Honda-SOHC
SOHC.co.uk Forums => CB500/550 => Topic started by: Davelu88 on March 26, 2019, 01:48:04 PM
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Hi all, 1975 K1 USA 550 with a carb issue it was running very rich & i could do nothing with it so i had to put it in local shop who had successfully done my 400 carbs for me so i have faith in them., The carbs are 087A and are a set of Gerbens, with 100 main and 40 slow jets. The mechanic has set timing/ points, done plugs , set float height , got it idling ok but it is still running extremely rich so much so that the plugs are very sooty straight away, carbs are not overflowing , no oil on plugs & no smoke from exhausts also air filter is clean . Im at a loss & so is he the only thing he aint done is adjust needle height, any help will be greatly appreciated.
Dave
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What is the air screw at ?
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He has adjusted the air screws Graham and got it idling ok but he does say the air screws on these do not make a whole heap of difference
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All my air screws on all my carbs make a huge amount of difference on where their position is set. In too far too lean, out to far too rich. +2 turns is a good average starting point and adjust in or out a fraction at at time depending on plug colour after a very good run.
Edit....i don't know why i have said all that Dave, you probably know anyway 🙄🙄🙄
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Also worth noting if the air screws are the correct ones as there are different tapers and ones with holes in them.
The air screw does not only control the mixture at idle but part throttle openings as well.
Regards,
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Hi all, 1975 K1 USA 550 with a carb issue it was running very rich ... but it is still running extremely rich so much so that the plugs are very sooty straight away,
What part of the plugs is sooty? The ceramic noses is what matters. The end of the thread will always be black. What other indication do you have it is running rich? I ask this because you say:
no smoke from exhausts also air filter is clean
Excuse me for asking: have you verified chokeflaps work as they should? Do you know what position the lever is for chokes open and chokes closed? You would not be the first...
Also know that all CB500s and CB550s of that generation will soot the sparkplugs real quick when they idle longer than necessary.
Verify aircleaner element is not wettened by that dreadful breather system.
You could do us a favor and unscrew a airscrew and inform us if it is the cross drilled type (as shown below) or the solid tip type (also shown). BTW, slow jets are supposed to be size #38. Airscrews are supposed to be around 11/2 out but with slow jets #40 probably more out.
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All help is appreciated Julie as my knowledge of carbs is zero, here is a pic of screw , Chokes seem to work ok and element isnt wet although it does start without any choke even when cold. Delta these carbs are 087A and i think 40 is right but not sure if correct for year of bike ? but i am reading conflicting statements as some say 38 jets and some 40 but CMSL sell 38 for a 1975 K1, . im starting to lose the will to live with this bike, everything is fine apart from this !!!
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Don't despair. This seems very easy to solve. I'm still in doubt if there even is a problem. If it really smells overrich, you could turn the airscrews out some more and see what that does. But first what is asked above. You wouldn't be the first to report sooty sparkplugs where the noses showed OK actually.
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Even when taken out for a quick ride the plugs look like they have been up a coal chimney for a week , its not just when idling . I appreciate all the help
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Even when taken out for a quick ride the plugs look like they have been up a coal chimney for a week , its not just when idling. I appreciate all the help
To rule out airfilter is the problem, remove airfilter element temporarily, go for a ride and report if that makes a difference. To make sure, read also this: http://forums.sohc4.net/index.php/topic,176725.msg2055185.html#msg2055185
This because: you haven't said you smelled an overrich running nor misfires by sparkplugs that have become too sooted. Why not post a pic of sparkplugs nose?
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Funnily enough ive just been reading that article and the soot is on the centre electrode & the ground electrode , not alot of difference with air filter removed , the only thing i can think of now is putting 38 jets instead of 40 and or adjusting needle height.
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The main assessment criteria will always be how the bike is running. If it runs ok, there is absolutely nothing wrong with having it on the rich side. I, and I'm sure everyone else, doesn't really worry about it running rich, as long as its not smoking from exhausts and the air filter is not dripping wet. It's when it runs too lean that disasters happen to the engine.
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It does stumble a bit at lower speed and smells overly rich , even the mechanic said it was extremely rich
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Is it all four spark plugs that are shooting up, or one or two? If two, is it 1 and 4 or 2 and 3?
Have you confirmed your exhaust pipes aren’t partially blocked?
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Hi its all four plugs , no i have not checked exhausts for blockages but i wouldnt have thought i would have a blockage in all four pipes or maybe im just very unlucky and i have :( , however i contacted Gerben as these were a set of his carbs and he politely replied stating that the 087A carbs should have a 38 slow jet & these have a 40 in them so would that be enough to cause the over richness
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I may have to go back and check figures, but I've got the 38 jet at 15.38% less area than the 40 jet.
So flow should be a noticeable difference to jetting.
When you adjust slow speed jetting and get no/little response in "normal " screwdriver adjustment range, then it is suggesting that the engine is "asking" for a different jet size to bring it within normal operating settings.
It does look like it needs the smaller jets.
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Thanks K2 ;D
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Definately says stock is 38 on these carbs , Question is how much difference would this make ?
Cheers
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yes i believe the pipes do go to the bottom of airbox , , after googling 087A carb specs it states 38 slow jet i have also messaged Gerben who built the carbs and he agrees that these carbs have a 38 slow jet , & looking on CMSL site the K1 & K2 both have 38 jets although the 500 does have 40 , so not sure why the 550 has a smaller jet.
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You can replace the slow jets with carbs in situ. Allen screws make it easier to remove the bowls.
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Have ordered 38 jets will let you know if any difference is made ;D
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Have ordered 38 jets will let you know if any difference is made ;D
Looking forward to that. I have always wondered if it really makes a big difference.
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Just a quick update on my carb issue , the 40 jets have been changed to 38 carbs balanced etc & it seems to idle , run ,accelerate ok , did a chop test on plugs and although a bit sooty they are nothing like they were so fingers crossed all ok . Many thanks for all the help on here.
Cheers Dave
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Where did you get your #38 slow jets from?
Raymond
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Got them from Dave Silvers, have to special order them & took about a week to arrive £30 for the 4 of them . part number 991240760380
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Try Sirius in Canada
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Or CMSNL in The Netherlands. https://www.cmsnl.com/products/jet-slow-38_991240760380/#.XKUPJ9hcJVc
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Sounds like a positive step towards optimum.
Longer running and more through heat range may see the plugs a bit better colour as it's used more.
Maybe it'll respond to airscrew tweak if not.