1979 cb650 resto-mod

Getting the mixture right is definitely tricky but its good to hear that your bike starts that easily! I just got back home from college ill tear into the carbs in the next week and let you know if i need any parts.

Scott84 said:

Getting the mixture right is definitely tricky but its good to hear that your bike starts that easily! I just got back home from college ill tear into the carbs in the next week and let you know if i need any parts.

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Yea, these bikes are pretty damn lean from the factory, which is why I went to such great pains to locate the proper airbox parts. I didn't want it running any leaner than it had to!

Let me know about the carbs - chances are if it's not part of the choke assembly, I have it!

Hey sorry I haven't gotten back with you about the carbs, I was riding my friends 4 wheeler and slid into a ditch and smashed up my hand so I haven't been able to touch my bike.

Ouch, that sucks. I crushed a couple of fingertips with a cylinder head a few years back, and that put me out of commission for months! I hope you feel better soon.

An update from beyond the grave...

I picked up a set of CBR600F4i coil on plugs for $30 with harness from ebay. I paired up coils #1 and #4 and #2 and #3 and hooked them into the ignition system to see if they would solve some of the lost of power at high RPMs I've seen with the bike. I guess Saturn ignition coils don't like to be revved over 6500 RPMs!



Yea, that's a hot spark - it fired without the choke in 28 degree weather! I pulled one of the coils and put a spare spark plug in it, and it fired half an inch to the cylinder head! The bike revved up to the redline like something was chasing it. Nice!

More updates when the weather allows road testing. I think I may need to lean out the mixture a bit now that I have the firepower for the plugs.

That's awesome what made you think to try and adapt those to the old cb650?

Scott84 said:

That's awesome what made you think to try and adapt those to the old cb650?

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They were $30 lol ;D

Turns out they won't work that well, as the current draw will be too high due to the low resistance of the coils. Stay tuned for more...

Worst cb650 ever said:

Welp, I pulled the carb needle shims, thinking I had fixed the idle issues that had been plaguing me.

I guess I should have not been surprised it idled like crap and had to have the throttle tickled to stay running until I turned the idle knob in big time.

After much head scratching and thinking, I came to the conclusion that the slow jets must be the issue - the bike has plenty mid range and up top when it is running almost exclusively on the main jets, but idles for crap, takes forever to warm up, and tends to stall when the clutch is let out. Rather than drop $22 + $13 in shipping for a set of new #35 slow jets (the press in jets are a real PITA to find), I opted to order up a $13 pin vise and drill bit set. A #80 drill bit is 0.3429 mm, which is pretty darn close to the 0.35 mm hole diameter of a #35 Keihin slow jet.

I carefully started to "drill" through the slow jet, and was surprised to dislodge crusty crap. It appears all the slow jets were reduced to almost half their diameter by crap. I had soaked these jets in old school carb cleaner, and then in the Pine Sol dip of doom, cleaned them out with copper wire, and there was still crap hanging on in them. Gah!

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I know this is an old thread, but I just wanted to drop in and say that my bike was acting similarly, and I gave the #80 drill bit a shot. Worked beautifully, and the bike runs many times better.

So thank you, for mentioning that. Saved me lots of time and a bit of cash.

Hey, you're welcome - I'm glad you were able to get your bike to run better! I have to swap on some decent coils to this bike and I'll hopefully be out there on the road too!

I think this will be the final update for a while, but I've fixed the bike's ignition problems. The coil on plug CBR600 coils were cool, but were drawing 3 - 4 times the current of the stock coils. That would have fried my ignitors pretty quickly

I did have a set of stock '78 CB750 coils I received with a pair of good 750 ignitors (to replace my melted ones), so I decided to throw them at the bike. I tested their resistance, and it was between 3-4 ohms for both coils. Neither coil was leaking that waxy stuff that insulates the coils, so that was good too!

I mounted them up, which was easy as they are identical to the stock 650 coils, attached the wires, plugged everything in, and rolled the bike outside. I turned on fuel, primed the bike with 10 twists of the throttle (probably five too many), fully choked it, and hit start. It started in seconds, and this is after being in storage for months!

Due to some oil I had put in the combustion chambers to check compression and my excessive priming, the bike smoked pretty good for a bit, but a quick ride around the back yard fixed that. I got my gear and proceeded to put 50 trouble free miles on the bike that day, hurray!

The bike pulled hard up to 80 on the highway (it has a little front end shake, so I stopped at 80), and happily cruised at 50-60 through the back roads.

I'm calling this one done and putting some miles on it! Woo!

Thats great hopefully I get mine to that point this summer!

Good luck man, I hope you get it there! I can't believe what a different (better) bike this is with good coils. Don't be afraid to rob the Honda parts bins - a lot of parts interchange between the 750s and Goldwings of the era.

Well I finally go to mine and got it going. And it runs awesome. I took your advice and robbed the honda parts bins and put on some cbr600 carbs and a coils off a night hawk and bought a v65 magna as a parts bike for 50 bucks. Its coming along nicely, thanks for all the help and inspiration.

Do you have a build thread detailing the CBR carb swap? That sounds like an awesome upgrade! What carb adaptors did you use to couple the carbs to the 650 head?

No dont have a build thread that is up to date. I used inch and half radiator hose as an adapter to the head. Im having a problem with the carbs overflowing out the back of the carbs because the carbs are meant to run at an angle and the way they are hooked up is flat. Im going to try to find some time to update the build thread. The bike runs amazing and starts really easily.

Scott84 said:

No dont have a build thread that is up to date. I used inch and half radiator hose as an adapter to the head. Im having a problem with the carbs overflowing out the back of the carbs because the carbs are meant to run at an angle and the way they are hooked up is flat. Im going to try to find some time to update the build thread. The bike runs amazing and starts really easily.

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Could you use a "prop" of sorts to adjust the carb angle? Maybe use a little more hose to provide a gentle bend combined with something to "prop" the carbs skyward?

I gotta say I am seriously jealous of your easy starting - time for me to start looking for an inexpensive set. Do you know what year CBR the carbs came off of? Thanks!

There's no room to prop the carbs up I think I'm going to try and raise the floats. The carbs are 1997 CBR 600 carbs.

doh, well hopefully bending the floats will help. It may cause some issues with the angles of the jets relative to the fuel in the bowls though. Good luck!