Fitting an air fuel ratio meter

[142 Guy]

Originally Posted by Rustinmotion

I’m not sure what cam it is but I suspect it’s A
I used to run a single wire O2 sensor that’s why I didn’t connect it, just for info I could get it to work when driving the car and no heater
The instructions give some guidance to what the led relate to but il take it as a guide rather than gospel, it’s doing the job I know something is not correct and this is helping to narrow it down, have ordered a pack of float valve spacers to try and lower the fuel level, this will allow me to open the jets at idle and add more fuel up the rev range

If you are running an A cam then my comments about having to run rich with a high idle speed are probably not relevant. I was clearly thinking of somebody else who was talking about using a D cam with SU carbs.

[Rustinmotion]

I will remove the grose jets and go back to needle valves just to rule out any odd inputs
I believe it’s something to do with fuel level so il set it up to base set up and hopefully I can then unscrew the jets to get a good idle which should then give a richer level across the rev range

Just checked and the intake valve is opening at 32 degree so think it’s a B cam

[Rustinmotion]

Originally Posted by Rustinmotion

I will remove the grose jets and go back to needle valves just to rule out any odd inputs
I believe it’s something to do with fuel level so il set it up to base set up and hopefully I can then unscrew the jets to get a good idle which should then give a richer level across the rev range

Just checked and the intake valve is opening at 32 degree so think it’s a B cam

Ok so viton tipped needle valves fitted Float level set and I don’t have same fuel level in both carbs, one carb had 10mm lower level than the other, made some adjustments with different jet gasket thickness
I still can’t get a good smooth idle without winding the jets right in, can someone take a photo of the jet position so I can compare with how mine are

[Ron Kwas]

RiM;

Presuming Metering Needle installation position is correct in Dashpot (flush with Dashpot lower surface) 12 flats down is where to begin with Idle Mixture adjustments. See: https://www.sw-em.com/su_carbs.htm#I...et_Replacement (includes pix)

Good Hunting!

[Rustinmotion]

Originally Posted by Ron Kwas

RiM;

Presuming Metering Needle installation position is correct in Dashpot (flush with Dashpot lower surface) 12 flats down is where to begin with Idle Mixture adjustments. See: https://www.sw-em.com/su_carbs.htm#I...et_Replacement (includes pix)

Good Hunting!

That’s my problem I start at 12 flats and have to wind it back in 10 to get it to idle smooth, the AFR meter is still showing rich even at that but goes weak under acceleration
The photos show the jets nearly flush with the bridge, I can find conflicting info on how far below bridge the fuel level is

[Ron Kwas]

RiM;

If you have verified MN in Dashpot is flush, and Jet is not worn, I guess the next thing I would look at also is fuel level in Bowl, although its not as critical IMO, as some make it out to be, because the fuel will still get pulled out of the Jet by the partial vacuum at Venturi, and the opening which it's being pulled through (0.100" - OD of MN at a given height) will limit this flow to a correct amount, so metering function of carb is thankfully not critically dependent on Bowl level (within reason!)... I'd remove Bowl Lids and compare fuel level on problem carb to other's (Floats will obviously be removed at that point, but a comparison between the two carbs to check for a gross difference is still fair).

What is the starting point here? Has the carb in question ever run satisfactorily, or is this first time since overhaul?

Note that a lean mixture will idle smoother, so it's doesn't surprise me too much that when you raise the Jet so much it smooths out...tht may be, but I bet it wouldn't have a decent throttle response (blip throttle) or make good power (road test) with jet set there! I would tune for good running and throttle response on the road first, then look at what AFR gauge is telling me, and make adjustments from there, not the other way around!

Good Hunting!

[Derek UK]

Float closes the needle valve to give a fuel level approx the top of the jets, when correctly adjust for idle. This is below the bridge. If the floats are adjusted to give a higher level the fuel will flow straight into the inlet manifold. As Ron says, airflow over the bridge sucks the fuel out of the jets. The needles taper meters the amount.
The jets should be wound up to be level with the bridge on both carbs. Winding the nuts up to the max will not necessarily position the jets correctly. Take the pots off to do the setting. If one doesn't quite get up level with the bridge make the the other one level with it. Wind down 12 flats from there. Refit the pots, top up oil and start the engine. Tune back and forth between the carbs, noting how you raise and lower the jets. Half a flat at a time should be OK but it's unusual for there to be be more than a flat difference.
Note, the white floats can suffer from ethanol in current fuel. This may cause them to leak and fill with fuel. This makes them heavy and gives an incorrect level. Burlen can supply black ethanol resistant floats. Expensive!

[Rustinmotion]

Originally Posted by Derek UK

Float closes the needle valve to give a fuel level approx the top of the jets, when correctly adjust for idle. This is below the bridge. If the floats are adjusted to give a higher level the fuel will flow straight into the inlet manifold. As Ron says, airflow over the bridge sucks the fuel out of the jets. The needles taper meters the amount.
The jets should be wound up to be level with the bridge on both carbs. Winding the nuts up to the max will not necessarily position the jets correctly. Take the pots off to do the setting. If one doesn't quite get up level with the bridge make the the other one level with it. Wind down 12 flats from there. Refit the pots, top up oil and start the engine. Tune back and forth between the carbs, noting how you raise and lower the jets. Half a flat at a time should be OK but it's unusual for there to be be more than a flat difference.
Note, the white floats can suffer from ethanol in current fuel. This may cause them to leak and fill with fuel. This makes them heavy and gives an incorrect level. Burlen can supply black ethanol resistant floats. Expensive!

Floats are dry inside, set them up with dash pots removed, it’s idling best around 2 flats unscrewed from the initial jet flush with bridge

As I seemed to be getting different fuel levels using the recommended set up I pulled the jets then carefully lowered them ( keeping them vertical) down the side of the fuel bowl and marked the bowl with a marker at the point fuel started to flow, this is the actual level of fuel in the bowl with floats fitted, it was 10mm different, I made both same as the higher level, maybe I should have adjusted to lower level
As I think I understand it
At idle the vacuum signal is weak so a lower fuel level would result in less fuel pulled into the intake requiring the jet to be lowered making the whole range rich

[Rustinmotion]

Today I fitted new floats and needles, one carb had a ZH needle the other had no marks so I fitted new KI needles
Car now pulls much better and it’s staying slightly rich across the rev range just leaning off on trailing throttle

[Rustinmotion]

Still not fully happy with the idle I did a hot cut on the plugs and this is the results, to me they look on the lean side
I noticed the fuel level in the filter king regulator was low so bypassed it and the car showed a change in idle and over rich on the gauge
After some adjustments I have a reasonable idle and the gauge shows 13 stoic under normal driving conditions, il do another hot cut test when I get chance
I’m using E5 petrol and a millers additive will it be possible to get the light tan colour on the plugs? Or do modern fuels burn differently