Author Topic: 78' cb750k8 Chopper/Bobber build (Read 3975 times)

conwaylale · « **on:** February 06, 2014, 05:58:04 am »

It's almost done now but I figured i post some pics of how it went together and if anyone has questions or comments/concerns let me know. Started with a stock cb750, with 7500 miles, that ran minus the brakes. When i test rode it I took off and hit the brakes with nothing. Guy could've told me about that. I brought it home with an idea of what i wanted already and started tearing it apart. Making sure to mark where everything went. I used TC bros hardtail kit, switched to 530 chain conversion, everything i could make in my garage i did. I'm a cheap SOB and a welder by trade so I'm confident in metal work. Anyway here's some pics.

conwaylale · « **Reply #1 on:** February 06, 2014, 05:59:50 am »

conwaylale · « **Reply #2 on:** February 06, 2014, 06:01:00 am »

conwaylale · « **Reply #3 on:** February 06, 2014, 06:02:24 am »

conwaylale · « **Reply #4 on:** February 06, 2014, 06:04:37 am »

I saw this on some other chop, put it in as a stiffiner. Maybe not pretty or neccesary but its solid.

conwaylale · « **Reply #5 on:** February 06, 2014, 06:06:33 am »

conwaylale · « **Reply #6 on:** February 06, 2014, 06:09:13 am »

I ended up hating the brown tank. Its a sporty King tank and didnt match well with the back of the frame so I found another sporty tank for $70.

Also had a couple sets of bars that I mocked up to decide what looked good to me.

conwaylale · « **Reply #7 on:** February 06, 2014, 06:11:16 am »

Started on some essential, make it run, stuff. Got a reg/rec combo. Just the basic wiring.

conwaylale · « **Reply #8 on:** February 06, 2014, 06:15:51 am »

This is where Im at now. I did the 530 chain conversion. The tail light is from a xs650 turn signal that i replaced the guts for a 2 way bulb. made the brackets for the oil tank out of the fender mounts, the rear fender mount is off an old pot (like in the kitchen) that my wife didn't use anymore. License plate bracket is just some old brackets i found laying around. I had to notch the oil tank to clear the chain. The seat I bought from some fella off chop cult. Epay solo seat springs and hinge. Paint is satin burgandy from Ace just rattle canned. I told you guys im cheap.

conwaylale · « **Reply #9 on:** February 06, 2014, 06:28:47 am »

The last major thing i want to do is put on a 21" front wheel. Ive already got the wheel off a harley just have to get the laces.

calj737 · « **Reply #10 on:** February 06, 2014, 06:32:45 am »

Be careful with the 21" that you don't create an interference to the exhaust (which is not currently installed). Yes, its only 1" fully larger, but adding the tire aspect and any fender, plus the protrusion of the exhaust, and you may kick yourself...

The "stiffener" you added was in the wrong place, ideally. It should have gone higher up, between the motor hangar bolts. I trust you've used quality tubing and welded the new rear back into the existing frame properly. That's a lot of stress by virtue of the extension, and rigid suspension.

conwaylale · « **Reply #11 on:** March 01, 2014, 03:08:34 am »

Ok. So i added my oil last night to my oil tank. 3.7 quarts or close to it. And I think all of it stayed in the tank and non went into the engine. I turned the motor over for several seconds (primed it) at a time to see if the pump would pick some up and the level in the tank stayed the same. Does the motor have to be at running rpm for the pump to work or do i have another issue? thanks

Medyo Bastos · « **Reply #12 on:** March 01, 2014, 04:42:14 am »

will you have this complete by september? you up for a ride to paris landing in september?

conwaylale · « **Reply #13 on:** March 01, 2014, 09:53:07 am »

I hope to have it done by the end of next week when my cycle x gasser exhaust get here. I'll ride wherever.

Medyo Bastos · « **Reply #14 on:** March 01, 2014, 01:54:01 pm »

jot paris landing into your plans

-save a tree, eat a beaver using Tapatalk

conwaylale · « **Reply #15 on:** March 02, 2014, 05:42:42 am »

Im in Knoxville so that might end up being a trailer it to Nashville and ride the rest of the way. I didnt build this thing for long trips. What is the date in September?

Medyo Bastos · « **Reply #16 on:** March 02, 2014, 05:55:44 am »

20-21. i will be coming from southaven and then across us 70. it looks like close to 15 so far!

conwaylale · « **Reply #17 on:** May 27, 2014, 03:47:38 pm »

conwaylale · « **Reply #18 on:** May 27, 2014, 03:51:22 pm »

Alright, Tore the engine down last night. Found that the rings and cylinders looked good. Doesn't mean they are but they look like it. Another issue was that cylinders 1 and 3 valves looked black while 2 and 4 looked tan. Whats correct and what is causing this difference in color? Also to my surprise this motor has had someone into it before. What they did I have no idea but they put a crap ton of J-B weld under the #1 cylinder cam tower. There are 4 bolts in the middle of the head that have to come out to get the head off and the one closest to #1 cylinder was full of this stuff. I had to scrape it out to get to the bolt. I don't know why they would have done this because I found no cracks or reason to do this. I am going to buy the cycle X drop in cam and 836 piston kit. Here we go.
My reason for the teardown is that I was having a lot of backfire and oil from cylinders 1 and 3.

Don R · « **Reply #19 on:** May 29, 2014, 08:51:55 pm »

The black could be from the burning oil you referred to or from excess fuel going into those cylinders. If there was excess fuel it could have gas washed the oil from the cylinders leading to wear and the oil usage.
Possible causes are leaking float valves, oversize or drilled jets, floats set too high, etc.

AintNoEasyWay · « **Reply #20 on:** May 30, 2014, 07:15:35 am »

Subscribed. Awesome to see another Knoxvillian working on CB's.

blue collar · « **Reply #21 on:** May 30, 2014, 09:32:31 am »

You've done a nice job with this project man.

Looks real good.

conwaylale · « **Reply #22 on:** June 12, 2014, 11:45:39 am »

I decided to just do a stock rebuild on the motor. Just the top end. I'll save the money from not doing an 836 and put it somewhere else. I lapped the valves and honed the cylinders. Put in new rings and gaskets.
After all of this i still have the popping and chugging. It has to be in the carbs. I have replaced idle and main jets, accellerator pump, float needles and seats, and cleaned them very well. I took them apart again and found that one float is not floating. Tested in gas and it sank like a rock while the other 3 floated evenly. I also noticed that the idle/ air mixture screws need replaced and one carb (the one doing the popping) did not have an o-ring in it. Also none of the needles had the shim in them. Does it deteriorate or has someone taken them out. Are they neccasarry? Chasing carb problems the whole time it seems.

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Author Topic: 78' cb750k8 Chopper/Bobber build (Read 3975 times)