1976 Johnson 70 hp wont come up on plane

[alangore]

I have a 1976 70hp Johnson on a 15 1/2' VIP fish and ski. I revs well beyond 2500 rpm in neutral. When Im under load it will not rev up and even stalls out while trying to plane. Will not go at all. I have replaced the CDI unit and the carbs are very clean. I have not yet replaced the plugs, but when I pulled them yesterday about 2 hours after being off the water they were still wet. Could the incorrect oil/fuel mixture cause this, and also would a low charging voltage cause it? I checked the charging voltage and only have battery voltage at the battery. I am an auto tech by trade, so this is somewhat new to me. thanks in advance for any assistance

 

[racerone]

The ignition system does NOT USE BATTERY VOLTAGE to make the spark.-------------Did you remove the high speed jets found horizontally in the carburetor bowls.-----Do you have spark that jumps a gap of 7/16" on each lead.-----Reving the motor in neutral proves nothing as it will do that running on 2 cylinders.

 

[alangore]

It has been about 6 months since I had carbs apart. I will check those after I check for spark. thanks for the tips.

 

[alangore]

I checked compression it came up to 90psi in each cylinder after 5 seconds of cranking. Spark jumped over 1/2" gap with good crisp electricity. Is it possible the fuel could be too old? I am somewhat at a loss. thanks for your help

 

[alangore]

could the throttle linkage timing adjustment cause this issue. I rechecked my carbs last night and everything was clean and clear

 

[Bosunsmate]

Do a drop test on each cylinder.
Do any plugs look different?

 

[Silvertip]

Plugs are wet = too much fuel or not enough spark. Did you replace the plugs? Did you totally disassemble the carbs or just remove the float bowl? Your an auto tech -- you have an engine, so troubleshoot rather than shotgun.

 

[alangore]

Yes I totally disassembled the carbs, removed all jets and cleaned and blew air through all ports in carb. I have checked and have enough spark to jump a 1/2" gap. I changed plugs, adjusted the throttle/timing specs. I got it on the water yesterday afternoon. I came right up on plane. It ran for about 20 seconds and then died. I chcked the primer bulb, it was soft. I checked the carb drain, and it just barely trickled fuel. the motor has sat for about 5 years, is it possible the fule pump needs overhauled and should i move the primer bulb from the tank up closer to the motor? thanks

 

[racerone]

Check the fuel pump as it just may need a new diaphragm.----Check the pick-up tube INSIDE the fuel tank.

 

[alangore]

I have a kit for the pump already. I am considering replaceing all the fuel line as well as moving the primer closer to the motor. It has a portable 6 gal tank. Is there anyway to remove the pick up tube. thanks,

 

[fireman57]

There is a service bulletin to redrill the carbs on this engine. I have the exact engine you have and had the same problem. Easy fix with the bits and was able to turn them with a screwdriver type holder and now have no problem. I will look for the bulletin and the number but it is on here if you do a search. Mister Joe Reeves has sent it to me twice but every time I try to find it I can't.

 

[fireman57]

I bet if you bump the primer/choke when you give it gas it will get up and go. If it does then the above definitely applies.