Doms CB550F1 project

[DomP]

Nah, 143mph sounds about right Dom. I take it you didn’t get it in ‘top’ then?


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No not this time Roo, this was just through town on the back wheel.

I'm considering taking the carbs off do double check the float heights, jets are all clear and that I've set the bench sync to bottom out with the idle screw out, somethings not right to be running rich 2 1/4 turns out and have a idle that keeps rising with the throttle shut.


What do you think regarding the throttle linkage Roo?

Just got home tonight axon, I’ll have a look tommoz, found a bottle of Landlord in the fridge and well that was that!


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Cheers Roo although is was meaning the 56mm distance thing but yes I'm still looking for the connecting plate

[McCabe-Thiele (Ted)]

On the 550 with the solid brass screw I thought the settings are 1/4 turn out as a base point. If you are over two turns out my understanding is that you have let so much air in it will be running  far too lean pulling fuel from the main jet when it can. Opening the screw slows down the amount of fuel from the idler jet so it's trying to  draw fuel from the main jet instead. Look at that video I posted about hanging throttles.

I believe on mine which are 069a's (550F1) the base setting is 1 3/4 turns out, if I richer it it stinks of fuel and soots up the plugs.  I'm happy to be wrong if it solves the hanging idle however 😄

The 550 manual on here shows air screw as 1 turn out plus or minus 1/8th turn - if I understand you correctly it runs far too rich when you try that. Do you have the solid brass air screws with the flat end? Are you on 40 pilot jet?

[DomP]

On the 550 with the solid brass screw I thought the settings are 1/4 turn out as a base point. If you are over two turns out my understanding is that you have let so much air in it will be running  far too lean pulling fuel from the main jet when it can. Opening the screw slows down the amount of fuel from the idler jet so it's trying to  draw fuel from the main jet instead. Look at that video I posted about hanging throttles.

I believe on mine which are 069a's (550F1) the base setting is 1 3/4 turns out, if I richer it it stinks of fuel and soots up the plugs.  I'm happy to be wrong if it solves the hanging idle however 😄

The 550 manual on here shows air screw as 1 turn out plus or minus 1/8th turn - if I understand you correctly it runs far too rich when you try that. Do you have the solid brass air screws with the flat end? Are you on 40 pilot jet?

 

Yes solid Ted and all jetting is standard keihin jets for an f1 but they are 1 1/2 +/- 1/2 turn

[McCabe-Thiele (Ted)]

Came across this post of a similar issue.


.
http://www.sohc.co.uk/index.php/topic,28462.0.html

[DomP]

Read that too Ted🤣 I seem to have opposing problems, of a hanging idle yet rich running

[McCabe-Thiele (Ted)]

Trying to think outside the box - could it be timing related - mechanical advance not falling back as it should?

[DomP]

Trying to think outside the box - could it be timing related - mechanical advance not falling back as it should?

Now you say that, I remember chatting to Ken about my trimmed advance springs.  I'd rather have standard untrimmed ones but someone in the past has cut and bent the end coil

[K2-K6]

Trying to think outside the box - could it be timing related - mechanical advance not falling back as it should?

Now you say that, I remember chatting to Ken about my trimmed advance springs.  I'd rather have standard untrimmed ones but someone in the past has cut and bent the end coil

That shouldn't, in and of itself, cause problem with tickover. It would make the "closed" position more assured to enhance stability at idle by not fluctuating at those low rpm.

Worthwhile double checking your static timing point against the F mark tough, as anything in advance (firing too early) would go to making it more difficult in settling back to consistent idle rpm.

I dont agree with shortened springs though, certainly without then getting quantification of how the advance curve plays out. Arriving too late will at the needed advance specification will reduce low rpm torque output. You'd need to accurately measure at what point in rpm range it reaches full status.
But, as noted though, that's an issue as you're asking for power and not lowest rpm stability.

[DomP]

Are correct springs still available?  I'm not sure I understand everything you've said there K2-K6

[Bryanj]

Springs were never available as a seperate part you have to buy the complete unit, pattern ones are now available BUT a member on the US site found the 750 one had the F and T marks incorrectly positioned, you need a 500 part anyway.
I think DS lists them and 4 into 1 in US but watch out for duties.
One bit i dont have lots of, could possibly lend you one for testing purposes

[DomP]

Thanks Bryan, I'll let you know if it comes to it.  Oh its a 550 though not a 500 not that that may make no difference

[Bryanj]

Same part as far as i know, lots of 500 parts fit and are even same part number!

[K2-K6]

Are correct springs still available?  I'm not sure I understand everything you've said there K2-K6

Supply, as Bryan notes, can't see any springs available.

Apologies for confusion.

To clarify;- the molded springs currently fitted should have nil effect on the idle issue you are chasing. They effectively (by tightening) make the retarded position more positive which would only enhance stability and repeatability at the tickover rpm. I'd dismiss them from suspect for this cause.

Two things to check though. Is the A/R mechanical not impeded by friction itself, all appears to rotate freely if you exhamine it ? And, have you checked that the static timing is definitely at the F mark accurately to make sure its getting that aspect right ?

[DomP]

Cheers Nigel(?)  I've decided to check it over from scratch but also to pull the carbs and bench sync them again.  Having watched Motormac on YouTube I'm going to follow his method and set the 56mm distance on the bell crank, I've fiddled with them so much I can't now be sure where they're at.  A bit more time spent now might save me further headaches.

[K2-K6]

Yes, Nigel is correct.

Probably worthwhile looking through them again. Youjust gain more experience in doing this, a very pedantic/ critical eye in evaluation of them will often turn up something that may be causing an issue.

They are just plain fiddly to get right if there's any impairment etc, that's carburettor in general, even for experienced practitioners of the art. Can go round and round until finally sorting them. A friend runs a garden machinery business and hates the run around that inevitably comes with sorting out simple problems.

The bench sync is absolutely fine to run the engine without problem from tbat aspect. It has the major advantage of knowing they are mechanically in synchronization and helps in diagnosis of other faults if you don't try and sync them after installation.

The carb rack should allow for adjustment of the major rpm stop screw to fully lower the slides after setting them (if you use the drill method on here) which ensures that the slides have the capability of full restriction once set to parity.

You can then connect them to cables, without installing on engine, to ensure the cables definitely don't conflict with that function.  Emphattge slides should sit at rest on that master tickover screw stop, and nothing else should impede that operation.

Adjustment of the airscrew idle function when running is then where the attention should be. The suggested opening point 1 1/2etc should be seen as competent start point, from which you need to test what exactly is needed.  That method is in the Honda manual officially to instruct you.

Effectively, it gets you to adjust leaner until that cylinder falters, this  is the air fuel mixture just going past its technical ideal of 14.7 to one ratio. Thats pertinent to the hardware in place AND the fuel in use at the elevation you are working.
Then it requires you to make it richer by adjustment to bring a 100 rpm drop (multimeter with frequency will register this if you've got one) to bring that carburettor and cylinder to ideal operating point.
Later Honda manual detail recording that absolute setting in service notes as baseline for the operation. It can be different for each of the for cylinders. If you don't get something competently in range at that point, this suggests something else maybe wrong, or some impairment is still there withing that idle circuit.