Topic: Regular or hitest gas

[Wheelhorse77]

Did the 77 750F require leaded fuel?

Lead was not only a great, cheap octane improver, but a valve to seat cushion as well.


BTW, up to 10% Eth is your only choice in Chicago and 100 mile surrounding cities. When alcohol was first introduced, all of the rubber swelled up, got soft in the fuel systems which then had to be replaced by alcohol resistant materials.

I bumped the timing up on my SOHC because 9 out of 10 times you get a slight increase in performance. Most cars see a 5-10 rwhp increase so my guess is the Honda would pick up 2-3 crank hp. Now before people get their SOHC's in a bunch...Honda tuned for a balance of EPA and performance. I have statistically proven and written reports on the relationship between timing curves and emissions and the factory timing was always the best comprimise between the two.

Some technology is great to adapt to our old rocket ships, but in order to run a piezo crystal sensor to detect bad ju ju, it needs to be in tune with the detonation and preignition frequencies that your particular mill makes. A trick to semi desensitize the sensor was to wrap pipe tape around the threads and try different depths into the port and tune it by ear.



For anyone who gets detonation, your advance mechanism maybe advancing prematurely, hence the detonation under low-speed high-load.

[TwoTired]

Did the 77 750F require leaded fuel?

No. The Owner's Manual says 91 RON or 86 Pump Octane minimum.

Lead was not only a great, cheap octane improver, but a valve to seat cushion as well.

True.  But, aluminum head engines have hardened steel seats where seat lube isn't strictly required.

Cheers,

[Tom Stark]

Did the 77 750F require leaded fuel?

No. The Owner's Manual says 91 RON or 86 Pump Octane minimum.

Lead was not only a great, cheap octane improver, but a valve to seat cushion as well.

True.  But, aluminum head engines have hardened steel seats where seat lube isn't strictly required.

Cheers,

Contray to popular belief, the seats in heads do not, (in normal engines, fuel engines excluded!), sink.  What happens is they contact weld to the valve, and the valve pulls a tiny bit off when it opens.  After a while, it looks like the seat is pounded into the head.  Cast iron is not real hard, and lends itself to this.  Aluminum heads need seats, and at least now are all good hardened seats.  Lead did help keep this contact weld from happening.  Lead also helped keep the guides lubricated.  And again, aluminum heads have guides in them, many heads using bronze or similar material.
Tom

[SOHC steve]

The other interesting thing about valve seat recession is it seems to be a bigger problem on fresh cut seats.I've personally seen cast iron head engines that have seen a fair amount of miles run quite happily on LPG (propane) without valve probs.It seems to be that the seats tend to work harden with use.
       As far as bike engines go,sure,they have seat inserts,are they hardened? Probably not as tough as todays seats,but if it was an older engine with miles on it I would say you have nothing to worry about due to the work hardening i mentioned.If I had a fresh rebuilt stock standard honda engine,I would probably be tempted to put some miles on it before cutting back to regular unleaded,thats just cheap insurance in my book.
        At the end of the day,it really depends on what you can get away with,do you wring its neck and have healthy amounts of comp?Do you have detonation probs? you need higher octane.None of above and you want to save a little?try regular,if you get away with it great.

[Gordon]

        At the end of the day,it really depends on what you can get away with,do you wring its neck and have healthy amounts of comp?Do you have detonation probs? you need higher octane.None of above and you want to save a little?try regular,if you get away with it great.

But that's exactly the point.  It's not a matter of "getting away" with using regular gas.  These bikes were designed to run on regular, so if you have to run premium to keep a stock sohc4 from knocking or pinging, then your bike is either out of tune or in serious need of a combustion chamber cleaning.  If you've modified the engine to have higher compression, then yes, you will probably need high octane, but if not, then it's just treating the symptoms and not the problem.

[SOHC steve]

I obviously have no idea on the quality and/or quality control of fuels in your part of the world,but,I can tell you the new "standard unleaded" seems to vary in quality over here.I have rebuilt/restored older low comp car engines (8.5/1) that were originally made to run standard.With hardened seats and all the good valves etc and original timing curves (yes it was correct curve and in fine condition) it would detonate occasionally under load with standard unleaded.Premium was not a prob.The owner was happier to stick with the original advance curve and run premium because of its limited use.I also have a early fuel injected car that does not have knock sensing,once again,timing is spot on and engine is fairly fresh,it too will be heard to ping occasionally with certain unleaded fuels.
      I would rather be safe and try standard unleaded and see if "you can get away with it" ...more than likely it will be fine,but I cannot honestly say that my experiences and comparisons between standard leaded vs unleaded has found them exact equals.
       These machines are over 30 years old now,they may have all been equals when they left the factory,but now? Who knows if the PO slipped in a mild cam,maybe you had a leaky head gasket and got the surfaces milled to true them up,maybe valves getting a bit thin...what I'm getting at is they are all no longer identical and I doubt their fuel needs are either