1982 CB750F...Better Devil

Sderbyshire

Into Sailing, classic Triumph cars and motorbikes.
Yeah, it's a Delkevic. It's pretty awesome, especially for the money. Easy install, really nicely made, beautifully clean welds, and a fantastic sound. Not obnoxious by any means, but a significant roar. If you get the megaphone muffler then there are a couple of adjustments you can make to increase the sound if you so wish. It's not chromed, so expect yellowing of the headers. I'd recommend it for sure.

Thanks Jimbo, i found one of those second hand on ebay yesterday, so snapped it up for an experiment !

i think i'll need a link pipe to angle the silencer up 20-30deg for the original 'wavy' header, but that soulddnt be a problem.

look out for updates on the 'Scruffy Racer' thread :)
 

Jimbonaut

Over 1,000 Posts
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Yup, too lean. I deleted the air cutoff o-rings when I last rebuilt the carbs, but didn’t know this meant it was necessary to enrichen the mixture. Turned out the screws a full turn (they’re now at 2½ turns out) and it sounds like, well, a new bike. Which it kinda is but damn it sounds good. No more lope or pulse, just a strong steady idle at 1000rpm. The clutch chatter which had developed has completely gone too -



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Jimbonaut

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I bought this tool from the same company in the UK that sells the CarbTune. When I dicked around with the mixture screws on Rhonda, all I had was a little flathead attachment (the kind you get in the Ikea toolkits, the little interchangeable magnetic screwdriver whatnots) and spent more time dropping the bastard and burning my hand on the hot engine than actually adjusting the mixture. This tool is the business however, makes getting to those screws 1000 times easier -

WQk3mTql.jpg
 

pidjones

Over 1,000 Posts
That tool looks great! So much better than the give-away screwdriver that I cut the blade to ~2cm and ground a new blade on then cut the handle off at ~2cm. Worked, but still fiddly.
 

Jimbonaut

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Thanks gents, amazing how a bit of know-how changes everything. One day I hope I can pass on some of the knowledge I've learnt here as well. This forum is the business. Standing on the shoulders of giants once again.
 

Jimbonaut

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Thanks fellas. Getting colder here by the minute, but Friday's opening up quite nicely, 13C. We had three feet of snow on the ground this time last year, so I'll take 13 degrees all day. Might be time to squeak in one last ride of the year.
 

Jimbonaut

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Both the rotor and the reg/rec shat the bed at the end of last season, but managed to get a few more rides in by installing a new rotor from Ricks and jimmying in a reg/rec from a CB650 Nighthawk. New Ricks reg/rec arrived today so got that installed, and have a spiffy Daytona electronic speedo/tach gauge on the way from Japan.

Got my eye on a new-ish bike (never owned one before), an XSR 700. If I can shift this bike for some decent scratch then might be time for some new wheels.
 

Jimbonaut

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Dumped the crappy and totally inaccurate (but very yellow so that was cool) speedo and tach and bought an electronic Daytona set-up called the Velona 80. Nice and clear, mocked up the wiring, so far so good -


Need to wire up the rpm sensor and speed sensor, and then calibrate
 

Jimbonaut

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Christ doing cartwheels. Spent 5 hours on the verge of having a stroke trying to calculate circumferences of the front wheel, pulses per revolution, input codes into the damn unit - then a mate showed up so I could bin all that and try the other method of calibration - ride the thing for exactly a kilometre. Did that and finally the needle not only moved, it indicated the right speed.

Calibrating the speed sensor on one of these? Balls to the manual method. Go automatic all the way. Thank me later.
 

Jimbonaut

Over 1,000 Posts
DTT SUPPORTER
Looks great. Got a link to it? Is it the same Japanese site where you bought the master cylinder?

Does it work on the standard magnetic pickup at the wheel ?
It's a Daytona gauge, the Velona 80. Yeah it's from Webike in Japan and comes in several different configurations. You'll need to also buy a speed sensor (I attached mine to the front fork, with a magnet on the brake rotor) and a rpm sensor (which attaches to your spark plug lead) separately.

https://japan.webike.net/products/23296288.html
 

Jimbonaut

Over 1,000 Posts
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Can anyone tell me what the pulse per revolution is for these bikes? Need it to calibrate the rpm sensor


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Jimbonaut

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Thanks man, have the thing dialled in now. However...

...bike's giving me fits. I can ride it around town for around 30 - 45 mins and then the idle bogs down and wants to stall at every light. Nurse the thing back home. I've pulled the carbs, messed around with floats (all now in spec at 15.5mm) and float needles, put back the o-rings in the air cut-off valves (I'd previously deleted then with plugs cut from inner tube) and cleaned the bejeezus out of the things. The messed up floats (I'd installed new ones last week as I noticed gas coming out of the overflow tubes) were sitting totally wrong and - I think - causing a high idle from the get go. With these binned and the originals out back the high idle calmed down a lot, but, sure enough, after 45 mins, bog-o-rama.

I'm getting a fouled plug on #2 and my next thing to look at are the coils. Thank god for Old Reliable the KLR - that thing I can treat mean and it just stays keen. So I'm riding, but damn. I put 1000kms on this CB last year, no drama. It sits over the winter and now it's gone squarely south.
 

doc_rot

Oh the usual... I bowl, I drive around...
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if a coil craps out its going to do it on two plugs at the same time. I would still suspect the carbs/fueling. what state are your carb boots in? high idle is indicitive of vacuum leak. how did the plug foul? is your bike charging properly?
 
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