Merc 20H Help Needed

[jackbquick]

I bought a "race ready" 20H last fall. Tested it over the weekend. Engine will start and run when on the cart and just the gear foot in the water. Engine won't start well and keep running when on the boat. Last ran 20H's in 1957 and 1958. Have forgotton about all I knew about the engine. Engine has the Carter model N with #2150531 stamped on the mounting flange. Fuel system is clean and float is about right setting. Ran Champion K2 and K3 plugs to prevent pre ignition back then. What is the modern plug for it now? Point setting was .016 on one and .018 on the other. What is the right point setting? Any and all info and suggestions will be most welcome! Jacknotsoquick

[A/B Speedliner]

The points are set at 0.018 then the are set to fire 180 degrees apart which is adjusted by adjusting the second set of points. Once you have the points firing 180 deg apart you set the max timing. There is a difference between the unconverted 20H and the converted engine. Unconverted I believe it is 0.325" BTDC and with the conversion it is recommended by the factory at 0.225" BTDC we have found that 0.265-0.275" BTDC works the best for us.

The K3 was the original plug used with the unconverted engine. We have found J6J plugs work and if you want a plug similar to the K3 there is a L61? plug that works. I am sure there are many people on here the can give you more information.

Where do you have the hi and lo speed needles set? With a prop on the engine is under load so the settings are different.

David

[dwhitford]

All Abspeedliner's info is right.

You carefully set one set of points at 0.018" with a feeler gage. Then you use a dial-indicator gage adapted to a spark-plug "holder" (might be an old spark plug w/ the procelain knocked out and adapted with a set screw to secure the dial indicator) to measure when the points open on the upstroke of the piston to which that set of points apply.

Then you back off the engine rotation so that that cylinder's piston is on the upstroke when you then rotate the crankshaft in the correct (clockwise looking from the top) direction.

You bring the engine rotation to top-dead center (TDC) as indicated by the dial indicator.

You then set the dial indicator's bezel to zero.

Then you back off the crankshaft rotation to whatever the spark advance you want. Use ABspeedliners recomendation because I have no better recomendation.

When some sort of continuity checker -- ohmmeter, flashlight and battery rig, or whatever, attached across your already-set 0.018" points -- indicates when the points exactly open, you're ready for the next step.

Set the engine's piston before-top-dead center (BTDC) at ABspeedliner's recommendation according to the dial indicator.

Rotate the magneto plate until your continuity checker just barely indicates that the points barely open.

Lock the magneto plate down.

Go to the other cylinder. Rotate the crank approx 180 degrees. Set up the dial indicator in the other spark-plug hole. Set the piston at the same BTDC as for the other cylinder. Adjust the points to just break contact according to whatever continuity checker you use. DO NOT WORRY whether the point gaps differ!!! They won't differ much anyway, and you can be sure that doing things my way will give you exactly 180-degree firing and good magneto performance with suitable points, capacitors, & coils.

As for the Carter Model N carbs, a good starting point for the high-speed needle is 1-1/2 turns open from fully shut + 1 turn open on the slow speed. You always want to start rich!

Better is to get the Tillotsen KA carb, which is bigger, faster, and less troublesome once you get it dialed in. It took stock racers in the 1960s awhile to get this KA carb figured out. The previous Carter was impervious to left-hand turns because of its center-mounted float bowl. The Tillotsen KAs that followed had float bowls on the "wrong side of the turning oval". Once the stock racers learned how to adjust mixture to compensate, all was well, and faster, with the Tillotsen.

[ZUL8TR]

All Abspeedliner's info is right.

........................

Go to the other cylinder. Rotate the crank approx 180 degrees. Set up the dial indicator in the other spark-plug hole. Set the piston at the same BTDC as for the other cylinder. Adjust the points to just break contact according to whatever continuity checker you use. DO NOT WORRY whether the point gaps differ!!! They won't differ much anyway, and you can be sure that doing things my way will give you exactly 180-degree firing and good magneto performance with suitable points, capacitors, & coils.

.....................

Clarification:
When going to the other cylinder reset the dial indicator to TDC before rotating the engine backwards (CCW looking from the top) to the same BTDC setting as the 1st cylinder, then set the points to just open at that piston position, this will give the 180 apart for firing.

[rumleyfips]

If the engine would run OK with no load but wouldn't get on plane, I always replaced the condensers. It usually worked.

[kev29p]

Make sure that you aren't trying to run a big 16:21 prop on a 1:1 gearcase.

[jackbquick]

WOW! Thank you all for the quick responses and the valuable insight. I really appreciate it. When I spoke of the engine starting on the cart, I was using the Merc 20H runabout prop so there was some load. When we ran the rpm up, there was good thrust. But no good starts in the tank or on the boat. I had the hi speed at 1 1/4 to 1 1/2 turns with the idle closed at first and then a couple of turns open. I will be going through the engine in the next day or so and will report back. I have good instructors, lets hope I am a good student. I have a KA carb but will try the Carter first. I remeber the Carter seemed to have issue back then. Jack Deck 100S

[Guest]

The Carter is plagued with issues when run on a runabout. There is a service bulletin that helped the float bowl flooding due to the float vibration and movement. If I remember correctly you had to cut off the tangs that held the float needle to the float. I will see if I can find it. I would recommend going straight to the KA-7A and a fuel pump if one isn't installed. A fuel pump with the carter tends to make the float bowl flooding much worse. Having run a B Merc going on 59 years I can relate to your issue. One other way to time the engine is to do it with a dial indicator on each cylinder. Easy way to do it if you don't have an old Mercury degree plate.

Alan

[rumleyfips]

In the 60's and 70's I had help from lots of people regarding Phelon mags. Doug Reed tested coils and condensors with a Mercotronic for me. When I got my own, I learned that they could test OK on Thursday and fail on Friday. Mike Rourke showed me that a meter was more accurate than a buzzer.

Herb Lanfear Sr. saw me watching him one day and told me all about points. They had to be adjusted until they were perfectly parallel. They had to be polished first with 600 paper then white writing paper until you got a mirror finish. I always set them at .017. After doing it 30 or 40 times a years setting them by eye was usually right on with the feeler guage.

I watched Fred Nelson one day and saw that point tension was important. I never found a Mercury point tension guage so I made my own using a spring loaded tire pressure guage. I put a hooked wire on the shaft and calibrated it to 2 pounds. It made a difference.

One Saturday night Mitch Myer told about his phone call to Repco and the importance of air gap between magnets and fields. He glued 2 sheets of writing paper ( .012 ) to the fields then adjusted them until the magnets just started to peel a little bit off. That got you to .010; right where the factory designed it.

Thanks guys. When setup right a Phelon mag worked pretty well.

John

[jeff55v]

All this talk about setting your points exactly 180 degrees apart is great info. But this is N'th degree stuff. None of that will prevent your motor from starting under a load. I wouldn't sweat the points dwell too much 'till you get it running good. If you pull the plugs and ground them against the block with the wires attached, you should be able to pull the motor over and get a strong blue spark. Not a thin blue spark, not a yellow spark, a bold blue spark that you can hear SNAP 20 feet away. I also recommend getting rid of that Carter carb, and putting on a good clean Tillotson with a new float and needle and seat.

[jackbquick]

Thanks for the updated infomation. I remember the Carter as a real pain and could never quite get the bloody thing to work properly. Fortunately, I have a Tillotson KA-7A from David so I will switch to that. It looks like I have to bend the throttle wire into a Z shape to match the wire with the linkage at the top of the carb. It appears to be about 3/4 inch difference unless someone has a better fix. I am not real excited about running with a bent wire. Will report back when I get it going. Jack Deck 100S

[mike mosier]

my recommendations are to take the covers off, put on the conversion recoil brackets. step 2 put on a fuel pump. step 3 ka7a or equivelent carb. step4 replace coils, i use omc coils for a early 70's omc and equivelent condensers, they are cheaper, readily available and have twice the voltage. setting up 180 degree timing is all important for racing and good performance, but not necessary. sounds like you got bad coils and condensers. been there many times. crystal lake next weekend i will be there to try for the turgeon memorial trophy, if i win it will be three in a row! any more questions contact me at duke7n@gmail.com. good luck! 20hs rule