JimmyZ1971 Posted August 19, 2009 Share #1 Posted August 19, 2009 Hi AllI got a really good deal on a set of Z Therapy SU carbs for my 1971 240 BUT they are 3 screw and I have 4 screw on her now. I don't want to remove the existing carbs until I know there is not any compatiblity issues. I have compared them as closely as I can and cannot see any design differences...BUT....I could be missing something !!! Any ideas out there??? Also what oil/fluid do you recommend for the float chambers?? Thanks for any help.James Link to comment https://www.classiczcars.com/topic/32890-3-screw-vs-4-screw-su-carbs/ Share on other sites More sharing options...
hls30.com Posted August 19, 2009 Share #2 Posted August 19, 2009 (edited) They are interchangeable-depending on the needles. We had a thread on damper oil recently-I don't remember the details other than two proper and easy to find oils were mentioned. http://www.classiczcars.com/forums/showthread.php?t=35474&highlight=oilWIll Edited August 19, 2009 by hls30.com Link to comment https://www.classiczcars.com/topic/32890-3-screw-vs-4-screw-su-carbs/#findComment-292384 Share on other sites More sharing options...
Bruce Palmer Posted August 20, 2009 Share #3 Posted August 20, 2009 Three screw has provision for water into the carb base: 4 screws don't. Link to comment https://www.classiczcars.com/topic/32890-3-screw-vs-4-screw-su-carbs/#findComment-292419 Share on other sites More sharing options...
JimmyZ1971 Posted August 23, 2009 Author Share #4 Posted August 23, 2009 Thanks for the information...looks like Sunday will be spent swapping carbs which really sounds like a perfect way to spend the day. :D Link to comment https://www.classiczcars.com/topic/32890-3-screw-vs-4-screw-su-carbs/#findComment-292560 Share on other sites More sharing options...
26th-Z Posted August 23, 2009 Share #5 Posted August 23, 2009 Learn someth'n new every day... Link to comment https://www.classiczcars.com/topic/32890-3-screw-vs-4-screw-su-carbs/#findComment-292572 Share on other sites More sharing options...
mayitin Posted September 20, 2009 Share #6 Posted September 20, 2009 Back in the old days every body used auto-matic oil I even heard 3 in 1, A few years ago there was a good article on one of the site ( I can not remeber what site it was ) but they stated that the best oil is 20W, I live in the outh and I can not get the 20W so I use auto-matic oil. My personal experience with the 3 bolt is that if you want to change the needle seat or jet is not as easy as the 4 bolt also the disk on the bottom is to thin for my fingers. I was just educated by B Palmer about water on the base, there is so much to know. By the way Z theraphy carbs are great. Link to comment https://www.classiczcars.com/topic/32890-3-screw-vs-4-screw-su-carbs/#findComment-295237 Share on other sites More sharing options...
DeesZ Posted September 20, 2009 Share #7 Posted September 20, 2009 Damper oil -My FSM dated 1972 recommends "Mobile Oil SAE 10W-30 for damper oil. Do not use SAE #30 or higher weight oils." If you wish to check the reference, this is found in the book under Engine, Fuel System, SU-Type Twin Carbs, Page EF-26. There may be other references in the book as well, but I came across this last night while researching something else. I hope it helps. (I have also successfully used SAE 5W-30, Marvel Mystery Oil, and 3-in-1 oil.) Link to comment https://www.classiczcars.com/topic/32890-3-screw-vs-4-screw-su-carbs/#findComment-295240 Share on other sites More sharing options...
Yarb
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