Another idle creep question but different

My question is: how does a electric load, lower rpms only in a certain circumstance? ie: hot.
no issues otherwise.
This is just a curiosity, just a small inconvenience.
85 700n
When engine gets hot, meaning after about a hour of riding, not hot hot, the idle will creep to 2000 at a stoplight. If I pull/hold the brake lever/pedal the electrical load will drop back rpm to 1250 [norm]
checked for obvious vac leaks with unlit map gas at warm idle.
removed rack and eyeballed carbs for anything that could air leak.
checked wet set.
carefully installed rack into checked for cracks intakes.
vacuum synced, after checking carb vac port caps.
new vacuum line to petcock.
new throttle shaft seals, fuel o rings and pilot o rings -2/19

 

When I set my idle at 1250 rpm on my XJ550, mine tends to creep up about 100-200 rpm after a hard run like you describe. Creeping to 2k seems excessive. I will let someone more knowledgeable weigh in on your particular problem.

 

putting a load on electrical system makes the alternator drag as it puts out voltage . that is one reason to go led bulbs with out load resistors less amperage draw increases milage and power just a bit.
but unless you have a big wattage bulb on your brake light it should not do what you discribe.
I think you need to look at your charging system and battery. could be your not charging well and the brake light is a big load on a low out put from alternator.
if alt is not working properly your rpms could climb due to no drag from the alternator.
possibly the brake switch too it may be all carboned up (burnt) causing more amps to be drawn throug the resistance of the contacts

do you have an led headlight?

 

Next time the idol's creeping up instead of stepping on the brake pedal turn on the high beams see if you get the same result. That would be an indicator that it is in the break switch circuit if you do not get the same results of the idle dropping when you flip on the high beams

 

Since the tach and brake share the common voltage source - flasher fuse - I would check the output of the fuse with a DMM when you are noticing the above.

Or, a simpler but not quite as accurate approach would be to look at the neutral light with the brake applied and see how badly it dims - a little is normal but this might be a lot. And, one more option is how do the horns work when hot like above and both the brake and horn applied.

It could be your RPM's are really increasing as the bike warms and that it either needs some maintenance or a simple idle adjustment at full operating temp.

 

update. before it was a curiosity, now the creep goes to 3000 after 20 min. operating .
I have a vacume leak. - same behavior as before replacing T.S.seals.
gonna break carbs apart again to check condition and reapply silicone grease.
all electrical works as it should. 13.4 v after aprox 2500rpm as it should. only difference I have 25w instead of 27w blinker bulbs.
being as we all don't know each of each other's mechanical skills, - I'm a wrench head, this bike is fairly simple for me.
I thank everyone who replied.

 

check clamps for proper instalation and are tight on carb to manifold boots.
could also be a leak at the manifold boots to head. both would show up after motor is warmed up

and are the nipple caps supple and clamped

I always check the simple stuff first. your going to undo the clamps anyways

as far as voltage goes 13.4 is a little low
For all XJ-series models, the maximum available charging output VOLTAGE should be as follows (all values are approximate):

* approximately 500-2000 rpms: 1.8 volts gradually increasing to 14.2 volts
* 2000+ rpms: 14.2 volts up to about 14.8 volts, with a maximum of 14.8 volts

 

I had a torn gasket between one of the intakes and the head. Check those carefully. The fact that it seems to happen after the engine gets hot would seem to indicate expansion as the engine gets hot. Try looking for the leak after the engine is hot and the rpm is creeping up.

 

xj550H
My bad, I posted idle v's - a senior moment.
tabaka-45
That's what I was thinking, when I checked with map gas [unlit] it was right after startup warm up.

 

Any progress??

I have an 85 XJ700N that does the same thing - once it gets good and warm the idle really goes up.

In my case, I am going to send the carb rack to @hogfiddles for some TLC later this year - I'm guessing the throttle shaft seals are garbage. I figure while the rack is off I will also replace the intake manifold gaskets and the vacuum port plugs, just to sure.

If you learn anything different I would love to know about it!

 

Give the mixture screws a half turn out - all the same, just to see what it does? Let us all know - promise?
Thanks

 

Well...
This ignores mixture requirements for fastest idle wrt engine temps. If you think about it, there are almost too many issues at play here together to make sense of it.
Engine oil temp increase - less drag
Ditto - more /increased clearances - less drag
Valve clearances reducing - changes to trapping volumes
Ideal mixture for fastest/best idle - varies with engine temps
Leakage - seals, gaskets etc
Contaminated oil - adds fuel vapour to inlet air mix
Vacuum balance changes due to heating of carbs - mixture variation mixture
All of the above can cause a change in idle speed...

Maybe there are more - I doubt its simple, and synching four independant carbs without a common idle mixture control is just 80's nuts, but they had no choice.

 

I've been procrastinating, I had thought this post had run it's course. I suspect manifold gaskets. and if so, dreading removal on manifold stud/bolts. I know what can go wrong and the headache repair.
minimutly
I originally set a/f at 2.5, then 2.75, then 3. it seems to like 3.
I have a bunsun colortune, but don't bother with it. I get blue from 2-4 turns out. always starts easy without enrich.
"Contaminated oil - adds fuel vapour to inlet air mix"
my crankcase vent hose is disconnected from the air box.
700 paper air filter, not taking chances.
I change oil about every 1000mi, cause it make me feel good.[shell rotella t4]. the valves are in spec. checked when I popped the rack recently. now I always check wet set every time rack is off, and vac/sync. in my origin post, I was curious about e.load it affected rpms whilst hot, "warm" it did not.
when motivated, I'm like a dog with a bone. I will find this leak and kill it.

 

i can't see one cylinder with a vacuum leak dragging the other three up that much. if one cylinder is running that lean, the plug would show it.
are you sure it's running on all 4 when the idle is low

 

polock
hmmm you have a point. the bike basically runs perfect. I'm familiar with how it runs lean, previously corrected by bumping a/f and a wet set.
duh, I didn't think to check plugs- thanks. could it be the yics actually works?