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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 11-01-2012, 10:14 PM   #1 (permalink)
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2001 Bonnie - Bogging/Coughing after mods

The bike: 2001 Bonneville 790cc

The mods: Emgo open mufflers (Bellacorse BCE-037), snorkel removed, airbox restrictor plate removed, K/N foam filter, AI removed, crankcase breather removed from airbox and capped with air filter.

Carb settings: 130mains, 40pilots, 2.75 turns(stock), stock needles, no shims, clean.

So I've read a lot of posts here trying to troubleshoot my problem, which is a bogging and coughing behavior when opening the throttle while parked. This behavior did not occur before opening the airbox and adding open pipes. While the choke is out the throttle revs normal, however once it's warm the throttle response is crap. The bike seems to start ok when cold, idles decently.

My first thought was an air leak. I sprayed WD-40 around the engine intake and carb intake and didn't notice a change in idle. However I noticed some bubbling around the rubber intake manifold (some very visible cracking). I replaced both and idle is better but the throttle still bogs.

Next thought was the ignition coil, which failed last year on a long road trip through hot Texas. I tested the spark plug caps with a multimeter and got a reading of 13 kOhms. I read that the normal range for the carb'd models is between 18-20 kOhms. Is this far enough off spec to cause this bogging?

What else might be the problem here? Do I need to rejet? Spark plugs are pretty clean and recently gapped. 22,000 miles on the bike, not sure about valve clearances. I'm looking forward to getting the bike running again so I can rip around with these new mods. I could also try posting an audio clip of the bogging/coughing if that would be helpful.

-Matt
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Old 11-02-2012, 05:56 PM   #2 (permalink)
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set up

Just perusing the available info on the 790 if you are using the stock needle you need to be 140+ if using the thrux needle 125+ you will need 1 or 2 shims and might well need to up to 42 on the pilots. Turns is what she needs 2.5 - 3.0.
A balance will be in order after the mods.
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Old 11-02-2012, 10:19 PM   #3 (permalink)
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I was under the impression bogging was a sign of running too rich...could I really be too lean? Others with similar setups as mine seem to be jetting in the 120-130 range. I did not ARK it, FYI.
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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 11-03-2012, 05:50 AM   #4 (permalink)
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There is a lean bog and a rich bog, they are both a little different but with your setup and 130 mains, it won't be a rich bog. Try 135-138 mains and one shim under the needle, if the bogging is still there try 2 shims and see how it feels.
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Old 11-04-2012, 01:03 PM   #5 (permalink)
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Went up to 135 and 1 shim, feels a little better but still bogging. I'll try a second shim. What about the resistance in the ignition coil? 13kohms is what I measured from the plug caps.
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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 11-04-2012, 01:16 PM   #6 (permalink)
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Quote:
Originally Posted by whalefish View Post
What about the resistance in the ignition coil? 13kohms is what I measured from the plug caps.
That's about right for the OEM GILL coil. If you have the Nology or PVL coil it should be around 18K Ohms.
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Old 11-04-2012, 07:07 PM   #7 (permalink)
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135 mains, 2 shims, 3.25 turns, great idle and no more bogging. Took it for a ride and really put it through it's rpms. Lots of power in the mid range, easily whipped my head back in 3rd gear going about 45mph. I did notice that the bottom end is a bit weaker than I would expect. Opening up the throttle in 1st and 2nd gear from low rpms makes a lot of noise but not as much pick-up. Any thoughts?
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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 11-04-2012, 09:54 PM   #8 (permalink)
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Quote:
Originally Posted by whalefish View Post
135 mains, 2 shims, 3.25 turns, great idle and no more bogging. Took it for a ride and really put it through it's rpms. Lots of power in the mid range, easily whipped my head back in 3rd gear going about 45mph. I did notice that the bottom end is a bit weaker than I would expect. Opening up the throttle in 1st and 2nd gear from low rpms makes a lot of noise but not as much pick-up. Any thoughts?
I also have a scarlet/silver 2001 with similar mods. The only differences are I did the Bella Corsa DIY airbox removal kit kit and I have TORS. I'm running 135 mains, 42 pilots, Thruxton needles with one shim and about 2.5 turns. I'm pretty happy with that tuning. The Thruxton needles seem to be a good $20 investment.
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