SU Float Setting Questions- Need yous help again z gurus

[spawpoet]

How do you guys vent your overflows? Our biggest issue with stumbling on track right now is a temporary rich condition we are getting on one carb in hard right hand turns, but only after the car has been on track for 4-5 laps. We have vented the bowl overflows back into the air cleaner, and I think when the bowls heat up we are overflowing back into one of the carbs (rear) in the hard righthanders causing the problem. Is it a mistake to vent the overflows back into the filter housing? As for the needles/oils/springs we intend on spending some dyno time experimenting with different combinations. We still have yet to get O2 sensors into the exhaust to get better mixture info, so that will help tune it too. Really it mostly ran very well, but the main problem was it "richening" out in those hard corners. We smooth that out, and our laptimes should be just 3-4 secs off the pace with an undeveloped car and driver. Thank you again everybody. I really appreciate everything the community on the forum has to offer.

[Ron Earp]

How do you guys vent your overflows?

I don't think I have a choice. My carb has an air horn that comes up right into the airflow stream into the carb. I'd love to move it because it certainly is probably 10% of the area of the opening. So, my bowls are vented into the opening of the carb that is in the air filter housing.

I'm not sure why this is done. Other carbs I've worked on that are somewhat similar have vents to atmosphere that are not in the airflow to the venturi.

[tim240z]

One of our thoughts was that the fuel was getting sucked out the over flow into the air filter housing and running straight into the carb... flooding it out... Do you think this might be the case or is it most likely over flowing into the carb body itself due to float settings?

We have a stock air filter housing w. stock vstacks modified to fit a single ITG air filter. The vent lines go to the stock location in the backing plate.

[pballance]

I am far from an expert in this area but here are a couple of observations.

My vent is a simple loop tucked in alongside of the carb and I have not seen/smelled fuel venting from the float chamber. I have read elsewhere that a 1/2" drill bit used as a gauge for setting float levels should result in proper float level with a slightly "loose" fit.

Needle height is important and float level gives you the gross fuel adjustment for the carbs. Just a thought here. remove the float valves from both carbs and see if they are different. I remember something about rear valve is different from the front and it is the length. I don't remember which is which, but it is to compensate for differing gross mixtures under g-loads in the float chamber. It has something to do with the way the floats hinge and the location of the bowls since they are on opposite sides of the carbs. I will have to check my notes when I get home.

Hope that helps. Work has been getting in the way of fun these days with travel.

Paul

[MIKEL]

Sorry to confuse the issue, on the EP car we are running a big cam in a higher rpm range. I agree you def need oil just go light wt was all. I have seen problems with heaver oils.
I talked to one of my english guys and he thought there was a either green or blue spring set they used on the race cars (I think they have colored paint spots on them?)
Also he said that there may be a float jet/seat issue and to replace them if in doubt, this was a common problem in the race cars. He has seen them stick when they heat up, also if you have bad vibration (I dont think the L series have much) will cause sticking and overflow (this was on the euro SUs so he was not sure if it applied to the jap stuff). But you def will want a set or two of custom needles.Sam makes good ones!
Good luck!

[kthomas]

Step 1: Buy Factory Service Manual.
Step 2: Do what it says for a stock car.

You can ignore those two steps if you have tons of money for dyno testing, in which case you will discover that in the end steps 1 and 2 are pretty dang close to best performance even for a fully developed ITS engine. I was constantly amazed over the years I was racing Z's in IT by how many guys I made faster by undoing the crap (ie speed secrets) they had done to thier engines in favor of getting back to stock. 20wt or 10w30 for damper fluid (ie per FSM), stock piston springs, stock float levels, stock needles (no SM's or "performance regrinds", we ran N54's), stock idle mixture setting. I always chuckled to myself on the grid looking BEHIND me at all the Z's that had to keep reving the motor to keep it cleared out from too much gas while we sat quietly purring along at a pleasantly stock idle.

Go back to basics and assume nothing is correct. Remove the float chamber lids and first confirm whether or not you have the same size float pin locator tangs on the lids or two different lengths. Then make sure you have the right needle housing for the tang setup (short tang housing aft, long tangs in front). By tang I mean the protrusions that the pivot pin is captured in. I'm just going from memory here, so somebody check me. I believe the '72 carbs (4 screw) were equal tang lengths, and float level should be 14mm. Turn the lid upside down, and when you lower the float lever seat (the curved metal piece that touches the needle stem) until it touches the needle stem the distance from the inside surface of the lid to the upper (when installed, lower since we're currently upside down) flat surface of the float lever seat should be 14-15mm. That gives you 23mm of distance from the inside surface of the lid to the actual gas when all installed and running. Of course that is practically impossible to measure. In the field I just turn the float lid upside down and see of the float is about horizontal, then I unhook the float and set it in the gas and the gas level should be about 3/4 inch below the gasket lower surface (ie top of fuel bowl). Bottom line- no tricks, make it stock. If these were Z Therapy carbs, unmolested by a previous owner, I'd be surprised if there's anything wrong there but assume nothing. Stock fuel pressure was 3.4 psi, so 3.5 should be okay assuming that's what you are actually getting.

Yiou should never have gas coming out the vents. Um, you don't have Grose jets in there do you?

[tim240z]

Step 1: Buy Factory Service Manual.
Step 2: Do what it says for a stock car.

You can ignore those two steps if you have tons of money for dyno testing, in which case you will discover that in the end steps 1 and 2 are pretty dang close to best performance even for a fully developed ITS engine. I was constantly amazed over the years I was racing Z's in IT by how many guys I made faster by undoing the crap (ie speed secrets) they had done to thier engines in favor of getting back to stock. 20wt or 10w30 for damper fluid (ie per FSM), stock piston springs, stock float levels, stock needles (no SM's or "performance regrinds", we ran N54's), stock idle mixture setting. I always chuckled to myself on the grid looking BEHIND me at all the Z's that had to keep reving the motor to keep it cleared out from too much gas while we sat quietly purring along at a pleasantly stock idle.

Go back to basics and assume nothing is correct. Remove the float chamber lids and first confirm whether or not you have the same size float pin locator tangs on the lids or two different lengths. Then make sure you have the right needle housing for the tang setup (short tang housing aft, long tangs in front). By tang I mean the protrusions that the pivot pin is captured in. I'm just going from memory here, so somebody check me. I believe the '72 carbs (4 screw) were equal tang lengths, and float level should be 14mm. Turn the lid upside down, and when you lower the float lever seat (the curved metal piece that touches the needle stem) until it touches the needle stem the distance from the inside surface of the lid to the upper (when installed, lower since we're currently upside down) flat surface of the float lever seat should be 14-15mm. That gives you 23mm of distance from the inside surface of the lid to the actual gas when all installed and running. Of course that is practically impossible to measure. In the field I just turn the float lid upside down and see of the float is about horizontal, then I unhook the float and set it in the gas and the gas level should be about 3/4 inch below the gasket lower surface (ie top of fuel bowl). Bottom line- no tricks, make it stock. If these were Z Therapy carbs, unmolested by a previous owner, I'd be surprised if there's anything wrong there but assume nothing. Stock fuel pressure was 3.4 psi, so 3.5 should be okay assuming that's what you are actually getting.

Yiou should never have gas coming out the vents. Um, you don't have Grose jets in there do you?

Thanks katman... No, they dont have grose jets and they are 4 screws... Its quite possible the fuel was building up in the carb and not coming out of the overflow. The more I think about it the more it seems to just be set too rich (float level) ((unless the needle and seat WAS stuck thus dumping excess fuel out of the overflow))

We're set to run the Turkey Trot next weekend and we'll have additional tools that'll help us with float setup. We also just finished modifying our airbox adding heat shielding between the carbs and header. Lastly, the wideband will be installed to get logged overall mixture readings.