Power loss on a road trip. Diagnostic help needed.

[MAC10]

I was riding my 78GS1000 on a road trip, and had an adventure. The bike has a stock airbox with a K&N filter, stock coils, and is 1500 miles post valve check up. It has a Dyna S electronic ignition. Spark plugs are fresh this season. It had been running very strongly for the first 500 mile leg of the trip, and had started perfectly for the past 5 years. Carburetor rebuild is due, last one 5 years ago,but no evidence of problems have shown themselves until now.

Yesterday I had just completed the first 150 of a 350 mile trip. This was on 70 mph roads. All was well until three hours in, when the bike began to sputter. It began at 70 mph on a strong 8 percent down hill stretch. Note that this bike rarely gets a chance to run on roads over 60 mph, and this was its first sustained high speed run in about a year. Bike would start, but needed lots of choke, and would not maintain idle without some throttle. Got it 10 miles into the nearest town, thankfully on a strong down grade, and checked it over as best I could.

It acted like it was not firing on all four, or had bad fuel or water in the tank. All four headers were warm indicating all four were firing. Checked all four plug leads, clipped them a bit shorter and reinstalled the caps. Oil was normal with no smell of gas, or over consumption. Strong smell of unburned fuel from the exhaust. Gave it a dose of methyl hydrate to dry the fuel, but this made no difference. There was no backfiring. Petcock was delivering fuel. Running on prime made no difference. Petcock screen is freshly cleaned. At first it would surge to normal power for a second or two, and then back to poor running. No signs of overheating, detonation, or backfiring, but a strong unburned fuel smell. After the first half hour, it stopped surging, and stayed in pig mode.

I eventually abandoned my original trip, after some contemplation and tinkering in the shade, and headed straight for home. I decided given what I could see that no harm would come if I proceeded cautiously, and checked the bike frequently to be sure. I was able to run it on the highway, 40 mph on uphill grades, 50 to 55 or better on the flat or on down grades. 4500 rpm tops. It would bog in 4th gear unless on a downhill, 5th gear was impossible. I stopped to check the engine frequently, and other than pig like performance, could find nothing. Keeping the revs up, it moved and eventually got me home. 5 hours later. I even enjoyed the trip, and learned to ride it as well as possible.

Fuel consumption was double normal rate. I needed to fuel up about every 60 or 70 miles when I hit reserve, instead of the normal 150.

Today, I am going to get to the bottom of it. The first suspect is a blocked carb. What else should I check?

 

[Guest]

Start with the carbs, also check and make sure your timing plate hasn't loosened up and moved

 

[DanTheMan]

I had a coil do that to me on the 1100 due to moisture (heavy rain). It could still be a coil even without the rain. Another avenue would be the ignitor (had that happen too), but it tended to make it run hot. I chased the fuel angle all over, and that wasn't it.

 

[steve murdoch]

The fact that it happened all of a sudden made me think of a dirty gas fill-up.
I would dump the gas[checking for dirt or rust flakes] and also have a look at the petcock especially knowing that you had a clean petcock screen to begin with.
The idea from hjfisk about the timing plate sounds legit as well.

 

[chris032188]

I'm actually having a similiar problem with my gs450.. If you rev it does it bog or does it sputter? Any gasoline in the air filter?

 

[barnbiketom]

if the timing plate is still tight, still check the timing..
cam chain? dyna unit?

 

[Gorminrider]

It sounds like a plug is not firing. Ignition or (second choice), wildly bad carburetion at the cylinder.

All four headers were warm indicating all four were firing

I can't tell from your comment but it sounded like a roadside indication on a hot bike. My personal experience of "feeling exhaust pipes for running condition" is only useful very near a cold start. The engine transmits heat pretty soon after, so I couldn't tell. Even a hand over the muffler to feel for heat is not a definite help, due to crossover pipe maybe.

 

[Guest]

It's not unheard of for a Dyna module to fail. I had one go several years ago. It would run than start cutting out in no particular predictable fashion. A GS1000 will run fine on three cylinders, looses power and sounds odd, but will run. When two cylinders go, it might spit and sputter, but when they cut out altogether the bike is going to stop running. It took about a week for the module to fail altogether.

 

[MAC10]

I just checked the Dyna s ignition. No evidence that any part of it is loose. The felt pen index marks I drew when I set it up are unchanged.

Tomorrow I will pull the tank and continue. I will run the engine with a timing light to verify all four firing.

Thanks Gorminrider-The thought of heat travelling on a hot bike occurred to me. Estimating temperatures of headers on a hot bike is not foolproof, just a quick and dirty observation

Thanks everyone for the suggestions.

I thought of it at first as bad gas, except it happened in the last 20 per cent of a tank, not immediately after filling it up. It was 10 miles into reserve, so nearly empty at the last fill up, so I would expect bad or watered fuel to cause problems right away, not nearly two hours from fill up. Weather conditions were hot, dry and cloudless, so no rain contamination. I ran four tankfuls from different pumps on the way home-no change batch to batch.

If the Dyna S is bad or has failed, how can I test it in my shop?

 

[850 Combat]

Verify that the vacuum side of the petcock is OK while you are in there. It sounds to my like thee is crap in the carbs.

 

[salty_monk]

Sounds like every other fuel issue to me.... (i.e. an ignition one! )

 

[Spyderman]

while your at it check the 2 hoses that let your carbs vent to atmosphere if one is blocked then you have found the issue
if they don't have outside air pressure then they don't work well at all

 

[barnbiketom]

while your at it check the 2 hoses that let your carbs vent to atmosphere if one is blocked then you have found the issue
if they don't have outside air pressure then they don't work well at all

+1 on this

 

[Spyderman]

while your at it check the 2 hoses that let your carbs vent to atmosphere if one is blocked then you have found the issue
if they don't have outside air pressure then they don't work well at all

+1 on this

yup learned this one the hard way on a trip through the mountains of British Columbia

 

[MAC10]

Had time to start the check up. Plugs 1 and 4 are fouled and black, and smell of gas. To me that indicates an ignition problem, either a coil failure, or the Dyna S left side module. Am I missing other possibilities?

My stock 5 year old petcock has been acting up recently, and I had carbs overflowing. That indicated the petcock is faulty and my float valves are not as strong as they should be. The petcock works, but shuts off only in the reserve position. It only drips in the run position, so that is a short term work around. Could I be getting a rich mixture, coincidentally and simultaneously from carbs 1 and 4? It seems possible, but unlikely. I need to do a carb rebuild this winter anyway.

I can temporarily reinstall my original points system if it is the Dyna S ignition which is the fault. I planned to replace the stock coils with new Dyna coils anyway; if that is the fault I just do it earlier than next season. A pain needing to spend shop time in the last month of my riding season. All part of tyhe fun, I guess...

 

[Spyderman]

well if you want you can try the points plate again and see if its the dyna if not then you need a coil maybe.
but more importantly you need to fix the petcock and change the oil because you most certainly have gas in the oil and that can bring a quick end to your motor.
the petcock and oil and needle and seats need to be fixed right away. this is be cause the fuel is running through the carbs into the engine when the bike is shut off it may right now be not leaking in the reserve position but if it leaks in the run position when your not riding then it will soon be leaking in the reserve position too

 

[btbarb]

I've seen VM carbs overflow and not really notice a power loss or idle problem and other times i've seen them overflow and make it impossible to hold an idle and basically shut the cylinder down at any throttle position. Maybe it's as simple as your petcock and seats and you're only running on 2&3 and at that, degraded. You mentioned your mileage was half of what it normally is, even crappy tuning won't cut your mileage in half, would assume you'd have to be dumping fuel to cut your mileage in half.

 

[MAC10]

Thanks guys. I understand my Vm29 carbs have drain tubes to handle carb overflow, so it does not go into the crankcase.The gas was dripping out of them. I checked the oil, there was no smell of gas, but I changed it anyway as a precaution. Not a good situation regardless. I need a new petcock.

Now that I have inspected the plugs and 1 and 4 are the culprits, then the 50 per cent reduction in fuel mileage is explained. Half the fuel was being blown out of the engine unburned. Two cylinders worth wasted. Ran on two cylinders and made it home. What a bike!

I will pull the carbs as time allows, and remove the bowls to inspect everything. When I do the rebuild, needle and seat replacement on all four makes sense, along with everything else.

 

[Guest]

A module failure is unpredictable, some just stop, others give you fits trying to figure it out before they quit. If you know anyone with a Dyna-S, swap the plates to eliminate or confirm the problem. Change your plugs, they can fail from fowling. You don't need two conflicting problems going on at the same time.

 

[MAC10]

I am focusing on the coils or the dyna s as the probable culprit, given that cylinders 1 and 4 are getting fuel but not firing. I have limited time right now, so work on it as I can.

I checked the coils with a multimeter:
Left coil, which runs cylinders 1 and 4- plug wire to plug wire, caps off 12.2 ohms
between orange/white and white 4.4 ohms

Right coil which runs cylinders 2 and 3- plug wire to plug wire , caps off 12.4 ohms
Between orange/white and black 4.5 ohms

These are within spec.

I set up my old points plate, and noticed that the left set of points does not turn off. The static timing light I am using stays lit whether or not the points are open. The right hand set of points, which runs 2 and 3, go on when they are open and off when closed as they should. The points plate was running well when I replaced it with the dyna, so it is a known good part.

Does this indicate a short somewhere?

I am moving this question to the electrical section, to keep it relevant.

http://www.thegsresources.com/_forum/showthread.php?226622-Coils-Dyna-S-diagnosis-help-needed