Really bad cold starting. Ign or fuel?

[Scottish Badger]

Oddjob, caps are new, fitted as part of the full service.....

Gareth, levels were all checked when the carbs were apart, all seemed good.

[TrickyMicky]

Just thinking outside the box for a moment, it would seem that most mechanical/electrical items have been checked, how about trying a supply of fresh, new petrol. The stuff that has been sitting in the tank, (for how long?), may well be contaminated, not unknown. If you have been using this wonderful new E10 fuel, the high ethanol content is very hydroscopic, and a significant water content could make it a bitch for cold starting. I only use Shell V-Power (E5) whenever possible.  Good luck, Mike.
     

[Scottish Badger]

Hi Mike, it's being fed new, fresh super-unleaded shell fuel at present (which in the north of Scotland has no ethanol), from a separate fuel feed container.

[K2-K6]

My 1980 650 is an absolute bitch to start when cold but once warmed up is perfect.

I found a way to get it to start first time every time no matter how cold it was and it sits there and idles perfectly.

Choke on full, kill switch off. Throttle open fully, turn over engine a couple of times.
Close throttle, kill switch on, press start button and it fires first time and idles perfectly.

Don’t know if this is the proper way to start it but works for me.

This is effectively, by closing choke and opening throttle (presumably not cv carb) forcing it to pull vacuum through opened main jet to pre rich the combustion chamber, a little like the old brit carb tickler to make it rich.

It does suggest idle circuit and or compression as initially being the places to check and verify.

This is what the squirt of e-z-start checks for, by giving it something to easily burn then it starts and subsequently pulls more vacuum on the jets to get it running.
Routine of not cranking and try with a squirt to see if you get response will confirm too little fuel, then you need to wotk out why.

[McCabe-Thiele (Ted)]

My 400 was exactly the same as yours before the rebuild - it was poor cold compression in my case.
Now after rebore it starts first kick from stone cold.
My cold compressions iirc were all about 120 psi from memory as I can't find a record - when checked hot they were closer to 150 psi.

A compression test will definitely give you an answer so you can rule it out if they are good.

[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.

[McCabe-Thiele (Ted)]

Good news that the compressions are reasonably good from cold - much easier & cheaper  to sort out the spark issue.

Pretty sure it's been mentioned here before that what looks good like a good spark can be something else under load inside an engine.

[Sesman]

Just a question on compression. How low does it need to be before experiencing cold start issues? Just wondering as the manual states 170psi so I’m wondering if the measurement methodology and/or equipment accuracy might mean the compression is lower than anticipated? Spark breakdown normally manifest’s as a misfire rather than a reluctance to start? Just wondering? Hope the ignition fiddling sorts it by the way.

[McCabe-Thiele (Ted)]

All I know is when mine were 120  psi it took a lot of cranking but would eventually fire up - no smoke particularly but would start first touch of the button for the rest of the day - I did test my readings when it was slightly warmed up - they all rose to above the 160 mark iirc - it was a cheap gauge as well. Never rode it before the rebuild or tested it since the rebuild - in high mileage fuel injected cars I found adding a small amount of 2T oil would raise compression and make them start much quicker.

I found poor cold start could  be due to the ignition being slightly retarded on cars or advance retard not working as it should. The whole coil LT /HT  impedance/ plug resistance are just a collection of words that I understand individually but as a sentence my eyes just gloss over.

[K2-K6]

Just a question on compression. How low does it need to be before experiencing cold start issues? Just wondering as the manual states 170psi so I’m wondering if the measurement methodology and/or equipment accuracy might mean the compression is lower than anticipated? Spark breakdown normally manifest’s as a misfire rather than a reluctance to start? Just wondering? Hope the ignition fiddling sorts it by the way.

I'd put a notional 130 psi floor on compression as practical limitations of all round running for these and most engine that start as specified around 170 psi book spec.  One of the giveaway is "its very smooth when warm" as low compression gives that characteristic and generally without the resonance in combustion of a higher compression engine. These motor are incredibly tolerant of low pressure though, and mask it well in general running.

To build a full picture, you'd need cold straight reading as base level, then plus some oil to see if the rings seal any better, then both the same when hot to give you reasonable analysis. That's any engine you suspect of being low though.

As noted though, it's not a show stopper on these for running them,  the smaller one's would have more trouble pulling higher gear uphill though 

[Cappodimonte]

Before you start it from cold next time open the fuel cap on the tank as it may have a blocked air breather hole. The other check is the fuel on/off tap, remove it and see if it has a collapsed internal filter or part blockage. Are you using E10 fuel ? Ethanol can strip older rubber fuel lines I have replaced all of mine with Viton tubing to prevent this along with an external fuel filter to catch any debris that the fuel tap filter misses. Good luck with your problem solving.