Doms CB550F1 project

[Laverda Dave]

I remember during a metalwork class at school one of the kids was using auto feed on the lathe when he decided to go walkies. The resulting bang and carnage was a sight to see. The teacher went nuts and hit him over the head with a tool post!

[Bryanj]

At college we had a large cardboard chuck key that the last person to leave one in had to wear until the next person did it!

[DomP]

I'll cut one out and where it tomorrow Bryan!

I'm not sure what the airbox lid brackets should look like exactly but here are my efforts complete with front and rear stamps because they ended up slightly different.

[DomP]

On the subject of filter lids, looking at photos I think the mesh aperture is around 2mm, can anyone confirm for me as it will surely make a fair difference in air flow restriction.

[DomP]

Is this distance correct, I've read there should be a measurement of 56mm between cable nipple and cable anchor point but the diagrams are near impossible to interpret.  What is the actual effect in real terms if the cables are not inder tension at idle? 

The upper throttle stop screw into near to making contact with the bell crank

[DomP]

I took my first real ride out lastnight just to see if any of the running issues might sort themselves out.  It seems to accelerate fairly well after bogging down a bit, the idle is the main problem though, it raises between gear changes and when coming to a standstill at junctions to the point I had to flick the kill switch on and off to settle it.  Other than that the front brakes are a bit woeful and I have a bobbly front end, could be a lack of wheel balancing or the oil weight maybe?

*oh and I hit 143mph, think I need to calibrate my speedo🤣

[Laverdaroo]

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


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[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?

[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.

The 500 has a different design of air screw so needs more turns to achieve the same effect.

[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 😄

Where the video Ted, worth a watch I think

[McCabe-Thiele (Ted)]

It's under Misc/open on here Dom although the video shows  single cylinder bike his explanation seems logical - up to now no one has commented on the post.

[DomP]

It's under Misc/open on here Dom although the video shows  single cylinder bike his explanation seems logical - up to now no one has commented on the post.

Oh I've watched that before, maybe I'm barking up the wrong tree then but the rich smell of fuel led me to think it needed leaning out not richening.  I'd say I have a climbing idle not a hanging idle though so I'll check for an air leak tomorrow

[McCabe-Thiele (Ted)]

When altering the mixture on SU carbs on cars my late father told me the best guide to lean or rich was the exhaust temperature a rich mixture gives a cold exhaust out of the pipe , a lean mixture gaves a hot exhaust  - he never mentioned petrol smell.

[Laverdaroo]

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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[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 😄

Where the video Ted, worth a watch I think

It might be I'm confused about the screw turns - it might be 1/4 turn for a 500 fitted with the 550 carbs.
I guess it's this table that you are refering to.