09-12-2024, 06:42 PM
Hi
At idle there is pressure drop across the nearly closed throttle plate, giving a partial vacuum downstream of the plate. This "sucks" fuel from the idle drilling on the engine side of the plate via the slow running jet. This idle circuit is the only fuel supply when idling.
At higher speeds, the increased airflow through the venturi (restricted cross section) upstream of the throttle causes its own small depression, and at a certain airflow this is enough to "suck" fuel from the main jet, the discharge point being a few mm above the float chamber level.
With careful design, the idle circuit and the main circuit "hand over" seamlessly from one to the other.
If you use the cold start strangler, the pressure drop across the strangler artificially increases the depression on the main jet and allows it to function even at low airflow, i.e. below its normal operational range. This seems to be what you need to do to keep the engine running and suggests the idle circuit is not doing its job.
As suggested above, check the idle (slow running) jet is clear. Being the smallest jet it is the most likely to succumb to blockage.
At idle there is pressure drop across the nearly closed throttle plate, giving a partial vacuum downstream of the plate. This "sucks" fuel from the idle drilling on the engine side of the plate via the slow running jet. This idle circuit is the only fuel supply when idling.
At higher speeds, the increased airflow through the venturi (restricted cross section) upstream of the throttle causes its own small depression, and at a certain airflow this is enough to "suck" fuel from the main jet, the discharge point being a few mm above the float chamber level.
With careful design, the idle circuit and the main circuit "hand over" seamlessly from one to the other.
If you use the cold start strangler, the pressure drop across the strangler artificially increases the depression on the main jet and allows it to function even at low airflow, i.e. below its normal operational range. This seems to be what you need to do to keep the engine running and suggests the idle circuit is not doing its job.
As suggested above, check the idle (slow running) jet is clear. Being the smallest jet it is the most likely to succumb to blockage.