Unstable idling.

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pierodn

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Hi.
The bike starts very easily, she has an old ignition Boyer and two old Amal 930 with standard setting.
With cold engine idle speed is set at 1000 rpm.
With the hot engine idle speed goes up to 2000 rpm and takes the time to go down to 1000 rpm.; sometimes remains at 2000 rpm.!!
The bike has a misfire between 1000 and 2000  rpm. but over 2000 rpm is perfect!
The two Champion N7YC spark plugs are very dirty black.
When I try to screw or unscrew the air pilot adjuster the idle does not go up or down.
The fire goes well to the parks.
What should I check?
Thank you.
Ciao.
Piero
 
A possible problem could be with the carbs. Especially if you don't know their history.
Usually with black plugs the bike would be really hard to start.

Try:
Remove the pilot air screws.
With a strong flashlight, look inside the pilot air screw hole.
Can you see the brass jet? The 0.015" hole should be cleared with a wire.

If you don't see the brass jet, some early Amal carbs have the .106 pilot jet
screwed into the carb bottom.

When you have the carb float bowl off, check the float level according to the manual.
 
Idle speed should always be set with the engine HOT.

If it doesn't respond to the air idle screws being screwed in or out,
then the little idle passages are blocked,
and it is trying to idle on the needlejet - ie very roughly.

You need to read here on cleaning out those little passages.
A very common amal problem for carbs left sitting for long times.
The fuel dries out, and leaves deposits or corrosion...
 
IMO, you simply have an air leak on the induction side.. Before spending $$$ on new carbs (unless you just want an excuse too) squirt some oil around the carb and manifold area when idling and if it revs up (cos the oil has blocked the crack/hole/gap) then its sucking air from a leak...
 
"she has an old ignition Boyer"

I would be less likely to believe it is primarily the carbs.
Any of the simpler E.I. have a steep advance curve right off idle.
Cold engines with molasses for oil need horse power to run/turn over. =1000rpm
Once the engine oil is warm/warmer the engine speeds up... causing increased ignition advance which cause the engine to speed up.=2000rpm
I've watched for over 25 years... people not understand this relationship and reluctantly offer it again.

conversely:
A mechanical AA unit in good condition reduces this effect significantly, because there is/should be NO further advance until 1400-1600 rpm.
 
dynodave said:
"she has an old ignition Boyer"

I would be less likely to believe it is primarily the carbs.
Any of the simpler E.I. have a steep advance curve right off idle.
Cold engines with molasses for oil need horse power to run/turn over. =1000rpm
Once the engine oil is warm/warmer the engine speeds up... causing increased ignition advance which cause the engine to speed up.=2000rpm
I've watched for over 25 years... people not understand this relationship and reluctantly offer it again.

conversely:
A mechanical AA unit in good condition reduces this effect significantly, because there is/should be NO further advance until 1400-1600 rpm.
Click to expand...

Thank you.
Very very interesting.
Please, what i must to do?
Regards.
Piero
 
pierodn said:
Thank you.
Very very interesting.
Please, what i must to do?
Regards.
Piero
Click to expand...

As Rohan suggested:
Idle speed should always be set with the engine HOT.

But.....It will make the bike unwilling to idle until warmed up. You can use the friction lock on the throttle assembly to hold the speed up during warm-up.

The second option is to change the ignition from the old style E.I. to one of the modern E.I. with an anti-stall feature in the advance curve.

third...go to an old mechanical AA with points...and hope it is to the correct specifications.
 
pierodn said:
Thank you.
Very very interesting.
Please, what i must to do?
Regards.
Piero
Click to expand...

first thing you should do is check if you have an air leak.......it may or may not be the problem, but weak mixtures will cause fast running at lower rpms, and worse at high rpms....when you are sure you don't have any air leaks, check again for symptoms....
 
dynodave said:
pierodn said:
Thank you.
Very very interesting.
Please, what i must to do?
Regards.
Piero
Click to expand...

As Rohan suggested:
Idle speed should always be set with the engine HOT.

But.....It will make the bike unwilling to idle until warmed up. You can use the friction lock on the throttle assembly to hold the speed up during warm-up.

The second option is to change the ignition from the old style E.I. to one of the modern E.I. with an anti-stall feature in the advance curve.

third...go to an old mechanical AA with points...and hope it is to the correct specifications.
Click to expand...

Hi thank you.
Pazon has the anti-stall feature in the advance curve?.
Ciao
Piero
 
SteveA said:
pierodn said:
Thank you.
Very very interesting.
Please, what i must to do?
Regards.
Piero
Click to expand...

first thing you should do is check if you have an air leak.......it may or may not be the problem, but weak mixtures will cause fast running at lower rpms, and worse at high rpms....when you are sure you don't have any air leaks, check again for symptoms....
Click to expand...
Hi and thank you.
Air leak?
I mean.
But from where?
Where i need to check?
Ciao
Piero
 
Air leaks are not uncommon around the manifold connections to the head - check that the bolts are tight.
Also that the o-rings on the carbs mating face are still in cood condition, and stand proud enough that they will still seal.
Also that the rubber pipe that connects the 2 manifolds is still in good condition, and not porous or cracked.

Its also possible that the (inlet) valve guides are really worn, which can be hard to check without having it apart.
This usually causes oil burning though, which makes it obvious.

I still think that if these carbs have been unused for a while, and the idle air screws make no difference when screwed in or out,
then the idle passages are blocked and the idle circuit is not working.
This has applied to about every old unknown Amal concentric I've ever worked on, they are ALWAYS blocked in the idle circuit.
A #78 size drill gets a lot of mention on these pages (or is it a #74 ??).

P.S. Have you tried yet to set the idle when the engine is HOT ?
Setting it with the engine cold will give you some very wrong settings....
 
Rohan said:
Air leaks are not uncommon around the manifold connections to the head - check that the bolts are tight.
Also that the o-rings on the carbs mating face are still in cood condition, and stand proud enough that they will still seal.
Also that the rubber pipe that connects the 2 manifolds is still in good condition, and not porous or cracked.

Its also possible that the (inlet) valve guides are really worn, which can be hard to check without having it apart.
This usually causes oil burning though, which makes it obvious.

I still think that if these carbs have been unused for a while, and the idle air screws make no difference when screwed in or out,
then the idle passages are blocked and the idle circuit is not working.
This has applied to about every old unknown Amal concentric I've ever worked on, they are ALWAYS blocked in the idle circuit.
A #78 size drill gets a lot of mention on these pages (or is it a #74 ??).

P.S. Have you tried yet to set the idle when the engine is HOT ?
Setting it with the engine cold will give you some very wrong settings....
Click to expand...

What Rohan said Piero....

To be clear, what we mean by air leak is that when there is a vacuum in the manifold air can leak in, weakening the mixture.....

tightening the bolts is good, but overtightening can warp the manifold.

I would suggest that the best way forward with this is to pull the whole carb set up off the bike and do a thorough carb cleaning (assuming you don't want to just replace them with new, which if funds allow would probably be a good idea).

Check the manifold face that mates with the cylinder head is flat and use all new gaskets and O rings, then refit CLEAN carbs and start again, remembering that eliminating the carb problems is essential to enjoying the ride, but a good ignition set up with sound connections is also very important.

Good luck.
 
Another air entry point can be if the carb tops have become loose from all the violent shakings. Found that recently, tightened down and purred like a kitten. :)
 
If the carb slides are obviously loose in the body, that will cause unstable idling too, and is easy enough to feel. There should be minimal play between the slide and the body. If there's over 10K miles on the carbs and still using original slides they will be too loose. I changed my old slides to the anodized slides, it helped a lot but not enough for me, I finally had them sleeved and now it idles fine, I can even take my hand off the throttle at a stop and it doesn't die. No more constant bliping.
 
"Check the manifold face that mates with the cylinder head is flat and use all new gaskets and O rings"

Pierodn

Remember NO Norton Heavy Twin used gaskets on the intake manifolds only the hard fiber insulator between the head and manifold. see here:
carb-manifold-head-gaskets-t20148.html

If the manifold is not flat then some one ruined it....probably with a gasket.
Same for the carb....only an oring,,,never a gasket....

This generally why I don't care for forums that much, since there is an overwhelming Alzheimer effect so even an August 2014 thread is totally ignored or forgotten.

LAB must be a saint to type the same crap over and over and over and over and over.....
coffee break over, back to work for me.
 
Hi,

Thank you.

As i can check if the little idle air passages is free after drilling with the guitar string?

Ciao

Piero
 
[/quote]


The second option is to change the ignition from the old style E.I. to one of the modern E.I. with an anti-stall feature in the advance curve.

[/quote]

Please,
wich one has the anti -stall?

Ciao

Piero
 
pierodn said:
which one has the anti -stall?
Click to expand...

Tri-Spark Classic Twin
Pazon Smart-Fire and Altair
Boyer Bransden Micro-Digital (red box), and Micro-Power (blue box).
 
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