Starting car for first time, baseline setting on carbs Options

[MattR]

Im about ready to start my 914 for the first time and break in the motor. I have a set of 40 idfs on there that im guessing are out of adjustment. How many turns out should I set the needles at to get it to fire? I know I have to tune it during break in, but Im just trying to get it to start up now. Hints? Thanks.

Edit: i should have clarified. This is a 2056, dual 40 idfs, raby split duration cam.

[Twystd1]

Hi ya Matt,

Question:
What idle jets ya got?
What imulsion tubes?
What size main jets?
And on and on?

Or are these a KNOWN good set of carbs off a running engine?

Might help a bit with this info...

Twystd1 In Mexico

And yeah i know you just want to fire it up and get it running for ring break in.

[MattR]

Hey clayton, thanks for responding down south!

The carbs came off a running 2.0 I bought off the club site. I havent seen them run, but they were sold as running carbs, and I did rebuild them and clean them out. rejetted them to jake's specs for my cam and combo (thanks again jake (IMG:http://www.914world.com/bbs2/html/emoticons/aktion035.gif) ).

130 main jets
F11 emulsion tubes
32mm venturis
175 idle jets

does that sound right?

[lapuwali]

You should start with 55 idle jets. Set the idle mixture screws to 2.5 turns out from lightly bottomed. Make sure the linkage isn't hanging up, and that the throttle stop screws aren't touching the throttle arms when closed (so the throttles really close fully). You'll need to keep your foot on the gas for it to idle, but the idle won't race away to high rpm, either. Run it for a bit, then set the idle speed with the throttle stops. Sync the carbs and set the idle mixture.

The mains, airs, and emulsion tubes shouldn't matter during break in, as you'll be on the idle jets the whole time.

If you haven't already blown out the carb's passages with air, do so first. If you haven't already cleaned your fuel tank, do this first. Use two fuel filters.

[Twystd1]

Yo Matt "A" Rama,

Are you sure Jake said 175 Idles? Jusss wondering.....

Twystd1

[MattR]

Yeah, 175 doesnt sound right. Maybe that was air correction? I pulled out the emulsion tubes and wrote those numbers down, but I didnt check idle. I had a bag I thought i used, but I know I have the "right" stuff installed.

I was talking about main needles and stuff. Should I go 2.5 turns out on the main needle?

[lapuwali]

There is no "main needle".

The parts on the jet stack (the two in the center of the carb, between the throats) are, the air correction jets (175-200 are typical sizes, lower number is RICHER), the emulsion tube (F7 and F11 being the only one's I've heard used on the T4), and the main jets (125-135 are common sizes, lower numbers are LEANER). None of these really have any effect until 2500-3500rpm. Below that, you're primarily on the idle jets. They're behind screw-head holders on the exterior sides of the throats, same side as the adjustment screws and the accelerator pump. 50 and 55 are the only sizes for idles usually seen, lower numbers are LEANER.

The idle mixture screws are the larger adjustment screws at the base of each throat, with the springs. Out (anti-clockwise) is richer. 2.5 turns out is the usual setting to start from.

The smaller screws (with the locknuts) are air bypass adjustments, to adjust how much air is allowed to sneak past the closed throttle plate. These are used to sync one carb throat against the other on one carb.

The last adjustment is the throttle stop screw, with a spring, on one end of the carb, which is used to set idle speed, and sync one carb against the other at idle.

The 175 numbers are probably air correction jets, at that's about the richest one normally used on these engines. It primarily controls mixture above 4500rpm.

[Mueller]

QUOTE (lapuwali @ Jul 14 2005, 04:45 PM)

There is no "main needle". The parts on the jet stack (the two in the center of the carb, between the throats) are, the air correction jets (175-200 are typical sizes, lower number is RICHER), ...........blah, blah, blah.........

man, I tried to read that, I am more confused now about carbs than before (IMG:http://www.914world.com/bbs2/html/emoticons/wacko.gif)


It is good to see people still knowledgeable about them however...who knows, in a few years finding a carb person will be as hard as it is to find an MFI person nowadays....

[lapuwali]

QUOTE (Mueller @ Jul 14 2005, 03:58 PM)

QUOTE (lapuwali @ Jul 14 2005, 04:45 PM) There is no "main needle". The parts on the jet stack (the two in the center of the carb, between the throats) are, the air correction jets (175-200 are typical sizes, lower number is RICHER), ...........blah, blah, blah......... man, I tried to read that, I am more confused now about carbs than before (IMG:http://www.914world.com/bbs2/html/emoticons/wacko.gif) It is good to see people still knowledgeable about them however...who knows, in a few years finding a carb person will be as hard as it is to find an MFI person nowadays....

Hm. Maybe I should rephrase that, then.

In between the throats, there are two brass screws with holes in the center. On some IDFs, this are really tall, some are short. If you unscrew these, you'll find a there's a top part, and middle part, and a bottom part. The top and bottom parts press into the middle part. The middle part is the emulsion tube. The top part is the air correction jet, and the bottom part is the main jet. The mains control fuel mixture from roughly 2500-4500rpm, the airs from roughly 4000-up. The idles jets control from 1500-3000, and the mixture screws below 2000. The overlaps are intentional.

Trouble for me is, I figured all of this out about Webers over the past couple of years, and the engine I'm getting at the weekend has Dellortos on it, so I'll be learning a new set of carbs (until I manage to fit PEFI onto it). I only have Weber books, so I'll be looking around for a book on the Dells soon.

[MattR]

QUOTE (lapuwali @ Jul 14 2005, 03:45 PM)

The idle mixture screws are the larger adjustment screws at the base of each throat, with the springs.

Ahh, okay. Thats what I thought was the "main needle." I see it now though... thanks! (for some reason I thought idle needle was the idle stop... very different, I know.

I have 55 idles and 175 a/c jets, just to clarify.

I should be starting my engine tomorrow afternoong (hopefully). Thanks for the help! And, is there a difference in application for the short and tall emulsion tube screws? My 912 has "short" (yep, it has webers) and the 914 has "tall".

[lapuwali]

Damned if I know what the difference is supposed to be on the jet stack heights.