Honda-SOHC
SOHC.co.uk Forums => CB500/550 => Topic started by: gary123 on November 05, 2022, 10:52:44 AM
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The initial start up on of my 500/4 went well, firing on all 4 but running a bit rough and petrol dripping from an overflow pipe. So I took carbs of and double checked float height's again.
Dont know why but one was way off (3). Replaced carbs, air box etc inc new filter and now No 3 wont fire at all.
If I take the air box off and put my hand over No 3 intake it strikes up till I take my hand away, do you think this is still a float height issue.
Ive double checked tappets, points, timing, plugs and leads.
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possible blocked idle passages or air leak?
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Sounds initially like the idle circuit jet is not flowing fuel on that carb from your description.
When you put your hand over intake it should just draw fuell through the main jet as that's it's only route to fuel, if that makes sense.
If you've got any easy start to spray down that csrb when running to see if it'll also chime in, this would confirm it's a lack of fuel through that idoe circuit too and give you a double/cross check.
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Crossed over with Mick there, both thinking along same lines though.
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Cheers guys, Ill get the easy start out the shed.
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Well the easy start brought the cylinder in, any advice on what to do now will be gratefully accepted.
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Hi just a couple of easy checks, maybe swap the plug with#4 and also drain the float bowl and measure, mine are all about 50ml. I used a cheap plastic water dispenser cup marked at 50ml, the petrol melts everything else plastic!
Ash’s excellent tip correctly says to drain tubes first for absolute accuracy, but a straight drain still gives an approx measure.
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Seems to confirm no fuel flow through that idle jet, which ultimately means clearing it. These can unfortunately (similar for any small flow jets on most carbs) require a few times cleaning when getting them going again. Frustrating, but often typical as any small amount of debris from anywhere in the system can get stuck in such small openings.
You could try firstly winding the air adjustment screw fully inwards while running it (gently) until it has no air supply (essentially the same as putting your hand on the carb, but just for the idle circuit) to see if anything soft that's restriction in there will get going again.
Otherwise it's pulling at least that jet and also blowing through the associated air passage to bring it back to fully operational.
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To be clear, closing the airscrew is just a measure to encourage the vacuum to draw any obstruction from the fuel jet on that idle circuit, if it supports running then it can be set back to desirable adjustment and monitor for running then afterwards.
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Hi just a couple of easy checks, maybe swap the plug with#4 and also drain the float bowl and measure, mine are all about 50ml. I used a cheap plastic water dispenser cup marked at 50ml, the petrol melts everything else plastic!
Ash’s excellent tip correctly says to drain tubes first for absolute accuracy, but a straight drain still gives an approx measure.
Ive tried swapping plugs and leads, made no difference, Ill drain and measure.
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Seems to confirm no fuel flow through that idle jet, which ultimately means clearing it. These can unfortunately (similar for any small flow jets on most carbs) require a few times cleaning when getting them going again. Frustrating, but often typical as any small amount of debris from anywhere in the system can get stuck in such small openings.
You could try firstly winding the air adjustment screw fully inwards while running it (gently) until it has no air supply (essentially the same as putting your hand on the carb, but just for the idle circuit) to see if anything soft that's restriction in there will get going again.
Otherwise it's pulling at least that jet and also blowing through the associated air passage to bring it back to fully operational.
OK Ill try all that. Thanks
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I think my 3 and/or 4 were slow filling up due to a combination of gummed up tank cap breather (due to over filling 🙄), a slope up in the fuel pipe, and maybe float height. After steady running it seemed like the fuel level was dropping so it struggled to reach the idle jet, being higher than the main jet, and wanted to stall, so it would run on the main jet with more throttle if I stopped, and then the fuel level ‘caught up’. Also while running, after running a bit, and changing down, blipping the throttle seemed hesitant.
I’m hoping I’ve sorted the tank cap by putting a rubber tube tight against the small hole and blowing plus squirting carb cleaner into the hole.
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Drained the bowls and there was an identical volume of fuel in each. So now Ive got the idle jet out . The hole that runs right through has some kind of restriction in it, is this how it should be, it looks like its meant to be there so I dont want to be ramming something down it.
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Try a wire out of a wire brush there is no restrictor just a tapered hole.
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There’s a whole debate about that, stand by! I didn’t see anything in mine as some were bunged up with deposits, and had to clear them out very gently using a kit of stainless slightly abrasive rods from eBay. If doing it again I’d use my digital vernier to measure the right rod. Some kits come with tiny brushes that are useful for the openings they fit in plus in my case the inlet. But best wait for more experienced comments.
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The restriction I believe is an optical illusion.
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Ta guys, Ill get back to it in the morning.
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There is a "spider" at the top of the jet to help atomisation of fuel
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I see the same "spider" restriction in them when held up to a light and looking through.
I've used brass wire on a suede brush to go through there as it passes the spider without damage. Or copper strand from mains flex stripped out, just gently wiggle it through.
Any compressed air use, go backwards through it to dislodge debris as it obviously wouldn't pass through in correct flow direction.
Also it can help leaving it in a pan of boiling water to soften fuel tarring if that's the root cause.
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There is a "spider" at the top of the jet to help atomisation of fuel
Thats good, I thought I was seeing things.
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You are. Spider my arse.
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The best way I’ve found to clear idle/ slow jets is to heat in a flame. This turns the resin fuel deposit into ash. I then push a plain wire through the jet (say 0.38mm through a 40# jet). The risk of damaging the jet is absolutely minimal…it’s brass and durable. I wouldn’t use a serrated type cleaner you associate with welding nozzles though. Though to be fair even these would have a hard time causing detrimental damage if used with care and the correct size. Jet cleaning is the easy bit, the internal carb passages are more challenging. Get to understand the three points of entry in the pilot passage ways and block them to force carb cleaner through the various routes. I found my jets were clear, but the passages needed a lot of attention.
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If I curl up my index finger to make a really tiny hole and look close up through it at a light, without glasses on, I can see a sort of web pattern… just an observation!
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😀😀
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You are. Spider my arse.
:) :) :) :) :) :) :) :)
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You are. Spider my arse.
;D ;D ;D
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;D ;D ;D
I've also seen The Lock Ness Monster so it must be true
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;D ;)
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Genuine pilot jets definately have something near the top so you cant get a wire all the way through, seen it on several but not pattern ones
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Mine are genuine, but don’t.
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I have proof.
[attach=1]
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But seriously mine have a "spider web" in them.
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Mine are genuine, but don’t.
No they're not................... ;D
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Oh yes they are ….(almost pantomime season).
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Ohhhhhhh, no they're.........................cant be arsed! ;D ;D ;D ;D ;D ;D ;D ;D
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I have proof.
Yep, that’s pretty conclusive. I stand corrected.
(Attachment Link)
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There is no spider web structure. It's an optical illusion. And here is the proof. http://www.sohc.co.uk/index.php/topic,22417.msg204301.html#msg204301
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Nope, you are wrong and Gary123 proved it😀
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I have proof.
See…😀
(Attachment Link)
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🤦
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To be fair mezzanine, we have been through this multiple times. I have internal photos of both genuine and pattern jets. It’s an interesting kaleidoscope effect caused by the internal drilling reduction. TBH, there is no Techncial/practical reason for anything other than a stepped drilling reduction to create effective atomisation under a partial vacuum.
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I agree, a carburettor specialist has said the same. Interesting that the internal drilling helps too.
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Ok, I have to agree it is an optical illusion. If you look down the tube while rotating it the "web" does not rotate. For me, at least, that draws a line under spidergate.
However, after following all the advice offered my bike now runs, revs and ticks over nicely on all four cylinders. Probably a bit of dirt in the jet. Thanks to all who contributed. :)
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Excellent news 👍 I think I cleared a minor blockage once by using full choke and revving a bit, shame that doesn’t cure everything!
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Good you've a successful outcome with fueling and now running well.
For interest, the idle jet circuit on these runs a long way up into rev range when used on light throttle. Any impairment has quite significant effect on clean running for most speeds up to about 40mph ish. It'll give you a weak cylinder further out too as the main jet blends in with higher slide positions. Having the idle circuits impeccably clean is a big part of getting them running smoothly and consistent.
I still think there's spiders in there though ;D probably trained Japanese micro ninja spiders that know their job.
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Good you've a successful outcome with fueling and now running well.
For interest, the idle jet circuit on these runs a long way up into rev range when used on light throttle. Any impairment has quite significant effect on clean running for most speeds up to about 40mph ish. It'll give you a weak cylinder further out too as the main jet blends in with higher slide positions. Having the idle circuits impeccably clean is a big part of getting them running smoothly and consistent.
You're right. Lots of wrong info on the international site by socalled experts, who always come up with the same generic scheme. Already in the 80s an old Honda mec who owned a CB500 himself, had informed me on this and experiments I did, proved him right.
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Some good info here, cheers guys.