What to do about octane?

[Caveman Charlie]

Re: What to do about octane?

You can still get 92 octane in my area. Usually at a station near a big lake. But, it's expensive. My 73 Mercruiser 140 says 93 octane Minimum Research Method on the engine. I had a valve job done last year and added better valve seats at that time. One thing I did that I believe helps is to throw away the breaker points and go to a aftermarket ignition system and hotter coil. Then I gapped the plugs a little wider. The hotter spark will light of the mixture faster and help to stop detonation.

 

[Squid Billy]

Re: What to do about octane?

You can still get 92 octane in my area. Usually at a station near a big lake. But, it's expensive. My 73 Mercruiser 140 says 93 octane Minimum Research Method on the engine. I had a valve job done last year and added better valve seats at that time. One thing I did that I believe helps is to throw away the breaker points and go to a aftermarket ignition system and hotter coil. Then I gapped the plugs a little wider. The hotter spark will light of the mixture faster and help to stop detonation.

Charlie,

What year is your 140? Also, did it make your boat run hotter?

 

[HT32BSX115]

Re: What to do about octane?

In reality, it's not "can I use unleaded".

You MUST use unleaded. It's all that's available. you don't have a choice.


The lead/no-lead thing of possibly damaging the valves is IMHO more old wives tail than not. I had a 1966 MarkTwain (150 Mercruiser) that my dad bought new. It got unleaded gasoline for most of it's 39 years that we owned it. It never once had the head removed. If it hurt the valves it didn't show it in 39 years. I wouldn't be worrying about unleaded fuel.

Just re-time the engine so it doesn't ping and go boating.

Ok well would I use or can I use 87 or 89? what about the leaded part of the sticker, or can I use unleaded?


I dont want to fry this lil jewel!

 

[Caveman Charlie]

Re: What to do about octane?

Charlie,

What year is your 140? Also, did it make your boat run hotter?

It's a 73.

And, if by hotter do you mean the engine temp? It's not going to do that. I didn't change the timing or nothing. All a bigger spark is going to do is allow the fuel to light off better. It starts better. It idles better with less misfires. I recently did the change but, I believe you'll have longer spark plug life. I can't say if it improved my performance because I haven't had a chance to test that out. If it did it would be a small amount that you probley couldn't tell by seat of the pants. But, I don't have to change points ever again! And, unlike points there is no wear causing the spark to drop off or even the timing drift as the points age! I can tell you more by the end of summer. I just did this modification last winter. I used a pertronix flame thrower II ignition system.