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Post by tucksie on Jul 23, 2021 17:09:32 GMT
Impressive work buster
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cb400a
Jul 23, 2021 18:07:27 GMT
Post by buster on Jul 23, 2021 18:07:27 GMT
Great news. That accelerator pump has to be the most pointless thing ever. yep along with the nest of superfluous vipers (hoses) that originally connected to the 'cannister', oh and not forgetting the air bleed through the rocker cover into the exhaust ports
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Post by comstar on Jul 23, 2021 19:01:27 GMT
So it was that they went down on the 400 Hawk from 32mm to 30mm carbs by 1980…..then added this?
Seems ridiculous even now much like the AIS system and carbon charcoal cannister they put on the 2001-on Bonneville (which we all remove). I’m sure the emissions produced to manufacture this stuff would have been at least ten times more destructive to the environment. Seems certain people are intent on destroying the planet but it’s certainly not those with at least half a brain.
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Post by buster on Jul 26, 2021 13:35:25 GMT
400t camshaft has just arrived, did a quick (rack of the eye job) comparison with the 400a camshaft but you can easily tell they are different, 400t visually has more duration. also bought a little superdream job lot on ebay the other day which included a tacho (mines a bit iffy) and an ignition coil all for a tenner
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cb400a
Jul 27, 2021 11:10:13 GMT
Post by buster on Jul 27, 2021 11:10:13 GMT
camshaft change first job remove the required odds and ends, plugs (so the compression doesnt shift the head), rocker cover and mag cover then carefully remove the rocker gear and the first sprocket bolt (dont drop it) then turn the crank 360 degrees and remove the second sprocket bolt (dont drop this one either ) and jiggle the sprocket off the cam and then the chain off the sprocket (fiddly but do-able) then just a case of wiggling the cam out through the cut outs in the sprocket and reversing the process to fit the new one (not the end of the world if you drop the chain these days as those telescopic magnet jobbers are marvelous). trickiest job with everything out is backing up the cam chain tensioner, my thuggish technique was to lean on it (well down the curve, get really low) with a tommy bar, this method didnt require that much effort, then nip it in place with the bottom nut.
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Post by buster on Jul 27, 2021 11:14:47 GMT
bike transformed, conclusion, erm 400 SD's and T's wont run right on a 250 camshaft, in similar news pigeons have been sighted in trafalgar square
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Post by terryc on Jul 27, 2021 12:07:35 GMT
bike transformed, conclusion, erm 400 SD's and T's wont run right on a 250 camshaft, in similar news pigeons have been sighted in trafalgar square Will you be trying the opposite next Buster ,a 400 cam shaft in a 250 .When I was at school there was a sign over the door of the science block it said " The impossible we do at once ,miracles take a little longer " seems like it could be your family motto
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Post by buster on Jul 27, 2021 13:30:02 GMT
bike transformed, conclusion, erm 400 SD's and T's wont run right on a 250 camshaft, in similar news pigeons have been sighted in trafalgar square Will you be trying the opposite next Buster ,a 400 cam shaft in a 250 .When I was at school there was a sign over the door of the science block it said " The impossible we do at once ,miracles take a little longer " seems like it could be your family motto could certainly be interesting, problem is the 400 camshafts are pretty expensive when they do come up. I'd guess that the exhaust ports would want a flow job to take advantage but again your into the unknown a bit (unless anyone knows different?). I used to have a tshirt with something similar on
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Post by buster on Jul 27, 2021 14:07:18 GMT
I'v been having an email chat today with Marcus from rexs speed shop (very knowledgeable and helpful guy), I mistakenly thought the advance system was built into the cdi, I was wrong (again ) its basically preset from the position of the high speed coil. it would seem then that I can carry on running the 250 stator/cdi combo and it should be ok. if I'm understanding this correctly then I can probably adjust the stator slightly to suit the 400 engine by undoing and turning slightly the two screws with the black paint on (the ones haynes tells you not to bugger about with but hey what do they know ). so come payday I'll send my spare stator in for a rewind and let the experimenting begin...
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cb400a
Jul 28, 2021 18:44:03 GMT
Post by buster on Jul 28, 2021 18:44:03 GMT
its a miracle! I'v found useful and relevant information in a haynes manual
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Post by buster on Jul 31, 2021 17:26:54 GMT
so swapped the ignition coil for a spare, still doesnt seem to advance. a bit of cross referencing between manuals would suggest that the 400a and the 400t/n both advance at the same point. so my latest barmy idea is to transplant the advance coils from the 400a to the 250 stator that the bike is running. 250 stator on top, 400a below, the bit circled in red is what I'm swapping transplant complete, the only visual difference is the slightly shorter doofers (circled) that leave a small gap, makes me wonder if the windings are the same?
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Post by buster on Aug 1, 2021 10:56:19 GMT
its advancing!
finally I think I'v cracked it. so it turns out you can convert a 250 ignition system to run a 400. so just a few little jobs to do, fit smaller main jets, swap the tacho and then I can start thinking about paint...
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Post by buster on Aug 4, 2021 14:36:02 GMT
so fitted the smaller jets into the 450 carbs the other day and all I ended up with was a pair of mismatched carbs, hmm, my best guess is that the pilots would need reducing by the same percentage as the mains? so back to the VB31's (I really hate being defeated) I adapted (bodged) a bit of rubber hose to allow me to properly blow through every orifice I could find and half a tin of carb cleaner and a lot of air later, the 31's are back on and running a treat, no more flat spot at 3000rpm, it now pulls cleanly and revs really nicely. the only other thing I'v done is go back to the 400a mag wheel as the extra weight smooths the engine out and just makes it that bit nicer to ride
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cb400a
Aug 14, 2021 21:31:11 GMT
via mobile
Post by johnjones on Aug 14, 2021 21:31:11 GMT
so fitted the smaller jets into the 450 carbs the other day and all I ended up with was a pair of mismatched carbs, hmm, my best guess is that the pilots would need reducing by the same percentage as the mains? so back to the VB31's (I really hate being defeated) I adapted (bodged) a bit of rubber hose to allow me to properly blow through every orifice I could find and half a tin of carb cleaner and a lot of air later, the 31's are back on and running a treat, no more flat spot at 3000rpm, it now pulls cleanly and revs really nicely. the only other thing I'v done is go back to the 400a mag wheel as the extra weight smooths the engine out and just makes it that bit nicer to ride This is the sediment trap fuel tap, a small magnet will fit in there...
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cb400a
Aug 15, 2021 10:52:24 GMT
Post by buster on Aug 15, 2021 10:52:24 GMT
if its any help I'd say that fuel tap is a pattern replacement that was on the bike when I got it and it looks very new to me, so they should be available
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