crank it up to make sure it is pumping water.

What fuel/oil ratio should I run on this engine? I have been mixing at 40:1 for test running in the barrel.

Pygmy Warrior wrote: What fuel/oil ratio should I run on this engine? I have been mixing at 40:1 for test running in the barrel.

This engine was built to run on 50:1 but actually 40:1 mix works great. A bit more oil in deference to its age, and the extra oil is also good for the piston rings' sealing.

Use a premium oil such as Mercury brand, and non-ethanol fuel if you can get it.

Thanks ed!

I have a couple more problems I am hoping you can help me with. The starter occasionally engages while the engine is running. Would that be the ignition switch or the solenoid? I don't see how the solenoid could engage without power coming from the switch.
Next problem is, I have three loose wires coming out of the harness at the ignition switch. One is the the black wire labeled ground, one is the purple wire labeled generator and one is the orange wire labeled temperature.
The wire length is the same as all of the others as if they should be attached to the switch. The engine operates as it should. It cranks, runs, generates power to the battery and shuts off. Please see attachment.

Black, return ground.
Orange, overheat buzzer.
Purple, tach output from rectifier.

All extras for dash gauges/accessories.

Pick the appropriate diagram at this site:

maxrules.com/fixchrywiring.php

You probably have battery-powered ign, there's a diagram for that. If not there are others

The starter solenoid thing sounds like a bad switch, if it's doing it enough to catch it in action, connect a test light from the small terminal on the solenoid to ground. If the light is lit when the solenoid inadvertently activates, then the switch is bad. If it does it with no power applied, the contacts must be rattling around inside. You could also disconnect the actuation wire after the motor is running, if the solenoid does or doesn't act up, you'll know what's up with it.

Thanks ed! That gives me a much better understanding of how the system works. I will get back on it tomorrow Do you know if the red power wire is heavy enough to carry the accessories such as navigation lights, horn, overheat buzzer, etc. or do I need to run a separate circuit for that? Thanks!!

The overheat horn was designed to run off the motor's electrical system. For the other loads, it's probably better to run a separate, fused circuit.

Btw a marine tach runs off the rectifier output and +12V, giving you that option.

I replaced the ignition switch and have run it several times in the barrel. I am happy to report that the starter has not engaged since the replacement.
I am having my maiden voyage this weekend after a month of going over the boat, making sure everything is in good working order. Here are a few pics.

She looks Sharp!
Good Luck on your Sea Trials...........ed

The boat looks amazing. Have fun!

I took the boat out this past weekend and only had a couple of problems. The first was that it wouldn't shift into drive but would shift into reverse fine. I made a cable adjustment and I think it is fixed. The other problem is a bit more puzzling. It fouled the top spark plug about 25 minutes into the run. The bottom spark plug looks like it did when I installed it new. It's a 2 cylinder 2stroke with 1 carburetor so it seems strange to me that it would foul only 1 plug while the other one looks new. I checked the top cylinder with a new plug and it fires fine. I am thinking it may be something in the ignition. I replaced the coil for the top cylinder when going over the engine a few weeks ago because it was bad. I checked the fuel pump diaphragm and couldn't see any holes. It is a new diaphragm also.
Any thoughts on what else it could be?

Could be points or condenser. Did you take apart the points and clean to bare metal? It also helps to burnish the points with some crocus cloth. Set points gap at .020"

I cleaned the points but I didn't take them apart. I set them to .020. I have never heard of crocus cloth. I will look that up. Thank you for your help!

They definitely must be cleaned to bare metal. I usually use a medium whetstone for the initial cut, then the crocus cloth will 'burnish' the points so they're very smooth and this surface has less of a tendency to burn from arcing.

Lay the crocus cloth (or other abrasive) on a file or similar thin, flat object such that you have a flat surface to bear against when sanding the points. This way you'll make sure to keep the surface of the points flat all the way across. If you just sand the gap back-and-forth, you're likely to round out the faces, and probably won't get the surface completely clean.

You could substitute a very fine grit sandpaper (wet and dry type) such as 600/800 and come up with similar results to the crocus cloth. But crocus is great for putting a smooth polish on things, such as crankshaft journals that run caged roller/needle bearings.

Be sure to degrease the points afterwards; any bit of petroleum products on the surface can cause burning. Lighter fluid works great for this (naptha) and doesn't leave a film. Substitute any solvent that doesn't leave a film and you're good to go.

If you want to mess around, you could swap condensers at the same time you re-check the points, and see if the problem goes to the other cylinder. If it does, you know for sure it's a bad condenser. If not, maybe the points are just bad. I've had some that were internally shorted or had other issues, and they were Just.No.Good.

www.ehow.com/facts_5559160_crocus-cloth.html

BTW it might be hard to find the stuff, I looked in a lot of places with little luck. True crocus cloth is made with iron oxide, not aluminum oxide, and the stuff they're selling on Amazon, for example, as "crocus" is aluminum oxide. So, probably some wet/dry 600/800 is your best bet, a lot easier to find. Used to be you could find nice large rolls of crocus, thin-cut so you could use them on crank journals, etc. Real handy 'cause you could just cut off a length long enough to grab both ends and polish away. Times have changed, got to make do with what's available!

Considering the almost-astronomical price for a set of these points, it's worth a bit of troubleshooting to narrow-down the problem.

That's a lot of good info ed! I will check out the points this weekend. Thank you!!

This past weekend I burnished the points, cleaned and re-gapped to spec., took it out and ran it and had the same problem with the top plug fouling. I swapped the plugs before it completely fouled out and the bottom cylinder would clean it in about 5 minutes of running but it would start to foul the top plug. I did that several times. So then, I swapped the coil wires and ran it again about 5 minutes and the top plug was clean. I thought the problem was solved so I ran a while, about 15 minutes, and put it on the trailer for the day. When I got back to the house I checked the plugs and the top plug was starting to foul again.
I swapped the coils and cut the ends off of the coil wires for the next test hopefully this weekend.

Well, you're getting somewhere! The coil swap should pin it down. Sure sounds like a weak spark issue and not anything with the top cylinder itself.

I agree. I checked the compression again and got 157 and 158 psi top and bottom, respectively. The spark on each cylinder is a strong blue. If this doesn't change anything, I will swap the condensers. Thanks for your input!

I ran the boat this weekend with the coil swap and the top cylinder is still fouling. I was able to find that running at wide open throttle cleans the top plug but running half throttle or idle makes the plug foul.
I swapped the points and condenser and will try it again next time. Unfortunately I stripped the foot fill plug and will have to repair that before getting it back out on the water.

Well, there's not much left after that! Next time it's out, if the top plug fouls again, before you clean it or do anything else with it, pull it and take a pic of the electrode end and post it here. We want to make sure there's no water intrusion issues going on.

p.s. Old Outboards! There's always something!!

I certainly will.
If I don't fix it soon, I fear the wife will tire of my tinkering with it while we are out trying to relax and pull the drain plug!!
All jokes aside, there's only so many things it can be.

Couldn't a leaking crankcase seal or intake manifold leak introduce issues like this in one cylinder as well? My thoughts is that some air may be introduced into one side causing a lean situation, then the carb is adjusted to correct by richening but now the mix is too rich for the other cylinder. keep going with your electrical testing first and see what the real experts say here about my comments. I do have some education in small engine repair (2 years in a skill center, junior and senior years of high school) but that was 30+ years ago and only tinkered here and there since then.

Crankcase leak would cause poor idling/running. Only the idle mixture is adjustable, main jet is fixed. So having one cyl lean won't affect the other cylinder much, at speed.

I'm assuming the top plug, when that cylinder cuts out, is all black and oily? If it's spotless white, then either that cyl is lean or the plug is being steam-cleaned by water ingestion. Any drops of water or foamy grey material on the plug?

When it is running on both cylinders, does it run well? How's the idle quality? If the plug is indeed fouling, it's typically a lack of spark energy. Not many components left to check, though. But it could be a condenser. Guess we'll rule that out when you next run the boat!

The plug is black and oily, no water of foamy grey material. The engine cranks with a quick bump of the starter and idles fine and runs fine at all throttle settings. I will take some pics the next time I run it.

I repaired the stripped foot fill plug this past weekend and will install the lower end next time I make it to the lake. I hope to have some warm weather for testing next time I go.

I took the boat out this weekend for a test run after swapping the points and condenser. It made no difference. The top plug is still fouling. Here is a picture of the two plugs. The one on the left is the top plug. See attachment.
I ordered a cylinder head gauge kit and will install and run it next time to compare the two cylinder heads temperature.

I was talking to one of my buddies that rode and worked on snowmobiles for many years, he mentioned checking out your reeds, One set could be allowing mixture to blow back and have less fuel to burn. and another possibility to check is (this one sounds very little chance of an issue to me but...) if the cooling system is clear. If you have some blockage causing one cylinder to run hotter than the other, this could cause inconstancy in how each cylinder performs/burns the fuel. I would think you would know if your overheating here but worth a check if you can check the temps of the top and bottom cylinders at the head when at operating temps.

That is exactly my thinking on checking the cylinder head temp with the gauge that I ordered. I bought a reed plate gasket a few weeks ago so I can open up the reeds and give them an inspection. I did look at them with the carb removed and didn't see anything unusual, but they need to be removed for a closer look. Thanks for the input! It looks like we are on the same page. I will let you know how the temps read on each head after my next run.

I can't recall if you've ever done a compression check. Maybe that will tell us something.

One thing that's easy to do is to take an old spark plug and bend the ground electrode WAYYYY out there so you have a very large gap. See if there's any difference between the spark of #1 and #2 cylinders when cranking. Both plugs out for this test. You'll definitely see the difference in spark energy if there's an issue with the top cyl. The extra gap raises the energy required to bridge the gap, and this will point out any weakness in the ignition components.

What cyl does the fuel pump come off of? If it's the top, I wonder if it's still leaking some into the cylinder. That extra mixture would foul the plug over time.

Checking reed valves may tell you something. At least it's not too difficult to do (try checking reeds on a Merc Inline!).

This Stone-Age Twin has certainly been a tough nut to crack, eh? We're gonna get to the bottom of it sooner or later!!!

I did some poking around at Marineengine.com and I wonder if a problem with the cylinder drain reed valve could cause fouling?? I recall a mention of that by one of the Johnrude Dudes about an old pressure-tank Twin. Haven't had much experience with those and they don't seem to be a huge problem area, since there are a lot of cheap NOS reed plate assemblies and gaskets on eBay. If it was a hi-demand part, you wouldn't find much or they'd be really expensive.

Anywho, something else to think about! I suppose if the top cyl wasn't draining excess fuel because the drain hole was plugged or the reed rusted to the plate or the drain passage clogged, maybe it could cause a fouling problem. Just another Shot in the Dark.

www.marineengine.com/newparts/part_details.php?pnum=MERF3A433757

www.marineengine.com/newparts/part_details.php?pnum=MER27-F93472-1&pass_title=27-F93472-1+%3A+Replaced+by+27-F93472-1+Gasket

The compression test showed 157 top cylinder and 158 bottom cylinder. I will try the spark plug test next time I work on it. I checked the inside of the vacuum hose on the fuel pump that goes to the top cylinder and it was dry.

This is something that I wasn't aware of! I found the gaskets on ebay at a good price so I will order those and check to see if the drain reeds are malfunctioning. Thanks for the input!!

I took the boat out yesterday for a test run with the cylinder head temperature gauge. Here is what I found.
Idle temp. Top Cylinder 150 deg. F Bottom Cylinder 153 deg. F
2040 RPM Top Cylinder 171 deg. F Bottom Cylinder 182 deg. F
3050 RPM Top Cylinder 166 deg. F Bottom Cylinder 192 deg. F
3700 RPM Top Cylinder 167 deg. F Bottom Cylinder 209 deg, F
5160 RPM Top Cylinder 214 deg. F Bottom Cylinder 216 deg. F (5160 RPM is Wide Open Throttle)

I checked the timing at the points with a continuity meter and a degree wheel.
Top Cylinder No Advance 0 deg. BTDC
Top Cylinder Full Advance 29 deg. BTDC
Bottom Cylinder No Advance 5 deg. BTDC
Bottom Cylinder Full Advance 35 deg. BTDC

The difference between cylinders seems extreme. I don't see any way to adjust the points independently. The manual says the total timing advance should be 32 degrees.

I also opened the spark plug gap to .080 and tested the spark on both cylinders. Both had a strong spark.

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?