Comments on CT90 Restoration Adventures: Honda CT90 Spark Advancer Assembly Build-Up

When adjusting the static ignition timing, tempora...

2020-08-17T18:30:46.544-07:00

When adjusting the static ignition timing, temporarily lock the spark advance cam in the full advanced position ( use a sparkplug washer that is the same diameter as the cam, between the cam and the washer on the spark advance fastening bolt ) and set the ignition timing to between the two full advanced marks on the stator rotor. This will compensate for weak springs on the spark advance unit. When done unlock the cam on the advancer unit to allow it to operate normally.

The motor operates with the ignition at full advance most of the time it is being ridden not at idle. Honda even recommends that to properly set the ignition timing, you need to use a timing light and set the timing to full advance. Check your Honda Trail 90 owner's manual.

Hi Rick, I appreciate your comments and also the ...

2017-10-25T09:14:34.466-07:00

Hi Rick,

I appreciate your comments and also the link to a source for springs. I agree that $27.00 seems like a bit much for two small springs, but in the end if thats what will get your CT90 running smoothly then its really not all that bad.

Mike

Excellent writeup and even with two ST90's, tw...

2017-10-25T04:35:41.562-07:00

Excellent writeup and even with two ST90's, two CT90's, spare engines and extra spark advancers in a sack around here, I have never seen that other style of spark advancer. I definitely learned something there. I have seen that some of these advancers have notches on the back of the counterweight arms that are cut more deeply which allows for the arms to extend further (provides more advance) at high rpm before the arm contacts the stop.

I use a tube of old Bosch distributor lube grease for my spark advancers. This stuff is stiff enough to not melt under high heat or migrate under high RPM. The stuff in the tube appears to be very similar to the grease that goes on the felt that greases the face of the cam where the points rubbing block rides. The Bosch stuff I use in the yellow tube with black letters seems to be hard to find these days.

I have seen quite a number of these advancers with weak springs after they get hot and this weakness fails to pull the arms back in once the engine returns to idle RPM. Replacement springs are hard to find but the same springs are used on the old Honda 750 bikes of that era and Yamiya has them in stock. Quite spendy at 3000 yen (less than 27 bucks USD) here:

http://www.yamiya750.com/index.php?main_page=product_info&cPath=246_21_250_55&products_id=2168

Great writeup!! Should help a lot of people.

Rick