Idle Speed after Running - too high

[Doug650L]

After cleaning carbs and running my 81 650GL on the road for 10 minutes, the idle speed (say while waiting at a stop sign) was way up to 3000, when it was at 1500 after being warmed up in my garage but before I road tested it. Is this a carb issue or something else?

[trippivot]

tune your carbs after a ride

#1 heat energy makes the engine more efficient at burning fuel.
#2 the spark plugs have come up to full temperature and self cleaned also making the engine require less fuel.

super common with stg.3 and pods have to turn up the idle screw when cold and turn it down when hot -it'll run best this way , means you are using least amount of gasoline totally

you can change it by going leaner on your pilot and making the choke/enrichener mandatory to start the engine- your bike will not run on it's own without the enrichener until full hot this way. also easy to foul plugs with this tune.

more than 1 way to tune your bike depends on how EPA compliant you want to be.

[tom203]

Same bike- the 83 or another? anyways in previous posts you said you put new o-rings at boot/head interface, how do your carb boots look,are they tightly clamped on carbs?

Try setting idle with idle stop screw after bike warms up- after road test. Then if it idles too low at next cold startup, try using a little "choke" to compensate. Mine needs a bit of choke for 5 minutes to wake carbs up.

[Doug650L]

Yes Tom - same bike. I forgot it was an 81. I'd rather run efficiently so I'll choke it a while longer until sufficiently warm. What is good idle RPM anyway - 1000-1500?

[850 Combat]

It can be a symptom of air leaks. If you are certain thatthe head boots and o rings are good, it wouldn't hurt to go looking at the airbox and carb to airbox boots.

[Dodik]

Are you carbs bench sync'ed or manometer sync'd after cleaning?
My guess would be you running a bit lean

[Steve]

What is good idle RPM anyway - 1000-1500?

Specs call for 1100 +/-100.

.

[Doug650L]

I put the carbs back just as they were and checked that the valves closed evenly and the pilot screw backed out 2-1/2 turns per the tutorial. The boots to the air box looked healthy but would consider replacing them if I had a source. The filter element was a dry foam piece wrapped around the element. Probably needs to be oil soaked, correct?

[Dodik]

Did you completely take them apart for cleaning or just open them up and sprayed some cleaner? Did you perform idle air/fuel mixture adjust afterwards?

[spyug]

I think 850 has it right. Probable leaking O-rings behind the intake boots. pretty common in my experience. I'd check those out.

[Nessism]

I put the carbs back just as they were and checked that the valves closed evenly and the pilot screw backed out 2-1/2 turns per the tutorial. The boots to the air box looked healthy but would consider replacing them if I had a source. The filter element was a dry foam piece wrapped around the element. Probably needs to be oil soaked, correct?

You can't diagnose running problems when the maintenance is not up to date.

Clean and oil the oil filter per the factory service manual direction

Vacuum sync the carbs

Make sure the carbs are not drawing false air from anywhere. New airbox boots are available anywhere OEM Suzuki parts are sold.

If all that fails, try opening the pilot screws to 3 turns and see if that helps.

Good luck

[Doug650L]

I had not done a vacuum sync and probably should. Can someone explain what it does, why it is important and what reasonable price to pay? Also, would I take just the carb assembly to the shop?

[tom203]

Remember that bench sync you did after you cleaned and reassembled carbs? It was close (hopefully) but now that carbs are on running bike, time to get the sync better by a vacuum sync. Idea here is to get all the carbs pulling their fair share of the engine load in the low range. You might have missed this link

http://www.bwringer.com/gs/carbsync.html

I'd either buy the gauge or borrow one. It's a good investment and much cheaper than paying some (potential) idiot to do it. Besides, you'll likely be doing it again on your next bike- or one of your friend's.

[Dodik]

I had not done a vacuum sync and probably should. Can someone explain what it does, why it is important and what reasonable price to pay? Also, would I take just the carb assembly to the shop?

Vacuum sync is important.

Basically every cylinder pulls slightly different amount of air this can be affected by valve clearances, rings, wear, build up and bunch of other things. Vacuum sync will more or less equalize that all four cylinders suck air at the same rate, and since with air comes fuel it is important.
bench sync only a ballpark to get the bike running.

it has to be done on the running bike, after that you set your idle mixture.

[Doug650L]

Thanks Tom for the link (I had not seen it before) and Dodik for the explanation. Aticipating a question as I read the instruction: Step 3 of the link says "adjust cylinder 3 to best idle". Is the Colourtune the device that he used to figure that out? What if I don't get one - how do I know best idle?