Topic: Early CB750 KO - Start Again

[Johnie]

Update Sept. 10th - I think we are getting closer to getting this #3 issue solved. I removed the carbs again today. Keep in mind my dealer used his expensive ultra sonic cleaner on my carbs in exchange for some venison. I figure all was well, but should have looked closer. Today I noted the small hole at the bottom of the carb plate was plugged. This would be the very small hole located north of the needle valve hole (see pic). Plugged solid. I cleared that up. Then wanted to take a closer look at the intake rubber and was pretty surprised at what I found (see pic). Could not see the cut until I squeezed the intake then it showed up REAL well. Can not get the KO intake from the dealer so I used one I had from a K4 with 5,000 miles on it. Checked it real close. It is thicker than the KO intake, but the fit was fine. So I have it all buttoned back up, but I can not test it as I have my tach seal out waiting for a replacement. That should be here tomorrow. I will let you know the outcome of the test...fingers crossed. I think either one of these issues could have caused this...but add them both and you have a poor #3 cylinder. I also rechecked the compression which was fine. I will let you know more after the test ride soon.

[Tews19]

Yep looks like you solved this riddle Johnie!

[Johnie]

Update and test ride Sept. 11th - those issues outlined above solved the #3 cylinder problem. This KO started right up on all 4 which was nice to hear. All pipes hot and ready to ride. Down the road at 50 mph into a head wind I started to get a miss. I knew what it was as I had it happen on my K1...the float bowl overflow tubes were to long and the wind was creating a venturi effect on the carbs via air pressure. Cut those tubes up higher and problem solved. Warmed it up and did another sync which smoothed it out even more. Put on 100 smooth miles and no oil leaks. Old scrambler knows the PO and says he had the top end rebuilt at a dealer to take care of a leaking head gasket. So this KO is ready to have the newly painted tins installed which should round out this build. I will post pics once the tins are installed. Thanks for all your encouragement and help on this project. It was fun...now I will have to meet up with old scrambler before the snow arrives

[Stev-o]

Good to hear.....looking forward to the pics.

[jerry h]

Good to hear.....looking forward to the pics.

+1   



(The GW is gassed up and waiting to stop over to see the blue beauty when finished!)

[iron_worker]

That hole is where the gas/air mix from your pilot circuit enters the carb throat so yeah that would definitely be a problem. lol

IW

[Johnie]

Thanks for the info...I was looking in my service manual to find out exactly what that hole was used for. So am I correct in that the air screw is connected to that small port?

[CB750faces.com (Lecram)]

The gauges...when I did the red KO in 2007 I ordered the Yamiya faces and covers as LeCram was not around yet. Never can go wrong with the Yamiya stuff. This time I thought I would try LeCram so I can compare. For this current KO I decided to use the original faces since they were in such nice condition with no warping. The only fading seems to be in the red zone which I can live with. I am not after a concourse here. In comparison, the Honda covers and Yamiya covers are a bit thicker than the LeCram covers. So when I put the LeCram covers into the gauge holders they would not tighten down. To remedy this I had to modify an extra set of gauge rubbers to make up for the lack of thickness on the LeCram covers. Once I doubled the rubber thickness they would tighten down fine. The other thing I noticed in comparison of the faces, Honda and Yamiya have the cut-outs for the miles and trip meter painted black on the inside lip. The LeCram has those areas unfinished plastic color. Not a big deal unless you are after the way it looked OEM. I was just going to use a black sharpie to paint it.

Thanks John,

It is true that the part where the rubber get around is slightly thinner. New rubbers fit fine, older rubbers are often thinner and stiffer. Some layers of black tape under de old rubber works fine.
The cut outs of the face plate have the same colour of the base plate. I always use a waterproof black marker to make these cut outs black. That will last for many, many years and takes less than a minute to do this.

Regarding the products of Yamiya (covers and face plates): these are now 100% the same as my products as Yamiya is reselling my covers and face plates.

[Johnie]

Thanks for the feedback Lecram. I hesitated to use the black tape under the gauge rubber because when it heats up in the sun it gets soft. Customizing an extra set of gauge rubbers worked very nice. Is there a reason you could not duplicate the exact size of the OEM covers so customizing would not be necessary?

[iron_worker]

The air screw regulates the air that reaches the pilot jet emulsion tube (the little holes around the base). The air works it's way through the small holes into the center hole of the pilot jet where it mixes with the fuel. The mixed fuel and air then comes up through that small hole in the throat of the carb (the one you unplugged).

IW

[SOHC4 Cafe Racer Fan]

Regarding the products of Yamiya (covers and face plates): these are now 100% the same as my products as Yamiya is reselling my covers and face plates.

Very cool!

[Johnie]

Thanks for the info Iron-Worker! Very interesting...does not tell you that stuff in the service manual

As an update on this 1969 KO project...it is about done. I removed the test tank I have been using to get her all dialed in. That tank is now off and the freshly painted blue / green tank is now installed. Just need to get gas in it and get it outside for some pics in the sun. Pics in the shop just do not give the paint justice.

[SOHC4 Cafe Racer Fan]

Holy crap.  Next month's BOTM is going to be a strong one.

[Stev-o]

Holy crap.  Next month's BOTM is going to be a strong one.

I second that nomination.

[Tews19]

Beautiful! We should plan a ride to your place Johnie to admire your museum quality bikes next summer!

[SOHC4 Cafe Racer Fan]

Beautiful! We should plan a ride to your place Johnie to admire your museum quality bikes next summer!

Johnie has the rideable museum collection!

[Old Scrambler]

A Ride! That's a very good idea..............Let's see...........a ride to Tews garage............maybe 6th and Wisconsin..............then to my friend's house near Menomonee Falls just to gauk at his shed full of 27 CB750s and a few others............then to Johnnie's place for lunch..............continue around Lake Winnebago for a stop at my place (late afternoon beverage)  and home before sunset.

Next week............next June..........

[seanbarney41]

That sounds like a great day in Wisconsin

[SOHC4 Cafe Racer Fan]

A Ride! That's a very good idea..............Let's see...........a ride to Tews garage............maybe 6th and Wisconsin..............then to my friend's house near Menomonee Falls just to gauk at his shed full of 27 CB750s and a few others............then to Johnnie's place for lunch..............continue around Lake Winnebago for a stop at my place (late afternoon beverage)  and home before sunset.

Next week............next June..........

Did any one else catch the comment about 27 CB750s in a "shed"?  That "shed" must be a decent-sized man-cave, garage.  The "sheds" we have out here could max fit a car.

[bjatwood]

Looks great John! 

[hoodellyhoo]

Maybe you should ride that bike to the Crud Run next weekend. Don't worry, I'll let you borrow my fairing so you stay warm for the ride down

Seriously though, bike looks fantastic. Can't wait to see pics of it outside!

[Johnie]

Got the KO out for pics yesterday. Still in the 70's here in WI and great riding weather.

[Greggo]

Looking GREAT Johnie!

[sallen]

Another Fanastic addition to your stable..Looking Good!!...Steve

[Stev-o]

Beautiful, really like that shot by the lake. Is that Winnebago?

How's she running??