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[Bullet Whisperer]

Well, clearly all my work to build race winning, championship winning and lap record setting Royal Enfields has been a complete waste of time, as I clearly could have left the ports and everything else bog standard [/quote]

Now now --there is a big difference in porting and matching gaskets. The 500 UCE with a hemispherical combustion chambers is pretty good in that respect.

You did'nt go into details but I would think the UCE would benefit from exhaust porting. But you are not talking about the UCE are you.
[/quote]
You are not paying attention. The 535 GT is a UCE and I opened up the inlet port and the exhaust port, as seen and discussed in my video. I am confident there will be an all round improvement in performance as a result.

[Bullet Whisperer]

Well, clearly all my work to build race winning, championship winning and lap record setting Royal Enfields has been a complete waste of time, as I clearly could have left the ports and everything else bog standard

Now now --there is a big difference in porting and matching gaskets. The 500 UCE with a hemispherical combustion chambers is pretty good in that respect.

You did'nt go into details but I would think the UCE would benefit from exhaust porting. But you are not talking about the UCE are you.
[/quote]
You are not paying attention. The 535 GT is a UCE and I opened up the inlet port and the exhaust port, as seen and discussed in my video, if you bothered to watch it. I am confident there will be an all round improvement in performance as a result.

[Cranky]

You are not paying attention. The 535 GT is a UCE and I opened up the inlet port and the exhaust port, as seen and discussed in my video, if you bothered to watch it. I am confident there will be an all round improvement in performance as a result.[/quote]

I admit that I had not been paying attention. I watched the VDo of this welsh bloke tuning his head

If I ever take my head off to remove tappet blocks I will certainly have a look at that. 4mm is a lot but I was particularly interested in the valve being close to the side. With my cylinder being now 88 I have a bit more room to play with.

Did you take out some of the head gasket to fit that.

Don't you have any trouble with reversion.

Did you take any from the valve guide boss.

Why do you retard the inlet a tooth and what to you gain from that.

What squish measurement did you aim for and what gasket are you using.

[Bullet Whisperer]

Welsh bloke, me? I am what some Welsh people call an 'Effing Saes'
There are a lot of things to try and answer there, but here goes -
The head gasket was left alone, as there was no problem with that and it should be ok for your projected 88 mm bore.
Around the back of the inlet valve [looking into the combustion chamber], a lot of the circumference of it is pretty much a dead area, so I eased out and angled the edge of the combustion chamber, to promote better breathing and I think this would be of greater benefit still, where a larger cylinder bore might be used.
The original squish clearance can vary a little from machine to machine, but is generally too wide to be of optimum use, at around 2.5 mm, so I take 1 mm from the base of the barrel, to close this up and increase the C.R. by a small margin.
Shortening the barrel is all well and good, but this brings the valves, which can already get close to the piston even closer and on the yellow CGT machine I tuned, the inlet was too close for comfort on the overlap TDC with the Hitchcocks cams, so I thought I would just retard the inlet cam by 1 tooth, as I do on many of the Bullets I tune and see if the performance was any good. The performance was much better than on the previous, green CGT I tuned, so a lucky accident, really.
The valve guides were left totally standard and in situ while I did the porting work, although I fitted the Hitchcocks valves and springs.
I hope this latest, red CGT will out perform the green and the yellow ones, both of which didn't hang about themselves, as can be seen here [best bit for the green one is just after 8 mins], while the overtake on the yellow one [around 6 mins] gives a fair indication of the acceleration available.
Green CGT ...
https://youtu.be/iO00SldM1J4
Yellow CGT ...
https://youtu.be/IRr8P0TnbBA

[Duke of Wybourne.]

the inlet was too close for comfort on the overlap TDC with the Hitchcocks cams, so I thought I would just retard the inlet cam by 1 tooth, as I do on many of the Bullets I tune and see if the performance was any good. The performance was much better than on the previous, green CGT I tuned, so a lucky accident, really.

This is good to know as I have work to do on one that has suffered a catastrophic top end failure within a miles of similar upgrades by an inexperienced person. Have you ever tried it on a dyno ? I've never felt the need, as a good thrashing on a known road usually reveals the necessary, but some figures would be nice non the less.

[Bullet Whisperer]

the inlet was too close for comfort on the overlap TDC with the Hitchcocks cams, so I thought I would just retard the inlet cam by 1 tooth, as I do on many of the Bullets I tune and see if the performance was any good. The performance was much better than on the previous, green CGT I tuned, so a lucky accident, really.

This is good to know as I have work to do on one that has suffered a catastrophic top end failure within a miles of similar upgrades by an inexperienced person. Have you ever tried it on a dyno ? I've never felt the need, as a good thrashing on a known road usually reveals the necessary, but some figures would be nice non the less.

I have tested quite a few 'Bullets' on a dyno, but never a 535 CGT, so I can't offer any numbers, but the green one and the yellow one both turned out to be pretty quick, going by the seat of the pants and the speedo needles on both being able to point at their ignition keys [which must mean they were doing a bit over 60 mph, officer]

[Wheaters]

Could be. The yamaha V max fits smaller carbs for more torque. Big carbs dont force in more fuel it only supplies --if the demand is there.

Are you saying they fit a small carb on a big port, leaving a “wrong way” step and get more torque?

[Adrian]

I'd heard BSA used to do that with comp shop Gold Stars, but the step between the larger carb and smaller inlet was very small, only somewhere in the order of 1/32" all round. Can anyone confirm this? But a 34mm throttle body or carb against this CGT's 30mm port before tuning gave a 2mm step all round, that couldn't have been helping performance.

A.

[Wheaters]

Two different principles are in play here.

A smaller Venturi will cause a greater pressure drop at the jet for the same airflow. This will tend to provide better atomisation of the fuel at low power settings and therefore a better low speed response. At the other end of the scale a smaller Venturi will provide more restriction to maximum flow.

A “wrong way” step will cause turbulence in the inlet port which will reduce maximum gas flow, negating the potential of a bigger carb.

In the past I fitted a tuned 850 Reliant engine with twin 1 1/4” SU carbs. I had it rolling road tuned. The engine produced a lot of power for its size. They were however impractical for a number of reasons (couldn’t get to the battery, couldn’t gain access to adjust the fan belt etc) so I wanted a single carb to replace them. I fitted a Weber 34 ICH single choke carb with a 25mm Venturi (cast in Venturi on this type, non adjustable). These were fitted to Ford Fiesta 1100s. I had it tuned so the mixture was optimised for power. It ran great at low speed, better than with the SUs. Unfortunately it was almost 15 mph slower. A carburettor expert suggested the carb was too small. I then discovered Weber made the carb in at least three versions, identical apart from different Venturi sizes. I found another with a 29mm Venturi. It produced almost as much power as the SUs but it ran like £rap at low speed. Gas speed was too slow. I later found out that this version was designed for 2.25 litre Land Rovers. Too big for my engine. Third time lucky I found one with a 27mm Venturi. This was designed for 1300 to 1600 cc engines and was the best compromise, good low speed pickup although not quite so powerful. I would have kept it but discovered that on very steep trials sections it would dump most of the contents of the float chamber into the manifold, causing the engine to fluff up and stall.

I gave up and fitted a bigger, single flat top type ISO (SU type design) and that worked very well, I gained best in class at the last trial I did with that engine fitted.

[Cranky]

Could be. The yamaha V max fits smaller carbs for more torque. Big carbs dont force in more fuel it only supplies --if the demand is there.

Are you saying they fit a small carb on a big port, leaving a “wrong way” step and get more torque?

I think some here are calling a step as different thing. I was referring to the exhaust port that was smaller than the pipe. I consider this as a step. This is so that the reversion shock returning ( some people think this is back pressure) has trouble getting over the step to the small diam exhaust port. I hope I explained that good enough.

Reversion is a horrible thing suffered particularly by motorcycles as they are limited to how long the exhaust pipe can be.

Harleys use a cone insert, and then there is a reversion stop that can be fitted. This is a swelling in the pipe like a pregnant worm. Bigger pipes is not good and will destroy your jetting.

The old fish tail was an attempt to stop reversion.