ST1300 – RPM pulsing, fuel smell, and exhaust rumble after spring service

[newowner]

HI All,

Pulled my ST1300 out of winter storage and did some basic maintenance before riding:

• Changed engine oil
• Changed transmission/final drive oil
• Replaced spark plugs (old plugs looked normal)

After the spark plug change, I started noticing a few issues:
1. RPM pulsing / blip

• On cold start, idle sits around 2000 RPM, but every 3–4 seconds there’s a noticeable blip (about +200 RPM).
• Once the bike is fully warm (3 bars on the temp gauge), base idle drops to about 1000 RPM, but the same RPM blip every 3–4 seconds is still there.
• Took the bike for a short ride thinking it might clear up—no change. (but unfortunately i filled the fuel tank)

2. Strong fuel smell when cold

• There’s a strong unburnt fuel smell during cold running.
• This goes away once the bike is fully warm.

3. Exhaust noise when cold

• When cold, I hear a rumble / abnormal exhaust sound, almost like excess fuel is burning in the exhaust.
• This also disappears once the bike warms up.

Relevant history: Last season, I removed the airbox and pulled the 5‑way tee (vacuum/air hose junction) and cleaned it. One of the branches was blocked, which I cleared at the time. The bike ran fine afterward and through the rest of last season. And I did not have that rpm blip when i put the bike in storage last season..

Where to start ? and Is it safe/ok to use the bike for an upcoming 400km trip ? thanks

 

[jfheath]

The only thing that I can think of is related to the fact that you say that you have replaced the spark plugs. It is possible to get the washer cross threaded / at and angle so that when you think it is seated before performing your half turn tighten up (or whatever it is ) , the plug is actually not properly seated. So when you perform your tightening turn, it is just trying to straigten out the washer, adn the plug remains unsealed. Depending which one - or which ones - this has happened to, the behaviour of the engine will be different.

Handbook says: New plug : tighten the plug after it seats : NGk half turn; Denso 1 turn. Then loosen the plug and tighten it as if it is a re-used plug:
Reused Plug: One eighth of a turn after it has been seated.

The first turn from new squashes the washer.

Whether or not that is the issue, you can expect all of those syptoms from a plug that isn't sealing properly. Remove the plug, check the washer is properly in place, insert the plug and this time you will have to torque it to the specifed torque for a re-used plug, No more. No less.

 

[aniwack]

Also gapping would make it misfire. I've had two this month with that problem where they bought plugs at the auto parts warehouse and just stuck them in.

 

[Larry Fine]

Air filter condition? Mouse nesting?