Honda-SOHC
SOHC.co.uk Forums => CB500/550 => Topic started by: DomP on July 20, 2024, 09:48:24 PM
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Am I missing something in all the carb sync guides, I read them as wind out idle screw fully then set engine side gap using a small diameter drill bit (1mm). This then means I can't bottom out the carbs though doesn't it?
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I've read back through Kens suggestion that he fully backs out the idle screw then adjusts every slide until he sees them just start to lift off bottomed out position, sets them all the same then adjusts the idle crew to open all four up.
This enables full closure if needed during set up. Is this a better method?
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That's pretty much what I did on my 500 however I found I ran out of thread on the stop screw to get it to idle - the spring was over compressed. I ended up using Epoxy resin & a metal tab to build up the stop cam on the throttle shaft.
I've not put the carbs back on (again) as I need to sort out a couple of bowl threads. I'm having a Sabbatical from the 500 at the moment - taking out the 400 instead until my former enthusiasm returns.🏍ï¸🏍ï¸🏍ï¸
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That's pretty much what I did on my 500 however I found I ran out of thread on the stop screw to get it to idle - the spring was over compressed. I ended up using Epoxy resin & a metal tab to build up the stop cam on the throttle shaft.
I tried watching the German bloke on YouTube with translation on, hilarious but not much help🤣
I've not put the carbs back on (again) as I need to sort out a couple of bowl threads. I'm having a Sabbatical from the 500 at the moment - taking out the 400 instead until my former enthusiasm returns.🏍ï¸🏍ï¸🏍ï¸
That's pretty much what I'm finding Ted, I'm quite configured by the many and varied opinions on the distance between the bell crank and throttle cable as well
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On my 400 I went for a small gap IIRC it was 3/32" ( close to a small Pop rivett shaft) no issues with the throttle stop thread - it idles a treat - I set it at 1100/1200 rpm but I have enough thread that I can easily set it at below 1000 or until it stalls.
Avoids any hanging throttle issues on the 400, I'm guessing it will do the same on my 500.
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I'll probably test my patience refitting the carbs tomorrow and see how it idles, hopefully an improvement on how it was, no3 carb float was at 23mm rather than 22 so that may have had something to do with it
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I am losing my patience setting up my 400/4 carbs. They have now been off the bike three times. I have been using a 1.5mm drill to set the slides (from the engine side). I put the carbs back on the bike and one of two things happen, it will either rev it's nuts off at 300rpm (throttle stop wound fully out as is the fast idle screw), OR it won't tick over at all and if it does it runs like a pig and the vac gauges are miles out between the carbs even though they have been bench synced!
I'll take them off again tomorrow as something is obviously wrong somewhere but I cannot find what it is or are my carbs just worn out?
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I would try either 1 mm or go for the point where the lifter just starts to rise.
I used this as a guide https://www.vintagebikebuilder.com/cb350-400f-carb-rebuild-demonstration.html
I did not have a 1/8" drill bit as per the vintage bike builder guide so went smaller I think it was 3/32" but not 100% sure it might have been a tad smaller.
If you go for the point where the sliders just start to rise on each carb you could then check if there is enough travel in the
throttle stop screw for it to adjust up to 1/8.
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1/8 is a bit big 1mm far better.
I back off the adjuster till the slides bottom then slowly open it till the drill just fits under one slide and adjust the others to suit
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1/8 is a bit big 1mm far better.
I back off the adjuster till the slides bottom then slowly open it till the drill just fits under one slide and adjust the others to suit
That was my mistake, not using the idle to open them up to take the 1mm bit before adjusting all to suit. I think I've got them right now, idle screw is nicely in the middle of its range and the throttle stop screws will adjust to meet.
*The only thing I've noticed is I seem to have too many threads showing on the adjusters, 4-5
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1/8 is a bit big 1mm far better.
I back off the adjuster till the slides bottom then slowly open it till the drill just fits under one slide and adjust the others to suit
That was my mistake, not using the idle to open them up to take the 1mm bit before adjusting all to suit. I think I've got them right now, idle screw is nicely in the middle of its range and the throttle stop screws will adjust to meet.
*The only thing I've noticed is I seem to have too many threads showing on the adjusters, 4-5
I am slightly confused by you mentioning the idle screw & throttle stop screws.
I assume you mean the choke link screws.
I also found there was always one pair of links that had more threads showing on the adjusters. I even took it to bits to make sure that both sides of the plunger/springs were in place.
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I'll try a 1mm drill today. To achieve the 56mm on the closing cable (the lower one) I found I had to rotate the bell crank slightly on the spindle, the adjustment bolts still sit on the flats of the spindle but that was the only way I could achieve the 56mm as stated in the Haynes manual otherwise it was 52mm.
I've watched so many YouTube videos of how to set these carbs up it has become confusing, everyone appears to have their own methods. One guy refuses to use four sync gauges and only uses one gauge with a separate manifold with tap offs!
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Yamaha supplied the one gauge with rotary tap and i found it useless as adjusting one carb alters the rest
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All back on and set to 1.5 turns out, no more hanging idle but smells very rich. Could it just be that I need to get out on it and get some miles on it now?
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Yes, get it all running then service at 500 miles
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All back on and set to 1.5 turns out, no more hanging idle but smells very rich. Could it just be that I need to get out on it and get some miles on it now?
Aside from it smelling rich are there other signs such as an overly cold exhaust - I assume you have tried opening up the air screws a tad.
I found a decent run often helps as you get the whole system up to temperature plus when riding you will burn up the fuel through the rev range moving onto the main needle jets.
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Sounds a plan Bryan!
I've gone to 1 3/4 out to see how it is, just a bit smokey and stinks when cold
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Well the ride out didn't go to plan, started kangarooing and lost power then cut out. Left it for a bit, got going then lost power again so I'm pushing it one mile from home up a steep hill😫
Hopefully not catastrophic, it didn't sound good
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My 500 kept doing that when I did a few pre-strip down rides.
It turned out my big feet in boots were pulling the choke lever up when I changed gear.
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I had noticed a noise coming from the generator side, this what I've found.
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Were the casing dowels both in place?
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Were the casing dowels both in place?
Yeah both there Ted, I can't work out what wound cause it. Initially I was worried it was engine internals noise but it was definitely from this side so I've had a look at the oil which initially looks as good as new still, might be an idea to drop the oil in any case to check for regurgitated engine parts?
Edit* I know what it is now, the three screws holding the coil on have all worked loose. I must have not done them up tight enough or used any threadlock on them, hopefully not too much damage caused!
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The steel should have protected the windings.
WARNING
DO NOT run the engine with that casing off or you will get a fully lubricated floor and loose to the farthest dirty area a nla plug
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The steel should have protected the windings.
WARNING
DO NOT run the engine with that casing off or you will get a fully lubricated floor and loose to the farthest dirty area a nla plug
🤣 I've read you mention that before Bryan, I'll make sure I don't. Presumably this will be the reason it sounded awful and lost power.
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All back on and set to 1.5 turns out, no more hanging idle but smells very rich. Could it just be that I need to get out on it and get some miles on it now?
Aside from it smelling rich are there other signs such as an overly cold exhaust - I assume you have tried opening up the air screws a tad.
I found a decent run often helps as you get the whole system up to temperature plus when riding you will burn up the fuel through the rev range moving onto the main needle jets.
Agree with this.
Would go further in this direction to evaluate what range you're actually operating in. Turn the airscrews out to 2 3/4 for a functionality check in establishing IF there's enough range of adjustment to correct what exists currently.
If they get to 3 turns out, and without correcting mixture adequately, likey that the idle jets themselves are flowing too much fuel. This is effectively what an "engine check light" on fuel injection is doing, telling you it's reached the maximum allowed in programmed adjustment but not successful in fully corrected output.
MOST of these carburettor would have the adjustment range of screw within 1 ~ 3 turns out, past those positions would indicate the fuel jet is too large or too small for application. That could be partly blocked, enlarged through cleaning, or the wrong size simply installed.
Going for maximum outwards is not to run it like that but to answer the question of IF it can be corrected within design parameters. Try it to find out. It could be that one size smaller jet is suitable in this case.
Before this though, are you confident of the air filter fitted ? That could also significantly skew results here.
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Thanks Nigel, that's very helpful. I'll try further out to see where it gets me. The air filter is a new genuine Honda 500 as I've done away with the vent pipe as per Kens recommendation and all jets are Keihin for this model of bike and the 069a carbs
I've just taken the plugs out to see if they are still sooty after the run that ended abruptly yesterday, this is what all four look like.
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Which plugs are they Dom and were they new?
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New Julie, NGK D7EA from the green plug company so I'd hope genuine
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New Julie, NGK D7EA from the green plug company so I'd hope genuine
I'm sure they are Genuine Dom, we've never had a dud one from The Green Sparkplug Company. Most of the plugs we've had from them have been Denso though.
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The picture of plug shows the tip oddly hot, in contrast to the running rich observation.
I'd doubt of there's any problem with plug and it's manufacturing if they all start and run reliablly.
Likely the short run wouldn't give a valid and more comprehensive view initially though. If it's all together and seems to be running without error generally., then more miles 5~10 run to then look at the plugs again would give more insight.
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So if I get 5-10 miles on it then hit the kill switch and get the plugs out
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I hate repeatedly taking spark plugs out as once you have fitted them correctly and the sealing washer has flattened that should be it until it needs a plug change. I'm also a tad paranoid about stripping a plug thread on alloy heads.
In my youth it was advised to change the sealing washer if a plug was removed for cleaning at a first service and put back in. You could buy replacement loose washers. I think it was also advised in the leaflets that came with spark plugs back in the 1960s. I'm remembering here that four spark plugs were less than a £1 back in the 1960's.
I am guided more by how an engine runs - does it idle okay, is the acceleration smooth without obvious flat spots when it's "on Cam" the colour of the exhaust pipe after a decent run, is the exhaust cold or hot at idle.
Since I rebuilt my 400 engine I have not removed the plugs as I'm happy with how it runs. My 500 is a different story so I am reading your posts with interest. I'm seriously thinking about replacing the four slow running jets before I put the carbs back on as I do not know for sure how many bits of wire might have been poked inside them - they are all stamped 40 iirc.
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So if I get 5-10 miles on it then hit the kill switch and get the plugs out
The miles should clean out combustion, allow it to reach full running temperature, and clean any fouling from the plug surfaces to avoid giving false perception after cold start etc.
Kill switch routine is ordinarily when you are checking fully loaded running at big throttle opening and hard on torque demand. That entails pulling it hard with substantial throttle, running up fully on main jet at maximum demand conditions to asses the mixture under those circumstances. Valid for those reasons as you want to suspend running right at that maximum demand to get the most accurate picture of the prevailing combustion conditions.
It's not for this scenario of general setup and checking if the very low speed system of jetting is accurate. A simple run out to get it fully warmed etc is just fine to build a picture.
I don't routinely replace plug washers, always use a light smear of copper type lubrication on threads, and lightly tighten. Never have any leaks or compromised threads in practice.