Another SM needle question

[cj71z]

I bought a colortune and tried to tune my carbs today. It seems that no matter what I tried the mixture always stayed rich(yellow). I read in a previous post that the SM needles are too rich throughout the RPM range. I got it running the best I could by listening to the idle, but it still smells rich and kinda smokey. Is this common for people with SM's? If they're bad because of their profile is there anything I can do to try to correct this problem? I also noticed that after cruising down a hill when I accelerate to go up the other side it puffs smoke out the tail pipe. It seems to be greylike, could this be caused by the needles? It seems more like a valve stem seal symptom to me, but what do you guys think?

Chris

[dogma420]

rings....how old is your lower end? and these symptoms...no smoke before the needles?

What do you think about the colortune device?

[cj71z]

The motor is original, it has 125K on it. I haven't done a comp check though so I don't know about the rings. Could a rich condition cause this smoke? I'm not sure how it was before because it's been sitting for 10 years before I rebuilt the carbs. It only seems to happen when I accelerate or when I pop the throttle when tinkering with the carbs. The colortune seems to be a good tool. During all my adjustments the color never turner blue, only stayed yellow/orange. Even though according to the instructions I'm running rich the car seems to run good. So I can't tell yet if it works, but I've read other stories of people who use it and like it.

Chris

[dogma420]

well do a comp check and get back to us. Without it, it's hard to move on to saying that the problem is that it is too rich...SM needles by themselves aren't going to cause it to be too rich at all settings, IMO.

The adjusters on the bottom of the carbs, screw those in all the way (UP) so its running technically lean...if its still yellow, I would say honestly that it isn't the carbs (if they are in good shape)....

do a regular compression test and write all the numbers down. Do a 2nd compression test by pouring a capful of oil into each cylinder (one by one) and turn over a few times....this seals the rings....then do the 2nd comp test--if it is a lot higher, then your rings are shot....if it doesn't change much (it'll change some, no matter what unless it has a new ring job)....it it doesn't change much, and the 1st test isn't at least 125 or greater, then your valves are compromised. I think 125 is a good number, any one out there want to interject?

Also, even if it is low on either test, as long as all cylinders are consistent, that is what you want....if 4 are low, and 2 are normal comp rates, then that is what can screw up a motor, imo.

Also, if your throttle shafts are not rebuilt (and unless you get rebuilt SUs from Z Therapy or somehow get new throttle shafts) if they're not rebuilt, then they might leak air, which will screw up your air/fuel ratio and make any adjustments on the SUs be affected by it.

While running, spray some 'carburetor cleaner' all over the throttle shafts right where they go into the carbs....if there are leaks, it will be sucked in and with the car idling, the rig will more than likely die all on its own.

The issue is that the SUs throttle shafts are brass, and the Japanese chrome plated them because they were notorious on British cars for wearing over years if they were just plain brass. But even the improved Japanese version of the SUs after 30 years will have worn throttle shafts. Z Therapy puts roller bearings of their design into the junction hole, which helps considerably with the leakings....The rebuilds are $600 for a set with exch (last time I checked) and I am going to get some as soon as that money is available....

Read up on the carbs at www.ztherapy.com absorb everything said....great site, with a lot of good information on the carbs. I've been to Z Therapy's shop (it's only 45 miles away from my house) and they know their SUs---literally hundreds of em sitting around and they race cars with them in them and are truly sincere about the SUs...if you go the rebuilt route, you must consider purchasing through them.

When making your carbs as lean as possible but still have the Zed run well, what I have done is I always adjust only to the point where if you are idling, you manually lift up the piston on the front all the way (leaving the back alone) if the car still runs, then they are fine....repeat for the other carb. Car should still idle if one of the carbs is dead, in other words. If it dies (or when messing with one carb it makes everything sound different than when you messed with the other carb) then they aren't running as lean as is necessary or synchronized. I use a syncro thingy that fits over the throat to match them, but by just using your ear and the way the motor is running, I can come within 90% of the sych meeter.

I'm rambling...sorry about that....check out Z therapy...and everybody, please reply and help this guy out....let him know that SUs are part of what make owning an older Z fun! (not the other way around)....

[cj71z]

Hey Dogma thanks for the reply. I've done plenty of research on the SU's. I bought the kit from Z therapy and rebuilt them myself. I know that working on these cars is part of owning them, but I'm just curious how come I can't get the mixture correct according to the colortune. I know that my throttle shafts are leaking(front a little more than the back) wouldn't that make me run lean though? When I tune them according to what I think is the way to do it then it seems to run fine, just a little stinky at the exhaust. Plugs are a nice tan color, not real black. What got me wondering is when I tried the colortune and it said I was running rich. When I screwed the nozzle all the way up I totally disabled that carb so obviously my floats arn't set too high which would make it rich all the time.

I know I'm lacking on the comp test readings, I gotta buy a guage. I got a couple other questions for you. While tuning your carbs when lifting the piston to disable that carb how much should the idle drop. I've read that if the idle stays the same then it's too rich, if it dies then it's too lean. I'm guessing a happy medium is what we're looking for? One more question, I went to adjust my valves the other day and I couldn't get any open end wrenches to fit the adjusting nut. I know this sounds stupid, but what do you use?

Thanks

Chris

[mlc240z]

you can get the carb bodies rebuilt (w/roller bearings) for $225+core. i rebuilt with their kit this year (coudn't afford the $600). i think i'm going to send my bodies to them over the winter to have them rebuilt. won't look as pretty as the full job, but the $$$ i save will be used elsewhere on the Z. might be an option worth considering.

[beandip]

First of all pull the SM needles and use them for a dart board. Go with 54s or if you are running a 280 try 27s . The SM needles are too rich for any Z eingine under 3K stroker. The leaner needles will make more HP and better mileage and wont contaminate the oil in the pan with unburned fuel. The color tune is not lying to you , you are running vary RICH . If you want more informaion send me a PM with your email address and I will forward some info from some engine builders that race Zs that tried the SMs needles. The roller bearings can carbon up and stick the shaft , which can cause a problem if you are going into a corner at hispeed after a wide open throttle aproach down a stright. How many times have you had your car pop back through the carbs ? When this happens carbon particles blow out under pressure , hellow. Some thing to think about . :sick:

[VaGuS510]

You could try to use a .99 nozzle. If you think you are running rich everywhere then this should lean you out everywhere.

I just installed some O2 sensors on my car and i got a nifty gauge that reads both o2 sensors at the same time. I also am going to need a richer needle. I am currently rich at idle and cruise but it leans out big time when i get on it. The only way to keep it from backfiring is to make it run really rich at idle and cruise. Therefor i get bad gas milage, about 10 mpg. I am currently running N54s on my L28. I am also leaning towards trying an SM needle as a baseline.

Also there are literally hundreds of su needles out there. The answer isn't always SM, N54, or N27. Check out this website for some more options.

http://www.teglerizer.com/cgi-bin/needle100db.cgi?Needlecode=

This is also a good website on how to tune su carbs.

http://www.triumphclub.co.nz/su_carbs.html

[SavannahZ]

That is a great read VaGuS (SU tuning)- I had no idea there were that many options.

[beandip]

vagus , great post and good info . Gary

[cj71z]

Hey thanks for all the info. That link with all the SU needle info is great. Looks like I got another project for the winter. I ordered a set of 54's from ZT so I'll post any changes. From the looks of it the 54's should lean out my idle, but give me more in the mid to top end. I'll see if these work, I'm also gonna invest in a cheap O2 sensor and make a mixture analyzer. Hey vagus where did you install both sensors? I got a nice new header that I don't want to drill, I'm thinking about putting one just past the collector.

Thanks

Chris

[xray]

Great stuff....

Also, a similar discussion takes place in Des Hammill's book, "How to Build and Power Tune SU Carburettors." I find most intriguing his description of self-tuning needles by putting them on a drill press and using fine sandpaper to "polish down" the diameters to fit your application. Almost makes you want to grind your own needles...almost.

Good luck,

Steve