Need help from the 850 carb tuning gurus.

[Steve]

I have been working on a 1982 850GL off and on for most of the winter. Primary project was rebuilding the carbs.

I have installed complete kits, including jets, o-rings and gaskets. I think I have the float level set correctly, but would appreciate a definitive answer on what part of the float to measure from.

Also, now that it is running, there is some MAJOR lean surging between 3500 and 5000 rpm, using steady- to light- throttle. The carbs were dipped in Berryman Chem-Dip carb cleaner and all the passages were blown out with compressed air. Jets should be clean as they are all new. Diaphragms are good, no pinholes. Carbs are synced. Air pilot screws are at 1 1/2 turns CCW from lightly seated. The main jets are 115. There were two sizes of air jet that came with the kits. I replaced the jets with the same number, 180. The other choice was 190. I am running stock airbox (with a recently-cleaned foam filter) and stock pipes.

We are looking at taking a 4000 mile trip next month, and need to have it running a bit better. Any suggestions will be welcomed.

 

[bwringer]

Is the airbox sealed? It sounds exactly like too much air is getting in. 850s like a nicely sealed airbox.

There are foam seals in the chrome end caps on the airbox. If these seals are "perished", as the Brits say, then you'll need to get some self-stick foam weatherstrip tape and put a layer around the inside of the end caps. I can take a picture of one of mine if this doesn't make sense.

Another thing to check is to make sure the air filter is LIGHTLY oiled. It's easy to get a little too much oil on the foam and choke it off a bit. However, it does sound like you have the opposite problem.

If you've already taken care of this, then I would carefully investigate the boots between the airbox and the carbs. It's very easy to get one of these folded instead of over the carb.

And you've already taken care of your intake o-rings, right?
http://bwringer.com/gs/intakeorings.html

 

[Steve]

Thanks for the quick reply, bwringer.

I am reasonably certain that the airbox is sealed as I replaced the foam between the halves when I had it all apart. The foam on the ends appears to be OK.

Filter is LIGHTLY oiled with K&N Filter Oil.

I did not know about, and therefore did not check, the o-rings.

I forgot to mention in the original post, the bike starts very easily, with minimal choke. Let it warm up while putting on the helmet, it's now OK to remove choke. Putting through the gears in town, shift between 3000 and 3500, it pulls like a tractor, smooth and quiet. Stumble through the 4000-5500 range, then, when you hit 6000, it moves like...well, choose: scalded rabbit, greased lightning, the proverbial bat, etc. It is only the light-throttle setting between 3500 and 5000 rpm, which just happens to be 55-75 mph, or normal running.

I was wondering if maybe turning in the air bleed screws from 1 1/2 turns to maybe 1 turn would help?

 

[KEITH KRAUSE]

What are your floats shaped like? (To answer your float level measurement question.)
Because errors can be made regarding the sizing of jets in re-build kits, I recommend cleaning and re-installing the original air jets.
The "air bleed screw" as you say, is really called a mixture screw. Turning it out will richen the mixture by allowing more air/fuel mixture. On stock bikes, they're generally 1 1/2 to 2 turns out.
I'm not sure if your model has o-rings in the manifolds. If the o-rings, or the manifolds themselves are leaking air, the classic symptom is a bike that starts and idles at about 1,100 rpm's while cold/warming up, but as soon as the bike is completely warmed up/hot, the idle will be significantly higher. If it's leaking, sometimes you're lucky and the leak can be loose clamps.
Are your two floatbowl vent tubes clear and no kinks?

 

[Steve]

Keith,

The floats are plastic, oval, about 3/4" by 1", and 3/8" thick. When they are inverted to work on, there is an addition to the top corner (really the bottom corner) where the float attaches to the arm that goes to the pivot. There is a step almost 1/8" high from the oval to the mounting arm. Do I measure from the top of the flat or the top of the oval?

I was calling it an "air-bleed screw" because I was told by a reputable mechanic that on the CV carbs it was an air adjustment. On the earlier carbs it was fuel adjustment. That would make their operation opposite. Turning the screw CCW on the early carbs would richen the mixture, while doing the same thing on CV carbs would lean it out. I will try turning them out to 2 turns to see if it helps.

I will save pulling the carbs (again) because they do not exhibit the symptoms you are describing. Once warmed up (which is quick), the idle speed does not change.

The vent tubes are clear. When I had the carbs apart for dipping, I made sure the T fittings and the tubes were all clear. The rebuild kits that I got even had the o-rings for the vent tubes, so they got changed, too.

The intake boots are not folded over. I can feel all the way around each boot, so that is assured. The clamps all pull down reasonably, but I might look into replacing the intake boots. That will also give me the chance to check to see if I have o-rings on them, and what shape they might be in.

 

[gspaul]

Because it's running well at the high range, I do not think It's float level.
Your mid range miix is controled by the hieght of you needle,did you lift it?
If not, get back to us, do you have adjustable needles or not.....................................By the by it was 15c today,rich blue sky,dry roads(hieght of winter),what do you think I was doing.

 

[Don Lobacz]

On the CV carbs, the adjustment screw on the top is a mixture screw and turning it out (CCW) will richen the mixture. I have found that the varnish that builds up on these needles does not come off with dipping alone - you need to actually scrub it off (I use a soft fiber pad if a toothbrush doesn't work). It sounds like the midrange is the problem and that should be connected to the needle and it's jet. Also, did you synch the carbs?

 

[Steve]

Paul, I do not have adjustable needles, but I did swap the washers to lift the needles. I put the thicker nylon washer just under the e-clip instead of the thinner metal one. Did not measure the difference, but the needle is lifted a bit.

Don, there is no varnish on the mixture screws (they were replaced with the rebuild kits) or on the needles. The emulsion tubes that the needles drop into were also new with the rebuild kits. I used one of those green scratchy pads from the kitchen to polish the needles. I usually use one that is worn out enough that my wife does not want to use it in the kitchen any more, but it works fine for what I want as a very mild abrasive. Yes, the carbs were bench-synched, then checked and adjusted on the bike with mercury columns.

Since I am now at work (the curse of the riding class), I will have to turn the screws out another half turn this evening when I get home.

Thanks for all the suggestions so far.

 

[KEITH KRAUSE]

You measure your floats at the top of the oval as you say. The raised part for the arm doesn't count. Be sure the gasket is removed from the bowl before measuring. Be sure the floats are "even". They are sometimes tweaked, one side being higher/lower than the other.
When I mentioned the two floatbowl vent tubes, I meant the rubber hoses. Be sure they are clear and not kinked. They should be routed under the seat??
If the bike is stock, why did you reverse the spacers for the jet needle? They should be put back the way they were.
The jet needles shouldn't be cleaned with an abrasive pad, only cleaner and a rag.
The throttle position your problem occurs could be either the pilot or needle circuit. Quite an overlap of the two circuits at that position.

 

[Steve]

Keith, I did measure from the top of the oval. I am using digital calipers, so it's easy to get a good measurement. The floats are not tweaked, the two sides measure within thousandths of an inch.

Yes, the rubber vent hoses are clear, too. They are routed back over the airbox, then down.

I had read many years ago that since the early '80s, when they were leaning out the carbs for emissions (and removing adjustability from the needles) that an easy way to get driveability back was to reverse the spacers. It was supposed to shorten the time on choke and improve response all the time. I have done it on other bikes of the era with good results.

The "abrasive pad" I used does not have enough abrasive in it to leave any marks on the needle, it's just a bit firmer than a rag. It's a worn-out green pad from the kitchen.

I was not able to adjust the screws yesterday as something else came up. Will try that this afternoon. I will let you know how it turns out.

 

[gspaul]

It could be interesting to compare an adjustable & non adjustable needle of the same model, I have a couple of set's of carby's on the bench.(650 Kat)We allways had adjustable.
Does that one groove on the non adjustable match up with the centre groove of the adjustable?
I allway's read about over lean carb's during that time in USA,was that down to just idle mix seting's? Kieth!

 

[KEITH KRAUSE]

OK. It seems the mixture screw would be a better choice to richen up the bike a little if you think it's lean from the factory. But if you say you've done it before with good results...
Are you sure the problem you have is a lean problem? If you remove the air box lid temporarily and test under the same conditions, I wonder if the problem worsens or improves??

 

[Steve]

I am home now from my morning appointment. I am about to go out and ride around the block to warm up the bike so I can adjust the carbs.

The first ride on the bike after everything was put back together, I had the airbox on, but no filter, no cover on it. It ran rather poorly. I put the filter and cover on and it ran much better, except for the surging from 3500-5000 rpm.

Am I sure it's a lean condition? It shows all the symptoms. Using the throttle lock at 55-60 mph, it surges 2 or 3 mph up and down, never really settling on one speed. Also, a plug check shows them all to be rather white. Can't say as there is any color on them at all.

Going out to the garage now to warm it up. You's think it would be plenty warm already, as it's 95 degrees outside (that's 35 for you, gspaul), but my bikes are babied in an air-conditioned, heated garage with lots of lighting, cable TV, phone and stereo. What a life they lead! Will come back in an hour or so to let you know of any progress.

 

[Steve]

OK, so it's been more than an hour. Had a major thunderstorm come through, with trees down just a few miles from us.

When I went out to warm up the bike, it noticed that it was not just surging, it felt like it was cutting down to about half power. Kept doing it worse and worse, and the last mile or so was just about half throttle just to maintain 45 mph. Pulled the clutch and hit the kill switch as I turned in my driveway so I could get some plug readings. On a whim, I carefully touched the exhaust pipes. #2&3 were hot, but #1&4 were only warm. Pulled the tank off to adjust the mixture screws and noticed that one of the nuts had come off one of the coils! Put a nut on and at least it now runs on all 4 cylinders. Adjusted the mixture screws to 2 full turns out, went for a ride. Better, but still surges a bit.

Plug color is still basically white. The side electrode has a slight tan color, but the ceramic is very white. Might try some new plugs, but one heat range colder. Might also try to get the right plugs. Bike shop was closed when I went to get plugs, so Auto Zone cross-referenced the NGK B8ES and came up with a Champion N3Y. My logic says 'a plug is a plug', but some people swear it makes a difference, so I will try another new set of plugs.

Will have to try again tomorrow.

 

[KEITH KRAUSE]

I would use the NGK B8ES. A colder plug is not the answer to the problem. Something is causing a lean problem. Going by your comments so far, I have to think you've missed something in the carbs. I still think you should put the jet needle spacers back, but that's just me.
If you completely seperated the carb bank and you have rubber float bowl vent tubes to connect the 1/2 and 3/4 carbs, any chance at all that the rubber is hard and you chipped off a piece and it's lodged in a vent passage to a bowl? I had this happen once and it drove me nuts. The bike would seem OK but at a steady cruising speed the problem was obvious. I kept thinking it was a lean problem (which technically it is) and even tried to re-jet for it. After a long time, I pulled things apart and happened to find a piece of the vent hose had lodged in the passage. Blew it out with 200 PSI and problem solved. However, this would not explain the lean reads all across, unless it happened to both tubes, which isn't likely.
I also wonder if the carbs are truly clean, especially the pilot circuit. I know you said the carbs are clean, but it's still a possibility. I would also put back the stock air jets. Nothing should be wrong with them if clean and new aftermarket jets creates the possibility of an incorrect size.
For a stock bike to be burning the plugs so lean, with the checks you say you've made is interesting.