Engine start is OK but dies when applying throttle

Question

Triumph Tiger 900 (1994)

The engine starts fine and idles with choke. When I reduce choke and try throttle it just dies. Regardless of choke position, when I throttle, the engine dies. Thus, I cannot ride it at all.

After 5+ minutes it was already at operating temp, ambient outdoor temp was 4-6deg so I was a bit shocked by this.

The triple carbs were serviced 2019. I have had this 4 years and only managed 1000+kms every year (very poor for me).

I am loathe to accept a carb problem as the Triumph dealer charged me an arm and a leg to service them, but would a failed spark plug cause complete throttle death? Air filter?

Answer 1

The triple carbs were serviced 2019. I have had this 4 years and only managed 1000+kms every year (very poor for me).

It's not always clear what "serviced" means. But for a bike this old the carbs surely needed a complete rebuild. Modern ethanol-containing fuels are very hard on carbs and riding only 1000 or so km/year means this thing sat around a LOT. So the fuel had plenty of time to separate out the ethanol which is quite corrosive and do its damage to your carbs.

First of all you need to assess what's damaged in the carbs. It may be as simple as to remove the "sludge" or "varnish" that collects in the bottom of the bowl and in the small passages. If it's worse than that you need to replace the damaged parts. After you're finished the carbs should look like new on the inside.

In the future you should drain the carb bowls when you are storing the bike. Many models have drain screws for this purpose. You might also consider storing it with ethanol-free (i.e. E0) fuel in the system. While it doesn't stay stable forever, it does last a lot longer than the E10 or E15 fuel that is commonly sold.

Answer 2

Carbs have multiple fueling circuits. One circuit is for idle. Another is enrichment, which gives extra fuel when you twist the throttle. Another circuit gives it fuel while at a steady state above idle. The enrichment and/or the steady state circuits are not providing fuel to the engine. An internal combustion engine needs three basic things to run: air; fuel; ignition. You can pretty much eliminate air/ignition as culprits, since the bike runs at idle without issue. Neither of these things are going to (basically) change when you twist the throttle. The only thing left it can be is a fueling problem. While you don't want to believe there's an issue, I'd give it about a 98% probability that is exactly where the problem lies.

Answer 3

I had a similar issue but with an estate car: began driving fine but then I drove up hill and increased the revs and the car stalled, again and again. It turned out there was a small perforation in the fuel line that drew in air at higher rates with higher revs. This in turn created a starved air/fuel mix and stalled the engine.

Could this be your problem? It should be quick to check by rubbing soapy water on the fuel lines and checking for bubbles

Answer 4

All of the above is good advice. As with RDavey, fuel lines age and crack. Look for seepage on the lines and where they fit over a fitting stub. Sometimes you can simply cut the end of the line and refit it. Be sure the clamp fits well.