48IDA accelerator pump
 

Has anyone experienced leaky accelerator pumps on 48IDA's? This is most likley due to worn out parts or, hopefully not, a worn out carb body. Does anyone know of a fix for this? Thanks in advance.

Brian Paul

Brian:

That is typically not a problem. In theory the diaphrapm used on the IDF is better for leakage control than the piston type on the IDA but the piston type is rarely a problem. What kind of problems are you experiencing?

Control of the spray can be altered by a couple of factors. The stroke of the pump is one; If the pump jet is small the delivery will be longer than if the pump is large; a heavier spring will will increase the rate of discharge for a given size of pump jet (jet meaning the discharge nozzle in the carb bore); and, finally, the bypass or exhaust valve size (sits in the bottom of the float chamber). This allows fuel to return to the float chamber from the pump, the rate depending on the size of the hole in the bypass valve--by a larger proportion when the spring is soft, to a lesser extent with a heavy spring.

The bypass valve is most critical when a stumble occurs at mid range. Enzo taught me that early on. A lot of people think it is related to jetting but what happens is that, often times, the stumble is due to a too rich shot--which for many seems like a lean condition. Putting in a 55 bypass valve will often cure the problem. Aggie 427 called me with this problem a month or so ago and a change in the bypass valve, which created a smaller shot from the accelerator pump, cured his problem immediately.

If the problem is with the piston, you can replace the unit. I would examine the pump for wear, however, and measure the outside diameter and give me a email, as I have new pumps from which to give you some point of reference.

Brian stop fiddling with those things till you have them in a car.....everything you do now will only change when you put them under load.

Matt

OOPS! I guess I didn't make myself clear. Fuel is leaking from the exit point at the bottom of the carb where the accel pump shaft meets up with the cam on the throttle plate shaft. I think it may be due to a very old gasket. Both of these carbs have the same problem. My other two do not.

Cal, the measurements are as follows. Piston 15.8mm, Pump shaft is 5.2mm, Brass sleeve in the carb is 5.5mm i.d. I have 55 bypass jets and the floats were calibrated by Enzo.

I hope that this is just a gasket problem. I am going to compare my other non-leakers and see what the differences are.

Matt, When was the SCAT meeting? I would like to go with you. Thanks.

Brian Paul

It sounds as though the top gasket must be shot and the fuel is seeping into the accel rod hole, although that opening has a slightly raised brass sleeve. In addition to the top gasket, check and make sure you don't have a bad needle/seat, as it would take a real high float setting, coupled with a bad gasket, for gas to seep down that rod bore.

Aggie:

How are things since the float height was raised to .190. Let me know. thanks.

Brian,

We haven't had the meeting yet but you are welcome to ride with me...I may not be able to bring the car though its giving me fits.

Not the carbs...they have been running really good but still a little rich with the 135 mains and 55 idles....I think I may step down another 5 on each but I need to get these freakin exhaust gaskets to seal up...

I have tried the paper and the copper and can't get them to seal worth crap...I need something thick enough but that can handle the head....oh well back to the drawing board...if I don't get these fixed by the next meeting the car is going nowhere because it is popping terribly and I can hear the spit back to the carb with the cam overlap and the gasket leak...

not fun not fun at all...but I don't have problems with the floats anymore :)

Matt