Backfire but wont start - Low Compression?

[Fat fifty hopeful]

Hello,

I found this forum and could use some help. I am in the process of trying to get my newly acquired 1959 Johnson 50hp running. I replaced everything I could and clean out the carb. When I try to start it I am getting backfiring and a tiny sputter intermittently but it will not start and run. The plugs are getting a little wet but some of the piston heads look dry. New plugs, new wires, getting a good spark, gas tank valve is open, choke on/off. fresh gas (albeit not 93). At this point I am beginning to thing it has too low of compression.

Can anyone tell me what the compression should be in each cylinder? I am between 75-81 on all cylinders.

what other reasons could it be not starting?

 

[merkdawg0084]

75-81 that is low in my opinion. I have a 15 hp and I’m getting like 110. Make sure throttle is wide open when you do compression check. Crank it about 6 times or until needle stops..

 

[boobie]

Got a model # ?? Will the spark jump a 1/4 " open air gap on a tester ??

 

[F_R]

I say it should at least start and run with that compression. If it were me, I'd remove the magneto from the motor and go through it completely. Are you up to that task?

 

[boobie]

Could also be a bad distributer cap.

 

[Chris1956]

Your compression is pretty typical for that motor. It sounds like the timing is off.
OK, from memory...turn flywheel until timing mark on it aligns with mark on rear of block and on pull starter. Look at timing mark on distributor pully. It should align with mark on pulley base. If not, pull top of pully off (3 screws) and adjust tooths of timing belt to make it so.

First set of points should be open .020". Turn flywheel until you see second set of points. They should be open a max of .020.

OK, now open throttle until distributor pully timing mark aligns with timing mark on black pully support. At this point, the brass throttle cam should just touch the throttle rubber pully at the timing mark on the cam.

That motor should start easy. I am not sure about initial low carb needles setting. Maybe 1-1/4 turns open?

High speed needles should be 5/8 turn open if memory serves. Maybe someone else knows... You get to adjust high speed needles on the water, under load. It is great fun.

The weak point on that motor is the shift dog and gears in the gearcase. The wear and slip under power. Sounds like a bang every 10 sec.

 

[webbd]

This is off-topic and it won't help you get your motor running, but it might help to keep it running well once you get it running (I suspect ignition timing or carburetors need another round)...

You mentioned good gas, but not 93. Most of the 93 octane gas I have seen is automobile fuel with ethanol. The ethanol in the fuel can wreak havoc with your fuel lines, carburetor parts, etc.

There are gas stations in every state who sell ethanol-free gasoline for carbureted engines. Some are on the water and cater exclusively to boaters and some are on land and also support people with lawn equipment, older cars, etc. Gas with ethanol has a shelf life from the time it's mixed of about 100 days. If it sits, it will separate like vinagrette salad dressing and the water/alcohol mix will be at the bottom of the container, while a lower octane gasoline component will be at the top. Detergents in the fuel like SeaFoam may help to keep everything in suspension longer, but don't address the corrosive nature of the ethanol in the gas. You can also reduce the issues by disconnecting the fuel line and running the engine until dry when you are done with it.

When I lived in Texas and they switched to ethanol in gas back in the late 80's, I started having issues with my lawnmower because the needle and seat would get clogged with an amber ring of crystals that prevented proper gas flow. The mower engine would surge and slow down over and over again, and I'd eventually need to drop the float bowl and clean the needle and seat. Once I learned about ethanol gas and switched to ethanol free, I stopped having those issues.

Look around for somewhere you can fill your cans or tank with ethanol-free. It's likely within 5 miles of where you live, and it will be worth it to you.

-DW

 

[F_R]

boobie wrote: "Could also be the distributor cap" True. Could also be the distributor rotor (they are notorious for arcing through to the shaft). Could also be a cracked coil. Or a coil with a pin hole arc-through to the side to the case (also notorious). And those,, my friends are just a few reasons I suggest removing the magneto and do a thorough diagnosis. By getting it off the engine you can work on it right side up. Furthermore, you can work to get spark from the coil first, then move on to getting it on through the rest of the distributor cap and wires. Your choice, how you want to do it.

 

[racerone]

Some folks are stubborn and would rather use the " crank and hope " method until the starter starts smoking !

 

[ct1762@gmail.com]

opening the throttle has zero effect on compression #'s!

 

[merkdawg0084]

opening the throttle has zero effect on compression #'s!

I beg to differ. Just watched a few videos about compression check with WOT

 

[racerone]

Throttle does not need to be open on these 2 stroke engines !!!----4 strokes then yes throttle needs to be open.

 

[Chris1956]

OK, upon further review, my memory is a bit off. Here is update to post #6

Your compression is pretty typical for that motor. It sounds like the timing is off.
Turn flywheel until timing mark on it aligns with mark on rear of block and on pull starter.

Now open throttle until distributor pulley timing mark aligns with timing mark on black pulley support, and leave it there. At this point, the brass throttle cam should just touch the rubber roller on the carb at the timing mark on the cam. If not adjust stainless arm to make it just touch rubber pulley. Advance throttle and make sure brass throttle cam will open carb all the way. Return throttle to previous position, with distributor support and distributor pulley base aligned.

Look at timing mark on distributor pulley. It should align with mark on pulley base. If not, remove top of pulley (3 screws) and adjust tooths of timing belt to make it so.

You should see points thru hole in pulley. First set of points should be open .020". Turn flywheel about 90* until you see second set of points. They should be open a max of .020.

That motor should start easy. I am not sure about initial low carb needles setting. Maybe 1-1/4 turns open?

High speed needles should be 5/8 turn open if memory serves. Maybe someone else knows... You get to adjust high speed needles on the water, under load. It is great fun.

The weak point on that motor is the shift dog and gears in the gearcase. The wear and slip under power. Sounds like a bang every 10 sec.

You can run that motor on any grade of gasoline with or without alcohol. It is a low compression motor. Run it 24::1 gas:il.

Run Champion J4C spark plugs gapped at .030. If she fouls (probably won't) you can go to J6C spark plugs.

Distributor spun by hand will give a real strong spark, if magneto is operating properly.

 

[racerone]

Fatfifty has not responded for a while.----Hopefully some simple trouble shooting has been done in the last few days.----Those early V-4 model 50's were thirsty.

 

[webbd]

Some folks are stubborn and would rather use the " crank and hope " method until the starter starts smoking !

Guilty!