Carb #2

[Lynx]

I think I've finally found the problem with my bike not running on pot 2 at idle. I've purchased an ultrasonic bath for a fourth attempt at clearing this issue which did get some crud out. However on a final blow through with carb cleaner before assembling, I discovered this hole on the carb (see pic attached). It runs straight through to the pilot system. I've checked carb #3 and this one is blanked off. I guessing when I've blown it through with compressed air I've dislodged something I shouldn't have .

Can anyone confirm this should be blanked off before I fill it in.

[Lynx]

Oh! It looks like the picture is not going to work. It's a moulded in passage on ther main carb body, near the bottom edge. It's at the front of the carb pointing forwards from the middle of the carb at an angle of about 60°, on the opposite side to the pilot air screw. Diameter about 4mm.

[PatM]

totally confused!- can you PM me the picture as Ive a few sets of carbs off the bike- patrickjmorgan@btinternet.com and Ill have a look for you.

[Lynx]

Hi Pat,

Thanks for the offer. I couldn't attach it to a PM. So I've posted it here:-




Cheers
Steve

[PatM]

From what I can see- its an orifice on the opposite side of the air-stub from the pilot-jet adjuster- if so, YES its supposed to be blocked. A dab of mastic or a more permanent solution would be some metal-glue- the stuff that you knead with you hands that looks like a stick of dynamite will fill it!

[PatM]

In addition- as your carb is so clean, and my spare set not- Ive re-checked- it actually on the same side as the adjuster but as it said- YES its blocked. Just shows to us all-- compressed air is a very powerful medium!

[Clem2112]

This hole puzzled me too,  when I re-cleaned the carbs yet again...
But they all have it 

I have a worn out No2 carb which I am looking at now ...... Sad !

The idle circuit takes a few turns and several holes are drilled to achieve this with some of them joining the others up.

On the outboard side you'll see the same cast feature but without a hole.
The drilled hole on the other side is there to connect the idle jet to the tiny hole inside where the fuel emerges.
It is then blanked from inside with a brass insert which you can see inside the float chamber, dead centre... see the line of the cast pipe on the inside.
Unless this tiny insert was blown out things are as they should be.

There are two more blanks in the chamber roof too.

[Clem2112]

Cross driiling is the phrase I was looking for.
The only way of simply creating oil galleries in crankshafts etc.

Footnote on the carburettor mystey hole.
I put a wire in and it seems to be plugged from the outside but quite deep down so it looks like an open vent at first glance.
Extremely unlikely to be air leaks past any plug but you could put some WD40 or fuel down there
to check.

[Lynx]

Hi Clem,

Thanks for the reply. Yes I know they all have it. The trouble was when I sprayed carb cleaner into the pilot jet hole on this carb, it came flying out of this manufacturing hole . Not any more! I tapped it with a 4mm tap and loctited a screw into it . This is more fun than squirting in some sealant and also I can remove it if necessary. I've got the carbs back together and on the bike but couldn't test it due to a lack of petrol. Hopefully tomorrow.

[Clem2112]

Ah... So you had tested it.
..so maybe worth blocking this off any way , belt and braces... Could be small leaks on many of these?.  May try this approach.

[Lynx]

Sorted !

I fired it up last night and balanced the carbs. Running sweetly and quieter. All four exhaust downpipes getting equally hot at idle. I wonder how easy it is to blow out the blanking balls without realising. This could be the problem for a few people complaining of poor idle and cold pipes.

I'll take it for a little spin at the weekend before stripping down the rear end for renovation. Still got those horrible clocks to do too (see Knocking Noise post).

[Lynx]

I took the bike for it's first run yesterday. Not as good as I hoped. Runs sweetly at low revs but just seems to run out of steam at 5k rpm  . I haven't looked into it at all yet. Decieded to start stripping thge clocks last night instead. Does anything commom spring to mind for anyone?

It's a similar feeling to the air intake getting blocked but I do have all the rubbers on the bottom of the seat. So it's not that.

[Clem2112]

Float heights?

[Lynx]

Float heights are fine. Could be the tank breather though.

[Clem2112]

Heard about the blocked breather issue... with the cap open and the bike upright, being careful not to slosh fuel about too much you could test this?
Would have thought the engine would refuse to rev at all with a lack of venting.

Mine was getting bogged down mid range and the more the throttle was opened the louder the exhaust got with very little response.
Convinced it was running rich so I set the float height to 24mm ithen checked that the fuel level was about right at 7mm below the joint face.
This improved matters a bit but the air screws then had to be set to one and a quarter turns out for steady idle.. So much for measuring fuel level. Now running lean at idle?
Had to be something else that was worn or out of spec.
The only original items left were the needles and tubes so bit the bullet, replaced these and reset floats back to 21mm ... Better response and pulls in top. Idle screws are now at about two and a quarter turns out.
Seemed to be down to the air/fuel mix being off at partial throttle openings.