2004 Speed Triple 955i - Spitting/spurting Noise

Hey guys,

Just realized I posted the original thread in the wrong forum, so here's it posted in the proper place.

I'm getting a spitting/spurting/compressed air blast sound when I'm at idle. I first noticed it after I accidentally yanked off one of the hoses from the EVAP system that hooked up to the IAC port. It would spurt and I'd see a little cloud come out of the port. I'm not sure why, since air is supposed to go in, not out. The rubber connector was broken, so it continued to spurt after that.

Anyway, here's the flow of the various things I've done since I noticed the noise. Please note that the noise started before any of this, and I don't know that some of this has anything to do with the problem. I'm just including it for completeness of information:

1. Noticed spitting sound, discovered it was from one of three ports on the back of the cylinder head (which I eventually learned are the Idle Air Control ports)
2. Removed Secondary Air Injection and closed off the ports and airbox.
3. Removed California EVAP system. The rubber connectors were all cracked and worn, so I ended up trying just rubber vacuum hose and fuel line to connect the IAC ports on the head to the ports on the IAC valve under the airbox. This always resulted in unsteady and low RPM.
4. I eventually removed all the hoses and went back to the corrugated plastic hoses that came with the bike, forcing on good rubber connectors. Idles great now, but the spitting is a lot worse again.

Has anyone encountered this spitting noise and knows what causes it? The bike seems to run fine now for the most part, except the engine seems to "miss" when the spurt happens. It's just really annoying and loud, and makes my bike sound like it's about to fall apart.

 

- It is EFI with a throttle body for each cylinder.
- There was a bit of low end power lost when I installed the new short exhaust, but I didn't notice any change in power when the noise started. Throttle response doesn't seem to be affected except when I had the other hoses on and it was killing idle RPM.
- It was idling fine before I removed the EVAP system, but it had many vacuum leaks because it was old and cracked. It did "lope" a bit, and seemed to idle a bit unevenly. When I removed the EVAP system, I put new hoses on (not factory), but I think they were too restrictive and wouldn't let it idle properly. I put the original hoses back on with jury rigged, taped up connectors and it's idling between 1000 and 1500 RPM again, which seems to be the comfort zone of the bike. It still doesn't stay at one RPM, though, and moves around a bit when I sit at a light.
- Fuel economy has dropped significantly. I was going 150 miles before the fuel light came on, then it dropped to 120, and it just came on again at 95. I would say my heavy hand on the throttle is the culprit, but I typically ride pretty aggressively.
- No fluid patches that didn't come from a spill while working on the bike.
- It occurs most significantly when it's cold, but it's not a consistent sound. It's a random spurt that sometimes happens several times in a row, sometimes only once in a while. Seems to calm down once the engine is warm, but I still get it fairly frequently. It sort of sounds like pressure building up somewhere in the system and then releasing in a spurt.
- I have a Coffman short exhaust fitted, which has an internal baffle to reduce noise and the loss of back pressure. That is the only drive train modification I've made. I installed the exhaust before I accidentally ripped that EVAP hose off, and it didn't make the noise at that point.

I'm fairly sure it's not a vacuum leak in the hoses, because I put brand new hoses straight from the ports to the idle air control valve. Like I said, it sounds like pressure is building up somewhere and then being released. Sometimes it's a rapid sound, other times it's just once in a while.

Thanks for the help!

 

I'll have a look at the fuel lines. It is an old bike, and probably has the original hoses. The fuel filter is inside the tank to my knowledge, so I'd need to remove a plate on the side to open it up and check.

 

So I was playing around with the setup this afternoon. Last week I broke the quick disconnector for the lower fuel line and had to replace it yesterday. I was tightening it up a little more after the fuel suggestions to make sure there wasn't a problem there, then I noticed that the rubber connector I had taped up had been torn and blown off again on the middle IAC port on the head. It was getting dark, and I noticed that there is actually light coming out of the port, which leads me to believe that maybe there is combustion backfiring back out of the IAC port? I can't be sure, but it looked like flame...or maybe it's just vapor and my eyes were playing tricks on me. Is that something that could happen?

As a side note, that made me think that maybe the backpressure is too high on the exhaust, so I opened up the collapsible baffle to get more air flow. Not sure if that will fix it or not.

 

So it turns out that too much back pressure kills idle quality. That's obvious I suppose, but my supposed performance exhaust apparently had too much and the pressure was causing the exhaust to spit out the IAC ports at idle. That was the "flame" I saw. I took out the adjustable baffle in the exhaust and all the idle problems vanished. Acceleration performance hasn't changed, but engine braking is highly reduced from the jerkiness it had before, and when I release the throttle it just drops to 1000 RPM and sits there now. Amazing how the last thing you would think to look for is alwyas the culprit. Thanks to all for the suggestions and help. I'm glad I can finally just ride the thing now!