A little direction on Carb Tuning

[Guest]

Hey Fellas,

I was getting some low-throttle bogging and mild popping, and I thought maybe I had a clogged jet under my mixture screw. A friend though it might be the switch to winter gas (an issue for bikes in AZ, not sure about elsewhere), so I was going to fiddle with my mixtures and realized that my air filter was filthy - it'd seen over a year of daily riding - maybe 12k miles.

So I cleaned and re-oiled it, and it seemed to help a little, but not much.

So this past weekend I warmed it up, pulled the tank, and set myself up to adjust my mixtures, but even after a 15 minute ride or so it still was having a hard time idling without some choke. I evened out the air screws to three turns each (maybe a mistake, I know) and I started moving #1 air screw and it had no effect. So, I dialed it all the way in - still no effect. Checked the others - #4 was the only one that seemed to change the idle speed at all, and I was getting smoke from the left-side pipe.

I thought it might be clogged under the air screw (a problem in the past) so I took out #1 and #2 screws and made sure that passage was clear. When I put them back the smoke was gone, but I can't get it idle off choke without dialing the idle up to about 1800rpm. I pulled the #1 and #2 plugs and they had whitish straps with wetness at the base of the threads.

So now I can get it to run without choke, but not below 1800 rpm. It also "hangs" when I goose the throttle, taking 3-5 seconds to return to 1800 rpm after I release the throttle.

I've got some time over the holidays, can you guys suggest where to start based on these symptoms. I don't have access to syncing equipment at the moment, so I'll avoid disassembling the rack if I can. I adjusted the valves about 10k miles ago, but not since.

Edit: I should mention that I did the GSR carb cleaning process to the letter (with all new o-rings) about 4 months ago, and had a mechanic buddy's help with the mixtures and vacuum sync. Also, I sealed my airbox and replaced carb boot o-rings and airbox boots about a year ago. The carb boots are original.

[Mark Harrop]

Sometimes carb problems are really ignition problems in disguise...

Id check to make sure you are jumping a nice fat spark off of each plug...

Then proceed with carb tuning...

[Roostabunny]

Cool deal - I'll check that.

Need a fully charged battery to make a good test on that, right? Cause mine isn't at the moment - from all the cranking trying to start it.

J

[BassCliff]

Hi Mr. Roostabunny,

I just wanted to remind you that the factory manual recommends checking the valve clearances every 4k miles. It couldn't hurt.


Thank you for your indulgence,

BassCliff

[chiphead]

It might be worth taking some WD40 or Brakekleen and while holding it at as steady an idle as you can, carefully spray each intake boot and sealing surface where it meets the head. Any fluctuation indicates an intake air leak.
Have the carbs been apart and throughly cleaned recently?
Food for thought.

[Nessism]

The hanging idle is a sign that the mixture is overly lean. You mention "air screw" in your post a few times but that screw is actually a Pilot screw and opening it up allows more fuel/air mixture to enter the engine at idle. Try setting these screws to roughly 2.5 turns from lightly seated and see how the bike runs. If the idle is still hanging try another 1/2 turn and tune for the highest idle. Based on the amount of mileage you have put on the bike I doubt you have gummed up carbs, but if you have rust in the tank some contamination particules could be fouling your pilot jets.

Hope this helps and good luck.

[first timer]

i would replace the intake boots, the rubber tends to shrink and seperate from the metal which allows air to pass through and runs the bike lean. Try spraying the boots with some carb or brake cleaner and see if the idle picks up.

[dwfranke1]

i had the same symptoms you are describing and it turned out to be to lean and clogged 2 clogged pilot jets, but i was switching back from 29 smooth bores to vm26 stock carbs with pod filters and open megaphone exhuast, ended up with #15 pilot jets, 120 mains and 2 and 1/14 turns out on the screws before i richened it up enough that the plugs would show any color, also i started with a dead battery, so do make sure the battery is charged,
good luck

[kokopelli]

goin thru similar problems with my new project... takin a break from the work right now actually lol
so far i found that the carbs were the filthiest i've ever seen, lucky me had some jets and things from the rebuild on my other 650 with identical carbs/jets
also, i've been playing with the air pilot quit a bit yesterday and today fluxuatin between 1 1/2-2 1/2 turns out thinkin it was the mix... didn't do much good but it's sittin at 2 1/2 out right now. still couldn't get it runnin right this mornin so had a brain fart about 30 mins ago to pull the dirty filter and see how it ran with out it... 2 1/2 turns w/o filter the bike is a beast!!! just gettin back from the test ride (they can take some time if they're fun) my only conclusion is the filter is too old and too dirty, doubt cleanin it would be any good either (did i mention this is also an old piece from my other 650 i still had laying around?) so i think it's just to restricting and i'm gonna have to break down a buy one... have you tried pullin the filter and seein how it runs w/o it? might beworth it, i could of saved alot of aggravation last couple days if i'ld of thought about the filter restricting air flow.
sorry for the long post but sounds like you're goin thru the same thing i am at the moment and since you mentioned the dirty filter and it doin little good cleanin just thought i'ld share my story and what i've found to be the colprets. hope this helps

also, i found that when i had the air pilots out too far if i would turn any one in till it seated it had little to no effect. however if i left one seated and began turnin in a second one it would start having effect almost immidiatly.i can only assume this is because the other carbs where set so far out it was gettin way too much to the other cylinders to slow it down.

[Roostabunny]

Update

OK, based on advice so far, I found an excuse to buy a battery charger and finally pick up a feeler gauge (to check those valves, per Basscliff's advice).

I mentioned my white plugs and hanging idle to a classic car tuning friend and like Nessism and Chiphead, he suggested an air leak.

I rebuilt the carbs about 5000 miles ago and ride daily, so I agree I could get a rust speck, but not gummy carbs.

So, I decided to check the air leak first. Once I got it warmed up there was a definite response to carb cleaner sprayed around #1 and especially #3 and #4 carb boots.

I replaced my airbox boots and carb boot o-rings a while back (good heat-resistant O-rings from Robert Barr), but the carb boots are original. I'll check the sync ports and the connections - if those check out - is there was way to isolate and test the boots for leaks? I'm pretty sure boot repair is out of the question, but is there a way to patch them for a week or two while parts ship if it comes to that?

Thanks fellas!

[Steve]

I'm pretty sure boot repair is out of the question, but is there a way to patch them for a week or two while parts ship if it comes to that?

If you can put up with it running the way it is, you will be better off. Just about anything you are likely to use to seal a leak will be dissolved by the gas mixture, so it would be better to not introduce any foreign material.

.

[mike-s]

id be careful running it "as is", i managed to melt a hole in a piston once from a very similar airleak, so riding the bike and not taking care of the leak is probably a bad idea (took less than 160km/100miles to burn the hole in it too).

Perhaps some flexible silicone could hold out "for the time being" especially if you really needed the bike. If you didnt and just wanted to ride the thing i would just hold off until the boots arrived and go with the new ones and leave it at that.

[Nessism]

There was someone here that speared their carb boots with liquid rubber or something similar and managed to get some good mileage out of the repair. I'd do something like this rather than run the engine with an air leak while waiting for the parts to arrive.

[Roostabunny]

Thanks, fellas, some good options here.

Any trouble-shooting/isolation tricks for the boots themselves? Anyone ever found pinholes in yours, and if so, how'd you find 'em? I don't want to risk burnt cylinders or valves, but I'm also not keen on spending the $120 on boots if I can help it right now, so I'd like to be as sure as I can be before I replace them.

Current plan...

1.) Visually inspect the boots in detail and also check the sync ports, hose clamps, and boot-to-head bolts for looseness.
2.) If I don't find anything to snug up, I'll pull the boots to check the o-rings and make closer inspection of the rubber.

Anyone had an experience of developing an air leak on a daily (or frequently) ridden bike?

Also, trouble-shooting-wise, do my "spray-the-boot" test results eliminate my air filter/air box as a potential culprit for now? I weatherstripped the airbox a year ago, but still concerned I might have under-oiled the filter when I cleaned it trying to solve the current issue. The filter clean/re-oil didn't seem to effect the bike's running much at the time.

Thanks!

[Bones]

I had the same problem with my 650E. After I cleaned the carbs (and dipped them) it ran good for a while and then I started having problems with the idle. I finally removed the carbs again and found "rust dust" in the pilot jets. (mostly in #2 and #3)
Since you have the time, I would give the carbs another cleaning and check for rust. If you find any rust dust, I would either get some POR-15, or take the tank to the radiator shop for cleaning.(that's what I did)

I hope this helps.

Bones