Friday, May 24, 2013
I was convinced it wasn't a fueling problem, after all the work I'd done on the tank, and the carbs, and the fuel pipes ... ! Starting from cold was OK - firing after maybe four or five spins of the engine on the starter.That's why I thought it was time to revisit the ignition system to look for an explanation. I'd previously had a problem with my Daytona cutting out when warm and that was due to electrical breakdown of the ignition pickup coil when the engine was hot. It had always started perfectly from cold and, after cutting out, would re-start from cold. In that case though, it was total failure with the engine stopping completely while riding at normal speeds.
With my Trophy, it was different because it would run reasonably well at normal speeds though would cough occasionally accelerating from low revs. I'd read about similar problems on some internet forums. They pointed to failing ignition coils as the potential cause.
On my Trophy, these are a pair of twin-outlet resin-encapsulated units manufactured by PVL in Germany. The PVL coils on my bike were the originals. I know because PVL stamp the production date just above the low-tension connections on their coils. Mine read 0491 - April 1991.
So that means they are 22 years and one month old. That's old enough to justify retiring them. The coils I bought from Sprint were marked 1112 and 0313 - November 2012 and March 2013. I was somehow amazed to see that their construction appeared to be identical in every way to the originals - same cases, same potting, same terminals.The only difference is the white print on the body, with the code 356 100. The PVL website lists that code as "High performance double Ignition Coil 2/4-cylinder Triumph, BMW", 1.1Ohm primary winding, secondary 7,66kOhm. My old analogue multimeter sort of agreed with this, given that the needle waves about quite a lot without ever seeming to settle. I noticed that the secondary windings on the old coils were reading about 10kOhm - higher than the new ones anyway. This measurement doesn't mean much though because the bike was cold when I measured the resistances and the problem only surfaces when hot.
I've been for one ten-mile run with the new coils so far and already the difference is noticeable. No more coughing on the throttle at low revs. Whilst idling on its centre stand after the ride, I got the bike hot enough or the fan to cut in. Whereas it would have been stumbling badly yesterday, there was just a hit of lumpiness. I was able to turn the idle speed right down to an indicated 500 rpm without the bike stalling. I must have left it running like that for a minute just to see before turning it back up to its regular 1000 rpm idle speed.
Sunday, May 19, 2013
|90mm spacer shown loose in stanchion|
|Top 3mm disk being installed over 9mm spacer and lower 3mm disk|
I rode south to the Sammy Miller Museum today and was pleased with the result. The ride is firm but not overly firm. This is a matter of personal preference of course. It feels more controlled than with the 90mm spacer but just that bit more compliant than 110mm.
|TriMoto 1200 outside the Sammy Miller Museum|
Sunday, May 12, 2013
|Patent plate and ally cover ready to fit|
|Patent plate with top two rivets just locating into ally cover|
|Top two rivets driven though patent plate and ally sheet into top yoke|
|Original steel spacer tubes are 110mm long|
The Ohlins spacer tubes are made of an aluminium alloy, rather than the steel ones fitted to the Trophy, and they were of a smaller external diameter. That meant there was a risk that they would not seat neatly against the fork top caps or on the spring seats. As it happens, the forks have a spring seats that fits between the top of the springs and the bottom of the spacer tube. It has a lip that by coincidence fitted neatly inside the Ohlins tubes. So the lower end of the spacer wasn't a problem. It wasn't as easy to be sure about this for the upper end of the tube, where it buts up against the fork top cap.
|Measuring up some aluminium disks as seats of the spacer tubes|
|Shortened alloy spacer tubes and seats|
Tuesday, May 7, 2013
Friday, May 3, 2013
A good dose of carb cleaner soon shifted the goo but still ... I'm hoping that it was just a very fine rust from the tank and that my efforts to seal the tank will mean the end of it.
The floats were about 1mm too low, at 13.5mm compared with the spec in the Haynes manual. That might explain why the bike was hesitating just off idle and the amount of fuel evident when I pulled the carbs out. The floats are measured with the carbs inverted so they are bearing down on the valve that admits fuel to the float bowls. Low floats mean high fuel - can be confusing. So I set them all to 14.5mm.
I remember having trouble setting them when I rebuilt the carbs last. I had removed the plastic cages that hold the floats and remember that it was difficult to re-seat them afterwards. They push into an O-ring, which was springing back. No such trouble this time.
I did two other things to lean off the mixture as well. This is silly from a scientific perspective: any change could be due to any one or a combination of any two changes. But I thought, "while I'm in there, I might as well", as you do ;-). These were:
- to reset the pilot jet screws which control slow running. Haynes says they should be two turns out from fully seated. As it was, they were between 2.5 and 2.75 turns out. So I set them all to 2 turns out.
- to lower the jet needles. They were on the standard setting, which is position three of five. I set them all to position two. This really wasn't necessary but I wanted to see what effect it would have on the middle rev range and progression off idle.
I put new fuel pipes in (again!) with new t-pieces but no filters this time. I also fitted a new thick-walled vacuum pipe between carb 3 and the fuel tap. The routing of these pipes to the carbs is now clean, with no horrible bends - and a shorter journey!
She started up when the float bowls were full - and idled really rough. Not what I wanted to hear. The carb balance was way out after these changes. I suspect resetting the pilot screws was the main reason. After balancing them up with my old Morgan vacuum gauges, nice and even. I managed to get a tick over at an indicated 500rpm. Sweet.
I've done about 100 miles since and there is no sign of fuel starvation. I'm guessing the big change was the new vacuum pipe for the fuel tap. Better still, that hesitation off idle is no longer there. Result. I think the mixture is probably a bit lean in the midrange but nothing drastic. I'll run the bike like this for a few hundred miles than may put the jet needles back to position 3 again. That's easy to do with the carbs in place.
The sun is out. It's time to ride.