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Messages - sprinta

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1
CB750 / Re: Vacuum screws
« on: September 01, 2023, 09:55:35 AM »
These may be of use to somebody who is not bothered with originality and would like the ability to just push on the vacuum gauge hoses without having to remove the screws and then fit the extensions as they can be left in place?

https://www.ebay.co.uk/itm/134331731567




2
CB750 / Re: CB750K2 petrol tank not venting
« on: August 26, 2023, 03:16:36 PM »
Thanks, that's something that I can do as I did stagger them. Grasping at straws possibly, but worth a try.

3
CB750 / Re: CB750K2 petrol tank not venting
« on: August 25, 2023, 11:40:31 AM »
Thanks Graham.

That shows mine was the same way when I took it apart, so it was correctly assembled and therefore not the likely cause for mine seemingly not venting?

Not sure as to if the small o-ring on mine has any relevance and may just have been fitted on the screw so that if it unwound it would not fall out?

Thanks for your help, much appreciated.

4
CB750 / Re: CB750K2 petrol tank not venting
« on: August 24, 2023, 05:47:50 PM »
Can't you just pucker your lips & blow into the cap from the underside to simply test it?

Have tried that, but it is not very conclusive one way or the other.

5
CB750 / Re: CB750K2 petrol tank not venting
« on: August 24, 2023, 05:31:52 PM »
Thanks Graham

If you carefully peel away the outer gasket it will separate the two plates and you should then see the inner gasket and smaller plate. Could take a photo of it and that would hopefully show if it is as my 1st or 2nd photo and therefore, which one should assume it the correct way.

Have you come across the small o-ring? you may find it between the two plate which would also locate its position?

6
CB750 / Re: CB750K2 petrol tank not venting
« on: August 22, 2023, 07:09:07 PM »
Thanks for your reply.

However, all the vent holes were clear which is why I was looking at if the internal rubber gasket had originally been fitted the right way round.

Hoping that somebody may also have one of the Yamiya caps and could check their and let me know which is the correct way round, as the first or second photo?

7
CB750 / CB750K2 petrol tank not venting
« on: August 21, 2023, 12:11:02 PM »
Having a problem which I suspect is due to the petrol tank not venting properly?

Went for a ride yesterday and parked the bike for a while, fairly sunny and warm day. However, when I restarted the bike it kept stalling, managed to get going having to rev it higher to stop it stalling but then started jerking and missing and would not pick up, went to reserve no changed then it just expired and came to a halt, very much like running out of petrol?

Lifted the petrol cap, helmet and ear plugs in so could not hear anything and then the bike started and ran home OK.

This morning I opened the cap and there was a distinct sudden rush of air into the tank, so suspect that the cap is not allowing air in and/or not venting properly?

It is an after market Yamiya cap so took it apart to find all vent holes clear. However, is it possible that it was not correctly assembled?

With reference to the attached does anybody have a Yamiya cap that they could check to see what the correct assembly is for the internal rubber gasket.

The 1st one is how it was when I took it apart or should it be as the second photo?

The small o-ring just appeared when I took it apart so I have assumed that is it's correct placement, which may not be correct?

8
Other Bikes / Re: 1976 Z900A4 Carb issue
« on: July 23, 2023, 03:36:55 PM »
It does not rise enough to come out of the overflow pipe, just goes to the bottom face of the carb body and stops there.

Swapped all the jets, seat float etc from No 4 to No 3 and vice versa and now float level seems to remain at the correct level, some progress, but No 3 plug still remains very sooty at both at a 60 mph chop and low speed.

Will try dropping the needle by one groove and see what effect that has?

9
Other Bikes / Re: 1976 Z900A4 Carb issue
« on: July 22, 2023, 07:53:02 PM »
Thanks for the suggestions, will try swapping some of the jets etc around and see if there is any impact

10
Other Bikes / Re: 1976 Z900A4 Carb issue
« on: July 20, 2023, 06:59:56 PM »
Thanks for your input.

As indicated all the seat and valves are new, but I have already tried the seat and valve form one of the other carbs together with another float from one which is OK.

As an update I have done another ride on the bike since swapping the No 2 & 3 leads and caps and the the No 3 still remains black and sooty. Then fitted a B7ES plug instead of the B8ES and it has remained black and sooty even with a hotter plug.

Compression test show that they are all around 100 psi, not great but they are all the same.

Everything is pointing to the No 3 carb but as to what it may be is a mystery at the moment as is the cause of why it also does not overflow but remains with a high float level whatever I do?

11
Other Bikes / 1976 Z900A4 Carb issue
« on: July 20, 2023, 12:56:10 PM »
Apart from my 72 UK CB750K2 I also have a 76 UK Z900A4 on which I am having a carb issue that some here may be able to offer some advice on?

No 3 pot is running very rich to the extent that the carbon fouling caused the pot to miss and back fire, which eluded me to the problem.

The other plugs were slightly rich but otherwise OK. Did a 'wet' float level check which should be around 3mm below the bottom flange of the carb body face. They were all high more or less at the body flange.

Carbs removed. Jets ultrasonically cleaned and carb bodies passageways cleaned with carb cleaner and compressed air. All passages as far as I am aware clear. New seats and valves fitted, Kester original Mikuni if available around £80 a set.  are Did a bench wet float level setting followed by static balance, all OK.

Re-fit the carbs did vacuum balance and colourtune, all set up OK so go for a ride.

Rides well but on return No 3 is still black and sooty and the No 3 carb wet float level has gone high again!

Remove float and bend the tang up a bit more, still remains high. Tape float up with bowl off with petrol tap on for around 4 hrs, no leak. Even with the tang bent up such that the float only has to move 1mm to close the valve the wet level remains high.

Take the bike for another ride and do a plug chop at 60 mph, No 3 remains black and sooty, so problems remains at higher rev range.

Plug caps on No' 1,2 & 4 around 4K8 ohms No 3 5K4 ohms, slightly high but not enough I would have thought to be causing the problem?

Have swapped plug leads of No' 2 & 3 (they use same coil so fire at the same time) but yet to go for a ride to see if it is a lead/cap problem?

But I am now running out of ideas. The floats float in petrol and water, but in desperation I have ordered set of replacements, at high cost, but doubt they will make much/any difference?

But the main thing that is totally mystifying me is that what ever I do to the No 3 carb/float the petrol level remains high. It does not overflow but the level is in line with the flange face of the body.

As to whether the high float level is the sole cause of the richness or if it is as a result or a commination of carb and electrical is uncertain at this stage?

If anybody can offer some advice or suggestions as to why what ever I do the float level remains high on the No 3 carb it would be very much appreciated as the carbs in operation are very much the same as the ones used on the Honda's, the main difference being that the Z900A4 has enrichment choke plungers against the air reduction slides of the Honda. The plungers have had the seats replaced with Viton as they were a first possibility of allowing extra fuel in causing the richness, but they have made no difference.

12
Misc / Open / Re: Painting Cylinder Blocks - best methods?
« on: July 09, 2023, 05:46:08 PM »
Try Simoniz silver paint SIMVHT31D

https://www.ebay.co.uk/itm/370978213486


13
CB750 / Re: Which oil for cb750k2
« on: May 21, 2023, 06:12:44 PM »
Have been using 10/40W semi synthetic in both my 73 750K2 and 76  Z900A4 for several years and have had no problems with the clutch on either bike.

14
CB750 / Re: Chain Oiler (CB750K)
« on: November 21, 2022, 02:20:30 PM »
An alternative is to just fit a modern O- ring chain. A 530 goes straight on without any clearance issues, well it has on my UK K2.

15
Project Board / Re: twin disc
« on: July 24, 2022, 09:43:49 AM »
I would agree with the above post. I still have the original master cylinder on my CB750K2 that I did a twin disc conversion on and it is absolutely fine giving more 'feel' to the brake lever and not the solid wooden feel that you very often get with the larger bore master cylinder.

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