zahid@neptune.amd.com (Zahid Ahsanullah) (02/13/90)
Hi All, I haven't been very active lately (a year that i.e) partly due to being cut off somehow from the mail system and mostly being incredibly busy. Started receiving mail about 5 months ago after a gap of 6 months and it has been to say the least addicting! For those that don't know me, my name is Zahid and I have been around since Dale started this list a couple of years ago. I have an '80 Spitfire in original yellow paint that is sitting in the garage since late summer. You see it threw a rod when all the oil leaked out on my way to Marble Falls; a beautiful lake area about 45 miles from Austin (Tx). I'll be getting a gift of a new engine pretty soon from a friend of mine in Dallas and intend to swap the old one with this come summer. The Spitfire was my regular car for over 3 years with absolutely no major problems except for the leak which was mostly my fault. I should have fixed it before it became bad. Now I drive a 1990 Acura Integra which is fun but there is something about the Spitfire that it can't replace. Not too long now. Someone asked about tuning su's on his new '77 B and I just happen to have an excellent article an excellent article on tuning SU's from Roger Garnett. This article appeared a long time ago and is being printed without permission. Hope you don't mind Roger. Subject: SU Carb Tuning Well, it's not really that hard to set up SU's, just different. Of course it always gets more interesting when you have more than one... Here is a laymans guide to adjusting SU's (long): step 1- Tune up the rest of the engine- REALLY! clean or replace, and set the points, set the timing, plugs, valve lash, and remove the air filters. (have new ones ready) All of these things can affect the setting of the carbs, which should be done LAST, (if at all). The carbs rarely need to be adjusted, once set. Also replace/install the gas filter. step 2- clean the carbs! use gum-out or similar stuff, clean all external linkages, shafts, and stuff. step 3- Remove the float bowl covers, clean the float bowls, remove old sediment, and check/adjust the float setting. (turn the cover upside down, and get a 1/8 in drill bit, set the drill bit accross the cover, the float tab should just touch the bit.) Make sure the needle is moving and seating properly. This is just like *most* floats. Replace the cover. step 3b- Go get a pint of ale, or something close, and set it nearby. step 4- Remove the piston covers. CAREFULLY remove the piston, DO NOT BEND THE NEEDLE. Set the piston down on a clean wadded rag to prevent rolling. Clean the inside of the carb. Check operation of the throttle. Check the throttle shaft slop- this is the most common place for wear on an SU, and is often where air/vacumn leaks occur. The bushings and shafts can be replaced, but it requires some machining. A small amount of leakage can be tolerated, the car just won't idle as evenly. (a cheap and dirty fix is to put o-rings on the shaft on the outside of the carb, to seal the opening. But dont restrice shaft movement). Clean the piston. Stare in awe at the odd carborator design, simple and effective, (constant velocity). Dump the old oil out of the damper if you haven't already spilled it. clean. Reassemble, check piston movement, raise it, then let go, it should fall freely. If not, check assembly again, make sure the piston isn't binding against the carb body, it should ride only on the damper shaft. Do not strech the spring. When all is operating properly, fill the damper with Marvel Mystery Oil for light damping, or use motor oil for heavier damping. (I use MMO) step 5- Start the car and warm it up, then turn off/disconnect/otherwise disable the choke mechenism. This will get set later- There are two types, thermostatic, and REAL (cable controlled). step 6- Check coarse throttle adjustments- make sure the throttle cable pulls on both carbs equally, and returns completly when released. This is adjusted by loosing the set screws on the throttle shaft and matching the two sides. You can also adjust the cable length at this time, using the cable set screw/retainer at the end of the cable. step 7- Syncronize the throttles- if you have a uni-syn, here's your chance to use it, (air flow guage), if not use a tube and listen to the airflow. Alternatly adjust the two idle screws on the carb, attempt to set the idle as low as possible (~800-1000 RPM). Adjust until the airflow is *close* to the same at each carb. The engine may now be running rough, just keep the idle speed high enough to keep running. Give the throttle a quick snap to make sure everything is settled, then check sync again. Periodicly snap the throttle to make sure everything is seated. Magic Time- Relax, and shake your voodoo rattle... step 8- Adjust the mixture- this is done with the spring-loaded hex fitting under the carb, where the fuel supply tube enters from the float. Turning the fitting raises and lowers the needle seat. Pick a carb, and turn the fitting 3 flats (1/2 turn), first in one direction, then back 3, then 3 in the other direction. Note where the engine runs better, idle speed should increase. Turn to the best setting. Repeat this proceedure until you get the best operation you can, (higest idle speed), keeping track of flats turned will help you remember where you were. If you get lost, turn all of the way in, then back out 12 flats and start again. Periodicaly snap the throttle and push up on the fitting to make sure everything is seated. When you think you're close, stop, uncramp your fingers, breath deep, and do the same to the other carb. Then retune the first carb, and then the second again. This serves to match the mixture of the 2 carbs, and prepare you for the beer sitting over there in the sun. (why do you think the British drink warm beer?) step 9- repeat step 7, setting the idle speed as low as possible, and re-syncing the idles. Now go back and readjust the mixtures. After a couple of iterations, the engine should be running smoothly (controlled by mixture) and at a low idle. Repeat as necessary. Set the final idle to 800-1000 RPM, depending on the condition of the rest of the engine. step 10- DRIVE! Take a quick spin up the lane, you need the reward of driving a properly tuned car. step 11- Adjusting the choke- I will ignore the thermostatic choke, they work (?) as a cross between regular old american carbs, and REAL, (manual) choke SU's. You can get conversion kits to add a choke cable. Check the manual for more info. The choke is supposed to do two things; the first half of travel moves a cam on each carb which opens the throttle, for warm up. The second half pulls down on the needle seat to enrichen the mixture, for starting. Start with the choke in the off position (knob in). Adjust the so that the cam only starts moving the throttle after you start pulling out on the cable (adjust with shafts and adjusting screws). Try to get both carbs adjusted the same, you can check this with your unisyn or hose, but the choke adjustment is less critical than the operating settings. After the cable is about halfway out, it should start engaging the lever which pulls down on the needle seats. Adjust so both carbs are acted on equally, you can do this by adjusting for even running of the engine. Of course, for a warm engine, the richness of this mixture will cause some roughness. Make sure the needle seats return freely when you release the choke.(please excuse the lack of detail in this step, EveryThing is from memory, and it has been a while since I adjusted chokes, but the Sprite is getting there...) step 12- Drink that warm beer (only one, no DWI now...) it will taste great at this point!, go wash up, and go for a ride. The first time through carb adjustments can be confusing, once you've done it, all of the stuff in the manuals makes sense. Go back and read them again- As always, I reccommend Bentleys, which is a repro of the original factory manuals, and then Haynes, and throw out the Chiltons. (orginal factory manuals are to be read in a clean enviroment, repros are for smearing grease all over, except, if that's all you got, use it!) ________ / _ \ Roger Garnett (garnett@batcomputer) / /|| \ \ Cornell Phonetics Lab (garnett@tcgould.TN.CORNELL.EDU) | |\/ || _ | Ithaca N.Y. (bitnet: sggy@cornellC | | || | | or garnett@crnlthry.bitnet) \ ||__/ / (plab!roger@cornell.UUCP) \________/ SAFETY FAST! okbye _____________ _____________ \____________\_____________/____________/ \__________ __________/ [this space availble] \________ AUSTIN-HEALEY ________/ \___________________________/ (this A-H emblem plagurized without permission, I couldn't get through in E-mail) Hope this helps out. By the way, does anyone know of a roadster called Ashley. My friend owned it when we were in high school in the late seventies and he says it was a Triumph. He had bought it in England while on vacation. It looked very much like a spitfire with the bonnet opening near the windscreen and all but I can't say that I remember much about it. His dad took it away from us because our driving became kind of reckless. I have never missed a car more than that one. Cheers Zahid