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Author Topic: 1979 cb650 resto-mod  (Read 33424 times)

Offline Worst cb650 ever

  • Posts: 1491
  • You can always get it running with time or money.
1979 cb650 resto-mod
« on: Apr 07, 2012, 23:47:33 »
Hi folks,

As I mentioned in my introduction, I obtained a 1979 Honda cb650 with 8,1xx miles on the clock.  It was a little rough as a result of sitting, and there were some electrical gremlins. 

I started by rebuilding the carbs - I used the rebuild kits from a '78 cb750, which fit except for the top cover gasket, which I was able to reuse.  I also replaced the accelerator pump and bench synced the carbs.  I used a mixture of hot water and pine sol to clean the carb bodies with, and that, combined with some thin copper wire strands, cleaned everything up pretty well.  Nothing like the color of clean raw aluminum!

I had discovered that the spark units had melted themselves, and both coil packs were cracked.  I was getting a spark, but it was a pretty pathetic one.  So, upgrade time!   :D

I used this schematic and some GM HEI parts to upgrade:
http://home.comcast.net/~loudgpz/GPZweb/Ignition/CBheiModCavCoil.html

I ended up using coil packs off a mid 90's Saturn, and made custom wires using non-resistor wire, the stock Honda spark plug ends/boots, and the stock Saturn coil pack ends and boots.  I cut the plugs off the melted spark units, and wired in the GM HEI ignition modules, heat sinking them and mounting them to some 1/8" aluminum flat stock.  Using the stock plugs made it "plug and play."  I mounted the Saturn coil packs in roughly the same place as the stock coils, and the tank covers them up just fine.  I can fire a spark about 1/2" now, and in a pinch, use the coils as spot welders!  ;D

I also had to re-wind the charging system rotor with fresh magnet wire - the resistance of it was less than 2 ohms, and since Voltage = Current x Resistance, at 12.5 volts, the rotor was using more than 6 amps!  :o  Sadly, this high current draw fried the regulator/rectifier, but I was able to use one out of an '83 Nighthawk 650sc. 

I used the instructions below as a rough guide for rewinding the rotor, but I used Kapton tape instead of epoxy to secure the windings together.  Epoxy was making the wire "donut" too big. 

http://deuceswild.yuku.com/topic/1603#.T4D67u03dh9

Anyway, I have 12.5 volts at 1500 rpm, and it just goes up when I rev it, so I'm happy for now. 

I had all kinds of problems keeping this thing running, but that ended up being due to there being no air filter or air filter cover on the bike.  I found a NOS air filter on fleabay, along with some plastic side covers, but I had to make an improvised air filter cover out of cardboard until I can get one ordered.  After all that drama, it starts right up and idles happily.

I also shimmed the carb needles ~1mm with some small washers, as this thing was running kind of lean. 

That leads into my current problem - the thing won't rev over ~5,000 rpms.  She starts popping and spitting and bogging no matter how much throttle I give.  She runs great up to 5,000, but then just falls on her face.  Any thoughts as to what I should check?  I am going to pull the exhaust pipes off and run it open to make sure there's no obstructions in them, but I'm thinking that's kind of a long shot.  Suggestions are appreciated!
DTT Blue (cause Winter is Coming) CB360 Club.

1995 CBR900RR - a winter flip not worth a DTT writeup - Sold

1986 Yamaha SRX600 - mailed to me from California - build coming soon?

1983 VF750F

1976 CB360T

1993 CBR900RR - Sold

1979 CB650 - Sold

Offline Worst cb650 ever

  • Posts: 1491
  • You can always get it running with time or money.
Re: 1979 cb650 resto-mod
« Reply #1 on: Apr 07, 2012, 23:49:12 »
Pictures!

What the bike looked like when I purchased it:

DTT Blue (cause Winter is Coming) CB360 Club.

1995 CBR900RR - a winter flip not worth a DTT writeup - Sold

1986 Yamaha SRX600 - mailed to me from California - build coming soon?

1983 VF750F

1976 CB360T

1993 CBR900RR - Sold

1979 CB650 - Sold

Offline Worst cb650 ever

  • Posts: 1491
  • You can always get it running with time or money.
Re: 1979 cb650 resto-mod
« Reply #2 on: Apr 07, 2012, 23:54:20 »
What the bike looks like today - I also tossed some cheapo Bike Master lower bars on it, and I think that alone cleans up the look of the bike.  The fender and grab bar will go back on for now, but it looks pretty mean now  ;D



DTT Blue (cause Winter is Coming) CB360 Club.

1995 CBR900RR - a winter flip not worth a DTT writeup - Sold

1986 Yamaha SRX600 - mailed to me from California - build coming soon?

1983 VF750F

1976 CB360T

1993 CBR900RR - Sold

1979 CB650 - Sold

Offline YoungBlood

  • Posts: 7
Re: 1979 cb650 resto-mod
« Reply #3 on: Apr 08, 2012, 00:07:53 »
Nice project and it sounds like you're off to a good start. Looking forward to how's it's going to pan out!

Offline Worst cb650 ever

  • Posts: 1491
  • You can always get it running with time or money.
Re: 1979 cb650 resto-mod
« Reply #4 on: Apr 08, 2012, 00:19:39 »
Yea, if I can get the bike to rev over 5k, it will be very nice!  The bike wants to run and is sooo smooth, so it's annoying to have the 5k problem. 
DTT Blue (cause Winter is Coming) CB360 Club.

1995 CBR900RR - a winter flip not worth a DTT writeup - Sold

1986 Yamaha SRX600 - mailed to me from California - build coming soon?

1983 VF750F

1976 CB360T

1993 CBR900RR - Sold

1979 CB650 - Sold

Offline YoungBlood

  • Posts: 7
Re: 1979 cb650 resto-mod
« Reply #5 on: Apr 08, 2012, 10:33:03 »
What throttle position are you at when you hit 5,000 rpms? 1/2, 3/4?

Offline Worst cb650 ever

  • Posts: 1491
  • You can always get it running with time or money.
Re: 1979 cb650 resto-mod
« Reply #6 on: Apr 08, 2012, 14:21:12 »
I can open the throttle all the way, and it will still spit and fight at 5k.  I can sneak up on it slowly, still doesn't matter.  It just won't rev over 5k :P
DTT Blue (cause Winter is Coming) CB360 Club.

1995 CBR900RR - a winter flip not worth a DTT writeup - Sold

1986 Yamaha SRX600 - mailed to me from California - build coming soon?

1983 VF750F

1976 CB360T

1993 CBR900RR - Sold

1979 CB650 - Sold

Offline YoungBlood

  • Posts: 7
Re: 1979 cb650 resto-mod
« Reply #7 on: Apr 08, 2012, 21:09:18 »
Maybe the ignition advance?

Offline Worst cb650 ever

  • Posts: 1491
  • You can always get it running with time or money.
Re: 1979 cb650 resto-mod
« Reply #8 on: Apr 08, 2012, 21:40:41 »
Maybe the ignition advance?

Yea, I'm going to check that out.  I checked the timing statically when I first obtained the bike, and tested and lubed the advance weights.  Everything looked and moved fine, and the inside of the timing cover was immaculate.  However, I've only just been able to get the bike to idle consistently, so I will test the timing and advance dynamically.  I think full advance occurs at 3,xxx RPMs, so that's well below the 5,xxx RPM cutoff I'm hitting. 

You know, all this just reminds me again that low milage old bikes that aren't ridden are a lot worse than high milage bikes that get regular exercise...
DTT Blue (cause Winter is Coming) CB360 Club.

1995 CBR900RR - a winter flip not worth a DTT writeup - Sold

1986 Yamaha SRX600 - mailed to me from California - build coming soon?

1983 VF750F

1976 CB360T

1993 CBR900RR - Sold

1979 CB650 - Sold

Offline YoungBlood

  • Posts: 7
Re: 1979 cb650 resto-mod
« Reply #9 on: Apr 08, 2012, 22:22:32 »
Haha. Sounds like you have a good game plan. I'm gonna crawl back into my closet and watch some more!