What octane should I be using ?

I was told by my two motorhead gas station attendants that 89 octane is fine. The new 10% corn juice 89 octane has the same anti knock features as the 90+ octane.
These guys are car crazy.

i ran my 76 kz750 twin on 87 and it ran like a champ. i was always told to run the lowest possible octane to avoid unneeded carbon buildup on the piston. besides, youre just throwing away money with a low compression engine.

650ed wrote:

Plummen wrote: "no reason why a stock 8.5:1 motor should need 93 octane gas."

I didn't know KZ750s had such low compression. The stock compression on the 1977 KZ650C1 is 9.5:1. Ed

I don't recall if the 1980 750 LTD is a twin or a four hole, but the 750 twins run 8.5 compression.

bountyhunter wrote:

To clean out carbon, do the seafoam thing where you draw it in through a vacuum line until it kills the engine. let it sit about ten minutes, then run it out. You will look like a crop duster for a while when you are riding from all the smoke coming out, usually lasts maybe 15 - 20 minutes.

How do you do this????

You don't need high octane fuel. Sounds like your timing ond or advancer needs lubed.

brianpclarke wrote:

bountyhunter wrote:

To clean out carbon, do the seafoam thing where you draw it in through a vacuum line until it kills the engine. let it sit about ten minutes, then run it out. You will look like a crop duster for a while when you are riding from all the smoke coming out, usually lasts maybe 15 - 20 minutes.

How do you do this????

You feed it into the intake manifold through a vacuum hose. Get the engine hot first. I used a hose with an adjustable clamp (small vise grips) and a little funnel to pour in the seafoam. I started it up and let it draw in slowly for about 30 seconds, then opened the clamp up and let it flood in which chokes out the engine but fills inside the cylinder surfaces with the cleaner. let it soak about ten minutes, close off the vacuum lines and run it until the exhaust isn't smoky anymore. It will raise a cloud of black smoke the size of your house as the carbon burns out.

+1 on the timing problem. I have a '91 Zephyr 750 with 9.5:1 compression. The manual says 87 octane and and runs fine with it.

Higher octane does not make for a better fuel. It's got additivives to make it ignite at higher temps, so compression alone would not ignite it. It is for TRUE higher compression engines. So unless you have increased your compression. You have a timing problem.

Bountyhunter wrote: "I don't recall if the 1980 750 LTD is a twin or a four hole"

The 1980 KZ750H1 LTD is a 4 hole.

You know, at first I was like WTF with this posting then in reviewing some the the replies and really thinking about it, this is actually a good topic...

Low octane for a STOCK motor I get (as designed back in 1976).... Regular (leaded) gasoline..... Smoke like a biatch. :laugh: Hell, can't even by this any longer around here.

But what about newer head/valve/seat re-builds and such... make a difference?

Way back when, motor heads where discussing where super unleaded was bad for valve seats, ate them up. Hold the same for motorcycle valve seats?

Also, here in AZ, in the fall we get the Ethanol fuels...

Wow... not I have a headache.... :S

There is a year that the KZ engines supposedly were designed to handle unleaded fuel, maybe somebody remembers. I think it was in the late 70's. Lead gas additive is still available for older engines.

I dont think I ever experienced pinging and am not sure I would recognise it if it occurred

I have a 1980 kz750 E1 (4 cyclinder). The Haynes manual says compression is 9.0 : 1 and it runs just fine on whatever is cheapest at the pumps, 87 or 89 or whatever it is. Does not matter if there is 10% ethanol in it or not.

i like bountyhunters tip for how to use the seafoam and if I could find some up here I might even try it on mine

Old Man Rock wrote:

You know, at first I was like WTF with this posting then in reviewing some the the replies and really thinking about it, this is actually a good topic...

Low octane for a STOCK motor I get (as designed back in 1976).... Regular (leaded) gasoline..... Smoke like a biatch. :laugh: Hell, can't even by this any longer around here.

But what about newer head/valve/seat re-builds and such... make a difference?

Way back when, motor heads where discussing where super unleaded was bad for valve seats, ate them up. Hold the same for motorcycle valve seats?

Also, here in AZ, in the fall we get the Ethanol fuels...

Wow... not I have a headache.... :S

id say any motor built after early 70s should be fine with unleaded fuel with stock seats