1971 evinrude 40 hp ski-twin

[DaveN28]

So I finally got this thing running on both cylinders but I still have 2 big issues with it. One being that it only pushes my 1988 alumacraft deep v lunker at about 15mph and correct me if i'm wrong but I think it should push this boat double that speed? The second issue is that I foul plugs like crazy, mainly the top plug. I try adjusting the low speed rich/lean and high speed rich/lean knobs but they don't seem to make a bit of difference in how the engine runs no matter which way I turn them. I checked compression and i'm getting 115 in both cylinders. I checked for a spun prop hub which I found it does not have. Can anyone help figure out why this engine that starts up no problem has good compression has no power?

 

[F_R]

The fact that adjusting the knobs makes no difference indicates that they are not turned in far enough. There is a point somewhere that turning it in will make it quit for lack of fuel. Think of it as a glorified faucet. If you turn it far enough toward "off" the water flow will decrease and will quit flowing completely if you keep turning it. This is further validated by the plug fouling--running too rich.

 

[racerone]

Does the fuel pump run off the top cylinder ??----Checked the diaphragm ??

 

[DaveN28]

The fact that adjusting the knobs makes no difference indicates that they are not turned in far enough. There is a point somewhere that turning it in will make it quit for lack of fuel. Think of it as a glorified faucet. If you turn it far enough toward "off" the water flow will decrease and will quit flowing completely if you keep turning it. This is further validated by the plug fouling--running too rich.

The knobs only turn so far do I have to take the knobs off and turn a screw under there?

 

[DaveN28]

Does the fuel pump run off the top cylinder ??----Checked the diaphragm ??

I will check that and report back. Would a faulty fuel pump be the reason its getting to much fuel and cause it to have no power? Also do you think i should try adjusting the low and high speed needles first?

 

[DaveN28]

Anyone know if i have to take the knobs off the front panel of the carb to adjust the high speed/rich lean settings? Like i said previously with the knobs on they only turn so far and it makes no difference in how the engine runs. Thanks in advance.

 

[Tim Frank]

Yes.
Read the instructions in the top secret files for setting carb.
Also, an OEM manual would help you.

All OMC motors of that vintage that I have worked on require removal of the "knob" to get sufficient adjustment. Then you replace knob when you have the adjustment almost correct.
Think of the knob as fine tuning only. Right now I suspect you are not even on the right channel.

 

[Tim Frank]

Anyone know if i have to take the knobs off the front panel of the carb to adjust the high speed/rich lean settings? Like i said previously with the knobs on they only turn so far and it makes no difference in how the engine runs. Thanks in advance.

Are you sure you have a 1971?
Didn't think they had a HS adjustment.

 

[DaveN28]

yes, 1971 has the high speed adjustment, i went on evinrude parts and looked at diagrams with my serial number to be sure.

 

[DaveN28]

I appreciate you taking the time to confirm what i had to do, Tim. I really appreciate it and can't thank you enough.

 

[Tim Frank]

yes, 1971 has the high speed adjustment, i went on evinrude parts and looked at diagrams with my serial number to be sure.

OK. I learned something today.

 

[DaveN28]

I really hope that is the issue, i wont get the chance to mess with it for a couple days but man would i love to be on the lake doing 30+ instead of 10-15 mph.

 

[lindy46]

Not sure exactly the configuration on that motor, but on older models, I usually turn the knobs around so they don't hit the stops. Once adjusted, I return them to their normal position.

 

[DaveN28]

Correct me if i'm wrong but shouldn't the slightest turn affect the way my outboard runs?

 

[lindy46]

You should notice a change. Close both needles down, then open the slow speed needle 1.5 turns and the high speed needle 3/4 turn. That will be a good starting point. Now adjust the low speed needle at slow speed so it trolls down nicely. Then run the motor at WOT and adjust the high speed needle for optimum RPM/speed. On both needles you should notice a change in the way the motor runs with small tweaks of the needles.

 

[DaveN28]

How is it to take off the knobs? Do they usually break or no?

 

[lindy46]

The slow speed knob can be removed by loosening the screw in the center. It then pulls off. On the high speed, you'll have to remove the remote adjusting rod from the (lower) needle valve arm. Then just adjust by the arm itself. Once optimum, reattach the remote rod/knob in the middle of the adjustable range. You may have to adjust the position of the arm by loosening the center screw to make it align properly.