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[Revband]

Yes of course Pete you are correct, but that is not the issue here, my point is that the jet size is unlikely to be the OPs problem. When you choose a carb size a lot of things need to be taken into account, the carb has to be matched to the diameter of the manifold putting a larger carb on just slows the airflow though the actual carb and upsets the low/mid range running and does nothing to improve the top end, a slightly smaller carb will lose a bit off the top end but make the bike far more pleasant to ride on the road. If tuning for speed then you need the best gasflow possible with a bigger carb/inlet tract appropriate to the engine involved, but for most road users this will ruin the pleasure of a good low to mid range, depends what you are using the bike for but honestly I have seen many a good road bike ruined by inappropriate tuning. PS how on earth do you put seperate paragraphs on here?.

[PeteF]

Interesting stuff Rev.
To make a line break type "
" without the commas.

[PeteF]

Ah, the commas didn't work.
it just picked up the line break anyway.

It's < followed by br followed by > withour spaces.

[PeteF]

That's it. It's html code and you can do lots of other clever stuff with it. Scalyback is a bit of a whiz at this.

[Revband]

Thanks Pete, will give it a try
Bikes engines and tuning I understand, computers are different.

[Thack]

Hey, Revband, could you enlarge upon what you said a little?



You said that changes AFTER the carburettor can't affect the mixture, because whatever increase/decrease in airflow results, the carburettor automatically maintains the right air/fuel ratio. That is, an increase in airflow causes the carb to deliver more fuel, and thus maintain the correct mixture.



This makes perfect sense to me: it seems totally logical - it is exactly what the carb is designed to do. But unfortunately it goes against everything I've read and heard about tuning up engines. Every supplier of freer-flowing exhausts for bikes like ours recommends increasing the jet size. Everybody who has reported on their experiences fitting such exhausts says they had to do similar. This seems to be universal across all cars and motorcycles that use a carburettor.



So, why doesn't the logical, reasoned argument you put forward work in the real world?



Please note: this is a genuine request for more insight - I am NOT taking the piss or trying to undermine what you said. I've been puzzling over this question for years.

[Scalyback]

Does your bike have a fuel filter and is it nearly blocked?



I had that, and of course, it wasn't until I had been running non stop at speed, that the fuel used would exceed the fuel coming through and after a short while, the float bowl level would drop and the bike splutter.



It was tricky to diagnose, and the bike would run faster ok, but only for a certain distance before sputtering.




HTML CODE

[Revband]

Hi ScalybackThanks for your informative post regarding code I am trying it here, hopefully I will do it right?. I should have asked my Grandson as I see that on another post where he copied some dictionary text for me he knew how it worked.

Thack I really don't know how I can expand on what I have already said, you ask why the logical, reasoned argument I put forward wont work in the real world?. Please read my post again I say it does work in the real world.
The only thing to add it as an engine becomes more highly tuned then the fuel air mixture becomes more critical and just possibly the suppliers of the replacement silencers feel happier thinking that the engine is now running slightly rich as opposed to the possibility of it being lean and melting pistons etc (with possible claims for damage), but of course I still maintain that if it is weak with the new exhaust it was weak to begin with but the higher state of tune makes it more critical.

Nice work on the circuit diagram by the way, I now see that Enfield India incorrectly refer to the alternator as a magneto so you leaving it as such was the correct thing to do.

[Revband]

Damn it almost worked

[papasmurf]

Revband, "Our Hosts" specify, the needle setting and jet size for the "universal" exhaust, for a very good reason, they have found out the hard way.