Main Motorcycle: My 09 Bonneville Black
Join Date: Apr 2009
Other Motorcycle: Want the new CB1100
|Twins Technical Talk Technical Talk for Hinckley Triumph Twins: Bonneville, T100, Speedmaster, America, Thruxton, and Scrambler. Sponsored by: Long Beach Motorsports|
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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.
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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