My 1981 Yezdi Classic 250 has starting trouble; Any clue what's wrong?

I tried different air screw setting between rich and lean but it really does not have any impact.

BHPian pratz recently shared this with other enthusiasts:

Hello everyone,
I own Yezdi Classic 250 from 1981. I recently changed the carburettor and installed a new one (Pacco 47 Y. Pics attached). I tuned the bike using the idle screw and the air screw and it rides fine. I test rode it a couple of time to get the right air mixture and have now settled somewhere slighty higher than a 1/2 turn out (counter clockwise). I have adjusted the needle clip of the main jet 3rd slot from the top. the Main Jet is 90 and the Idle is I guess either 40 or 50 (cannot make out). Now the problem is as follows

The bike does not start whatever I do unless I do one of the following
I loosen the idle screw quite a bit (almost 3 more turns out from its normal setting) and then the bike will start or
I place my hand and partially block the air intake (after removing the rubber pipe) of the carburettor and the bike will start almost immediately. It seems the vacuum/ pressure that is created helps

It almost seems it needs a good air pressure (vacuum) to start. Since when I loosen the idle screw it does reduce the aperture of the slide and when I put my hand on air intake it does create more air pressure in the carburettor

So can anyone help me with what could be the possible reason for the same? The bike usually restarts if I just switch off the engine and start within a couple of minutes. But maybe after an hour or so, it wont start again till I do either of the two tricks !

I tried different air screw setting between rich and lean but it really does not have any impact. I changed the spark plug, and I even serviced the point. I also tried different main jet needle position however, the problem persists.
Any clue whats going on?
Pratz

Here's what BHPian Motard_Blr replied:

The symptoms suggest the mixture is too lean for starting.

I suggest that you check the following:

- float valve setting to enquire sufficient petrol level in the bowl
- correctness of the jets for this bike
- spark plug condition and gap
- ignition timing and strength of the spark
- vacuum leaks causing lean mixture (check gaskets and rubber seals for cracks, breaks and deformation)

I hope this helps.

Here's what BHPian pratz replied:

Solved!

Thanks Motard_Bir. It was the float level problem. The float was set too low leading to low fuel level and hence not enough during the starting stage. Once I changed that, the bike is starting just fine. Perfect single kick start!

Pratz

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