Idle Air screw and RPM method for setting

[shawzygs850]

Trying to reset air screws after a thorough cleaning and need some help...

Couple questions:

1) How much does rpm change when using the "set rpm to 1k and adjust slowly until max rpm reached" method? Turning the idle air screw doesn't seem to have any effect on rpm - how subtle is the change?

2) Plugs show a lean condition and there is popping on decelaration from high rpm (7k) as well as popping during full choke at idle - improves a bit once warm. I therefore believe I need to richen the idle, can someone confirm I need to turn the air screw INWARDS (thereby reducing amount of air in idle circuit) - or do I have this backwards?

 

[Dave8338]

You are correct with turning the screws in, and as far as a huge change in the RPM's, once you reach the max as far as leaning out the mixture, you will notice no increase in the RPM's. Also, make sure that you have plenty of air circulating past the engine while you are doing the set, if not, your mixture setting will be to lean for the " normal" opperating conditions. I use a large squirrel cage fan, however, a couple of 24" box fans will do the trick. Start with a setting of 1.5 turns out and adjust from there. I think mine are set slightly leaner than that---1.7 out.

Hope this helps.

 

[gerwintown]

i actually have the same problem as question #1, and if the OP doesnt mind, id like to add quickly: i can get a consistent idle everywhere but where its supposed to be (1200ish), and it changes constantly with the increased warming of the engine. how this relates is that when im trying to do the procedure asked about it in #1, the engine rpm changes on its own or dies.
also, how is this accurately done with 4 carbs....?

wish i could help shawzygs850, and sorry if i hijacked your thread

 

[Steve]

1) How much does rpm change when using the "set rpm to 1k and adjust slowly until max rpm reached" method?

That sorta depends on how far off they are. Might be as little as 50 or as much as 200 rpm. I like to go through and set each carb, then go through and do them again. Don't forget to reset the idle back to 1100 or so after each carb setting.

2) Plugs show a lean condition and there is popping on decelaration from high rpm (7k) as well as popping during full choke at idle - improves a bit once warm. I therefore believe I need to richen the idle, can someone confirm I need to turn the air screw INWARDS (thereby reducing amount of air in idle circuit) - or do I have this backwards?

I think you have it backward. Assuming you are talking about the idle mixture screws on top of the throats on the engine side of the carbs, in is leaner, out is richer. Start with them about 2 turns out and adjust from there.


.

 

[Dave8338]

I think you have it backward. Assuming you are talking about the idle mixture screws on top of the throats on the engine side of the carbs, in is leaner, out is richer. Start with them about 2 turns out and adjust from there.


.

Wow...now you have me thinking...in, sets the tapered tip deeper in the carb body. Why am I rembering this as a metering rod for air and not fuel? It's been a long week, Am I messed in the head (as far as this issue anyway)? :? Wouldn't be the first time, that's for sure.

 

[shawzygs850]

OK - so the air screw meters FUEL and not AIR so I was backwards.

Screw In = lean, Screw Out = rich

Thanks I will turn out 2 turns and give 'er a go. Dave8338 I don't have any fans avail so I will have to do without.

I have found that I can leave fuel tank on and get to the screws if I undo rear bolts and prop it up with one hand whilst tweaking air screw with the other.

 

[KEITH KRAUSE]

OK - so the air screw meters FUEL and not AIR so I was backwards.

Screw In = lean, Screw Out = rich

Correct name for your CV carb screws is pilot fuel screw or mixture screw.
It meters a mix of fuel AND air. It assists the pilot jet and allows you to fine tune for each cylinder.
By increasing the mixture flow, you're richening it.

 

[amartina75]

if your plugs show a lean condition, you need to determine if it is lean at idle or lean in main circut. there are many factors that could cause you to be running lean, adjusting your pilot mixture screws may not solve any of your problems.

 

[General Zod]

I am constantly adjusting my idle screw when I ride. It never stays at 1200rpm.......

theres a bit of pop on deceleration also.

but I hate having to mess with the idle ......it never stays put.

so I adjust the air screw 1 1/4 out (from bottom out), then I adjust it another 1 or 1 1/4 turns out and set the idle.....

well...I still have the same problem when engine is running warm. the idle keeps going 1500+...

when I set it down to 1200 hot,....it wants to croak.


so, I am going to repleace the o-rings in the intake boot and pray that this is the answer on top of having the carbs synched........

but then again.....what the hell do I know?

if your plugs show a lean condition, you need to determine if it is lean at idle or lean in main circut. there are many factors that could cause you to be running lean, adjusting your pilot mixture screws may not solve any of your problems.

 

[shawzygs850]

After fiddling with this for over a month I am ready to call it quits.

While trying to eliminate the 'popping' on deceleration in (2nd and 1st only it seems) I continued to richen the idle circuit on those cylinders that looked lean based on the 'plug chop at idle' test. Each time I would turn 1/4 turn out, perhaps this is too much.

Seems like I just can't find the correct balance, now she bogs down and is too rich, fouling the plugs and causing stumbles when reving to 6k. If I lean out again, she pops.

Driving me bonkers, now seems like guess work.

At one time she was so smooth...

My questions:
- The engine rpm does not change when adjusting pilot screw, no matter how many turns I make on any carb; 1/8 turn or 1 turn out rpm is same; what does this imply?

- If I start again with screws 1 1/4 turns out, what is the max-min range screw should fall into? i.e. 1 1/4 - 2 1/2 ? by how much should I turn each screw when attempting to find the 'sweet' spot?

- Do I have another issue at hand aside from idle mixture that could cause some popping on decel

- Should I simply take the machine to a wrench and have them set idle mixture and sync carbs before loosing any more hair; I see this as giving up which kills me but I need to know when to throw in the towel, I feel like I am wasting my time at this point with fiddle here, fiddle there, and no tangible result.


Cheers

 

[pvtschultz]

Before you pull your hair out, have you checked (replaced would be the operative word here) the intake manifold o-rings? Popping on decel isn't bad, but would be a good indication that you have a vacuum leak since this is when you have the most vacuum. Also, check the boots, it might save you a few grey hairs by simply spending the $100 and getting new ones. Also, when was the last time the carbs were gone through? Might be time for a "spring cleaning" and new rubber parts in there as well.

How about a carb synch? If you are adjusting a "light" cylinder, you won't see a speed increase since it is already not doing anything at idle. Valve clearances? Same thing as bad carb synch.

There are a lot of things that affect how these bikes idle. When a problem pops up, sometimes the best thing for you to do is start at the begining and save yourself the hassles.

1. Replace old rubber (sometimes redundant...)
2. Check to see if air filter housing is sealed well.
3. Valve clearance check
4. Carb synch
5. Mixture screws

I'm sure I missed something, but 1-4 all affect how the engine responds to 5.

 

[shawzygs850]

Intake o-rings looked ok, but are likely old. Boots don't look bad either but I will look again. Carbs were just done, full strip and dip with all-new rubber for all. Perhaps pulling the carbs has cracked the old boots just enough to cause issues. Would hate to replace only to have problem still around.

Valve clearences a-ok. Carbs not synched.

I will do the ol' wd40 trick on the boots and check for idle change

Your tips helpful thanks!

 

[bwringer]

Intake o-rings looked ok, but are likely old. Boots don't look bad either but I will look again. Carbs were just done, full strip and dip with all-new rubber for all. Perhaps pulling the carbs has cracked the old boots just enough to cause issues. Would hate to replace only to have problem still around.

Valve clearences a-ok. Carbs not synched.

I will do the ol' wd40 trick on the boots and check for idle change

Your tips helpful thanks!

If you reinstalled the old intake o-rings, I will guarantee that they are leaking now.

The WD-40 trick does not always work -- an air leak has to be very large for WD-40 or water to make a difference.

GS850s are famously touchy about their air supply:

1) Seal Airbox
Remove both the left and the right airbox covers and seal them with foam self-stick weatherstripping. They do fit tightly, but this isn't enough -- they MUST be sealed airtight.

2) Seal Air Filter
Replace the rotted scraps of foam on the top of the air filter cage with more weatherstripping (clean the metal thoroughly, obviously). Put some grease on the top of the foam so it'll slide into the airbox when you replace it.

3) Correct amount of oil on air filter element
If you have a foam air filter element, replace it with a Uni filter element if it's deteriorated. DO NOT soak it with motor oil -- a three second spritz of air filter oil is all you need. If you've already soaked it, get as much oil as you can out of it with paper towels, then wash it thoroughly with warm water and lots of dish soap. Dry it with compressed air or let it sit overnight -- it must be absolutely dry before installation. The slight film of oil left after washing is all you need. You can also install a new filter without any oil.

If you have a K&N filter, get a K&N cleaning kit and follow the instructions to clean and re-oil it. Be careful to only use the correct amounts of the correct oil and cleaner.

4) Carefully check the boots between the airbox and carbs. It's very common for one of the inner boots to curl up a bit and get caught behind one of the inner carbs instead of slipping over the mouth of the carb, and it's very hard to see this. Consider replacing these boots -- they're fairly inexpensive.

 

[KEITH KRAUSE]

shawzy, you said at one time "the bike was so smooth"...and I assume no other problems.
What has happened since then? What has been done? How long are we talking and did the bike sit mostly unused/unused during that time?
Is the intake and exhaust completely stock? Did you ever verify what jetting is in the carbs? Any other symptoms? High idle once warmed up?

 

[Nessism]

3) Correct amount of oil on air filter element
If you have a foam air filter element, replace it with a Uni filter element if it's deteriorated. DO NOT soak it with motor oil -- a three second spritz of air filter oil is all you need. If you've already soaked it, get as much oil as you can out of it with paper towels, then wash it thoroughly with warm water and lots of dish soap. Dry it with compressed air or let it sit overnight -- it must be absolutely dry before installation. The slight film of oil left after washing is all you need. You can also install a new filter without any oil.

Bwringer is a VERY helpful and experienced guy but I disagree with him regarding oiling the air filter. Suzuki puts oil on the filter. Purchase a new one and you will get a full dose of the stuff on your hands when you take it out of the package. The factory service manual calls for oil on the filter as well - they just warn against wringing it out by twisting.

Washing the filter and reinstalling dry does not leave anywhere near as much oil on the filter as Suzuki applied when the bike was new and not as much as a service replacement filter.

I recommend oiling the filter using spray oil, such as K&N brand, or motor oil. A small amount is all that is needed. Squeeze the filter in your hand to distribute the oil through out the foam followed by blotting with a paper towel. You want oil on the foam to catch the dirt but not too much.

Again, Brian is THE MAN and helps lots of people around here. Don't mean to step on toes. \\/

 

[Guest]

Carbs not synched.

You can't adjust an out of synch carb.

Set the mixture screws the same across the board. SYNCH THE CARBS. Do chop tests. Adjust accordingly. Synch the carbs again.

 

[bwringer]

Don't mean to step on toes. \\/

No offense taken! Opinions vary on this issue and many others. I think the common Uni filter elements may be more susceptible to over-oiling than the OEM elements. I've corrected over-oiled Uni filters a couple of times with excellent results, but I've never even seen an OEM filter element.

I've talked this over with Rob from CRC2, and basically he recommends installing Uni foam filter elements (at least on GS850s) with no oil or just a very light spritz of actual filter oil instead of motor oil. Even if you install the filter with no oil, it quickly becomes oily from the crankcase vapors.

Anyway, the original poster's problem is probably an air leak, since he's describing a lean condition -- an over-oiled air filter will cause a rich condition. I just mentioned air filter oiling to be complete.

I would suspect that the intake o-rings are leaking, and/or the airbox is not sealed. There may also be an exhaust leak.

As far as the idle screws, I'll confess that I've never, ever been able to discern the slightest difference in idle speed or quality while twiddling the screws individually with the bike idling. YMMV, of course -- maybe others can hear something I can't, but I've got a pretty good ear, and I can't tell any difference unless I turn them 1 or 2 turns.

Instead, I tune these by test riding to fine-tune the quality and smoothness of the off-idle transition and adjusting in 1/4 turn increments. The smoother the transition off idle, the sooner you can get back on the gas in a corner, and the smoother and faster you'll be.

And the smaller and smaller those pesky squids on CBRs and GSXRs get... :twisted:

But in order to fine-tune the idle mixture screws, everything else must be spot-on. In this case, I think the original poster has another problem casusing a lean condition that must be corrected first before he can dive into fine-tuning like this. For now, I'd set them all at 2 to 2.5 turns out and leave them there until the lean condition is handled and the carbs are synced. Mine are all set the same, and are somewhere around 2.5 turns out. (on CV carbs, in is leaner, out is richer).

Another often-neglected element of fine-tuning is float height -- I've found adjustments of 0.5 mm make a definite difference in the low-end and low midrange. Mine are set right at the minimum height noted in the manual.

 

[slugsride]

1. Replace old rubber (sometimes redundant...)
2. Check to see if air filter housing is sealed well.
3. Valve clearance check
4. Carb synch
5. Mixture screws

I'm sure I missed something, but 1-4 all affect how the engine responds to 5.[/quote]

Would like to add a step "3 1/2" ,compression check. If any are very low doing 4 & 5 may make things worse.

 

[shawzygs850]

shawzy, you said at one time "the bike was so smooth"...and I assume no other problems.
What has happened since then? What has been done? How long are we talking and did the bike sit mostly unused/unused during that time?
Is the intake and exhaust completely stock? Did you ever verify what jetting is in the carbs? Any other symptoms? High idle once warmed up?

Thanks so much to all for their feedback you guys rock. You provide the confidence I need to continue. I will replace rubber o-rings on the intake, hopefully I don't have to replace the entire boots themselves. I will also check air box sealing.

In answer to your questions Keith:

Background: the bike sat unused in a garage for about 12 months; before hitting the garage, I did not notice any drivability or running issues whatsoever (i.e. she ran and idled smooth, although granted she wasn't ridden frequently, say an hour a week). Once taken out of the garage and started the bike was in horrible running condition; after advice from this board I cleaned the carbs (remove, strip and dip); discovered air jets were quite dirty;

Once carbs cleaned and re-mounted, the bike started easily and ran wonderfully with the exception of popping symptoms as mentioned above; valve clearance checks out okay;

Bike is completely stock; jetting in carbs is also stock I assume (not sure how to tell)

I've been trying to adjust idle screws in vain if I have a vacuum leak as it buggers my plug reads no doubt. I have likely made things overly rich as a result.

I will follow slugsride steps above and post my findings.

Thanks again all!!

 

[slugsride]

I actually added the comp. check to "pvtschultz's" earlier post...must give proper credit.:-D

In my own nightmare, even though I probably fixed the root problem in the earlier steps, the damage had already been done (in my case carbon chips on the exhaust valve seats) and I had low compression on two cylinders.