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Bike: 96 Intruder 1400 with baffled straight pipes. Had it for 2 months. Carbs were already drilled for mixture adjustment. Starts right up and runs great at low and mid range, but above 60 MPH the response is kind of flat and rough. It will certainly go faster, but it just doesn't sound that smooth and the acceleration is poor, again above 60. The seller claimed that the carb jets were "all set" for the straight pipes, but he was kind of a hack. The plugs look nice and clean. Does it sound like I should re jet a size bigger?
Thank you kindly, and again, Intruder 1400.jpg thanks for having me.
 

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If the engine is breathing easier then you need bigger jets/carbs. What size carbs is it running and do the main needles have adjustment via a clip and groove? If not you can slip a small thin washer under to raise the higher rpm fuel supply. The only problem with doing this is the mid range may suffer. Idle is taken care of mostly by the idle circuit and jets. If the bike has CV carbs there may be a problem with the diaphragm in the form of a small hole. Sometimes the return springs can get 'cocked' over or tangled preventing the slide from rising fully.

You may want to check the carb syncronisation...if one carb is rising more or sooner than the other the engine speed will struggle and feel hesitant/lumpy and performance will be lacking.

You may also want to check the emulsion tubes if fitted...usually underneath the main jet...for clogging. These introduce extra air into the system via tiny holes as the needle rises and the main jet comes more into use. Sometimes a bogging down is due to too rich a fuel ratio. Finally what condition is the air filter and is it standard? What about fuel filters and fuel tank venting?

Before doing any of that I would run some good quality carb cleaner through it and leave it overnight. Any improvement will tend to indicate blockages somewhere and may need more than one treatment. It is certainly a lot easier than pulling carbs down.

Good luck
 

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but he was kind of a hack. The plugs look nice and clean. Does it sound like I should re jet a size bigger?
This is a slippery slope.

The "adjustment" under the plug is for low speed only.

My suggestion is that you find some stock pipes and start there.

But a good independent shop should be able to test it and tell you what needs to be done.
Often pipes that flow better need an air intake that flows better too......for good performance.

If the PO didn't change the main jets, then that probably explains your present problem.
 
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