Carb synchronising issues

[El__burro]

Hello,
I've been trying to get the carbs balanced and after a while I could not get a better result than the one in the picture below.
What could I be doing wrong?
Does the carb 4 variance means something wrong with engine pressure or leak?

Thanks
el__burro

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[royhall]

It means that cylinder four is drawing more air than the other 3. The carb slide need adjusting down to reduce it. Failure to be able to balance the carbs could be a sign of air leaks at the isolator rubbers. Try spraying carb cleaner on the rubbers one at a time, with the engine ticking over, and see if the engine speeds up at all. That shows the carb cleaner is being drawn into the engine and therefore you have a leak. How hard are the carb rubbers?

[gtmdriver]

Adjusting and balancing the carbs should be the last thing you do after all the other engine adjustments.

Are all the valve clearances OK?

Are the plugs gapped correctly and the ignition timing spot on.

It might be worth doing a compression check to see if all the cylinders are roughly the same. This test can pick up worn rings or burns valves.

If everything is fine then you could certainly be looking at an air leak on the intake side.

[royhall]

GTMdriver is right about carb balance being the last thing to do.When you do the compression check, do it with the throttle fully open. Ignition wont affect the flow through the carbs. If the cranks turning there should to be even air flow across the cylinders. If the compression is even, only the intake and valve clearances will affect this. I strongly suspect carb isolator rubber leaks.

[El__burro]

Plugs are gapped correctly,  carbs rubbers are quite hard but ok, timing is fine too.
i guess carb slide and valve clearance my next things to tackle.

ps, i have lost the vacuum screw and washer, any idea where to buy it cheap.
thanks a lot
el__burro

[El__burro]

Mmm.. tried to do a compression test but my equipment doesn't have the adaptor for the Honda cylinder. Can anyone tell me what size I need to look for and eventually where I can get one?
Thanks
El__burro

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[El__burro]

I've been looking all over, in my front garden and online but this screw it's not easy to find.
DSS, wemoto and other suppliers have no stock.
Does anyone have any idea where I could get one (for under £5)?

Part number 16161590004

thanks
El__burro

[Bryanj]

I got some washers but not the screw, it should be a standard thread so try getting some allen bolts from a fastener supplier

[mike the bike]

It's a bog standard M5 x 0.8 screw

 Search for 42401 in Screwfix

[El__burro]

Thanks to both of you.
iIl be looking in my spare screw box tomorrow.
Can anyone confirm for the spark plug adaptor (for the compression test adapter) is 12mm?

thanks
el__burro

[mike the bike]

Aye, 12mm.  You can also get the rubber cone type

[neat street]

when doing the compression test, full open throttle to get proper reading. if one or more is out, put a small dose of oil into each pot and test again. if you get even readings this would be a piston/cylinder issue? if the same (one or more is out (by +- 10%) would point to valve issue?
Hope this helps

[El__burro]

Thanks, i've been reading about the test. While i am waiting for the adapter to arrive I've cut 4 M5 bolts to replace the vacuum ones. (no washers)
what do you think?

[K2-K6]

They look like theyll do the job you want but make sure you remove the burrs on the end of the threads first so they don't chew up the carbs when you put them in.

One way to help you do it is to put a nut onto the screws before you cut them,  then when you wind it off the cut threads it helps to clean out the lead in to the threads.

Careful filing with a small taper on the end should get them fettled into good shape.

[gtmdriver]

when doing the compression test, full open throttle to get proper reading. if one or more is out, put a small dose of oil into each pot and test again. if you get even readings this would be a piston/cylinder issue? if the same (one or more is out (by +- 10%) would point to valve issue?
Hope this helps

....and take ALL the plugs out before you start.

Keep the motor turning over with the throttle wide open till the reading stops rising. All the cylinders should be within 10% of each other.

If you can't get a 12mm adaptor you could, as someone has already mentioned, use a gauge with a tapered rubber adaptor. You just push these into the plug hole as hard as needed to get a seal.