SOHC.co.uk Forums > CB350/400

Really bad cold starting. Ign or fuel?

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Johnny4428:
My 550k3 uses the same method to start from cold. I think that this method of starting is written in a Honda handbook for starting in cold conditions. On the subject of float levels, I was quite sure mine were correct until I checked again after setting them a couple of years or more ago, I had set mine to 14.5mm
but they should have been 12.5mm. They are all now set correctly.

Deano400:
Don't know if you've checked the Fast Idle when you overhauled the carbs, but if not might be worth a look. Could be an issue from the PO as you say it was a bad starter from the day you got the bike. When you put the choke on the Fast Idle lifts the slides (and therefore the needles) to give extra fuel for cold start.

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Scottish Badger:
This morning I did a cold compression test.

1. 135
2. 135
3. 135
4. 125

I'm not at all worried about these readings, I actually think they're reasonably acceptable for a 36,000 mile bike in a cold workshop in the north of Scotland, haha.  I'm figuring no.4 is slightly lower because of that cylinder having previously been running rich due to the previously mentioned carb needle circlip being in the wrong groove when I bought it last October (Yes, I did say no.1, but I got it wrong, it was no.4, sorry.)

I then put the plugs back in and tried cranking with kill switch off, full choke, full throttle for a couple of seconds, then went for a start.  Almost exactly the same as previous, the odd cylinder firing, but no start.

I then pulled the air filter and gave it a squirt of brake cleaner (not a lot, that stuff causes bad detonation!) and it was exactly the same.....!!!!

At this point I decided - because it was an option I hadn't tried - to replace the ignition coils with the spare new "di" marked ones I mentioned earlier and tried again. It fired up after about 4 or 5 seconds of cranking, roughly, coming onto all 4 within a few seconds more.  Now, I had a big fat blue spark with the original coils, so I've no idea why this has made any difference.....

I'm off to Glasgow tomorrow then on to the Borders to pick up some XL500 engine parts, so I'll try it again from cold with the new coils fitted on Sunday or Monday and we'll see what happens. If the coils have cured it, I'll be quite happy, but I still don't understand why when the spark at the plugs was really good!

K2-K6:
Have you got a primary circuit Ohms rating for the di coils ?

Electronic system can often use lower resistance as standard to match different dwell control. If they are, then with points its effectively running them as a "hot" coil from extending saturation which may account for the performance difference. 

Scottish Badger:
K2-K6, that's an interesting point (no pun intended, haha).  It never occurred to me to measure them, it was one of those "what the hell" moments..... I'll check next time I'm in the workshop.

However, I've done some digging back through old forum posts and found a bit of info on resistance - to be precise, the resistance of plugs and suppressor caps.  Julie had said earlier to remove the Iridium plugs (which goes against the grain, to be honest as I've had such good results from them in the past) and fit a set of standard D8EA plugs, so I went back out to the workshop and found the original plugs I'd taken out and guess what - they're DR8EA! Cross-checking the suppressor cap part numbers, they are also 5Kohm items, so it seems there are two resistances, plug and cap, which won't have been helping. Your theory on the coil may be the reason it's giving a stronger spark now, if indeed it is?  I've ordered a new set of D8EA plugs that should hopefully be here on my return, I'll fit those (and check primary resistance) and see if that helps matters.

I do have an electronic ignition setup that came with the bike (new in box, never fitted) so I'll look into that in more detail as well and see if it's compatible with these replacement coils.

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