Topic: What does it mean when the air screws have little to no effect?

[Scott S]

 What does it mean? What is it a sign of when turning the air screws a turn or more in and out base baseline doesn't seem to effect the idle?

[flybox1]

you're either too lean or too rich.  pilot jet needs to be changed.
I find its easier to use the spark plug insulator color as an indicator of where your mixture screw should be set for each carb.
you will have visual confirmation the mixture is (near) correct.
listening for just one cylinder out of all four while under a fan just adds too many variables....

[Scott S]

 And it's acting rich. It feels like it's loading up at part throttle and, especially,  when coming to a stop.

 But everything is stock.....exhaust,  air box, jets, etc. So frustrating.

[flybox1]

acting rich or IS rich?
what do your plugs tell you/us?
pic pls.

if everything is stock (note your mixture screw setting), put in a new set of plugs, let it idle under a fan for 5-7 minutes.
pull them and have a look.

[oldhatt45]

Scott S

When was the last time the Carbs were Cleaned?  Serviced?
What was done to them?

Charlie

[Deltarider]

First: what bike?
Second: what means 'no effect'? Do you mean RPM?
Third: what means 'turning the air screws a turn or more in and out'? All four at the same time?
It's not uncommon to have no effect in RPM within a turn.
The CB500 and CB550 must have a rich idle (K3 excepted) to facilitate good throttle response accelerating. Don't be tempted to tune the airscrews for the highest rpm at idle. You'll have an engine that purs like a kitten but... you'll have a rotten acceleration.

[PeWe]

Flooding floats? This will cause very rich idle and pitch black plugs.
(I have  some not much used plugs that all are very sooty since my carb exercises with flooding floats)

[Scott S]

 This is the 550 I've been asking about in this thread:

http://forums.sohc4.net/index.php/topic,149599.0.html

 It's definitely rich, especially off idle and at lower throttle openings. The plugs were as black and fuzzy as a velvet Elvis painting. Put in four new NGK D7EA's and within 5 miles they look the same.

 It seems to load up and bog when coming to a stop. I have to feather it and clear it out.

 The carbs have been cleaned THOROUGHLY....and I've inspected them many, many times. I would bet you the title of the bike that they're clean. Genuine Keihin mains (100) and genuine Keihin pilots (38).

 I pulled out the UNI air filter and it runs much, much better. Almost as it should. No more bogging/stalling when coming to a stop, no more lugging under load at part throttle. I even tried a stock Honda paper filter and it was even worse. Runs best with open air box....no filter.

Since I had a problem on my 550F with an upside down main, I just pulled the bowl on #4 to double check that. It was in correctly. I think I remember checking the one on #1 when I was messing with that carb...and all 4 cylinders are acting the same now...rich.

 My next thought is to verify the needle clip position and maybe even go ahead and lower the needle. I'm running out of other things to try.

 (cross posting this to that other thread, too)

[Scott S]

 Oh...and I've verified fuel valve operation and fuel valve level (clear tube method) as well as float height.

[flybox1]

UNI filter?
i thought you said it was stock?  

still no mention of what your mixture screws are set at 

...but turn your mixture screws LEANER by one full turn with the HONDA filter, and report back.
sooty plugs wont help the situation, so new ones or REALLY clean used ones are preferable.

[Scott S]

 These plugs were new, 5 miles ago.

 UNI foam filter in stock air box.

 I've tried everything from 1 1/4 turns to 3 turns on the mixture screws. Currently, they're back at the stock baseline: 1.5 turns.

[Scott S]

 If I've been through this thing from stem to stern and tried multiple jets, coils, cleanings, plugs, etc., etc., etc., what would it hurt to lower the needle one clip from stock? If that's what the bike needs?

 Give the bike what it wants, right?

[oldhatt45]

Scott S,

From your replies:
"Pulling out UNI filter it runs much, much better"
And "With the stock air filter it runs much worse"
And the Plugs look Fuzzy and Black.

All these say to me is that the carbs are running RICH.  Apparently too Rich.
Have you done any plug chops?  At Idle?  At WOT?
It may be that the Idle mix is way too Rich and the WOT mix is OK.
If that is the case then leaning out the Idle mix or possibly a smaller Idle jet would be a place I think I would look.

Just guessing here, but these carbs are (from what the experts say   ) are not all that complicated.  LOL
There are (if memory serves me) 4 zones
And maybe one of the experts can give us the info but there is a direct relationship in each zone as to what part of the carb to start looking at when faced with a problem.

Sorry I can't be of anymore help than this.

Charlie

[Scott S]

 Today, I pulled the needles...and I don't give a damn what anyone says, you can't get the inner two on the bike....

 Confirmed that they are the correct needles and the clip was in the correct groove, 2nd from bottom.

 I moved it to the 3rd/middle groove. While I had the carbs on the bench, I backed out the idle screw all the way and lowered all four slides until they bottomed out. Then I went in on the idle screw enough to bench sync them with a drill bit.

 Reinstalled, warmed her up, and put on the vacuum gauges. Made small adjustments to #3 and #4.

 Took a short test ride and played with the idle mixture screws a bit. Ended up at 2 1/8 turns out. The stock specs are 1 1/2 turns, +/- 1/2 a turn, so I'm only an 1/8th of a turn past "specs".

 I cleaned the plugs (only about 15 miles on new plugs) and adjusted the throttle cable to take out some slop, and I think I have it! I haven't done another plug chop yet. I want to really get it hot and put a few miles on it first. There's maybe the teeniest, tiniest burble or chug going down the road. For all I know, it's just what the stock 4-4 exhaust sounds like and is so faint that I probably wouldn't hear it with my helmet on. (Yes, I rode without a helmet around my neighborhood. I know...bad, bad idea).
  And when coming to a near stop... a rolling stop, if you will.... there's a very slight feeling of lugging. It's not really something I hear so much as a very, very slight feeling of "not quite 100% crisp".

 If I had put this bike back on the road and didn't have the issues that I did, NONE of what I'm describing now would even be enough to mention. I think maybe I'm LOOKING for issues now. If this thing isn't 100%, it's in the very high 90-something percentile.
 Nice and crisp when rolling onto it going down the road. Nice steady idle at an indicated ~1100-1150 RPM. All four pipes are within 5 degrees of each other.

 At this point, I'm ready to start racking up some miles on it!

[flybox1]

Just be sure you havent over-lean'd mid throttle range by dropping.your needle.  Most of us spend the most time in this range.   It would suck to hole a piston by running too hot.
Be sure and do a good chop to verify. 

[HondaMan]

I pulled out the UNI air filter and it runs much, much better. Almost as it should. No more bogging/stalling when coming to a stop, no more lugging under load at part throttle. I even tried a stock Honda paper filter and it was even worse. Runs best with open air box....no filter.

There it is...
I just fixed 2 such 550 bikes here in Colorado this last year, same setup. One of them was sold to the new owner because the old owner got tired of fouled sparkplugs and parked it 5 years ago. The problems were identical on both bikes. To fix them:

1. Threw away the foam UNI filter, installed a single "pod" type filter with a flat steel faceplate on one bike, and got a stock paper filter on the other.
2. Installed new O-rings in the castings that hold the carb hoses to the head. They were as hard as plastic, and leaked vacuum a lot.

Both bikes immediately ran like they should, still do...

[78whiteorbs]

I went through the carbs and ignition countless times before I sold it to Scott.
Didn't think to try and move the needle clip from stock but had the same rich outcome he was having everytime I made a change . Glad to hear you got it sorted. It was one of the strongest fastest running 550's I have owned/rode. Well done and don't forget to report back with some plug chops.

Fwiw HondaMan also suggested I replace those o-rings  8n the manifolds and I (like a true idiot) never did. I lightly smeared them with sealsall think8ng if it was an induction leak then that'd tell me quick enough to buy some proper size orings. It never changed but zi am think8ng I would definately change those now Scott. Especially  after reading the above post.

[Scott S]

 I changed the O-rings at the manifold...replaced them with new. I tried running a stock, genuine Honda paper filter and it ran even worse.

 I thought I had it figured out, but it's still rich down low. I'm thinking about trying some 35 pilot jets now.

 This thing is frustrating. I've been through all the normal stuff two or three times and just don't see why it's acting like this. It DOES run very strong, especially mid range and up top. It just loads up down low.
 It's rideable now, but still rich on the bottom end.

[Scott S]

Just be sure you havent over-lean'd mid throttle range by dropping.your needle.  Most of us spend the most time in this range.   It would suck to hole a piston by running too hot.
Be sure and do a good chop to verify. 

 Will do. But I'm pretty sure it's running rich enough to not have to worry about that!

 Some more questions/observations:

* One of the mains was aftermarket. My carb guy SHOWED me that it was smaller than the stock Keihin jets by using a drill bit shank. Now.....while this bike is stock, anything is possible. I didn't ask what SIZE bit he was using. I guess someone *could* have drilled out the main jets.
 But would that cause low RPM/low range richness? Does it have an overall effect, like needles do?

*Harisuluv has suggested that new needles and emulsion tubes might fix it. I can't guarantee that the needles and tubes have been kept as a matched set. Needles/tubes are out there, but can be expensive and might take time to get four.

*If it responded to leaning it out by removing the air box.....and responded to leaning it out by moving the clips...but I'm still rich on the pilot jet circuit, what's wrong with changing to a 35 pilot jet? I am starting to see some response on the air screws now that I've changed the clips, but it's still mild. That, the riding experience, and the plugs still indicate a rich condition from idle to part throttle.

[bender01]

2. Installed new O-rings in the castings that hold the carb hoses to the head. They were as hard as plastic, and leaked vacuum a lot.
I cant wait to try this on my 10k mile 550f! She sat a lot over the years. Ive sprayed wd around but not there. Ive had hanging idle issues for two years and 3 carb cleanings.
 Thanks

[riverfever]

Scott you can get those needles on the inner two carbs out while on the bike. If I can do it...it can be done. I used a short Phillips bit that would go in a drill or multi-head screwdriver. Very short. The I used a 7 or 8mm wrench to turn it while I pushed it down with the tip of a finger from the other hand. I hate pulling those carbs.

My bike had a UNI filter in it when I bought it. I stole Desert Dans idea and found a FRAM air filter that would fit in the stock box and cut it up to get it how I wanted. So much better than that stupid UNI.

[jonda500]

Scott you can get those needles on the inner two carbs out while on the bike. If I can do it...it can be done. I used a short Phillips bit that would go in a drill or multi-head screwdriver. Very short. The I used a 7 or 8mm wrench to turn it while I pushed it down with the tip of a finger from the other hand. I hate pulling those carbs.

+1  That's exactly how I do it! - I also hate pulling the carbs, but I have to do it to put my new #35 pilots in as I have found no other way to undo the little float bowl screws?
John

[turboed13b]

This isn't directed to Scott as I think he is on the right track but for other posters. If you have a hanging idle check your idle screw. The manual calls for a 1000rpm idle you might get lucky and it doesn't happen but bumping the idle past 1000rpm will give you a hanging idle. I can't count how many times someone has called me with a hanging idle and I ask them if they messed with the idle screw. 99.9% of the time people adjust it too high because they are too lazy to wait until the bike warms up or their bike is not properly tuned to idle correctly.

If the bike does not idle at 1000rpm then there is something wrong most of the time it is due do a rich condition. A lean idling bike will sit at 1000 all day long.

[lrutt]

So you say the jets are stock size. I assume this is because you are reading the size that is stamped on the jet. Did you actually verify this wtih a pin gauge?

I had a bike I bought that would not run for #$%*. PO said he had gone through the carbs many times, checked timing. all parts new. So I did check timing then tore into the carbs. The pilot jets were marked stock size but in looking at them the holes were as big as the main jets. Some asshat had hogged them out some how.

New pilots and the bike ran like a champ.

If you do get new low speed jets, get good Kehien jets from jetsrus or some such. Don't get some cheap KL kits with new jets.

Your needles won't be helping with what you are describing IMO. if you can adjust the screws and get no change, the needles have NOTHING to do with that.

[HondaMan]

So you say the jets are stock size. I assume this is because you are reading the size that is stamped on the jet. Did you actually verify this wtih a pin gauge?

I had a bike I bought that would not run for #$%*. PO said he had gone through the carbs many times, checked timing. all parts new. So I did check timing then tore into the carbs. The pilot jets were marked stock size but in looking at them the holes were as big as the main jets. Some asshat had hogged them out some how.

New pilots and the bike ran like a champ.

If you do get new low speed jets, get good Kehien jets from jetsrus or some such. Don't get some cheap KL kits with new jets.

Your needles won't be helping with what you are describing IMO. if you can adjust the screws and get no change, the needles have NOTHING to do with that.

I wish I had $1 for every SOHC4 carb I have fixed like this, by replacing the jets with Keihin jets. The "jet size" numbers were the same, but the holes were something else.

Back "in the day" we sometimes got the Yamaha Mikuni jets mixed into our jet stock for the Keihin carbs. Their numbers were similar, but they were different sized holes, and the tapers to feed those holes were a different angle. I suspect there is something like this afoot in our "parts supply" today, much like the "Head Puck Seal" debacle we suffered starting in 2009, where similar-looking pucks from 1990s bikes were subbed into Vesrah (and other) gasket kits for the SOHC4. The result was many, many, many leaking, oily, messy engines after a rebuild (all through our threads!).