carbon build up valves

85 octane? Good grief, where did you find that? I thought all "low test" was 87. You may want to run higher quality fuel, that is to say brand name, as the higher quality fuel (even that with fairly low octane) has detergents that keep the valve system cleaner. Ed

I've seen as low as 83 sold here in the US. Not fit for anything but you "Rock Mower" Briggs. Mid grade Min in this bikes. I stick to the 91/ 92 as that's what I have found for premium. Can't remember the last time I say anything higher. At my buddies in Bend Oregon, there's a station that sells Ethanol Free Premium @92, it's about .50 a gallon more than the Ethanol stuff.

The octane issue has also been covered on this web sight. In actuality, it is best when you use the lowest octane fuel with which your engine will run without detonation. With stock vintage KZ motors that are clean, that would be "regular" fuel. "Premium" is used by some of the guys, because their engines are carboned up and the compression is higher than it should be. When using premium fuel in these carboned engines, it will cause the carbon to build up even higher. When that happens, what do you do than? Start using Octane boosters to prevent the detonation? The best solution is to keep the combustion chambers clean in the first place. Here in the US, we have some of the worst fuel in the civilized world. In Europe and Australia, fuel burns quite a bit cleaner.

Well as you know these were 9.2 ratio, and 85 isn't going to cut it. The Factory states 87 as the Minimum Octane requirement, look at the tag under the seat. This may have some to do with the low cold compression figures. The ring land clearance may be worn due to detonation. A lot of times you can't hear it, but it is there. 85 No thanks, especially in a air cooled, mechanically advanced ignition system. Mid grade would be at least 87, much better, but depending on other issues the so called Premium might be better.
Most of those octane boosters don't do what they claim, there has been a lot of articles on this for years.

Here is the best test results for octane boosters I have seen to date. In a "nut shell" it rates the "Lucas" booster the best.

volvospeed.com/Reviews/octane_boosters.html

Myself, I run BP "Premium" fuel in my 11:1 MTC piston engine with no problems at all. In the Chicago area we have problems with Shell premium fuel, due to being inconsistent in blend from pump to pump and season to season. Citgo and Exon / Mobil also seam to be good in this area.

But his motor is stock and has a compression issue, he has been running 85 octane. Was his problem already there before he owned it? Its an old Police bike but how many owners since it had a scheduled maintenance and Gas from mostly 1 source? I've tried to, and others, to get a leak down test done. But the way it picks up so much when warm, sounds like the cylinder and piston sealing.

Try to clean out the chambers, and see what happens. The cost and time required are both negligible. There is nothing at all to loose and everything to gain by doing so.

I heard the bogus stories about problems using premium fuel before - I can only say based on my experience these stories are a load of bullsh!t. I wouldn't use 85 octane in my '77 KZ650-C1 even if it was free. I've owned the bike since new (April, 1977). When I bought it the dealer said use premium. I've been using 93 octane since day one. I ride the bike in a spirited fashion and do not hesitate to run it up to the 9k redline alone or 2 up. I don't ever run past redline. I've never experienced pre-ignition (detonation). I've never pulled the head. The valves have never needed adjustment even though I check and record the clearances every 3000 - 5000 miles; the clearances barely fluctuate up or down but never out of spec. I've cleaned the carbs once because the bike sat for 14 months when I could not ride and I have replaced the carb holders once because they let in unwanted air at idle. The engine runs great and after 50,000 miles will still zip up rather quickly to an inidicated 120 MPH. No hesitation, lag, etc. I'm using points, stock airbox, original pipes, and Mobil-1 synthetic motorcycle oil (since Castrol GT ruined their formula). If premium fuel creates a problem, when will I see it? 100,000 miles; 200,000 miles? I refuse to believe that running 85 or 87 octane in a motor with 9.5 / 1 compression is a great idea, so thanks but I'll stick with what has proven to work for me for over 33 years on the same bike. Ed

Absolutely Nothing Like An Original Owner Bike. Sounds like you take good care of that beauty 650ed.
When I buy from the 1st owner I expect and do pay the premium, as most times they are well care for.
The 1100 I bought from the 1st owner, had several guy's try to talk him down, I just looked and started counting the US Green Stamps! :laugh:

i only ran it once all other times was 87 to 93 but since then i ran carb cleaner and sea foam combustion chamber cleaner, i put it in threw the vacume ports in the carbs then after it sat (with fresh 93 octane) and the sea foam in the carbs then i ran it untill it stoped smoking from the additive, then i took it out and rode the piss out of it about 30 miles and it ran real good.125 psi to 120 compression when warm (no change when i put oil in the cylenders and retest)then when it cools down the compression drops and it wont start, unless i put the batt. charger on it and turn it over for a long time then i noticed that the exaust tubes from #1 and #4 get warm and #2 and #3 is cool. and if i set it out in the sun and it gets warm from the sun it starts easer than if its in the garage and cool. so confused...
( i only ran the lower octain when its a small town and nobody buys the 93 oct. and it gets old, there choice was 85 or 93 stale or push the bike 20 miles to the next station).

tmstoltz wrote:

i noticed that the exaust tubes from #1 and #4 get warm and #2 and #3 is cool.

This is new, possibly important info. #1 & 4 are fired by one coil; # 2 & 3 from the other coil. I would check the 2&3 side of ignition system from points through the coil and make sure everything is up to spec. Ed