SU Float Setting Questions- Need yous help again z gurus

[Ron Earp]

Wish I could help you out but my carbs are a totally different design than your carbs. You've got external bowls and so on. Mine is basically like a big Mikuni carb - float on the bottom, piston, dampener rod, jet, needle. You've got to get your float height to a happy place though and that may not be the factory setting. My factory setting is fairly close, but not quite perfect.

And you've got to get the right amount of oil in the dampener section. I'm sure the 240Z guys could help you there, on the 260Z it is about 2ccs.

[spawpoet]

Wish I could help you out but my carbs are a totally different design than your carbs. You've got external bowls and so on. Mine is basically like a big Mikuni carb - float on the bottom, piston, dampener rod, jet, needle. You've got to get your float height to a happy place though and that may not be the factory setting. My factory setting is fairly close, but not quite perfect.

And you've got to get the right amount of oil in the dampener section. I'm sure the 240Z guys could help you there, on the 260Z it is about 2ccs.

Ron, was it the float height that was causing you to have one carb's egts going cold Ron?? I have the bowl sight tool on order from z-therapy, which should give us a little more accurate look at the float settings. Actually what you've said is a help. I've been trying to religiously follow factory settings, but it's helpful to know we might have to drift a bit from stock specs to find what's going to work for racing. Moreover I just never realized that the amount of oil added to the dampeners was all that important. BTW have you run your car with the new motor in it yet?

[MIKEL]

We ran 3in1 oil vs 20wt also look into diff spings in the dampners some of the english stuff is lighter than nissan. Also look into custom ground needles the two you mentioned will leave you fighting lean a lot(they are designed for mid range response). Remember most of the time you are at full throt. and slowing the piston will only help at low rpms and makes response slugish in the higher rpm range.
The MG guys can tell you where to get the light wt springs and several people have custom ground needle sets cheap or if you are talented try your hand at grinding your own (we modifed a set of english ones for our autocross car back in the day).
I think you will find at top rpm is when you are leaning out and either the needle profile is wrong or you are not getting full piston travel. On the EP car we dont run any oil and just use the spings for idle, pistons go wide open at 1500 and have the needle profle set for the cam. We run 7400-8000 on 3.5 psi pressue and have no problems with lean out.

[Ron Earp]

Ron, was it the float height that was causing you to have one carb's egts going cold Ron?? I have the bowl sight tool on order from z-therapy, which should give us a little more accurate look at the float settings. Actually what you've said is a help. I've been trying to religiously follow factory settings, but it's helpful to know we might have to drift a bit from stock specs to find what's going to work for racing. Moreover I just never realized that the amount of oil added to the dampeners was all that important. BTW have you run your car with the new motor in it yet?

With respect to one of the problems I fought for a few races I had a carb that was a bit off on the float setting and the fuel level was too high. I have sight glasses but the carb that had the setting off had a poor glass that didn't allow you to see the level. After resetting the floats many times I finally got my hands on proper glass and fixed the problem. I then further fixed the problem to make it easy to set the floats by using a "go no go" wire gauge inbetween the float tab and a fixture cast in the bowl so I don't have to worry about it - I set it with the wire gauge and I know it is good. I arrived at the proper setting by using the carb that was working well as a master.

Damper oil - Steve P and I have compared notes here and both of us agree that no damper oil doesn't work well. It worked well on Sam's dyno, but on track having no damper oil seemed to allow the pistons to slam open quickly and we both experienced throttle transition stutters. Bear in mind Steve has a 240, I have a 260, but we both had the same experience.

Too much oil, like filling the tube 2/3 full or higher, seems to cause a bit of a sluggish response. I know that description is hard to quantify but that is about the best I can do.

Mine seems to like about 2ccs (2 mL), and I use 20 weight motorcycle fork oil (I don't think this makes such a bid difference, you just don't want a multiviscosity oil in there). Why 20W motorcycle fork oil? It was what I had on the shelf that was single weight. I'm sure you could get similar results with 30W motor oil.

We have run the new motor on the track but not the dyno. On track I think I think what we have is a bit more hp throughout the range than the old motor. Beyond that they seem somewhat similar. I'm looking forward to putting it on the dyno and actually getting out and doing some racing with it!

[dspillrat]

You do need springs, you do need oil. Withoutem piston slams open at slightst throttle opening.......throws mixture outta whack...IMHO.
Try a little lighter weight to 5-10 weight....YMMV.... Yeah, and hope Katman will throw his 2 cents worth in.....

david

[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.