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Vintage Technical Tips & Tricks Technical and maintenance tips and links. DO NOT POST YOUR QUESTIONS HERE!! Please post questions to the general forum.

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Old 08-06-2012, 04:53 AM   #41 (permalink)
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If you're only using cams with the valve-lift of a standard T140 intake (0.380" net),you can reduce the port diameter 1/16" between the carb and the valve-guide,with no loss in flow.The port is already too big and the valve doesn't flow enough even at full lift.
You can also reduce the port size between the guide and the valve seat to about 1-1/8",with no loss in flow at full valve-lift.

On the other hand,if you were able to get 1/2" valve-lift,the standard port size between the carb and guide would be fine and still keep up with flow at the valve.Some relieving around the valve guide will increase flow a little.You could still reduce the port size between the guide and the seat to gain some intake velocity advantage.Intake velocity keeps filling the cylinder after the piston reaches BDC,and has other advantages.

Exhaust ports have always been too big.They say if you weld the floor of the port to form a "D" shape,it helps.

Last edited by Mr.Pete; 08-06-2012 at 05:06 AM. Reason: "Exhaust ports - - - - it helps."
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Old 08-06-2012, 06:52 PM   #42 (permalink)
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Quote:
Originally Posted by triumph rules View Post
you have to get rid of anything that is a sharp edge -where the seat goes into the port , on the 750 head i've got here it has a sharp edge on the inner part of the port as it comes up to the seat ,make it like the outer side of the port.
iff you are going to rev it, the port can go slightly bigger
with bigger carbs ,i lost a bit down low but it came alive about 3000
Hi,,,Thanks for that....exactly what im trying to achieve >3-4000 rpm...will look into it..
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Old 08-07-2012, 03:08 PM   #43 (permalink)
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yeah pete the valve pocket is too big for the port size, do you use port bog?
i'd like to get a head cast with raised inlet port and proper shape and sizes
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Old 08-07-2012, 10:31 PM   #44 (permalink)
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JB-Weld is the best filler I know of for an intake port.
Only welding will work on the exhaust.

The position of valve-springs stops you raising the standard port much.I've seen heads modified with intake ports facing out the side more,and using a steep downdraft angle.
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Old 08-08-2012, 05:40 AM   #45 (permalink)
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Good info in here guys thanks to all the contributors. I don't have a lot of need to drain every last bit of power out of the old t140 but this has been an interesting read.
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Old 11-30-2012, 10:50 PM   #46 (permalink)
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One sort of performance mod I have done on other bikes is to the coils - and it only costs a few bucks. I don't know if Triumphs are wired the same as Japanese bikes and whether this is relevant, I haven't had mine long enough to get into it all of that yet, so please excuse me if I'm talking crap. On 70's Jap bikes they send the coil feed through the ignition switch and then the kill switch. Over time with corrosion and dirt plus some of the iffy wiring connections it's not long before you perhaps only have 9 volts at your coil. If you use a relay with a feed coming directly from your battery with an inline fuse and use the existing circuit to the coil to operate the relay you will have a solid 12v feed at the coils and you wil be amazed at the difference in starting and running performance. I did it to my KZ650 and it was amazing the difference it made.
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Old 03-29-2013, 09:56 PM   #47 (permalink)
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Red hawk, seems very interesting. I'm a big fan of strong spark, especially on a kick start bike. Sounds like it wouldn't be that expensive, either. This could also help folks with EI , as I've heard they require a strong feed to work correctly.
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Old 03-31-2013, 12:41 PM   #48 (permalink)
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That's an interesting idea. On a positive ground Brit bike with EI, I am thinking that it might work as:
Feed line from battery negative with a fuse to relay. Output line to white wire on ignition box. Wire from kill switch (original feed to white wire) to switch relay.
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Old 03-31-2013, 01:26 PM   #49 (permalink)
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or just disassemble and clean the switch?

They're often full of 40 year old crud. Granted they will corrode again but often it's time that is the killer, rather than the design. They are a pig to assemble though
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Old 04-16-2013, 05:52 AM   #50 (permalink)
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Quote:
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or just disassemble and clean the switch?

They're often full of 40 year old crud. Granted they will corrode again but often it's time that is the killer, rather than the design. They are a pig to assemble though
If you squirt a bit of ACF50 into the switch occasionally, they won't corrode. ACF=Anti Corrosion Forumula
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