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Discussion Starter · #1 ·
Hi, my bike is a 97/98 T509.

I was getting a high Idle for the last couple of months, so I changed the IACV hoses, wich were in bad shape and not the factory hoses anymore.

I got some 5mm vacuum hoses because I wanted a tight fit on the 7mm nipples, and I deleted the check valves after asking and reading opinions from a bunch of people who said they were not necessary.

Now the idle is fine BUT, under deceleration situations, I feel like the bike has less "engine braking" than before. Feels like I have a little bit of throttle open (but the cable isn't sticking). It's not terrible, but doesn't seem right like before.

Do you guys think it could be caused by the smaller diameter 5mm hoses, or the lack of the check valves?

Thanks!
 

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I don't think the hoses could affect it at all. There really isn't any flow to speak of, they are just communicating the manifold pressure to the sensor. I don't know what the check valves do so I can't comment on that. When you blip the throttle does it quickly return to idle speed or does it take a bit to drop down? If the idle is hanging up a bit before decreasing this may be what you are feeling.
 

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Discussion Starter · #3 · (Edited)
The throttle response is pretty crisp and it quickly returns to idle. The only problem is really on deceleration. I thought that maybe the intake can't get enough air with the 5mm hoses, as the iacv hoses are the only source of air when the throttle is closed.
I can squeeze the cylinder 1 hose while I'm riding, and when I do that, the effect on deceleration is more significant. I mean, less engine breaking.
 

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Discussion Starter · #6 ·
I did a test while riding. I disconnected the biggest hose from the IACV and put my finger on that port on deceleration. When I did this, the deceleration was correct. So I assume the check valves should actually do something to avoid the air flow during deceleration, or the IACV is letting air flow when it shouldn't... I know the IACV is not leaking because when I put my finger on the big port at idle, the engine dies. I'll try to put the check valves back and see what happens.
 

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I'm having an issue with my bike (that was sitting for 7 years before I bought it) that after I installed some new vacuum hoses (after the originals were perished) and giving the IAC valve a quick clean it ran like a dream for 10 minutes, switched it off then wont start again? Are the IAC valves known to stick closed?
 
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