Topic: CB350F Cold start issues

[ChuffChuff]

Hey folks,

So, since my last post about gremlins - had a shop who knows these bikes look at it and they also couldn't work out why it wouldn't run properly... turned out, a previous owner in messing with the head had completely crushed the oil channels running through the head... Anyway, I was then overseas for a bit but came across a 350F engine (from a race bike) up for sale, so grabbed that and said shop put it in for me. Bike now runs great... when it starts...
When the bike is cold it's near impossible to start, requiring a good number of cranks. It won't start or run at all with the choke on, but plugs are looking perfect. When it does start, it will die if the choke is turned on, or if the throttle is blipped until it's warmed up. Once it is warmed up though, as far as I can tell, everything works perfectly (save that the bike prefers to idle quite high, ~2000rpm). The shop thought since it was a race bike engine someone might've ported it or something like that. I should also note that the air filter is visibly dirty, and the filter cover isn't on.

What would you folks suggest the problem might be/first steps? I must admit I'm reluctant to dive into anything major since I'm fairly inexperienced and the bike rides perfectly - if only I could keep it warm...

[robvangulik]

What I would do is replace the filter, easy and necessary anyway, and find out why it idles that high, porting has nothing to do with that, my 400 idles steadily at 1200rpm with a Webcam camshaft and ported head. Probably synchronised with the throttleslides a bit high.
And in your old engine, you mean the copper oil channels on top of the head? Those can be easily replaced with new/better ones!

[carnivorous chicken]

AS suggested -- air filter is a good place to start. Then do the 3000-mile maintenance: adjust valves, set timing, check plugs, sync the carbs, etc. Then you know you should be working from a solid baseline.

But it could also be as simple as this: these bikes like a touch of throttle when you are starting them. Do you give it a little gas when kicking it over or hitting the starter button. It's definitely a learned skill, and it's especially true if your bike has been sitting between rides. Don't hold the throttle wide open, but rather as though you are revving the engine a little as you hit the button or give it a kick.

[Robbo]

In addition to the above, if it hasn’t already been done, I suggest you disassemble and inspect the petcock/fuel tap.  Clean and/or replace whatever parts as needed.

Check your tank is venting properly through the fuel cap vent.

This should rule out any fuel flow problems...especially when switched to reserve (speaking from experience).


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