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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?
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?
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