SOHC.co.uk Forums > CB500/550

Raising that needles.

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K2-K6:
The overheating is not really an issue.

To seperate it from running an engine under load (dyno work) in static air is important.  That's not reasonable.

Idling they'll effectively do all day without technical problems as the fins are specifically sized to cope with this by radiation.  Certainly I've sat with very little air movement going into and out of bike race meetings in summer temps for extended periods without ever having a problem.

The heat coming off the engine definitely increases,  but that's what fins are supposed to do.

The PD carbs are very finely metered (one reason why those setup are generally good for fuel consumption) and this proceedure may tell us something in understanding the issue. It may end up showing different set point for fuel in use as likely it's now running e-fuel, unless specifically avoid by OP.

It'll be interesting to see what the manual set up routine gives in the way of screw settings.  Certainly testing like this is reversible and effectively no cost to judge it.

deltarider:
I agree that the danger of overheating, like in the international forum, is often exaggerated. Some live their moment of fame by not only echoing others you must have a fan, but in some cases added you need two. ;D ;D I never felt the need to use one like when syncing. Procedure was done within 20 minutes though.
The procedure you have described is good ofcourse... in theory. More than once I have scanned the internet hoping to find a video, like on Youtube, where it is demonstrated with success.
So far: not one. So anyone is invited. ;)

Johnny4428:
Appreciate and understand all your interesting comments. You know what, if my 550 never runs any worse I would be quite happy. But just thought that I could improve on that midrange hesitance. I guess fuel was different and with everything new in the 70’s things were different, especially with settings being quite critical.

K2-K6:
Thoughts to hopefully add a little to this and maybe influence that hesitation.

It's something that all petrol engines and their different metering systems have to cope with. Running at constant demand takes a prescribed amount of fuel in mixture balance to be effective, this is insufficient to get the motor to accelerate quickly.
Most system on opening the throttle do the opposite in metering terms, in that as the throttle restriction is opened it causes the metering to move leaner and can prevent the motor accelerating as commanded.
All the different systems cover this in a different way. Plain old type slide carbs run too rich most of the time to avoid this, CV type hold the floating valve (through damping) to keep the vacuum constant as their name indicates, can even be set to give raised vacuum at this point of acceleration to help increase fuelling. Fuel injection, monitoring of throttle position applies additional fuel if the rate of throttle opening is measured as faster than mapping equivalent to avoid this lean stumble. PD on 750 F2 uses accelerator pump to dump additional fuel into carb if you increase throttle in fast application.

These other PD type rely more on idle jetting to give some increase to help. As it's brought up from closed throttle under load the idle circuit more quickly hits saturation in delivering more fuel at that point through it's balance against venturi depressions. That circuit is very accurate in it's original design specification to give emmisions clean idle in that period on manufacturing, and so there's very little "fat" to work with. What may seem like very small changes can really help in setting the idle circuit to try and remove hesitancy in driving.

Some things you could try in assessment to see if you can improve.

Use R plugs and R plug caps together, set the gap to minimum book specification and ride it to see if there's any change. This appears to improve firing at marginal mixtures (slightly lean under throttle roll on) that can exist to give that flat spot hesitancy.

Using something like a piece of fleece material taped over the airbox inlet just to see if you can bias the mixture in encouragement to slightly richer bias. This to assess at low cost and work levels to see if it improves it and what colour the plugs then run.

As you note, it's more annoying then anything else,  but won't take a full step on moving the needles.  This shows it's really close to not existing, so dealing with small margins.

Hopefully something to play with and see if you get something out of it.

ST1100:
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--- Quote from: deltarider on March 16, 2022, 08:30:02 AM ---In the meanwhile you are plaguing the engine with prolonged idling and possibly overheating.
--- End quote ---
I plant two office fans on HIGH in front while tinkering with carbs & settings... (also driving exhaust fumes out the gate...  8) )

My (new) electronic synX has a pretty sensitive/precise tachometer...

https://www.louis-moto.co.uk/artikel/synx-synchroniser-classic/10034539

To some degree down-pipe temperatures are also an indicator for rich/lean mixtures...

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