1981 CB750 Build - "Renee"

Got her put together this weekend. More pics on the blog, but here are my favorites. And should mention that my wife's a badass for being so supportive and putting up with all the time I've spent in the garage.

Still some work to do, but plan on riding her for a bit to work out the kinks, mess with some paint schemes, then do it all over again.

Before


After

Hell ya!!!

Man thats a sweet machine. i really dig the seat and risers. why so many pieces of tube in your hardtail? i have a thread on an 81 cb750 as well. Check it out. would be cool to see what you think of it.

Any idea of who you are going to have paint it?

Chemical Candy in Austin does some cool shit!

Originally Posted by Irish669

Man thats a sweet machine. i really dig the seat and risers. why so many pieces of tube in your hardtail? i have a thread on an 81 cb750 as well. Check it out. would be cool to see what you think of it.

Thanks. The hardtail was a trial and error process to fit the larger rear tire...and I don't have a bender, not the best way but it works.

Originally Posted by RuffShod19

Any idea of who you are going to have paint it?

Chemical Candy in Austin does some cool shit!

No idea man...I'll check em out for sure. I'm trying for this winter, but we'll see how the cash is.

First need to figure out these carbs. I'm running very weak in the mid range. Already rebuilt em, should I try replacing the old vacuum lines and syncing the carbs? How do the plugs look?

I'm not exactly a motor man, but it looks like you are runnin a little on the lean side. Have you rejetted?

I haven't...still running the 102/68 setup. Found these posts that were very helpful:

http://deuceswild.yuku.com/topic/5/FAQ
http://www.chopcult.com/forum/showth...c+small+issues

Going to get some larger jets in there (110/75 seems like a good start), and hopefully be running strong soon! Thanks for all the help.

Jesse

Had my first breakdown! What a blast. Motor was pulling stong, still a bit lean I think. Then she started to miss and eventually just cut out. Smoke was coming from the electrical box so I pulled out the electrical and the main fuse was melted. Could running lean cause the main fuse to blow?

Had the wife bring me some tools and was able to fix it and limp back home. Just kept the revs low and she did fine. Any ideas??

The lean mixture shouldn't have caused you to blow the fuse. I'd look at the grounds and make sure the regulator is working.

Also try taping off a little bit of the pods too to restrict the airflow just a little bit.

Looks like you had a nice one to start with, Looking even better now though!

looking at the spark plug, it doesn't look real lean on fuel, but if anything you are a little rich on the oil jet.

Seems to me if it got hot....and didnt pop the fuse.....the voltage regulator is bad.

Fuse would have popped due to higher amperage, so the only thing other than that is higher voltage. Higher the voltage....the lower the amperage.

M2C

Originally Posted by rustrocket84

The lean mixture shouldn't have caused you to blow the fuse. I'd look at the grounds and make sure the regulator is working.

Also try taping off a little bit of the pods too to restrict the airflow just a little bit.

My air/fuel screws are 2.5 turns out right now...going to back them out as far as 3.5 and see if that helps. If she's still lean will tape them off...saw you mention this to another feller and seemed to work for him.

Originally Posted by SLAUGHTERWHORE

Looks like you had a nice one to start with, Looking even better now though!

Thanks!

Originally Posted by riceburner

looking at the spark plug, it doesn't look real lean on fuel, but if anything you are a little rich on the oil jet.

Think that pic is kind of deceiving...hoping a few more tweaks will solve the problem

Originally Posted by RuffShod19

Seems to me if it got hot....and didnt pop the fuse.....the voltage regulator is bad.

Fuse would have popped due to higher amperage, so the only thing other than that is higher voltage. Higher the voltage....the lower the amperage.

M2C

Gotcha...I think something just shorted in the elec box. Going to pull the guts out again and see what all got hot and where.

Just an update: sorted out the electrical...it was an undersized wire to from the solenoid to the battery terminal on the key switch...the wire got too hot and shorted out causing the main fuse to blow.

Yesterday I went for a longer run and started to lose power after about 20 minutes of riding. Got home and pulled the plugs. Is it spark, compression, or carbs?...I hope to find out soon.

Symptoms:
- flat spot / gurgle at mid range
- leaking valve cover gasket
- lots of corrosion on negative battery terminal
- #1 and #2 plugs look good, #3 plug lean, #4 plug fouled

Next steps...what do yall think?:
- check compression
- check alternator charge to battery
- sync carbs

By the way, love this bike; love the feeling of riding something so personal, and love the stares I get on the road. Thanks for the input.

Jesse

"Dry" Compression Test
Cyl 1 = 120 psi
Cyl 2 = 129
Cyl 3 = 134
Cyl 4 = 140

Charging System Test
@3000 RPM 14.0 Volts accross battery

Valve Clearances (spec calls for 0.002" - 0.005")
Cyl 1 Intake = 0.003" / 0.0025"
Cyl 1 Exhaust = <0.0015 / 0.004
Cyl 2 Intake = 0.003 / 0.0025
Cyl 2 Exhaust = 0.0025 / 0.003
Cyl 3 Intake = 0.003 / 0.004
Cyl 3 Exhaust = 0.003 / 0.0025
Cyl 4 Intake = 0.004 / 0 0025
Cyl 4 Exhaust = 0.003 / 0.003

Next Steps
The clearance on the Cylinder 1 exhaust valve in nonexistent...waiting on the tool / new gaskets to replace the shim and button her up. This may also explain the lower compression on Cylinder 1 and why my valve cover gasket is leaking (blow by from the cylinder 1 combusion?). Hopefully it also explains the flat spot in my mid range and the loss of power after 20 minutes of cruising. Ready to move on to fine tuning and syncing the carbs!

Small update: got the clearance on the #1 valve sorted, brought compression up to 130 psi. Replaced the valve cover gasket/grommets and had to RTV the tach hole since it was leaking and couldn't find a new gasket.

I taped up 1/3 of the pod filter (per rustrocket's suggestion) and turned the air/fuel screw to the recommended 2.5 turns out. Also had a chance to sync the carbs. This was pretty damn tedious, my boss lent me an old mercury filled sync tool which helped, but still took about 30 minutes to get just right.

Hope to test ride soon to verify no more leaky valve cover and, most importantly, see if that flat spot is taken care of. Keeping my fingers crossed.

I write this broken down, half way to work.

The valve clearance seemed to help the flat spot, but still losing power after 20 minutes of riding. And there's oil leaking from cam covers and the cam chain tensioner, but only after 20 minutes of riding.

I'm not sure where to go now. Previous owner had an oil cooler, is she getting too hot? Alternator read 14V at 3000 rpm, is the charging system weak? Anything will help...

Been at it for a couple weeks and making progress, almost 100%. Been through the entire charging system, replaced many gaskets, removed and bypassed the vacuum operated petcock, and going through the carbs for a 3rd time now. Getting some help from the guys at cb750c.com (although they hate the pods) and some guys around town (mechanic Jim at the salvage yard was a huge help).

Here's a video of me puttin' around town, that flat/lean spot is what I'm working on now.

Great work!! Love it!

Great work.

I like the bike and the stance.

With your skill set, I would have liked to see you fab up a different fuel tank.

Just my .02 cents...which is worth nothing...