Honda-SOHC
SOHC.co.uk Forums => CB500/550 => Topic started by: paulbaker1954 on December 16, 2019, 05:03:51 PM
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Hi folks
I am still having running issues and sure it’s a carb issue.
Bike starts fine and idles smoothly but then feels like fuel starvation on the road.
Seems to run ok with full choke on but than as soon as I come to a stop she stops, I think due to too much choke.
Close choke restart one off ok again but then feels like it’s fuel starved and has no power.
I have adjusted the idle screws but makes no real difference and float levels are ok.
On reflection these carbs have never been right and I am seriously thinking of sending them to Gerben for a full overhaul or trade in for one of his refurbished sets.
That said it’s a big expenditure and just wondered
a) are his carbs usually spot on
b) am I wasting my money
c) Any bright other ideas
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A refurbished set of cabs still need to be adjusted.
I bought a vacuumgauge set on ebay for small money and did it myself.
Took me whole afternoon but the bike runs great.
Even without the original filter (I bought a design breadbox).
Come to think of it...
Couple of things to think about:
- is your airfilter new or 40 years old?
- I have noticed that the original clamps to secure the intake rubbers on the manifolds might not tighten enough after 40 years.
These clamps have a maximum of how tight you can tighten them. I replaced them for nice looking rostfree clamps which don't have a maximum. You can tighten them more than the original ones so any false air (?) can be prevented.
How big are your main jets?
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Have you considered something like this http://www.sohc.co.uk/index.php/topic,18831.0.html to at least get a quantified look at what it's burning, or not.
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I just received some 350/4 carbs I bought from Roy that Gerben had restored and they look generally spot on, for my 400/4. They don't have KeiHin jets in them though (not sure on needles) so I am going to swap for original KeiHins, as I need to jet up anyway from 350cc to 408cc. I know he doesn't fit or recommend Cruzinimage parts .... so that's a big bonus IMHO. ;)
If I am being picky he spray paints the carb plate by the looks of it when this item was bare alloy originally (not sure on his reasoning for doing this). I am also going to swap some of the screws for original style JIS ones .... but I am a picky s*d.
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I have noticed that the original clamps to secure the intake rubbers on the manifolds might not tighten enough after 40 years.
How did you find that out?
I replaced them for nice looking rostfree clamps ...
Where did you find those?
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I noticed that (after I've bought several used sets on ebay) those rubbers between the carb and head were a bit loose.
Every one of them. I didn't pay attention to it first but after putting on the original clamps I noticed that when I would tighten them till maximum (those 2 stops hit each other) there was still play.
Naturally after putting the rubbers on and pulling them off again in the last 40 years they were not as tight as they should be.
So I have bought these:
https://www.ebay.de/itm/Schlauchschellen-Edelstahl-V2A-mit-Schneckengewinde-DIN-3017-W2-von-8mm-180mm/253264148517?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649
quite cheap I think 8,90 and free shipment in Germany for 10 - and they look good too.
With those clamps I could get te rubbers on much tighter. Or actually as tight as they needed to be.
Since then I am advising everyone to get rid of those original ones.
Of course they are not original. That might be a nono for many. But the bike preforms really well with those.
I am going tho replace them on my 750 as well..
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Thanks Menno. They look good. I had planned to 'line' the originals with a thin layer of rubber, but I might go for these. I mean who could resist Edelstahl? ;) Which 'Spannbereich' did you order?
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Hi folks
I am still having running issues and sure it’s a carb issue.
Bike starts fine and idles smoothly but then feels like fuel starvation on the road.
Seems to run ok with full choke on but than as soon as I come to a stop she stops, I think due to too much choke.
Close choke restart one off ok again but then feels like it’s fuel starved and has no power.
I have adjusted the idle screws but makes no real difference and float levels are ok.
On reflection these carbs have never been right and I am seriously thinking of sending them to Gerben for a full overhaul or trade in for one of his refurbished sets.
That said it’s a big expenditure and just wondered
a) are his carbs usually spot on
b) am I wasting my money
c) Any bright other ideas
Paul,
I assume bike was working fine before. Are you sure that fuel is flowing into carbs w/o any blocking? Don't you use fuel filter? If so, try to remove it.
If fuel flows OK and float levels are OK - then it looks to me you have some air leak (too lean mix on idle). Are you really sure your float levels are OK? Did you make clear tube test?
before sending carbs to Gerben, I would check if fuel flows through petcock (sometimes vent in tank cap can be clogged), check airleak and eventually check/clean jets.
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I agree with Erny. Things I'd do first:
A. Remove any inline fuel filters. They gave me nothing but trouble.
B. Make sure fuel tubes are exactly the right dimensions knowing:
18 and 30 cm when you have the old bowltype petcock or 17 and 28 cm with the newer style petcock. Don't be tempted to cut them even one cm longer 'to be on the safe side'. You will only increase the risk of kinking. Only the precise length can guarantee the right fuel flow. Ideal internal ⌀ is 5,5 mm, outside ⌀ will be 9-11 mm. Use the soft metal clamp front side carb rack to guide the tube to 3+4.
C. After a long period of inactivity float needles may tend to stick. Also the floats swivel pin may need some 'lubrification'. A fuel system cleaner like Redex can do that (some just add a few oz of kerosene). BTW, I have the feeling K3 owners cannot escape using this stuff on a regular basis. You could also remove the floatbowls to inspect for yourself and 'polish' float valve and needle and the swivel pin very lightly with something non abrasive. Usually the swivel pin can be removed with your thumb and forefinger. When you need pliers, make sure you do not pinch the pin. Careful, some have managed to break the towers.
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Ok I have bitten the bullet and ordered a Gerben set as he will give me £100 trade in for my old set
Decision is based on the fact that my carbs have just never really been right despite a number of strip downs replacement jets etc etc etc.
I recently switched back to another set of pilot jets which has just made it worse and am basically fed up with spending so much damn time trying one thin after another
I have checked fuel lines, petcock, float levels. There are deffo no air leaks and I have new rubbers and clamps etc and all is squeaky tight
Given how much more time I could spend messing about with yet more brassware, stripdown ....... I don’t think it’s a bad investment at around £220
If nothing else I will get a nice shiny set to fit that can only make the bike look better
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I got mine refurbished by Gerben for the 400/4 I had overflow issues and inability to reach top revs, they arrived back and went straight on and without any adjustment the bike was 100% better, I synced them with a set of vacuum gauges and they required only minor adjustment. Bergen had to replace the four slides and float bowls.
For me it was worth every penny
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I got mine refurbished by Gerben for the 400/4 I had overflow issues and inability to reach top revs, they arrived back and went straight on and without any adjustment the bike was 100% better, I synced them with a set of vacuum gauges and they required only minor adjustment. Bergen had to replace the four slides and float bowls.
For me it was worth every penny
Good to know👍👍
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I noticed that (after I've bought several used sets on ebay) those rubbers between the carb and head were a bit loose.
Every one of them. I didn't pay attention to it first but after putting on the original clamps I noticed that when I would tighten them till maximum (those 2 stops hit each other) there was still play.
Naturally after putting the rubbers on and pulling them off again in the last 40 years they were not as tight as they should be.
So I have bought these:
https://www.ebay.de/itm/Schlauchschellen-Edelstahl-V2A-mit-Schneckengewinde-DIN-3017-W2-von-8mm-180mm/253264148517?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649
quite cheap I think 8,90 and free shipment in Germany for 10 - and they look good too.
With those clamps I could get te rubbers on much tighter. Or actually as tight as they needed to be.
Since then I am advising everyone to get rid of those original ones.
Of course they are not original. That might be a nono for many. But the bike preforms really well with those.
I am going tho replace them on my 750 as well..
You can also get these clamps from INOX fasteners in Southampton, found them to be a good source for fasteners
www.inoxbolt.co.uk/ (http://www.inoxbolt.co.uk/)
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The problem with jubilee clips is that they cut in to the rubber as you tighten them up and can cause leaks. The inside of the jubilee is serrated and drags across the rubber as you tighten . A better option is Mikalor supra hose clamps which are smooth ;)
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Delty rider: 32 - 50 mm
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Thanks again, Menno. Strange as it may seem, so far I did not have to replace my 43 year old rubber boots, by the new ones that I have bought decades ago and that are still in their packages. I've tested a couple of times by spraying brake fluid, but never detected a leak.* When revved, rpm drops to idle immediately and from 6000 rpm, bike pulls like a rocket. I presume I must be an exception. Nevertheless it's good to know where good clamps can be obtained because the OEM clamps do stretch eventually.
* I did detect a leak caused by a defect O-ring between manifold and head however.
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I have the original carb to manifold rubbers on mine and no problems at all, only tip I would give is warm up the engine and tighten the clips when the rubber is softer and more flexible.
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Fitted m Gerben set of refurb carbs today, all synced up and my bike is running better than it ever has.
Wish I had made this investment ages ago he sure does a good job an highly recommended😀😀😀
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Congrats, Paul!
So, now just ride ;)
happy New Year 2020!
:D