1976 6HP Johnson Outboard issues with idle and starting

[crashogie]

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!

 

[saltchuckmatt]

In my opinion either your gauge is off or the motor is wore out.

You say it runs good at high throttle.....is this on a boat in the water?

 

[crashogie]

In my opinion either your gauge is off or the motor is wore out.

You say it runs good at high throttle.....is this on a boat in the water?

correct...on a boat, on the water, it runs well. It runs well basically all the time unless we idle down to low rpm's...and then sometimes it even works well at those lower rpms. Re starting it while its warm is difficult but can be done.

 

[cyclops222]

Do you know what 700 rpm in Drive sounds like? While tied to the dock?

 

[Crosbyman]

IF...compression is 60 try another meter with a short hose .

it should be decent like >75-80 psi. my 9622a 9.5hp run perfect at 65 psi so don't give up.

you may be just starving out of fuel.
I assume you have good strong sparks...on both plugs !

easiest to try is pump the fuel bulb when you idle it down to see if it will keep up.
If it does keep up the fuel pump is suspect or any form of fuel restriction from tank fuel pick-up... to hose and poor carb job on the idle circuit. The side channel feeding the top idle chamber under the dime size plug is very narrow and must be flush out. see 18hp carb similar to yours

make certain you adjust the carb and mag plate timing. the cam follower on the carb must just.. line up with the small bar on the cam with the throttle just..starting to open .
don't get to hung up on the exact position of the START throttle when starting it .. a little more won't hurt.

if fuel does reach the carb and the crankcase vacum can't suck it in then you have loss of vacum somewhere. put a piece of paper in front of the carb face while cranking it to see if the paper " pulls in" the carb face.

what was the condition of the motor... old beat up thing or pampered with TLC even after 60 years ?

 

[crashogie]

This is excellent info above! Thank you very much. I'll play around with it this weekend. We just got the motor and the guy we got it from was selling it from someone else, so I'm not sure how well it was taken care of, but as we've been messing with it, it seems to be in decent shape. Interesting info on the welch plug...I was a little hesitant to hit it too hard when replacing it, so I'm wondering if I have an air leak around that. I'm going to give that a few more taps tonight (and maybe even seal the top of it). I'll look into adjusting the carb and mag plate. I have not done anything there, so will look for some videos. I appreciate your detailed response.

 

[Crosbyman]

no need to tap hard .

To remove... Drill a small (NOT DEEP) hole in the plug and use a pick or small nail to just pry it off. When done cleaning everything incl side channel.... the new one is fitted in and I use a square head (Robertson) screw driver to tap it in (not to much just enough to secure it in the the rim. When done apply a touch of clear fingernail polish on the rim to seal it.(or any color )
if you do the timing thing in the video below it takes care of electrical issues but... the carb mag follower roller at the START position must line up to the bar on the cam ..to do so if not aligned ....you can simply loosed the cam and adjust it