Top speed issue?

86 interceptor 500 , runs great all cylinders are firing, spark plugs also look good- might be running slightly lean, but I prefer that. BUT top speed is only 105 mph - seems like it’s dogging from about 90mph on up.. What do you guys think?


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First items that I would check are the Air and Fuel filters.

 

Both are good and clean..


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Has this been a recent developement? How many miles are on it? Stock sprocket gearing?

 

Time for a compression test. low compression=low performance.

redlining an old 500 poses a risk of valve damage, engine blowup.