Author Topic: Revs rising on tickover  (Read 715 times)

Offline paulbaker1954

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Revs rising on tickover
« on: December 01, 2019, 04:40:03 PM »
Started bike today for first time in weeks.

 Left to warm up and tickover keeps randomly jumping to around 2k. Drop back down with idle screw and then does it again.
New plugs, carbs clean, Boyer ignition recently fully tested at Boyer, idle mixture set ok and carbs balanced

Anyone any bright ideas? I seem to recall a similar post a while ago
If you think there's light at the end of the tunnel it's usually another train !!

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Offline Nurse Julie

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Re: Revs rising on tickover
« Reply #1 on: December 01, 2019, 04:42:24 PM »
With everything you have done and changed recently Paul.... it can only be one thing, an air leak.
Im a Nurse, trust me, this won't hurt.....much !!!

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Offline paulbaker1954

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Re: Revs rising on tickover
« Reply #2 on: December 01, 2019, 04:49:45 PM »
With everything you have done and changed recently Paul.... it can only be one thing, an air leak.

No chance I am afraid, new OEM rubbers and new really tight clips and new o rings on head/manifold as well
If you think there's light at the end of the tunnel it's usually another train !!

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Offline Nurse Julie

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Re: Revs rising on tickover
« Reply #3 on: December 01, 2019, 04:54:04 PM »
With everything you have done and changed recently Paul.... it can only be one thing, an air leak.

No chance I am afraid, new OEM rubbers and new really tight clips and new o rings on head/manifold as well
Mmmm, only other obvious thing I can think of then is the plugs. I know you have fitted new ones but I take it they are NOT resisted plugs along with resisted plug caps?.
Im a Nurse, trust me, this won't hurt.....much !!!

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Offline Mr Helicop

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Re: Revs rising on tickover
« Reply #4 on: December 01, 2019, 08:43:35 PM »
I had the exact same problem and I thought I had tried everything, I don't know which carbs you have but mine had the wrong pilot screws fitted, should be solid rather than drilled ones which also have a different profile, I had also fitted a cheap set of jets and needles, I rebuilt he carbs again with the right jets and pilot screws and put a lot of effort into cleaning the pilot circuit which is covered in detail on the forum somewhere. I have 069 carbs. Mine now runs and ticks over a treat at all temperatures, and I am running on pod filters with standard jets.   

Offline paulbaker1954

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Re: Revs rising on tickover
« Reply #5 on: December 02, 2019, 08:16:33 AM »
I had the exact same problem and I thought I had tried everything, I don't know which carbs you have but mine had the wrong pilot screws fitted, should be solid rather than drilled ones which also have a different profile, I had also fitted a cheap set of jets and needles, I rebuilt he carbs again with the right jets and pilot screws and put a lot of effort into cleaning the pilot circuit which is covered in detail on the forum somewhere. I have 069 carbs. Mine now runs and ticks over a treat at all temperatures, and I am running on pod filters with standard jets.   

Thats interesting I fitted Cruzinimage pilot screws and was wondering about them. I have the old Honda ones knocing about somewhere so will see if I can find them and fit those
If you think there's light at the end of the tunnel it's usually another train !!

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Offline Mr Helicop

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Re: Revs rising on tickover
« Reply #6 on: December 02, 2019, 08:49:57 AM »
I don't think the Cruzimage jets should be a problem as long as they are the correct ones, when I say I used cheap rebuild kits I mean unbranded from ebay, cheap for a reason. If I was starting over again I would advise to keep all the old jets and just change the gaskets, we live and learn!

I have taken this from another post - it might help to identify the correct parts.

CB500 [Area code: G,H,ED]
ID 649A
Keihin "Type 1"
Slow jet: 40
Main Jet: 78 Needle: 272304, 3rd groove
Air screw: drilled, taper 12°

CB500 [Area code: A,D,E,F,U]
ID 627B
Keihin "Type 1"
Slow jet: 40
Main Jet: 100
Needle: 272304, 3rd groove
Air screw: drilled, taper 12°

CB550F1
ID 069A
Keihin "Type 1"
Slow jet: 38
Main Jet: 98
Needle: 273004, 2nd groove
Air screw: undrilled, taper 18°"
« Last Edit: December 02, 2019, 08:56:34 AM by Mr Helicop »

Offline Nurse Julie

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Re: Revs rising on tickover
« Reply #7 on: December 02, 2019, 08:59:34 AM »
Can't personally see how idle jets would have anything to do with unstable revs and if it was idling OK a few weeks ago with the same jets fitted it should idle fine now. Have you got the correct / new washers fitted to the sync port screws?
Im a Nurse, trust me, this won't hurt.....much !!!

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Offline paulbaker1954

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Re: Revs rising on tickover
« Reply #8 on: December 02, 2019, 10:31:17 AM »
Can't personally see how idle jets would have anything to do with unstable revs and if it was idling OK a few weeks ago with the same jets fitted it should idle fine now. Have you got the correct / new washers fitted to the sync port screws?

Sorry to be dumb but what screws are you referring to? Do you mean the ones that you adjust when syncing carbs. If so yes I have the "fat" correct washers
If you think there's light at the end of the tunnel it's usually another train !!

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Offline Nurse Julie

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Re: Revs rising on tickover
« Reply #9 on: December 02, 2019, 10:48:02 AM »
I'm talking about the ones on the manifold stubs where you attach the vacuum gauge sync tubes to Paul. I'm sure you have got everything correct though Paul as you have been so thorough.
Im a Nurse, trust me, this won't hurt.....much !!!

LINK TO MY CB400/4 ENGINE STRIP / ASSESSMENT AND REBUILD...NOW COMPLETE
http://www.sohc.co.uk/index.php/topic,14049.msg112691/topicseen.html#new

Offline paulbaker1954

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Re: Revs rising on tickover
« Reply #10 on: December 02, 2019, 10:49:37 AM »
I'm talking about the ones on the manifold stubs where you attach the vacuum gauge sync tubes to Paul. I'm sure you have got everything correct though Paul as you have been so thorough.

Ah yes OK these are fine. I will have a squirt around with some carb cleaner again to double check next time i use her. Too bloody cold and wet right now  >:( >:(
If you think there's light at the end of the tunnel it's usually another train !!

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Online Lobo

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Re: Revs rising on tickover
« Reply #11 on: December 02, 2019, 11:24:54 AM »
... just to get all the obvious stuff out of the way, is the Advance / Retard in good fettle / working smoothly? (Unsure whether the Boyer retains this... my electronic ignition does)

Also you mention ‘first time in weeks’. Is the fuel fresh / no water etc.
« Last Edit: December 02, 2019, 11:27:57 AM by Lobo »

Offline paulbaker1954

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Re: Revs rising on tickover
« Reply #12 on: December 02, 2019, 12:10:30 PM »
... just to get all the obvious stuff out of the way, is the Advance / Retard in good fettle / working smoothly? (Unsure whether the Boyer retains this... my electronic ignition does)

Also you mention ‘first time in weeks’. Is the fuel fresh / no water etc.

Recently had Boyer tested and all OK (it replaces the mech advance/retard)

We were in Brisbane last year for a few days - loved the city especially the Pine Koala place
If you think there's light at the end of the tunnel it's usually another train !!

2016 Yamaha MT09 Tracer
1971 Honda CB500 Four K0

Offline Rob62

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Re: Revs rising on tickover
« Reply #13 on: December 02, 2019, 06:41:25 PM »
Don't assume that just because the inlet rubbers are new and the clips are tight that it can’t be leaking..... unlikely as it may be it needs to be checked along with all the other basic stuff...same goes for the copper exhaust gaskets.

Offline Erny

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Re: Revs rising on tickover
« Reply #14 on: December 02, 2019, 06:49:40 PM »
Paul, you recently had head off if I remember well.
What's about o rings between manifolds and head? Have you had manifolds off? Did you replace / check them? If they are still original one (>40 years old), they could be hard and when you take them off and then again on they might not seal
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