Gt186 carb and exhaust

[Adam_Winstone]

Keep in mind that it is 'horses for courses' though... it is as much a case of your state of tune not suiting the BGM clubman as it is that the clubman doesn't suit your state of tune (2 sides of the same argument). If you were to change your state of tune, the BGM clubman might be the right choice of pipe.

You also need to consider whether or not you want the look of a classic Lambretta with an expansion's muffler sticking out of the side of it?!

I'm making the above comments so that people bear in mind what it is they are trying to achieve when they buy kits, pipes, carbs, ignitions, etc. as it seems as though far too many people buy a load of different bits from different places and HOPE that they'll work together in harmony, rather than buy all parts in consideration of how they will work together and what the end result will be. BHP is only one factor.

Adam

[eden]

True Adam, however my state of tune probably isn't anything like what you think it is.
Port timings are definitely lower than you may think.

Timings on my gt250 are way way lower than my cast 240 which is tuned specifically with the fran race in mind.

Tbh I think that the ignition curve was the thing not working with the box pipe but as there were 15 of us taking lambrettas on the dyno that day I didn't have time to re-map it for the box pipe. However, later in the winter I will be doing just that.

[jonzo172]

Maybe a GT specific pipe could be a future project for Rich T?

[Darrell Taylor]

the clubman pipes from bgm are too small on outlet size(18mm) for higher hp/larger cc engines they gas up and progressively get worse as the situation compounds then as they age will carbon up and become smaller still.... ,seen them do 22bhp on a well tuned 186 where the gas production is less and outlet size more suited ,,,better on a 125 though at that size ... but seen no more than 25 on a big cc/hp motor as they become strangled ,a gt specific pipe is not neccessary theres some great ones out already that work really well when well built to a good spec... ive put some up on the gt dyno thread

[eden]

Maybe a GT specific pipe could be a future project for Rich T?

A few things in the pipeline for next year from the GT base camp

[hendy]

I've just had a new build engine on the scooterotica dyno with a gt186 kit on.

I was slightly disappointed with just under 10bhp.

I'm running 25phbl through a drilled airbox and an ancillotti clubman. 58 107 crank. Exhaust raised by 1mm. Varitronic with 24degrees at tickover.

Am i getting what you'd expect? Dan reckons it's about right, but i just wanted to double check as I was expecting closer to 15. Maybe I'm just expecting too much.

I'm prepared to fit an open 30phbh and even a different exhaust (although I'd prefer to keep the standard looks of the ancillotti).

Thoughts?

I've quoted myself above as reminder what the thread was originally about. In a nutshell I was disappointed in the performance I got and was looking to improve it by changing the carb/exhaust. I bought them but never fitted them as I wasn't convinced that this was the right tack to take. Basically I was questioning the standard of the build.

Also, I promised Rich Taylor that I'd report back as what the issue was when I found it rather than just starting a thread which might cast doubt on the performance of the kit.

Anyway, I eventually got round to putting the motor on the bench and having a proper look to see if there was a leak etc.

This is what I found when I removed the left hand footboard. These marks indicated to me that there was a head leak.



When I removed the head cowl the real problem was staring me in the face. For those who aren't familiar with the kit, this red anodised plug is to allow a central plug and should be wound in flush. It had backed off as far as the cowling would allow it and was clearly the cause of the leak. Also, this would increase head volume thereby reducing compression.


Neither the head nor the piston have suffered any damage. Probably because it was set up by Dan on the dyno and his jetting (over rich compared to the norm) has protected them.



Now I think this graph is very interesting. You can see that the power just flattens off as the revs increase, due to the torque dropping off proportionally to the rpm. I've seen a graph on here from someone who was disappointed in their engine's performance (an Avanti I think) and the graph did exactly the same thing. Anyway, he holed a piston due to a head leak!

[shamrockexpress]

Good findings there Hendy looks like a cheap fix ( tube of thread lock)
good luck and cant wait to see the outcome>>>>>>>>>>>>>>

[Mick Abbey]

Hendy although you have found a problem with the plug in the head leaking This will only cause a very small loss in power if any your main problem is your pipe as Darrell has mentioned that the outlet on your clubman pipe is to small and will be choking the engines performance I have tried a couple of clubman styled pipes on a tuned motor and all it did was kill performance over an expansion chamber and cause the engine to run hot also the shape of your graph is very similar to the graphs that I was getting with a clubman, Change the pipe Mate you won't be sorry.

[Doom Patrol]

This is interesting stuff. It would be good if someone were to draw up some sort of chart as to what exhaust is good with what tune. I know there has been talk before of using Clubman style pipes on tuned engines, but I wasn't aware of any issues with them clogging up.

[Rich_T]

Thought I'd covered this in the manual but a quick check confirms I didn't. The best stuff to use is a soft thread lock compound as it makes the blanking plug serviceable in the future.