Topic: Cb750k0 810cc overheating

[turboguzzi]

kind of surprised that nobody is mentioning a key factor in overheating - compression ratio vs octane you are running. you might be running very close to detonation, one qucik test could be using some octane adittive and see if it helps. wouldnt hurt to measure with a pipette how much CR you have in that motor. woulndt want to run more than 10.5:1 - 11:1 for steet use with pump fuel

another factor  could  be a too restrictive silencer, that could kick up temp too.

[BPellerine]

I have run boyer mk111 on twins and the plate never ended up that far one way or the other after timing light.looks wrong but you never know.bill

[AdrenalineReaper]

I have run boyer mk111 on twins and the plate never ended up that far one way or the other after timing light.looks wrong but you never know.bill

Yeah I bumped it back a bit per the instructions I found. But now it starts hard. Still getting hot fast though. Runs a little more sluggish to, I think it really needs more timing still.

[Medyo Bastos]

have you done any plug chops?

[scottly]

I have run boyer mk111 on twins and the plate never ended up that far one way or the other after timing light.looks wrong but you never know.bill

Yeah I bumped it back a bit per the instructions I found. But now it starts hard. Still getting hot fast though. Runs a little more sluggish to, I think it really needs more timing still.

Have you checked the timing with a strobe? Around line 17 of the instructions, they mention locking the part that replaces the point cam to the advancer plate, then, once you determine its proper position with the pickup plate in the center of the slots, filing grooves and such to make the rotor part stay in the proper position. It appears the Boyer was not a "plug and play" system??

[01Thomas]

I run a BB ignition (blue box) on the sidecar (mechanical advance removed).  Mine is set to give 37 degrees full advance.  You need to use a stobe to set the advance timing with a BB.  The initial setup / install is done static using the engine timing marks.

I've scanned mine but this one on the site is in better condition - mine has oily fingerprints etc. all over it...

Here is the install / setup instructions from BB site for the Honda 4 (black box).
http://www.boyerbransden.com/pdf/KIT00055__BOX00014_.pdf

[turboguzzi]

ahem... repeating my question:  do you know how much compression ratio you have in there? pretty important...

[AdrenalineReaper]

No I don't know the ratio, but it gets hot with 87 and 100 octane makes no diff.

[scottly]

I just ran across a short article in Hot Rod magazine about optimum oil temp:
"A quality conventional motor oil will tolerate oil sump temperatures of up to 250 degrees, but starts breaking down over 270 degrees. The traditional approach is to try to hold oil temperature between 230 and 260 degrees."   

[turboguzzi]

No I don't know the ratio, but it gets hot with 87 and 100 octane makes no diff.

ok then. would do no harm measuring it. can be done with engine in place. best on cyl number four wiyh bike on sidestand so air bubbles can get out

[AdrenalineReaper]

Ok I feel real stupid...... Well the problem was a bad gauge the whole time. Bike runs at 180, and I let it sit for 15 min idling and it only got to 220, so it's good to go. Thanks for all your help.

[johno]

Good result man 

[KJ790]

Glad you got it figured out and it wasn't something major. At least it is easy to fix.

You may still want to check your ignition timing with a timing light though, as the timing plate should not be turned all the way to the end of the adjustment. To set up a Boyer ignition you need to put the timing plate in the center of the adjustment range, line the mark on the flywheel up with the mark on the engine case, then put the ignition rotor on so that the mark or hole on the rotor line up with the mark on the timing plate. Tighten everything down in this position, that will get you close enough to get the engine to start. Once started, adjust the timing plate to get the correct ignition timing using a timing light.

[BPellerine]

that's the way I remember it.bill