1978 55HP (55EL78S) Throttle linkage setup

Hi all,

Hope someone can help. Does anyone have a detailed guide on how to correctly setup the throttle linkages? I have both the service manual and the clymer manuals but none tell me the initial length of this rod or how to set the initial timing position on the adjustment screw.

The engine i got second hand and someone had already been in there and tampered with things and im trying to put it all right but just cant work out how to set the length of this correctly as the guides just say setup the carb end.

Thanks,

Mat

If you're speaking of setting the "Idle Timing" and the "Link & Synchronization".... What "Degree Setting" does your manual state?

Setting the length of this rod??... I assume you're speaking of the horizontal rod leading from the vertical throttle arm to the metal cam that slides against the throttle roller?

That is exactly the rod I want to set!

Manual says "timing at WOT 19 Deg" pickup C note 4

Note 4 and the related procedure just says how to set the cam roller. Not where the initial length of the rod is to be set to even start the thing.

The other manual says the same but gives a idle timing setting

Throttle pickup degrees BTDC 3 degrees

So while I get that, and I can see the screw on the arm sets the base timing, how do I adjust the idle speed without moving the timing, do I adjust that linkage to do that?

Sorry for all the questions the original guide is not very clear at all and the aftermarket one kinda makes sense but very little pictures on where to make the adjustments.

The "Idle Timing" is what is needed. I checked my books... it is indeed 3 degrees +/- 1 degree so you're okay anywhere between 2 to 4 degrees, however 3 degrees would be perfect.

Don't mess with the WOT Full Spark advance unless absolutely necessary.
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1 - loosen the set screw of the throttle roller so that the roller is NOT touching anything.

2 - Adjust the linkages between the carburetors so that the throttle butterflies open and shut at the same time. You do not want one butterfly shut and one ever so slightly open!

3 - Now, adjust the throttle cam roller so that the throttle butterflies just start to open when the scribe mark on the cam is dead centered with the throttle roller... and lock the roller set screw to hold that setting.

4 - And finally.... Attach a timing light to the top (#1) cylinder spark plug wire and set the timing as close to that 3 degree mark on the flywheel as possible.

It is at that 3 degree setting where the scribe mark on the cam should be aligned with the center of the throttle roller. If it is not, then adjust that threaded nylon connector one way or the other as needed.

The rod is at its proper length when:
1 - The idle timing is at 3 degrees.
2 - The cam scribe mark is dead center on the roller.

That's it... Let us know how you make out.

Thanks I will give that a go tomorrow when i pop down to the boat. I assume then that the screw on the arm adjusts the timing, and the rod adjusts the cam position. and there is no idle speed adjustment screw at all? like the mixture etc thats all fixed?

mlevett said:

(1) I assume then that the screw on the arm adjusts the timing..... (2) and the rod adjusts the cam position..... (3) and there is no idle speed adjustment screw at all?..... (3a) - like the mixture etc that's all fixed?

Click to expand...

1 - The screw on the vertical throttle arm is simply a "Stop Screw" to be set when you have the idle exactly where you want it.... It's purpose is simply to prevent the idle from dropping lower due to vibration etc. Bests to back it out so it doesn't touch anything, then when all is well and the idle is favorable, simply screw it in until it touches it's stop. It has nothing to do with the timing.

2 - The length of that horizontal rod adjusts the "Idle Timing"... and the distance of the cam from the vertical throttle arm.

3 - The fuel flow of the carburetors is governed by brass fixed jets. No adjustments as far as combining fuel w/air.

3a - The idle rpm itself is adjusted via the threaded trunion you see clamped in to the hood pan area. When you have the idle rpm where you want it, adjust the idle stop screw as in Step #1 above.
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FYI............. On a flushette, the idle on the various length shaft engines should be set to:

20" shaft - 1000 rpm
25" shaft - 1200 rpm

In the water, the idle rpm will drop to normal.
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Thanks for the help so far. however ive hit more issues today. so I used your guide to set the max advance on starter to 15deg which is 4 less then the 19 it should be. The end stop i had to wind out a lot to get it to this point. it was screwed in quite a bit and over advanced.

I then moved the vertical lever all the way back to its stop and checked the timing. i used the stop screw to get 3 degrees at this point.

Lastly i did the sync and link. and set the cam roller to the middle of the mark.

Now it starts and runs but bady with surging, i.e. if feels like a misfire, then will kick almost like a the second cyl has kicked in and as if you cracked the throttle open, then it splutters and drops back. also in this configuration i cant get full open on the carbs, it hits the stop (the small one by the spring pivot) on the vertical arm even with this screwed all the way in. if i adjust the nylon link so i can, then i cant get the marks to line up or it puts the two timing points back out again.

Does this stop look right? (carbs removed as i want to clean them again) https://chimera-labs.com/IMG_20190924_171757.jpg


Im sure ive messed something up. it also only want to start and kinda idle with the timing in the advanced stop.