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Dibnah Offline OP
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Steam locomotives are the closest thing to mechanical life that mankind has created, classic bikes must be a close second.

For several years, the starting procedure for my mongrel 650 (no choke fitted) from cold was:
Free the clutch
Petrol on
Copious flooding of the Premier AMAL
Ignition on
Throttle closed
One kick (generally!)
Engine starts and runs at low rpm
No throttle for a minute or so, or it will cut out
Rev engine, engage 1st gear and forward progress

After a recent "failure to start" episode, this has now changed to:
Free the clutch
Petrol on
Copious flooding of the Premier AMAL
Ignition on
Throttle closed
One kick
Immediately open throttle as the engine fires
Blip throttle for 30 seconds or so
Engage 1st gear and forward progress

Something has obviously changed, I have no idea what though. I suppose eventually it won't start, and then I'll find out what has changed.

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So the only change seems to be that once your engine would start and idle slowly from cold, but lately it needs a little throttle for a minute till it will idle.

I would say that both of these experiences is not what I would expect.

The engine would not normally idle until it had warmed up after perhaps 5-10 minutes running. I wonder if the idle circuit is set richer than it should be.

Why it has changed may be another matter. Possibly a partial blockage in the pilot jet.

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Dibnah Offline OP
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Thanks koan58.

The previous cold start process was as described by the previous owner, I successfully continued with it for several years. The idle jet has been cleaned with the #78 drill bit on a couple of occasions in my ownership. It is possible that the current cold start operation is as designed, For interest, I'll have to see how long it now takes to reach a steady idle from cold when stationary; I generally move away as soon as the bike is capable of making forward progress, which can now be before a stable idle is available.

General fueling seems subjectively OK, although with the occasional hiccup when blipping the throttle for a downchange when hot. This can be avoided by using a bigger handful of throttle.

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I have three, each with its own starting drill.
One has chokes, one has none, the third has Mk2 carbs.
The enrichers need to being taken off soon after starting and the bike won't idle on its own for a few minutes.
The Trident with chokes needs tickling and full choke to start but idles immediately. Chokes come off after a mile or two.
The A65 needs tickling to fire and attention to the throttle to stay running. I might install chokes if it gives trouble once the temps drop.
In all cases if the bike doesn't start in one or two kicks opening the throttle usually works.
These old tarts are all different, and finicky. I've been embbarassed a few times not being able to start another man's engine.


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Originally Posted by DavidP
. I've been embbarassed a few times not being able to start another man's engine.

HAHA at least it was not another (wo)mans engine ... (ducks away....)


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...I am not sure if its good if a classic bike idles after started the engine. I prefer to work a bit with the throttles at more RPMs for a moment then let it to try to idle.


About Man and Wo man. May be in the past that came from: wow!; man...

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Dibnah Offline OP
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@reverb. Previously, the engine would not accept any throttle when starting from cold without cutting out. Now it appears that throttle immediately after kicking is essential.

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...may be jet or needle started to wear out then the proceed changed to obtain the same?

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kind of a longshot ,
but maybe the tickle pin has slipped ... so its not flooding the carb with its old/usual zeal .

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Dibnah Offline OP
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Thanks again for the replies.

The degree of flooding for cold starts is measured by the amount of petrol that spews from the carb onto the engine casing during flooding.

The change in procedure was noticeable on one particular day at the end of September.

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Dibnah Offline OP
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Originally Posted by Dibnah
For interest, I'll have to see how long it now takes to reach a steady idle from cold when stationary; .

About one minute before an unassisted but ragged idle is possible, ambient 12'C / 54'F.

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“About one minute before an unassisted but ragged idle is possible, ambient 12'C / 54'F.”

This suggests the idle circuit is rich.

Have you set the idle speed/air screw when the engine is fully warmed up? Say after 20 minutes of riding.

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The only thing that has changed is your petrol station maybe ????


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or maybe the plugs just got sooty.

Like the rest of us, I really enjoy these old things. When I was a kid, we had an ancient RCA record player, which had a logo picturing a dog with a quizzitive look on its face--"it's master's voice" was the RCA slogan. That slogan could just as well describe the unique starting procedures we discover for our Brit bikes. We ride these things for years and discover, for each one, specific, unique starting procedures. When they change even slightly, we notice. You may never know why it changed a little, but as long as it keeps starting, well, maybe that is the new "normal."

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It's a Tiger, single carb, check the inlet manifold for loose nuts or gasket leak.

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Dibnah Offline OP
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Thanks again for the replies. Dragged the bike out of the lock-up earlier, one carb to manifold fixing took about 1/16th of a turn, the other carb to manifold fixing was secure. All four manifold to head fixings were secure. The next time I start the bike, I'll spray some carb cleaner around the exterior of the inlet manifold and see if the idle increases.

The plugs have been getting sooty for several years, it's probably the burning engine oil!

Three different petrol stations used since the change in starting procedure.

I set the idle mixture and idle rpm a couple of years ago. No rev counter, so slowest steady idle and then lift the idle speed a bit on the throttle stop screw. I'll have to try and measure the idle speed. I have a laser tachometer for non-automotive use, will need to find an easily accessible engine component that rotates. An alternative being one of those inductive digital tachos.

To clarify a couple of points:

I mentioned a ragged idle as the bike warms up in an earlier post, "erratic" would be a better description of the idle during warm up. A strong, steady but ragged idle is probably a good description when the bike has warmed up, if that makes sense. It's never a smooth idle

With my "cost-effective" classic Brit bikes, I generally follow the philosophy of "that'll do" , particularly if something is working; I recognise that other posters take the "as good as factory or better" approach. Currently - for me - the change in starting procedure is interesting but nothing more at this stage.

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Air filter, take it off. Does it change anything?

If I'm not mistaking you are looking for a decrease in RPM when spraying the carb cleaner on the intake gaskets. I had to change that gasket recently. I made my gasket from cereal box cardboard and very small amount of gasket maker goop evenly smeared on one side. I didn't want to order and wait a week for a piece of cardboard.

Also, is one plug much cleaner than the other?

Pictures are worth more than words! wet sooty or dry sooty?

Last edited by splash; 10/26/20 9:55 am.

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Since we aren't blessed with californian sunshine over here, it'd be worth your time fitting a choke mechanism. at around 12 degrees C as we are now I find that my bike prefers choke. If I was not to use it then your previous experience of having to wait for it to warm up so you could open the throttle would be the same as mine, fitting the choke eliminates that so you can start it faster.

Sounds like the carbs richer now as Koan has suggested, but this will give you more problems when its warmed up.

So my advice, get a choke system fitted, then go for a run, do about 20 miles so the engine is nicely heat soaked then adjust the idle mixture until the motor is running as fast as it can (not the diagnal screw!) then screw it back in until the revs start to drop, then back out a fraction.

What ever happens here on in is relative to other areas of your carb.


Also if your plugs are foulled up this will effect matters also.


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Dibnah Offline OP
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Thanks for the replies.

Fitting a choke is certainly an option, but my current "to-do" list for mechanicing on several vehicles is extensive. When last used, I adjusted the throttle stop screw (not the mixture screw) to achieve the lowest stable idle speed with a hot engine, so the next cold start will be a good test of how long it takes to reach a stable idle from cold.

I'll remove the plugs at the weekend and take a couple of photos..

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Dibnah Offline OP
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Two weekends later:

[Linked Image from i.postimg.cc]

[Linked Image from i.postimg.cc]

Not a plug chop, mixed riding followed by some idling

Lowest stable idle when hot = no idle when cold for five minutes, gave up waiting, still wouldn't idle without assistance after four miles running. 14'C ambient. Have now wound the throttle stop screw (not the mixture screw) back in a bit, really need a tacho to measure idle speed.

Focus on photos could have been better, I'll have to ask someone how to manually focus the camera.

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No evidence of richness there, if anything quite the opposite.

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Dibnah Offline OP
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Thanks Koan68. Subjectively, I can't fault the carburetion, although revs are limited by vibration rather than reducing power on the other side of the bhp curve. Must get a rev counter of some variety.

Somewhere, I have a "Colortune" for checking the mixture at idle, never used it on a bike.

I'm pleased at the lack of burnt oil on the plugs, although this does beg the question: "Where does the engine oil go?"

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Dibnah, I’ve just read through the whole thread and I don’t see any mention of oil consumption until your last post.

How much oil is it using? Has the oil consumption always been similar, or did it increase when your starting procedure changed in September?

Does it smoke from the exhaust at all? Have you tried a catch-bottle on the breather outlet?
If it doesn’t leak much oil from a simple oil leak, then it must be escaping through one or both of the above routes.

Returning to your plug pics, the plugs do look to be running hot. The insulators are very pale, the ground electrodes are also very clean for almost their entire length.
I am used to seeing black soot on the circular end of the plug, again yours show little of that.
The purple discolouration on the plugs, particularly marked on the second pic, with the coloured ring half way up the threads, re-inforces my suspicion of excess heat.

If the plugs are running very hot, possibly they will not exhibit evidence of oil flow through the combustion chamber. Indeed such oil flow could itself lead to some detonation and hence higher temperature.

Just ideas.


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