1971 750 Commandodo not start

pierodn · Feb 20, 2015

Old Boyer MKIII.
The fire arrives at spark plugs.
Old Amal 930 reconditioned (new sliders, trottle needles, needles and float, gaskets and seals), 220/106, needle trottle clip the central position, float like per Amal setting.
From the right tickler, after a lot of push, do not come out gasoline.
The bike do not starts, any sign of life!
Sparks plug new, and after a lot of kich start seem to remain very clean and wet.
It seems that gasoline does not arrive to the cylinders yet but the float chamber are full!
What should I do?
Thank you.
Ciao
Piero

ILLF8ED · Feb 20, 2015

You mention several changes to the carburetors. Two things that come to mind that would prevent starting.
The clip for the throttle needle has come loose and the needle has dropped into the needle valve, and the pilot screws need to be completely seated then opened 1.5 turns as a starting point. The first item can happen easily when trying to get the slides back into the carb body.

gtsun · Feb 20, 2015

Or it could be a clogged pilot jet, if I was you I would pull out the screw and run a .016" wire or #78 drill in to clear it.

pete.v · Feb 20, 2015

pierodn said:
Old Boyer MKIII.

From the right tickler, after a lot of push, do not come out gasoline.

Piero

What about the left?

If you hold down the ticklers for 5 seconds, the gasoline should pour out of the tickler ALOT. If not, then not enough gasoline to start.
FYI pumping and repeated pushing of the ticklers does not pump. Holding them down constantly is how they work. By doing this, the button pushes on the float allowing the gas to flow into the carb and seep from the tickler.

You either have no gas to the right side, or need to adjust float height.

1up3down · Feb 20, 2015

Piero,

both carbs should have gas coming out between the carb bodies when you depress the ticklers for a second or two

if not you need to take the lower bowls off and gently tap the brass seats down that the float needles go into so that the needles
go down farther allowing the bowls to fill with more gas than the normal level is at, this excess gas is needed when cold starting

pierodn · Feb 20, 2015

1up3down said:
and gently tap the brass seats down that the float needles go into so that the needles
go down farther allowing the bowls to fill with more gas than the normal level is at, this excess gas is needed when cold starting

Hi.
I mean, but i need to tap the brass to have the float more than 2 mm under or upper?
Now the float is about 2 mm under.
Thank you
Piero

worntorn · Feb 20, 2015

Take out plugs, squirt a little gas down each hole with a syringe, quickly replace (dry) plugs and kick over. See if if fires. If it does not at least fire after a half dozen kicks, then start looking at potential spark problems.

Glen

Peter R · Feb 21, 2015

Piero, The float level should be adjusted as follows :

Take the float bowl off and push the plastic tab of the float down untill the needle rests on its seat. Note : push on the float, NOT the needle itself.
Now check the distance between the float and the upper edge of the float chamber, (opposite of the needle) this should be 2mm.
If this is not the case, the float height must be adjusted by moving the brass seat of the needle .
This can be done by heating the floatchamber in hot water, an move the seat to the correct position with a drift.

You also say that no fuel is coming out of the carb when the tickler is moved.
Could it be that the pin of the tickler is not sticking out far enough ?
This can be adjusted too by pulling the pin of the tickler a bit further out.

PS: I feel ashamed for the behaviour of the dutch football fans in Roma this week.

gjr · Feb 21, 2015

pierodn said:
1)... float like per Amal setting.
2)From the right tickler, after a lot of push, do not come out gasoline. ...
3)Sparks plug new, and after a lot of kick start seem to remain very clean and wet.
4)It seems that gasoline does not arrive to the cylinders yet but the float chamber are full!

Replies:
1)If you are using the new Amal specs for the float level, it may be too low.
2)I always have to push the tickler several times to get any fuel to come out - sort of like typing .......... I don't know why just pushing it down doesn't work.
3)Are the plugs wet ? If so, they are flooded. Remove the spark plugs after trying to start the bike, do you smell fuel in the cylinders ?
4)How is your valve adjustment and compression ?

Greg

Hobot · Feb 21, 2015

I got a unstartable stored 74 850 going though carbs and getting floats set closer to right then diddling the initial ign timing a bit this way and that till happy and not wearing out pilot or kick lever splines. A clean flame cleaning heating of plugs has helped me get spark on semi-fouled plugs after too many failed kicking myself sillys. I've also has new plugs fail to start til I dug old plugs back out of trash. A nail tapping can move the needle seats almost too easy w/o heating but some put carbs in hot water to ease theirs. Definitely a thinking mans hobby horse that so easy overwhelms mine. Of course me & my buddy have had ridding ruined away from home d/t no starts d/t hidden bad connections, ugh who hasn't.

pierodn · Feb 21, 2015

gjr said:
pierodn said:

1)... float like per Amal setting.
2)From the right tickler, after a lot of push, do not come out gasoline. ...
3)Sparks plug new, and after a lot of kick start seem to remain very clean and wet.
4)It seems that gasoline does not arrive to the cylinders yet but the float chamber are full!

Click to expand...

Replies:
1)If you are using the new Amal specs for the float level, it may be too low.
2)I always have to push the tickler several times to get any fuel to come out - sort of like typing .......... I don't know why just pushing it down doesn't work.
3)Are the plugs wet ? If so, they are flooded. Remove the spark plugs after trying to start the bike, do you smell fuel in the cylinders ?
4)How is your valve adjustment and compression ?

Greg

Hi,
The float is 1,5 mm under the top of the bowl.
Piero

DogT · Feb 21, 2015

If you can't flood the carbs with the tickle and see fuel it's nearly impossible to start. Best to get the new floats with the steel tongues that are adjustable. Fuel level in the float bowl is critical to starting and also idle and idle screw. Could also be a too short tickle rod but unlikely. Raise the float level a bit and see what happens.

gjr · Feb 21, 2015

pierodn said:
The float is 1,5 mm under the top of the bowl.
Piero

Ya, but where is the fuel level ? I bought new bowls with the drains and the level was too low. Went back to the original bowls and it was cured. Try putting 1/2 teaspoon ( ~2.5 ml) fuel in each cylinder and give it a few kicks. Anything happen ?

hoboT's idea of warming up the plugs over a gas flame ( get them too hot to touch ) helps many a reluctant motor start.

Greg

pierodn · Feb 22, 2015

DogT said:
Raise the float level a bit and see what happens.

Hi Dave and thank you.
Raise means more than 1,5 under or less up?
Ciao
Piero

DogT · Feb 22, 2015

Just enough so you can flood the carbs with the tickler. But make sure the tickler is not too short, broken or something like that. Compare it to another.

pierodn · Feb 22, 2015

worntorn said:
Take out plugs, squirt a little gas down each hole with a syringe, quickly replace (dry) plugs and kick over. See if if fires. If it does not at least fire after a half dozen kicks, then start looking at potential spark problems.

Glen

Done!
The bike do not start but the spark plugs have both fire!
What i need to check more?
Thanks.
Piero

worntorn · Feb 22, 2015

pierodn said:
worntorn said:

Take out plugs, squirt a little gas down each hole with a syringe, quickly replace (dry) plugs and kick over. See if if fires. If it does not at least fire after a half dozen kicks, then start looking at potential spark problems.

Glen

Click to expand...

Done!
The bike do not start but the spark plugs have both fire!
What i need to check more?
Thanks.
Piero

Not even a hint of life with the gas down the hole? A pop or two or a brief start then die?

If not perhaps even though you have spark, it is a weak spark that will not happen under compression.

Also, is compression normal? You don't need to use a compression tester, just as long as you can feel a good amount of compression when kicking over that is enough for it to run.
What is the battery resting voltage. Old Boyer needs >11.5 just to fire, preferably >12.25.
Glen

pierodn · Feb 22, 2015

Hi Glen,
Thank you.
Whit the gasoline into the two holes no hints of life, nothing of nothing!
The engine has a very good compression.
The spark plugs are two new Champion N7Y CC.
The battery is a new 12V 10 Ah.
Yes, a weak spark (but the bike would start the same),i can try to change the two Lucas 17 M 12 ?.
The kill switch works well.
I do not know what i can do more!
Ciao
Piero

worntorn · Feb 22, 2015

Have you tried bypassing the igniton key switch and the kill switch? You might rig a jumper wire directly from the battery to the ignition 12 volt supply side.
what voltage does the battery show on a voltmeter?
A weak spark with plugs checked outside the combustion chamber often means no spark with plug in the head and under compression. It takes a great deal more electrical energy to make the spark under compression than at atmospheric pressure.
Glen

kerinorton · Feb 22, 2015

hi mate, what Glen just told was that the battery voltage should be 11.5 volts or more to start easily. If it is flat and below 10 volts, you may have a problem. Your answer to his suggestion was that you have a 12v, 10 amp hour battery. You did not tell him what the actual voltage in the battery was.

When you push in the tickler, you must get petrol coming out the hole in the carb. if not, it wont start. My 750 starts first kick every time after tickling, and using a slight amount of throttle. My 850 is similar but cant use throttle at all till it kicks in.

Often a good thing to do with a warm bike when it has been left stopped for 1/2 hour or so is to lightly press the tickler on one carb, and you will start easily.

Dereck

1971 750 Commandodo not start

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