Please Help me Diagnose the Problem!!

[Tim Tom]

So about 3 weeks ago, while riding my '82 850G, after about 2 hours on the road, the bike began to bog and loose power around 4500 RPM. Power would come back in a quick burst around 6k, then it would bog again. In all the gears. I did a valve adjustment, and that seemed to make it better. However yesterday the problem came back, only worse.

The bike ran fine for the first 2 hours of the trip, however on the way home, it started to bog again. At first his time it was only at 4500, the upper RPM's were still smooth. However after about 40 mins, the bogging was happening all over. Also I lost almost all of my acceleration, I had the throttle wide open, and was still not going anywhere. As you can imagine, this is not what you want happening on the North Jersey highway system. You need all the power you can get to stay out of the idiots way.

My buddy riding behind me said the bike smelled of gas. It did. I'm thinking that the carbs are dirty, and so not letting all the gas into the cylinders. Then when it does get through, it is more then usual resulting in the burst of power
Could this be it? Thanks for reading, I love my bike, and want to get him back to running right.

[DanTheMan]

If you haven't done the complete carb cleaning & rebuild as per Basscliff's page you need to. Make sure your petcock is working and not clogged as well. Also, make sure the vacuum line that operates the petcock is on tightly and not clogged. Check you air filter, make sure it and the airbox are sealing properly and that the air filter is clean (sometimes a massively fouled air filter element will cause all the problems you just described).

[gearhead13]

If you havent dipped and cleaned the carbs with new o-rings, I would suggest that you get that done. Could be a bad ignition not burning all the gas as well. Check your plugs how dirty are they, fouled? Check spark to make sure its nice bright blue spark.

[rustybronco]

Check the petcock. both for a clogged screen and for a ruptured diaphragm.

[Danjal]

Check your tank for rust and your petcock filter. The same for any in line fuel filters. Yours sounds like what mine was doing except it started in the middle of a ride. Sadly mine is not a petcock problem. I had rust in the tank, but thats not my problem it seems. Also if it does it again pop your fuel cap and see if that alleviates the problem.

[bonanzadave]

Also if it does it again pop your fuel cap and see if that alleviates the problem.

Yep. All good suggestions. As finicky as these petcocks can be Id switch to PRI right away.....and maybe get off the freeway .

[Tim Tom]

Thanks for the help guys. I replaced the spark plugs when I did the valve adjustment a few weeks ago. My tank is clean with no rust, so that leaves a carb clean, air box, and pet cock to inspect. I was hoping to put off the carb clean until winter but it looks like that plan needs some adjusting...

[bwringer]

It sounds more like there's a problem with one of your coils. Dropping two cylinders would produce exactly the symptoms you describe -- massive power loss, gas smell.

I'd investigate the wiring to the coils and inspect the coils carefully for any signs of physical damage or overheating. Check voltage to the coils, too -- something could be intermittent or marginal in the ignition switch, any of several connectors, or the wiring in between. If the voltage is right on the borderline, one coil might respond better than the other.

If you can locate a spare set of coils (search the forum -- there are lots of alternatives), swap them in and see if that helps.


Perfectly clean carbs are very important, of course, but they don't generally cause sudden intermittent problems like this. And the power loss caused by a fuel delivery problem is generally not sudden, and won't cause the noticeable gas smell.

[Guest]

I'm with bwringer. Sounds like you're losing power to a coil. Mine did that spiratically, could pull on the throttle and go know where. It could be bad wiring to the coils or simply a bad coil. To make testing even more difficult sometimes they won't fail until they are heated up and under a load so it makes testing in the driveway difficult (you could always set up a temporary fuel tank, hang it from the handle bars, have a friend drive the bike and you sit on the bars with your voltmeter!). It always pays with these things to spend an afternoon cleaning every single ground and every single connector, amazing the difference it can make, who know's maybe you'll be lucky and fix a short. Good suggestion to swab a coil out with a known good one.

[gs road racer]

Ditto that now you have three guys telling you go check the coils!Other then the petcock nothing else except near total lubrication failure would cause what you describe.

[SKD]

id break the tie here but im just looking to learn...lol
but both make sense to me.

[Tim Tom]

Good call with the coils. I'll check them today or tomorrow. This does make sense, as the problems only happen when the bike has been running for a while at high RPMs.
How should I check them, with a voltmeter, but what exactly should I be looking for?

Many Thanks

[BassCliff]

Hi,

I found this on some guy's website:

Testing The Ignition System


There's more electrical information here:

*Electrical Odds and Ends*



Thank you for your indulgence,

BassCliff

[Tim Tom]

What next?

So I followed the spark plug test on Basscliff's site (many thanks). I however was not so lucky as to have a wire that came loose. I have spark across all the cylinders. However this spark is very weak, not the bright blue that it should be. Somewhere along the harness I think I am loosing some voltage. I am gonna try to clean the connections into the coils then see if I get a better spark.
Also I was unable to take out the air cleaner foam to inspect this. Is there a trick to removing it?

[BassCliff]

Hi,

Remove the air filter from the airbox. The air filter element should be held onto the air filter frame with a couple of screws.

What is your voltage at the coils? It sounds like you may need the "coil relay mod". But clean all of your electrical connections and grounds first.


Thank you for your indulgence,

BassCliff