Coaxing life out of the old girl...the second attempt!

[ManicGTI]

Ok, so this is my second attempt at coaxing life into the four ('75 CB400F).  It's never run in my ownership...and here we are at the second attempt after finding a broken valve:

What's been done since my last attempt:
- Replaced knackered piston and valve, cylinder hone, new rings, lapped in all the valves.
- Tappet clearances set.
- All four Carbs have been rebuilt with cruzinimage rebuild kit.
- Float heights ~21mm.
- Gapped both points.
- Start attempts with Choke closed, No throttle and Full Throttle, no Airbox, Exhaust refitted.

So what was the result?:
- Turns over on the starter fine (but battery runs out of steam quickly)
- It did 'splutter' once or twice randomly, but didn't 'run' at all.
- Dry Compression test on the starter gives all 4 cylinders at approx 100psi, I believe this is acceptable.  New rings so they won't have bedded in yet.
- All 4 carb bowls are filling with fuel, no leaks. 
- I'm getting spark at all 4 plugs.
- No visible fuel on the spark plugs, as the carbs are filling now, I had thought this would be more obvious?


TO DO:
- New Battery.  Battery is a small one that Isn't holding charge and doesn't last long when turning it over.
- New Fuel.  The fuel is now a bit old as it's sat in the garage, so i'll swap that out next time i'm up, I drained the carbs in the meantime.
- Check Cam timing isn't 180 Deg out, I did check but I'll do it again.
- Ignition timing check,  I don't see how I can get this massively out as the points plate only bolts on one way, or am I missing something here?

Is there anything obvious i'm missing here? I thought at this stage I would be getting at least stuttering/bad running.  I get that my carbs likely need setting up properly, I've set them to the basic bench setup as per the Workshop manual.

Thanks for any input in advance, always appreciated!
 
David

[royhall]

What bike is it your working on? I should know as I read your previous posts but cant remember.

When you say you rebuilt the carbs, did you remove all the old petrol gunge (varnish) especially from the idle circuits. On start-up most of the fuel comes from this circuit. Its a bit strange your cranking the engine and its not wetting the plugs at all. May be wrong but that's where I would look.

Good luck with it. Cheers.

[ManicGTI]

It's a '75 CB400F.

I believe I did clean out the carbs fully (I fully stripped them all), however if there's a specific idle circuit I could go back and check then I'll be more than happy to do that. To eliminate an option as much as anything else!

Thanks for the pointer.

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[mike the bike]

Check the points cam is on correctly,  it's very easy to put it back on 180 degrees out.  Done it once.  Woke up at 3 o'clock in the morning with a eureka moment,  turned the points cam 180, it started for the first time in months - very loudly and smoky.   The neighbours all though I was mental.

[ManicGTI]

I have the Coils feeding 1/4 and 2/3

I can't get it out of my head that I don't think fuel is getting through, is there anyway of simply bench testing them off the bike to check fuel is getting through the idle system?

Maybe an Air leak between carbs and block, or blocked Idle channels in the carbs?  Seems strange that all four carbs would have the same issue though.

[royhall]

Have you set your carb slides too low so they are fully closed. Managed to do that on my 350f.

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[mike the bike]

If it was an air leak it would still run but not very well

[Rozabikes Tim]

Seem to remember when I had similar problems with my 400 after gummy carbs, it was blocked emulsion tubes. Have you removed them and inspected all the small holes are clear. I then found it would start but not run at lower revs - then it was the slow running jets.

Tim

[stevush]

I'd use easy start. If it fires up better then its likely to be fuel, if theres no change look at the ignition.
Easy start is not good long term but in this situation it almost eliminates one or the other.
I learned that from an ex RAC breakdown chap.

Steve

[tom400f]

Have you cleaned your carbs ultrasonically, Dave? My feeling is they are gummed up inside...

[ManicGTI]

Have you cleaned your carbs ultrasonically, Dave? My feeling is they are gummed up inside...

A fair point...I haven't.  I cleaned them with white spirit, tooth brushes etc.  A friend at work has just bought a small cleaner so maybe I can call on his services.   Maybe I need a cutaway of a carb so I can work out what channels I may not have cleaned sufficiently.

Have you set your carb slides too low so they are fully closed. Managed to do that on my 350f.

Have I missed something when 'bench syncing' the carbs?  My understanding from the Haynes book was that I set the Sliders to the same level at WOT.

Seem to remember when I had similar problems with my 400 after gummy carbs, it was blocked emulsion tubes. Have you removed them and inspected all the small holes are clear. I then found it would start but not run at lower revs - then it was the slow running jets.

I did clean the OEM Tubes, but have now fitted new ones from the cruzinimage rebuild kit.

[totty]

Sounds like the bench sync could be the issue, you can do them open or closed, but doing them open can result in them ending up fully closed.

To check all passages are clear and gain an understanding of what leads to where just spray carb cleaner in each hole and see where it comes out.

[ManicGTI]

Ok, I'm back!

I moved house in April and insisted on getting a garage (incredibly rare in London), happily it means that last weekend at last I was able to get the old girl out of storage and down to the house.  Should make the trouble shooting process a little more achievable.

Dave