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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 07-29-2010, 04:54 PM   #11 (permalink)
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Hmmmmm. (scratches head)
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Old 07-29-2010, 08:59 PM   #12 (permalink)
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Well, some more head scratching is in order, I just had the coil out and checked it with a multimeter, the primary and secondary windings do indeed share a common ground (being the one spade connector on the coil). Furthermore, the coil core is totally isolated from both windings.

So, anyone have any theories why my bike stutters with a poorly grounded core? Why do Triumph ground it? Perhaps an ungrounded core causes EM or radio noise that interferes with the ignition system in some other way.
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Old 07-29-2010, 09:11 PM   #13 (permalink)
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Got this from the NGK website:

"When a spark plug fires, it creates a great deal of radio frequency interference (RFI) and electromagnetic interference (EMI). Uncontrolled, this can show up as static in the radio or other electronic devices, or much more seriously, in electronic ignitions, fuel injection, and engine management systems. This interference with EFI and engine management systems can cause "cross talk" between wiring harnesses resulting in poor running, misfiring and decreased performance."

Only question remaining is whether or not a grounded coil core suppresses RFI and/or EMI...
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Old 07-30-2010, 12:56 AM   #14 (permalink)
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Only question remaining is whether or not a grounded coil core suppresses RFI and/or EMI...
Come to think of it transformer cores in high frecuency switch mode power supplies are grounded for EMI reasons.
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Old 07-30-2010, 01:40 PM   #15 (permalink)
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Your ground wire might have fixed a ground problem somewhere else on the bike would be my best guess.I didnt think they had changed how the coils work on the efi bikes.If the plug side of the coil wasnt grounded right it would burn a hole through the coil dont ask me how I know this lol.
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Old 08-04-2010, 06:45 PM   #16 (permalink)
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So I've been doing quite a bit of reading and it seems the reason for grounding the coil core is indeed for EMI suppression. Triumph must have run into some interference issues on the changeover to EFI, necessitating a switch in coil style to allow the core to be grounded, hence why the EFI bikes have a coil of different design (exposed core). Another option might have been to use suppressed (carbon) HT leads, but obviously Triumph did not go down this route for whatever reason/s as the spark plug leads are still copper based (more on that later).

As planned I've built a custom aluminium bracket for my coil, not only to better ground the coil without the need for a wire shunt, but also to move the coil higher and dryer. I also figured the alu will act as a heat-sink, cooling and prolonging the life of the coil. In any case, during the construction of the bracket I made another interesting discovery when I decided to remove and check the HT leads while I had the coil out....

Lo and behold, Triumph saw fit to grace me with 2 short HT leads, instead of the correct long/short configuration. Not a big deal? Well, the Tec coils on the EFI bikes have different depth HT sockets (where the HT leads plug in), the one being about 20mm deep the other 40mm. On my bike this meant that the one HT lead was too short (by 20mm) to make contact with the pin inside the coil, necessitating the spark to jump this gap before getting to the wire and then to the spark plug! I'm amazed that the bike could even run in this condition. Quality control my ass, they probably ran out of the long HT leads at the factory and some smart-ass decided the short ones will do just fine on both sides.

A quick visit to the auto parts store, $1 for 1 meter of HT lead, some measuring and cutting, a few o-rings and I've a new set of HT leads. Bike runs so much better now, even the usual slight flutter of the tachometer around 5,000rpm is gone. I suggest that everyone with an EFI bike should check their HT leads, this can be done with the bike as is, no need to remove the tank or anything. The longer lead (and hence, deeper socket) is the one on the bottom of the coil as fitted to the bike. Unscrew the cap, pull out the lead and measure, it should be about 40mm from the rubber seal to the tip of the lead, if so, all is 100%. If it measures about 20mm, then it's a 'short' lead and you need to sort it.
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Old 08-05-2010, 04:19 AM   #17 (permalink)
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Good find, thanks. That's something else to check.

I did find another little British bodge in the connection of the MAP sensor to the manifolds.

Basically the flexible rubber adaptor piece that attaches the rigid PVC tubing to the manifold stub has an internal diameter of 4 mm so this fits over the PVC pipe nicely as that is 5 mm OD. The stub however is 4.2 mm, rising to only 4.45 mm at the point where the metal has been swaged or expanded to hold the pipe securely. In addition to being undersized for the rubber hose, it's very poorly formed. Looks as if I made it From some other posts we also gather that the internal finish of the manifolds is also suspect, probably to match the vacuum stub!.

I also imagine they're using and adapting the old carb manifolds to get rid of the skipful they got at the back of the works...

This diameter difference between rubber hose and stub simply isn't enough to secure a good seal, even with a hose clamp (non-existent on our bikes) so Triumph in their wisdom have smeared the stub with some foul, black sealing compound to stick hose to stub.

This is not standard practice on hose connections, in fact this is the first time I meet up with this. I've been wrenching for years, and have never seen a pipe connection made by sticking it permanently with sealant. Connections always rely on correctly-sized hoses, stubs and hose clips. The upshot of it all is that as you try to prise the hose off it breaks up, rendering it scrap.

I obtained another piece of flexible hose of the same length and ID and re-made the joint without any sealing compound. I started up the engine to check everything was OK. It wasn't.

The right cylinder refused to run at idle, it would only run at over 2k rpm, just at the point where the MAP sensors have no say in the fuelling and the TPS position takes over, as we've seen earlier. Not only did it refuse to run, but it fouled the spark plug with massive over-fueling. A raw fuel cloud could be seen exiting the silencer when the engine resumed firing at over 2k rpm...!.

I couldn't believe that the new connection would cause this, and changed the plug and did other checks. In the end it was due to a tiny air leak in the hose to stub connection that fooled the MAP sensor into a low vacuum reading and therefore assumed a higher load on the engine and increased the fueling to match. You won't believe the amount of trouble a tiny leak causes at this point.

In a carburetted engine, such a leak would cause a minor weak condition that you might not even notice, but in these EFI jobs it's exactly the opposite: The MAP sensor will send signals to the ECM that will catastrophically over-fuel, and eventually kill the affected cylinder by wetting the spark plug.

I wasn't prepared to repeat the sealant bodge again, so found another piece of silicon hose with a smaller ID of 3 mm. This fits very tightly over the PVC pipe (5 mm OD) and nicely snug on the manifold stub. Note that the old sealing compound still adhering to the stub has to be scraped off first to present a smooth, clean surface to the new tube. To ensure a good connection I added suitable spring hose clips to both sides of the hose.
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Old 08-05-2010, 08:31 AM   #18 (permalink)
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Great stuff Forchetto, sorting those tubes will most likely be my next mod. As you've pointed out, those seemingly insignificant little rubber tubes can leave one stranded. Funny thing, while reading your post the first thing that came to mind was silicone tubing, because of its stretching ability without tearing or cracking with time. I wonder if we can source some silicone tubing that steps in diameter...

The way they sealed the airbox also elicits contempt, I've been itching to remove the brown gunk and reseal neatly with silicone. But I've been too lazy.
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Old 08-05-2010, 11:08 AM   #19 (permalink)
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Originally Posted by Grubscrew View Post
Great stuff Forchetto, sorting those tubes will most likely be my next mod. As you've pointed out, those seemingly insignificant little rubber tubes can leave one stranded. Funny thing, while reading your post the first thing that came to mind was silicone tubing, because of its stretching ability without tearing or cracking with time. I wonder if we can source some silicone tubing that steps in diameter...

The way they sealed the airbox also elicits contempt, I've been itching to remove the brown gunk and reseal neatly with silicone. But I've been too lazy.
I bought a kit from these folks... NOT cheap, but good quality.

http://www.hosetechniques.com/
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Old 08-06-2010, 03:40 AM   #20 (permalink)
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Originally Posted by Forchetto View Post
Good find, thanks. That's something else to check.

I did find another little British bodge in the connection of the MAP sensor to the manifolds.

Basically the flexible rubber adaptor piece that attaches the rigid PVC tubing to the manifold stub has an internal diameter of 4 mm so this fits over the PVC pipe nicely as that is 5 mm OD. The stub however is 4.2 mm, rising to only 4.45 mm at the point where the metal has been swaged or expanded to hold the pipe securely. In addition to being undersized for the rubber hose, it's very poorly formed. Looks as if I made it From some other posts we also gather that the internal finish of the manifolds is also suspect, probably to match the vacuum stub!.

I also imagine they're using and adapting the old carb manifolds to get rid of the skipful they got at the back of the works...

This diameter difference between rubber hose and stub simply isn't enough to secure a good seal, even with a hose clamp (non-existent on our bikes) so Triumph in their wisdom have smeared the stub with some foul, black sealing compound to stick hose to stub.

This is not standard practice on hose connections, in fact this is the first time I meet up with this. I've been wrenching for years, and have never seen a pipe connection made by sticking it permanently with sealant. Connections always rely on correctly-sized hoses, stubs and hose clips. The upshot of it all is that as you try to prise the hose off it breaks up, rendering it scrap.

I obtained another piece of flexible hose of the same length and ID and re-made the joint without any sealing compound. I started up the engine to check everything was OK. It wasn't.

The right cylinder refused to run at idle, it would only run at over 2k rpm, just at the point where the MAP sensors have no say in the fuelling and the TPS position takes over, as we've seen earlier. Not only did it refuse to run, but it fouled the spark plug with massive over-fueling. A raw fuel cloud could be seen exiting the silencer when the engine resumed firing at over 2k rpm...!.

I couldn't believe that the new connection would cause this, and changed the plug and did other checks. In the end it was due to a tiny air leak in the hose to stub connection that fooled the MAP sensor into a low vacuum reading and therefore assumed a higher load on the engine and increased the fueling to match. You won't believe the amount of trouble a tiny leak causes at this point.

In a carburetted engine, such a leak would cause a minor weak condition that you might not even notice, but in these EFI jobs it's exactly the opposite: The MAP sensor will send signals to the ECM that will catastrophically over-fuel, and eventually kill the affected cylinder by wetting the spark plug.

I wasn't prepared to repeat the sealant bodge again, so found another piece of silicon hose with a smaller ID of 3 mm. This fits very tightly over the PVC pipe (5 mm OD) and nicely snug on the manifold stub. Note that the old sealing compound still adhering to the stub has to be scraped off first to present a smooth, clean surface to the new tube. To ensure a good connection I added suitable spring hose clips to both sides of the hose.
Any chance on seeing a few pics of whatever can be ilustrated in this mod at this point Forchetto?
Cheers, Ted
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