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Uaaghhh Carbs!

  • Thread starter Thread starter Outlander
  • Start date Start date
O

Outlander

Guest
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?
 
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?
 
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?
 
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....
 
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?
 
Is the "soot" shiney? Just checking to see if its oil fouled...what kind of bike? Stock or no?
 
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.
 
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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.
 
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.
 
Outlander said:
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?
Click to expand...

Outlander said:
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? ....
Click to expand...

tkent02 said:
Changing heat ranges to make up for another problem is asking for trouble...
Click to expand...
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.

.
 
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?
 
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
 
if your running cv carbs than those air screws are actually fuel screws... turning them out gives more fuel, in gives less fuel....
 
if your running all stock componants, airbox and exhaust.. than they should be realtively close to the factory settings, if your having to run them more rich, than you probably have an airbox leak or some other kind of seal problem
 
80GS750 said:
if your running all stock componants, airbox and exhaust.. than they should be realtively close to the factory settings, if your having to run them more rich, than you probably have an airbox leak or some other kind of seal problem
Click to expand...

In my experience the factory settings are very lean and opening them up an extra turn or so helps a great deal.

I still think the carbs should be vacuum synced before going too much farther. It's pure guess work in terms of what's wrong unless you verify a few things first.
 
Well, I pulled the carbs and checked my 2 troubled carbs. I completely went thru 2, blew out the passageways, inspected for dirt etc. I checked float level, all good. I reassembled it. Set my "fuel/idle mix screw to 3.5 and went to 4. I think I found the problem. When I pulled the carbs originally to clean them, I had a dickens of a time getting the needle seat out. Apparently, I must have bent it enough where the needle could get stuck. So even if the float was normal, the needle would not shut off fuel. So, I replaced it with another one, and the needle moves freely. I am surprised I didn't see that earlier.....damn eyesight going.

I put everything back together, and tried to get the bike to start. No go. A couple of sputters, but that is it. Being that it is 94 degrees here, and I am working outside, I stopped working on it, partly from frustration, partly cause I am just too damn hot, and this was AFTER a dip in the pool. I have to pull the carbs out again, as I found that my choke rod assembly is in um, upside down. I was wondering why I couldn't get my choke to work right, and found that I think I may have installed it upside down. The actuator, is colliding with my throttle linkage at the carbs. Surprised it worked at all.

I should know better.....Haste makes waste.

Anyone got a pic of their carbs with how the choke assembly should be? I don't know how it goes back together, I just know it is wrong the way it is. It should not hit the throttle linkage assembly.

Thanks
 
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this pic is from the carbs off my 82 gs850g. let me know if it helps


100_0108.jpg
 
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