E: Engine Comet will not start when hot

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Monkeypants

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When it won't start, have you tried dumping a little gas down the plug hole to see if it fires?
If the mag is good, it should give a pop or three. A teaspoon of fuel in a plastic syringe with a short bit of small tubing at the end works well for this.

Glen
 
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Bill Thomas

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Not sure I like your plugs , Champion N5 or N9Yc would be better. As Glen says a squirt of petrol down the hole with the throttle open, Then close it , Be careful !!.
You can get something called easystart spray would work the same, Just to see if the Mag' is OK.
Have you tried bump start in first gear, Have you a Son or somebody can give you a push ?.
Your youtube thingy does not seem to work.
Cheers Bill.
It's been said on here before, If you just get it over compression, Then move with the kicker a small bit,
Let the kicker return ,
Then give it a kick, Seems to get the flywheels in a better place for starting on some Comets.
 
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vibrac

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It is worth trying different kickstart moves after compression before THE kick.
When I first tried to start the Egli it was an absolute B**tard then on the forum someone said with an AMC box take the kick start way past TDC till almost the ground return and Kick! Bingo! it works every time. However that is with coil ignition and a Mikuni Carb but worth playng the variations
I do have a single BTH that I raced on the Comet Racer for years double and single plugs I had a decko inside before I moved it to the electric start Comet it looks rusty inside so I will be sending it for refurbishment when funds allow so I put an old Lucas on instead it worked OK till the engine blew but I will try and put the refurbished BTH back next year as I have always had good results with them.
 

Roslyn

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erm one thing every one may have missed is the humble mistreated and forgotten spark plugs they also fail and play up worth taking a look and checking as sometime new ones fail as well after all there are a lot of fake spark plugs about?
 

Roslyn

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So far. after reading the post from magneto man I took his suggestion, removed the float chamber, polished up the float needle and put it back together. Now it will not start at all, hot or cold, so I suppose that is progress of a sort.... I was aware of the need to keep the float vertical, it always dies immediately on the side stand or even slightly leaned over, another reason for considering a different carburetor. I can see the level with the float cover removed, not sure what is supposed to be. It does not appear to leak if the fuel tap is open and the tickler is not touched. Tank is full, cap is vented. No problems getting gas to flow.

Re the magneto, it has a spark hot or cold. I opened up a spark plug about 3/16" it sparks when I kick it over with the plug removed.
Spark plugs I tried among others, new Champion N7YC, also NGK BPR7E and BP7E and some NGK platinum tipped. All the spark plugs except the Champions have resistors, other than Champion I can't find spark plugs that do not have resistors. Spark plug resistance checked with ohmeter.
The HT wire and cap do not have resistors, checked with ohmeter.

Since the no start at all I did a rough timing check, the points are opening at about TDC on the compression stroke, ignition retarded, so that is good.

Re my starting technique, since I played with the carburetor settings, I start with gas tap open, kick it a few times, close the choke, kick it a few more times, one stab at the tickler, a few more kicks, another stab and so on, until finally there is gas all over the place and still no start.
Pull the plug and it is still dry. Kicking it through with the compression release pulled in I will get the occasional gun shot bang as unburned mixture fires in the exhaust pipe. I also try various throttle openings, including WOT when I figure it should be flooded.
As far as my technique for starting singles goes, I also have a Yamaha 500 XT which also has magneto ignition, and a reputation for being a bitch to start when hot. I can usually fire it up with one kick when it is hot, two or three when cold. There is a muscle memory thing happening there I am not totally aware of. It did take time to learn how to start the Yamaha, and it was hard at first but I can't really say what I am doing differently other than following the owners manual technique exactly and not over using the enricher thingy.

I have been chasing the comet starting problem since I got the bike a couple of years ago. Along the way I found the cam and followers badly worn, and replaced them. Cam timing was set using a degree wheel, not the the marks on the timing gears. As I posted earlier, when it does run it runs very well. https://www.youtube.com/watch?v=qAoWlDEmGo4
See for yourself,
Comet Running
(Corrected the link. BigEd)

I am leaning towards magneto replacement-rebuilding, guy has a rebuilt one on ebay uk for sale, he also sells dresses and ladies shoes, not that there is anything wrong with that :)

I would be a lot more confident about mag replacement if the effing thing did not have any sparks, but I also get that any one who thinks they know how electricity works is delusional.
Have you looked at the spark plug caps they do play up sometimes and found it frustrating chasing that elusive problem so you not alone.
 

Magnetoman

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I am pretty sure they would agree with me, "If you think you understand quantum mechanics, you don't understand quantum mechanics." Richard Feynman
I loved quantum mechanics, and by the time I was a senior undergraduate I thought I had a pretty reasonable understanding of it. However, by the time I finished my advanced quantum mechanics class in graduate school I realized I barely had a clue.

Teaching of quantum mechanics is by necessity done with a variation of bait-and-switch. If we let undergraduates know how truly difficult the concepts were, they'd all give up at that point. So, we string them along, making them think they are gaining ever greater comprehension with each new class, until they get to advanced levels in graduate school, by which time it's too late for them.

Electricity and magnetism (and magnetos), on the other hand, we do understand.
 

Bill Thomas

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Must say your a bit rough with the throttle !, The poor old carb' Can't keep up :D .
I have seen some people do that when starting, Might be better to set the throttle at a steady opening ?.
 

Roslyn

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I loved quantum mechanics, and by the time I was a senior undergraduate I thought I had a pretty reasonable understanding of it. However, by the time I finished my advanced quantum mechanics class in graduate school I realized I barely had a clue.

Teaching of quantum mechanics is by necessity done with a variation of bait-and-switch. If we let undergraduates know how truly difficult the concepts were, they'd all give up at that point. So, we string them along, making them think they are gaining ever greater comprehension with each new class, until they get to advanced levels in graduate school, by which time it's too late for them.

Electricity and magnetism (and magnetos), on the other hand, we do understand.
Not every one with a masters or a high IQ knows every thing I have some friends who are in mensa have degrees in math physics etc and I can hold mine own as I am just simple unsophisticated provincial so please let collect all this life time of knowledge together as this forum is here to let us all help each other with moral and technical support in these time when we cannot meet up so let give the support to the members who is far away and have a interest in motorcycles and Vincent motorcycles to ride and use them to keep the make alive
 
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