CB750 Barn find project - First Timer

[Underdog1]

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 

[Underdog1]

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

[Nurse Julie]

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

I think doing that may give you a false reading at the oil pressure switch but those who know alot more than me maybe able to comment further. It's more about getting oil to the top end that is important.

[Underdog1]

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?

[Nurse Julie]

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 🙂🙂🙂

[hairygit]

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!

[Underdog1]

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  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!)

[Underdog1]

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?

[Bryanj]

There are  only a few reasons for carb overflow,,
Float height incorrect
Bad needle tip/seat
Crack in brass standpipe inside float bowl

[Underdog1]

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

[Rob62]

Nice work ud!... getting there 

[Underdog1]

Nice work ud!... getting there 

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

[Nurse Julie]

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?

[Underdog1]

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?

[Rob62]

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....