1970 johnson 6hp

I am new to this site.I've

I am new to this site.I've got a 1970 6hp Johnson model 6RL70M.I've tried to use it as a trolling motor on my 16 ft Mirrocraft.It will troll for awhile then it will start running rought.I've tried adjusting the rich/lean knob but it doesn't seem to be able to maintain a good trolling speed.1.5 /1.8 mph.Thanks in advance for any help.

"There are a few things it cou

"There are a few things it could be. Some of which are:
It could be sucking dirt into the jets of the carb, causing it to starve for fuel. It could be overheating (check water outlet and make sure it's not pumping out steaming water).
You've made sure you unscrewed the vent screw on the gas tank, correct? Another thing to try if all the above is ok is to pump the primer bulb to see if it is firm, and if the motor runs better when you do.
Other than that, what fuel/oil ratio are you using (should be 50:1 TCW-3 oil).
That's only a start, but if the motor hasn't had a basic maintenance routine performed on it in a few years, it should. That means check ignition (I'm assuming that thing still had points and condenser), carburetor cleaning (new carb kit preferred), and new water pump impeller. As well, I'd make sure the compression on the motor was good. I don't have numbers, but would assume somewhere around 100PSI per cylinder, more importantly, each cylinder reading should be close.
Have you used the motor recently where it ran good, or is this a new occurance? Sorry for being so generic, but hopefully this gives you a good starting point."

The fact that it runs Ok for a

The fact that it runs Ok for a while suggests to me that several of things that Wayne suggests will probably be Ok. but check them anyway.

Overheating due to inadequate cooling water flow at low speeds I reckon. Does it run Ok again for a while if you give it a few minutes at higher speed. New impeller if not been changed for a few years

No telltale on that model to check the pump performance is there?

Could also I suppose be flooding due to the needle valve not seating

"1) The gas tank and fuel

"1) The gas tank and fuel are new.2)The primer bulb is new too,but it's so stiff to squeeze that it feels pretty firm before priming the engine 3)I'm using Quick Silver at 50:1 4)It's pumping water at a good volume 5) the vent is open and I've unscrewed the gas cap 6) I haven't done a compression check yet. The motor ran fine at mid range and topend but not so good at a trolling speed.I don't know if I should adjust the rich/lean knob to richer or leaner at trolling speed.I haven't pulled the carb off yet but it looks like the starter gear and bracket need to come off first.Is that correct?The nut on the right side off the carb seems to be buried. Thanks for all of the suggestions"

"If the only thing you do with

"If the only thing you do with the motor is trolling and everything else checks out o.k., you might want to use a higher heat range spark plug to prevent fouling over extended periods at low RPM. If it is subject to all around usage, this would not be the case"

"All good points, One thing co

"All good points, One thing comes to mind, the throttle linkage. Check for proper adjustment and ware on the contact points at the throttle plate. Check for worn throttle plate shaft. Also check that the idle is not to below minimum. Changing prop pitch to raise the rpm is an option."

I'll start going down the

I'll start going down the list and see what works.Thanks for all of the suggestions.