running rough under 2000 rpm

Information and questions on GL1200 Goldwings (1984-1987)
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Joined: Mon Nov 22, 2010 5:32 am
Location: Australia
Motorcycle: 2003 GL 1800 Goldwing

running rough under 2000 rpm

Post by loopy » Mon Jul 21, 2014 7:11 am

My 1984 Honda 1200 runs rough under about 2000rpm but excellent on highway running.
Low speed has hesitation when accelerating etc.

How can I fix.

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Joined: Sat Jul 05, 2014 11:53 am
Location: Courtland, Va.
Motorcycle: 1984 GL1200 Interstate
1981 GL1100 Interstate

Re: running rough under 2000 rpm

Post by HawkeyeGL1200 » Mon Jul 21, 2014 8:07 am

The first thing I'd do is pull the plugs and have a look at the color of the electrodes to see if one or more of the cylinders is getting more (or less) fuel than it should. While I had the plugs out, I'd check the tightness of the screws that hold the resistors in the boot of the plug wire. If you haven't changed plugs in a while, it won't hurt to replace the old ones with a fresh set of properly gapped plugs, so you have a baseline to go from.

Next, I'd get a set (if you don't have them) of vacuum gauges and synchronize the carbs to ensure they are balanced. While you're messing with the carbs, you can spray a little starting fluid around the carb boots, elbow flanges (where they bolt to the heads) and linkages to see if you've any vacuum leaks.

I would also verify the rubbers that connect the runners to the elbows are well made up. I loosened the clamps on mine, rotated them to where I could get a good "bite" on the screws with a screwdriver and tightened them as much as I could while the engine was still hot, to ensure they weren't leaking.

It sounds like your fuel pump is flowing enough fuel. I like to run some fuel system cleaner in my fuel every few fill up, because here in the US, the Government mandates we have ethanol added to our fuel.

One other thing that comes to mind is the condition of the air filter element. If the filter element is getting plugged up it will effect low speed running. If yours hasn't been changed in a while, it would probably make sense to change the filter or at least clean it before trying to synchronize carbs.
I am wrong as often as I am right concerning what is wrong with someone else' motorcycle without having seen the machine in person. Guessing with limited information, as to the source of the trouble, is sketchy at best.

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Re: running rough under 2000 rpm

Post by virgilmobile » Mon Jul 21, 2014 2:37 pm

It comes back to the basics too....Spark,fuel and compression...
Divide and conquer...
When the bike is stone cold..start it,try not to rev the engine,just let it idle as best as possible for 7 or 8 seconds then shut it down...
LIGHTLY tap each header...a warm one is a firing cylinder..a cold one is a dead cylinder...

From there you can compare spark,spark plugs and compression between the running cylinder and the non-running cylinder...
Eliminate each part as the cause will lead you to why it's not firing....
Spark,fuel, is out of specs..

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