Can anyone diagnose my bike?

[rcklobster]

The bike in question is a 1982 GS650G.

The previous owner really had no clue what he was doing and the bike was a mess when I got it. The exhaust cam was 180° off, there was vacuum line where there should have been fuel line, the plug wires were on incorrectly, and the fuel gauge sending unit had been broke, just to name a few of the previous issues.

So after many hours of almost literally rebuilding everything from the cams up, the bike fires right up and has ran not perfect, but well enough that I literally rode every day in September except for one, ever since... until now.

Here is what's happening. The bike starts right up with less than a second of cranking. Keep in mind that the choke was on about half this entire time. Runs fine for about 45 seconds or so. After that, it begins to get a little choppy, initially I just though it was because it tends to be cold natured, and I just dismissed the thought. A few seconds after that, it begins to pop and crack a little out of the right pipe, (# 3 and 4). This got my attention and I began to play with the throttle some. It was running very weak. It would not rev very fast at all and you had to baby it to get it to even do that much. Very soon after it lost so much power it wouldn't rev any more, but it would hold steady at about 3k, where it had been running the whole time. After a few more seconds, it will just die. It won't slow down or sputter, it just dies. It is like someone turned the ignition off.

But it gets weirder. It will refuse to even give a sputter after this happens. I could crank on it until my battery died and it wouldn't do a thing. If I wait an hour or two, until it cools down, it will start right up and do the same thing all over again.

Here is what I have done so far:

Yes, there is gas, and it is at least getting as far as the carbs.

I checked the spark on all of the plugs, they all spark, quite well actually. But, there is something interesting it noticed. The plugs for No. 1 and 2 were paper sack brown colored, something I had always taken as a good sign, at least on my two stroke dirt bike... but no. 3 and 4 were dark colored, not wet, but they were dark. I found this odd because 3 and 4 belong to different coils...

I was suspecting an ignition problem, so I then checked the resistance of the coils:

Coil for number 1 and 4
Primary: 5.3 ohm
Secondary: 31.5k ohm

Coil for number 2 and 3
Primary: 5.3 ohm
Secondary: 29.7k ohm

The service manual says that the primary should be between 3 and 5 ohm and the secondary should be between 30k and 35k ohm if I remember correctly anyway.

The coils are not perfect, and really should be replaced, but they had always worked up until now without a single problem. Isn't it odd for coils to go all at once like that?

Also, the bike will not idle anymore, it won't run below 2k.

I suspect that the bike is ready for coils, but I have gotten some great advice from you guys before and I wanted another opinion. Do you think that the coils are the problem? It is a 1982 bike with 17k miles, all original. It would make sense if it was ready for coils.

If so, I am open to any recommendations as to where to get them. I am a college kid and well, money isn't exceedingly plentiful so I would rather not be faced with needing a pair of $75 (guess) coils. I had read somewhere about using honda coils to replace the suzuki ones because the honda coils were almost identical and way cheaper. Although I really have no gauge of how valid that statement is...

Any help will be greatly appreciated. My goal is to get my bike back on the road ASAP, my car is too much of a fuel hog.

Thanks!

[Charlie G]

Have you gone through the carbs yet? I would start by making sure they are in good order.

Charlie G

[5azzmonkey]

Before you spend a lot of money on new coils have you looked at the carbs?

Were the carb boots replaced, you could have a leak causing a lean situation?

Have you checked the fuel petcock, does it run ok on prime?

When were the carbs completely rebuilt (dipped properly) with new o-rings?

-Dave

[rcklobster]

The carbs were rebuilt, with new gaskets and rings. However, the boots were not replaced. And also for the record, there has always been a lean spot from about 4k to 5.5k revs. I couldn't really figure out why. The exhaust is original, but very loud. I believe that it has been pretty much burnt through, or someone has tampered with it in the past. Because of this, I hypothesized that it might need to be rejetted to 115's because of the extra flow through the exhaust, and that was why it was lean in the midrange.

I did forget to mention one thing that might also shed some light on the issue.

After checking to see that there was a spark on all of the cylinders, I primed the motor directly by squirting a small amount of gas in through the spark plug holes. (no where near enough to flood it) I was hoping to get a sputter, but I got nothing.

If it were the carbs, would you say that 3 and or 4 were the ones to be most concerned with, considering that is where the motor was popping?

[Matchless]

Clip a strobe timing light over the HT leads to see if spark is missing when she refuses to start or pull a plug and physically check.

Your carbs are probably the culprit. Were they soaked in carb cleaner and every orifice probed during the rebuild?

[BassCliff]

Hi,

The coils look like they are "close enough" so as not to be the problem. Have you gone through the maintenance lists in your "mega-welcome" and the supporting documentation I've collected on my website? Everything starts with clean carbs, adjusted valves, and a healthy charging system. Most bikes need new intake boots and O-rings, and the airbox needs to be sealed. Don't forget fresh fluids, clean filters, etc. Here, let me just copy and past the "to do" lists here:

(Quoted from our good friend and GS guru, Mr. bwringer)
***********************
Every GS850 [and most other models] has (or had) a set of well-known issues that MUST be addressed before you have a solid baseline for further troubleshooting. It's a vintage bike, and it's quite common (as in, every single GS850 I have had contact with) that there are multiple problems that have crept up and slowly gotten worse over the years. It's not like a newer vehicle, where there's generally one problem at a time.

These common issues are:

1. Intake O-rings (install NEW OEM or Viton only - common nitrile O-rings will quickly deteriorate from heat)
2. Intake Boots (install NEW -- these cannot be repaired)
3. Valve clearances (more important than most people think)
4. Carb/airbox boots
5. Airbox sealing
6. Air filter sealing
7. Petcock (install a NEW one)
8. On '79 models, install new points or Dyna electronic ignition (or at least verify that the old points are working correctly)
9. On all models, it's fairly common to have problems with the spark plug caps. These are $3 or $4 each, and often worth replacing if you're keeping the stock coils/wires.
10. Stock exhaust with NO leaks or holes -- good seals at the head and at the junctions underneath.

What I have noticed at the rallies is that very, very few 850Gs are actually running right. Make VERY sure it's actually running the way it's supposed to before busting out the modifications.

Brian's E-Z and fun plan for GS850 happiness:

1) Seal the airbox and air filter with weatherstripping.

2) Ensure no intake leaks. Spraying WD-40 or water doesn't tell you much, since very small air leaks can cause problems even though they won't suck in enough WD-40 to make a difference. Replace your intake boot o-rings and boots if needed, and seriously consider spending the lousy $28 for new airbox/carb boots.

3) Ensure clean carbs with correct settings, new o-rings, and original OEM jets. No, not just squirted with something. I mean completely disassembled.

4) Check/adjust valve clearances (Manual calls for every 4,000 miles. This is not optional.)

5) Ensure healthy electrical system.

6) Seriously consider upgrading coils and plug wires.

7) Install new, stock NGK B8-ES plugs gapped to .031".

8 ) Fine-tune float height and idle mixture screw to ensure best off-idle transition.

9) Clean air filter and reinstall with only the lightest oil mist -- over-oiling and/or letting the filter get dirty is a common and critical mistake, and will make the bike run funny at low speeds and run rich. This may take a few tries.

10) Make sure the exhaust seals are sealing.

11) Ooh, much better now, huh? You're gonna need upgraded suspension - Progressive or better fork springs and shocks. Set suspension sag appropriately.

12) Upgrade brakes with new pads and stainless lines to deal with all that extra speed.

13) Install new petcock, since I'm going to head to the roof with a rifle if I have to read about yet another #2 plug fouling and failed hillbilly attempts to rebuild the petcock and/or deny there's a problem.

14) Oh yeah -- check compression somewhere in there to ensure the valves and rings are reasonably healthy.

15) You'll probably need new OEM clutch springs -- the clutches last forever, but the springs get tired after 20 years or so under pressure. E-Z and cheap.
****************************

Please note that your bike uses different spark plugs. But everything else is applicable.

Thank you for your indulgence,

BassCliff

[TheCafeKid]

Plugs: black as in black and chalky/fluffy or black and shiny/oily?

The former will mean you could be having a petcock issue, float sticking, or are just overly rich (but they'll also colour that way if you keep the "choke" on a lot) or a few other things, but the later would mean you have oil passing seals or rings somewhere. Any smoke from the pipes?

Obviously you need to do the things that were not done, carb boot Orings, sealing the airbox etc. While I understand money is tight, not doing them may end up costing you more in the long run. Intake leaks cause lean running conditions and aren't controlled. They'll get worse, the bike will run worse, hotter, and then you could end up with lots of burnt bits in your engine. Ya don't want that. A valve adjustment (I only scanned your "DID" list, sorry) would be a wonderful idea if you've not done it already.

When diagnosing problems, the quickest and surest way to find the culprit is to start from a known good base. Otherwise you're hunting and pecking, doing multiple things at once that may or may not help, or could make things worse, but since you've done so many things you don't know what made it worse. See what I'm getting at? I made these very same mistakes when I first started wrenching...getting impatient and wanting to ride or get the bike done so I could move on to the next. But i soon figured out that it was actually slowing the process, and causing many a headache and bout of wrench throwing frustration.

Get to your known good baseline (carbs clean, intake/exhaust leaks dealt with, valves adjusted, electrical components checked/cleaned, greased) and move from there my friend. You'll likely be surprised at how many symptoms you're describing get checked up...whittling your problems down to one or a couple of easy to figure out ones.

[bwringer]

I still find it somewhat startling every time Basscliff posts my "list" rant.

"Hey, that looks familiar. That guy really knows what he's... oh yeah."



Anyway, I have little to add aside from re-emphasizing that you need to check the valve clearances, your exhaust is one big leak that rejetting may or may not cure, and you very, very likely have developed intake leaks.

Also, you need to do a compression check somewhere in there. You may have some burned valves from running around with a leaky exhaust and intake. DAMHIK...

Maybe we need to amend the "list rant" to include a line saying "If your GS isn't running perfectly, stop riding it and solve the problem or your lovely vintage motorcycle will hurt itself, and you will become sad."

[tom203]

Well, if it ran in Sept, I'll guess your carbs were adequate after your "rebuild". If it suddenly dies, maybe the ignition is cutting out.Those coil ohm readings are close enough, but I think you should check the connections from signal generators to ignitor-then there's the plug that connects ignitor to ignition coils ( under seat right side) might need attention; it has to have decent connection to the coils.Also, if you pull the wiring diagram off Basscliff's, you can see where to attach a jumper wire to power the ignitor directly via the accessory fuse- this will bypass the key, kill and clutch safety switches in case one of these is behaving oddly.

[BassCliff]

Hi Brian,

I still find it somewhat startling every time Basscliff posts my "list" rant.

"Hey, that looks familiar. That guy really knows what he's... oh yeah."

I usually give you credit, but I forgot this time. I'll fix it.



Thank you for your indulgence,

BassCliff

[BigD_83]

Hmmm,

Your symptoms seem similar to mine. 1/2 dry and tan, 3/4 wet and sooty and intermittently running on cleaned and adjusted carbs.

I was in the garage fixing a throttle cable problem and decided to fire it up to investigate the lack of fire on the right side. Bam...all four cylinders firing. I noticed after I started adjusting the fuel mix screw that the caps (previously checked for proper resistance) were not fully seated on the plugs. Pushed them down, and uh-oh...no fire on 3/4. I know I have read about cracking ceramic insulators and caps somewhere on this or another forum, and that pulling the caps off improved the situation. I pulled them off a little, and running again.

If you haven't already, swap your caps around to see if you can replicate the situation on your 1/2 cylinders and see if you get fire back in your 3/4 cylinders. There is always the possibility there are small cracks in the wiring or caps.

Also, there is a very recent thread about looking deeper in the wiring harness, but in that thread the OP has the classic 1/4 or 2/3 not firing situation.