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Al Eckstadt
Al Eckstadt
Jordan, NY
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#703979 08/04/17 9:56 pm
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A good friend has a stock single carb 71 650 trumpet , its stock with E3134 type cams and 7.5 CR , stock pipes but short reverse cone megas and the air box is deleted , fitted with a 930 AMAL Mk1 and a chrome cheese grater old style filter. , the sort of megas that blare in your ears at 4k, sound fruity at idle, his MJ is 230 , Ive ridden it and it picks uo when rolled off from full throttle suggesting lean-ness, The less restrictive "silencers " probably need a bigger MJ , we will trial a 250, any other takes? I have no Triujmph experience is a 930 correct , ?

Last edited by gavin eisler; 08/04/17 10:52 pm.

71 Devimead, John Hill, John Holmes A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
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That's the recipe I would recommend for a holed piston.

At the minimum, put proper mufflers on it. It will run MUCH better anywhere else but the race track.

Cheers,
Bill



Bikes
1974 Commando
1985 Honda Nighthawk 650
1957 Thunderbird/T110 "Black Tiger"
Antique Fans: Loads of Emersons (Two six wingers) plus gyros and orbiters.
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thats what i thought, it was un bearable to ride, 60 MPH was 20 miles max , he is thinking Peashooters . Glad you agree.
BSA single carb A65Ts are 28 mm, that's why I asked about the 930.

Last edited by gavin eisler; 08/04/17 11:06 pm.

71 Devimead, John Hill, John Holmes A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Joined: Aug 2001
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Thanks gents , will pass this on.


71 Devimead, John Hill, John Holmes A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
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I'm 99% sure a 30mm carb (930) is right for an OIF 650. The 230 main jet surprises me. The standard main jet for a single carb 750 is 270, and that's with the massive silencers which strangle the poor engines. Without a silencer my TR7 needs a 330 main jet.

If your friend want maximum performance (general efficiency, not just power/speed but also fuel consumption), please tell him/her not to heed advice about running open exhausts being some kind of bad thing! It isn't. These engines only work at their best when allowed to breathe freely. They also happen to sound very nice when not muffled to death.


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Kind of an odd comment that Triumph mufflers strangle the performance. I've yet to see one that wasn't just a straight through glass pack. Perhaps some of the 70's bikes had restrictive exhaust?
I focus on the earlier bikes myself and have found through a lot of trial and error that for street use, the stock mufflers provide superior power spread and reasonable sound. No one (but me) likes a really quiet bike so it tends to be acceptable to most.
They are heavy so those wanting to reduce weight will opt for something else.
One thing I have done regularly is to can the balance pipes for individual ones. The has an effect on the power, slightly, and does increase the noise a little but to get rid of all that extra stuff, most find it's worth it.
In particular the early 70's 650's have really nice power characteristics that I would hesitate to mess with. They're pretty much perfect just the way they are, in my opinion.

Cheers,
Bill


Bikes
1974 Commando
1985 Honda Nighthawk 650
1957 Thunderbird/T110 "Black Tiger"
Antique Fans: Loads of Emersons (Two six wingers) plus gyros and orbiters.
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The stock mufflers with a crossover pipe on my 72 was agony. I knew it should have been faster and it was, noticeably, with stock 68 mufflers and no crossover.


1968 T120R
1972 T120RV
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Yes, I was thinking about the '70s silencers Bill - especially after about 1974. One fell off my first T140 and it immediately ran a bit better so I took the other one off when I got home and the difference was amazing.


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Thanks for the carb size and jet info, possibly he miss read 280 as 230, any hoo i have a known 280 handy, will try that.


71 Devimead, John Hill, John Holmes A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod

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