Topic: K2 Carb Setup

[jwurbel]

Original owner of 1972 K2.  657 A carbs cleaned and put back together. Currently has 110 mains and 40 pilots which is what it came with.  Running no numbered exhaust with clip at 4th notch.  Air mixture starting at 1 turn.  Is this a good starting point? Living in Phoenix where altitude is 1100 feet.

Jim

[HondaMan]

Original owner of 1972 K2.  657 A carbs cleaned and put back together. Currently has 110 mains and 40 pilots which is what it came with.  Running no numbered exhaust with clip at 4th notch.  Air mixture starting at 1 turn.  Is this a good starting point? Living in Phoenix where altitude is 1100 feet.

Jim

With today's gasolines, this will be slightly rich - even using Regular grade gas. If the No-number pipes are the ones with the more-open fiberglass baffles you'll want the needles in the middle notch (slightly leaner by 1% at 3500-ish range RPM) or you'll hear it 'burble' while running along at 3500-4500 RPM (often hiway speeds in top gear nowadays), which is indicating the slight richness. This will foul the sparkplugs pretty quickly, too. You can test this with yours by using all 3 grades of gasoline: when you get it spot-on it will like the Midgrade best as it burns closest to the speed of 1970s Premium grade gas, now.

Honda moved the mainjets down to #105 in 3/72 and later builds of this engine/pipe arrangement with the HM341 pipes (more restrictive above 6000 RPM) and the increased backpressure at 3000-ish RPM made them run lean, so the needles then moved to the 4th notch, which was where yours started. In the 3/72 and later 657b series carbs the mainjets also dropped to #105, where they stayed until the PD carbs came along, although some of the 750F0 bikes (earliest ones) had #110 mainjets again for a while, then those also dropped to #105.

[jwurbel]

So mid setting on needle.

Due to ethanol issues, a friend told me to use Sunoco Optima which is 95 octane, unleaded, and no ethanol.  Would that make a difference in the setup?

[PeWe]

I have the K6 carbs on my K2 with Yamiya no number pipes. Diffusers in without "wool".
Stock filter box. First paper filter later K&N.
Began with K6 stock jetting.
Air screw 1 turn
Pilot 40
Needles middle 3 from top
Main 105
It had bad middle range not much response.

Increased main jets to 110, 115 and finally 120 where it woke up.
Higher speed way too rich.

Raised needles 1 notch to 4 from top.
Reduced main to 115.
It ran well with paper filter.
It got K&N filter after this.

I never tried 110. I guess the K&N filter need 115.

All jets are old stock except for main jets, new keihin.

[HondaMan]

So mid setting on needle.

Due to ethanol issues, a friend told me to use Sunoco Optima which is 95 octane, unleaded, and no ethanol.  Would that make a difference in the setup?

No, no change to the setup: after the bike is well-awake again, try the lower octanes. I use Regular in town use, Midgrade for freeways, and rarely Premium unless pushing it hard, like all-day interstate. The gasolines with ethanol are slower-burning "base" fuels so help light off catalytic convertors, which is useless in these bikes. The ethanol is added to ensure they will supply early ignition at lower temperatures in the cylinder, then burn fully away in the catalytic chamber(s) to  lower tailpipe emissions. To these bikes, this means nothing, so the base-fuel rating and speed is what will run them.

[newday777]

So mid setting on needle.

Due to ethanol issues, a friend told me to use Sunoco Optima which is 95 octane, unleaded, and no ethanol.  Would that make a difference in the setup?

No, not in the setup: after the bike is well-awake again, try the lower octanes. I use Regular in town use, Midgrade for freeways, and rarely Premium unless pushing it hard, like all-day interstate. The gasolines with ethanol are slower-burning "base" fuels so help light off catalytic convertors, which is useless in these bikes. The ethanol is added to ensure they will supply early ignition at lower temperatures in the cylinder, then burn fully away in the catalytic chamber(s) to  lower tailpipe emissions. To these bikes, this means nothing, so the base-fuel rating and speed is what will run them.

Mark,
Your wording is a bit confusing. The ethanol explanation in the center is where the confusion comes in to my 5:30 am fog brain. Just need some clarification here.
Are you saying
"No,don't use the 95 non ethanol during his settng up his bike? To use the regular ethanol gas until he after he has his bike fully awake and fully set up and dialed in and then once he is ready to go at high speed all day riding on the Interstate highway, then he can use the 95 unleaded, no ethanol Sunoco Optima"?

[jwurbel]

No offense but I am a bit confused.  When the bike is “awake”? Either I am using the non ethanol or not.
I had a bad experience with insulators becoming soft and then starting to disintegrate with ethanol so I am trying to avoid that situation again if at all possible.

[willbird]

They sell a fuel here called "REC91" which is non ethanol. Not sure if they really care if you pump it into something you rode in or drove in or not. It is about $5 a gallon tho. It is sold for vehicles not used on the road.

There used to be a BP station about 8 miles form me that sold 100% gasoline 87 octane and the other grades, the guy folded up when Circle K added a huge fuel complex to their convenience store.


Bill

[MauiK3]

I use non ethanol too, I'm very concerned about ethanol's effects on rubber parts.
I followed Mark's guidance for my carbs, seems to work well, I may be a little rich but it seems ok.

[HondaMan]

Sorry if I'm getting cloudy on ethanol: truth is, I detest it (that's the most polite word I can use...).
But, all the non-ethanol fuels we seem to be able to get now are always Premium grades, which will foul plugs in these bikes today because it burns very, very slowly compared to the 1970s gas that the bikes were designed to. Airplane gas (which is non-ethanol) is even worse: one local rider here who has a CB750F0, which has a bit higher compression, had to jet all the way down to #100 mainjets because he uses aviation gas that he can get at the airport where he works: it kept fouling his plugs with normal jetting, but he wants to use that gas (120 octane rated). This isn't a great idea either, because if he takes off to the flatlands below 5000 feet high he will burn the valves when the "normal" premium will ping/knock with the #100 mainjets - too small.

Mostly, I recommend Midgrade or Regular today, primarily because of the slow-burn nature of modern fuels in order to support catalytic convertors. The old 1970s Premium burn speed was somewhere in between the modern Regular and Midgrade fuels.

My 'best' advice about the gas situation now is: add a little oil to the gas, whatever gas you use. If it has ethanol in it, this will bind with the ethanol so it won't attack the rubber intake hoses on the 750 (the others SOHC4 bikes have aluminum intake pipes). If it DOESN'T have ethanol in it, it will still lube the valve stems and guides, which unleaded gas won't do. This has worked on my 750 ever since ethanol started (and it also helped a LOT against MTBE when we suffered that). My intake hoses only died at 126k miles because I had the engine out for other reasons (storm-caused oil leak) so I just got new ones then. My old ones still worked, and are in my SPARES box today. They are still softer than most of the ones I get with engines now for rebuilds.

[Tracksnblades1]

JW,

If you have a Casey’s general store, check to see if they have a red pump that says “no ethanol”.
It’s available ar most all Caseys here in the heart land. Its 91 octane and several cents higher than 10% ethanol premium.
We use it in small engines and two strokes that don’t run frequently. Spares all the carburetor woes with the short shelf life of the ethanol blends.

[jwurbel]

Mark, 

Appreciate the clarification re: gas.  Will reconsider the ethanol blends with the additional oil as an additive.

Trying to survive in the “New World Order” is a #$%*.

[willbird]

Sorry if I'm getting cloudy on ethanol: truth is, I detest it (that's the most polite word I can use...).
But, all the non-ethanol fuels we seem to be able to get now are always Premium grades, which will foul plugs in these bikes today because it burns very, very slowly compared to the 1970s gas that the bikes were designed to. Airplane gas (which is non-ethanol) is even worse: one local rider here who has a CB750F0, which has a bit higher compression, had to jet all the way down to #100 mainjets because he uses aviation gas that he can get at the airport where he works: it kept fouling his plugs with normal jetting, but he wants to use that gas (120 octane rated). This isn't a great idea either, because if he takes off to the flatlands below 5000 feet high he will burn the valves when the "normal" premium will ping/knock with the #100 mainjets - too small.

Mostly, I recommend Midgrade or Regular today, primarily because of the slow-burn nature of modern fuels in order to support catalytic convertors. The old 1970s Premium burn speed was somewhere in between the modern Regular and Midgrade fuels.

My 'best' advice about the gas situation now is: add a little oil to the gas, whatever gas you use. If it has ethanol in it, this will bind with the ethanol so it won't attack the rubber intake hoses on the 750 (the others SOHC4 bikes have aluminum intake pipes). If it DOESN'T have ethanol in it, it will still lube the valve stems and guides, which unleaded gas won't do. This has worked on my 750 ever since ethanol started (and it also helped a LOT against MTBE when we suffered that). My intake hoses only died at 126k miles because I had the engine out for other reasons (storm-caused oil leak) so I just got new ones then. My old ones still worked, and are in my SPARES box today. They are still softer than most of the ones I get with engines now for rebuilds.

It is a shame that somebody does not do a show like Engine Masters devoted to the kind of engines we are interested in. A youtube guy I follow Cletus McFarland just did a vid where they put nearly 100% Nitromethane in a stock 5.7. The HP and torque gains were stunning :-). They were able to get to 90% nitro before running out of injector. Needed about 40 degrees of total timing at 7000 RPM too.

But I would love to see a dyno series with "our" engines where the only change was fuel. Especially the REC 90 non ethyl fuel.

https://en.wikipedia.org/wiki/REC-90