DSJ666 Posted May 12, 2022 Report Share Posted May 12, 2022 (edited) Hi All, I'm struggling to get the mixture correct on my 4A. I can't seem to raise the jet high enough on the front carb, the adjusting nut bottoms out before the mixture is lean enough. I did the basic starting setting at 1.25mm down from the bridge, but it was not possible to set it level with the bridge to start with. This setting is too rich. Although I could with the rear carburettor and it is fine with plenty of adjustment up to the bridge and able to get the correct mixture. It seems the front jet is too short! Is this possible? Perhaps are AUD284 jets shorter? My carbs are AUD209's Any ideas? Thanks Edited May 12, 2022 by DSJ666 Quote Link to post Share on other sites
peter clarke Posted May 13, 2022 Report Share Posted May 13, 2022 Same carbs same needles............. Have you checked for manifold air leak/ wear on front throttle spindle / same fuel levels in the float bowls Quote Link to post Share on other sites
Ralph Whitaker Posted May 13, 2022 Report Share Posted May 13, 2022 (edited) 13 hours ago, DSJ666 said: Hi All, I'm struggling to get the mixture correct on my 4A. I can't seem to raise the jet high enough on the front carb, the adjusting nut bottoms out before the mixture is lean enough. I did the basic starting setting at 1.25mm down from the bridge, but it was not possible to set it level with the bridge to start with. This setting is too rich. Although I could with the rear carburettor and it is fine with plenty of adjustment up to the bridge and able to get the correct mixture. It seems the front jet is too short! Is this possible? Perhaps are AUD284 jets shorter? My carbs are AUD209's Any ideas? Thanks Firstly, have the carbs been in bits? and have any parts been replaced? On my own carbs (H6s) I found that I had 2 copper washers instead of 1 at the top of the jet holder as the original one had stuck into position and didn`t come out on dismantling. Are the needles new? They do wear over time and should be replaced along with the jet tubes. Having done all that I was still struggling to get the mixture lean enough and resorted to dropping the needles out of the pistons slightly. While on that subject the needle shoulders should be level with the bottom of the pistons to start with and not pushed fully in. Make sure the float chambers are not flooding, and worthwhile fitting viton tipped float needles. It was the front carb on my car that was rich too and it was fuel passing the Grosse jets I had fitted, when I replaced it with a standard needle jet the problem was solved. Hope some of the above helps. Ralph Final thought, make sure the choke mechanismn is not sticking and holding the jet tube down. Edited May 13, 2022 by Ralph Whitaker Quote Link to post Share on other sites
DSJ666 Posted May 13, 2022 Author Report Share Posted May 13, 2022 Thanks, some very useful points there. Floats etc. seem OK and choke mechanism is good. I did change the needles and jets many years ago (from the Northern TR centre....so that dates them somewhat!). But probably done less than 20K miles since than as the car was laid up many years due to family commitments! I have not had the jet assemblies apart, so I think that's the next thing to look at and I'll also check the needle shoulders. Quote Link to post Share on other sites
DSJ666 Posted May 17, 2022 Author Report Share Posted May 17, 2022 (edited) Sorted! Turned out the jet WAS too short! Tried a cheeky fix which worked......I carefully removed the ferrule which then freed the jet from its plastic housing....reset the jet position and refitted the ferrule which secured the jet. (There is actually a small groove around the lower portion of the jet which seem to coincide with the correct length) Don't know if it was always like this and I hadn't noticed or it had got pushed in sometime, although I can't think how as they are very tight in the plastic housing. I know they look old and are in age but not in usage! Anyway a rather unusual situation sorted and all good now. Thanks all for your comments. Edited May 17, 2022 by DSJ666 Quote Link to post Share on other sites
Lebro Posted May 17, 2022 Report Share Posted May 17, 2022 Well done, I have rebuilt a few of these, but never thought the jet could move in the plastic ! Bob Quote Link to post Share on other sites
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.