I am on vacation and riding in very hot 98-102 degree temps. I am riding a 2004 Midnight Star 1700,Vance&Hines slash cuts, ported intake with mr c's airfilter mod, pms 2 turns out. I noticed after about 300 miles a change in my exhaust:however, the bike is running as normal no loss in power or gas miliage. I'll detail:

1 exhaust suddenly got louder (I was running about 75mph) when I decelerated it sounds like straight pipes for a short time and then normal sound. This sound like maybe on one cylender or exhaust pipe. If I ease off on the throttle when slowing down it does not pop.It does pop when changing gears.

2 I checked both baffles, they are in place (thought maybe one had came out) maybe silly thought anyhow just checked.

3 put seafoam in two tanks of gas no change. Adjusted pms a couple of times, to 2 1/4, 2 1/2 turns out with no change. Changed back to 2 turns out.

4 replaced spark plugs with no change.

Any suggestions would be appreciated. I have about 300 miles to go before I will be at a relatives house if I need to do much work. I have a pretty good selection of tools and can do most minor work. I'm thinking maybe valves?? no excessive valve noise that I can detect.

Thanks in advance for any suggestions or advise.

You got a leak in your exhaust somewhere!

yup, sounds like a leak.

Do the simple test by lighting some incense (you choose the flavor, i prefer vanilla) and waving it around the exhaust while running. A leak will blow the smoke around.

Sounds like mine did when the vacuum cap came off the intake. Has the ais been removed & the intake capped. If so is the intake cap still on?

yes the ais has been removed. I'll check the intake cap, that is the rubber cap on the rear cylinder correct?

Sundance

Sounds good to me, if the wind is still I'll check that tomorrow when I check the ais intake cap.

Sundance

Check the baffle in your pipes, I had the stay bolt fall our of one of mine and the forward end of the baffle fell out of its seat as it vibrated backwards.

sundance wrote:
yes the ais has been removed. I'll check the intake cap, that is the rubber cap on the rear cylinder correct?

Sundance
That's the rubber cap that's put on the intake where the vacuum tube to the ais was connected.

Well I have checked the exhaust for leaks with a incense candle and found nothing, also checked the ais input plug and all checks ok. If anyone has other suggestions please let me know. I also changed the spark plugs since I had them, the ones I took out looked fine a little blac maybe because I changed the pms to 2 1/2 turns out, which I have since changed back to 2.
This is really getting to me, I like my vance&hines because they are loud but this sounding like straight pipes is to much.

thanks for any more suggestions,

Sundance

Usually an exhaust leak, especially if it ran OK for 300 m and then started.

If you're positive that you have no leak, change out the 37.5 to the 35 (don't change anything else).

Doc