Tim's Motorcycle Diaries: Triumph 955i triple throttle body synchronization

Sunday 30 May 2021

That Darned Tiger: Stalling issues on a Triumph Tiger 955i

The Tiger worked for a couple of months this spring but started recently stalling again. The engine was getting rougher and any time I came off throttle quickly, such as downshifting, the engine would 'fall' right through where it normally idled and stall. If I didn't downshift and let it drop to idle on the clutch it wouldn't stall.

If you're familiar with the blog then you know this isn't my first dance with Triumph's early fuel injection systems. I've replaced the vacuum housing for the idle control system (a plastic piece that looks a bit under-engineered) and all the hoses and gaskets last year when chasing this thing, but looking over the deep winter maintenance I did I don't think I rebalanced the fuel injection after taking it all apart to clean it.

Balancing the FI on these 955i Triumphs is tricky because you have to take apart a lot of the bike just to get at the adjusters. I've been in and out of this so many times that I'm quick - I don't even have to keep the fasteners sorted because I know where they all go.

To balance the fuel injection on a 955i Triumph engine, take the fuel tank and airbox off. On the Tiger, if I put the fuel tank next to the bike the fuel lines are just long enough to connect so I can run the engine with the tank attached but off the bike.

I was going to use the Tuneboy to balance the injectors this time but couldn't figure out how to do it so just went back to good old-fashioned vacuum balancing.

Evidently you can balance throttle bodies off this but it jumps around so much I found it easier to use the vacuum balance I use for carburetors instead. Perhaps the Inj #1, 2 & 3 P/W can be used to balance?

The Triumph triple is quite easy to balance once you've pulled it all apart. The left side throttle (#1) isn't adjustable so you use it as your reference. With that hose plugged in I balance the one next to it to #1 and then did the same with the far one.

I got this TecMate Carbmate Synchronizer from Fortnine last year and it makes the job quick, accurate and easy. Just keep adjusting the screws between the throttle bodies until you have equal vacuum between them.

Don't balance two to three, just two to one and then three to one, so you don't need a non-existent three cylinder vacuum synchronizer. I ended up buying the extender so I can do up to four carbs, but it isn't necessary for the Tiger, though it did come in handy on the Fireblade.

It took me about ten minutes to get everything from way out of whack to right on the green balanced light on the CarbMate. Once I had it done the engine sounded less rough even with no airbox and missing sensors.

Running it like this pisses off the computer and throws up a whole bunch of warnings because you're not getting readings from the airbox sensor or the vacuum to engine management computer. If you don't have a Tuneboy to clear the computer errors it takes a few runnings for the ECU to reset itself. I just reset the errors in the Tuneboy system and then put it all back together again.

The bike immediately felt smoother and there were less backfires and hesitation when turning the throttle. I took it out today and went for an extended ride and couldn't get it to stall even when doing things that caused frequent stalls last week, like down shifting to a stop and pulling the clutch as the engine was dropping in RPM.

If you're having stalling issues with a Triumph 955i fuel injected triple, balance the throttle bodies before you start chasing other issues. Unbalanced throttle bodies cause stalling once the engine is hot.

I put some LockTite on the throttle body adjusters this time so hopefully it won't 'fall' out of adjustment again this riding season. I'm still very concious of rubber parts perishing on this nearly twenty year old high-mileage bike. Last summer's issues revolved around vacuum leaks in the idle control system so I'm going to keep a close eye on other rubber bits if I run into stalling issues again, but this time around it was just throttle body synchronization that seems to have done the trick. Maybe next time I can work out how to do it with the Tuneboy so I can get it even more precise, though the CarbMate seems to have done the job with high fidelity.