Post by: Scottish Badger on February 22, 2023, 08:30:02 PM
So far, I've checked the valve clearances, ignition timing, removed the carbs and given them a full overhaul, fitted NGK Iridium plugs, new air filter, oil change and new battery. The carbs were bench-synchronised so can't be that far out.
Once the engine is running and warmed up, it's really smooth and quiet and after tweaking the idle mixture screws (max adjustment about 1/4 turn from factory on one carb, 1/8 on another two) it idles beautifully. When switched off, hot, it will re-start on the button instantly.
My problem is cold starting. No amount of throttle or choke seems to have any effect, after what seems like ages cranking it, it'll fire randomly with the choke almost fully off, repeated attempts will get it to go a bit longer each time until eventually it'll pick up and run. I've tried more and less fast-idle on the adjuster, altering the idle speed screw, and every combination of throttle and choke imaginable! I get nothing at all trying to kickstart it. The carbs have been back off and re-checked, the plugs have a lovely fat spark whilst cranking and are clean....
Help, it's doing my head in!!
Post by: McCabe-Thiele (Ted) on February 22, 2023, 08:35:14 PM
Post by: Nurse Julie on February 22, 2023, 08:54:40 PM
Post by: Scottish Badger on February 22, 2023, 09:14:58 PM
Julie, the Iridiums were fitted to see if they made any difference - they didn't. It was exactly the same with the D8EA's previously fitted. I've used Iridiums in all my bikes to good effect, my XL500 fires up first kick from cold since fitting one - ok, different ignition system type, but the plug made a big difference.
Post by: K2-K6 on February 22, 2023, 09:29:46 PM
Have you got any compression figures for it ?
Post by: Scottish Badger on February 22, 2023, 09:35:59 PM
Post by: McCabe-Thiele (Ted) on February 22, 2023, 09:51:09 PM
Post by: Oddjob on February 22, 2023, 10:06:41 PM
Post by: Scottish Badger on February 22, 2023, 10:18:07 PM
Carbs have been off and fully stripped / rebuilt - all jets checked clean and correct, needles checked (one did have an incorrectly positioned circlip originally, causing #1 cyl to run a little rich). Choke functions correctly, all choke plates synchronised properly, spark is fat - checked each cyl individually, cranking on starter with the other three still fitted and yes, you can really hear the difference in compression so as much as I haven't actually done a compression test, I doubt there's any issue there to be honest and it doesn't produce any smoke on startup or when riding.
I'm 57, been working with bikes and engines in general since I was about 14 - everything checks out, yet first start of the day is horrendous!
Post by: SteveW on February 22, 2023, 10:24:02 PM
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.
Post by: Laverdaroo on February 22, 2023, 11:08:47 PM
I had done same as you and found similar results although I never ran it until hot, hot as it was only in the workshop but she was at operating temp. The old leads had just lost the poke and a bit of verdigris had crept up leads causing a crap or weaker spark. If you have the length, it’s a good tip to get a better zap out of the plugs.
Obvs if you’ve already done this then I’m sure somebody that actually knows stuff will be along soon to add something of relevance to your discussion
Hope that’s at least good for thought……
Post by: Scottish Badger on February 22, 2023, 11:49:25 PM
Roo, I have a big fat blue spark at all of the plugs, checked one at a time with the other three still fitted so the electrics were actually loaded up by the starter working against compression. Thanks for the tip about the leads though, I do have a spare set of new, unused coils that I may try (same as these, no idea of quality.. https://www.ebay.co.uk/itm/144813238373).
Post by: Laverdaroo on February 22, 2023, 11:54:32 PM
Just seen the rest of the posts as I went to the van for summut and put my hotspot thingy on and got some decent interweave .
Sent from my iPhone using Tapatalk
Post by: Oddjob on February 23, 2023, 12:22:25 AM
Post by: taysidedragon on February 23, 2023, 12:35:51 AM
Post by: Scottish Badger on February 23, 2023, 08:27:21 AM
Gareth, levels were all checked when the carbs were apart, all seemed good.
Post by: TrickyMicky on February 23, 2023, 09:33:11 AM
Post by: Scottish Badger on February 23, 2023, 09:37:15 AM
Post by: K2-K6 on February 23, 2023, 09:58:27 AM
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.
Post by: McCabe-Thiele (Ted) on February 23, 2023, 10:00:10 AM
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.
Post by: Johnny4428 on February 23, 2023, 10:30:28 AM
but they should have been 12.5mm. They are all now set correctly.
Post by: Deano400 on February 23, 2023, 10:39:01 AM
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Post by: Scottish Badger on February 23, 2023, 05:21:53 PM
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!
Post by: K2-K6 on February 23, 2023, 06:00:03 PM
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.
Post by: Scottish Badger on February 23, 2023, 07:13:05 PM
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.
Post by: McCabe-Thiele (Ted) on February 23, 2023, 10:46:45 PM
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.
Post by: Sesman on February 24, 2023, 07:52:51 AM
Post by: McCabe-Thiele (Ted) on February 24, 2023, 08:20:49 AM
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.
Post by: K2-K6 on February 24, 2023, 08:44:40 AM
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 :)
Post by: Cappodimonte on March 01, 2023, 07:19:19 AM
Post by: Scottish Badger on March 04, 2023, 08:13:10 PM
K2-K6, the coils are 4.8 Ohm so ought to be ok......
Not had a chance to do any further investigation this last week, the clutch went on one of my cars so that's been taking up my time. Turned into a nightmare of struggling to bleed the system, finding out I'd been supplied incorrect parts and now delays getting the right parts! Hopefully it'll be resolved early this coming week and I can get back to the bike!
Post by: Scottish Badger on March 20, 2023, 07:57:05 PM
Hi folks. I finally got to the bottom of the bad starting. It was nothing to do with the ignition system, nor the carbs themselves.... but everything to do with the carb adaptor elbows on the head and the filter box connecting rubbers!
In frustration, I took the carbs back off and went through them meticulously - and found nothing untoward! I'd ordered up new mounts and rubber stubs in advance for the new engine (when I get round to building it!) but decided to fit them anyway. That was when I discovered that someone in the past has fitted the stubs the wrong way round and basically distorted them forcing the carbs into them - the combination of time and heat has kind of "set" them into that position, and most likely not sealing correctly. I also found silicon sealant on the o-rings between two of the adapters and the head, not good! The rubber connectors between airbox and carbs were hardened with age as well, and probably not sealing onto the carbs all that well - which I appreciate will cause midrange and possibly top-end fuelling issues, but shouldn't really have much effect on cold start.
My theory - the elbows onto the head weren't sealing properly and the cylinders were drawing air past them when cold, but they were sealing up after a little thermal expansion kicked-in, which is why I wasn't finding any leaks, I was checking with the engine hot!
After putting it all back together this afternoon, it started straight up within 2 seconds of pressing the starter button. Re-balanced the carbs again, engine purring like a kitten! The needle on no.1 gauge appears slightly different, that's how the camera "froze" them, the needles were constantly fluctuating a couple of degrees. [attachimg=1][attachimg=2]
Post by: McCabe-Thiele (Ted) on March 20, 2023, 10:12:30 PM
Post by: Johnny4428 on March 21, 2023, 07:27:32 AM
Post by: K2-K6 on March 21, 2023, 08:26:40 AM
These (well most small engines) have such a small concise flow through the idle circuit that any spurious air supply route can make quite a difference.
All the better when you get something running on point.
Post by: Sesman on March 21, 2023, 08:26:54 AM
Post by: taysidedragon on March 21, 2023, 09:44:50 AM
Hallelujah. Glad it worked out. I genuinely didn’t know there was a right and wrong way round for the carb rubbers. Is this just a 400/4 thing?
On the original 400f rubbers they are numbered, 1&4 and 2&3 so they get fitted in the correct position.
Post by: Sesman on March 21, 2023, 10:42:12 AM
Post by: Scottish Badger on March 21, 2023, 10:55:55 AM
Just ventured back out to the workshop - fully cold, started first prod of the button with 3/4 choke. Happy days!
Post by: taysidedragon on March 21, 2023, 05:36:49 PM
Gareth, the adaptors were in the right positions, but one was mounted 180 degrees out! Someone must have had one heck of a time and really persevered to force the complete carb set back in initially.......! I've found a few "bodges" as I've been working my way through the bike, at least I now know it's safe to go out on (when it warms up a bit, lol).
Just ventured back out to the workshop - fully cold, started first prod of the button with 3/4 choke. Happy days!
Great news. All ready for the good weather. 😎
Post by: Sesman on March 21, 2023, 05:39:09 PM
Post by: Johnny4428 on March 22, 2023, 07:13:31 AM
I must add that these were replacement rubbers so can’t vouch for originals.
Post by: Sesman on March 22, 2023, 07:29:12 AM
Post by: PatM on March 22, 2023, 12:59:18 PM
It will start like it did when it was brand new after its been running- but leave it a couple of hrs till it gets cold, and its a real bugger. its also running week on one pot, yet when I did a compression test, it was the same for all 4. Ive even tried another bank of carbs- and same problem.
Now, due to ill health and such personal reasons- Its not turned a wheel for nearly 3 years and I think the cam chain tensioner may be siexed- as the nut/bolt has been repalced at some time and loosening it has little effect. My fear is- snapping off bolt/studs- but my next move would be to tape the top cam cover off and check the cam-chain and horizontal mark to make sure its NOT a work cam-chain.
Post by: Sesman on March 22, 2023, 01:53:01 PM
Post by: PatM on March 22, 2023, 05:17:25 PM