air cover on ’68 Johnson 20hp – needed?

[johnyrude200]

Working on the same motor I posted about yesterday –

Doesn’t have the air cover that goes on front of the carb. I was wondering if this would cause the ‘too lean, yet blubbering’ condition some of these motors show in the early 70’s era. I don’t see a fuel recirculator hose on this motor, but to make it idle correctly I have to set the carb rich – then it blubbers like hell above idle. Lean it out to 1 turn and it runs great at mid to high range, but stalls at low RPM.

I am going through the usual stuff on the carb to try and detect any air leaks, but figured I’d ask if the lack of air cover somehow helps meter the air/fuel mixture. It doesn’t really seem to restrict much air given how big the gaps are around it (as in, basically 360° air gaps), so wanted to ask the panel.

[frankr]

That’s a real good question. I’d say it probably does make some effect, but hard to predict how much. Of course it doesn’t really restrict the air, but it does affect the sound waves, which in turn affects the air flow. It is there to act as a silencer. As for your blubbering problem, is the carburetor throttle pickup right on the money?

[johnyrude200]

It looks to be set right. Im going to pull the carb to check for filth. Are the ’68 models known for blubbering?

[frankr]

Well, that was the year they removed part of the crankcase drainage system, and in my opinion they didn’t run as well as previous years. But they ran better than later years when they managed to improve it so much they screwed it up good.

BTW, your motor is supposed to have a drain hose leading from the intake manifold to the lower, front bolt/nipple on the lower bypass cover.

[johnyrude200]

I pulled the carb, seemed pretty clean but gave it the once over since it was apart. I did replace the boss gasket and low-speed packings and slightly changed the pickup on the follower/timing cam. I was able to get it down another 1/4 turn on the needle and it seems to run a little better at mid range, then clear out after 5-10 seconds at 3/4 throttle. Motor is running cold though, despite a new impeller and new thermostat and a thorough cleanout.

This motor does not have a drain hose from the manifold to the lower intake bypass cover. It is a 1968 model, unless someone switched powerheads at some point (I don’t think so, I am pretty sure I am the 2nd owner, and no evidence of mis-match stuff). I might be splitting hairs here but it evens out when making adjustments to the carb when running cold, so I think it is good ‘nuf.

Perhaps the water restrictor has crapped out on this one too. I seem to have luck getting motors of this era that like to run cold after I make the cooling system work properly again (less, the water restrictor). Fortunately most of the people who are buying the budget motors are those with jon boats or 14 foot aluminums who just want to push a crew 4 (well 5, if you could the cooler full of beers) and troll all day long with a light motor. They aren’t the types that are fishing in freezing cold weather…

[fleetwin]

OK, well I am not quite sure what the correct initial needle adjustment is supposed to be for a 68 20hp. I am "assuming" it is 1.5 turns, but need confirmation. So, how far out is your needle set when it idles OK? When you say the engine blubbers at midrange, again I am assuming it is running rich/rough, not sneezing. Are you sure you have the carb pick up set properly? Perhaps try advancing the pick up just slightly to see if that helps, but the throttle plate MUST be completely closed at idle.
The air silencer wouldn’t have much of an effect at dead idle, but it sure could have an effect at midrange. So, I would reinstall it and try again before going much further (sorry should have suggested this first).
But again, these engines are surely cold blooded, so they are bound to idle poorly and not warm up sufficiently in the cold weather we are still having. You might try plugging the water bypass around the thermostat temporarily to see if the helps idle performance in the cold weather. If so, the engine will probably idle OK in normal summer temps, and you can remove the temporary bypass plug.

[johnyrude200]

At idle, it needed 1.25 turns out to 1.5 turns. The initial calibration settings call for 1 turn out, which it runs great at from mid to top end. But at idle, it stalls out and spits back. Basically adjusting the carb back and forth has it running really well (no air cover). Makes sense about more air at mid to high range having affect with the air cover. This very well could have to do with the cold running condition (I think the highest it reached was about 115-120° even at mid throttle).

The timing was set as far out as it could on the follower cam and the pickup was basically between the two setting marks. What I have noticed is the linkages on these motors are pretty sloppy; even with tight brass fittings and metal linkages (the ones that basically look like bent fence wire), there is some play. It is not only at the linkages, but also at the throttle assembly articulation which connects to the stator arm (the one that is brass, which rotates the magneto plate). I also notice on these 20hp motors that follower cam really doesn’t do much in terms of opening up the carb flap until the top end, I saw basically no opening of the carb flap for at least 1/2 of the time the follower was rolling on the cam.

I think it’s splitting hairs at this point, because with this much ‘slop,’ there’s only so much that can be done IMO.

[fleetwin]

You are correct, trying to do a perfect job with sloppy linkage can be a waste of time. But, you can usually "adjust out" the slop by advancing the pick up a little bit. In other words, you may see the carb linkage starting to move before the cam line bisects the roller, but the carb isn’t actually starting to open until the cam bisects the roller.
I don’t ever remember hearing of an older engine like yours with an intial setting of 1 turn out, but sure could be mistaken. What manual are you using? And yes, some of those throttle cams are very strange, very little throttle opening until almost the end of travel. 115-120F is plenty warm enough for this engine to run normally, so I would ignore my advice about plugging up the thermostat bypass in the head.

[enrico-italy]

The 1964-1977 Fastw in/sportster have only a sound screen, no air box, so it is totally uninfluent on carb setting.

It is needed to support the choke knob and the low mixture arm: You can use also the 1977-79 and 1983 metal bracket of the bigger 25/35. It fits perfeclty on johnsons but in "arrow shaped" Evinrudes.

[fleetwin]

Well, most likely not, but it may have a slight effect on off idle running quality. And, it might affect fuel air flow at high speeds as well. So, I thought it best to try running the engine with the screen/baffle installed to make sure it is not an issue.

[Author]

Posts