1975 70 HP won't idle or run in no wake speed

My brother and I just spend $350 to have this motor worked over good by a known and trusted professional mechanic. For all accounts, we got every penny worth of that money, it runs like a champ if you start it, warm it for 10 seconds, and hit the gas hard. IT didn't do that before we gave it to him.
However, if we try to let it idle or run slow... or simply try to push the gas into gear slow without goosing it.. it dies. It might idle for 30 seconds.. then die. it might run in "no wake" speed for 30 seconds then die. It only does this in the water. Once you get it going.. just out of the "now wake" zone on the throttle.. it will run fine forever.
Things the mechanic did. Cleaned all carborators. checked all ignition coils, power packs, etc. We bought a new gas tank, eveninrude adaptor, fuel filter... etc. kept hose, but it was only like 3 years old.
To the mechanics defense, it only does this in the water... no way for him to test it. It does everything fine with bunny ears on.
I don't even know where to start. And don't have any more money. lol
Any help would be greatly appreciated.

Re: 1975 70 HP won't idle or run in no wake speed

Sounds like the idle is to low, put it in the water and have the mechanic come to the boat and set it for you.
You spent the money to have it fixed and he should make it right.

Re: 1975 70 HP won't idle or run in no wake speed

Mechanics know they can't test run a motor on the muffs, completely unloaded. That's why they have "test tanks" and put "test wheels" in place of the regular propellers, which put the same load on the motor as if it were pushing a boat through the water. So they don't hand a motor back over to you lacking the final adjustments.

The price he charged was normal for the service he provided, plus I bet he did a "compression test", and wrote the numbers down on your bill of work. Keep that as a baseline for future reference.

in case you want to try it, the idle set screw is marked on the photo below (it's a later model than yours, but the parts are the same). Make it idle at 900-950 in the water in gear.

[btw, the motor needs a little while to warm up -- give it one or two minutes at least]

Re: 1975 70 HP won't idle or run in no wake speed

Thanks guys. I'll try it. We thought that... but when I got to looking I thought the roller was where you set it. Now that i see it in the picture.. i'll adjust it. Would the idle setting affect it not running in no wake speed? I would think once in gear and going ... an idle setting wouldn't matter.. but i'm no mechanic.
In defense of the mechanic we paid.. he is a friend and an auto mechanic with some experience on this motor. He doesn't have the tanks and stuff and he has given us free work hours after the initial payment. I live very close to the river and it's not a big deal for me to run down and test it.
Thanks for the reply's I'll let you know if it works or not.

Re: 1975 70 HP won't idle or run in no wake speed

You say he cleaned the carbs, but did he rebuild them with new kits? I have cleaned carbs and it worked fine but I have found that it usally takes a good soaking and new carb kits.

Re: 1975 70 HP won't idle or run in no wake speed

l0rd_z0d said:

We thought that... but when I got to looking I thought the roller was where you set it. Now that i see it in the picture.. i'll adjust it. Would the idle setting affect it not running in no wake speed? I would think once in gear and going ... an idle setting wouldn't matter.. but i'm no mechanic.

Click to expand...

At idle, throttles stay closed, and RPMs are controlled by spark timing. When you start out too low, you might (with enough finesse) be able to idle out of the no wake zone but as you learned, can be downright impossible. The roller controls the carb throttles -- the cam has to hit it right on that mark, or else there won't be enough timing advance when the throttles start to open...she'll fall flat on her face when you put the hammer down.

Other possibility here is misadjusted float height, carb float valves not closing off completely, gradually flooding you out. Or like patrick says, if worn out float valves (needles and seats) weren't replaced. Let us know if the idle adjustment works.

l0rd_z0d said:

In defense of the mechanic we paid.. he is a friend and an auto mechanic with some experience on this motor. He doesn't have the tanks and stuff and he has given us free work hours after the initial payment. I live very close to the river and it's not a big deal for me to run down and test it.

Click to expand...

mechanic friend, almost as good as a lawyer friend...maybe even better....