To lean or not to lean,that is the question?

Rapidrob

Rapidrob

#1
#1
I've noticed that my Greyhound 6.5 engine is burning a little rich at my 8,000 foot elevation. The engine never bogs down and response of the throttle is very fast. No backfire.
The spark plug is black at the electrode and the exhaust pipe is as well.
Should I re-jet or adjust the carb? Leave it alone? Too lean burn the valves?
What say you?
 
Docdc

Docdc

#2
#2
Rapidrob said:
I've noticed that my Greyhound 6.5 engine is burning a little rich at my 8,000 foot elevation. The engine never bogs down and response of the throttle is very fast. No backfire.
Click to expand...
I am a STRONG believer in leaving things alone if they are working. So you may clean some carbon out once in a while. I have had occasion to find the perfect tune. Of course I had to mess with it one more time and then I can't find it again. Just my thoughts. Don't place heavy value in them.

Doc
 
Joe-405

Joe-405

Member
#4
#4
My bsp does the same thing. Black plug but it starts everytime runs perfectly smooth and never misses a beat. I just changed the plug after 2 years. Lol.

So I say leave it alone.
 
Rapidrob

Rapidrob

#7
#7
WOW, the most I can get is 75% of the total HP. A 60 jet seems to be needed. Thank you for the info. I doubt this engine will ever be run at sea level.
 
FirePowerMinis

FirePowerMinis

Active Member
#8
#8
If they haven't reduced the octane of the fuel available up there, high altitude engines can typically handle a fair amount of extra compression.
Many OEMs had special heads for their high-elevation engines, pre WWII even. You'll gain back some of the lost performance.
1.3 rockers and a little port smoothing help cylinder filling, even if it's much thinner air.
 
Evil Tweety Bird

Evil Tweety Bird

Member
#11
#11
Two ways to look at it. If it's doing the job, leave it alone. May require some additional maintenance and fuel.
On the other hand the plug is telling you it's not right, or at least it's not at peak performance.

I'm from the second one, blame it on being raised by a family that raced cars from back in the late 40's.
Always you were looking at plugs, they told you what was going on with the engine. And you tweaked things to get the plugs that lovely brown shade.

All that said, maybe there's a third thing. Cost. Is getting it to run right worth what you are spending on extra fuel with it running rich?
 
FirePowerMinis

FirePowerMinis

Active Member
#13
#13
Rapidrob said:
The engine being an older Greyhound 6.5, which head on the list would be appropriate?
Click to expand...
Does it have a 4 bolt valve cover or 5? You'd need a cover and gasket to update if a 5 currently.
14cc is going to up the squeeze the most, and the shrouding issue on a stocker is minimal.
Normally listed as 5.5hp, 163cc head, as they were used on some GX160s.
 
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