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Messages - Underdog1

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46
Project Board / Re: CB750 Barn find project - First Timer
« on: August 25, 2018, 07:08:54 PM »
Could be  vacuum in the tank caused by a blocked breather. Take the fuel cap off when it conks out and if air rushes in it could be the culprit.
Tried this at the time, didn’t make a difference

47
Project Board / Re: CB750 Barn find project - First Timer
« on: August 25, 2018, 05:13:09 PM »
Conking out after 15 mins then not starting till cooled down sounds like an electrical component failing at higher temperature... coil maybe. Or it could be fuel starvation but unlikely....

Could be the condensers, they are the original ones.

Didn’t have any tools with me to check the spark, was thinking at the time it would be ideal to have a spare spark plug in my pocket as I could do it with no tools

48
Project Board / Re: CB750 Barn find project - First Timer
« on: August 25, 2018, 10:47:27 AM »
Your bike reg number actually comes up on DVLA as a 400 Yamaha, registered in UK May 18 Something not quite right there. Have you insured it as a Honda 750 or a Yam 400?
As a Honda 750. I’ve checked my DVLA paperwork and it all checks out so I’ll give them a call in case they’ve made a mistake on their system somewhere.

Had the old girl out again this morning, keeps dying after 10-15 mins and then doesn’t want to run until it’s cooled down.

Is this likely to be battery related? Don’t think it was fully charged when I set off but doesn’t make sense why it would spring back to life after cooling down. The other thing that has crossed my mind is air leaks around the carbs opening up when things start expanding?

49
Project Board / Re: CB750 Barn find project - First Timer
« on: August 25, 2018, 08:49:26 AM »
Nice work ud!... getting there  8)

Painted the side covers late yesterday and have contacted a local upholsterer ability making a seat cover (unfortunately my friend isn’t able to do it).

Also I’ve insured it with Go Skippy. £90.97 fully comp with only a £50 excess. Wasn’t sure on value so I stuck 4.5k down (gotta be optimistic!). Strangely you can find these old bikes on a  lot of comparison sites and on others where you have to put the VRN in it was coming up as some 400cc Suzuki..!? Double checked my paperwork from the DVLA and it’s all correct

50
Project Board / Re: CB750 Barn find project - First Timer
« on: August 24, 2018, 08:44:30 PM »
There are  only a few reasons for carb overflow,,
Float height incorrect
Bad needle tip/seat
Crack in brass standpipe inside float bowl

The carbs have been fully rebuilt with a cruzin image kit, I set the floats to 26mm above the carb body, no cracks in any standpipes.

It’s intermittent and seems to happen after I shut the engine off which in my head makes me think potential stuck float - maybe there’s a burr or something.

Will have to get the bowls off again and have another look, for now I’m just turning the pet cock off when I stop

51
Project Board / Re: CB750 Barn find project - First Timer
« on: August 24, 2018, 06:05:15 PM »
Today was a good day

Found that one of the kill switch wires was going into the lighting circuit rather than to black, sorting that out sorted the power to the coils, not sure how I missed that the other day!

Popped the clutch out and rubbed down each of the metal plates with 600 grit, plenty of wear left all round so just reinstalled and voila, my clutch is working.

Popped the tank and seat back on along with some half painted side covers and took her out for her maiden voyage (private road of course). All seems great, apart from a lumpy idle, carbs haven’t been synced so that may help but I don’t think pods do the idle any favours, had to set it to >1000rpm to avoid stalling. Brakes need adjusting but no real dramas there.

Was very surprised with how nicely it pulls especially as I’ve just stuck #42 and #120 jets in there as just somewhere to start, was fully expecting It to be rough whilst I dialled it in.

Where’s best to go from here with the carbs - sync them and get some miles on the clock and then note down flat spots etc check  plug colour and adjust from there?

Also one or two carbs are overflowing when the engine is switched off, floats aren’t stuck and the pins are nice and clean, any usual suspects to look out for?





52
Project Board / Re: CB750 Barn find project - First Timer
« on: August 20, 2018, 03:34:57 PM »
Well done. Take the tappet covers off to see if oil is spitting out and maybe you should locate the tacho drive cable in correctly 🙂🙂🙂

Already done the tappets and there’s oil spitting about in there  :D with regards to the tacho cable it’s a super cheap one from mandp and isn’t a very good fit despite them saying it fits the bike

As regards power to the coils, check that you have 12v reaching the kill switch on the bars (inside headlamp). As regards the clutch, it's not a difficult job to strip it out and free it off, and far safer than bumping it and hoping it will free off, especially if you have hotwired the coils!

Nice one mate that’s why we ask these questions (so I don’t end up in my neighbours hedge!)

53
Project Board / Re: CB750 Barn find project - First Timer
« on: August 20, 2018, 02:58:53 PM »
It’s a runner! (Well kind of)

https://streamable.com/yyij3

No power to the coils so have jumped them off the battery to get her fired up

Few issues:

Obviously need to sort power to the coils properly
It’s idling at 3k, probably due to mebench syncing with too much thread out the top of the throttle slides (can’t reduce it with idle screw any more)
Intermittently dumping fuel out a few carb overflows which I’m a little confused about as I spent ages setting up floor heights etc and most bits have been replaced.
Clutch not engaging, obviously the bike has been stood a LONG time so presumably the plates are stuck together.

I can figure out most of the above it’s just the clutch, is it worth bumping in first and taking on a little ride to see if it unstick or is this always a strip down and rebuild job?

54
Project Board / Re: CB750 Barn find project - First Timer
« on: August 20, 2018, 10:59:16 AM »
Wow, oil pressure at 10 kicks....thats bloody amazing, well done.
Just on this I don’t know whether it helped but I poured as much oil as I could into the gallery above the points, might have helped I’m not sure

55
Project Board / Re: CB750 Barn find project - First Timer
« on: August 19, 2018, 10:42:24 PM »
BTW, bikes looking great but the drive chain looks very, very tight, needs about 1" play in it.

Precisely 22mm at the mid point, checked it earlier  :) :)

56
Project Board / Re: CB750 Barn find project - First Timer
« on: August 19, 2018, 09:58:24 PM »
Here is the specific part you need to comply with, copied from the regs.

The rear registration plate must be lit. Most motorcycles will light the registration plate with a rear position lamp, but some will use a separate registration plate lamp.
Some registration plate lamps may be fitted behind the number plate.

Yeah no dramas thought there was something out there covering it but I saw this https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/449526/mot-inspection-checklist-motorcycle-vt29m.pdf and thought I wouldn’t need to bother

Like I said I’ve got one to go on anyway

57
Project Board / Re: CB750 Barn find project - First Timer
« on: August 19, 2018, 09:23:16 PM »
Made a lot of progress over the last few days, got the engine back in and built the bike back up, getting oil pressure light go out  now after 10 kicks or so which I’m happy with.

Just been doing the points gaps and timing , think I’ve got it as best as I can. Filled some fuel in a remote tank and tried to fire her up but not getting a spark. Condensers were working before strip down.

Any common things I should be checking? I’ll recheck that something crazy hasn’t happened with the points gaps tomorrow, happy with progress but I’m unsure what to look at regarding the sparks




How are you going to run the wires for the number light ? I had to run mine inside the swinging arm so not to snag anywhere.

I’ve got one I can fit but after seeing that it’s not an MOT requirement (despite the bike being MOT exempt) I haven’t fitted it yet. Granted that an MOT doesn’t cover all legal requirements if I do put I on illprobably just zip tie the cable on the inner side of the swing arm rather then drill just for ease


58
Project Board / Re: CB750 Barn find project - First Timer
« on: August 19, 2018, 08:30:26 PM »
Obviously start with checking all wires you have disturbed, and the connectors are clean and tight, especially the ones where the leads from the points join the main harness, where the rear brake light wires also join the loom. I assume the engine kill switch on the bars is set to the centre position (run)If after that you still get no spark, test for 12v + on the blue then yellow points wires, using the points plate for the 12v - lead. you should get 12v there with ignition on and kill switch in run position.

Thanks mate will work though that in the morning and see where I’m at   ;)

59
Project Board / Re: CB750 Barn find project - First Timer
« on: August 19, 2018, 07:21:47 PM »
Made a lot of progress over the last few days, got the engine back in and built the bike back up, getting oil pressure light go out  now after 10 kicks or so which I’m happy with.

Just been doing the points gaps and timing , think I’ve got it as best as I can. Filled some fuel in a remote tank and tried to fire her up but not getting a spark. Condensers were working before strip down.

Any common things I should be checking? I’ll recheck that something crazy hasn’t happened with the points gaps tomorrow, happy with progress but I’m unsure what to look at regarding the sparks


60
Project Board / Re: CB750 Barn find project - First Timer
« on: August 17, 2018, 10:01:04 PM »
Great, fingers crossed all goes well this time. Just checking.....you did clean out all the swarf after your re modeling with the dremmel ?

Yeah I covered everything with cling film to stop it getting places and then wiped out where needed

I’ve heard these babies run well on swarf anyway

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