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My GS850 Bogs down when accelerated quickly

  • Thread starter Thread starter Bob Gibson
  • Start date Start date
Status on 81-GS850 that bogs down at high speeds

Status on 81-GS850 that bogs down at high speeds

For all of you that helped me out with ideas and suggestions back in mid-February . . .

I thought I'd give you a status. Many of you suggested that I check the valve gaps and shim adjust if necessary, even though this was probably not the problem. Well I check them. By-the-way, the step-by-step pictorial on the web site was extremely helpful. Thank you! Upon inspecting the intake and exhaust gaps I was disillusioned on how far they were off from your suggestions (one was at .155mm gap instead of the .03-.08mm requirement!). Relying on your expertise, I went ahead and replace 7 of 8 shims to get the gaps within the web site guideline. After hand cranking the engine over about 5-6 times I check the compression and had good improvement (about 10 psi on average). So I rode the bike down the street and it still ran poorly (I'll get to that later) but I did have a noticable improvment in power. After sitting for a week, that is, until last weekend (limited time to work on my bike - darn) at which time I checked the compression again and was astounded on the significant increase. You all l were right. As a reminder, on my original compression test, I had 115-105-90-90. Now I'm at 130-130-135-140. Wholly Toledo! What a change. So my hand turning the engine over did not seat the valves properly. After riding it just a block, they apparently all seated. But the bike now has the same problem plus another.

The two areas I fiddled with since my last write-up were the valve adjustment and the carb idle screws. Since we know the valve adjustment went well, I'll have to blame the idle adjustment on the new problem, since the bike idles poorly. I had to turn the idle screw up a fair amount to get the bike to idle. I adjusted the idle screws to about 2 turns from gently closed, eventhough most of the idle screws were originally at four to five turns out. Hummm. So now the bike needs lots of gas to keep from dying when I start moving and I'm still limited at top end, but now it's bogging at about 7K rpms. It almost feels like it could be a timing issue, but this bike has the electronic ignition (no points). I then went back and turned the the idle screws on each carb to 3 turns and no improvement.

I've got the original type airbox now, so once I replace the polyurethane foam insert, I'm ready to add that on. And so far, everything appears to be stock. So much for being built to race. I also checked the carb-to-engine boots out and the rubber is still fairly soft with the original phillips head screws. Spraying ether around the boots did not change the idle at all.

So any ideas? Is it time to rebuild the carbs (I've already got the info off of the web site), or do any of you have any suggestions of things to try that could lead me to a better diagonosis prior to carb rebuilding?
Thanks again for any help.
Bob Gibson
 
Bob, thanks for the update.

I'd thoroughly check out that airbox for potential air leaks and then fit it up with a new lightly oiled, foam filter. Make sure that the filter assy seals tightly along the top sealing strip.

Set all the pilot fuel screws at 3 turns off the seat and see how it idles. If its ok, take it for a run to see if the bog at 7k has dissappeared. I think you'll find that you have a marked improvement.

If neither improves, it's time to give those carbs a decent clean. While you're in there, record the size of the pilot and main jets and the needle positions/shiming. If you post these here, someone will guide you on how well your PO has done when tuning for pods.
 
Bob Gibson said:
So any ideas? Is it time to rebuild the carbs (I've already got the info off of the web site), or do any of you have any suggestions of things to try that could lead me to a better diagonosis prior to carb rebuilding?
Thanks again for any help.
Bob Gibson
Click to expand...
Race prepped? ha ha... more that likely all that has been done was to put pods on it.
my thoughts are, because of the idle mixture screws @ 5? turns and...
When the rpms are high and I let off the throttle, I get a lot of backfiring through the mufflers

Brand new spark plugs out of cylinder 3 and 4 appear slightly Black with only about 100 miles of use. Plugs 1 and 2 appear clean.
Click to expand...
stock jets and pods is my guess. a lean condition it would make...

get the intake boot o-rings and the allen head cap screws for the boots from cycle o-rings http://www.cycleorings.com/ take the carbs apart, clean them and check the jet sizes.

jet sizes are located in this thread http://www.thegsresources.com/_forum/showthread.php?t=73723.
report back if they are different than stock.

reseal your air box, including between the air filter "cage" and the air box. tack glue the end rubbers on. properly oil the air cleaner element.

bench synch the carbs, after the carb rack is fully assembled ready to be put back on the bike.

does it have exhaust leaks?
 
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Now for the latest on my 1981 GS850G bogging down

Now for the latest on my 1981 GS850G bogging down

Now, I can?t get the bike to start very easily. It is appears that it?s either not getting proper spark or fuel. I can eventually get the bike started after about 5 minutes of cranking and adjusting the carb idle screws and yes, charging the battery. I?m not sure the carb adjustments are the reason I?m getting it started. Once it starts, it appears to run poorly in neutral, especially at low end revs, yet once I put it in gear and gently start to let out the clutch it instantly dies and then won?t start for another long bout of cranking. So here?s what I?ve done since taking it around the block after the valve adjustment a few weeks ago.

Ignition/Spark: When I did the valve job a few weeks ago, I noticed that the signal rotor tabs were pretty rusty, so a few days ago I popped off the ignition cover and very lightly polished the tips of these rotor tabs. Less than .002 inch was removed (gapped before and gapped after), and I adjusted the signal pick-ups inward slightly to get close to original gap. I also noticed that my 2 signal pick-ups did not consist of 4 wires as the manual states (Blue, Green, Yellow & Black), but 3. A blue wire goes to one pick-up, a Green wire goes to the other pick-up, with a Red wire attaching from 1 pick-up to the other pick-up. I checked the resistance across the Blue and Green wires with a multi-meter, near the ignitor box, and got 320 ohms. Dividing in half gets me 160ohms, so does that indicate I?m within range? And does this ignition system seem to be an ?after market? or for a later model? I?m asking that since my ignitor box has only 6 wires out, not the 8 described in the manual. The colors of my 6 ignitor wires match 6 in the manual, but I don?t have the solid Yellow and solid Black wires. The ignitor unit also indicates it?s a 12volt system, but about 8.5 volts is the most I get checking across any wire combination (Orange/white stripe across Black/white stripe). The ignitor unit number is 32900-45110/131100-1901. Now I?ve checked for spark at the plugs and I do have a spark. I expected a stronger visual spark, but that may be due to my auto background, however I do have a spark.

Carburetors: I took the complete carb 4 pack off the bike and thanks to Mario Padilla supplying me with 4 viton o-rings, I replaced in the intake o-rings as suggested. Inspecting the inlet ducts did not indicate any rubber cracking or poor seating. Now, while I had the carbs off I adjusted the butterfly gaps with a drill bit as the article suggested. They were not off by much. I could have left them as is, but trying to be a perfectionist? I also blew filtered compressed air all around each carb, above the idle screws and through each air jet. I then adjusted the idle screws to 3 turns out, reassembled the carbs onto the bike, checked the petcock (functions properly), added the new air box (it?s properly sealed and with a new air filter) and started cranking the bike over, but to no avail. Then adjusting the idle screws out by 2, then 4 then in 3, then 5 and then it started, ran poorly then died as mentioned above. I then took the airbox off, reinstalled the air pods and the result was the same. I can?t believe that a very slight butterfly adjustment or air in the idle screw or into the air jet could cause such a calamity, and that?s why I started verifying I had a spark, but there?s spark.

Help once again!
Bob Gibson
 
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