1959 Evinrude Lark 35hp Backfire

showngo2000

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I'm in the process of reviving a 59 Evinrude 35hp (35516). The motor has been sitting for quite some time, so I read the "awake a sleeping outboard" thread to get going. Here's what I've done:

* Let the engine sit for 24hrs with a little bit of 2 stroke oil in the cylinder head, while sitting with the spark plug holes straight up.
* Compression - 90PSI on both cylinders, a little low, but granted it has been sitting for a while
* New Coils, Condensors, Points (gapped at .020), Spark Plug wires (7mm copper core), Spark Plugs (JC6 gapped to .030)...have spark verified with tester
* Carb Clean - disassembled and cleaned.
* New fuel lines everywhere


The engine tries to start, and then backfires super loud, with some smoke coming out of the exhaust. It sounds like it is trying to run, but backfires after about 10 seconds of cranking with the starter. What would cause this? I've torn the flywheel off again, and verified that everything is ok, including the crankshaft key, nothing is rubbing/out of the ordinary, and re-torqued the flywheel to 720in torque. It still backfires.

Help! Thanks!
 

showngo2000

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Don't think so. I actually tried reversing them, and the backfire grew louder/bigger!
 

oldboat1

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carb needles set? initial setting (idle) about 1 to 1/2 open, high speed (lower needle) 1/2 to 3/4 open.

wire tucked in? (not striking flywheel).
 

showngo2000

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Thanks, oldboat. Would the carb needles make it backfire like that? Sorry, I'm new here. Is there a place that I could look to adjust those?

The wires are tucked in, and not touching the flywheel. Checked the coil wires, condensor wires, points wires, and spark wires.
 

oldboat1

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can be a lean sneeze (needle setting slightly lean). I'm pretty sure there are instructions in the stickies up at the top of the forum, but those initial settings are from lightly seated. Open counter clockwise (richer). Initial setting should allow you to start and run engine, then make finer adjustments in gear after warm up. Need some back pressure for carb settings (in a barrel or in the lake -- latter is preferable). High speed final setting is made at or near WOT on the lake.
 

showngo2000

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A lean sneeze...never heard of that. I guess that's similar to a backfire? Would that cause the engine not to start at all?
 

oldboat1

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sounds like a backfire (call it a light backfire or cough). It's a lack of fuel, and that could cause the engine not to start. Think most people say something like "wants to start, but won't quite catch". The needles adjust the air/fuel mix -- lean means more air than fuel, on balance.
 

showngo2000

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All of the adjustment how-to's talk about starting the engine first. Is it just a guessing game adjusting them without the engine being able to start and run?

(I'm looking at the 'How Do I adjust my carbs?' article at the top of the forum.)
 

oldboat1

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Need the initial setting just to get the engine to start and run (that part isn't very experimental, although engines and condition can vary some). Once the engine is running, you tweak the settings -- that's the fine tuning that is experimental (but some history to go by). My vintage 35s usually ended up with the idle needle at maybe 3/4 open, and the high speed needle at a little better than a half turn open. But you have to get there by trial and error.

With the engine warmed up and idling in gear, I start by leaning the idle mix 1/8 turn at a time (clockwise) until the engine "lean sneezes" or stalls, then open it about 1/4 turn. That often turns out to be close to the right setting. As you lean the mix, rpms will increase. Throttle the engine down to a comfortable idle (600 to 700 rpms), and continue with adjustments. You also want to be sure the engine goes into gear without stumbling or stalling at idle. If it stalls, you probably need to adjust slightly richer.

Don't confuse throttle settings with air/fuel carb mix settings, or fuel to oil ratios used in filling the tank (24:1, btw, for your '59).
 

showngo2000

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Sorry for the ignorance...are you talking about the knobs on the front of the carb with labels on them?
 
Last edited:

III_Hammer_III

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Just to keep the overview: To be sure no fuel is entering the cilinders, open a spark plug and sniff. Or if the plug stays dry after long attempts: no fuel. You can also hold the palm of your hand close to the hole, someone start engine and some fuel spray should hit your hand.

Fuel obstruction can be found here (in order of line up from source to cilinders);
1. Fuel tank not ventilated
2. Fuel connectors jammed, leaking or wrong connectors
3. No original OMC hose and connectors (fuel + air)
4. Fuel filter dirty
5. Fuel pump dirty or out of order
6. Hoses from tank up to the carburator jammed at some point
7. Carburetor inside
-needle stuck (floater)
-jets dirty
-broken gaskets
-residu jamming circuits
8. Carburetor adjustment
-wrong mixture (what oldboat explained, and indeed those are the knobs in front of the carb)
 

lindy46

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Your description sounds like a backfire, not a lean sneeze. Make sure front coil wire is going to top cylinder and that coil wires are connected to the right set of points (coil wire should be connected to point set to its' right). Flywheel key in place and not sheared? And flywheel properly torqued?
 

showngo2000

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Thanks everyone. The explosion is every definition of a backfire that I know of. Loud pop, with fire out of the exhaust port. I'll re-check everything this evening and try to take a video of what's going on. So a backfire would definitively relate to ignition problems? There's no valves or anything that could be stuck open/closed, right? Remember the motor has been sitting a while.
 

F_R

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Too Much fuel can supply more than the burnable fuel/air ratio. Then all that fuel goes out into the exhaust housing. Then a spark/almost ignition can set fire to all that fuel lurking in the exhaust housing. BAM--a loud backfire.
 

showngo2000

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Too Much fuel can supply more than the burnable fuel/air ratio. Then all that fuel goes out into the exhaust housing. Then a spark/almost ignition can set fire to all that fuel lurking in the exhaust housing. BAM--a loud backfire.

So...carb needle adjustments?
 

F_R

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Yes, or over-choking, or manually squirting gas in the cylinders. Or no (or weak) spark to ignite it.
 

showngo2000

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Ok, so I made some progress!

--Took the flywheel off (AGAIN!) and re-inspected everything, buckled it all up, and torqued the flywheel down.
--Tested the spark, and have a bright blue snap on both cylinders jumping 1/4" with the tester.
--Adjusted carb needles to the "initial settings" in the Carb article in "Top Secret file".

The low speed carb need looks like it may be missing some rubber piece on it. Will that affect the motor running?


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The engine is trying to start, and not backfiring anymore! I've attached a video of what's it's doing now. It will kick, but won't run or attempt to stay running. Any ideas? Fuel problems? I'm getting fuel to the carb with the primer bulb.


Here's a quick video of it trying to start now:
 

oldboat1

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Close! When it wants to run, try pumping the primer bulb a bit and see if that keeps it going. I'm not sure if it's running long enough to empty the bowl, but might be. Squeezing the bulb will test the fuel pump -- if squeezing the bulb keeps it going, it's likely the fuel pump diaphragm.
 

showngo2000

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Thanks for the help, oldboat. I'll give that a shot tomorrow evening. Is there anything that I can check visually on the fuel pump? What if it's not emptying the bowl?
 
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