Terry Field Posted May 22, 2005 Share Posted May 22, 2005 When the engine is cruising on a 'neutral' throttle it spits back through the carbs. It doesn't do it during acceleration or at any other time. I have tried to adjust the mixture but had the following results: The synchrometer measures 5 Kg on number 2, 3 and 4 trumpets but only about 3.5 - 4 on number 1. Is this important and how do I correct it? On the mixture adjustment, each screw is currently open about three full turns. With the engine hot, if I turn down the screw all the way in, the engine slows, and then picks up again after about a turn and a half out, but after that there is no discernible change if i keep opening it. Certainly I cannot get to a point where the engine slows with, say, a quarter turn either way. Is this lack of sensitivity unusual? I'm confused about where the setting should be, and worried about running too lean, especially as I intend to do a longish run next weekend I have checked the timing at 12-14 deg btdc at 1000rpm. Off to see the start of the GP now, so let's hope it's a good one! Terry 1700XF - Team Lotus with flares. Link to comment Share on other sites More sharing options...
stevefoster Posted May 22, 2005 Share Posted May 22, 2005 Aim for the fastest audible tickover on each idle screw and then + a quarter or if still seems lean = spitting, try half a turn extra (a further 1/4 turn). Balance using ear / tube or a proper balancer. If it's spitting at more than about 1500 rpm i would suspect something else or you have the wrong jets in. The idle screw only affects idle and a bit of progression to more throttle. Above that it's the black art of jetting 50F6, 45F8 etc I bought a 1600 XF that had a terrible cough / spitting at about 2500. I changed the jets for fatter ones and it went like a dream. If you are really stuck I have some standard jetting advice tables that may be of use. Mail me offline with your email addr and I'll send these to you to compare. If you are near me I pop round and I'll tweak it for you. I may still have my bag of various jets that can be tested... Not sure without checking. There is some jetting advice on this site / the web if you search. Hants (North) and Berkshire Area club site here My racing info site here Edited by - stevefoster on 22 May 2005 17:50:46 Link to comment Share on other sites More sharing options...
Terry Field Posted May 23, 2005 Author Share Posted May 23, 2005 Steve, Thanks for the advice. I think what you are describing is spitting back during tickover. I don't get this, it only spits when I am driving it, when I am cruising - i.e. neither accelerating or decelerating. At all other times it seems OK. It is not particularly bad, more annoying, but I didn't have the problem my earlier engine and I am concerned in case it is bad enough to cause damage. The carbs were rejetted by the engine builder 1000 miles ago, so I am assuming they are OK. As you said it is a black art and following the normal tuning advice doesn't seem to be working! Terry 1700XF - Team Lotus with flares. Link to comment Share on other sites More sharing options...
Normans_Ghost Posted May 23, 2005 Share Posted May 23, 2005 Terry, unless it's very bad I wouldn't woory too much. Mine spits on a steady throttle. If the colour of the plugs is a dark grey then leave it alone. (if light grey it's running weak, if black and sooty it's too rich) The answer is to drive foot flat too the floor all the time Norman Verona, 1989 BDR 220bhp, Reg: B16BDR, Mem No 2166, the full story here Link to comment Share on other sites More sharing options...
Terry Field Posted May 23, 2005 Author Share Posted May 23, 2005 Norman, That's what I was hoping. I will check the plugs again, but I think dark grey is a fairly accurate description. Any thoughts about the difference in the air intake levels, reading about 5 on intakes 3, 4 and 5, but not quite 4 on intake No 1? Terry 1700XF - Team Lotus with flares. Link to comment Share on other sites More sharing options...
wonkey eyed barmaid Posted May 23, 2005 Share Posted May 23, 2005 terry, Im by no means a carb expert - but im learning - as you can see from a cuple of other weber/1.6vx related threads. i too would like to know how you can have a significantly different air flow reading for cylinders 1 and 2. I was under the impression that the air-flow balance could only be adjusted between the pair of carbs, and that each individual "pair" was pre-set. im not IF you can adjust the airflow within a pair? Link to comment Share on other sites More sharing options...
Graham Sewell Posted May 23, 2005 Share Posted May 23, 2005 Before starting anything, check valve clearances as this can have a profound effect and if the imbalance is recent then this is a likely cause. Then, balancing individual barrels on a carb is by adjusting the air bypass screws. These are located under white caps at the back of the carb. Start with both screwed fully home and then open up the one with the lower flow until they are even. Then lock them with the locking nuts and replace the white caps. Then balance the two carbs to each other. Then finally adjust the mixtures as before. Low tech luddite - xflow and proud! Link to comment Share on other sites More sharing options...
wonkey eyed barmaid Posted May 23, 2005 Share Posted May 23, 2005 aaaaaaaah, thats what the white caps hide. thanks graham. hijack over. you can go back to your homes now.. Link to comment Share on other sites More sharing options...
Nigel Riches Posted May 24, 2005 Share Posted May 24, 2005 I don't seem to have any "white caps" would nice brass ones do? 1982. 5 speed, clamshells. B.R.G / Ali. The True Colours. Link to comment Share on other sites More sharing options...
Terry Field Posted May 24, 2005 Author Share Posted May 24, 2005 Mmmm! Webers with brass knobs on 😬 Terry 1700XF - Team Lotus with flares. Link to comment Share on other sites More sharing options...
wonkey eyed barmaid Posted May 24, 2005 Share Posted May 24, 2005 fiddled with my white caps, but not my brass knob - although it was bloody cold. 😬 air flows and balance now perfect cheers. Link to comment Share on other sites More sharing options...
Terry Field Posted May 24, 2005 Author Share Posted May 24, 2005 Well done granteuk. I will try to have a go later this week (but tonight I'm out for a beer from work, tomorrow is the football etc etc.......) Guess I won't win many Brownie points this week 😬 Terry 1700XF - Team Lotus with flares. Link to comment Share on other sites More sharing options...
Graham Sewell Posted May 24, 2005 Share Posted May 24, 2005 Nigel, For those poor souls who have lost their white caps, the screws I refer to are near the cylinder head side of the carb sticking out at a slight angle with an obvious locknut. On the diagram see parts 25/6/7 Low tech luddite - xflow and proud! Link to comment Share on other sites More sharing options...
Terry Field Posted May 24, 2005 Author Share Posted May 24, 2005 Thanks Graham. No problem with my knobs *wink*but a useful diagram all the same. Terry 1700XF - Team Lotus with flares. Link to comment Share on other sites More sharing options...
Nigel Riches Posted May 25, 2005 Share Posted May 25, 2005 Graham thanks for the diagram of the white cap location, but I find my carbs (40 DCOE Type 18) are of an earlier vintage, mid '60's if I recall, and no air by-pass screws are present, so I'll live with the spitting and popping it all adds to the character and driving experience, cheers all the same, regards Nigel. 1982. 5 speed, clamshells. B.R.G / Ali. The True Colours. Link to comment Share on other sites More sharing options...
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