Topic: Carb jetting and adjustment 1973 CB500

[BoCoJohn]

I just picked up my dads 1973 CB500 from his barn in Parker, CO.  He bought the bike new when we lived in California.  The bike has been parked in the barn since 1983.  It's in great shape-cosmetically - not a bit of rust.  However,  it has taken me over two-8 hour days just to clean the muck off the outside. 

I've had the carbs soaking for the past few days.  They are just now starting to free-up.

I don't know too much about the carbs but I did notice all the slides are adjusted evenly.  I pulled the bowls and jets and everthing else I could reach from the bowl and sprayed air into every orifice, again and again and again.  I need to order carb kits and determine what size jets to run.  I live at about 6,000 feet above sea level.  I'm sure I need to also adjust a bunch of other stuff.  Does anyone have any ideas of what size main jet I should run?  Also is there a manual anyone could suggest on how to set the standard adjustments.  I'm not sure how to adjust the float level and if there are any other adjustments I can make without getting into the top end of the carbs.

The bike cleaned up real nice.  I hope to get it running as well as it looks.  My dad and I used to tool all over the country on this bike when I was about 8 years old.  I have a little daughter that's about the same age and can't wait to travel on the bike again.

Thanks for all you help and, I'll apologize now for asking what I'm sure will sound like dumb questions to some of you.

thanks,

John
 
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[DavePhipps]

Always good to start at the carb FAQ http://forums.sohc4.net/index.php?topic=5410.0 and go from there.
Does it have the stock airbox or individual filters per carb?
Also somewhere the is a Shop manual download thread.

[BoCoJohn]

The bike is completly stock (single air box,  4 into 4 exhaust). I pulled the main jets and the number is 18 stamped on the jet.  There is a funny looking star in front of the number 18.  Not sure what that means.  Did I miss something...

Thanks for the link,  I'll check it out

[TwoTired]

The star like symbol is for the manufacturer Keihin.
The stock main jets for 627b carbs were #100s, the pilot jets s/b #40.

If your carbs are 649a then they should have #78 mains and also have a humped restrictor atop the air filter box.
Very unusual to find 649a carbs in the US, though.

Cheers,
 

[BoCoJohn]

Thanks a bunch for the info.  I looked at the carbs and couldnt a number that would depict which type of carb.  Is there a way to tell which type?  Are the jets interchangable and if so what size do you think I should start with riding mostly at about 6,000 ft about sea level.

[BoCoJohn]

oops.  the carbs are a 627b.  but the jets do say 78.  Does that sound right for this elevation?  about 6,000ft above sea level

[dave500]

the higher you go,the less air so the engine will run richer,maybe its been changed already?as two tired said the stock jetting was 100,this equals one millimeter,78 = point seveneight of a millimetre,the keyster brand rebuild kits come with 100 and 78 jets,id use the 78 and see,i think itll be ok,have you got the slides out?a bit more fiddly,if you have what position is the clip on the needle that hangs in the slide?download the manual and also search for all the carb info you can gather and study up.,youll be asking about the points and plugs next.,check the advancer is free to move,make sure you have a spark when your ready to try and start it so you dont crank the battery flat then try and find a spark,also remove the bowl on the bottom of the fuel tap,it has a screen to be cleaned,also remove and flush the tank,blow air through the fuel hoses as well,they might be old and crunchy now and need replacing though.,of course your going to dump the oil and filter,good on you and good luck getting it running.

[TwoTired]

If you don't have the humped/scooped inlet restrictor (see pic), I'd say somebody rejetted your carbs along the way.
If you can also make the assumption that it was running at your altitude before being parked, maybe you should leave it alone.

But, if you take the bike to sea level, you can expect it to run lean.  #78 seems kind of small.  Note, I have never rejetted a bike for higher altitude.

Cheers,

[BoCoJohn]

You guys are a world of help - thanks

The bike does not have the hump at the top of the airbox (thanks for the pic). I already cleaned the tank and pepcock, replaced the gas lines, filters, dropped the pan and changed the oil.  I did notice a lot of carbon build up on the valves as I looked through the intake and exhaust ports.  Is there any way to clean the carbon out without pulling the head.  I figure I'll run a little bit of BG44K in the tank once I get it running.

I think I should be ready to give it a start once I get the carbs back in order.

Thanks again-I really appreciate the help

[dave500]

id leave the valves for now and see how it runs,dont forget when an engine is stopped some valves will be closed and be seat to seat,some will be open or partially open and the seats can corrode,drop some oil in the spark plug holes and turn it by hand a few times and let it sit for a couple of days,itll blow some smoke when first fired up though,dont let it idle for the first few minutes,keep it revving a little,i think itll be alright if it fires straight up,worst case is pull the head to re lap the valves,after a good couple of runs a compression check will put you in the picture,if it runs good leave well enough alone maybe?plan A soon becomes plan B when the head comes off.

[Deltarider]

I did notice a lot of carbon build up on the valves as I looked through the intake and exhaust ports.  Is there any way to clean the carbon out without pulling the head.

There are additives to adress this. I believe overthere Seafoam is popular. In Europe we have different brands. I don't know about the choice you have in gasolines nowadays. Here Shell's V-Power and BP's Ultimate are excellent gasolines that prevent and clean up carbon build-up on inlet valves and upper pistonrings. BTW, the travels I made in the USA made me join the European choir of USgazhaters. It's the worst and every bike I rode performed worse than the same bike here. Why is it the American market always mistakes quantity (cheap gaz) for quality.