Fireman049 Posted November 10, 2015 Report Share Posted November 10, 2015 (edited) . Edited November 20, 2015 by Fireman049 Quote Link to post Share on other sites
Lebro Posted November 10, 2015 Report Share Posted November 10, 2015 Nominal setting is 2 turns down from top of jet being being level with the bridge. Then adjust from there. Fuel level in the jets should be around 9mm down from bridge but this is not critical. Bob. Quote Link to post Share on other sites
Fireman049 Posted November 10, 2015 Author Report Share Posted November 10, 2015 (edited) . Edited November 20, 2015 by Fireman049 Quote Link to post Share on other sites
Ian Vincent Posted November 10, 2015 Report Share Posted November 10, 2015 The 35 thou figure is one that Ashley used to espouse. (I can't remember his surname at the moment). It's a good place to start from. Rgds Ian Quote Link to post Share on other sites
Fireman049 Posted November 10, 2015 Author Report Share Posted November 10, 2015 (edited) . Edited November 20, 2015 by Fireman049 Quote Link to post Share on other sites
stuart Posted November 10, 2015 Report Share Posted November 10, 2015 Those settings are nominal as every engine is different so they are not definitive just a guide and I normally start at 2 1/2 turns down. Stuart. Quote Link to post Share on other sites
Fireman049 Posted November 10, 2015 Author Report Share Posted November 10, 2015 (edited) . Edited November 20, 2015 by Fireman049 Quote Link to post Share on other sites
McMuttley Posted November 10, 2015 Report Share Posted November 10, 2015 Those settings are nominal as every engine is different so they are not definitive just a guide and I normally start at 2 1/2 turns down. Stuart. Hi Stu, is that because it is easier to start rich and work back, or just your experience that 15 flats is closer to where you end up than 12 ? After the carbs are checked again i will be re-setting the jets this weekend - when I tried the Gunson last week, they never went blu (ish) - always a bright yellow, but stupidly I fiddled without remembering where i started from, so now need to re-set Going to try and get airflow consistent before adding fuel ! Quote Link to post Share on other sites
stuart Posted November 10, 2015 Report Share Posted November 10, 2015 That setting is nominally a bit rich so you will always get the engine to start, make sure you bring the engine up to normal operating temperature and rev it between each adjustment to clear it. Stuart. Quote Link to post Share on other sites
rogerguzzi Posted November 10, 2015 Report Share Posted November 10, 2015 Hello All In Des Hammill's The SU Carburettor High-Performance Manual. He says intial setting 1 1/4" 0.030" , 1 1/2 0.040", 1 3/4" 0.050", 1 7/8"? 0.060" down from the top bridge as a starting point. Roger . Quote Link to post Share on other sites
peejay4A Posted November 10, 2015 Report Share Posted November 10, 2015 Does it really matter which starting point you choose because you're going to tune from there anyway? Rhetorical question btw. Quote Link to post Share on other sites
littlejim Posted November 11, 2015 Report Share Posted November 11, 2015 (edited) Be interested to know whether Suart uses any gadgets for the final bit. I use a Carbalancer* to to get them equal; the Gunson Colourtune* for the mixture, it's a bit 'broad' in its range but I have a go. *both of 70's vintage not the latest ones. Edited November 11, 2015 by littlejim Quote Link to post Share on other sites
Lebro Posted November 11, 2015 Report Share Posted November 11, 2015 I use a length of hose pipe & my right ear for balancing, & the built in piston lifting pin for initial mixture tuning - 1st check ignition timing, then with engine at slow tickover (& fully warmed up) lift one piston a tiny amount. if revs drop its too lean, if revs increase & stay higher then too rich, if revs increase, then drop back down then that's about right. Repeat for other side. then reset idle screws if necessary. Final adjustment is by driving - how long does it take to pull cleanly from cold without choke - too long & it may be too lean. Then after a good thrash (really hot) does it tickover nicely, or is it hunting (too rich). Don't forget to have 20 - 30 grade oil in dashpots for the first test this helps pulling away before warmed up. Bob, Quote Link to post Share on other sites
stuart Posted November 11, 2015 Report Share Posted November 11, 2015 I use a length of hose pipe & my right ear for balancing, & the built in piston lifting pin for initial mixture tuning - 1st check ignition timing, then with engine at slow tickover (& fully warmed up) lift one piston a tiny amount. if revs drop its too lean, if revs increase & stay higher then too rich, if revs increase, then drop back down then that's about right. Repeat for other side. then reset idle screws if necessary. Final adjustment is by driving - how long does it take to pull cleanly from cold without choke - too long & it may be too lean. Then after a good thrash (really hot) does it tickover nicely, or is it hunting (too rich). Don't forget to have 20 - 30 grade oil in dashpots for the first test this helps pulling away before warmed up. Bob, Same way I do it, old school. Then road testing and plug chop.I do have a car balancer type of gauge as well Stuart. Quote Link to post Share on other sites
stuart Posted November 11, 2015 Report Share Posted November 11, 2015 Does it really matter which starting point you choose because you're going to tune from there anyway? Rhetorical question btw. Very true which was why I said the amount of turns down is nominal as its all going to change depending on each individual engines requirement. Stuart. Quote Link to post Share on other sites
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