SU's suddenly running rich

[Captain Obvious]

Yeah, beautiful car. And you're right. Way too pretty not to be running better.

 

So I thought somewhere you had mentioned that you were running stock needles, but after re-reading the thread, I didn't find it and am assuming I imagined that. So I second Blue's question... What needles are you running?

Did you find that thread where Blue and I were exchanging stories about not being able to get the float bowl levels to adjust predictably? Don't keep adjusting the tang so many times that it cracks off. The 240 floats aren't easy to come by. Last I heard, ZT was close to having repros done, but until they're in stock, you should treat them as irreplaceable?

 

Blue, he's in Atlanta Georgia. If he weren't so far away, I'd pack some tools and go help.

 

 

[madkaw]

I would say the needles you have, the 1.7 is a sizing number and they are actually smaller than the original. 2.0s.

Did you save the old ones to compare? Did you try putting the old ones back in?

Also, you have adjusted the floats so many times, you haven't marred up the tang so the needle is hanging up?

Not that I am demanding an answer, but you didn't directly answer(sorry if I missed it) if you check tightness of the needle assembly or made sure all washers were in place.

[240260280z]

I'm in atlanta georga now ! SteveJ and I will meet on Fri. I may be here on the weekend.

[240260280z]

PM me with your phone number metalmonkey

[siteunseen]

I'm in atlanta georga now ! SteveJ and I will meet on Fri. I may be here on the weekend.

You won't want to leave!

 

Traffic sucks though.

[metalmonkey47]

I am guessing you may have a set of needles for a different style carb. This happened to me once. I bought a "240z" SU kit but it was mislabelled. The needles were shorter and ran rich as stink.

Nice car btw!

 

Possibly so the gaskets/instructions all matched 240Z can had different float adjustment specs for '70 and '71-'72 so I suppose it's possible the company made a 'one size fits all' and the needle valves are incorrect for my year carbs. It's good to hear that I'm not the only one that's had that happen, because I'm about 90% sure that's where my issue lies. 

 

Yeah, beautiful car. And you're right. Way too pretty not to be running better.

 

So I thought somewhere you had mentioned that you were running stock needles, but after re-reading the thread, I didn't find it and am assuming I imagined that. So I second Blue's question... What needles are you running?

Did you find that thread where Blue and I were exchanging stories about not being able to get the float bowl levels to adjust predictably? Don't keep adjusting the tang so many times that it cracks off. The 240 floats aren't easy to come by. Last I heard, ZT was close to having repros done, but until they're in stock, you should treat them as irreplaceable?

 

Blue, he's in Atlanta Georgia. If he weren't so far away, I'd pack some tools and go help.

I don't know if I ever mentioned, but for the record, the carbs (in fact, the car itself) is pretty much ALL bone stock. The PO said for the time he had it he never had anyone touch the carbs. I recall years ago he came in with fuel spitting from the carb vent, and knew I was a Datsun guy. I pulled up a diagram of the SU's having never looked at one before, and we popped the bowl off and fixed the sticking needle valve in the parking lot of my store. We fixed a few problems now and then... that's actually how I ended up getting first dibs on the car when he decided he couldn't afford to fix it, and sold it to me for $1000. 

I figured as much about the floats. I've been on the lookout, and fortunately quite a locals have spare carb parts laying around so if anything broke, I'd only be out a couple bucks. 

 

I would say the needles you have, the 1.7 is a sizing number and they are actually smaller than the original. 2.0s.

Did you save the old ones to compare? Did you try putting the old ones back in?

Also, you have adjusted the floats so many times, you haven't marred up the tang so the needle is hanging up?

Not that I am demanding an answer, but you didn't directly answer(sorry if I missed it) if you check tightness of the needle assembly or made sure all washers were in place.

Madkaw, that's a good possibility. There is a VERY slight difference in length between the 1.7 and 2.0 needle valves. Probably just enough to really throw off my mixtures. I do have the old ones, but they leaked so bad before, it's hard to tell when re-installing them if they're flooding from a separate issue...or because they're simply worn out. The needle tang seems to be pretty smooth, I've finely watched the operation under a magnifying glass and don't physically see anything hanging up. 

Sorry I believe in all of the confusion I may have missed it. The washers between the float cover and the needle are all in place and snug. I took a spare washer and tried shimming it down a hair but it made no difference. 

 

I'm in atlanta georga now ! SteveJ and I will meet on Fri. I may be here on the weekend.

Well that's convenient PM incoming! 

[madkaw]

Well if the assembly is shorter-couldn't that be the issue? If the new assembly is shorter I would shim it out with washers to match the old assembly to if that makes a difference. There probably is a limited amount of travel that can be done at the tang that can't overcome the actual assembly length issue.    

[Captain Obvious]

Wait a minute... I suspect there's a little communications issue here. When Blue and I asked what "needles" you were using, we were talking about the long straight needles that install in the undersides of the suction pistons, not the float bowl valves.

 

My suggestion would be to stop referring to the valve that the float tang pushes against as a needle valve and simply call that one "the float bowl valve" instead.

 

So about the needles... The stock needles for the first couple years are N-27's but often they have been replaced with SM needles from ZT.  Blue has had issues in the past where the needles that came new in rebuild kits were completely unsuitable for use in the 240 roundtops.

So... What needles do you have installed in the suction pistons?

[Stanley]

The front float valve is about 2mm longer than the rear one, so the front fuel level can be adjusted 2mm lower without distorting the tang on the float (so the fuel levels at the both nozzles will be the same, discussed at length in previous threads). Most of kits have one of each.

 

Sometimes the float can rub against the side of the bowl (when the float setting is fairly high), preventing it from rising enough to shut off the flow. I had fuel coming out the vent. A light touch with some sandpaper on the float fixed mine when that happened, it took a while to figure out the problem. I verified it was sticking by looping some nylon monofilament around the float and out the vent (so I could pull the float up with the fish line) and using the plastic straw to check float height.

 

Also, if the pin in the float valve doesn't contact the tang at about a 90 degree angle it can wobble to one side, which keeps it from shutting off properly. I think the newer valves that have a skinnier pin than the original ones, so they're more apt to wobble.  Fun stuff, huh?

 

If you check out the nozzles at MSA, there's some stuff about what needles go with what year nozzles.  

[metalmonkey47]

Sorry guys, I don't mean to be confusing, I might be using some confusing terminology. It has unknown needles in the suction pistons. There's no markings at all on the top, likely worn away with the numerous times they've been touched while I try to get this right. 

 

Anyways, I'm gonna side track for a second. 


HUGE thanks to Blue! Turns out, he was right around the corner all along and stopped by a few nights ago to lend a hand and help me learn a bit. We took the carbs apart on the car to check out a few things, and to teach me a little about how they function so I can better understand how to track down my issues. Turns out, I did have a few issues to be sorted. We didn't bother to mess with the floats because it seems that the primary issue lies in the nozzle on the rear carb. When doing the drop test to set the needle height on the rear carb, we saw that the needle was sitting 1-2mm below the deck.with the nozzle full up. Turns out the nozzle at full up STILL sits about 1-2mm lower then the front. The nozzle also looks misaligned. I had issues with that from the beginning and thought I fixed that, however while it fixed the piston hanging up (months ago, just after buying the car) it is still not 100%. I'll be reading into Blue's thread on that simple fix-it and going at it soon. Probably also going to look into new proper needle/seat's for the float's. I'm still very sure that they are leaking. The plugs look way better after doing some fine tuning with Blue help, and it's not nearly as rich and runs much better....but occasionally I get raw fuel smell in the exhaust and I believe the rear carb may be flooding over into the venturi slightly. 

[Captain Obvious]

Cool. Sounds like you turned up a couple concrete things to look into and took some steps in the right direction! So the nozzles being at different heights (even when both confirmed to be fully up) is odd. That 1-2 mm could certainly affect gas mileage. Refresh my memory... What's the history on the carbs? Are these ZT refurbs?

 

Looking forward to the next time Blue comes to my place!! 

 

 

[siteunseen]

And here I was 2 hours away with SU parts strewn all over the place.