750 carbs troubles?.

After changed the left broken manifold I thought the carburation was good.
The bike run at first kick start, maintains the idling to 1000 rpm, revving up well when you open the throttle when is on the central stay, but misfires when she runs on the road between 2000 and 3000 rpm and returns to be set above 3500 RPM.
On the left cylinder the spark plug is very very Carbon fouled while on the right cylinder the spark plug is very normal.
I know that one or more of the following can cause carbon fouling:
1. Rich fuel mixture.
2. Cold spark plug heat range.
3. Clogged air filter.
4. Improperly operating ignition component.
5. Ignition component failure.
6. Low engine compression.
7. Prolonged idling.
The carbs, old like the bike from 1971, are 932 with 930 setting.
The electronic ignition is a Boyer, sure not the last; the spark plugs get the current both.
What controls do I need?
Maybe the left carburetor do not has the air ways opened well?.
I await suggestions.
Ciao.
Piero

pierodn said:

What controls do I need?

Click to expand...

you need to give more details,is it smoking? what work has been done to the engine?doubt if its plugs but have you swapped from one side to the other ? have you done a compression test ? it is sometimes possible that the needles and needle jets wear out this can cause symptons like this but if the carbs are a pair it is unlikely you really need to go back to basics on this one and check everything ,how did the left manifold break? good luck with it regards baz

If I'm reading right you have a stumble between 2-3000 rpm and one fouled plug.

I'd look at the throttle needle to see if it worn and needle jet to see if it is oval.

Try switching the plugs and wires to the opposite cylinders and see if the problem stays with the cylinder or moves with the plug and wire.


Greg

baz said:

pierodn said:

What controls do I need?

Click to expand...

you need to give more details,is it smoking? what work has been done to the engine?doubt if its plugs but have you swapped from one side to the other ? have you done a compression test ? it is sometimes possible that the needles and needle jets wear out this can cause symptons like this but if the carbs are a pair it is unlikely you really need to go back to basics on this one and check everything ,how did the left manifold break? good luck with it regards baz

Click to expand...

Hi Baz,
No work to the engine, only a change of oils.
The engine turns free and has a good compression.
No smoking.
The left manifold was broken, i dont know why.
I swapped the plugs but it is not the proble.
Ciao.
Piero

pierodn said:

baz said:

pierodn said:

What controls do I need?

Click to expand...

you need to give more details,is it smoking? what work has been done to the engine?doubt if its plugs but have you swapped from one side to the other ? have you done a compression test ? it is sometimes possible that the needles and needle jets wear out this can cause symptons like this but if the carbs are a pair it is unlikely you really need to go back to basics on this one and check everything ,how did the left manifold break? good luck with it regards baz

Click to expand...

Hi Baz,
No work to the engine, only a change of oils.
The engine turns free and has a good compression.
No smoking.
The left manifold was broken, i dont know why.
I swapped the plugs but it is not the proble.
Ciao.
Piero

Click to expand...

ok check the plug leads and try swapping them over ,try swapping the coils over take a look at the needle jets and needles swap them over check the carbs again are you sure there is no smoke? you need to know if its running rich black smoke or oily blue smoke rings valve guides etc regards baz

Hi Baz,
I mean, but there is no smoke!
Ciao.
Piero

Hello Piero,

At what throttle opening is the engine missing between 2000 and 3000. ?

Hello Piero,

You told me there is no difference with the miss between 2000 and 3000 regardless of throttle opening. You have swapped plugs, leads and coils and the fault persists.

You have 1 sooty plug.

1. Make sure your slide needle is correctly installed on that side.

2. I believe you have a Boyer. Bad connections can cause this type of issue. Boyer users can help here.

Regards

Mark