Lazy return to idle

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ukking
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Lazy return to idle

Post by ukking »

I recently purchased a '79 CBX wih just over 2000 miless and have a minor problem with return to idle when changing gears. The carbs have been rebuilt and it starts and idles great (idle speed is correct). When riding it feel normal throughout the rev range and pulls like a champ. The problem is return to idle between gears. The revs do not drop between gear changes as fast as they should. Althought not bad (ie. the revs do drop somewhat) its not quite right and it detracts from spirited riding. I experienced the same problem once before on a (dare I say it...) '76 Goldwing and checked everything (timing, carbs, compression, valve clearances etc.) and never really found the answer. Any advice/insight here would be appreciated.

Great site by the way.. Thanks. Graham.

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Post by Chris »

Graham,

It can be several things but what I would check first would be......

1. Throttle cables. Make sure they are adjusted properly and not binding.
2. Choke. Make sure your choke is not sticking slightly shut. This is a common problem where the choke cable is attached to the carbs.
3. Possibly carb synchronization is needing adjusted.

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Post by EMS »

An air leak is another possible culprit. Spray some starting fluid or maybe even WD40 around the intake manifolds between carb and cylinder head and see if the rpms go up.

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Post by ukking »

Thanks for the suggestions. The choke may have been the problem. Having fiddled with it to make sure it wasn't sticking, the idle dropped and I had to turn the throttle stop screw in a couple of turns to get it back to normal.

A new thing I noticed today was some sparking between plug cap 2 and the frame mounting point when the engine was hot. The clearance seems very tight at that point. Is this a common problem with #2 when the original CBX caps age? All the other caps seem fine.

Thanks again ...

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Post by alimey4u2 »

ukking wrote:
A new thing I noticed today was some sparking between plug cap 2 and the frame mounting point when the engine was hot. The clearance seems very tight at that point. Is this a common problem with #2 when the original CBX caps age? All the other caps seem fine.

Thanks again ...
ukking, Tis a problem with all HT components of this age, the rubber breaks down & becomes hygroscopic. Change to silicone, Accel or Dyna S.
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ukking
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Post by ukking »

Interestingly its arcing through the cap itself, where the cap is closest to the engine mounting point, all the HT leads are good....

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Post by alimey4u2 »

ukking wrote:Interestingly its arcing through the cap itself, where the cap is closest to the engine mounting point, all the HT leads are good....
Electricity travels the easiest path...If it is travelling across a wide gap, I would think the plug cap is bad &/or the plug gap is too wide or open . Under compression the smaller spark plug gap is more difficult to stride but in all I stand by my diagnosis... :wink:
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ukking
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Post by ukking »

Thanks for your reply. No question, the old plug caps are bad - I wasn't disagreeing with your diagnosis. My point was I found it unusual to see sparking through the cap rather than through the lead. I swapped the caps around and they all sparked through to the frame to some extent at the same point when in #2 position but were fine everywhere else. The plugs are all brand new and gapped correcly.

Unless I'm missing something, all the other plug caps (including #5) seem to have additional clearance by comparison to #2. Because the frame mounting point is so close to the #2 plug cap, I suspect this might be a common problem with bikes still using the OEM plug caps. It only happens when the engine is hot, after running for 10-15 minutes or so and is really only noticable during idle as a very slight misfire from the left hand exhaust - barely discernable over the clutch chatter....

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Post by Terry »

I have Taylor braided wires on the 79 and I think, stock but probably not OE stock, wires on the 82 and have never had this problem. I have a set of Accel wires and a spare trio of coils just in case though. BTW, if you didn't know, a good carb synch can sometimes get rid of some of the 'clutch chatter' you spoke of. :)
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Post by alimey4u2 »

Graham, If all the HT components are good, proximity to the closest potential grounding point would be irrelevant. However, those that are still using the original OEM HT components could come across the phenomenon you speak of. Most have upgraded to quality aftermarket components but those who want to keep the stock "look", I spose replace with new stock (if available) ? Personally, I use Dyna S components which haven't failed in 25 years.....

If you want a quick fix for your existing cap, soak it overnight in WD40 & then give it a fresh dose now & again..... :idea:
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ukking
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Post by ukking »

Thanks for the WD40 tip. I'll try that. The bike is totally stock apart from the tires and I prefer to keep it that way as long as I can still ride it without any problems...

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Post by alimey4u2 »

WD40 is a dispersant, It will wrap around water molecules & migrate the moisture to the surface & allow it to freely evaporate. The cause of your "tracking" is moisture absorbed within the aged plastic/rubber spark cap...
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