'82 GS650G Project

[BestScrubLord]

I've been working on an '82 GS650G I recently acquired and had a few questions I've been having trouble finding answers to.

First, do these bikes have a particularly loud top end? Mine has more noise than I expected and am hoping that nothing too serious is going on. After looking up a couple videos it seems like it may be normal but I'd love to have some confirmation there.

Here's a video of the rough idle and top end noise I'm talking about:

https://youtube.com/shorts/oWnu2zrtrlA?si=A-AnLfbO9r6Serb8

On a potentially unrelated note, I can't seem to get cyl 3 to fire. Could the misfire be the noise I'm hearing and is there any advice as far as diagnosing a misfire? The cylinder walls seem okay from what I can see, the plug is getting spark, it doesn't get start firing with more/less fuel and more/less air. It was fine before I did a carb rebuild and all of a sudden it just doesn't want to fire.

Final question, does anybody have a pretty reputable vendor for miscellaneous parts? I bought a new front master cylinder and it's one of those cheaper parts that's already begun to seize up on me.

Any help is appreciated as this is my first bike project and I'm learning as I go.

 

[rphillips]

Welcome scrub, a lot of info around here & you'll find many see things different. The "search" feature may answer many questions before you ask them. A lot of info. on front master cyl. I think Kawa. EX 500 front masters have been recommended a lot... It was fine till I did a carb rebuild... If it ain't broke don't fix it. Sounds like if it was fine before, now it's not, you have created a problem. Sometimes a plug will fire in open air, but not under compression, easy check, swap your plugs, 3 to 4 & 4 to 3, if problem follows plug to 4 you found it. Sounds OK for poor running eng, no excessive noise & will sound much better when running properly, but still a little noisy.

 

[BestScrubLord]

Thanks for the quick response rphillips!

I'll have to use the search for info on the front master cylinder, i had only tried using it for the top end noise.

Glad to hear the top end noise is probably just tuning related. I haven't yet tuned it using a vacuum gauge on the carb since I can't get #3 to fire. Perhaps that is more necessary than I originally thought.

I tried swapping the plug in #3 and #4 like you said but unfortunately no change, #3 still does not fire. Perhaps I need to take the carb off again and take another look. Unfortunately I had to rebuild them in the first place as the floats in #2 and #4 were not working.

 

[rphillips]

Yes, seems like a fuel problem. Carbs are a place many here would agree with you & I too understand the reasoning, got them off so complete rebuild. Not always a good thing. If needle & seats were problem, if you'd just removed the 2 bowls, fixed what needed fix'in, then back together, you'd probably be out riding instead of trying to chase this problem. Anyway good luck with both problems

 

[BestScrubLord]

Probably would have been a good idea to just play with the 2 carbs instead of all 4.

Thanks for the help!

 

[rphillips]

There's some really good carb guys around here, hoping they'll have some good places to look first.

 

[Nessism]

First off, 1&4 fire together and 2&3. Switching 3&4 sounds dangerous. Please don't do that.

If you haven't already done it, go into your profile and turn on "view signatures", then check out mine. It contains a list of common problems for new owners, a carb rebuild tutorial, which it seems you need, and a source for carb O-rings.

BTW, the engine sounds fine, other than the misfire.
BTW2, the EX500 master cylinder is the wrong size. You need a 5/8" bore master. Try the EX650 master cylinder, the rectangular master type, which has a mirror boss. Those are good units.

 

[rphillips]

OOhh, I'm confused, how could it matter which hole a sparkplug is screwed into. If you swap the #3 sparkplug to the #4 hole & the #4 sparkplug to the #3 hole if the miss fire, that was in #3 is now in #4, that particular sparkplug is the problem... Isn't it???

 

[Rich82GS750TZ]

I think Ed may have misread. Either that or I have. Only the plugs were swapped from 3 to 4, not the plug wires, to eliminate the plug as a problem. That right?

At no point in the OPs first post did I read anything about valve clearances. Are they good or not? This should be done before any carb tuning.

And I keep going back this line from the first post “It was fine before I did a carb rebuild and all of a sudden it just doesn't want to fire.​” Occam knows what’s up.

If you haven’t already, you should reference Ed’s CV carb rebuild tutorial.

 

[BestScrubLord]

First off, 1&4 fire together and 2&3. Switching 3&4 sounds dangerous. Please don't do that.

If you haven't already done it, go into your profile and turn on "view signatures", then check out mine. It contains a list of common problems for new owners, a carb rebuild tutorial, which it seems you need, and a source for carb O-rings.

BTW, the engine sounds fine, other than the misfire.
BTW2, the EX500 master cylinder is the wrong size. You need a 5/8" bore master. Try the EX650 master cylinder, the rectangular master type, which has a mirror boss. Those are good units.

I didn't swap the plug wires, just the plugs themselves to eliminate the possibility that the plug itself is the issue.

Those links already show up for me, thanks for the info! I'll check those out and see if I messed anything up. When I rebuilt them the first time I was using the guide listed in the GSResources technical page.

Again, glad to hear that the top end is being somewhat noisy is normal. Had me very worried.

Thanks for the recommendation on a specific master cylinder.

 

[BestScrubLord]

I think Ed may have misread. Either that or I have. Only the plugs were swapped from 3 to 4, not the plug wires, to eliminate the plug as a problem. That right?

At no point in the OPs first post did I read anything about valve clearances. Are they good or not? This should be done before any carb tuning.

And I keep going back this line from the first post “It was fine before I did a carb rebuild and all of a sudden it just doesn't want to fire.​” Occam knows what’s up.

If you haven’t already, you should reference Ed’s CV carb rebuild tutorial.

​​​​You were right about your plug wire vs plug guess. I only swapped the plug, not the wires. Thankfully I know enough to know that would be a terrible idea.

Is there a good guide for checking valve clearances? I assume that's to see if they are sealing the cylinders properly after wear and age.

Yeah I'm wishing I had done a little more research before digging in but I tend to learn a lot by doing and making mistakes haha.

 

[Rich82GS750TZ]

​​​​You were right about your plug wire vs plug guess. I only swapped the plug, not the wires. Thankfully I know enough to know that would be a terrible idea.

Is there a good guide for checking valve clearances? I assume that's to see if they are sealing the cylinders properly after wear and age.

Yeah I'm wishing I had done a little more research before digging in but I tend to learn a lot by doing and making mistakes haha.

I suppose what you wrote about clearance is somewhat accurate. Valve clearance tighten up over time/use, so the clearance needs to be adjusted periodically, via swapping out shims, usually for a smaller thickness. You've got some reading to do. Everything you need to know regarding Valve Clearance checking, shim swapping is in the Factory Service Manual. If you can't see signatures, you need to get into your settings and turn that on. Many of us put these links in our signatures so you don't have to hunt for them.

​

Bike Cliff's Website: https://gsarchive.bwringer.com/
8 valve clearance procedure - also found on BikeCliff's: https://gsarchive.bwringer.com/bikecliff/images/gs850valve_adjust.pdf
Supplement for one possible way to help hold valves open to swap shims - also found on BikeCliff's: https://gsarchive.bwringer.com/bikecliff/images/valve_tool_zip_tie.pdf
Ed Ness's CV Carb Rebuild Tutorial - also on BikeCliff's: https://gsarchive.bwringer.com/bikecliff/images/valve_tool_zip_tie.pdf

 

[BestScrubLord]

I suppose what you wrote about clearance is somewhat accurate. Valve clearance tighten up over time/use, so the clearance needs to be adjusted periodically, via swapping out shims, usually for a smaller thickness. You've got some reading to do. Everything you need to know regarding Valve Clearance checking, shim swapping is in the Factory Service Manual. If you can't see signatures, you need to get into your settings and turn that on. Many of us put these links in our signatures so you don't have to hunt for them.

​

Bike Cliff's Website: https://gsarchive.bwringer.com/
8 valve clearance procedure - also found on BikeCliff's: https://gsarchive.bwringer.com/bikecliff/images/gs850valve_adjust.pdf
Supplement for one possible way to help hold valves open to swap shims - also found on BikeCliff's: https://gsarchive.bwringer.com/bikecliff/images/valve_tool_zip_tie.pdf
Ed Ness's CV Carb Rebuild Tutorial - also on BikeCliff's: https://gsarchive.bwringer.com/bikecliff/images/valve_tool_zip_tie.pdf

Okay, so I managed to check the clearances between the shim and the camshaft lobe according to the 8 valve guide you supplied me with. The .0015" feeler fit under all of them so no gaps are under .03 mm (roughly) and the .003" feeler fit under all of them so no gaps is larger than .07 mm (roughly). The .004" didn't fit under any.

Am I right in believing this is within spec? It should be within .03 mm to .08 mm right? If so that's good that I don't have to swap shims but I was hoping it could be related to cyl 3 misfire.

 

[Rich82GS750TZ]

I’ll let someone else answer. I gave you the specs, or at least the resource to find the specs. Sorry. I’m not going to try to read a sentence that mixes inches and mms and try to make sense of it. My small brain can’t flip flop like that.

 

[BestScrubLord]

I’ll let someone else answer. I gave you the specs, or at least the resource to find the specs. Sorry. I’m not going to try to read a sentence that mixes inches and mms and try to make sense of it. My small brain can’t flip flop like that.

I feel you, I'm having the same issue myself lol. Before assuming I'm correct I'm just looking for confirmation that I am right from someone with more experienced.

 

[BestScrubLord]

First off, 1&4 fire together and 2&3. Switching 3&4 sounds dangerous. Please don't do that.

If you haven't already done it, go into your profile and turn on "view signatures", then check out mine. It contains a list of common problems for new owners, a carb rebuild tutorial, which it seems you need, and a source for carb O-rings.

BTW, the engine sounds fine, other than the misfire.
BTW2, the EX500 master cylinder is the wrong size. You need a 5/8" bore master. Try the EX650 master cylinder, the rectangular master type, which has a mirror boss. Those are good units.

Would you mind taking a look at my conversions from feeler gauge size to mm for me? Like I mentioned above, just looking for confirmation or denial before I move on from this.

"Okay, so I managed to check the clearances between the shim and the camshaft lobe according to the 8 valve guide you supplied me with. The .0015" feeler fit under all of them so no gaps are under .03 mm (roughly) and the .003" feeler fit under all of them so no gaps is larger than .07 mm (roughly). The .004" didn't fit under any.

Am I right in believing this is within spec? It should be within .03 mm to .08 mm right? If so that's good that I don't have to swap shims but I was hoping it could be related to cyl 3 misfire."

 

[Nessism]

.03-.08mm is the spec, but it's perfectly safe running up to .12mm.

 

[BestScrubLord]

.03-.08mm is the spec, but it's perfectly safe running up to .12mm.

Excellent. Thank you for the confirmation.