BwanaDik
Well-known member
I've got a '96 Triumph Trophy 900 that I use as my back up bike and loaner when friends come to visit. An embarrisingly low 11,000 miles on the clock but it is my back up bike.
A couple of months ago I decided to sync the carbs as it hadn't been done for a while. Apparently the o-rings and rubber were so old that even the small amount of fooling around with the carbs was enough to make them leak fuel all over the place and into the engine. At one point I tried to start it, not realizing the fuel had probably filled one of the cylinders from all the leaks, and I think it hydro-locked as it quit turning over. Out come the plugs and sure enough, lots of fuel spray from the cylinders on cranking. Did a compression test later to check if I had bent anything but all OK. Don't remember the absolute readings but they were withing less than 10% of each other and the factory specs.
Long story short, I rebuilt the carbs (Mikuni 36mm), got new rubber boots between both the engine and carbs and carbs and airbox. Fired it up last night (hard starting at first) and drove it around for about 10 miles. Waaaaay low on low end torque (this engine is usually a stump puller) but still ran pretty well at full throttle north of 7000 RPM. I figure at that point there's so much airflow that any leaks would be insignificant.
I came back and checked for air leaks. I had tried the "spray on brake cleaner/WD-40 and listen for stumble" method but no stumble. I got a new vacuum gauge and checked all three cylinders, vacuum was 3" hg at idle on all three, could only get to 7" on the over run after a full wind up to 7000 RPM's or so.
Is the 3" normal? Seems really low, my truck is at 20" or more at idle. Also, I'm assuming (you know where that get's you) that the sync nipples on the Mikuni's are connected to the intake manifolds down stream of the butterflies and so are giving me manifold vacuum? Or is there something about the Mikuni's where you can sync them but not on absolute manifold pressure? What's really throwing me off is that everything is the same across all cylinders. No apparent leaks. You'd think that there would be some variation in the leaker but nope! If that's the problem.
Help help, really at a loss here of what to do next.
A couple of months ago I decided to sync the carbs as it hadn't been done for a while. Apparently the o-rings and rubber were so old that even the small amount of fooling around with the carbs was enough to make them leak fuel all over the place and into the engine. At one point I tried to start it, not realizing the fuel had probably filled one of the cylinders from all the leaks, and I think it hydro-locked as it quit turning over. Out come the plugs and sure enough, lots of fuel spray from the cylinders on cranking. Did a compression test later to check if I had bent anything but all OK. Don't remember the absolute readings but they were withing less than 10% of each other and the factory specs.
Long story short, I rebuilt the carbs (Mikuni 36mm), got new rubber boots between both the engine and carbs and carbs and airbox. Fired it up last night (hard starting at first) and drove it around for about 10 miles. Waaaaay low on low end torque (this engine is usually a stump puller) but still ran pretty well at full throttle north of 7000 RPM. I figure at that point there's so much airflow that any leaks would be insignificant.
I came back and checked for air leaks. I had tried the "spray on brake cleaner/WD-40 and listen for stumble" method but no stumble. I got a new vacuum gauge and checked all three cylinders, vacuum was 3" hg at idle on all three, could only get to 7" on the over run after a full wind up to 7000 RPM's or so.
Is the 3" normal? Seems really low, my truck is at 20" or more at idle. Also, I'm assuming (you know where that get's you) that the sync nipples on the Mikuni's are connected to the intake manifolds down stream of the butterflies and so are giving me manifold vacuum? Or is there something about the Mikuni's where you can sync them but not on absolute manifold pressure? What's really throwing me off is that everything is the same across all cylinders. No apparent leaks. You'd think that there would be some variation in the leaker but nope! If that's the problem.
Help help, really at a loss here of what to do next.
