E: Engine Blind jetting

[vibrac]

Hi I have been invited to the heritage center for the flywheel festival and there are no noise police so I have taken off my 105 Db 2" absorption silencer and fitted a 2" dia extension on my 2" pipe (a bit shorter than the back wheel spindle to allow for the paddock stand and the foxley starter) engine is Mk2cam Grey Flash with 1-1/8 TT I have taken a surreptitious run up the local road and as expected get a missfire/stutter at 2-3000+ smooth as silk under that and mechanically she is tip top, so my guess is I need to up the main jet and perhaps the needle upping. The main jet at the moment is 340 I note 370 in my old books for my old twin before the noise limits but not a good comparison and a long time since I had a TT on open pipes. Trouble is I have to take a guess -one run on the roads is enough for the neighbors (perhaps I could get 1 more in) and there are no practice runs at the event what do you guys think 360 and needle 1 notch?

 

[Vincent Brake]

Maybe make the pipe as long as an Lightning,
specially with open pipes the lenght is most important.

not that i know any about it, but its an idea

 

[roy the mechanic]

340 mj sounds very large to me. The norvin runs big cams, 9-1 36mm mki's and is happy with 240 mjet 3 and a half slide. Oh and it has open pipes.Reckon the plugs are black+ wet. Be lucky.

 

[vibrac]

I think the TT are a lot richer in jets that MK1's the GF performed a lot of parades on the 340 with 2" pipe and an 2" absorption silencer- same length as the open pipe the absorption silencer was 2" perforated and a minimum O/A diameter thats why I was hoping to get away without a long departure from my setting for it.

 

[Robert Watson]

I have a 1 5/32 brass 10TT9 on the TTR. I don't know if you recall it from Montana but it just went flat at about 4000. Changed the pipe to 2" X 34 from the head and it absolutely came alive hitting 6000 before I could grab the clutch and get another gear. It is running a 360 main jet as per Richardson's recommendation.
Old pipe in my Avatar, new pipe here

 

[Bill Thomas]

I would have thought Main was Ok, Maybe lift the needle or richer slide. Cheers Bill.

 

[davidd]

This is a summary of dyno runs with a 10TT9 32 mm, No. 7 slide, needle in middle slot and a two inch straight pipe. Started at 44".

I found the bike did not like the long pipes that are usually recommended and that 28" was the best with this set-up. On a bike that made 35 BHP stock, it was nice to get almost 5 more BHP just by cutting the pipe.

David

 

[greg brillus]

Sounds like the slide cut away to me, at those rev's main jet not part of the equation yet. What number slide are you running, and what fuel while we're at it.

 

[vibrac]

Sounds like the slide cut away to me, at those rev's main jet not part of the equation yet. What number slide are you running, and what fuel while we're at it.

With hind sight and thinking about it I think I agree with you Greg no way was I on main jet
the slide is unmarked but its cutaway is .409" which is about 13/32 which is 6.5 1/16ths so its a 6-1/2 slide
needle is third notch down and I am running pump premium Esso (no Ethanol) guess around 95 octaine
I would have thought the slide was generous enough for open pipe

 

[Bill Thomas]

Have you not got a choke/ starter cable, To see if it's too rich or too weak, I must admit I did not have them on my T.T. carb's. Cheers Bill.