40 IDF or 44 IDF which ones to get?

[sweater914]

I've got a '72 914 with the 1.7L engine. Right I'm using 40 IDF 19 carbs that apparently are not the right ones, i've been told that they've been jetted and made to work with 356s, the main venturi 36. I believe the carbs were thrown onto the engine as an after thought.

Trying to remedy the situation which carbs should I purchase 40 IDF or 44 IDF?

[SteveStromberg]

Just change the Venturis to 32mm and they should run better of course you will need to rejet the carbs to some like 55 idle. 130 mian , 170 air, F6 or F12 emulsion tubes. Set timming at 32BTDC. Steve
See: for tunning tips: www.teglerizer.com/dcoe/webertune.htm

[sweater914]

The biggest problem is the car has a hard time idling and the poor thing backfires pretty bad when I let off the throttle. The car has a Supertrapp exhaust and header. Also it runs rich all the time, as evidence of the black soot on the luckily chrome bumper.

The idle jet number is the only one close. I don't have the numbers in front of me but this is what i do from memory:

idle 55 or 50
main 155
air 115
emulsion F10

[Joe Bob]

You might want to consider an 050 dizzy, I would bet that you have the 009.....

[sweater914]

if you're talking about a bosch blue coil, yes it has a 009, or the distributor?

[Joe Bob]

Yeah, the 009 distributor is junk....get a 050, more advance.

[DSPTurtle]

I was reading my SCCA rulebook today and it says that you can go up to a 40 for the prepared class. Not sure if this matters to you but going to the 44 may throw you into a class that is gonna be impossible to run in!!!

[sweater914]

not really worried about running SCCA just yet, just trying to keep the poor thing running until after college, it getting a full blown restoration after school loans are paid back, thank though

[Conrad W Peden]

The backfire may be a symptom of an exhaust leak or backpressure issue. The problem with just chucking a fancy exhaust on a motor such as a 1.7 is that it cant take advantage of what the exhaust has to offer. The 'note' of the supertrap maybe masking the leak if there is one.

When a motor is designed to wind up fast and rev high it needs an exhaust that the motor doesn't have to push the exhaust through. Not your typical 1.7.

A mechanic once likened it to having your backside open an inch all the time. If you were in a big rush its not so bad but its not quite practical for everyday use. Having an exhaust like this can make the car tough to tune. He told me to get rid of mine before he would waste my money tuning my car.

My motor is a 1.9 L, high compression with a mild/med cam and he told me I still should be using stock type exhaust. We ended up tuning the car down to run on pump gas anyways.

Good point on the carb size for SCCA rules I know in PCA just having carbs is a big penalty.

[sweater914]

pretty sure its a back pressure issue the exhaust doesn't have any huge leaks to cause the backfires(small one around the clamp for the trapp), trying to make do with what i have, will have to play the setup a little