71' Johnson 9.5 wont idle

[jhohanshelt]

I'm new to outboards but know enough to tinker with the motor. I've posted a few post so far about my 71' Johnson 9.5hp not idling well. I have cleaned the carb 4 times, adjusted the lean/rich knob (has no effect it seems on the shudder idle problem), change the impeller (not that is has much to do with idling problems), and changed the spark plugs. I noticed it idled better with either the choke half way on or with the cowling (hood) was ON. This is telling me I'm still having a problem with the air/gas ratio?? Could the head gasket have an air leak? I have not pulled the flywheel yet to see what the magneto components look like. Should I?? I tired a compression test but either the tester was broken or I have ZERO compression because I could not get it to pick up any readings. I pulled both plugs, cranked the throttle to fast and plugged the compression fitting into the spark plug hole... So I'm lost there. It starts with a few pulls every time so I have to have compression right?? Either way, I have a spark tester and it has a continuous spark on both cylinders while running. The motor feels like it is running hot to the touch after I run it for a minute or two in the test tank. Could this mean anything?? Sorry for the long post but I'm at a loss with this idle issue and there are no outboard mechanics anywhere close to where I live. Any info would be great! Thanks

 

[Daviet]

Re: 71' Johnson 9.5 wont idle

Lets start at the beginning.
You need to get a compression tester that works and find out what your compression is. You must have some or the engine would not start. Low or uneven compression will cause idle problems.
If you cannot change the idle with the low speed needle adjustment you still have a carb problem. When you cleaned the carb did you remove the core plug and clean the passages in there? By idleing better with the choke half on tells me you have a restriction in the low speed circut of the carb, maybe trash in the passages under the core plug.
Before you pull the flywheel, check the spark with an air gap tester, the spark needs to jump a 1/4" air gap and be bright blue. If the spark checks out, I wouldn't worry about pulling the flywheel at this time.
You should be able to hold your hand on the cylinder head for a count of 4-5, when was the last time you replaced the water pump?

 

[Bob_VT]

Re: 71' Johnson 9.5 wont idle

Here is a very good guide to that motor
http://www.leeroysramblings.com/OMC_info/OMCinfo.htm

 

[jhohanshelt]

Re: 71' Johnson 9.5 wont idle

I have cleaned out and replaced the plugs, and set the float (in the carb). I know I've cleaned the three (low speed?) orifices in the throat of the carb well and I think I've cleaned the high speed orifice the best I could with out taking the special tool screw out behind the drain screw. I put a flash light on it and I could see through the high speed orifice and it looks pretty darn clean from what I could see. Could the high speed orifice cause bad idle though? Or will it just cause it higher speed problems? I will need to try another compression tester. What if the compressions test shows I have different compression in the cylinders? What will I need to do to correct this?

 

[Bob_VT]

Re: 71' Johnson 9.5 wont idle

The proper way to test compression on that motor is with a rope wrapped around the flywheel since the pull start does not spin it fast enough.

An improper gasket seal (leaking) will cause idle problems and drive you nuts.

 

[jhohanshelt]

Re: 71' Johnson 9.5 wont idle

The head gasket seal? Just pull the bolts and put a new gasket in? I think I need a torque wrench to reseal the gasket in, right? Thanks

 

[Rick.]

Re: 71' Johnson 9.5 wont idle

The head gasket seal? Just pull the bolts and put a new gasket in? I think I need a torque wrench to reseal the gasket in, right? Thanks

Yes torque wrench is required.. Also a good idea to re-surface the head. Put a piece of sand paper on a dead flat surface and figure 8 your head surface on it to see if you have high/low spots. If you do then keep at it until she is all evened up. Best of luck. Rick.