1982 CB750F...Better Devil

Before I do anything else I checked the gas cap and fuel line. Blew compressed air through all the vent holes in the cap and poked some wire in there to clean it out for good measure. Also cut an inch off the fuel line to “flatten” out the flow from the petcock to the diaphragm assembly on the carbs, as I saw there was a noticeable incline in the line as it left the tank.

After reinstalling everything there was noticeably better fuel flow through the clear inline fuel filter. A bit more finagling and I think I can improve it a little more. Got our first snow of the approaching winter last night so that’s put the kibosh on taking it out for a ride, but we’re in for a warm spell (up to 18C next Monday with any luck) so there’s still time.


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Fuel line looked like this -

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Maybe the incline was causing an airlock in the line?
 
Little to early to say for sure, but took the bike out for a couple of laps round the block and it definitely seems to be running better. What's changed? Not a lot, but maybe enough...

- filled up the tank
- trimmed and removed incline in fuel line
- cleaned out vent holes in gas cap as much as possible

Need to take it out for longer to see if it starves again but optimistic.

Question - on the last few rides (when the bike was running poorly and - seemingly - gas starved) I was having a lot of difficulty changing gears. That is, really having to get my foot under the pedal to the point where it was really uncomfortable. On this last ride however the bike changed gears really smoothly.

Would a lack of fuel make it harder to change gear?
 
Fuel would not effect shifting but engine revs would. Poor running may make it shift poor. Sometimes to get neutral on tje gl a blip of the the throttle helps, same with getting first gear on first ride. Just clicking down wont engage, a blip of throttle then clicking and it slips right in. Revs effect shifts and fuel effects revs so I guess fuel could effect shifts lol
 
Well, that was a day. Got a last minute mechanical inspection appointment, kicked things into gear before I'd barely opened my eyes this morning. Hooked up the wiring harness for a would-be trailer (damn trim in a CR-V is a nightmare - fuck it, ripped it off and will deal with the aftermath later), legged it to U-Haul to rent a trailer and hauled the Better Devil up to the north of the island, optimistic but realistic. Indicators far too small, fenders not big enough, no exhaust heat shield...the list went on. Guy that inspected the bike knew what it was right away and loved that it had taken me two years to build - dude went easy on me and the bike passed. Hauled ass over the SAAQ (department of vehicle registration here in Quebec) to get it road legal, called my broker and got the thing insured. Bolted on a plate, threw on helmet and went for my first legal ride on the thing downtown.

The bastard rips. Fuel delivery problem sorted, no more stalling or cutting out (the fuel line re-route took care of that, or maybe it was clearing out the fuel cap). Adjusted the clutch and now it just flips right through the gears no drama. Only one thing that's pretty significant is the oil. It's not burning oil through the exhaust, it's steaming from the engine. Must be coming from a breather hose or something, maybe somewhere else, hard to tell. Any idea what would cause that, and what I can do to fix it?
 
Jimbonaut said:
20 or so hours in and this stuff is already tough as nails. There’s a little flexibility which is a good thing, but I can’t mark it with a fingernail. As long as it’s bonded to the steel then all will be well. I’ll leave it another day, give it a rinse out with some gas and then try it out.

View attachment 229244


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I just did my BMW tank with the Caswell dragon’s blood stuff and it’s sitting and curing. I lined a triumph tank the other day with Red-Kote. I MUCH prefer the Caswell stuff. The big old 6.2 gal beemer tank took the entire kit to line with very little pour out. Nice work getting it going. First ride is always a thrill and tense just waiting for the first thing to go wrong. :)
 
Glad the Caswell worked out for you. My tank used the whole lot too, just a small amount of pour out. Holding up well so far.

Gotta figure out why the engine is steaming off oil. Maybe a hose incorrectly routed? Something more sinister? Never had this problem before.

Still, feels great riding this thing around. Really smooth, engine sounds great and fits me like a glove. And for the first time I’ve built a bike with a really light clutch. Every other one has given me an rsi in my left arm, this one I can pull with one finger. Sweet.


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Jimbonaut said:
Glad the Caswell worked out for you. My tank used the whole lot too, just a small amount of pour out. Holding up well so far.

Gotta figure out why the engine is steaming off oil. Maybe a hose incorrectly routed? Something more sinister? Never had this problem before.

Still, feels great riding this thing around. Really smooth, engine sounds great and fits me like a glove. And for the first time I’ve built a bike with a really light clutch. Every other one has given me an rsi in my left arm, this one I can pull with one finger. Sweet.


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Where is the oil coming from? the breather? How's the oil level?
 
SONICJK said:
Where is the oil coming from? the breather? How's the oil level?
Click to expand...
Oil level's maybe a little high, but not much. I lost the cam chain tensioner rubber plug from the front of the engine on the first shakedown ride which is leaking a little oil - that could definitely be the culprit for the oil steam on the front of the engine. The other oil steam is coming from the breather hose off the small plastic box (I think it may have something to do with emissions?) underneath the battery cage.

Still, that said, bike is (or was - more on that later) running great. Put 300kms on it over the weekend - absolutely terrific. Engine sounds great, really strong acceleration, good braking, no problems at all really. Still seating the rings and scrubbing the tires so not redlining the thing, but 140kph no drama whatsoever. Could not be happier.

Then, 15kms from home and it dies at at stop light. Like, dies. Thought it may be gas related as I'd noticed the rpms had surged - it was idling at close to 2000rpms. But no, pretty sure it's the charging system. Luckily for me a mate was in the area and trailer'd me home. Batt was at 12v. Charged it overnight, and spent the day going through the charging system. No smoking gun yet.

So, really happy I got 300kms on the speedo (we're having some amazing weather here at the moment until Tuesday) and hope I can get to the bottom of this problem soon. Also, need to find out why the rpms are high - vacuum leak? Here are some shots from the ride -

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pretty sexy. as for the stall out, look for a lose connection in the harness, something may have vibrated lose or got chaffed etc.
 
Looks Fantastic !

is that a Delkevic exhaust?, if so what do you think of it as I'm thinking it ( or the smaller straight one) might work on my 550
 
Thanks gents, really happy with this bike too. Christ knows it took a while, and spreading design and technical decisions out over a couple of years means it only really comes together (or doesn't) at the end. I think this one came together not too shabby.

So the charging system was shot. Checked the rotor rings - 0.4 ohms. The messed up thing is that Clymers says that's within spec, but that's bullshit. Should be more like 4 ohms. Binned that one and got hold of a used but perfectly serviceable used one for the time being - I'll order a new one from Ricks. Also found out that my reg/rec was shot. Jimmied one in from a CB750 Nighthawk which did the trick, and will order a new one from Ricks as well. So that's the charging system taken care of.

Also discovered that the cam chain tensioner bolt was stripped. Don't know how I missed that, but hey. Heli Coil'd a new thread in there and jobs a good'un.

Jesus Murphy today was a corker, 23 degrees. What a day. Put another 200 kms on the clock, bringing it up to 500 and change. Turns out the tach is a pos and wasn't zero'ing out. So what looks like 2200rpm is actually 1200rpm. No drama. I think the carbs may need another synch just to dial them in, but all in all a pretty thorough 500kms shakedown.

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.
 
Took the valve cover off to check the torque on the cylinder stud bolts, all good, none needed tightening. Checked the valve clearances too while I was in there - all within spec except two (exhaust cylinder 2) which were borderline loose at .007. I'll have to live with that for now, but may see if I can find some shims over the winter to tighten them up a bit. Tomorrow I'll vacuum synch the carbs again as I think they may be a little off.
 
Vacuum'd synched the carbs but they were pretty much on the money already. Put some more air in the forks (they're now at around 15psi) - totally different bike. Much firmer, more planted. Dialled in the damping on the shocks, it's a bit of a dark art. But after a quick blatt round the block I think I've hit the sweet spot fore and aft. Getting the suspension right is so important I'm realizing, more on this machine than on my past bikes. It really makes all the difference. Everything just clicks when the springs are working as they should.

Talked a mate into taking the day off and went for an excellent ride along the Richelieu river, 200kms round trip. No customary halfway ice cream sadly but damn it was cold enough already. He's got a KTM 950 SM - if I've had more fun on two wheels I don't remember when. Now have about 700+ kms on the new engine. The idle is a bit weird, almost sounds like it's slowly pulsing. I'm convinced it's fuel delivery. But can't get more of a downhill flow to the carbs without either re-working the tank bung, removing the inline fuel filter, or saying bollocks to the vacuum diaphragm on the carbs completely and routing the gas directing to the fuel rail on the carbs. Worth a try. Also, after a decent ride the rpms are higher than at the beginning of the ride.

Ricks rotor and reg/rec showed up today so will get them installed stat. The borrowed rotor in the meantime is doing the job with aplomb.

Fuck I wish the season wasn't over.
 
>>Also, after a decent ride the rpms are higher than at the beginning of the ride.< <
That's what I experienced on the '79 CB750F. On one of the F forums, I was told that they aren't really warmed up until after at least ten minutes hard riding. I found myself considering an extension on the idle stop adjust screw, but sold the bike (and warned the buyer).
 
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Pulsating or loping is probably lean. May still be slightly off on jetting for the new exhaust
 
Too lean, did not think of that. The engine has been bored to 823 as well so could well have affected it's thirst. I was thinking I'd try routing the gas line directly to the fuel rail on the carbs first - to rule out that it's simply a fuel delivery problem - the line is pretty much horizontal from the petcock to the intake on the vacuum diaphragm on the carb body at the moment, so maybe it's just not getting enough constant fuel? If not then, well, it's carb-o-rama?
 
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