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can't solve rough idle

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Guest

Guest
79 GS850G. Valves done, carbs dipped and rebuilt with all new o-rings, and several fuel mixture screws replaced. New: intake o-rings, intake boots, airbox boots, plug caps, sparkplugs, airfilter, battery. Air box rebuilt/resealed. Coils mod done and coils checked and they seem to be working fine. As far as I can tell with carb spray I don't have an air leak. The problem is the idle will not stay steady. I have a carbtune and colortune and both have been done but the bike won't idle smooth. At 1000 rpm it will be idleing fine then drop to 800 them back up to 1050. When I take it out she lacks quick response from initial throttle if a quick pull and once I hit 5000 rpm she starts to crap out. #3 and #4 consistantly show rich and #1 and #2 more to the lean side but still have some black a bit. This is drivnig me nuts. Any suggestions? I"ve dipped the carbs 3 times and all my jetting is stock. The pipes are the original stock ones with the baffles partially rusted but there are big piles of crap in there. I've even resealed the airbox just to make sure and checked the breather hole to make sure it wasn't plugged. I haven't rechecked the valves but really don't think I need to. But I"m open to anything.
 
You've about covered EVERYTHING that would cause your condition. One suggestion that I did not see: Have you run a voltage test on the battery while at an idle? Could be low voltage. '77 should have the points, have you checked/cleaned them and readjusted? Advance working and easy to move?
 
Voltage at battery is good on idle. I forgot to mention I have put in new points and condensors as well as a new reg/rec. The advance is working as it should, as far as I can tell, moves easily. I checked the charging system as well to make sure the stator is working and all is good.
 
Strong spark? My bike showed some of those symptoms when one of the coils was on it's way out....

Other than that it sounds you're rich or lean on the idle. I would say too rich listening to symptoms.

Did you make sure the air jets are all clear, float heights set correctly? Have you got the vent tubes on?

Dan :)
 
It's always run rich and no amount of adjusting will get rid of it, it will improve it but not enough. It's as if there is a vacuum leak the way it misses during firing but I can't find it. You mentioned the vent tubes (nipples on the bottom of the float bowls). I don't have the hoses on no, I figured being open to air was fine enough. I've only ever had #1 spill over down the vent tube but I readjusted the floats after that and they seem to be fine. I am going to UNFORTUNATELY have to wind up pulling the carbs AGAIN I'm sure so I'll check the floats again. But let me know if for some crazy reason I'm supposed to actually have the vent tubes on.
 
Supposedly no vent tubes can cause problems but I've never experienced any.

Did you change your clamps for all the boots? They stretch over time.

Can only be carbs or ignition... - or a twisted crank maybe.. :D (doubt it would come & go then, would just be rough I would think).

Dan :)
 
no I didn't change any of the clamps for any of the boots, they all seemed to synch on fine but I'll check them, thanks.
 
One more thought. Is it possible that you over oiled your filter or do you have the paper element? I've seen and heard that this will cause similar issues. Was it Bruce? :-$ :p
 
make a fitting for the bottom of the float bowl, run clear tubing along side the fuel bowl and check the fuel level that way.

did you check for cut/damaged fuel inlet seat o-rings?

about it dying out over 5K rpm's, did you check to see if the petcock flowing well?
 
I did originally over oil my air filter (its foam) but I cleaned it well and since then have actually bought a new one and veryyy lightly sprayed it. But there was never any improvement to the idle when I opened the air box. The petcock is working perfectly, it's new. I've seen pictures of that float hookup hose, I'll have to try and figure something out. What/where exactly is the fuel inlet seat o-ring?
 
What are your fuel and air screw settings? Standard start point is 3/4 open for the pilot fuel screw and 1.5 for the air screw. Also, how do your points look? Clean and properly gapped?
 
I've had my setting everywhere from 5/8 and 1 1/4 which is stock settings to 1 1/2 and 3 trying to sort this out. Right now they are around 1/2 - 3/4 and 1 1/4 - 1 5/8 set with a color tune and ear. The points are set perfectly all new including condensors. The fuel inlet valve seats (the copper washers) have been replaced on a couple of them as I had to order two rebuild sets. I couldn't "see" anything wrong with the others. I've heard it mentioned that these tend to wear out. When I pull them apart 'again' I'll have a look at them all and replace them. I never order rebuild kits for all the carbs as everything with the exception of two broken fuel screws looked fine but I am thinking I'll spend the extra $50 and do them all. All the O-rings and gaskets for all four carbs were replaced as I ordered an O-ring kit from the website.
 
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When the fuel screw tips were broken off, did you get the tips out of the carb body?
 
lol...wellll...I wound up making my own very fine tipped punch and hit it out with a hammer, ha,ha,ha,ha....since then I have replaced that carb with another. I'm going to pull the carbs all apart and double check that all the jets and needles are what they are supposed to be. I was looking at my bits and pieces box and noticed that my main jets are numbered 102 not 102.5 as per the factory spec, but shouldn't be a real problem I don't think. I've thought about moving the clip on the main to compensate for being rich..but...I don't really want to go off stock until I figure out what the actual problem is first.
 
azr said:
What/where exactly is the fuel inlet seat o-ring?
Click to expand...

Your '79 uses VM carbs, so you don't have an O-ring on the fuel inlet seat.

It's a very common source of problems on bikes that are just barely newer than yours.
 
Thanks for that, I thought it was refering to the copper ring at the float needle.
 
azr said:
... But I"m open to anything.
Click to expand...
Lots of suggestions on the intake side of things, but this is what caught my eye:
azr said:
The pipes are the original stock ones with the baffles partially rusted but there are big piles of crap in there.
Click to expand...
Have your verified that your exhaust pipes are not plugged up? :-k

Straighten out a clothes hanger and poke it through the header pipes.
Stock pipes are double-walled, so they might look great on the outside, but the inner pipe can be rusted away and clogging the passages.

.
 
I checked the pipes and although I can see rusted away baffles at the end of the pipes there are no lumps of rust in the pipes at all. Hopefully that means the baffles aren't as bad as I thought.
 
azr said:
lol...wellll...I wound up making my own very fine tipped punch and hit it out with a hammer, ha,ha,ha,ha....since then I have replaced that carb with another. I'm going to pull the carbs all apart and double check that all the jets and needles are what they are supposed to be. I was looking at my bits and pieces box and noticed that my main jets are numbered 102 not 102.5 as per the factory spec, but shouldn't be a real problem I don't think. I've thought about moving the clip on the main to compensate for being rich..but...I don't really want to go off stock until I figure out what the actual problem is first.
Click to expand...

Sounds like your ride has not been loved by it's PO. I'd check all the jets
to make sure that their sizes are, as you think they are. You really need a jet drill set to confirm that their hole sizes are as marked on the jets. Some bad people do actually drill them out.:-\\\
Without this information, you're "prodding in the dark".

If you weren't careful when drifting out those broken mixture screw tips, you will have enlarged the orifice. This will severely richen your mixtures at normal settings.

You also said that you replaced one carb, but that two screw tips had been broken. Wasn't the second carb damaged? Are you sure that the replacement carb/carbs are exactly the same specs as the originals?
 
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