276 bigger jets

[Minto]

Thinking of increasing the main jet and or needle jets on a pre mono 276 to try to get a bit more go out of my GF (bike not girlfriend).
Is there any serious downside to a bigger main/ needle jet?
Only thinking 1 or 2 sizes up on either. Never had much experience with carb tuning.
Cheers folks

[muskrat]

G'day Minto.
 What's the colour of the plugs? Is she burning oil? Standard gearing 19/46?
1952 A10 jetting is A10    
276BR/1B Bore 1 1/16", Main Jet 170, Slide cutaway 4, Needle position 2 from top, Needle jet .108.
All that would be true with a new/not worn carb. If it's a 68 year old carb I'd imagine it's sucking a bit of extra air around the slide so going up across the board won't hurt. 180 main and lift the needle 1 notch.
Cheers

[Minto]

Cheers Musky
As far as the carb serial number, I'd have to check again, memory cells abandoning me at an alarming rate nowadays (rats n sinking ships spring to mind).
Doesn't seem to be burning any oil and the plug colour seems ok to my colour blind peepers.
At present it has a 170 main, 107 needle jet, number 4 slide cutaway and i lifted the needle a notch to the middle as it was spitting back (this improved things).
It has no air filter so probs running way lean on the current set up?
Hokey dokey, plan for the weekend afoot.
Thanks again

[Black Sheep]

You could go back to basics rather than relying on guesswork.
Find a long hill. Take it at full throttle in top. Try closing the choke a bit. If it goes better, fit a larger main jet. If it runs rough, it is already running too rich so consider a smaller main jet.
Simples really.

[Swarfcut]

 Published data assumes the bike has the air filter fitted. But we all know the present day value of this unique cheap metal pressing which was, in previous times, usually discarded. Oh, if only we has known  that then.
 Fitting an aftermarket filter is well nigh impossible, there is just no space. The other downside is that without a filter, you can count on scored bores and pistons. Its duck tape, cardboard, kitchen wash up pads and a bit of lateral thinking to fake something in the short term.

 Bit of a dilemma there Jase. Looks to be too weak.

 Swarfy.

[Greybeard]

Published data assumes the bike has the air filter fitted...

I was very happy to have the original air filter on my bike. The element was rather tatty so I improvised one from a K&N filter intended for the Triumph/BSA triples. Details in the forum somewhere. As you say, the jetting was set up for a filter so don't expect standard jetting to work satisfactorily.

[Minto]

Cheers folks.
Seeing as I ordered a repair kit and new needle and some oversize jets about 6 months back, I may as well give it some experimentation.
Blacksheep, trying to find a road near me long enough or quiet enough for this is not easy unless I sneak out at 3 am (unlikely) for a thrash down the A442 eastern primary but thats got cameras on it and a 50mph limit now.

[Black Sheep]

 I did my testing on the M74 and M6. Not much traffic and plenty of long hills. Just living in the right place! Pic is at Tebay Services. Carb on this one is a 389 but same reasoning applies. No air filter but no bore scoring in the last 50 years either. Too much rain here for dust to be a problem.

[Minto]

Krikey BS, that hill looks vertical. Or has my phone turned the pic 90 degrees?
mod edit: fixed

[Joolstacho]

Jeez Minto, if you could get a bit more GO out of the other GF too that'd be wins all 'round!

[Worty]

Jeez Minto, if you could get a bit more GO out of the other GF too that'd be wins all 'round!

If you have any ideas about getting more go out of the g/f, let me know will you.  I've tried reducing weight, a good clean, and general fettling but with little success so far.  Was considering bigger jets, a top end rebuild, new valves and stronger con rods, but not sure if it's worth the expense.  Battery seems ok, but wiring is definitely duff.

[Slymo]

I did my testing on the M74 and M6. Not much traffic and plenty of long hills. Just living in the right place! Pic is at Tebay Services. Carb on this one is a 389 but same reasoning applies. No air filter but no bore scoring in the last 50 years either. Too much rain here for dust to be a problem.

I remember the entry in a handbook for an M16S I had that showed an air filter fitted for Colonial use only. No dust in Blighty! 😂

[Minto]

Worty, Have you tried buying her flowers and plying her with loads of gin?

[orabanda]

Interesting.
1954 A10 swinging arm A10 with 276; I have just increased the main jet to 190; tad lean with a 180. Standard A10 air cleaner fitted, and riding close to the coast (up to 200 metres above sea level).

[Worty]

Worty, Have you tried buying her flowers and plying her with loads of gin?

Heh, thought my natural charm would be enough - I was wrong!   

Apparently, talking about bikes doesn't float her boat , but flowers, holidays and meals out she likes - I'll never get women!