Author Topic: My buddy asked me to get his bike running. (Read 10458 times)

thrutheframe · « **on:** March 03, 2012, 10:13:07 AM »

My buddy asked me to get his CB750 F running. I've never seen it, he said its a 77 or 78 and the VIN is:

Rc04-2115365

With engine #

Rc04e-2115077.

Just because I'm crazy enough to think I can get it running HE thinks I can really do it.

Tim2005 · « **Reply #1 on:** March 03, 2012, 10:56:38 AM »

I think RC04 is a twin cam 750.

thrutheframe · « **Reply #2 on:** March 03, 2012, 11:41:48 AM »

Yes. I found that out. If I continue posting about this project I'll move it over to the "Other Bikes" section. The bike fired up on leaky carbs and old gas. It ran but knocked like a cylinder wasn't firing. The carbs are Keihin VBs and gas leaks out of them all over. A clean/rebuild of the carbs and a 3000 mile treatment and she should run real nicely.

thrutheframe · « **Reply #3 on:** March 03, 2012, 03:40:47 PM »

Ahhh moved without my request . Thank you Bob.

thrutheframe · « **Reply #4 on:** April 16, 2012, 08:52:50 AM »

Here is the first "customer bike" to come into my shop. I've done a few repairs for people on a "friendly house call" basis. The bike just needs some TLC, the plan is to rehab and rebuild the entire fuel/air system and do the 3000 mile service.
Step one is a compression test followed by step two, inspection of the slide diaphragms. I have all the carb kits, carb boots, accel pump kit and air cut off valve kits. I'll post pics and questions as I go.

thrutheframe · « **Reply #5 on:** April 16, 2012, 07:08:15 PM »

Got the carbs off, pretty easy. You just have to start with the rear fender and pull stuff back as you go. Couldn't do a compression test, I don't have the small size spark plug adapter, could have sworn that I had one.... Aren't the F plugs the same as K plugs? Also I didn't know that these carbs don't have the rubber diaphragms, that was a pleasant surprise. I haven't really torn into them yet, I'm definitely going to read the rebuild manual that Cliff pointed me to before I go any further.

The trap for the airbox blow by was filled with years worth of water and oil mixture, evidently the drain side was clogged. The carbs themselves are incredibly varnishy. I'll post a pic tomorrow before I tear them down. The air box is in good shape, the boots are in ok to poor shape but that doesn't matter because I made sure the guy bought all new rubber. I didn't take a lot of pics because the guy IS paying me by the hour.

Hush · « **Reply #6 on:** April 17, 2012, 12:00:18 AM »

The DOHC Honda 750 got a lot of bad press when it arrived after the SOHC4 models but they are a pretty good rider for all that. We have tons of them touring NZ and it's a rare weekend when I don't run into one of these 750's.
Owners I have spoken to love them, that one looks in pretty good nick so you may have a clear run with just some cosmetic fixes......have fun.

Magpie · « **Reply #7 on:** April 17, 2012, 07:18:08 AM »

Download this manual before opening up the carbs, it's a great book. http://www.cb750c.com/publicdocs/SeanG/Honda_Carb_Manual_revE.pdf Cliff.

70CB750 · « **Reply #8 on:** April 17, 2012, 08:55:21 AM »

Subscribed

thrutheframe · « **Reply #9 on:** April 17, 2012, 09:57:58 AM »

Cliff that's manual is the best! I broke em down this morning. Had to leave cause my ventilation sux. I'm having lunch then I'm going back and I'll find a box fan somewhere to blow the gas smell away. I had to EZ out 1 rack screw and two cap screws.

Magpie · « **Reply #10 on:** April 17, 2012, 10:22:45 AM »

A good soaking solution is Pine Sol believe it or not. I tore mine apart and soaked them for a couple of days and they came up nice. I had to brush and pick at some of the real bad spots. The only thing bad was the smell, it turned my stomach.
Hopefully this link will work to see a good tread on it http://www.cb750c.com/modules.php?name=Forums&file=viewtopic&t=11174&highlight=pine+sol
and http://www.cb750c.com/modules.php?name=Forums&file=viewtopic&t=9866
Cliff.

thrutheframe · « **Reply #11 on:** April 17, 2012, 03:01:38 PM »

So far so good, the air cut off diaphragms are gooey and the accel pump diaphragm was perforated, my buddy/customer was smart enough to buy all the parts I recommended up front.

Prospect · « **Reply #12 on:** April 18, 2012, 11:02:22 AM »

Quote from: Magpie on April 17, 2012, 10:22:45 AM

A good soaking solution is Pine Sol believe it or not. I tore mine apart and soaked them for a couple of days and they came up nice. I had to brush and pick at some of the real bad spots. The only thing bad was the smell, it turned my stomach.

What's pine sol/water ratio did you use?

Magpie · « **Reply #13 on:** April 18, 2012, 11:13:15 AM »

Straight out of the bottle, full strength. Cliff.

thrutheframe · « **Reply #14 on:** April 18, 2012, 11:16:58 AM »

I'm using the pine-sol method on this set. I'll let them soak til early tomorrow.

thrutheframe · « **Reply #15 on:** April 18, 2012, 11:50:22 AM »

Yup full strength.

thrutheframe · « **Reply #16 on:** April 19, 2012, 11:18:52 AM »

The DOHC Carb guide is awesome. Stopping to do things his way has slowed me down but I'm sure it's right.

Magpie · « **Reply #17 on:** April 19, 2012, 12:32:08 PM »

Yes! I followed his instructions and the bike fired up and idled nicely on the first go round.
Cliff.

thrutheframe · « **Reply #18 on:** April 19, 2012, 06:50:40 PM »

This afternoon went well until I started to put the air screw in carb 4. It went in about 80% then nothing. I pulled the new screw and used the old on to massage whatever was in there out. It looked like clean threads, my carb cleaning needle went thru the passage and the screw came out undamaged every time I eased it a little further. It took about 20 minutes of rocking back and forth but it finally seated and I put the new screw back in.

thrutheframe · « **Reply #19 on:** April 20, 2012, 09:22:01 AM »

Floaters

thrutheframe · « **Reply #20 on:** April 20, 2012, 03:16:46 PM »

This project is officially put to bed for 3 weeks. I have to go work at my audio gig for awhile. I feel really good about how this has gone so far. I have a lot of time in it some of which is inexperience with these carbs and part is my decision to clean the pucks and needles by had with no dipping. I wanted to re-use the stock needles and I didn't want to risk bending them thru mishandling. Next time I will get a smaller container for the pucks and soak them separately.
I have 18 hrs and 15 minutes in this bike. That includes pulling them off which involves the rear and inner fender being dropped and the battery box coming out. LOTS of rust removal, the air mix screw on #4 being a b***h, and 2 hours figured in because I picked it up. Not sure if that's slow or super slow.

thrutheframe · « **Reply #21 on:** May 09, 2012, 10:22:48 AM »

I'm back at it. I worked 2 hours this morning and got 1&2 and 3&4 together, I'm ready to re-rack them after lunch. I'm going to hit Ace Hardware on the way back for some stainless steel screws and some other odds and ends.

thrutheframe · « **Reply #22 on:** May 10, 2012, 12:58:10 AM »

Not a lot of pics but I managed to get them re-racked and bench synced. I was a little confused by the high idle/choke adjustment description in the manual. The manual says to bend the tines on the choke idler arm until the front or "adjustment" tine just touches the throttle arm. Mine was short of touching by about 3mm. The butterflies are opened a tiny bit by fully engaging the choke so I'm not sure if I misread that part or not.
I'm not sure what the "Spawn of Satan" device is but I assume it's a vacuum feed mechanism that attaches to the petcock? This bike only has one tit on the petcock and since I don't have any parts left over I think it's safe to assume I have no SOS.
I am working on this bike again tomorrow. Barring any unforeseen issues I should be able to get them back on and at least ready to test. I hope I can do more but I know better than to assume its all going to just fall back together on it's own.

70CB750 · « **Reply #23 on:** May 10, 2012, 05:31:20 AM »

Good progress.

thrutheframe · « **Reply #24 on:** May 10, 2012, 11:55:53 AM »

The throttle isn't snapping closed. Sure it's a cable routing issue. They check out fine on the bench. I'm eating lunch... I'm sure I'll sort it out.

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Author Topic: My buddy asked me to get his bike running. (Read 10458 times)