carbs revisited

sweater914 · 11-10-2001, 05:05 PM

This a follow on to a previous thread. Having carb trouble runs really rich and back fires regularly most of the time lifting off the throttle. I'm running Weber 40 IDF 19 carbs(came with the car) on a 1.7L engine with headers and Supertrapp.
With the following:
idle jet 50
aux choke(venturi) 36
main jet 115
air corrector 200
emulsion tube F11
needle valve(haynes manual vague) 175
pump jet EW 50

Can the carb nuts out there help? Could somone out there give me a baseline to start from so at least my '72 914 will idle properly, not run so bloody rich, and quit backfiring. Thanks a lot fellas!

bpick84 · 11-10-2001, 05:12 PM

How many discs are you using on the supertrapp? Too few discs can cause the engine to appear to run rich. The backfiring and jet sizes appear to be lean. The Supertrapp could cause problems tuning the carb. I found this out the hard way.

paulhagedorn · 11-10-2001, 05:14 PM

Not sure on what kind of jets you should run..if I had my carb book with me, I could tell you what jets were in the Dell's that the PO was running on the old 1.7, but I don't think they would help you much.

Anyway, take out the idle jets and clean them really well. Blow compressed air through them and stick them back in. That might help you some, hopefully. Also, you might want to install an inline glass fuel filter in the engine compartment so you can see if the gas is dirty.

Have you checked the floats? Have you put a unisyn to the carbs?

sweater914 · 11-10-2001, 05:19 PM

thanks fellas, here's the story, rebuilt the carbs, everything is very clean, new floats also, i do have the uni-syn and have balanced both carbs, i have glass inline filters on both carbs, in addition the one before the fuel pump, the suptertrapp has all 13 discs on it

DSPTurtle · 11-10-2001, 08:31 PM

From what I remember about 'Trapps is that that is way too many discs. I think that many actually reduces back pressure to nil. Try taking about half of them off and tune your exhaust before you do anything rash to the carbs.
Good Luck!!! Let us know if you get it figured out. I am thinking that Dell's and 'Trapps are in my future so I am definitely interested.

sweater914 · 11-10-2001, 08:56 PM

hate burst everyone's bubble but i won't get this until about late december, car is at home and i'm at school 1300miles apart, mom wanted to know what i wanted for christmas, a new set of carbs seems unlikely(collective birthday/christmas for the next 2 years), but i will let everyone know what i find out, i've been dealing with this problem since i got the car, the supertrapp is really loud for all those wondering, interstate cruising at 70mph is uncomfortable