Author Topic: My 550F Carb Revalations  (Read 996 times)

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Offline Accolay

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My 550F Carb Revalations
« on: July 11, 2010, 07:59:19 PM »
So, after replying to another member about carbs and poking around, I find I actually have the carbs stamped for a '74-'76 550K model. I have the 022A carbs for those models built with the 4 position groove needle jet and 100 main jet but with the F model's 069A carb's setup 38 slow jet. What the heck?

I guess the carbs work seemingly well, so I'm not too concerned. How would getting the original setup change things?
1977 CB550F

Offline TwoTired

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Re: My 550F Carb Revalations
« Reply #1 on: July 11, 2010, 10:39:43 PM »
You have stock air box and exhaust?
Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

Offline Accolay

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Re: My 550F Carb Revalations
« Reply #2 on: July 12, 2010, 07:42:41 AM »
Air box yes, but not the exhaust (I wish!)
Exhaust is a MAC like this http://www.denniskirk.com/jsp/product_catalog/Product.jsp;jsessionid=KYSVTPW2YHFD3QFIDYFCM4WAVAPAQIV0?skuId=25565&store=Main&catId=403&productId=p25659&leafCatId=&mmyId=

I checked out my plugs yesterday and they indicate a bit hot/lean, about #22 on Dan's page http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html

When I took the carbs apart, the jet needle clip setting was at the first position (toward the pointy end) and I moved it up one position.
« Last Edit: July 12, 2010, 08:05:48 AM by Accolay »
1977 CB550F

Offline TwoTired

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Re: My 550F Carb Revalations
« Reply #3 on: July 12, 2010, 10:08:06 AM »
The #98s and needle position/type were tailored for the stock exhaust and air induction.  You can't expect those settings to be ideal for a different exhaust system.  The MAC was originally designed (and I use that term very loosely) to replace the exhaust of the K model.

So, in essence, I would expect an F model to run better with stock induction and MAC exhaust and carb settings closer to the 022A set up.

The F muffler was pretty quiet, far more so than either the MAC or the stock 4 into 4's.  The higher exhaust pressures these developed, fed the need for a different needle position/taper and smaller Main jet.

The main needle has 5 clip positions.  The 022As have the clip in the 4th from top normally.  The lower the clip is on the needle the richer the range of mixtures it provides.


If your plug read was a general read rather than a plug chop at a fixed throttle position, you are reading average conditions on your plugs.
You should also know what numbers are on the Jet needles if you plan on doing further fine tuning.

The overriding question I have is; "what problem are you trying to fix"?

If you are using today's oxygenated gas, I'm, not sure pic #22 is so out of tune at all.  In essence, that is what the government and oil industry wants your plugs to look like.  They don't care if you machine doesn't have adaptive fuel metering via sensors and computer controlled mixture injection so you will automatically use more fuel.

It also matters at what altitude you generally run the bike.  With carburetors, this is a factor in "state-of-tune".

Cheers,






Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

Offline Accolay

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Re: My 550F Carb Revalations
« Reply #4 on: July 12, 2010, 01:02:51 PM »
Thanks for the response TT. Well, damn the Man and his (its?) industry.

I think a plug chop is on the horizon then. If my plugs look about the same after that, then maybe I'll move the clip position to where it was before.

Thanks again.
1977 CB550F