Author Topic: 67 bs 90 moumtain  (Read 1089 times)

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Offline montanabike

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67 bs 90 moumtain
« on: October 16, 2016, 01:35:29 PM »
 67 bs 90 mountain ,acquired recently. great shape for age .one problem I haven't figured out that is plug will not stay clean very long .it has oil injection.starts missing after short ride.has 85 lbs compression cold .am using ngk 6 plug.doesen t seem to be flooding. I think the oil pump had been replaced .is there any adjustment on that .any body got ideas? thanks

Offline OldSwartout

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Re: 67 bs 90 moumtain
« Reply #1 on: October 16, 2016, 06:12:14 PM »
There is an adjustment.  The 50-175 Service Manual available for download from this site says: When the carburetor adjustment has been made, the oil pump control should be checked and adjusted. With the throttle completely closed, the oil pump outer
cable should have 1/16 of an inch of free play at the oil pump cable stop before it moves the control arm
on the pump from the stop pin. Adjustment is made by the cable adjuster located in the cable by the
transmission oil filter plug.

A fouling spark plug may indicate that the spark is too weak. The contact point surfaces may need to be cleaned up. You should be able to get at least 1/8" spark kicking it through.

Hope that helps.
« Last Edit: October 16, 2016, 06:13:58 PM by OldSwartout »
Karl Swartout
Mooresville, IN
BS175 Roadracer

Offline BRT-GTR

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Re: 67 bs 90 moumtain
« Reply #2 on: October 17, 2016, 03:18:20 PM »
        Compression looks a little low at 85psi. If I've read the manual correctly, should be 120 standard with a min of 100psi. May just need new rings.
       Is the air cleaner blocked, that will give a rich/oily mixture. Try the simple fixes first before delving into the engine.
     There is an adjustment on the oil pump itself which is factory set and shouldn't require attention unless a previous owner has played with it. Intructions in the manual but make sure you fully understand them before making any changes to the's critical to get it right.
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Offline montanabike

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Re: 67 bs 90 moumtain
« Reply #3 on: October 24, 2016, 01:47:16 PM »
 :)hi thanks . did those  things  ,seemed to help  ,but I think it may also need rings,



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