Hello from Cambridgeshire

[Alan4]

 Hi from Cambridgeshire – I am new to the sohc forum.
I started riding again a few years ago after a break of 25 ish years , and the number of bikes in the garage has  grown to 4   unfortunately not all on the road. Presently there is:
1958 – Francis Barnett Cruiser – mid restoration – and has been in that condition for a few years  slowly getting there.
1967 BSA Barracuda – on the road
1976 2x Honda 400 Four’s  ………
 One now fully restored and on the road after a total rebuild .
 The other one was the donor bike for the rebuild [ since there was a lot of parts missing] ,which I am now collecting replacement parts for a rebuild .   

So apologies having said hello  I now would like to ask for some help …………
As part of the rebuild, I rebuilt the engine in 2 stages:
1 replaced the missing parts, carbs –sump oil pick up etc etc ,  had the engine running  did a couple of hundred miles  but the engine was rattley and the cam chain adjuster was not working …. But the engine ran ok  …..
2 … so out came the engine  total strip down to allow the fitting of  new cam chain ,      [at some time the chain had been allowed to be slack and had riveted the pivot point on the adjuster- apparently a well-known 400 four problem] new rings, Seals , gaskets etc.  Adjusted the clearances and set up the timing static and with a strobe.  Balanced the carbs, then keeping the revs down started to run in the engine.
………..But ………..
Below 2000rpm if you open the throttle the engine has no power and dies back for a couple of seconds then will pick up ….. is ok above 2000 rpm  …. Really frustrating trying to pull away at a junction.
Checked all around the carbs for air leaks etc   ….. rechecked the timing ….  checked I was using the right marks  Even checked that TDC is TDC all ok…  then advanced the timing approx. 5 to 10 degrees and the bike runs 95% better ………. What Have I done wrong?? I was very careful about setting up the cam chain alignments / timing but maybe its wrong???
Anyone seen this before?

[K2-K6]

Hello Alan and welcome to the forum.

It's a bit unusual as you say as you appear two have most things covered in your build and checks. I think it would be worth it to check the cam timing for your own piece of mind and I think it's fairly easy on that engine to go through a check in situ. I'm not so familiar with th 400 (more the 750 on which you can't get access to the cam after installation) so others may be able to contribute more as to routine on that one.

As you think though, my first guess from experience of people getting a tooth out on cam position would be you can to a certain extent mitigate some of the effects by altering the timing as you've done so well worth a look back through fundamental setup to verify your original buildup.

You've checked timing, but have you verified the advance and retard is working ok? Although it seems not to fit the problem you have stated it's again worth confirming all is ok.

[Alan4]

thank you for your suggestion  of rechecking the cam set up ... yep I agree ...I  was sort of coming to the same conclusion that I needed to go back  and set it all up again, .... bit of a pain but I think that with a bit of fiddling  I may be able to do it with the engine in the bike  ........   regarding the advance   I have tried it with both the original points etc and an electronic ignition .
Thanks again for the suggestion

[mike the bike]

Its easily do able with the engine in.  Remove the breather cap, then the rocker cover and with the crank set to the T mark on the advance retard unit, tne 2 lines on the cam sprocket should line up with the cylinder head, as per the manual.
Let us know how you get on.

And welcome to the forum from a fellow 400four owner, restorer and rider.

[matthewmosse]

I had a similar issue on a cb500 once, turned out that at some point a wrong part had got in there, the advance mechanism was a wrong un, took me a while to spot, and I could only tell after checking the wrong unit to 3 or 4 others from my spares stash, and carefully comparing them side by side, very similar units but the odd one was out for my engine, no idea what it was off, one of the few bits I chucked as far as I could throw it into the bushes, cost me a lot of headscratching.

[UK Pete]

Hi Alan welcome aboard fella
pete

[Alan4]

Thanks for all the welcome's , reply's and advice. Spend yesterday going back to basics again ,  removed the Cam cover  hoping that I had done something stupid and had it out of alignment  but it looked ok ....so I moved it one link either way and that was way out of alignment , so set it back to where I started . Checked the carbs balance was ok , played with the air screws  ...  could make things worse but no better , reset up the timing etc  again .. Result  no difference /same problem .   With the timing advanced 5 - 10 degrees it becomes better - by late afternoon today had done enough running in miles to start opening it up a bit  ... had a silly smile on my face when I got home  it certainly goes ok  ...just the low revs issue   .... noticed that it is worse when the engine is hot  ... so thinking carbs  [ I will grab any idea at the moment  ]  ... unfortunately  I had not done anything to them  as part of the engine strip and they worked ok  before .... I have another set of carbs  may try them ...   

[mike the bike]

I'm thinking the pilot jets are clagged up. Giving the carbs a strip and clean wouldn't hurt.

Note, I wrote jets and not jet's. 

[AshimotoK0]

Welcome ...manuals here if you don't have already

http://www.sohc.co.uk/index.php/topic,8884.0.html

[Trigger]

Welcome to the mad world of the SOHC, Enjoy.

[Alan4]

Took  the advice to look at the pilot jet area , so prior to removing the carbs  to strip down  , I screwed all 4   pilot jet mixture screws in and out  a few times , then set them to 2 ¾  turns out rather than the recommended 2 turns  …. Having sort of guessed that since issue was worse when the engine was hot more air was needed  [ I assume that is how it works]   ….   having played with them before  I was not that hopeful … but    wow  it has cured it …..    put the mixture screws  to 2 ½  and still ok  ………    must of just been the settings ?     ….   …. It works so  I will leave alone ….. thanks for all the advice , help, links to manuals + rebuilds  ….