John Ryan Posted May 17, 2010 Share Posted May 17, 2010 I originally thought your problem would be the same as the one I had a couple years ago, with the misfire eventually found to be the electronic ignition unit (or the coil) breaking down as it got hot. However, as the misfire only occurs under heavy acceleration, it would suggest to me that the issue is fuel starvation caused by the mechanical fuel pump becoming less efficient over time. Link to comment Share on other sites More sharing options...
Clousta Posted May 17, 2010 Share Posted May 17, 2010 You mentioned fuel starvation. I had a misfire/stutter at high revs last autumn. This year the misfire had gone away so I was happy. When Elie Boone was fitting my tonneau a month back he gave the car a good check over. He noticed that the electric fuel pump continued to tick slowly once the carburettor bowls (?) had filled. There was no evidence of leakage or overflowing at the Webers. On Thursday at the Ypres Lotus Day fuel starvation problems reared their ugly head on the third satge. I diagnosed that the electric fuel pump was on the way out and it appeared to be heat related. We got recovered home. I put the car up on axle stands and had a good look underneath. All appeared in order. Then I noticed that the fuel hose to the fuel pump inlet looked very slightly darker (possibly damp). I poked the hose with my finger and got a fine spray of petrol back. The hose was split and must have been sucking in air. Fuel/air mix made for a noisy fuel pump and fuel starvation at higher revs. Once stopped the carburettor bowls would refill and the engine would run again for a while. So a check of fuel hoses/connections or renewal of the hoses might be a cheap fix. It would certainly rule out that possibility. Gavin 1988 1700 Supersprint (LA, long cockpit) Link to comment Share on other sites More sharing options...
Bob_Rich Posted May 17, 2010 Share Posted May 17, 2010 hi again I still find it hard to see how the tacho could break the Aldon unit but no matter -we all live and learn though I would be interested in an explanation of what the interaction between them actually is. On the post subject of misfire at high output it could still be spark , or lack of, related. As the throttle is opened more air is drawn in so the compression pressure will rise and the required voltage to produce a spark will increase markedly. This may result in something else in the system breaking down rather than the plug gap so giving the misfire. Driving the car at night with the bonnet off and a passenger looking for "little blue sparks" can some times give a clue--BUT use a passenger! U need to keep your eyes wide open and on the road giving a 7 full blat in the dark!! hope this helps and you get your problem sorted best of luck Bob Link to comment Share on other sites More sharing options...
Graham Sewell Posted May 24, 2010 Author Share Posted May 24, 2010 It seems that the major culprit was the dizzy cap where the king lead entered. However, a minor oil weep seems to have destroyed the offside engine mount rubber and the carbs were resting on the bonnet - and the filters were distusting underneath. So some air starvation, some frothing fuel and a weak spark. Poor little crossflow just could not master all three. Should get it back by the end of the week and see if we have found all of the causes. Cheers, Graham ------ Low tech luddite - xflow and proud! Link to comment Share on other sites More sharing options...
Eugene Posted May 24, 2010 Share Posted May 24, 2010 Graham, got my finger's crossed for you!!! Small Boy - with Loud Toy! Co-founder of the BOG Club See Eugene here and see what I do here Link to comment Share on other sites More sharing options...
Leloby Posted May 24, 2010 Share Posted May 24, 2010 After the fix, clean or change the plugs because they may be sooted up. I had a similar problem - exactly the same misfire - but it was attributed to the actual carbs being slack! My wifes cousin noticed this while using a flow meter to balance them. He leant on one and it seemed slack, hence why No. 3 & 4 plugs were sooty. Incidentally, I'm new to all this but old adage "if it ain't broke...." seems to hold true. And I've found that an air-flow meter is really handy for Webers. Cheers, Derek Link to comment Share on other sites More sharing options...
Irish Posted May 24, 2010 Share Posted May 24, 2010 I had this and the guys in 7 Indulgence fitted a breather pipe on the tank and that was that. Never had the problem again. It had got to the stage where I was stuttering to a halt on the M25 as I accelerated! Link to comment Share on other sites More sharing options...
Graham Sewell Posted May 25, 2010 Author Share Posted May 25, 2010 Leloby, The plugs were all a nice even pale grey (unleaded - yuk) and the carbs are balanced on a regular basis. Cheers, Graham ------ Low tech luddite - xflow and proud! Edited by - Graham Sewell on 25 May 2010 08:29:09 Link to comment Share on other sites More sharing options...
Leloby Posted May 25, 2010 Share Posted May 25, 2010 Ha! Well, as I said - I'm new to all this How often is 'regular' when it comes to carb balancing? I seem to be spending an awful lot of time fettling this thing - the grass is getting long and my cycling runs much shorter these days Derek. Link to comment Share on other sites More sharing options...
Graham Sewell Posted May 25, 2010 Author Share Posted May 25, 2010 Based on the fact that I have not driven very far in the last 12 months - about every 300 miles! However, it must be said that the balance between chokes in one carb should never go out of balance and the balance between the two carbs should be reasonably static unless their mountings as dodgy (broken springs between the cup washers) or the small brass connector between them is worn. Please note that they MUST be some play between the carbs and the manifold otherwise you will get fuel foaming inside the carbs. The two methods are springs or rubber bobbins between the cup washers on each mount point. Between these 8 sets of washers you tension them evenly to allow some movement of the carbs but not enough to allow air leaks past the o-rings/misab plates between the carbs and manifold. IIRC, if you have the older springs, there should be about 25thou gap between the cup washers - but I could be wrong on that figure. Do NOT tighten these nuts until the carbs are solidly mounted. This cannot be stressed enough. I know some folk have created an aluminium plate that screws into the bottom of the carb - using the 4 screws on each carb around the square plate - but I have never had them that unstable. Cheers, Graham ------ Low tech luddite - xflow and proud! Link to comment Share on other sites More sharing options...
Eugene Posted May 25, 2010 Share Posted May 25, 2010 So what's the conclusion Graham - all working now??? Small Boy - with Loud Toy! Co-founder of the BOG Club See Eugene here and see what I do here Link to comment Share on other sites More sharing options...
Graham Sewell Posted May 26, 2010 Author Share Posted May 26, 2010 Find out on Friday :-) Cheers, Graham ------ Low tech luddite - xflow and proud! Link to comment Share on other sites More sharing options...
jonboylaw Posted May 26, 2010 Share Posted May 26, 2010 Leloby - Derek, I know a man that is good with Webers, posts on here as Alex Tangent, did mine last weekend and after a small issue of a sticking float they are now spot on. Where are you based ? Jonathan My Flickr ----------------------------------- 95% there :) 92 Supersprint, Ford LSD LA, RK AX Crossflow. Link to comment Share on other sites More sharing options...
Leloby Posted May 26, 2010 Share Posted May 26, 2010 Near Falkirk. I'd like someone to look at these ones if thats possible but I don't know anyone suitably skilled. Cheers, Derek. Link to comment Share on other sites More sharing options...
jonboylaw Posted May 26, 2010 Share Posted May 26, 2010 Derek, You have mail Jonathan My Flickr ----------------------------------- 95% there :) 92 Supersprint, Ford LSD LA, RK AX Crossflow. Link to comment Share on other sites More sharing options...
Eugene Posted May 26, 2010 Share Posted May 26, 2010 Graham, saw you 7 at The 7 Workshop today - looks like Chris has it sorted! As you say, a combination of problems just as you described 😬 😬 😬 Oh, and I had a quick peek at your rev counter - it's fine! Wont bugger the Aldon! 😬 Small Boy - with Loud Toy! Co-founder of the BOG Club See Eugene here and see what I do here Link to comment Share on other sites More sharing options...
Graham Sewell Posted May 27, 2010 Author Share Posted May 27, 2010 Sounds like I'll have a fun day driving home tomorrow - assuming the rain stops Cheers, Graham ------ Low tech luddite - xflow and proud! Link to comment Share on other sites More sharing options...
Graham Sewell Posted May 28, 2010 Author Share Posted May 28, 2010 Chris has done his magic and restored my smile (from ear to ear) - took the long way home via Hertford, Hatfield, St Albans, Hemel Hempstead, Chesham, Amersham, etc.... 😬 😬 😬 😬 Cheers, Graham ------ Low tech luddite - xflow and proud! Link to comment Share on other sites More sharing options...
Eugene Posted May 29, 2010 Share Posted May 29, 2010 Really pleased to hear that! 😬 😬 😬 Small Boy - with Loud Toy! Co-founder of the BOG Club See Eugene here and see what I do here Link to comment Share on other sites More sharing options...
barry watts Posted June 28, 2010 Share Posted June 28, 2010 hi all, after following this thread about the tacho affecting the ignitor unit can anyone comfirm if a 1997 caterham labeled tacho would be a suspect. thanks barry. Link to comment Share on other sites More sharing options...
Eugene Posted June 28, 2010 Share Posted June 28, 2010 Hi Barry, that should be ok - it's the earlier 'Smiths' ones that are a problem (engines originally with points when delivered)... Small Boy - with Loud Toy! Co-founder of the BOG Club See Eugene here and see what I do here Link to comment Share on other sites More sharing options...
barry watts Posted June 28, 2010 Share Posted June 28, 2010 thanks for that. just fitted new ignitor and flame thrower coil. car flew for two 20 mile blats and then going to poole on friday developed exactly the same symtoms as this post. the new coil seemed quite hot, at a loss now as changed just about everything. barry. Link to comment Share on other sites More sharing options...
Griff Posted June 29, 2010 Share Posted June 29, 2010 I appreciate this post has been going for a bit and maybe I've missed someone making a similar suggestion. I too had similar problems but only when giving the car a workout. I've since switched to a Megajolt system which was a huge imporvement - until the block decided to crack (another long and unrelated story). In my case coil overheating was diagnosed, possibly caused by the oil inside being insufficient to cover all the inner working properly and dissipate heat. It was suggested I invert the coil so terminals and HT lead faced down rather than up to be sure the oil covered everything and kept things cooler. It worked for me and costs nothing to try. Good luck! Link to comment Share on other sites More sharing options...
Eugene Posted June 29, 2010 Share Posted June 29, 2010 Ah, yes, I too had problems with their coil! Changed to a 'Something Blue' one...??? (Long time ago)... Try your old coil? Small Boy - with Loud Toy! Co-founder of the BOG Club See Eugene here and see what I do here Link to comment Share on other sites More sharing options...
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