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Twins Technical Talk Technical Talk for Hinckley Triumph Twins: Bonneville, T100, Speedmaster, America, Thruxton, and Scrambler.

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Old 11-07-2012, 07:26 PM   #11 (permalink)
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Whalefish...
42 pilots and thruxton needles will richen up your low to mid range which from what you say is where you're having lean conditions.
As for loss of mpg, you'll use more fuel if you use the extra power gains. I get 53 + mpg when ridden sensibly, that drops to the low - mid 40s at "playtime".
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Old 11-07-2012, 08:59 PM   #12 (permalink)
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Best way to get more low end torque is to get more displacement .... in other words, if you want low end, trade the bike for something bigger. By the time you do all the various mods to try to coax a strong low end out of a sub 800cc carburetted vertical twin, you'll spend more than the cost of a trade up.
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Old 11-07-2012, 09:09 PM   #13 (permalink)
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I think I'll try the thruxton needles and a 42 pilot, one at a time. Definitely not ready for a bore kit. I'm more curious about the tuning, since it feels like there was more low end power before the mods, and now I've got a flat spot. I'm pretty sure it's a fuel/air thing that I need to tweak.
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Mods: AI gone, restrictor plate gone, snorkel gone, Emgo open mufflers (BCE-037) with JC Whitney baffle insert, K/N filter, crankcase breather filter.
Carbs: 135 main, 40 pilot, stock needle, 2 shims, 3.25 turns
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Old 11-07-2012, 09:23 PM   #14 (permalink)
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You say you do a lot of long distance touring riding?

Then I can't see why you would want your engine having to cruise at a higher rpm to maintain the same road speed by reducing the size of the sprocket from 17 to 16.

I can see doing that if you did NOT do a lot of touring and simply wanted a little faster acceleration in exchange for less top end.

In addition, a smaller sprocket is a tighter turn for the chain, not a big deal but also it may accelerate chain wear.
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Old 11-07-2012, 11:02 PM   #15 (permalink)
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Quote:
Originally Posted by whalefish View Post
What can I do to get more power in 1st gear/low rpms?
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Originally Posted by whalefish View Post
2004 790 T100. De AI'd & de baffled - DNA - 137.5 mains - 42 pilots - 1 turn - Thrux needles - Velo stax - EMGO shorty rev cones - Pieman 8100 igniter - Wilburs prog. springs - TEC prog shox, s/damper & fork brace - 19T - EMGO cafe fairing. Tutoro.
Part of the trade-off in running a 19 tooth sprocket is the loss of some acceleration off the mark. Maybe you should consider compromising to an 18 tooth sprocket.

As plenty of people have said a capacity increase is an easy way to improve low end torque. An often overlooked way to increase capacity on a 790 is to fit a standard set of 865 cylinders:-

http://www.ebay.com/itm/2010-Triumph...item2c675bf405

http://www.ebay.com/itm/04-Triumph-T...item2ebd3e587e
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Old 11-08-2012, 03:39 AM   #16 (permalink)
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To clarify, not wanting to change the sprockets or the cc's. I realize this is the most direct route, but I was more interested in the fuel/air ratio or some other problem that might be sapping my low end since the intake/exhaust mods.
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2001 Bonneville - Red & Silver
Mods: AI gone, restrictor plate gone, snorkel gone, Emgo open mufflers (BCE-037) with JC Whitney baffle insert, K/N filter, crankcase breather filter.
Carbs: 135 main, 40 pilot, stock needle, 2 shims, 3.25 turns
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Old 11-08-2012, 06:13 AM   #17 (permalink)
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Whalefish -
Seems that some of us have been mislead by your opening post.
You're actually seeking the restoration of pre mod performance and tractability, not additional low rev stump pulling umph...right ?
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Old 11-08-2012, 08:16 AM   #18 (permalink)
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Are you sure you gave anything up at the bottom end? Opening things up in the intake & exhaust will make the top end considerably stronger, thus making the low end feel pale in comparison. If just going on seat-of-the-pants measurements, everything is relative...including perceived flat spots.

Since you aren't keen on displacement or sprocket changes, my recommendation would be to optimize your jetting first...an A/F gauge or EGA at a speed shop will point you in the right direction. Maximizing intake tract length will improve low end torque. Playing with exhaust baffles to adjust back pressure can also lead to maximum torque outputs for a given state of tune. Both of these come at the expense of flow/upper end power...and both will subsequently affect the optimum jetting/potentially require jetting tweaks to compensate.

Regards,

--Rich

Last edited by beemerrich; 11-08-2012 at 08:18 AM.
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Old 11-08-2012, 01:29 PM   #19 (permalink)
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Denbow, sorry if my first post was confusing. I'm looking to create a linear level of acceleration from bottom to top, which existed before the mods although with less umph. Beemerrich is right though, it's all relative and perhaps it does just feel flat in comparison to the increased power at the top end. Everything I've done on the bike so far has been seat-of-the-pants measurements since dyno-tuning isn't really something I can afford right now.

I've selected some of the cheapest and easiest mods for the bike for now while money is tight, not to say I wouldn't love to bore the cylinders later and put some shiny velocity stacks on the intake.

Sounds like getting an AF gauge would be a great way of optimizing the tuning for me. I've also thought about adding a polaris bellmouth to the snorkel hole to smooth the air, or even cutting out the airbox DIY ARK style. Keep hearing this kills your MPG though, since you gotta balance all that new air with more gas.
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2001 Bonneville - Red & Silver
Mods: AI gone, restrictor plate gone, snorkel gone, Emgo open mufflers (BCE-037) with JC Whitney baffle insert, K/N filter, crankcase breather filter.
Carbs: 135 main, 40 pilot, stock needle, 2 shims, 3.25 turns
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Old 11-08-2012, 03:09 PM   #20 (permalink)
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Whalefish.
If you're on a budget ARK and AF gauges aint cheap and the best bang for buck is to get the jetting sorted out.
1/ You MIGHT be a little rich with 135 mains but with baffled open EMGOS they won't be far out if you enlarge the inlet cover as I suggested earlier, or better still.. invest in one of Pieman's (Triumph Twin Power) inlets to replace it...they're better than Polaris or anything else currently on the market.
2/ Your biggest problem seems to a lean condition in the low & mid rev range. This is easily rectified with 42 pilots and Thruxton needles. Note that after fitting 42s the mixture screws won't need 3.25 turns, one or a little less should be ample.
The above should have your bike running strong and smooth but I do recommend a dyno run to complete.
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