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1976 6HP Johnson Outboard issues with idle and starting

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crashogie

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I've been using topics in these forums for the past 3 months and they have been very helpful. My son worked to save up and get a boat and motor this summer and we've made a project of fixing it up together. First time for either of us. With youtube and these forums, we feel like we've done a pretty good job. I'm at the end of my rope though. The issue we're having is that sometimes it won't stay running at low rpms, and most often to start, the handle needs to be rotated a little towards "fast" from "start". Sometimes if it dies after running for a while (when we slow down), it is extremely hard to get started again. Here's what we've done (in order):
  1. Replaced tank pickup
  2. new spark plugs (gapped correctly)
  3. replaced gas lines
  4. replaced fuel filter/pump
  5. rebuilt carb (including new low speed needle, gaskets, float, etc)
  6. new coils, points and condensers (gapped to 0.020)
  7. New impeller and seals
  8. new thermostat and gasket
  9. new head gasket (and lapped the head with piece of glass with emery cloth on it)
It runs like a dream once it's running and has some rpm's, but often, when we lower the rpms, it stalls. We finally checked compression (borrowed a gauge from Autozone) and both cylinders are almost exactly 60psi (maybe 62). The gas tank hose is around 8' long...not sure if that matters at all. Just wondering if anyone had any thoughts. Is that compression low enough that it will struggle to pull gas in at low rpm's? What else might I be missing? Thanks in advance!
 
Check to see if the handle grip spring is in place. Part number 0301656. Some times they are removed and not put back. This will allow the throttle to slowly creep down to a stall our shut off without it. I experienced this one myself.
 
I'll check it out, thanks! I was wondering if the compression gauge is just not calibrated, or if it's actually 60psi. I see them pretty cheap on amazon, but don't know if those would be any better than what I borrowed. As for the spring, that may be something, but it's not what I'm describing. When I intentionally bring it down to idle (or lower rpm's), it will die. But, yesterday, we had the gas tank on a shelf next to the motor (in a bucket) and it ran perfectly even at low rpm's. That's what got me thinking about the fuel line and or compression not being enough to get the gas to the carb at lower rpms. Maybe I'm just an idiot for thinking that raising the tank a few feet will help it fight gravity and fuel will flow better...
 
Was the fuel pump a factory replacement or an amazon " special "----I replace the diaphragm on the QUALITY factory pumps.---And why was the low speed needle replaced.?
 
fuel pump was from amazon (carbhub 18-7350). I replaced the low speed needle because I was replacing everything else and couldn't tell if the old one had worn away at the tip. When I got the new one, it looked like I probably could have been ok with the old one, but I replaced it anyway. I really wish I wouldn't have tossed the old fuel pump and just bought the rebuild kit...
 
I would not even think of installing a pump made by the ---" hooflungdung " --- Company.----And I own more than 1 of these fine motors 5.5 / 6 HP from 61 to 79 models.----The diaphragm is in stock here and is about the only thing that goes wrong in normal use,
 
crashogie said:
fuel pump was from amazon (carbhub 18-7350). I replaced the low speed needle because I was replacing everything else and couldn't tell if the old one had worn away at the tip. When I got the new one, it looked like I probably could have been ok with the old one, but I replaced it anyway. I really wish I wouldn't have tossed the old fuel pump and just bought the rebuild kit...
Click to expand...
I would never have tossed the old one. At some point you may crack the inlet or outlet nipple. That pump had valuable spares, & if rebuilt is worlds better than those cheap Amazon units.
Right now I have 4 of those motors, & that pump will work on 9.9s, 15s & a bunch of others.
 
Hindsight is 20/20. If I knew then what I know now, I would have just rebuilt it as I mentioned. I may look around to see if I can find a used OEM one somewhere. Dropping $119 in a new one isn't in the cards since this is my son's build and he's trying his best to save money.

I haven't gotten a new compression tester yet, so if we assume 60psi (I know it should be 80+), would that be enough to operate a good fuel pump? I guess I'm questioning if I should be focusing on the fuel pump or looking at new rings. When we had the head off to put the new gasket on, the cylinders looked great, but I'm not sure if that means much. Or should I try some sea foam first? I don't know enough about running that through, but to me, it seems like it would make the compression worse by removing buildup, but I'm a noob, so could be wrong.
 
If it runs for any length of time at mid speed, I doubt the problem is the fuel pump. If you don't have to pump up the bulb when it stalls, you are fine. Have you touched the head when it stalls? If it burns your fingers, it's overheating.
 
Try the existing gauge on your lawnmower, or someone else’s small outboard.
If it also shows low pressure, you know the gauge is crap, (your mower should show well over 100),
 
Thanks Racerone - good to know about the pump operation.

It doesn't appear to be overheating. I did find something while googling and that was with the welch plug (it was mainly about cleaning out the orifices below it and the low speed needle), but I don't know if I put the new welch plug back in well enough. I was struggling to get it to seal properly and wonder if air leakage there could be causing some of the issues. I'm going to try tapping that in again tonight an possibly putting some sealant around the outer edge. Not sure if that would be the issue but seems simple enough to try.

good tip about checking the gauge....I already returned it to autozone, but if I do try another one later, i'll check it out. Thanks all!
 
I pick up these motor ( have more that 1 ) for parts or rebuild.-----I make no attempt to start them.------They come apart for inspection and repair.----Amazing what happens to these wonderful little motors , and what owners do to them.----Repairing them is so easy.
 
Re-reading your initial post. Don’t put much thought into the twist grip not being at START. Those little collars often don’t line up with what the engine is doing.
When you say it dies when you throttle to idle…are you turning the twist grip all the way to idle? That will kill the motor for sure.
There is no STOP button on that year. Turning the twist grip keeps retarding the ignition til the motor won’t run. The last year or so, (1979 for sure), has a kill button & a thumb screw near where the tiller pivots up/down. That can be turned in to create a faster idle, & acts as a stop - prevents turning the twist grip any further towards idle.
Those little pumps, when working, only put out 1psi at idle.
I have an 8 hp that did what you are describing. It would quite often die at idle, hard to restart unless I turned the throttle way up. I found it was sucking air, as the previous owner had left the screws for the fuel pump loose. As soon as I tightened them it ran flawlessly. If you have an air leak- in any of the lines, (cracks, or loose where lines connect), it may lead to fuel starvation at low power.
 
Confirm that the cam roller on the carb throttle is set in the proper opening position in relation to the twist handle.
 
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