Hot breath

[MrDavo]

Well after 4 months I finally went for my first legal ride on Candy, with the new black and silver plate that had turned up in the post from Chestnut. It all seemed a bit (/lot) gutless, after wondering if I had expected too much I took her for a short spin to Stockport on the M60, to find the top speed flat out was, er, 75mph.  The expression 'wouldn't pull the skin off a rice pudding' sprang to mind - who the hell would do that using a motorbike anyway?

On the way back, approaching the lights by the Blue Pyramid, there was a backfire, and I nearly lost it as the missing cylinder kicked in!! The clue's in the badge on the sidepanel, '750 Four'.  I can only think that a carb passageway was blocked with crud somewhere, or I'd wet a plug starting up - I did clean the float bowls out and spray brake cleaner through the jets, but you cant get everywhere doing that. I may put some fuel injector cleaner in the tank before my next ride.

After that she flew, and the HM300s made a glorious din! On the way back on the motorway I was able to go fast enough to remind myself of what the CB750 speed wobble feels like - only mild, I used to make it much worse on my old K1 in my youth by loading up the carrier at the back with full camping gear, or all my worldly goods when I went off to Uni. It never chucked me off, but scared me silly a few times. I got used to shifting my weight over the bars, if it got bad the trick was to open the throttle. That bike had suspiciously long looking Girling shocks, which probably didn't help the steering head angle any, but I never measured them, as I wasn't really aware of such things then, I just rode it like I stole it (and still do!).

Anyhow, the 'hot breath' refers to the tacho - despite putting in a new oil seal in the cam cover, which stopped the oil leak it had before, the engine is breathing down the tacho cable and fogging the glass on the tacho - I've never seen that before! I think I need to find and check the breather tube from the engine, but is there a seal at the tacho end that I could check or replace?

I cant see anything in my parts book, but the tacho is just sold as a single unit, no parts are listed. has anyone any tips on checking the breather?

[r1_pete]

The breather in the head is a pretty simple affair, comes off with 4 screws, I think you can get it off with the engine, it'd be a daft design if you cant. Just make sure it and the hoses are clear, it must be pretty gummed up if its venting up the cable, I would think it would blow the breather hose off before reaching the tacho head...

I'm wondering whether I'll ever ride mine when they are done, they are going to feel pretty lame after Fireblades, GSXRs, R1s and now the XJR1300.....

[MrDavo]

Thanks Pete, I'll have a butchers tomorrow, it looks like a garage day as the weather forecast is pants.

I think you can get it off with the engine, it'd be a daft design if you cant

I thought that about the cambox, so there's no guarantee that you can, but at least I can take the hose off and see if its blocked.

[Johnwebley]

run it with the hose off,

 if your getting enough pressure to push up the tacho cable,you will have a serious ring issue,
see if you can feel,or see fumes jetting out of the breather

[MrDavo]

Hmm, the thought of a 'serious ring issue' doesn't fill me with deep joy, though she wasn't smoking. It is possible that they may have become stuck during storage though - she runs ever so sweetly though (having just said that she was on three pots yesterday) 

Hopefully, as nearly everything else made of rubber on the bike had perished during years of dry storage in a hot climate, the rubber breather hose may be shot and has collapsed inside - we'll see soon enough.

[SteveD CB500K0]

I'm wondering whether I'll ever ride mine when they are done, they are going to feel pretty lame after Fireblades, GSXRs, R1s and now the XJR1300.....

Don't worry Pete.

It's not about performance, it's about riding a 40 year old bike.

My Triumph triples go fast, stop fast, handle well, start on the button and howls at 8k revs.

It doesn't draw a crowd, attract knowing nods from 50-something guys on the street, and doesn't make a sound that makes the hairs on the back of your neck stand up 

Steve.



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[MrDavo]

News from the garage, she disappointingly fired up on 3 again, using the old spit on the exhaust trick I found no 1 was absent. I checked for a spark, fine, then whipped the floatbowl off to check all was well (I'm amazed how easy that is with the spring clip, though carbs 2 and 3 must be harder). Next I checked the air screw, 2.5 turns out. All the others on one turn, confirmed as the default baseline setting when I checked online. (I used to have to dick around with no manual and no info, now a few seconds on my phone and I'm looking at the info I need). Anyway, I set no 1 to 1 turn out, and she started on 4 straight away. Hopefully that's it, job done. 

The breather is baffling. As far as I could tell I can't get the screws out that hold the breather cover on as there isn't the headroom. I was hoping to find a blocked pipe, but although rock hard you can blow straight through. Revving the bike on the stand, there doesn't seem to be any substantial pressure coming out, though we know there is enough for it to blow down the tacho cable.

I'm not sure what to make of this, surely if I had blow by issues there would be an oily gale. My mate with a classic bike shop says it could just be condensation, with heat rising through the cable, and suggest taking the clock off and drying it out over a radiator overnight. He also told me a horror story of a customer bringing in a bike with a leaky tacho drive, and a cable wound so it acted as an Archimedes screw, actually half filling a tacho with oil!!

[MrDavo]

This is turning into a blog of me snagging the K1 after years of inactivity, I'm back from the garage and finished for the day.

Tacho - a close look at my new oil seal, and I decided to tap it some more with a 10mm socket - it moved a centimeter or so further up the bore! I'm hoping that was my problem, we'll see. No test riding in this monsoon - more wanting to keep the bike pristine than being soft, but I also noticed that the tacho has lost its 'jerkiness' that I noticed yesterday - with the oil seal further up the bore it is engaging the spade with the fork better and not slipping out, I think.

I also gave her an oil change, and changed the brake pads. I noticed when I bought her that the disc was oily on one side, cleaned it with brake cleaner, but after a ride it was greasy again. CB750 brakes aren't great without being oiled, so a new set of pads went in today.The outer pad was in a right state, it had become contaminated at some stage (not sure what with - brake fluid / fork oil, or maybe the bike had been sprayed with something as preservative) and when it got hot the oil was  rising out.