Motorcycle does fine in 1st through 3rd but when I hit 4th and 5th at around 60 MPH, there is resistance to speeding-up. Got up to 75 and then the motorcycle started slowing back down. Only other thing I have noticed is that number three plug is black while the others seem fine (all plugs are new). Any suggestions as to what the problem might be?
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Running out of gas? I think a bit more detail is needed. How has the bike been running up till now? -
No, has fuel. No major issues except using more fuel than in the past. Sometimes a little backfire. It's just when you open the throttle in 4th and 5th, it seems it is working against something to speed-up. I was on the highway doing 75 and then it started slowing down back to about 60 and then fine. When I have adjusted the fuel/air screw on carb three to lean it out, it appears to do nothing--not even affecting the idle.Comment
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Sounds like it's time to clean out the carbs and remove the (possibly) broken tip of the mixture screw.
One more item: are you sure it's #3? Carb 1 is under your clutch hand, carb 4 is under your throttle hand.
Many times, new guys get them numbered backwards.
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mine: 2000 Honda GoldWing GL1500SE and 1980 GS850G'K' "Junior"
hers: 1982 GS850GL - "Angel" and 1969 Suzuki T250 Scrambler
#1 son: 1986 Yamaha Venture Royale 1300 and 1982 GS650GL "Rat Bagger"
#2 son: 1980 GS1000G
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It could be a number of things starting from clogged air filter to carbs needing a rebuild. What maintenance have you done on the bike? And Steve's right, if you're adjusting the mixture screw and it's not effecting the idle it does make you think there's an issue in the carbs, but start with ruling out the easy things first.Comment
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Definitely #3--throttle side. Will check out the mixture screw as you suggest. Do you think that would explain why only #3 sparkplug is black while the others are tan colored?Comment
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if it is #2....not #3 then i would remove the vacuum hose and see if fuel is running out of it.
if so then the fuel valve is bad and fouling that plug/letting in huge amount's of gas into that cylinder.
i ass/u/me these shaft bikes feed the vacuum the same as a chain driven model.Comment
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It is #3 not #2. The petcock was replaced in 2011 but that does mean it is still good. However, no leaking of fuel.Comment
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to much fuel.
to low of compression.
no/weak spark but this happens normally in pairs.
checking the compression when hot and plugs out and throttle wide open(strong battery) may show you something in the bad hole.Comment
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When you say this happens in pairs would it normally be like 2 & 3 or 1 & 4?Comment
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Have you checked the spark on all 4 cylinders? carbs that are 'properly' cleaned should last for years. Possibly it's a spark issue.Comment
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Plan on running some electrical tests in the morning, on plugs and coils. Valve shim clearances were recently updated as well.Comment
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