Uaaghhh Carbs!

[Outlander]

Its like if it isn't one thing, its another with these things. I got my choke situation fixed, bike starts fine now. Great! Take it for a drive, after making more adjustments to mixture screws, and plug four is still rich.

Originally, when I pulled them apart, when I drilled out the mixture screw caps, the mixture screw was set at 2 turns. After my rebuild, I set all carbs at 3.5 turns, and tested it. Bike ran, but not all that well. I now have cylinders 1,2,3 somewhat nice. Could be a little leaner, but I won't mess with them, as it isn't that big of a deal. Cylinder 4, however, is black, soot covered, and if I don't clean the plug, it will quit altogether. Today, I set the mixture screw at 2.5 turns out. Big improvement with idle, and response. Good power throughout the range. Pulled the plug, again, black and sooty. Now I know how bald men got bald......

I guess tomorrow, I will turn the screw in a half turn, and try again. I think this process is more trial and error, than skill and maintence. There seems to be no set solution for carb settings. They get you close, but the real work comes from the tweaks and fiddling that must be done to "tune" them in.

If this doesn't work, I am thinking of trying to run a hotter plug in just that cylinder. How does the number system work? The lower the number, the hotter the plug? Or is it the other way around?

Question on fuel additives. What would be a good one to add to a tank? I know in cars we use fuel injector cleaners, would that trash a motorcycles sensitve parts?

[tkent02]

Have you done any plug chops to find out what's actually happening inside the combustion chambers, or are you going with the "keep guessing until it runs almost as good as it did before I started" technique?

[Outlander]

Please define plug chops?

[tkent02]

Run the engine at a certain throttle setting which uses a certain circuit of the carburetors, kill the engine, look at the spark plugs to determine if it is too rich or too lean under that condition.
There's a write up with more detail in Basscliff's site.

Which bike is this anyway?

[Outlander]

Yeah, I have done that. Both slow and high tests revealed that she is hitting rich on 4. That is why I was thinking a hotter plug? Or dropping the needle down a notch, if it has one, though I doubt it, if it had the caps in to prevent idle mixture tamperings.

Valves all within specs, thought ignition, but 1 would have been affected too. So must be carburation....?

Found air jets that bore the number 155, instead of factory 150. All the rest of the jets have the normal specs on them. Just the air jets were changed. I don't know the reason behind that....

[tkent02]

What bike is it?
Someone with that model may be able to help you more.
Changing heat ranges to make up for another problem is asking for trouble...
What all have you done to it already?

Carbs cleaned, floats set, timing adjusted correctly, airbox sealed up tight and all the rest of the normal maintenance caught up?

[TheCafeKid]

Is the "soot" shiney? Just checking to see if its oil fouled...what kind of bike? Stock or no?

[Outlander]

The bike is a 1980 GS550E. I rebuilt the carbs as the resource forum outlined. New o-rings, floats were all checked, everything cleaned. Intake boots are sealed with new o-rings as well. Air intake boots replaced and clamped. Air filter cleaned and lightly oiled. New set of plugs...or were new.

Bike is completely stock except the air jets which for my model should be 150, but all 4 carbs have 155 in them.

Air/mixture screws at factory were, Carb 1. 1 1/8 turn out. Carb 2. 1/8th of a turn out. Carbs 3 and 4 were at 2 turns out. After rebuild, I set them all at 3.5 turns out, as a starting point. Tweaked until highest rpm was achieved. Cylinders 1,2,and 3 are nice. Just 4 is not. Perhaps bad plug?

Plug has black "dry, flakey soot" not wet or oily. I have good compression on all 4 cylinders.

I also bench synched the carbs before putting them back on. I don't know what else is left to try.

[Nessism]

Ignition caps sometimes develop resistance. You can check resistance or just replace them with NGK caps which cost about $5 each. Also, you should vacuum sync the carbs and adjust the valves if you have not done so already. Tight valves result in low compression which can lead to fouled plugs. Cross off possible problems and you will eventually find out what is wrong. Keep going...

Good luck.

[chef1366]

I would check the float heigth on the troubled carb.

[TheCafeKid]

I agree with Chef on that. if your float level is ok, did you replace the float valves when you redid the carbs? Its possible that one has gone bad.

[Steve]

If this doesn't work, I am thinking of trying to run a hotter plug in just that cylinder. How does the number system work? The lower the number, the hotter the plug? Or is it the other way around?

Yeah, I have done that. Both slow and high tests revealed that she is hitting rich on 4. That is why I was thinking a hotter plug? ....

Changing heat ranges to make up for another problem is asking for trouble...

Changing to a hotter plug may clean up the plug, but it will still be running rich.

Here is a link to BassCliff's plug chop write-up.

.

[Outlander]

Okay, this is odd. After attempting to do another adjustment on my carbs, meaning, adjusting mixture screws to highest idle, I read in Basscliffs tuturial that you turn them in, until idle falls off, then back out slowly until highest rpm is achieved.

So, I did this, carb 1. Worked like a charm, in until idle fell off, then out to highest rpm. Carb 2. In all the way....no change in idle at all. All the way out...still no change. So carb 2 is not responding, yet is burning good, according to plug pull, so I left it at its setting of 3.5 turns. Carb 3, in until idle fell off, then back out. That one worked great as well. Carb 4, the troubled one, in and it died off, then back out to highest rpm, was at 4 turns out.

Took her for a ride after setting idle back to 1100, and she performed well. No bogging, no surges, run fine. Got home and let her idle for a minute, and she dies.

So two carbs I am wondering about now. 2, since turning the screw in or out did not do anything, and 4, as it is still rich. I replaced the plug, and still got the same results. Could 2 affect 4?

[80GS750]

if you got no response with 2 than i would think something is wrong there....

maybe some passages dirty or clogged.. something is wrong..

2 will not affect 4. if 4 is running rich, turn that screw in half a turn at a time until that cylinder starts looking better... its getting too much fuel.. period.

if your only really running on 1 and 3 than i wouldnt trust the highest idle thing when adjusting 4... cause it could be wrong.. i would pull the carbs.. and check the passages on 2, and the float valve on 4. just my thoughts

[80GS750]

if your running cv carbs than those air screws are actually fuel screws... turning them out gives more fuel, in gives less fuel....