1982 CB750F...Better Devil

I don't know what the specs are for this bike but usually the float level is lightly lower than the top of the bowl. also you can polish the needle seat by putting a cue tip in a drill with some polish. seems to help when using old float needles
However, tell you what I didn't do before and that's stick the q-tip in the drill. Along with switching out a known good needle (from non-leaking carb 2) with the needle from carb 1 (which was leaking), I re-polished the seat (thanks a lot for the tip) and then tried hooking up a gas supply to the carb rack with them on the bench. Big fail - I guess the carbs need draw from the engine pistons to create gas draw through them, so all I achieved was a minor Exxon Valdez reenactment on my workbench. Installed them back in the bike but minus the airbox (just for ease of installation) and fired the bike up to see what gives.

Well, it ran but like utter shit, only to be expected I guess without the airbox. However once I finally got the bike firing on all four it definitely looked like the leak from carb 1 had stopped and - with what I thought may have been a dodgy needle now in carb 2, no leak from carb 2 either. All this was done at 8.30pm last night with thoroughly irritated neighbours so had to abort before confirming the test. I'll reinstall the airbox and properly install the carbs again and see what happens.
 
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Sometimes all it takes is one little bit of dirt to cause a leaking carb. I fussed over a friends sons leaking carb for an hour. I had asked did you clean the needle and seat, he swore he did. I put a little twist of PT up and a little spec of black something came out and all of a sudden it stopped leaking gas. your re-polish of the seat may have done the same.
 
Sometimes all it takes is one little bit of dirt to cause a leaking carb. I fussed over a friends sons leaking carb for an hour. I had asked did you clean the needle and seat, he swore he did. I put a little twist of PT up and a little spec of black something came out and all of a sudden it stopped leaking gas. your re-polish of the seat may have done the same.
At this point I'm not even being cautiously optimistic. These carbs have been in and out so many times now that I've learnt not to expect much until I know I'm in the clear. But one new thing I've learnt is the q-tip in the drill routine (thanks doc). I'd just been manually twizzling the thing in there with a bit of polish - but drill routine definitely gets them cleaner
 
Another thing that I learned with them is to tap on the leaking carb with a screwdriver handle. Guess the needles hang or don't self-center and the tapping is like starting it.
 
Another thing that I learned with them is to tap on the leaking carb with a screwdriver handle. Guess the needles hang or don't self-center and the tapping is like starting it.
This^^^ I've installed brand new carb kits and had the needles stuck wide open. a couple quick raps with a screw driver and they seat and stop flowing.
 
Well, stopped the leak. Got the carbs properly installed with the airbox (polished all the seats this time with the drill/q-tip), fired it up, no leak.

Next step is to take the bike out again for a ride and see if gets past 45 mins without crapping out.
 
Hasn't happened yet - hoping to get it out tomorrow but forecast is for wall to wall rain. Weather's sucking balls here
 
Ha, I just tracked the CB125 float and they are out for delivery but it is also going to piss rain until Sat so same boat here.
 
Still can't get the bike running right. Better maybe, but still not right. I replaced the floats with new ones - they sit higher in the bowl (when measured against the gasket surface - specs say they should be 15.5mm, these new ones are +1mm higher) but the fuel level in the bowl is lower -

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The clear-tube test is a good comparison too. The old floats -

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and the new -

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I've also bypassed the vacuum fuel pump on the carbs and am now running a fuel line direct from the tank to the carb fuel rail. Yesterday the bike seems to run better, definitely a solid idle for the first 35 mins or so around town but a slight drop by the end of the ride, and then pretty rough when I fired the bike up again after sitting for half an hour. Also rechecked the float level and it had risen -

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How in the hell does the level go up? There's no overflow from the tubes. Some kind of back pressure in the fuel line?
 
Maybe just gravity, now that the fuel is gravity fed rather than vacuum fed?

Christ it's a good job there are no parties at the moment. Because if there were I'd be no fun at them
 
Been a while whole season. There have been more than a few times I've questioned the sense of calling this bike the Better Devil, and I don't suggest anyone following suit. It definitely came back to haunt me more than once. More than a few times I came close to pouring gas all over it and setting the fucking thing on fire, but in the end I won ugly.

Finally.

A lot's happened. New OEM floats, float needles and seats finally saw to the overflow problems I was having, but not before ditching the entire rack I had as I discovered there was an air leak through the throttle shaft linkage and replacing it with another. It's a one-in-a-million problem I'm told and took months to figure out. Fuck that anyway. Carb situation sorted, or so I thought. Still had an air leak, but only manifested itself after 40 mins or so of riding. Idle would bog down, oil light start flickering and the bike would stall. So chased that issue around for a couple of months until figuring out it was caused by the bloody carb boot clamps. The heat would cause the boots to enlarge, and the clamps I had weren't up to the job of securing the boots to the head and carbs. Got through at least three sets of boots until I worked that one out.

However, still an engine light flickering after 50 mins of riding, and idle drop and stall. What the hell. A friend asked me when I'd last changed the oil and I couldn't exactly remember (at least, I could not remember if it was after the last carb rebuild or before). So, drained the oil, and - again - it looked iridescent and brown, rather than the usual black. Did it smell like gas? Not overpoweringly, but to be honest I couldn't tell.

Finally, rather than using my go-to Rotella T4 (15W 40) I went with a suggested straight 50W dedicated motorcycle engine oil - now the thing is howling like a banshee with no engine lights in sight.

Problem solved. Turns out the stuck float was flooding the cylinder, dumping gas past the rings into the engine oil. Thinning the oil, buggering up the oil pressure when hot and everything then shitting the bed. With the carbs now correct, that's no longer an issue, but clearly I hadn't changed the oil since the rebuild and the oil was still gas-contaminated.

Quebec is famous for many things but good roads are absolutely not one of them. But down here they're great, and there's a stretch I like to call the Golden Miles for all sorts of reasons but lets just say you can give it the beans without the usual raft of concerns. This thing is f-a-s-t (I don't make a habit of going balls out but I do like to find out what I can wring out from the bikes I build at least once) - at WOT this thing'll get up to 200 without breaking much of a sweat. I on the other hand was sweating bullets but hey. Done the ton and then some.

Couple of flat spots on the torque curve but there's no way in hell I'm pulling the carbs again. I'm going to try shimming the needle and see if that helps - the flat spots seem to be at about 4- 5000rpm at ¾ throttle but I'm kinda ball-parking that as I most definitely had other things to concentrate on at the time, like mortality.

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I'll try and stick up a vid of it running. No engine rattle, no clutch rattle, it sounds pretty bloody great. I think I'm calling it done. Only took three years.

 
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Nice now if only I can sort my baby CB the same.
Still giving you shits Mike? Man I feel for you. Chased my tail for months with this bike. Stick with it - if I can figure this shit out then anyone can.

That or torch the bastard.
 
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Carb issues can be so frustrating. I learned not too long ago that I was reading plugs wrong, once again I am late to the party.
Your bike still looks great.
 
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