1968 Commando: left cylinder does not start (2016)

pierodn · May 10, 2016

Hi.
My friend Mario has a stock 68 Commando with the points.
Both the spark plugs have fire.
The Amal 930 have the air circuit and jets well cleaned, the needles trottle work fine, the floats setted like per manual.
The bike starts at third chick but only the right cylinder works, the left doesnt start.
The fuel seems to arrive to the left spark plug.
We have inverted the sparks plug but without result.
What we must check?
Thanks.
Ciao
Piero

tomspro · May 10, 2016

if you have spark and fuel, no or low compression would the only reason i can think of.
easy enough to check with a gauge in the spark plug hole.

concours · May 10, 2016

With it running on one cyl., spray a small amount of starting fluid (ether) in the dead cyl. carb inlet. A quick acid test to see if you're REALLY getting fuel into the cyl. :idea: (Gasoline in a spray bottle works too)

DogT · May 10, 2016

Try swapping coils and high tension wires. I've seen spark that will not start an engine. Check running in the dark for high voltage arcing. Battery/alternator good?

pierodn · May 11, 2016

Hi.
Points cleaned, checked and setted.
Changed left 12v coil, condenser and spark plug.
930 Amal recleaned, the circuits are opened.
Compression test made, good result.
Valves open and close well.
Battery charged.
The bike under 2500 rpm fires only the right cylinder, upper goes great both cylinder!!!
I think i must change the right cab, may be doesnt work to lwer rpm.
Suggestions please.
Ciao
Piero

Nater_Potater · May 11, 2016

pierodn said:
930 Amal recleaned, the circuits are opened.
The bike under 2500 rpm fires only the right cylinder, upper goes great both cylinder!!!
I think i must change the right cab, may be doesnt work to lwer rpm.
Suggestions please.
Ciao
Piero

Did you try Concours' suggestion? It sounds like you're still suffering from a plugged pilot circuit. They can be real stinkers to clear out.

pete.v · May 11, 2016

Nater_Potater said:
pierodn said:

930 Amal recleaned, the circuits are opened.
The bike under 2500 rpm fires only the right cylinder, upper goes great both cylinder!!!
I think i must change the right cab, may be doesnt work to lwer rpm.
Suggestions please.
Ciao
Piero

Click to expand...

Did you try Concours' suggestion? It sounds like you're still suffering from a plugged pilot circuit. They can be real stinkers to clear out.

True that. And it's not just the jet but the entire circuit.

acotrel · May 11, 2016

You might have a hole in the piston or a bent valve.

Rohan · May 12, 2016

It wouldn't run well with a bit of throttle if that had happened. !

Classic symptoms of blocked idle jet and passages.
Tries to run on the needle jet, very rough down low (if it will run at all),
and runs perfectly with some throttle.

Might need a few goes at cleaning out those little passages, tricky getting them perfectly clean.

DogT · May 12, 2016

You should be able to tell if the idle circuit jet is clean by shooting compressed carb cleaner in one of the 3 ports and watching it come out the other 2. Try all 3. Sure sounds like the problem, can be a buggar and can easily re-clog itself quick.

rivera · May 12, 2016

Hi Piero!
It´s sometimes the simple things that makes life difficult.
I also had problems with my carbs, the right one did not react to any change of the air screw.
When I opened the drain screw at the bottom of the float chamber to get the fuel out the main jet just fell out!
Obviously I did not tighten it!
I put about 250 miles on the clock with that!

1968 Commando: left cylinder does not start (2016)

pierodn · May 12, 2016

DogT said:
You should be able to tell if the idle circuit jet is clean by shooting compressed carb cleaner in one of the 3 ports and watching it come out the other 2. Try all 3. Sure sounds like the problem, can be a buggar and can easily re-clog itself quick.

The idle circuit was well cleaned.
I have changed carb with one of another my running bike: the cylinder didnt start the same!
There is spark at plugs.
The valves open/close well.
Compression test made.
Electrical, carbs ?????
What is the problem?
To morrow i will change points and wires.
Bah!
Cio
Piero

pierodn · May 12, 2016

rivera said:
Hi Piero!
It´s sometimes the simple things that makes life difficult.
I also had problems with my carbs, the right one did not react to any change of the air screw.
When I opened the drain screw at the bottom of the float chamber to get the fuel out the main jet just fell out!
Obviously I did not tighten it!
I put about 250 miles on the clock with that!

Hi.
I mean.
With a dirty carbs you ride bed.
In this case, the left cylinder doesnt start.
Is another problem!
Ciao
Piero

texasSlick · May 12, 2016

pierodn said:
Hi.
Points cleaned, checked and setted.
Changed left 12v coil, condenser and spark plug.
930 Amal recleaned, the circuits are opened.
Compression test made, good result.
Valves open and close well.
Battery charged.
The bike under 2500 rpm fires only the right cylinder, upper goes great both cylinder!!!
I think i must change the right cab, may be doesnt work to lwer rpm.
Suggestions please.
Ciao
Piero

In a later post you wrote: "I have changed carb with one of another my running bike: the cylinder didnt start the same!

Did you mean to write "THE LEFT CARB?" It seems to me that is the one to change.

Slick

pierodn · May 13, 2016

texasSlick said:
pierodn said:

Hi.
Points cleaned, checked and setted.
Changed left 12v coil, condenser and spark plug.
930 Amal recleaned, the circuits are opened.
Compression test made, good result.
Valves open and close well.
Battery charged.
The bike under 2500 rpm fires only the right cylinder, upper goes great both cylinder!!!
I think i must change the right cab, may be doesnt work to lwer rpm.
Suggestions please.
Ciao
Piero

Click to expand...

In a later post you wrote: "I have changed carb with one of another my running bike: the cylinder didnt start the same!

Did you mean to write "THE LEFT CARB?" It seems to me that is the one to change.

Slick

Hi.
Yes.
I changed the left and nothing changed.
I have ready another one.
But at first i will change points, coils, condenser and wires.
Ciao
Pieo

rivera · May 13, 2016

pierodn said:
Yes.
I changed the left and nothing changed.
I have ready another one.
But at first i will change points, coils, condenser and wires.
Ciao
Piero

Before you do that, go check the valve clearance on the inlet valve!
Had that symptom on my BMW R75/5 , rebuilt the carbs an double checked inition etc with no result.
Last was valve clearance and BINGO!

texasSlick · May 13, 2016

There is possible fault in the throttle cables. Have you checked that the throttle slides open together? Check visually over the full range as you twist the grip operator. Also do the test with two 1/8 drill bits. PM if you are not familiar with that test.

Slick

Roadrash · May 13, 2016

Boy Piero, with all the problems you seem to come across it wont be long before you are telling the rest of us how to properly sort out a Norton. I respect your persistence.

pierodn · May 13, 2016

rivera said:
pierodn said:

Yes.
I changed the left and nothing changed.
I have ready another one.
But at first i will change points, coils, condenser and wires.
Ciao
Piero

Click to expand...

Before you do that, go check the valve clearance on the inlet valve!
Had that symptom on my BMW R75/5 , rebuilt the carbs an double checked inition etc with no result.
Last was valve clearance and BINGO!

Hi.
Clearance are like x manual.
Ciao
Piero

pierodn · May 13, 2016

texasSlick said:
There is possible fault in the throttle cables. Have you checked that the throttle slides open together? Check visually over the full range as you twist the grip operator. Also do the test with two 1/8 drill bits. PM if you are not familiar with that test.

Slick

Hi.
The cable work well and the slides open at the same moment.
The slides are set with 4mm drill.
Ciao
Piero

1968 Commando: left cylinder does not start (2016)

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