Topic: Idle problem cb500- plug read

[tennesseebreeze]

Got a little problem maybe some of you can help me with. Here's what I've got:
'72 cb500
4 into 1 exhaust
stock airbox, new carb boots tested for vacumn leaks
paper filter
new plugs NGK D8(?)
stock keihin jets #40 slow jets
mix screws out 1 1/4 out, needle second from top
carbs are clean and synched (though the carbs have been out since synching)
clear tube test done- checks out (2mm below carb body, a tiny bit low on #2)
stock ignition with brand new TEC points, gapped to .28 mm
ignition timing by static method (looking to get a strobe)

So the bike runs good, with power through most of the RPM range. The weak point is definitely in the lower range where the bike burbles like it's getting too much or not enough of something. Occasionally, it takes more throttle than is comfortable pulling out. Additionally, when the tank is on reserve, this condition seems worsened (while there is still adequate gas in the tank).

The idle is the real pain, revving high in the 2-3000 range. Then when I try to adjust the idle screw down, the idle drops and begins to stall, where I have to throttle it to keep it going. Sometimes, after riding for a time, it will just stall on pulling into my house.

With all I've done, what would you recommend I fiddle with first? Here's a picture of the plugs 1 through 4 left to right.

[calj737]

You really can't judge your fuel condition from those plugs if you've ridden them across a range of throttle positions. You need to do an idle plug chop with fresh plugs. You stated D8 plugs, aren't D7 standard for the 500? If so, the hotter plug may help solve some of your problem.

You list 2mm for the fuel height, that's a tad high and could be causing flooding or too much fuel also.

I would encourage you to check the plug caps for resistance also, as this is a common issue for spark health with stock caps. This can appease some problems until you are able to correctly verify advanced ignition timing too.

[flybox1]

+1 to calj's satements
D7EA's are standard.
Fuel level is a bit high
Check Plug Cap resistance
Do an accurate idle plug chop once done.

[tennesseebreeze]

Thanks for the response. Before pulling those plugs I let it idle for a couple minutes. I had been riding before that at a range of RPM's. D7's are what is stock, and that's what I asked for at the parts store. But I'm writing this from work and for whatever reason I remember seeing D8 on the plug. I didn't think much of it at the time, and I could be wrong. It may well be D7's. I'll check that later.

What is the method for an idle plug chop? Just new plugs and idle it? Thanks.

[flybox1]

Ride the bike around for a bit so the engine is up to temp.
Install the new plugs, start it and let it idle as low as it will comfortably idle (no throttle blipping) for 3-5 minutes (fan on the engine)
Pull the plugs and take a picture for us to see.

[tennesseebreeze]

Will do. Thanks fellas.

[Deltarider]

I'm not too fond of doing plugchops at idle with these carbs. Reason is the CB500/550 run relatively rich at idle and will ALWAYS blacken the plugs somewhat when idle is prolonged unnecessarily. Is that worrying? No, normal practice is that soon enough after departure the revs will be high enough (and so will be the temperature at the plugnoses) to burn the soot of the cold start and initial idle. I always had the D8ES-L (recommended by my dealer - overhere the D7ES was seen as the plug for break-in period only) and it has always been a very good plug. Only thing to avoid was too much idling.

[calj737]

I'm not too fond of doing plugchops at idle with these carbs on board.

So shall he remove the carbs, replace with a different model and perform an idle chop with them instead? A 3-5 minute idle will perfectly normal and its not undue. You could easily find yourself idling in traffic or at a stoplight here in the US for 2x that length of time. Are you suggesting that under those circumstances, his plugs would foul? Or that these bikes would be unrideable?

Sorry, you're mad or mistaken. Or both.

[tennesseebreeze]

Before we argue over plugs I guess I should find out what plugs I actually have.  Also, I need to check the gaps. They are supposed to come pre-gapped, but I never checked. Also, help me out- how do I check the plug cap resistance? Do both wires go into the cap, or do I use one to go to ground?

[flybox1]

Remove the cap from the wire, check for identification stamp on it.  Might say 5K ohms and the part # (ie. VD05F)
Set your meter to K ohms, one lead on each end.  If its a 5k ohm cap, its resistance should be under 7k ohms.
Any higher than that and the cap should be replaced.  Too much internal resistance to create a strong spark.

[Deltarider]

So shall he remove the carbs, replace with a different model and perform an idle chop with them instead? A 3-5 minute idle will perfectly normal and its not undue. You could easily find yourself idling in traffic or at a stoplight here in the US for 2x that length of time. Are you suggesting that under those circumstances, his plugs would foul? Or that these bikes would be unrideable?

Sorry, you're mad or mistaken. Or both.

You don't get it and you never will if you concentrate on what is said in schemes, books and what not. Point is that, if you've adjusted idle mixture so that you have nice tanned sparkplug noses you will have when it concerns a CB500/550 a bike that runs bad. So what's the use of idle plug chops then and sending people in the woods with a lot of work and every time the risk of damaging sparkplug porcelain, threads and what not. With only books and scheme's that speak in general backing your advice? Thank you very much.

[tennesseebreeze]

So shall he remove the carbs, replace with a different model and perform an idle chop with them instead? A 3-5 minute idle will perfectly normal and its not undue. You could easily find yourself idling in traffic or at a stoplight here in the US for 2x that length of time. Are you suggesting that under those circumstances, his plugs would foul? Or that these bikes would be unrideable?

Sorry, you're mad or mistaken. Or both.

You don't get it and you never will if you concentrate on what is said in schemes, books and what not. Point is that, if you've adjusted idle mixture so that you have nice tanned sparkplug noses you will have when it concerns a CB500/550 a bike that runs bad. So what's the use of idle plug chops then and sending people in the woods with a lot of work and every time chance of damaging sparkpluk, threads and what not. With only books and scheme's backing you. Thank you very much.

I think both of you have good points. It's clear to me, especially after reading all of Hondaman's notes in the FAQ section, that these bikes were not perfect in stock form. Improvements can definitely be made, IMO. Starting from some kind of base-line seems prudent though. And the base-line would be what is found in the manuals with stock specs. But I'm not starting with a totally stock bike. Every change to the bikes effects something else, and it comes down to a balancing act. Even if I get this thing running well as it is, down the road I'll want to make further performance enhancements that will have me chasing rabbits again.

[Deltarider]

There could be a misunderstanding by me using the world 'fouling'. Maybe I'd better used the word 'blackening'. All oldstyle 500/550s will blacken the plugnoses somewhat at idle. Nothing to worry about, you'll burn it of, that is: when you go riding. These models do not have acceleration jets and the chosen plugs have to perform from as low as 1000 to as high as 9500 rpm! How the American Honda Motor Company in their booklet can have recommended 2 turns out for the airscrews remains a mystery to me, btw. Mine won't even pick up well when it's a tad further out than 1¹/₈.

mix screws out 1 1/4 out, needle second from top

In Europe it's 1 turn out ⁺/_- ¹/₈. In US for some reason it's 2 turns. Needle in Europe is in middle (3rd) position) In US for some reason it's 4th from top, to avoid misundertanding not tip but top.

(though the carbs have been out since synching)

Doesn't affect sync.

clear tube test done- checks out (2mm below carb body, a tiny bit low on #2)

Fine

stock ignition with brand new TEC points, gapped to .28 mm
ignition timing by static method (looking to get a strobe)

That's good so you can see if the advancer does what it should. On old bikes sometimes the grease in the advancer has hardened and this will affect proper performance.

So the bike runs good, with power through most of the RPM range. The weak point is definitely in the lower range where the bike burbles like it's getting too much or not enough of something. Occasionally, it takes more throttle than is comfortable pulling out. Additionally, when the tank is on reserve, this condition seems worsened (while there is still adequate gas in the tank).

This could be an indication. Are you sure fuel supply is OK and consistent OK? Not hampered by kinks or inline fuel filters?* Tank ventilates? The so popular floatlevel check here is no guarantee that level will stay OK whilst underway. What about your fuel. It wouldn't hurt to ad some additive that cleans the fuel system. Worked a miracle for me and freed float needles that would stick intermittently.
* On the 4-4 500/550s that originally had these oldstyle carbs, fuel lines standard length were 18 and 30 cm with the oldstyle petcock and 17 and 28 cm with the new type petcock. Ideal diameter is Ø 5,5 mm. Guaranteed no kinking!

[tennesseebreeze]

To answer your questions, I took the advancer apart and cleaned all the old crud in there. Lubricated it and it appears to function as it should. I've tried a number of octanes of fuel, and put in ethanol-free whenever I can, which is about half the time. It doesn't seem to affect the idle performance, neither do additives like seafoam or chemtool. As far as the fuel lines, they are not kinked or obstructed, and I have no secondary inline fuel filters to hamper flow. The lines are the right size and are Honda brand. As far as the tank venting, I believe it is. I would think it would impede top end as well as idle.

How much can the ignition timing affect idle if the advancer is operating correctly?

[scottly]

How much can the ignition timing affect idle if the advancer is operating correctly?

Incorrect timing can affect the idle a whole lot, and even more if the advancer isn't operating correctly: when tested with a strobe, the timing on both sets of points should be at the F mark at idle, evenly advance as the RPMs increase to full advance at about 2500+ RPM, and return to the F mark. The timing should be set before attempting to sync the carbs.
I thought all your issues were resolved when you replaced a condenser?
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