Old OMC motor - problem with hot starting - please help!!

[Swell]

I have a 1968 Johnson Seahorse 6hp which cold starts pretty reliably after around 3 pulls. However, if I stop the motor after a run of say 20 minutes i.e. enough time for it to fully warm up I have a hell of a job getting it started again. It goes eventually but only after a lot of pulls. I don't have a thermostat fitted so it's actually running cooler than it probably should. I'm basically stopping the motor to fish while drifting and then powering back up to return to the start point.

Are there any tips for a successful hot start?

I'm using an equivalent of the correct spark plug for the motor - could a change of plug type help this?

It's had a full set of new ignition parts which have been fully tweaked.

Compression is a little low, but both cylinders are within 10%.

Is it just getting flooded?

Any tips would be greatly appreciated!

 

[TN-25]

Re: Old OMC motor - problem with hot starting - please help!!

Hmmm, one thing to do is pull the plugs after a shut down and ?read? them. Are your plugs wet? They can be a little wet but the electrodes should be dry with either gray or tan deposits. Make sure the gap is set correctly as well.

A change of plugs can help. In theory the brand shouldn?t make a difference but in reality it does. Champion plugs always worked on my OMC motors. Run a ?hotter? plug if you do a lot of trolling, but be aware that destructive pre-ignition can occur if you run too hot a plug while running at higher throttle.

Mixture could also be another item to verify. A cold motor needs to run a little rich until it warms (the choke accomplishes this). Once up to operating temperature, running too rich will make it bog and hard to restart.

Does your 6 start well with the choke on but not so well without the choke? If so it indicates a fuel-related issue, most often debris in small carb passages, but sometimes it also indicates an incorrectly set float. A thorough car cleaning (NOT excessive soaking in cleaner, actually using compressed air to blow out passages.) In a carb rebuild don?t forget to remove the knockout plug and clean it in behind.

A properly tuned motor with a clean carb & no fuel pump or fuel line / tank issues will run. Perhaps a good tune-up should be performed. That will also include the link and sync procedure (see sticky in this forum) to make sure timing and throttle are set properly. This procedure will ensure good performance and economy, plus more reliable starting.

Just a thought, I wonder if heat is soaking into the carb causing percolation? If the carb body is hot after you shut down, that is an indication. Make sure that proper gaskets are used so that leaks don?t occur and heat is not transferred into the carb.

That is my 2 cents, and it is worth every penny

The 1968 Johnson 6 is a fine little motor.

 

[jonesg]

Re: Old OMC motor - problem with hot starting - please help!!

Pump the bulb to refill bowls with cold fuel, try again.
Champion plugs, if it needs NGK's theres something wrong.

 

[Swell]

Re: Old OMC motor - problem with hot starting - please help!!

Cheers for the replies. The carb has been cleaned to within an inch of its life, so there's no debris, and I set the float very carefully so I'm sure that's fine. I'm not sure how to change the mixture other than the idle mix. Does idle mix also impact running on the throttle? It doesn't idle very well and does tend to cough at some point and stall which I put down to the low compression. Could be something else though I suppose.

It tends to need choke to start cold, but only to chuck fuel in and get it firing. As soon as it fires I always push the choke in and leave it in from then on and it goes fine. With the hot start I tried it with and without and it didn't seem to make much odds. I imagine it didn't help at all as it was probably flooded after the first few pulls.

I suspect the low compression isn't helping especially when warm when the oil will be thinner and probably reducing the seal around the pistons. I remember an old car which often stalled after a long journey - put down to thinned oil and associated lower compression. It always flooded when trying to restart and the trick was to put your foot to the floor which would clear it out and it would start.

I'm wondering if starting the outboard on full throttle might have the same effect?

I'll also fit the recommended plugs - can't do any harm!

 

[jonesg]

Re: Old OMC motor - problem with hot starting - please help!!

Try a decarb with seafoam to bring compression up.
Install thermostat to prevent carbon buildup.

Its not going to run right until you baseline the setup to factory spec, running without thermos doesn't help.