[Troy74]

Thanks ! If I remove that air valve spacer thing is there some replacement grommet to make up the space between the carb and the inlet or just replace the fitting studs and refit the carb direct to the inlet ? (obviously with the rubber gasket)

[Paul W]

Not sure what you mean by “rubber gasket”.
My bike is now as follows:
Engine / gasket / nylon spacer block / gasket / carburettor.

The rubber hose from the carb mouth would not then reach the original air-box outlet, hence a different type of filter on my bike (as I mentioned, no air-box now fitted).

[allanfox]

I did try some 'S' cams on mine but too noisy for me so on Adrian's recommendation I fitted some standard cams from an iron barrel bullet, had to also fit some Hitchcocks extended adjusters that meant I had to lose the pointless cam lifter  (really not needed), this transformed the bike and it goes so much better. Don't be scared to rev it, if you are needing to stay in third as it won't pull there is something wrong, these rev freely, maybe the carb is too big for it?

[Mac350]

Don't be scared to rev it, if you are needing to stay in third as it won't pull there is something wrong, these rev freely, maybe the carb is too big for it?

If it won't rev freely the carb might be too big? I'm at the beginning with understanding carbs and that seems counter intuitive can you explain a bit more?

[Adrian II]

The carb on your bike is the standard VM24 Mikarb fitted to most 350 Bullets in later years. The old Redditch Bullets had slightly larger 1" Monobloic carburettors fitted, so what's on there is NOT oversized!

A.

[Raymond]

If it won't rev freely the carb might be too big? I'm at the beginning with understanding carbs and that seems counter intuitive can you explain a bit more?

Carbs work by the venturi effect - air speeds up as it passes through a narrow gap. It's why doors slam - as the door closes, the air rushes faster and faster pulling the door with increasing force. A small carb might give better torque than a larger carb because it promotes higher speed air flow at lower revs - although ultimately the small carb will limit the engine's maximum power at high revs when it can't deliver enough fuel and air. Conversely, a large carb can lead to bogging down especially at low and medium revs as the larger gap leads to slower air flow - although at high revs the larger carb might give optimum power. The jets need to be optimised to give correct fuel/air mixture at all rates of air flow. Hope this helps.

[Adrian II]

Yes, The Lore is that bigger carburettors aren't so good on our sort of machines. Having run an Electra-X with 32 as well as 36mm carbs, I have to say it ran very sweetly on the 36 too.

My 350's inlet tract was opened out to 28mm, I could happily take it out to 30mm if I wanted to fit the 1³/₁₆" Amal GP carb I have lurking in the garage. In my BSA days I had a B40-engined bitsa with a VM32 Mikuni on it, which ran beautifully. The B40 had a short-stroke engine at 79x70mm, compared to the 350 Bullet's 70x90mm, so it probably liked the revs a bit more.

A.

[Mac350]

Carbs work by the venturi effect - air speeds up as it passes through a narrow gap. It's why doors slam - as the door closes, the air rushes faster and faster pulling the door with increasing force. A small carb might give better torque than a larger carb because it promotes higher speed air flow at lower revs - although ultimately the small carb will limit the engine's maximum power at high revs when it can't deliver enough fuel and air. Conversely, a large carb can lead to bogging down especially at low and medium revs as the larger gap leads to slower air flow - although at high revs the larger carb might give optimum power. The jets need to be optimised to give correct fuel/air mixture at all rates of air flow. Hope this helps.

Many thanks you've made that easy to understand. So its always a compromise then with carbs.

[Mac350]

Yes, The Lore is that bigger carburettors aren't so good on our sort of machines. Having run an Electra-X with 32 as well as 36mm carbs, I have to say it ran very sweetly on the 36 too.

Good to know that its not that finicky about it. Presumably the lore is based on logic and some experience of massively oversized carbs.

My 350's inlet tract was opened out to 28mm, I could happily take it out to 30mm if I wanted to fit the 1³/₁₆" Amal GP carb I have lurking in the garage.

I wasn't expecting to be porting a bike at my age When I was 16 a friend of mine ported his big bored Kawasaki AR50 and got it to go over 90mph. He did it so often he could change the little end in the time it took us to fill up with petrol.

What does this refer to? "but with a modified alloy barrel to help it pass emissions laws" https://www.bennetts.co.uk/bikesocial/reviews/bikes/royal-enfield/royal-enfield-electra-x-2004-to-2008-buyers-guide Is this something that needs to be undone on a 2004 bike?

[Paul W]

That may refer to the tendency of an aluminium barrel to dissipate heat better than a cast iron one. A “lean burn” engine will tend to run hotter by nature.

[Adrian II]

but with a modified alloy barrel to help it pass emissions laws

Is this something that needs to be undone on a 2004 bike?

Typo, should have referred to the cylinder head, which on the Electra-X is just a bigger version of your Machismo's, it's just a more efficient pent-roof design with a flat-top piston compared to the classic Bullet's hemispherical combustion chamber and domed piston, which was common on loads of old British bikes way back when. The EFI/UCE models have a very similar combustion chamber, although the cylinder head casting itself is quite different. The actual alloy cylinder barrels on the AVL 350 and 500s are nothing special, though as Paul points out, alloy was in this case probably essential for heat dissipation.  That said, Hitchcocks' 4-valve top end conversion for the CGT535 has a cast iron cylinder!

The cylinder head is actually a good one, keep it! It works very well if your bike is configured for non lean-burn, too.

The heart of the lean burn system on these is the exhaust pipe, which has a narrow bore inner pipe, this helps the engine run deliberately hot along with the lean-jetted carburettor in order to burn off more of the partly combusted hydrocarbons in the exhaust. On the 500 AVLs this was often replaced by a "straight through" down pipe from Hitchcocks' along with a sportier silencer and carburettor combo when the bikes were tuned up a bit. Beef up the bottom and and fit the right cams, and what was intended as an emissions dodger turns out to be a surprisingly fun old banger which can actually get a bit of a move on.

A.

[Mac350]

The heart of the lean burn system on these is the exhaust pipe, which has a narrow bore inner pipe, this helps the engine run deliberately hot along with the lean-jetted carburettor in order to burn off more of the partly combusted hydrocarbons in the exhaust. On the 500 AVLs this was often replaced by a "straight through" down pipe from Hitchcocks' along with a sportier silencer and carburettor combo when the bikes were tuned up a bit. Beef up the bottom and and fit the right cams, and what was intended as an emissions dodger turns out to be a surprisingly fun old banger which can actually get a bit of a move on.

A.

you're a mine of good info! It might be that i've struck lucky and a PO has already done this, theres a non-standard pipe and bigger carb, rumoured different cams and it does hustle along well enough.

Are there meet ups for Enfields anywhere down Devon way? Would be good to let someone who knows them have a look over it

[Adrian II]

Devon branch of the Royal Enfield Owners' Club? They meet, according to The Gun magazine, at the Swans Nest, Exminster on the 3rd Thursday of the month, 7:80 for 8:00pm. Is that your part of Devon, or would you have to cross Dartmoor to get there? I don't know to what extent the branch membership is split between newer models, obsolete Indian Bullets and Redditch originals, but someone there must have enjoyed an Electra-X between sprag clutch and big-end failures!  You never know, there might be the odd Machismo or Thunderbird owner lurking.

I'm over to the east a bit in 'ampshire, not too far from Sammy Miller's but a fair old way from prime cream tea country, I'd have to get past all that Dorset apple cake first...

A.

[Mac350]

Devon branch of the Royal Enfield Owners' Club? They meet, according to The Gun magazine, at the Swans Nest, Exminster on the 3rd Thursday of the month, 7:80 for 8:00pm. Is that your part of Devon, or would you have to cross Dartmoor to get there? I don't know to what extent the branch membership is split between newer models, obsolete Indian Bullets and Redditch originals, but someone there must have enjoyed an Electra-X between sprag clutch and big-end failures!  You never know, there might be the odd Machismo or Thunderbird owner lurking.

I'm over to the east a bit in 'ampshire, not too far from Sammy Miller's but a fair old way from prime cream tea country, I'd have to get past all that Dorset apple cake first...

A.

crickey you'll be needing all the torque to get you home by the sound of it. I'm down in Torbay so not too far to go but the bike's not ready for a long run yet. Hopefully by the next one it will be.

[Adrian II]

Had a great holiday down in Dartmouth for my 50th er... some years ago. There was a barge moored in the middle of the river converted to a bar/restaurant, you could sit up on the sun deck with a G&T and watch the steam trains come and go from Kingswear.

A.