Re: pidjones rat bike project - '79 CB750F

Posted: Fri Dec 14, 2018 8:24 pm

Been trying to rescue a '79 750F that was seriously abused last century, then left setting in the East Tennessee weather since about 1999 (last it was tagged). I've cleaned the fuel tank (luckily last run on non-alcohol gas), checked and adjusted valves, changed the front end (someone had put Kaw leading axle forks on it yielding a trail of ~3") to GL1000 front, corrected brakes, replaced wheel bearings, cleaned electrical connectors, cleaned the commutator (yech, that was bad!), yadayada. Doing nothing for appearance as I'll leave it a rat bike. Rebuilt the carbs (I've done several GL1000 carb rebuilds, and these are quite similar). She fires up and idles, but #1 cylinder hasn't joined the team. Carbs just remounted for the third time. I've swapped coils (#4 pipe isn't getting as warm as 2 or 3 either, but 1 stays cold) with no change. Ne plugs, wires, and caps. Building an aux fuel cell this weekend so I can attempt a balance (not going to do much good until #1 kicks in). Compresdion is 125, 125, 120, 125 psi. I'm sure that will improve once it can be ridden. No serious leaks so far. Charging system keeps ~13.2 at idle and ~14.2 when reved. Still needs a new chain and tires, but they will come once its running right.

Tried to join here last month, but found the Comcast spam blocker trashed the admin email.

I'm piddling with bikes as a retirement passtime. I normally ride a GL1800 and hope to do some grand touring on it soon. Also have a cafe-styled '78 GL1000 with '75 engine that I show some.

Posted: Fri Dec 14, 2018 8:56 pm

G'day pidjones, welcome.
I loved my 750f bought new in Feb 81 (750's didn't arrive in Australia till late 80) and did 250,000Km on her.
Do you know the miles on the motor? After sitting so long it may take a while for the rings to come back. I'd check the valve shims next then a carb balance.
Keep the rat look, I luv it.
Cheers

Posted: Sat Dec 15, 2018 12:59 am

Welcome, I'm following your thread on the Do The Ton. Looking forward to the finished project.

Posted: Sat Dec 15, 2018 4:25 am

muskrat wrote:

G'day pidjones, welcome.
I loved my 750f bought new in Feb 81 (750's didn't arrive in Australia till late 80) and did 250,000Km on her.
Do you know the miles on the motor? After sitting so long it may take a while for the rings to come back. I'd check the valve shims next then a carb balance.
Keep the rat look, I luv it.
Cheers

I believe around 32k miles are on the odometer - have no idea of the accuracy. Agree on tbe rings. Not worried about compression, but would like to see all four cylinders contributing. I've already done the shims, but plan to check them again. Carb balance next week after building an aux fuel cell and the rain ends. Definitely keeping the rat look. Pulled ~.6" thick chunk of Bondo off the front left corner of the tank!

Posted: Sat Dec 15, 2018 11:17 am

Welcome to the site.
Looks like you have a lot of work on your hands with that project.
If the Konis on it are worth salvaging this place in Az. does nice work on those shocks.
https://www.restocycle.com/

How about a pic of the GL.

Posted: Sat Dec 15, 2018 1:34 pm

smurdoch wrote:

Welcome to the site.
Looks like you have a lot of work on your hands with that project.
If the Konis on it are worth salvaging this place in Az. does nice work on those shocks.
https://www.restocycle.com/

How about a pic of the GL.

I'm in no hurry. Had to replace the entire front end as a PO had spread the front tripple clamps to fit leading axle KZ750 36mm forks in the 35mm trees. I had a good but ratty looking set of GL1000 forks left over from the Hunley build, and found a GL1000 tripple on ebay. These fit perfectly in the CB750F headstock, just requiring the GL1000 headlight ears (I had spares) and a couple brackets to mount the meters. GL1000 forks are 37mm and have pretty good performance. May be a bit stiff for the weight, but I'll wait and see for that.

"The Hunley" project got its name when I bought a semi-basket case '78 GL1000 in 2013 as a future retirement project, intending a restoration. As I was loading it on the trailer I saw the kick start quadrant on the back of the engine and knew it was not a '78 engine. And that a true restore couldn't be done, so it became a cafe style "resto-mod". Upon taking belt covers off, it became evident that it had spent a considerable time at least partially submerged. Thus came her name Hunley in honor and memory of the brave men the built and sailed the world's first successful military submarine.
I have my build thread here: CGW Huley build thread

Posted: Tue Dec 18, 2018 2:55 am

Got a little more checked (or really, re-checked) today. Did the ignition test with screwdriver on the pickup coils - good hot spark on old plugs with the gap opened to ~ 3/16". Voltage test on spark units in spec. Buttoned that up and pulled the valve covers. checked the valve clearances again. Tightest is .003, loose one was .006 inch. Need a couple 295s to get any closer to the .004-.005 I'd like to have. Spent a lot of time getting RTV off of the valve cover from a PO putting it on the gasket. Now, I believe in tacking the gasket on the cover to make it more convenient, but not squishing RTV out everywhere. Anyway, cleaned that up and tacked the gasket to the cover with Indian Head.

Then, while digging out the RTV from the head I noticed something that I had not seen before. Right end intake cam holder is broken. This thing just keeps getting worse! Anyway, found a full set on eBay for $40 and ordered them.

Finished up my aux fuel cell. Presently using a 1/2 liter isopropyl bottle for the reservoir. Can go bigger if ever needed by just getting a bigger bottle to put the nipple in the bottom of. I like this one because I can just cap the bottle when I'm done with it and take it out to the shed, drain it in a tractor.

Posted: Tue Dec 18, 2018 7:10 pm

A good test this afternoon. Backed her out of the garage and hooked up to the aux fuel cell. Fired as soon as I touched the start button, and came off of the choke a lot faster than before. Reved up fast, not lethargic as before. All pipes are getting warm (~50F outside today)! Didn't bother with balancing carbs yet. #3 float must be sticking as it was overflowing (I put clear drain lines on this time). But it is firing on all 4 finally!

Holiday duties will be keeping me busy soon, so when I bring it in (have to leave it outside to air out so the wife doesn't complain as much about the exhaust smell) it will be pushed aside for a while to make room for getting the Hunley prepped for a show mid-January. Guess it is time to order a chain for it, too. Still won't be able to ride it as the tires are too old to even ride up my driveway, but at least it can be taken through the gears on the center stand.

Posted: Thu Dec 20, 2018 6:22 pm

"L" cam holder is broken pretty badly. Could have been over-torqued, but I really suspect they just rammed in a too-long screw for the valve cover (only had a couple proper valve cover bolts when I bought it). Also, this is not the first holder to need replaced. As I looked at the others to see if they were damaged, I found a J in position for an F (far left end of intake cam). And yes, there is a J in the J position. Guess this one need to be Plastigage checked and also check oil hole alignment, too.

I was going to see what I could do to fix up the tail section on the seat as it seemed to have a lot of repair fiberglass under it. Turns out, almost the entire tail is packed with Bondo and fiberglass, which is all separating from the remaining ABS part which is the top part. Need to figure out what to do with it. I could just glue it back together with ABS cement, but it weights 3.4 pounds with all of this Bondo packed in it! Think I'll check forums and ebay for another. Cracked/broken doesn't matter as I can always glue with ABS cement and reinforce from below with fiberglass cloth, but all of the bottom/back of this one is missing.

Posted: Thu Dec 20, 2018 7:38 pm

Already posted elsewhere about the cam cap, but thought I'd mention that you can make a slurry out of ABS and Acetone or MEK to use as a filler. Just cut up some ABS pieces small and let them stew in the solvent for a few days in a Mason jar or such. You can use fiberglass weave or cloth for strength. A buddy in OK repairs Oldwings doing this.

Posted: Sat Dec 22, 2018 6:10 pm

Honestly, I need to stay away from this bike for a while. But, parts are supposed to be in this afternoon, so.... Good thing, too because I decided to check that J cap in an F position. They had jambed screws in the cross-drilled supply holes in the cap, and RTVed the bolt holes. And of course, broke one of the cap bolts off. I was able to remove the broken bit with little drama, then spent time picking out RTV. Bolts are supposed to be included with the caps I bought, so hopefully things will get better.

Gene, I just buy ABS plumbing cement on Amazon and use multi-material primer (includes ABS).

Posted: Sat Dec 22, 2018 11:41 pm

Swapped in new (used) F and L caps after first Plastgage testing them - both between .003 and .004 inch. Measured with both cylinders on respective side with lobes away from lifters. Final assesmbly with assembly lube on the bearing surfaces. New chain came in too, but it will wait for tomorrow or Monday for installation. Good weather forecast for next week, so hopefully there will be a chance to run it through the gears to make sure that is all fit.

Posted: Thu Dec 27, 2018 5:59 pm

Rolled it out this morning, hooked up the aux fuel cell with ~ 1/2 liter real gasoline, and fired it up. Once warmed enough to take off the choke I ran it through all 5 gears (on center stand). Clutch engages/disengages well, all gears work and sound pretty good (chain is hitting the plastic chain guard some, so need to adjust that). Then shut it off and hooked up the mercury sticks (old MotionPro unit). Balanced the carbs, lowered idle, balanced again. Have not touched pilot screws - all set at 3 turns open. Aircut valves are disabled.

Guess the next thing other than fixing the seat rear cowl assembly is tires (ouch$$). Thinking maybe getting a bunch of wrecked Honda plastic from the dealer and gluing it together to patch the existing cowl assembly now that I've pried 3 pounds of Bondo off of it..

BTW, if anyone has a dohc F with 4-2 stock pipes, I need some info. PO took off the final baffle pipe that goes in the rear diaphram. Sounds awful to me. How long is this bafgle tube, and is it just a straight tube, have joles, interior features, etc.? Wish I had paid more attention to the 750F dohc at Barber, and the one at the Hilton we stayed at.

Posted: Thu Dec 27, 2018 7:49 pm

I have a tail section (undamaged) for you, if you want to pay shipping. Will probably need paint, but may be better than what you have...

Posted: Thu Dec 27, 2018 11:50 pm

cliffiec wrote:

I have a tail section (undamaged) for you, if you want to pay shipping. Will probably need paint, but may be better than what you have...

Great! PM sent!

Posted: Fri Dec 28, 2018 3:48 pm

Ordered new Kenda 657s for the '79 CB750F rat bike. Not in a hurry for them, as it will be a couple months before decent riding weather, and I have a showw in a couple weeks to get the GL1000 ready for, plus rides scheduled for the GL1800 (weather permitting).

Posted: Wed Jan 02, 2019 6:41 pm

cliffiec wrote:

I have a tail section (undamaged) for you, if you want to pay shipping. Will probably need paint, but may be better than what you have...

If I can't get this tail section from you, I think I'll go down to the Honda dealer and get a box full of wreck take-off pieces and glue something u. y tail section is missing all of the bottom part and a piece out of the top. The part that screws under the seat is intact, however.

BTW, did you get the basket case '77 GL1000? I had offers to buy two in August (although I would have to travel ~400 miles one-way to get either) for ~$500 each. Decided to wait because I'd really like to restore a '78 or even better a '79 (not the most popular or attractive models). I had a '77 back in 2004 and they are a great bike - still point actuated ignition but super-simple. CV carbs very similar to some on the CB750. I now have a '75 engine in a '78 frame set up cafe style. Don't let the big motor hold you back - I just screwed doubled-up 2x4s to a Harbor Freight furniture dolly, ratchet-strapped the motor to it, pulled the wheels and suspension and then pulled the frame off of the motor. Did the reverse to put it back together.

Posted: Sat Jan 19, 2019 3:15 pm

The Kendas are mounted and wheels back on. That's about as far as the weather and my health could take her this week. Came down with a cold that knocked me out until yesterday, when I went to the funeral of a high school classmate and then to see a cousin in a nursing home that is not doing well at all. I still need to drain the fuel from the tank into my waste gas jug to get rid of the fogging oil and storage spray grease that I'd put in the tank and never flushed out. I'm sure that is a major cause of the smoke that she displayed before, because she doesn't smoke on the auxiliary tank. The weather has turned its typical East Tennessee January/February crud. Maybe the middle of next week it will settle and I can at least try to ride around the neighborhood.

Posted: Sat Jan 19, 2019 3:25 pm

BTW, I showed the Hunley last weekend in the Knoxville Cabin Fever show. She took 1st place Honda (but, there were only three entered). Had a great time!

Red CB1100F Joined: Jul 19, 2010 Posts: 6422 Location: Ct

Nice

Posted: Tue Jan 22, 2019 8:57 pm

Made it to the 40s (F) today, so she was pulled out and given her first run. Only ~2 miles total in the adjacent subdivision and back around our house (not tagged or insured yet) revealed that the engine is getting better and better, the trans shifts fine (I just need to get used to it) at least up through 3rd. The problems; front brake is spongy but improving rapidly, rear brake feels firm but does nothing to slow me down, and there was a bit of a problem with the speedometer. Pretty happy with it overall. Guess now work on brakes, repair the speedo (I already have it apart), and go down to buy tags and register. Feels a bit different from the GoldWings that I've been riding the past 15 years or so.

Posted: Sun Feb 03, 2019 9:04 pm

Took the Rocket for a little over 8 mile loop today. After lowering the idle, it ran great! Brakes working well, and even the rear suspension seems to be functioning well. The GoldWing front suspension works real well for this bike and my weight (~185 lbs). Didn't hold it at high RPM, but got it over 8500 a couple times. Don't know how accurate speedo or tach are, but the speedo indicated 60 mph @~4700 RPM 5th gear. Brought it back home and let it idle while I took gloves and helmet off. Listened around as best I could, and didn't hear anything of concern. I'll probably change the oil this week so I can check for anything in it.

Posted: Wed Feb 13, 2019 6:59 pm

Made up final baffles for the exhaust to knock the racket down some. Hopefully they are pretty close to the original (Thanks SteveG!). Used 1" tubing cut ~5" long tacked to some disks that I made out of some spare 20 gauge. Really sounds a LOT better setting still. Only ~45F today, so I will wait for the forecast 60F tomorrow to try it some.

Posted: Wed Feb 13, 2019 7:01 pm

I like the rims... correct Comstars.

Posted: Wed Feb 13, 2019 7:30 pm

genesound wrote:

I like the rims... correct Comstars.

Untouched (green mung and all).

Actually, a lot of it is correct original, I think. Not the front forks, though. They are a GL1000 transplant. She is about as prettied-up as I plan except for the rear cowl. I'll build something out of busted Honda plastic from the dealership service department as soon as they have done enough wrecks and saved me up some (or maybe go to Deal's Gap in April and collect a day's worth). They said that some people actually save their busted plastic. Wish I had from my 2016 get-off on the GL1800!. Would have been plenty to do the job. I also have a mesh seat cover due in from Aliexpress to cover up the taped-up seat. Nothing too good for the Rocket rat bike! (BTW, oil change yesterday showed no shiny metal particles, but a piece of gasket sealer that leads me to think I need to drop the oil pan and clean the strainer.)

Posted: Wed Feb 27, 2019 6:49 pm

Nice day today, so I took the CB750F for a loop over Norris Dam. Running great, I think. Accelerates much harder than my GoldWings but vibrates a lot more. Handles well. Everything mechanical that I could find wrong has been fixed except the speedometer error, which is ~ +10mph @ 55mph. She really smooths out at ~5000 RPM (~55 mph by GPS) all the way to ~7500 RPM - the highest speed I took her. Didn't have the GPS then, so I don't know how fast that was. I was wearing ear plugs, and above 55mph all that I could hear was the air intake and wind noise. So different than a GoldWing though! I like the ergonomics with these Euro handlebars. Only a little 40 miles but the 66 year old body felt like I had done it on the GL1800. The original bars were identical to the GL1000 stock bars, and I always got stabbing back pains in 15 miles with them.

I guess she will go on Craigslist soon. She was always meant to be a winter project that I intend to get my investment back from, so I'll let her go for $1500. Not bad with it running well and new tires and chain, GL1000 front end, all sorted. I doubt anyone on here is interested but if you know of anyone wanting to do a custom CB750 but not needing to fix mechanicals - or someone that wants a "rat bike", let them know.

Oh, and this afternoon I took the GL1800 over the same loop, trying out the new GPS and front tire!

Posted: Sat Mar 09, 2019 1:09 pm

The last few days (while the skys have been pouring the wet stuff) I've been working on a replacement for the missing under-seat-cowl plastic. Knoxville Honda service department saved busted ABS for me - turned out to be from a Gen 2 GL1800. Big, fairly flat pieces that made it pretty easy. Cutting it with a Harbor Freight multi-tool. Cut, fit, file, glue, cut, fit, file, blue. Time consuming but starting to shape up. Had to fill in some pieces of busted upper cowl, too. Won't be perfect, but appropriate for the rat bike it is. Still leaves space for the luggage rack which will go back on with it. I'll probably rattle-can it flat black.

After it gets mounted back, I'll take a few more speedometer comparison runs and call it done. Then it will go in the For Sale sections in several forums and Craigslist/Facebook Marketplace. It's a great ride, but I'm too old to do the sport bike thing.

Red CB1100F Joined: Jul 19, 2010 Posts: 6422 Location: Ct

Nice work, looks fun. I would be so temped to sand down the tank and and pull out the old flat black spray can haha. Keep going Cool

Posted: Sun Mar 10, 2019 12:01 am

ctluba wrote:

Nice work, looks fun. I would be so temped to sand down the tank and and pull out the old flat black spray can haha. Keep going Cool

Yes, but I want it to keep its well-earned rat bike look. Going any further is just going to increase the $$$ put into it, and it has so far to go!