Fast-fouling plugs mystery. Suggestions?

[Guest]

Greetings,

Just checking to see if any of the following symptoms immediately point to something more specific than the obvious, as I'm guessing that the mechanics at the local shop have already been trying the obvious solutions.

The patient, a 1980 GS400ET, ridden not nearly as often as I would like, generally a few hours on weekends and significantly less during the winter (I don't mind the cold, but won't ride when there's salt on the roads.) Currently at about 60,000 kms.

The earliest sign of trouble (and this may be unrelated but I figure I'll include everything) was a change in behavior during start up this summer. My 30-odd years of past experience with this bike is that it takes about an 80% draw on the choke lever when I first start the cold engine to get a roughly 2000 RPM engine speed, and then after three or four minutes, the revs increase and I can close the choke and pull away. During the summer I was increasingly having to juggle combinations of both choke and throttle to get the engine started and running, and no matter where the choke was set, if I let go of the throttle the engine would die. (While on the road at normal cruising speeds, everything was fine.)

A standard tune up mid/late last summer seemed to fix the starting problem, but after a few rides, the engine started coughing and sputtering at idle in a way that one gets the impression that Harleys are specifically tuned to do. (Still fine at cruising speeds) Back to the shop, and it was deduced that the ignition points needed some attention, and everything seemed alright after that.

But again after a few rides, more changes. Now when starting the cold engine, instead of having to set the choke at about 80%, in fact the engine would be racing until I almost completely closed the choke. And on a ride in mid December, after one of these very energetic starts, after about 6 km I had to give the bike increasingly more throttle just to keep the same engine speed. I pulled into a parking lot and took my hand off the throttle, and the engine died immediately. All attempts to restart either by battery or by bump start were unsuccessful.

Bike was picked up and taken to the shop, at which point it was diagnosed as being loose battery contacts - leading to intermittent sparking to the point that the plugs were fouled beyond the ability to fire. This struck me as odd, because the connections seemed to be tight when I removed the (long in the tooth) battery to recharge it (in case that had been the original problem), but after they put a new battery in, replaced the spark plugs, and test rode it, it seemed to be fine so the bike was dropped off again.

One ride three weeks ago circling around the city close to 'home base' (a heated self-storage bin) for about 45 minutes, and apart from the fast start, all seemed normal during riding. Then this morning I went over to just run the engine for a few minutes since the bike been idle for so long (something I've done for years during winter months when the roads are 'un-ridable' just to move some gas through the carbs and shift the oil around a bit). After another overly enthusiastic start (almost no choke required), after about 5 minutes I again experienced the situation of having to give an increasing amount throttle to hold the same RPM. Soon, taking my hand off the throttle would again lead to the engine dying immediately (while I was able to restart, no doubt because of the brand-new battery, it still wouldn't run if I took my hand off throttle).

When the engine had cooled a bit, I took the left side spark plug out and saw it was completely black and coated in carbon deposits - this after less than an hour of engine running time. (The plugs are DR8ESLs, which, when I look back at decades-old maintenance sheets, are what the bike has always used, so presumably, they aren't the problem.)

So that's the saga. I know the obvious choices are overly rich fuel mixture or ignition problems, but I'm guessing those were also be first things the mechanics investigated, and I would think that if either of those were extreme enough to kill the engine within an hour they'd be pretty easy to spot in any event. I also can't help but wonder if this change in the cold start choke behavior is related to the problem with the fouled plugs down the road.

Any educated or based-on-hard-experience guesses would be appreciated, if only so that I can make suggestions when the bike is picked up the next time.

Thanks in advance.

[tom203]

While I digest this, are you sure this bike has ignition points - our 1980's had electronic ignition (no points to "need attention" ) ?
Do you have a vacuum operated petcock? does the vacuum line connect to left carb?

[tkent02]

I would suggest doing all of the maintenance that has been neglected or done by some shop that doesn't care about it, and do the work yourself so you know it's been done right.

All of the maintenance, adjusting the valves, cleaning the electrical connections, and especially cleaning the carburetors properly, and all the rest.

If that's not an option get a newer motorcycle.

Quit running it in the winter if you are not going to ride it. Put it away properly and leave it alone until spring.

When things change, there is a reason. Find it. Don't wait until it fails completely.

Post your location, there are probably some forum members nearby who would be happy to help you figure it out.

[shinzon1]

Tkent has it right. Take care of all the basic maintenance that these bikes require. It's a lot to catchup on, but once it's done you can pick things here and there to do each year. If things have been kept up properly then check air filter for any restriction, valves for proper clearance, and spark to make sure it isn't getting weak. A bad connection can also cause weak spark. You r looking for a hot blueish white spark.

[jharvey]

While I digest this, are you sure this bike has ignition points - our 1980's had electronic ignition (no points to "need attention" ) ?
Do you have a vacuum operated petcock? does the vacuum line connect to left carb?

Yes, apparently 1980 was a 'transitional' year regarding ignition - either the 450s did have it and the 400s didn't, or the 400s changed during the model year. In fact, years ago I had a problem that took longer than normal to diagnose when the mechanic in that case assumed electronic ignition and only later realized it was a points problem.

Yes, vacuum operated. About 6-7 years ago, the old diaphragm gave out and I had a case of the left cylinder not firing (from too much gas) until after the engine got hot enough to 'help things along.' But in that case the left exhaust wasn't expelling exhaust during normal warm up. Currently both exhausts are acting the same from the moment of startup.

Thanks

[Big T]

What did the "tune up" consist of?

It should be

Valve adjustment
New points and condensors
New plugs
Carbs synched and adjusted

What was actually done?

[tom203]

OK, you've had petcock problems in past- maybe again, so rule it out by disconnecting and pluging its connection to carb, (you'll have to run on "PR" to test).
this stuff you said...

"After another overly enthusiastic start (almost no choke required), after about 5 minutes I again experienced the situation of having to give an increasing amount throttle to hold the same RPM. Soon, taking my hand off the throttle would again lead to the engine dying immediately (while I was able to restart, no doubt because " ....combined with fouled plug says that cylinder is overloaded with fuel. maybe bad carb, bad plug firing but check easy stuff first

I'm sure there's plenty of maintenance to check/correct, it's not that hard and no one cares more about your long term friend than you!

[jharvey]

Thanks for the input everyone. I'll try to cover the various questions in one post;

Tuneups and other related maintenance including, carb cleaning and syncing, valve adjustments, air filter check, points maintenance, have all been done during various visits between mid-December and last April. I don't doubt the professionalism of the mechanics at the shop - in fact one of the mechanics working there is the same person who assembled the motorcycle when I bought it 34 years ago, raced the same model for a while, and was 'introducing' the younger techs to it when I dropped it off last spring. But at the same time, like an episode of House, it wouldn't surprise me if something happens rarely enough (especially given the age of the bike) that it might not immediately come to the 'diagnostician's' mind, which is why I was checking here in case something unusual might pop up.

Much as I'd like to have a closer, more personal relationship with my motorcycle's engine, home maintenance isn't really an option in my current living conditions. The place where I park my motorcycle is on a gravel lot and so tightly squeezed between another car and the side of the building that I have to walk sideways once I get off the bike to move away from it - and there is no place in the vicinity where I can move it to in order to have the room to do work on it, and nowhere I can leave it indefinitely in an in-progress maintenance situation otherwise.

For the same restricted-income reasons as my living conditions, I cannot afford to simply get a newer motorcycle. When this one is done so will I be, and I'm acutely aware that as the years pass and the number of age-related failures is likely to increase, there will come a point where I just can't afford to keep it running anymore. And while, after three decades of service, I'd have absolutely no complaints if fell apart like a clown car tomorrow, I still have a very strong interest in keeping it running for as long as possible.

As for winter riding, I generally ride this thing at least a couple of times a month through the winter and have done so for the entire time I've had the motorcycle. I see no reason to stop just because the temperature drops a few degrees, but in this particular case we're in a long stretch roads white with salt, and with no way to thoroughly wash the bike after a ride, I keep it off the roads to protect the chrome. When these stretches have occured in the past over the last 34 years, I do run the engine from time to time if only to keep the carbs from gumming up, and it's a method that's always worked fine. (Along with Stabil.)

The type pf petcock that this bike uses doesn't have a PRime position - only On and Reserve. I have the same feeling that the cylinders are just getting too much gas - but I guess (at least until my income improves to the point that I can move somewhere with room to do the work myself) I'll have to let the folks at the shop try to figure out why.

Thanks again

[chuck hahn]

Also clean all the connections from the harness to the coils, frame grounds, and freshen up the boot to wire connections by snipping the ends back about 1/4 inch and rescrewing the caps on tight.

Also, if they are stock caps, youve probably got resistors in them.Look into the boots and youll see that the brass plug connectors are slotted. Unscrew them and dump the resistors out and replace them with the same length of 1/8 inch brass or copper rod. There is no need for the resistors in there really.
Note that numbers 2 and 3 have a spring that goes in first, then the rod, and then the brass thing screws in. 1 and 4 do not have the springs.

[koolaid_kid]

If your petcock has a small brass screw on the side, that is your prime.. Simply open it slightly to prime.

[chuck hahn]

Be sure the plugs are gapped correctly too.

[tom203]

Get yourself some clear vinyl tubing (hardware store, aquarium supply) to fit snugly on petcock's vac fitting. Suck on opposite end and watch for signs of petrol headed your way. You need to rule out the petcock as a problem.
Post your location -might be a member near you!

[jharvey]

So, the bike was picked up this afternoon and I suppose in the next few days I'll find out what was the cause for the problems.

Electrics (checking that connections were secure, multimetering, etc.) were checked when it was in during December. Of course, this doesn't rule out an intermittent problem, and if I had the space to work on it, I'd like to eventually replace all the wiring - if for no other reason than that the existing wiring is 34 years old - but that's not feasible at least for now.

I mentioned the past petcock problems (this was successfully dealt with at another shop that I lived much closer to for a while), and added an observation of my own regarding the air filter.

It's a shot in the dark, but between now and the last time the filter was checked during the summer, the foam has started to deteriorate, and what should be a smooth surface now has a few minor craters in the side towards the engine. (It's old enough that I'm not surprised by this, but during the summer it still looked to be holding together.) Anyway, whatever fragments came away from the foam were small enough to not be caught by the steel mesh between the airbox the carburetors, so presumably they got at least that far. Presumably if they got THROUGH the carbs and valves, they would've just been burned up in the cylinders with the gas, but I suppose there's always the chance that some fragments might have got stuck before incineration and started to gum things open.

Probably not the cause, but you never know. I'll post here when I get the final diagnosis.

Thanks again for all the input.

[duaneage]

I think the diaphram in your petcock has sprung a leak and is pouring gas into that cylinder.
Remove vacuum line from petcock and plug it with a screw.
Set petcock to PRI
Test bike. If gas starts to run from the open vacuum port on the petcock shut the engine off ( safety first) and there you have the problem.
Rebuild or replace it as you see fit. I would rebuild it.

[jharvey]

Months and Months Later, and probably forgotten...

...but I said I'd share the final diagnosis, so JUST in case anyone was still curious...

It took a month or so for the necessary parts to arrive, and when I got it back, I wanted to have a dozen or so hours of riding time before I was confident that the fix worked (and I've been having an unbelievable string of bad luck when it comes to good weather on days off), but those hours are in now, and as you'll see from the before and after image below, the plugs are back to indicating a proper fuel mixture and combustion.

The final fix was essentially a carburetor overhaul/rebuild , with jets, needle valves, gaskets etc. replaced. But from what I gathered, the main culprits were probably the floats, which after all these years weren't quite as buoyant as they used to be and weren't completely cutting off the fuel supply when they were supposed to.

Petcock and diaphram were still operational (a similar problem some years back (though it was only flooding the left-side cylinder) was traced to a leaking diaphram), but showing age. And given the likelihood that such parts would be even more difficult to find even another year or so down the road, I had it replaced as well. (To their credit, since they didn't find and fix the problem first time around, the shop discounted the parts and didn't charge anything for labour on the return visit.)

So after enough hours of riding to feel the fix is permanent, the plugs look good, startup and choke operations are predictable again, and I can once again take my hand away from the throttle at stop lights without fearing the engine will stall without my babysitting the fuel supply. (And, whatever comes next, I can at least say that I got 34 years of riding out of this bike (milestone passed in May).)

Thanks again for all the input and suggestions way back in February,