boat takes a long time to plane out

[1970kayhydro]

i have a 11' hydroplane with a 1971 40hp johnson long shaft. the motor starts up and sounds as if it is reving up when i tank test it but when i take it to the river it does not want to rev and takes a long time to plane. after it does plane it starts getting short burst of power. i was told it needs to have a short shaft motor would that cause this? i have a carb rebuild kit on the way but i checked and it apears to be clean. what should the needle valves be set at?

 

[tashasdaddy]

Re: boat takes a long time to plane out

you have more drag with the long shaft, as you have more motor in the water. dirty carbs, spark just on one plug, weak fuel pump, compression, could all be part or all of the problem. start with spark and compression check both cylinders.

(Carburetor Adjustments - Two Adjustable N/Vs)
(J. Reeves)

Initial settings are: Bottom high speed = seat gently, then open 1 turn out. Top slow speed = seat gently, then open 1-1/2 turns.

Setting the high and low needle valves properly:

NOTE: For engines that DO NOT have a shift selection, obviously there is no NEUTRAL position. Simply lower the rpms to the lowest setting to obtain the low speed needle va /lve adjustment.

(High Speed) Start engine (it will run pretty rough), shift into forward gear, take up to full throttle. In segments of 1/8 turn, wating for the engine to respond between turns, start turning in the bottom high speed needle valve. You'll reach a point whereas the engine will either start to die out or spit back (sounds like a mild backfire). At that point, back out the needle valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest setting.

(Low Speed) Slow the engine down to where it just stays running. Shift into neutral. Again in segments of 1/8 turns, start to turn the top needle valve in. Wait a few seconds for the engine to respond. As you turn the valve in, the rpms will increase. Lower the rpms again to where the engine will just stay running. Eventually you'll hit the point where the engine wants to die out or it will spit back. Again, at that point, back out the valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest slow speed setting.

When you have finished the above adjustments, you will have no reason to move them again unless the carburetor fouls/gums up from sitting, in which case you would be required to remove, clean, and rebuild the carburetor anyway.

 

[1970kayhydro]

Re: boat takes a long time to plane out

I have checked and i am getting spark on both cylinders. The prop is about 13 inches below the bottom of the boat. What is need to short shaft the motor? I will check the compression, what should it be?

 

[ezeke]

Re: boat takes a long time to plane out

The horizontal plate just above the propeller should be even with the bottom of the boat and should be parallel to the water when at WOT.

 

[Chinewalker]

Re: boat takes a long time to plane out

Not only do you need a short shaft, there's a good chance you can jack the motor up even higher than "short" on a small hydroplane. We ran our 1956 Johnson 30hp (similar lower unit to your 40) at about 19-inches on the transom of our old Sid Craft racing utility. It was a short shaft motor and we raised it further with a motor bracket. We ran a 2-blade Michigan racing prop on it which threw plenty of water into the water intake.

To go to a short shaft, you would need to take out the 5-inch extension housing, find a short shaft driveshaft, either take out the 5-inch shift rod extension or cut down the shift rod exactly 5-inches, and take out the water tube extension.

- Scott

 

[1970kayhydro]

Re: boat takes a long time to plane out

I have looked at every 40hp for the year of 71 on the evenrude/johnson website and there all the same part for the drive shaft, how could i find a short drive shaft? the transom really doesn't alow to move the motor up any. Could timming be part of my problem? The motor was in parts when i got it, i used the repair book and put it back together so im not sure if the timming is set or if it can be set. Iv'e had this boat for 7 years and never got around to putting it in the water till this year.

 

[ezeke]

Re: boat takes a long time to plane out

Look near the end of the parts list and you will find the long driveshaft part number. The first listing at the beginning of the list is short or "standard".

You would be money in to find a complete standard gearcase; Try Ebay, Craigs List and the salvage yards.

 

[1970kayhydro]

Re: boat takes a long time to plane out

I did find the long at the bottom of the parts list and its 5" longer than the standard at the top, Thank you. Are the gear boxes different?

 

[ezeke]

Re: boat takes a long time to plane out

The gearcases are the same. The difference is the driveshaft and the lower section of the shift rod.

The rest of the difference is in the 5" kit and the connecting parts shown in the upper right hand corner of the gearcase diagram.

 

[1970kayhydro]

Re: boat takes a long time to plane out

What parts would i need besides the drive shaft?

 

[ezeke]

Re: boat takes a long time to plane out

As Chinewalker said, you have to either replace the lower section of the shift rod or cut it down. Replacement requires disassembly of the gearcase.

 

[Chinewalker]

Re: boat takes a long time to plane out

If the shift rod needs to be cut, you need to take out EXACTLY 5-inches. Then you can dress the tip to match the tip of the section you cut off so it engages the bolt in the shift rod coupling. If the motor came as a long shaft, it probably has the long shift rod. If it was converted to a long shaft, it probably has the 5-inch brass extension.

- Scott

 

[TN-25]

Re: boat takes a long time to plane out

What parts would i need besides the drive shaft?

Well, your shift rod & water tube will need to be shorter versions than what you have now. On the port side of the midsection there is an oval access cover held on with 2 screws. You will need to remove that in order to access the brass joiner, a device that joins the upper shift rod to the lower one.

Shown below is a longshaft 1971 Johnson 40 (from the brochure), and beside it a 1970 Johnson 33 shortshaft (courtesy of e-Bay). The external differences between a long and short shaft are obvious once you know what to look for.