Honda-SOHC
SOHC.co.uk Forums => CB500/550 => Topic started by: RBoss on February 23, 2022, 05:13:45 PM
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Hi All,
Recently I have rebuilt my engine by putting in a new primary and cam chain. After reinstalling it into my frame I went for a test drive. All went pretty smooth, the engine is nice and quiet, but it doesn't want to "pull through" at higher rpm. It holds power in when I want go above around 6/7000rpm. Spark plugs are also very white so it appears to be running lean. How I don't know... Before the engine rebuild I rebuilt the carbs and had them cleaned.
My setup:
- jet size 100
- stock airfilter
- airscrews 1 full turn outward
- electronic ignition
- new rubber inlets
- new spark plugs NGK D7EA
- 4 into 1 exhaust
Anyone have an idea what could be it?
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If you need to keep running it like that initially, then change the plugs to #8 as it'll give you more safety margin. This won't fix anything but with the plug tips getting very hot (white colour on #7) then it risks making pre-ignition which will lead to melted pistons if you're not careful.
Do you know the needle position and what size the idle jets are ?
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Did you remove the inlet manifolds? always replace the o-rings in them if you did as they grow hard and won't reseal after removal. It's the heat cycle which does for them. I'd imagine that the engine is sucking air in from somewhere causing the weak mixture.
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If you need to keep running it like that initially, then change the plugs to #8 as it'll give you more safety margin. This won't fix anything but with the plug tips getting very hot (white colour on #7) then it risks making pre-ignition which will lead to melted pistons if you're not careful.
Do you know the needle position and what size the idle jets are ?
Yes needle position is in the middle. Idle screw I don’t know for sure but I figure that is stock either.
Did you remove the inlet manifolds? always replace the o-rings in them if you did as they grow hard and won't reseal after removal. It's the heat cycle which does for them. I'd imagine that the engine is sucking air in from somewhere causing the weak mixture.
I did replace all those o-rings… really can’t think of a place where it sucks extra air from… the air mixture screws should not be twisted in any further right?
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Check the carb sync screws on the inlet mainfolds to make sure they aren't loose. You could try the carb cleaner trick , run the engine and spray around the carbs to see if the revs increase, if it does, you've got an air leak. Any splits in the manifold rubbers?. Did you remove the cylinder head?
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which carburettors do you have ?
are the carburettors statically synchronised?
do not screw in the throttle any further if the engine has not been softened.
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Check the ignition timing, it could be over advanced.
If you can, use a strobe at 4,500rpm
Sent from my SM-A750FN using Tapatalk
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When you rev and snap close the throttle, does RPM quickly return to idle* or is it with some hesitation**? Are your jets etc. genuine Keihin or aftermarket?
* If it returns quickly, which is good, I'd verify fuel supply is sufficient riding. Any 'extra' inline fuel filters that can impede fuel flow? You may want to read this: http://forums.sohc4.net/index.php/topic,187633.msg2176352.html#msg2176352
** Verify the operation of advancer is smooth. If operation is smooth (good) I'd check for air leaks.
When you are in doubt of airscrews position, I may be able to help; where about in A'dam are you?
Can you make it to my garage near the Weteringcircuit?
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Thanks for all the replies!
I have the feeling it is the ignition timing. I rebuilt the engine without adjusting the timing again and I think that should be done, I did put the plate in the same position but maybe something is off. I have the feeling that it can’t be the carbs as I had them rebuilt before I rebuilt the engine and I tested them on the bike before that and all went well.
I may be able to help; where about in A'dam are you?
Can you make it to my garage near the Weteringcircuit?
@deltarider, very nice offer! The bike is currently in Driebergen and I’ll try to fix the ignition there. Might that not work, I live close to the Oosterpark so the Weteringscircuit (schans?) is very close, I will keep you posted on the ignition timing!
Ruben
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All the symptoms you have pointed out, point to timing but, i would check the cam chain is not one tooth out first before, you go on a wild goose chase with electrics ;)
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I’m a bit confused by this one and I’m watching and learning. I thought Erny began this thread stating he had a very obvious and extremely lean burn? This may have precipitated his subsequent query about appropriate air boxes/filters. Purely out of interest, would a single tooth cam timing error create this lean mixture situation?
Sounds like poor Erny will have to start a sequential diagnostic programme…..cam timing….ignition timing and advance…valve settings….fuel supply. This will then only leave the carbs and air system?
Just wondering…
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Ignition always comes first in diagnosing. No matter what ignition you have, concentrate on a correct timing at full advance. I like mine to be just a tad more advanced than the outer mark. Then just accept the timing @ idle it will result in and live with it. Although I recommend using a strobe timing light, I myself don't do the actual adjusting dynamically. I set and then check using the timing light. If I need to readust, I first kill the engine, do an extra adjustment and check again. If necessary, I repeat this. This works best.
The position of the airscrew you have now, is a good starting point. A genuine Keihin one will look like shown below.
You're welcome anytime. I'm interested to see yours, as a 'K(0) 1975' is a rarity. ;)
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I've been talking to Mark Paris (Hondaman) a lot lately. Did you know BTW he's writing a book on the 500/550, the same type as he did for the 750. Anyway, he recommends removing the advance/retard springs and cutting a half turn off the end of them both, reshape to match original curl and refit. The stronger spring evidently changes the engine from its characteristic "switch ON, Switch OFF" torque sensation at 5000+ RPM to one of more linear response with more torque on hand all the time.
Off topic I know but very useful information which is sort of on topic in a way.
I'd second checking the valve timing before anything else, if it's one tooth out there is a great potential there for major damage. Might be a waste of time checking BUT it's worth it for peace of mind, if of course the engine ran just fine then you've clearly got it right but that's not the case here.
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I’d love to see a physical representation of the spring modification. Any volunteers?
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I've been talking to Mark Paris (Hondaman) a lot lately. Did you know BTW he's writing a book on the 500/550, the same type as he did for the 750. Anyway, he recommends removing the advance/retard springs and cutting a half turn off the end of them both, reshape to match original curl and refit. The stronger spring evidently changes the engine from its characteristic "switch ON, Switch OFF" torque sensation at 5000+ RPM to one of more linear response with more torque on hand all the time.
What makes you think this will be benificial? So far I haven't read one positive result, not one. One was frank enough to say he has experienced a negative effect... And I have followed it closely. Don't you think Honda was able - in a highly competive market - to design the best overall advance? It was never even clarified what advancer this was about: the Hitachi or the TEC? When you have sloppy springs, it may affect the idle somewhat. Then you can either tweak (no need to cut) the end of the spring or order new ones, about € 12,- a pair.
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Does anyone know if the springs change their rate with use when they get 'slack' on the auto advance? I have loads of used auto-advancers for various bikes and a few NOS ones including the 500/4, CB450 K0 bomber and CB250/350K.
I just built a test rig for where I work, which uses a linear stepper motor, load and displacement transducers inputted into an Agilent VEE based PC XY plotter, primarily to test the force/displacement characteristics of the solenoid coils we use....... but it will be ideal for measuring the spring rates of small tension or compression springs (Max force is about 20kgs)
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According to Mark Ash the springs get "annealed" by the constant hot/cold cycle and as they get older he recommends doing one spring at first and then the other as the bike ages. However at the age of our bikes i'd say that 40 odd years is enough to say do both.
As for being beneficial? Well it's not my theory but it is a suggestion from a mechanic with a whole wide reputation, there isn't much Mark doesn't know and he's well respected by everyone. As for Honda, in the age when the 500 was produced there was no competition except 2 strokes and those are not exactly equal. Honda did what Honda did due to economic pressures, it was designed for multiple markets so it was a compromise for varying air density etc
The theory seems to be to make the engine slower to advance, new springs aren't going to do this as they will just act as Honda designed them.
Here's a extract from Marks replies "most likely because the design suffers from a too-soon spark advance that causes the engine to spit back toward the carbs until about 2500-3000-ish RPM, which then makes the carbs run slower and richer than they should at that RPM"
I got a lot of suggestions for improving BHP, improving response and making the engine better for round town along with some stuff for track. I suppose all these will be in the new book. As the 750 book is regarded as a sort of bible I'd imagine the 500 will be regarded in the same light.
Phil, I'll be doing the mod BUT I'll also be doing quite a few other engine mods, like the camshaft one we talked about, matching the inlet manifolds, porting the head etc.
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Should be a sweet motor, Ken. Would be interesting to do a dyno contrast and compare exercise with an unmodified 500 in decent nick?
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Does anyone know if the springs change their rate with use when they get 'slack' on the auto advance? I have loads of used auto-advancers for various bikes and a few NOS ones including the 500/4, CB450 K0 bomber and CB250/350K.
I just built a test rig for where I work, which uses a linear stepper motor, load and displacement transducers inputted into an Agilent VEE based PC XY plotter, primarily to test the force/displacement characteristics of the solenoid coils we use....... but it will be ideal for measuring the spring rates of small tension or compression springs (Max force is about 20kgs)
They don't appear to be fully "spring"steel by cursory examination (you wouldn't be able to re-bend the ends otherwise) and look more like mild steel.
The difference is primarily in the carbon content which is used to set the steel spring by quenching (hardening) then tempering to remove brittle aspects and prevent it snapping during use.
Mild steel lays below this in alloy properties (doesn't respond to heat treatment) and therefore can show creep in extension during use (won't pull itself back to designed form) they are just made long enough, a coil spring is just a torsion bar wrapped into a neat package, that any twist is usually insignificant in angle to move the material past it's elasticity point in the extension needed.
I can't see them changing in property from heat cycles as they don't appear to be a category of material that responds to heat.
Worth testing them just through intended range to see if they are hugely variable from average.
Not do critical in ignition performance really (honda do know what they are doing) as the sooner the engine can take advance the more torque it can make at that rpm. They all run effectively too much mixture to make it risky in broad terms.
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I’m a bit confused by this one and I’m watching and learning. I thought Erny began this thread stating he had a very obvious and extremely lean burn? This may have precipitated his subsequent query about appropriate air boxes/filters. Purely out of interest, would a single tooth cam timing error create this lean mixture situation?
Sounds like poor Erny will have to start a sequential diagnostic programme…..cam timing….ignition timing and advance…valve settings….fuel supply. This will then only leave the carbs and air system?
Just wondering…
Just wondering why I see my nick here :o :D
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If I may contribute with my story:
Back in 2019, I was working on low RPM hesitation/too rich problem with my CB550K1 / 022A carbs (engine hesitating in lower RPMs and felt like too rich)
Finaly I fixed that:
1. I first replaced points and advancer by Boyer ignition (I kept stock coils). Result - engine hesitation at lower RPMs almost gone! This for me confirms Mark's advice with worn/annealed advancer springs as Boyer has built in advance/retard in ECU. Checked with strobo, it now works as it should. But back to this topic reported too LEAN by RBoss - I think that advancer spring issue is rather too rich "effect". I discussed that with Mark Paris too BTW ;)
2. Too rich problem was caused by corroded emulsification tubes (genuine Keihin) that had bigger ID holes due to corrosion. Replacement by new Keyster (OEM needleds kept) and later by new genuine OEM set (tube+needle) fixed that. Engine now runs smooth on idle and also very smooth from idle RPMs, it picks from ~1500-2000 RPM smoothly. Current issue is that it is too lean now ::) (only tubes and needles changed, jets are the same)
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If I may contribute with my story:
Back in 2019, I was working on low RPM hesitation/too rich problem with my CB550K1 / 022A carbs (engine hesitating in lower RPMs and felt like too rich)
Finaly I fixed that:
1. I first replaced points and advancer by Boyer ignition (I kept stock coils). Result - engine hesitation at lower RPMs almost gone! This for me confirms Mark's advice with worn/annealed advancer springs as Boyer has built in advance/retard in ECU. Checked with strobo, it now works as it should. But back to this topic reported too LEAN by RBoss - I think that advancer spring issue is rather too rich "effect". I discussed that with Mark Paris too BTW ;)
2. Too rich problem was caused by corroded emulsification tubes (genuine Keihin) that had bigger ID holes due to corrosion. Replacement by new Keyster (OEM needleds kept) and later by new genuine OEM set (tube+needle) fixed that. Engine now runs smooth on idle and also very smooth from idle RPMs, it picks from ~1500-2000 RPM smoothly. Current issue is that it is too lean now ::) (only tubes and needles changed, jets are the same)
It's an interesting input, but I feel that crosses over too many causes in this area. The problem of too rich mixture will ordinarily be assisted by a good electronic system especially compared to one that is not certainly performing well (it's one of few areas it may hold distinct advantage) and so mask the real problem of fuel metering.
The true fix is to correct the mixture as you're finding I believe.
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In fact, I first did ign replacement back in 2019. This fixed most (not all) of engine hestation in lower RPMs that I felt as if engine has too much advance/too rich mix. However, still rough/uneven behaviour stayed in idle to low RPMs (typically, cruising in the city, you want to open the trottle a bit from closed).
This is no totally gone by replacing corroded emul.tubes last year. Now just with bench sync (using steel balls from bearings) engine runs very smooth! before it was impossible to sync carbs properly, even with gauges
Once I fix current too lean mix I hope I'm done... But knowing myself I'll be hunting to reach at least 100mph topspeed ;D ::) 8)
corroded tubes topic here: http://www.sohc.co.uk/index.php/topic,25641.msg235103.html#msg235103
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I have two TEC advancers and none of them give a problem. I never understood what could be gained by cutting the springs. When under 2500 rpm a somewhat fluttering idle and near idle annoys you, you can order a fresh set of springs. In normal riding practice, when I open the throttle, revs will be over 2500 rpm in a split second anyway, the advancer weights having reached the stops. What is there to gain then, that Honda overlooked? I can imagine however, that on snap closing the throttle, there may be a slight hesitive returning to a dead on steady idle, but I don't see that as much of a problem. On the contrary, it could make driveability less nervous. Let's await the results of Andreas Milke, who has made a programmable EI. When I look at the CB500/550 engine in standard form: four 125cc lawnmower engines put on a crank sharing a very tame camshaft for breathing, I don't expect much of it. But Andreas has ofcourse another reason for his experiment as the gas in Brazil contains a lot of alcool.
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Honda never supplied the springs seperate
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Honda never supplied the springs seperate
Correct Bryan .. Yamiya do these though but I wonder what they mean by 'racing' ..pretty pricey too.
[attachimg=1]
Deltarider probably means these ..but not sure if that German club sells outside of the EU
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For the OP, worth noting that it's not very far away from correct it seems and you're not looking for a big error to bring it within range.
The comments about camshaft timing (if it's been apart before this) are extremely relevant as you'll not solve it if there's an incorrect assembly there.
In addition, when it "fails" to give increased revs, then applying the choke a little to see if it will go further is useful in diagnosing if it's just lean mixture stopping it. Then you'd have to find the cause, but it would confirm it's mostly mixture for some reason.
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A member on the German forum has been making the springs for years. They're also in the shop now: https://www.cb-four.de/cgi-bin/shop/__Fliehgewichtfedern-Satz-Z%FCndkraftversteller-Honda-CB350-400F-CB500F-CB550F%2BK-CB750Four-neu__20-059-02_02.03.html
Servus
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Thread here has gone multi-strand :)
I read much of that which Hondaman writes and think he is an original thinker with very good knowledge.
However, I don't understand what he's saying there ("Here's a extract from Marks replies "most likely because the design suffers from a too-soon spark advance that causes the engine to spit back toward the carbs until about 2500-3000-ish RPM, which then makes the carbs run slower and richer than they should at that RPM") as the cylinder has it's inlet valve closed before the ignition timing, sealing off the inlet tract (it can't really work if you fire it with any valve open, can it? ) and so can't really affect the mixture as such.
In engines that use a version of the Atkinson cycle ( Toyota Prius) the inlet cam is retarded at low speed low demand to increase smooth running and efficiency as it bleeds off some compression back out the inlet to reduce effective compression. But it still doesn't interfere with the combustion being sealed from going out there during initial burn phase.
The suggestion to increase camshaft duration for inlet will affect this area of dynamic flow (it usually needs more rpm to work effectively) but no engines I I understand will fire ignition with port open.
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First of all, according to not only me, but also to Dave500 in Austalia, to name just one, there is no flat spot. When you accelarate hard from standstill, bike goes like a rocket. I test it every year at least once. What some experience as a flat spot, is something else. If you cruise at say 4000 rpm and then open the throttle, there isn't much in house (as the Dutch expression is). This was already signalled in roadtests back then in Holland and France and IIRC it has to do with the engine design, bore X stroke. This 'shortcoming' can't be helped, but can be adressed by shifting down one or even two gears.
Now, do you see Americans, used to HD's (bikes) and 7 litre V8 blocks (cars), do that?
Until I see proof, I maintain the whole thing is about nothing; it's a created problem. Always good if you want to sell something or establish a reputation.
Note, that, as always, my comment at least can be falsified. Please do.
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What about the wasted spark Nigel, could he be referring to that spitting back on the open cylinder?
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A few years ago I bought a nice condition CB550K3 from someone relatively local and it had a lean running problem. I made the point that I didn't know much about bikes & that it would have to be put in to a bike shop to be fixed.
In reality, I had a good idea where the problem was from the start & once home I pulled the carbs & replaced all four of the inlet manifold 'O' rings (part #14 on the fiche) as one was snapped & the other 3 didn't look in good enough condition. For what they cost it wasn't worth looking for cheap alternatives & having resolved the lean running it pulled in a similar way to the wife's CB550F2.
https://www.cmsnl.com/honda-cb550k3-four-england_model14671/partslist/E02.html#.Yhp5PrunzIU
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What about the wasted spark Nigel, could he be referring to that spitting back on the open cylinder?
I was thinking that through too Ken, but to me it reinforces that it's not ignition rather than causes doubt .
Taking the piston on power stroke, as it comes to bdc and looses any useful drive pressure the exhaust valve opens, then with piston coming up pushes spent gasses out past valve (wasted spark is arriving anywhere from static time to full advance on this stroke) but critically before the inlet opens. There's effectively no available fuel to ignite present, and so the spark is truly just wasted. Bringing more ignition advance to this scenario just moves the spark further down the approach and further away from any inlet opening time, and so should have less effect not more if were present.
The same sequence ends, at TDC, with valve overlap but only after the spark has gone out. Increased overlap does bring compromise though (but not controlled by the spark) because the inlet tract is exposed to exhaust pulsing which with the right design of exhaust can aid cylinder filling. This is a dynamic situation though and with more overlap in the cam will have best performance at higher speeds, giving a classic "cammy" engine that fits-and-spats until that point (often around 4,500rpm) when the dynamics clean up the exit and entry to the cylinder and the motor takes off.
Honda made the cam timing to run clean at 10,000tpm but restricted the cam to best give a conservative wildness and make it run sweetly all the way down to very civilised tickover. Quite a balancing trick to do in reality, with very basic design. I still think Honda were peerless in four stroke design during that period.
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[...] I made the point that I didn't know much about bikes & that it would have to be put in to a bike shop to be fixed.
In reality, I had a good idea where the problem was from the start [...]
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(no comment)
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Question for the OP, have you changed the fuel tap, fuel lines or installed fuel line filters on the bike recently? We've seen a few examples of restricted fuel flow that can do this in preventing the carburetor from refilling as it should and caused the bike to run lean, not go up into higher rpm.
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I have not changed the fuel line but the tank was very empty, filling it up with the fuel I had left in a jerrycan didn’t help unfortunately. There might also be something else that causes issues, the other day I did a test ride again and the bike just broke down. No electrical power whatsoever; turned out to be a melted wire at the electrical board. I bought a replacement wire harness and will install it soon. Could this have been a problem?
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Yes, the electrics need to be competent to let you judge it running. Ignition is the main draw when running, without having that in good condition you'll not know if it's contributing to the problem.
Old fuel will run (more problem starting it) but won't help you with looking for problems.
A matter of closing out these bits and then having another look to see where you are with it then. It's not far off, but fixing the obvious bits will lead you closer to getting it running well.
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Maybe no need to replace the complete wire harness, which may be quite a job. Something I've noticed in your picture; do clean the contacts on top of the solenoid (disconnect battery first). Verify the wiring of your bike is fused at all and... by the proper 15A (and not higher) one. When needed, consult wiring diagram.
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That wire has overheated due to the corrosion(green crap) at thr connector causing resistance which makes heat
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So I replaced the wiring harness… and it definitely is a lot better, it doesn’t hold in above 5000rpm anymore so I guess the problem was the faulty wire.
Good comments on cleaning up the contact points as the corroded contacts where not only on the wiring harness side.
Anyway problem solved! Thanks for all the advice everyone!