FC Another Tassie car

[NickZ]

I did have a 058 in it and changed it to a 051 but didn't change the surging, but ran much better in other areas and the long jet in the middle. the carb was of a 202 and i changed the base.
Ive just bought a remanufactured one, see if that fixes it.

[Harv]

The 202's had a lot bigger venturi - typically 1 7/32" compared to the grey motor 1 1/32". The 3/16" difference in venturi diameter means the 202 carb develops less vacuum signal on the grey, and needs bigger jets to cope with the lower "suck". Changing from a 0.058" to a 0.051" will make it run leaner at low revs (where vacuum is higher), but probably make the cruise surge worse if anything.

Interesting to see of the new carb fixes the issue.

Cheers,
Harv

[NickZ]

ok, yes it did make it worse, i never thought of it that way.
I do have a external adjustable jet here that i was going to fit, maybe i will and try it out.

Thank you.

[Harv]

ok, yes it did make it worse, i never thought of it that way.
I do have a external adjustable jet here that i was going to fit, maybe i will and try it out.

Thank you.

Could also be some crap sitting in the main metering jet circuit. Put your hand over the carb while it is running until the engine nearly stalls. Repeat a few times. This gives extra "suck" to the jets, and can suck through the crap.

I'm not a fan of adjustable jets, but it will be a good tool to help identify your issue. As a starting point, gently seat the needle, then open it 3 turns. This will get you a jet close to 0.061". If that doesn't cure the surge, open one full turn more (total of 4 turns) to give a 0.067" jet. If it is still surging, then the issue is not jetting... 0.067" is a damn big jet.

Cheers,
Harv

[ardiesse]

Nick,

Surging at cruise is also a symptom of over-advanced ignition timing.  You can check for this by disconnecting the vacuum advance pipe from the distributor and going for a drive, or just running the engine at 1500 - 2000 rpm and seeing whether it still stumbles with the vacuum advance disconnected.

I have a similar light-throttle lean-out condition in my FC.  My first cure was a 52 main jet; but now I've gone back to a 51 main jet with a no. 68 idle tube from a red motor carburettor (the greys run a no. 70 idle tube).

Rob

[NickZ]

I found another grey motor carb today, stripped it down , cleaned it up and fitted it to the car. Same problem still, i can't work it out.
also checked the advance, all with in spec.

when reving its fine, but pull on some throttle, you can see the fuel coming out down the throat of the carb, but as you hold it the throttle the revs slowly die down the fuel just stops flowing out and it stalls.

[FCRB26]

I would be investigating the fuel pickup in the tank and fuel lines rule out a part blockage also has the fuel pump had a kit thru it ?

Just start at the back and work ur way forward also put the points back in while doing so i have had 2 set of petronix electronic ign fail now.

[NickZ]

it will drive ok if i keep modulating the throttle. Trying to make/fine a throttle body with injector that i can adapt, I hate carbs and as i make my own EFI computers i think its going to be the best way.
I was going to try boring out the centre of a standard carb body and mount injector/s inside the oil bath air cleaner spraying down the throat so it still looks standard, still working on that idea.

[FCRB26]

you could do it so clean and on a budget as well. use your electronic ignition for your trigger and a coolant temp sensor run something like this
http://jeremylawsonblog.com/post/28635142410/rodandcustomshow-autotrend-efi-has-captured-the#.Vy8VDiFv4uc

Or rochester make one as well.

[NickZ]

Fix my carb problem, fitted the external adjustable jet i bought some time ago. runs fantastic.
Ill hold off on the efi.

[Harv]

Cool  :). Glad it was the main metering jet as suspected.

Cheers,
Harv

[fe350chev]

Congratulations on finishing your build mate.