Advice: what's causing my Triumph America to hunt and stall?

Published: 09 June 2010

I have a 2001 Triumph America that I fitted a freak kit to several years ago (that's a set of K&N filters and carb rejetting) together with a set of pipes.

Everything has been fine until recently when I decided to use a K&N cleaning kit (for the first time as I never oil my filters). Since then, and on a recent 100-mile+ run, she got quite lumpy and started hunting at tickover and stalled several times in traffic.

I thought I'd over oiled the filters so have since run her up without them. Guess what? When she's hot she is still doing it! At tickover, the revs will keep dropping away every few seconds and then she will eventually stall. I can also feel her missing a bit when cruising. Could it just be muck in the carbs? I have an in-line fuel filter and that’s OK. Just seems a bit of a coincidence it's only started since I oiled the filters?

I have since washed the filters out with tins of spray brake cleaner and they have cleaned out well. Problem is she still does it when the filters are off completely, but only when she gets hot. Wouldn't you say that she was running too rich? But why start playing up now, she's been fine for years? And yes, I've fitted new plugs, new oil and filter as well.
Captkirk750, MCN forums
 
Hunting at tickover and stalling is a sign of a rich mixture, but revs dropping away and stalling is shortage of fuel. It’s possible the fuel level is changing in the float chambers. I cannot understand why it’s started after cleaning the air filter. I would uncouple the feed pipe at the carb to see if petrol is peeing out after going through the filters.

Also make sure you have not left the airbox pressure sensor disconnected or the vacuum pipe from the bike’s ECU, depending on which style of ECU it has. Also check you haven't trapped a fuel supply pipe or connector when you moved the tank.

It seems strange that it has only happened since you opened the airbox to get at the filter. I would have the tank off again and have a really good check of all connectors and pipes.

It may also be the crank position sensor, this has a habit of playing up when hot if the unit is failing. They seem to go between 20-30,000 miles.

Symptoms are 'usually' but not exclusively, weak running/lack of power as though the fuel has been shut off. If your clean-out hasn't solved the problem, this could be worth a look; when was the last time you had the shims/clearances checked? If the valves are tight then it will also produce this kind of running as they will not shut properly. The inlet valves on modern Trumpets close, so if you are around the 24,000-mile check it will be worth a look at these too.