Throttle Cam Adjustment

[StickyWidget]

1976 75HP Evinrude

My understanding is the throttle cam rod should be 4 31/32 inches from the "end of the rod to the face of the yoke"IMG-20120617-00168.jpgIMG-20120617-00169.jpg

Is that measurement from the farthest left side of the rod in the second picture?

It doesn't appear to be the correct length unless you are measuring from the center of the rod as it goes into the bracket.

It also doesn't appear as though its length has been adjusted judging by the weathering, if you look at the adjustable end of the rod.

Does the length of the rod look long?


The roller is supposed to make contact with the cam exactly at the lower short mark.

IMG-20120617-00170.jpgIMG-20120617-00171.jpg

The first picture is in idle with the gear in neutral. The second picture shows where it currently comes into contact well above the lower mark.

The engine will idle fine. If you gradually increase throttle it will die. If you go from idle to WOT in one motion it will run at WOT fine.

If I move the roller lower towards first contact at the mark the engine won't get to WOT before dying no matter if its gradual or fast.

My guess is the rod is too long, which in turn effects how soon the throttle plates are open. And lowering the roller means that the throttle plates are opening too early and flooding the engine.

I am hesitant to adjust the rod length if it appears it hasn't been adjusted ad the 4 and 31/32 comes from a Clymer's manual so I somewhat doubt it's accuracy.

Should I shorten the rod and see if I can then adjust the roller lower?

[schematic]

The rod length is determined by what is known as "pickup timing". Ignition Timing should be TDC when the cam contacts the roller. If is is not....then adjust the rod length. Also, be sure you adjust the roller to contact the cam at the lower mark. This is adjusted by loosening the screw on the roller bracket on the throttle shaft. If you are stalling just off idle, you may need a carb clean.

[StickyWidget]

Can this only be adjusted with a timing light?

[schematic]

Yes, you need a timing light to set pickup and max timing. You should get a manual if you aren't familiar with the procedure.

[StickyWidget]

Does the ignition fire at TDC when the timer base touches the rubber stop?

[schematic]

When it hits the stopper, its at maximum timing.

[StickyWidget]

So after reading up a bit if I have it correctly the timing pointer should be hitting TDC at exactly the same time as the cam and roller meet, then as the throttle lever is moved forward it will adjust towards the maximum timing at which point it hits the rubber stop.

I know that my engine should be at 16 BTDC at full advance, Does that mean that when the engine is at idle it is at some degree ATDC?

[Haffiman]

It might be. Timing at idle will depend on how far you need to advance it to obtain the idle speed when engine in forward gear and boat moving freely. Low pitch prop most likely ATDC, and high pitch prop that gives more resistance, probably BTDC. Even water level on leg (back pressure) may be part of the play.

[StickyWidget]

So if it was the case that at idle the spark was ATDC, wouldn't that mean that the cam and roller would have already made contact? And isn't the idle specifically not supposed to use the throttle plates?

[Haffiman]

The key settings in your case is 'Pick Up Timing': When cam starts to open the carbs (hits the roller).
Max Timing: Timing at full throttle.
At idle, you may end up with the roller not hitting the cam at all, which may give an ATDC timing.
On your pic above, setting might not be correct. The roller should be at the Start mark when idle lever in remote is lifted(warm up) and the pick-up point is at the smaller mark before START.

[StickyWidget]

My manual states pickup timing should be TDC, so that means that any contact point on the cam is going to be BTDC and when the two are not touching which should be at idle an ATDC reading, correct?

Sorry to beat this to death but I have never adjusted timing on anything and don't want to screw it up.

As it is the engine will idle and go to WOT but usually only if you move quickly from one to the other, if you move the throttle slowly it dies. I am sure that its all these adjustments that are not quite right that is screwing it up somewhere.

But I don't have a timing light or tach so I have been just making minor adjustments here and there, but it's not getting me anywhere.

It just seems that if it will idle and go WOT that it can't be that screwed up, don't really like the idea of buying a timing light for this one use, but looks like I am going to have to.

[Haffiman]

Without a timing light, you might as well lean back in a rocking chair and start knitting, that might save the engine at least. Get it wrong and you may start burning pistons which costs a lot more than a timing light.

[StickyWidget]

So I bought a timing light and made sure that the ignition was at TDC when the roller and cam meet.
I can still achieve WOT if I mash it in. But a gradual increase will kill the engine.

Any other ideas on what might be causing this?

[retiredfornow]

Go to the "Top Secret" file at the top of this forum and read up on Joe's timing thread. I think it will help.
It's called "TIMING Johnson Evinrude Carbed motors". It worked for me. Good luck.

[Haffiman]

What is happening is that the engine does not het fuel.
The reason might be multiple.
-Too heavy prop, engine does not reach max recommended RPM. (Like starting your car in 5th gear on a manual stick shift).
-Synchronization is not correct. Timing - carb opening, carb synch.
-One or more carbs does not work properly.
-Gasket air leak in the intake system.
-Blow-back due to faulty reeds.
Just to mention a few.

[StickyWidget]

What is happening is that the engine does not het fuel.
The reason might be multiple.
-Too heavy prop, engine does not reach max recommended RPM. (Like starting your car in 5th gear on a manual stick shift).
-Synchronization is not correct. Timing - carb opening, carb synch.
-One or more carbs does not work properly.
-Gasket air leak in the intake system.
-Blow-back due to faulty reeds.
Just to mention a few.

I reached 5400 RPM at WOT, the recommended RPM is 5500. Close enough?

As best as I can tell the link and sync is correct, valves are closed and tightened together, roller hits cam at TDC, Goes in gear then timer base starts it's movement followed by carb opening.

Admittedly I have not actually rebuilt the carbs, I will do that when I get the parts. But I have cleaned them with carb cleaner and blown compressed air in about every hole on them. I looked through all the high speed and low speed jets and they do not appear obstructed anywhere. Knowing my luck it's in one of those internal passages that you have to pull the plugs off to get to.

If I spray carb cleaner at the gasket surfaces behind the carbs that would tell me if there was an air leak correct? Is there another spot besides just behind the carbs I need to focus on?

ls there anything I can do to test the reeds?

Is there a way to tell at which point you transfer from the low speed to high speed jets?

[Haffiman]

Those carbs are rather sensitive.
Float hight must be correct.
The small center gasket (0343512) must be replaced almost every time the carb is assembled. (Order some extra!!)
The 3 plugs in the front cover must be in place and gaskets sealing properly to obtain a maximum 'vacuum' in the intake box to assist the carbs to start the main circuit.
The opening of the carbs must be in 100% synch, and sometimes might be an advantage delaying the carb opening a couple of degrees from the TDC. (let the carbs open at 2BTDC)
All settings given by the manual is for a 'new' engine and with tear and wear some tolerances will have to be used.

[StickyWidget]

So I sprayed carb cleaner on all the joints I could find and did not notice any engine rpm change at all.
What 3 plugs in the front cover are you referring to?

In a prior response you had stated that the engine isn't getting enough fuel. Wouldn't delaying the carb opening only make the engine get less fuel?

If I just tap the key in (Choke), and then push the throttle wide open it will go WOT and stay running, anything short of that and it will die.

[Haffiman]

That the engine picks up, and carbs 'starts' by bumping the choke, indicates a lack of vacuum in the carb throats.
By slightly 'delay' the pick-up, the engine will slightly increase the revs by timing advance, the vacuume will increase hopefully enough to start the carbs.
Somewhere air is leaking in, might be butterfly shafts or other 'wear', might be low float settings.

[StickyWidget]

What about the 3 plugs in the front cover you mentioned?

[Haffiman]

They do not seem to have a part number, but visible in the cover #41:
http://www.marineengine.com/parts/jo...ntake+Manifold

[StickyWidget]

IMG-20120628-00214.jpg

If you are talking about the 3 circles that run vertically up the cover, those are not holes, it is only a raised area on the casting of the front cover.

[Haffiman]

Then ok, in most cases they are holes covered with a plastic plug. Used when fogging down the engine, but they often goes missing!