81 GS650G Rebuild

[SierraKiloGulf]

Hey guys, long time lurker- which has got me by quite for general maintenance for the last 5 or 6 years I've had this GS, but now is the daunting task of a total rebuild. I bought my baby off a friend when in it had around 18000K, it sat in his garage for 19 years and was calling out for some love and ran like a dream after a bit of adjustments. Today however she's at 52K and needs a bit of work. Power has obviously overtime reduced, and I suspect its from carbon build up, valves need adjusting, ect. It's been quite a while since I've adjusted adjusted the valves so that is long over due- so while going in that far, I want to overhaul as much as I can and freshen this old girl back up. I did a compression test back in the fall, and I believe #4 was low around 80psi, and spark was getting pretty bad. Still very easy on oil, although oil pan and filter gaskets are now leaking, so those need replacing, carbs need a tune up/ cleaning. The stator also needs replacing for the 3rd time, really seems like there has to be a better way?!!?

I've gone ahead and ordered a top end gasket seal kit, carb rebuild kit, new piston rings, clutch plates and gasket, oil pan gasket, new ignition coils, stator/recitifier, and some other goodies not related to the drivetrain. What else should I pick up and replace? I'm hoping to just get away with a hone and not a re-bore, as up until the end of last riding season it ran great and was my daily driver, but I won't find out until I can dig deeper into the bike on the weekend and check tolerances. It doesn't hurt to have spare parts, I just want to be prepared once I open and clean the engine I can assemble right away.

 

[Burque73]

HI there.

Seems like a weekend of catching up on some maintenance may help tremendously. If you've been lurking for that long you no doubt are aware of how important good electrical connections are to the life of a stator. Also, that tight valves can reduce compression readings and rob it of power, at the very least. Seems like you missed the last four factory recommended valve clearance checks.

Anyway, it's good of you to post and make yourself known! Good luck with the rebuild.

 

[alke46]

Welcome to the site. Also as noted by Roger, since you've been lurking for a few years, you must have missed the part about carb rebuild kits. They aren't necessary, all you need is the o-ring kit from www.cycleorings.com. He's a member here. Another miss on your part, is the replacement of stators. If you do the connection clean up and do the stator pages, you should eliminate having to replace any more stators for several years.

Don't mean to be harsh to you, just want you to reap the benefits of lurking. Good luck with your refreshing the 650.

 

[Steve]

Before you do ANYTHING ELSE, ... do the valve adjustment, then do an "Italian tune-up".

A lack of valve adjustment will cause some degradation in performance. Some of that might also enhance some carbon build-up. Just do the valve adjustment, maybe install some new spark plugs, then run the heck out of it for about 500 miles. Be sure to wind it up to redline a few times. Heck, do that a few times per mile. Let it breathe, it will likely get rid of some of the cobwebs that have built up.

After all that, then you can decide whether it still needs to be rebuilt. Unless you have visible oil leaks from bad gaskets or you are burning a lot of oil from faulty valve seals, leave the engine intact, just do the valve adjustment and ride.

.

 

[tom203]

Yes, do the overdue valve adjustment and then the italian tuneup....you might get lucky! Internal engine parts for this critter are expensive. Note that this is plain bearing crankshaft engine - if no unpleasant noises were noticed,maybe your performance issues are in top end. Plenty of these 650's still around,looking for new homes!

 

[SierraKiloGulf]

Sorry for my absence but work really takes its toll on a man...
Soooo, I ordered the shims I need and surprisingly for missing g the last 3 adjustments they weren't as bad as I would have thought, and they should be here any time next week. In the meantime, I have done quite a bit to the bike, but just can't seem to get it running great. Painted nearly everything except the frame (still got chop the rear of the frame off for new seat hoop and seat). Replaced the regulator, as the connections had melted together presumably from over voltage, and ordered a new rectifier to swap out just in case that's no good either, and the stator is tomorrow's job if the multimeter test proves its faulty. I rebuilt the carbs and cleaned the heck out of them, they weren't too bad, but the main jets were quite clogged. I changed both coils, put in new spark plugs, threw on a 4 in 1 from Mac because the stock one was falling apart literally, and slapped on some pods. It starts right up and idles nice, and is very responsive to the throttle just as I remember it, but I'm having a bit of sluggishness once weight is put onto the back tire and having a little bit of backfiring issues, along with a stumbling idle (around 950-1000 ramp but suddenly will stumble for a split second around every 20 to 30 seconds, sometimes a little more frequently, if that makes sense) to the point where its keeping me from riding right now. Floats are set according to the service manual, and I went up to a 120 from the stock 110 main. It had 140 for the pilot jet and my rebuild kit came with 160s so I threw those in as well as those ones that were in there looked like ****. Honestly, that rebuild kit for the carbs was worth every penny I spent, and was necessary in every sense, as the gasket was shot, and all the jets and the float needle were quite clogged and was a pain to try to get wire through em to try to clean them out, so it has all new hardware inside.

I'm trying to hold off on the rebuild until the winter time, so if anyone has some advice to figure out these issues so I can go for a ride and redline this bitch to clean out some buildup (and to get my juices flowing) that would be great

 

[SierraKiloGulf]

Thought I'd add these videos just to make it easier to understand my issue. The first was started from cold (not entirely cold, went for a ride around the block for about 2 minutes about an hour previously) and ran for about a minute until I started recording. No backfiring and sounded quite alright. The second was taken right after, being a little harder on the throttle, still no backfiring and running acceptably well, very responsive to my throttle input. The third was taken about 5 minutes after, once warmed up it began popping quite a bit. Not noticing any backfiring on deceleration, only seems to occur during idle and when giving it throttle.

 

[tom203]

Your idle (however you achieved it) sounds ok...no load throttle response sounds like mine. Based on the ok idle, the last video suggests a missfire to me.

As was stated already, you seldom need no oem carb rebuild kits- they tend to be iffy- all the original jets will clean up nicely unless they have been tortured. So just how did you clean these carbs?
And are you using the stock airbox setup? If yes, then the 120 main is off...you could fiddle it into holding a decent idle, but it would be too rich later.

 

[SierraKiloGulf]

Running pods with a 4 in 1 exhaust. Got it running GREAT today, and put on 350km on the odometer. Slight hesitation and a little backfire from about 10%-50%, it sounds and feels a bit lean through that range but its pulling harder than it ever has since i purchased it. Im going to play around with the jets a little further in the next day or so. Boys, it felt great to finally get this girl back on the road. I forgot how amazing these little bikes are, havent had this much fun in a while. Going to check plugs in the morning and will update on the hesitation issue inthe coming days, any input on that in the meantime will be great.

Edit: added video because who doesnt like the roar of these ol gals. I think after a carb sync, adjusting the valves and fine tuning my jets it will sound and run even better

 

[tom203]

" I forgot how amazing these little bikes are, havent had this much fun in a while."

I know the feeling... The stock needle does not do well with pod setup in mid range, but have some fun!

 

[SierraKiloGulf]

Yes, it for sure would be them needle jets/ jet needles that are causing that leaning condition. I think im bang on the main jet though, but wont know for sure until i set this mid range up properly so i can work from bottom to top. Excuse my ignorance but is it possible to go up a size or two on the needles? The manual has a weird letter/number combination as opposed to just numbers like the mains and pilot. How would i go about richening that up a bit? Aside from that i was very impressed with the ride tonight, bike turned a lot of heads in our downtown district. Burmed just over a tank of gas, and im still smiling ear to ear

 

[tom203]

The pros here recommend the dynojet kit when you leap to pods...this saves you tuning grief. But you sound enterprising, so experiment and have fun. I can tell you that this bike has a wonderful midrange with stock airbox setup
Have a look here... The needle is likely the key component

https://www.z1enterprises.com/dynojet-carb-kit-gs650-1981-82.html