Poor high-end performance '57 35HP Evinrude Big Twin

[FurFinFeatherFun]

Experiencing poor high speed performance (about 1/2 speed) on my 1957 35HP Evinrude Big Twin. I just replaced both coils, points (set to .020), condensers, plugs J4C (set to .030). I couldn't find new plug wires although the old ones look "sort of" OK. Rebuilt the carb (noticed the high speed needle is blunt and doesn't come to a point like the idle mixture screw). I don't know if that's a concern or not because it looks like it was machined that way and not worn away. I'm running 32:1 gas/oil ratio. It idles and starts well. I get NO control of high speed while adjusting the high-speed needle. It runs the same with the needle completely closed or turned WAY out. The throttle is opening all the way and is not binding, The choke is also open all the way and is not binding. I'm running the old style pressure tank and am thinking about changing to a fuel pump. I'm not sure what pressure the tank is holding but it does hold quite a bit of pressure for a long time (days). I'm also looking for a generator but don't want to dump any more money into it until I get it running well. I already have the wiring for the generator. I just need the generator, belt and possibly mounting bracket. I am also getting either a miss or jumping in and out of gear while running wide open. The engine doesn't appear to rev during the "jumps" so I'm hoping it's just a miss. I'll worry about that more once I get full power restored if it's still there. I checked for play in the shift rod and have NONE. I have the 2 piece rod with the "inspection window". Compression in both cylinders is almost right on at 120psi each. Fuel filter is clean. I also checked synchronization and it appears to be right on. The pointer on the manifold is right on the flywheel mark just as the throttle begins to move. When I first ran it about a year ago I had full throttle and it ran great for about 15 minutes. It then bogged down and I haven't been able to get the power back since then. I also replaced the water pump before my first run, just as a precaution, and I get loads of water out the exhaust. The water pump was the only maintenance performed prior to my first run. All other parts were replaced after I lost power. Inspection of the plugs on several occasions shows a rich mixture. They are wet and dark but have no fouling deposits. I haven't inspected the reed valves and I'm not sure if that would affect high speed performance only or not. I guess my root questions are:<br />1). Should the high-speed needle be blunt or pointed? If pointed, where can I get a new one?<br />2). Could the pressure tank be holding too much pressure and could it cause the engine to run rich?<br />3). Where can I get a generator (once the engine runs well)?<br />4). Would it be worth replacing the pressure tank with a fuel pump and if so, where can I get a conversion kit i.e. new tank & pump?<br />5). Where can I get plug wires? I tried a few dealers & none of them have them.<br />6). Could the reed valves cause poor high speed performance even though the engine starts & idles fine?

 

[DSL DOC]

Re: Poor high-end performance '57 35HP Evinrude Big Twin

EXCELENT POST i have a 62 big twin 40 and am waiting on some follow ups to this good info way to explain yourself

 

[Chinewalker]

Re: Poor high-end performance '57 35HP Evinrude Big Twin

Hi,<br /> 1. Yes - high speed is supposed to be relatively blunt on the Big-Twins.<br /> 2. Tank holding too much pressure - not an issue unless the float needle is questionable in the carb in which case the motor could be pre-flooded by gas expansion in the sun, etc. Simple cure - release tank pressure when done running at the end of the day. If you're tank is holding pressure, you're good to go.<br /> 3. I would skip the generator route. They're heavy, rob you of power, and aren't all that reliable - belts alone retail for big bucks - if you can find them. Better solution - get a solar trickle charger to keep the battery topped off, or get another battery and keep one fully charged in reserve. You can go a long time on one battery if all you're doing is starting the motor and occasionally using the lights.<br /> 4. If you want to update the fuel system (not necessary since the dual line tank seems fine) you can rob the associated fuel pump, intake port cover, etc. off a later model 28/33/35/40hp. Be sure to block off the pressure feet nub on the intake manifold.<br /> 5. You need 7mm metallic core plug wire - available at dealers, NAPA, etc. by the foot. If you can't find it there, I have it available by the foot.<br /> 6. Reeds are only an issue if they're broken or bent. If you're getting blow-back out the front of the carb while the engine is running, the reeds may be an issue.<br /> 7. The "jumping" may be as simple as a slightly lean condition on the carb, or as serious as a worn clutch-dog. If it sounds like a sneeze in the engine itself - think carb. If it feels like you hit something submerged, think clutch-dog....<br />- Scott

 

[Yepblaze]

Re: Poor high-end performance '57 35HP Evinrude Big Twin

Make sure the roller that operates the throttle butterfly is not severely worn. Just make sure it starts to hit at the little mark and manages to open the throttle plate fully.<br /><br />On many of those old OMC's you will find the adjustment knob is held to the shaft with a screw and taper arangement and on some the full needed range of adjustment can't be made till you loosen the screw and adjust the knob to the shaft acordingly.<br /><br />How much power do you expect to get from the old girl?

 

[FurFinFeatherFun]

Re: Poor high-end performance '57 35HP Evinrude Big Twin

Yepblaze, thanks for the reply. My roller does have a noticeable groove in it but it appears as though the throttle starts to move at the mark and it does open fully. In response to your question: As previously stated It was running GREAT for the 1st 15 minutes on my 1st run then bogged down. I have a brother-in-law with a similar boat which we put my 10HP Mercury on. We were running at about the same speed wide open. I would expect to get the performance I first experienced which is what I would expect the motor to be capable of producing. If I were to guess at the speed I would estimate about 25-30 MPH. My boat is a 14' Duracraft fiberglass v-hull.

 

[FurFinFeatherFun]

Re: Poor high-end performance '57 35HP Evinrude Big Twin

Chinewalker, thanks for the reply. In response to your suggestions: Thanks for informing me about the high speed needle being blunt. It's not squared off and there is a bit of a taper on the end. I didn't know if it was seriously worn away although it looked as though it was machined that way. From your description it appears that it's probably OK. I'm reconsidering the generator. I didn't think it would be such a power drain and thought they were reliable. I replaced the carb's needle & seat when I rebuilt it so I don't think I'm getting any flooding condition from wear I just thought that if there was too much fuel pressure it could force the needle to open causing the flooding condition. I'm pretty sure I'm running rich as opposed to lean since my plug inspections revealed a dark wet condition. The "jump" I'm experiencing is the "feels like I hit something" kind of thump so I guess I might be opening up the lower end and inspecting it before long. I still have my fingers crossed for the "miss" scenario but I think I'm being overly optimistic. Can you give me your price on the plug wires? I'm hoping that they might be shorting out somewhere as there are several hold-down locations which are suspect. It would be nice if it was just a spark leak but I wouldn't be willing to bet on it. Lastly thanks for the reed info. I didn't think they could cause a "high speed only" problem and from your response you just confirmed that.