Needle jets

[Waggles]

Hi,

My F1 restoration is proceeding well and I have reached the carbs. The originals that came with the bike are horribly bunged up with a hard residue I can't budge any ideas what might soften it up?

Next I have obtained some other 750 carbs ( presumably not F1 ) which are much cleaner so I plan to re jet those suitably. As a matter of interest does anyone know if the actual needle JET ( not the needle ) is different on the F1 compared to others? tried to compare part numbers but other models seem to list needle and jet separately but the F1 shows needle and jet together as a kit so part numbers are bound to differ. Finally, before I bugger something up do the needle jets just push / tap out? if so is it downwards towards the float bowl? Haynes manual tells you to replace them regularly but not how to!

cheers

Andie

[Spitfire]

Hi there, my F1 carbs were a mite gummy as well, I cleaned them with a mixture of carb cleaner, petrol, white spirit and elbow grease, I removed the main jet, float, pilot jet, needle jet holder and fuel valve/filter (fuel inlet to the float bowl). All the jets are screw fitting, seems a bit strange that the Haynes manual is telling you to replace them, mine are still the originals and in great condition.
I keep fiddling with this post, the part numbers are-
99114-246-1050 JET MAIN #105
16165-341-004 HOLDER, NEEDLE JET
16012-392-004 NEEDLE SET, JET This is the complete needle set.
99124-076-0400 JET,SLOW #40

The gum was that bad that I could not open the throttle slides. Here's some photos.

[Waggles]

HI there,

Thanks for this. My F1 stood for over 25 years and the residue has gone beyond that lovely gunge you had! The residue is now hard, rock hard! some of it you can crumble away so float bowls etc are OK but the jets I just cant clear, soft wire won't touch it and I know enough not to use anything more vicious than that. Have sourced new jets now from Mr Silver so I guess I will chuck the old ones in some petrol / diesel for a few months and see what happens.

All the jets are screw fitting EXCEPT the needle jet I have found, the new ones are just plain bush type. You have discovered the same as me that you can't compare needle jet part numbers so I guess I will have to replace them to be sure I have the jetting correct as I have no idea what model of 750 the carbs I plan to use are from and I don't see any easy way to compare them ( at least while the old ones are still fitted to the carbs ) There is a step in the side of the needle jet so by careful examination I should be able to see which way to push them out, wish me luck!

[SteveD CB500K0]

I had a set of 500/4 carbs like that. I used cellulose thinners (5 gallon can bought from Kempton Park Autojumble) and let them soak for about a week.  Then good old elbow grease.

[Spitfire]

I've just looked this up in Hondaman's book (Mark Paris) and he recommend not to remove them (needle jets), the gist is "there is usually little of nothing to be gained by removing them as they are exceedingly soft. Tapping them out with a wooden dowel is often enough to distort them"
So if you can I would recommend to persevere with cleaning them up, or renew them as a set.

Cheers

Den

[K2-K6]

It seems like more of a "varnish" that is left after they dry out, I suppose paint is also made from petrochemicals traditionally so it may be worth trying one with paint stripper to see what happens.

[Waggles]

Hi All,

Steve, yes thats more like mine but mine are a bit worse  thanks for the thinners tip, will try that.

Re the needle jets, I seem to have mis led a bit ( my fingers and fried brain never work at the same speed  ) the needle jets are NOT blocked, the only reason I am talking of replacing them is coz I am going to use a set of carbs from e-bay hence no idea what model 750 they are from so I need to re jet ( am using these carbs for two reasons, 1. The state of the originals probably means there are some other tiny drillings that are bunged up and 2. I broke one of the float spindle supports  know I could repair it but bearing in mind 1. decided not to bother )

So I have new jets ( main and slow are simple obviously ) will swap the slides in case the cutaway differs, that just leaves the needle jets ..... can use the original needles as they are fine but I have no way of knowing if the actual jet differs between models hence why I am considering replacement. Guess it doesn't matter if I distort the originals getting them out as I have replacements, bit concerned I might distort them fitting them though ....... perhaps I should just use F1 needles and suck it and see?

[SteveD CB500K0]

..... perhaps I should just use F1 needles and suck it and see?

I wouldn't recommend that - petrol tastes aweful!

[Waggles]

So does the dried crud, don't ask me how I know