Starting from cold issues

[paulbaker1954]

My 500 four K0 starts on second kick in summer but does still need choke.

I don’t really use the bike in the winter but went to the other day and getting it going was an ordeal after it had stood not run in a cold and damp garage for around a month.

I have tried the priming trick, various combinations of throttle position etc but it’s just a pain to start.

Once going and not even fully warm starts on the button.

Carbs are fully rebuilt Gerben units, no air leaks, float levels all bang on.

Fitted with Boyer ign and micro coils.

I have just ordered some new plug caps in case some damp etc is affecting them.

I have tried altering the pilot air screws 1/4 turn either way but no luck.

Is this hard starting just down to not being started for a while and is this usual ?

[Bryanj]

Yes and yes plus the boyer, like most electronics, needs a top notch battery to fire

[Erny]

Paul, interestingly I have the very same issues as you on my CB550K1

I would say starting with kick is practically impossible on cold engine in colder weather and pretty difficult on warm engine (using choke usually helps). This is with current carbs 069A (40/100 jets)

Interestingly, previous carbs set I had 022A (38/100 jets) were better for warm kick start (started on 2nd kick, w/o choke), I never tried them with kick when cold so cannot judge.

Col start on 069A requires using choke much longer at the beginning compare to 022A before in order to keep engine running on all 4 (of course I still need to keep some trottle to prevent engine stop until is warm enough)

I have boyer ign too with stock coils. And both carb sets were rebuilt by Gerben. All brass genuine Keihin

[Erny]

Yes and yes plus the boyer, like most electronics, needs a top notch battery to fire

In my case low battery is out of question, always fully charged before cold start

[K2-K6]

You've ordinarily got most conditions (as stated) going against you to initially fire petrol into combustion.

Full choke and "priming" may not help in this instance. With the plug and whole combustion chamber metals cold,  along with ingesting damp cool air,  then the mix is difficult to propagate a flame front fully so it snuffs itself rather than advances.  As soon as you get even a modicum of heating and normalising combustion conditions the problem will reduce.

You could try initially cranking it with no choke and listen for any firing,  then without stopping turning it over, start to bring the choke in slowly to see if that catches it.
This is just trying not to overwhelm the air with too heavy a fuel load initially so that the cold mixture is moved more toward "dryness" to favour getting it to light up. A bit like holding a newspaper across an old fire place to get it to draw 

[Bryanj]

Biggest problem today is the fuel, its simply crap compared to the 70's mix. The ethanol separates out and the "volatiles" evaporate away.
Even a perfect engine does not like starting after more than a week of sitting, it can make a difference if you drain the carbs but i have on ocassion had to drain the tank as wall(usually if stood over a month though)

[paulbaker1954]

You've ordinarily got most conditions (as stated) going against you to initially fire petrol into combustion.

Full choke and "priming" may not help in this instance. With the plug and whole combustion chamber metals cold,  along with ingesting damp cool air,  then the mix is difficult to propagate a flame front fully so it snuffs itself rather than advances.  As soon as you get even a modicum of heating and normalising combustion conditions the problem will reduce.

You could try initially cranking it with no choke and listen for any firing,  then without stopping turning it over, start to bring the choke in slowly to see if that catches it.
This is just trying not to overwhelm the air with too heavy a fuel load initially so that the cold mixture is moved more toward "dryness" to favour getting it to light up. A bit like holding a newspaper across an old fire place to get it to draw 

I like the idea of cranking with progressive choke actuation. I agree with your combustion theory as the engine catches with full choke on no problem but just doesn’t seem to pick up, it’s almost feels like a flooding scenario

[shifter]

Hi , I had the same problem with the 550 f1, on 69a carbs in the cold weather , the only way I over come this problem was to warm the motor / Carb by waving the hot air gun around the engine area , I don’t have these problems with the two CB200’s , S90 and Cbr , they all start with a nearly flat battery .don’t miss the 500/4   ,

[K2-K6]

"I like the idea of cranking with progressive choke actuation. I agree with your combustion theory as the engine catches with full choke on no problem but just doesn’t seem to pick up, it’s almost feels like a flooding scenario"

It's almost exactly that Paul, the initial fire as it starts to draw fuel through into combustion lights off as it's only just beginning to suck the fuel,  subsequently with choke full closed the atomisation and quantity break down into too large a droplet size to be easily encouraged to burn,  hence the flooding feel.

If you can think of how to coax it over those initial few seconds of running then the localized temperatures start to rise and off it goes.

It's one of those fascinating areas of combustion,  that the spark plug only lights the mixture within it's immediate vicinity,  subsequent mixture is effectively daisy chained on one fuel molecule to another to reach the outermost perimeter of chamber. If the droplet size is not within range (everything cold etc) then as it goes away from the plug it just can't handover the torch, as it were. 
Often it'll give a few chuffs as the ignition advance is trying to get it going before TDC,  with failure before that point producing no crankshaft impetus.

So although it's cold and logic suggests max choke is needed, this can work against you. If you get it back into range by reducing the restriction then the conditions become more favorable to develop full combustion happening around TDC.

[peterengland]

Always use the bike in winter if conditions are ok, pain to start when left for a week or so but never fails, usually start it twice a week to keep everything up and running. If its freezing cold and I've been away then a hairdryer on the intake manifolds works fine

[paulbaker1954]

Thanks for all,the input, glad to know it’s not just my bike but a more generic issue. Reminds me somewhat of the good old days of pre electronics and injection etc.

I seem to recall the favourite winter reason for not getting to work was “car wouldn’t start” and thinking back I too remember juggling with cranking and choke combinations on various vehicles to coax them in to life on cold Misty mornings.

I guess these days we are all just conditioned to much higher levels of reliability.

But then again is it as much fun......

[JezzaPeach]

It would be interesting to hear if anyone has tried some ‘cold start’ spray via the air box, particularly on a colder day.
I had left my 500/4 for at least 3 months at a neighbours garage, and it started virtually first kick. Good sign? Actually not, as I believe the petcock had been letting a little fuel past, keeping the float bowls full, and a lot of vapour in the carbs, so it started that easily despite spark plug no 2 not working, and plug lead 3 being semi connected!

[flatfour]

My 500/4 was never a good starter from cold after standing for more than a couple of days - symptoms as described earlier.

The 750 however, seems to start immediately regardless of length of time stood, air temperature etc. though it runs rather poorly and needs much juggling with choke and throttle for the first few minutes. (1972 750 K2, U.S. spec).

[SteveW]

Wonder if super unleaded fuel would be better?

[flatfour]

I don't know whether better fuel would help - I often run all of the bikes on Super Unleaded (the BMW needs it anyway) and in the past, I frequently used Avgas 100LL (low lead) with no change in the situation.

Today I wheeled the CB750 out after almost four weeks of rest due to really poor weather and, as expected it started third kick (I always use the kickstart from cold) and ran really badly for a couple of minutes until it had warmed a little, when everything settled down.