High idle after riding for about 30 minutes

[Troll]

If you've got a) the money, B) the time, and c) the facility, it might be profitable to do the dyno thing...but don't expect it to mean anything unless you have a way to modify the fuel program. If you're happy with how it's running, then maybe just ride it. The dyno and dyno tuning will not mean anything unless your goal is to tweak every last performance parameter, and make a monster...then do it, but for the vast majority of riders, I would suspect that a good running reliable and fuel efficient ride would be their goal. IMHO....

[Driftaway]

I did change the crush gaskets when I changed pipes so I shouldn't have an exhaust leak. What I did after I went for a long ride that weekend was to just adjust the idle down. It seems to be great now. But I found it suspicious having it creep up after exhaust change over.
Is the best overall way to see how the bike is running to put it on a dyno or just use the ol Butt Dyno to tell?

[chief]

And be sure you don't have exhaust leaks. I assume you replaced the crush gaskets when you changed pipes.

[Bucko]

Good point!  A vacuum leak will also cause a high idle.

[John Hopkins]

I don't know how much the idle speed is increasing by but if it is a lot then I would say you have too much air getting into the combustion chambers..I would have to look at the air filter..

John.

[Troll]

That is mostly true, but the newest ones as required by federal law are adaptive, and actually "learn" people's habits....scary, huh? They all use basic settings, but the ones with O2 sensors are able to modify their output based on left over oxygen in the exhaust stream. The ones on the Drifter, and the ones on the early H-Ds are more like the "open loop" phase or a car, when the engine is cold. They are very similar in design and operation to the Bosch Jetronic systems of the late 60's and 70's...no feedback, just a table of values. Some of those systems even had a potentiometer on the computer to modify the program in the field..
I've been dealing with these systems since 1968, on the VW variants, and some of the SAABs..

[Bucko]

I was under the impression that all FI systems, even newer ones, use a look-up table (or 'map') and simply use the sensor feedback to compare to the lockup table and make adjustments the the fuel mixture accordingly (O2 sensor simply confirms if more adjustment is necessary).  When people 'reprogram' their 'chips' (as some vehicles allow for) they're simply changing the values in the look-up table and the system makes adjustments accordingly based on feedback from the sensors and the new map.

[Driftaway]

I think I have some reading to do during the winter months Troll

[Troll]

You have fallen into the trap of thinking that this system is like all the modern systems that can actually compensate for changes. It can, but only within the parameters of it's simple look up table. There are very limited automatic adjustments. My experience with this system is that the two that have the most effect are the IAT and the BARO sensors. TPS is a minor factor, until you get it too lean, and MAP, TEMP and RPM just simply address the look up table. The fuel pressure regulator actually seems to have more effect on output than the MAP sensor, since it raises fuel pressure with engine load. There is no O2 sensor, so all values are fixed. Please not that the part under the greyed out area is where MOST of your riding is going to be done....

[Driftaway]

Thanks for all the help. No, PC, doesn't fix it by blipping the throttle. Chokes not pulled out. Only mods engine wise are the V&H exhaust with the dual mod. I'm going on a good long ride tomorrow so will warm it up good then do as Troll and you all are saying...adjust idle to see if that helps. On warm days I do get some decel popping Chief but figured that's not too bad as I get it on my Yamaha as well and the pipes on it have the baffles drilled out. I will have to look into what something like the PCIII or the cobra box do.

[chief]

The ECU is limited in how much it can compensate for modifications of the exhaust and intake.

In the real world pipes make a difference. Different pipes different problems. With most Drifters simply replacing the pipes or the air box will not change things enough to require an additional FI box, like the PCIII or Cobra. BUT, with my pipes I needed the Cobra to stop decel popping etc.  I also had to adjust the fast idle. 

If you change out the pipes and the air box 99% of the time a FI addon will be needed.

Could be as simple as some previous owner tinkered with the fast idle and its only now a problem because of the pipe change. Also don't know what other mods have been made to the bike.

[Bucko]

I don't get the possible lean condition when a better flowing exhaust is added.  The ideal fuel mixture calculation performed by the ECU takes into account the intake pressure (as well and ambient pressure).  If the exhaust makes the system flow better - that would imply a lower nominal pressure at the intake but the ECU should automatically compensate for the lower pressure the same way the system compensates when one drives up a mountain into lower ambient pressure (even more so since the difference between ambient and intake is even greater if there is an increased flow due to an exhaust change).  What am I missing?

In theory this should apply to a better flowing intake as well unless the change is so great it's outside the ability of the system to make the required compensation.

[chief]

What troll said... the fast idle knob... adjust after the bike is warmed up. And, what PC said... I've had that happen a time or two.

Also check and be sure you don't have the "choke" pulled out. (I know its not really a choke!).

[Troll]

By changing the exhaust, you effectively leaned out the mixture a little bit. This will cause the idle to rise. The change in back pressure is the culprit. You will have to readjust the idle after the engine is completely warmed up. As an afterthought...you don't have the "choke" pulled out, do you? Mine idles low when it's cold since I removed the idle speed solenoids, but just fine after it warms up. No big deal. The idle must be set to 1,000 rpm +/- 50 rpm. That little black knob on the cable, down by the water pump is what you use.

[Bucko]

I used to have this problem on my old Honda.  The problems was that it was so cold blooded that when starting up from cold, the idle had to be turned up in order to keep it running (they're jetted very lean from the factory). Then, of course, once the engine warmed up, it idled to fast.  It was that way for years until a buddy clued me in that if I cranked open the idle jets a couple of turns over the factory spec, the cold idle would work much better - which it did and it's been working perfectly ever since.  Tweaking idle jets is not an option of course for the Drifter, but maybe your cold idle is set to high to compensate for a similar situation.  I've had some cold idle issues lately - still not entirely sure why but I have my suspicions (water temp sensor either faulty or corrosion on the connections to the sensor).

[pcarrell]

Sounds to me like maybe something is sticking open.  If you blip the throttle does it go back down?

[Driftaway]

Hi just joined VDR and loving the wealth of information. I have a 2001 1500 and I changed out the stock exhaust for the Vance and Hines and converted to the dual mod. It now starts the same. but after 30 minutes of riding it is idling to high. Not sure why it starts and idles the same but only after getting in some miles does it idle high. Any help you can offer this drifter loving newbie would be very appreciated.