Weavie Posted March 9, 2021 Share Posted March 9, 2021 I have a Super 7 1700 Crossflow to which I have recently fitted replacement 40DCOEs, a new distributor and coil and leads. The fuel tank have been cleaned and an in-line filter fitted. It went on the rolling road at Lloyds in Warminster and it was all set up properly to 6000 rpm and 135bhp. On the way home, I found a good bit of road and pushed the car up to 4000 rpm, at which point it started to misfire, splutter, smoke and there was a significant loss of power from the engine. I pulled over and the fault disappeared and I drove home but the revs were below 3500 rpm. Since then, every time I go out, the same problem happens at 4000 rpm. If I sit in a lay-by afterwards, the engine revs to 6000 rpm without a murmur. I have replaced plugs, coil and leads and bypassed the fuel pressure regulator that was on the car but there is still the same problem. I don't know what to try next to stop it happening. Any help would be greatly appreciated before I go mad! Link to comment Share on other sites More sharing options...
Richard K Posted March 9, 2021 Share Posted March 9, 2021 Sorry I don't have an answer but to be clear......The engine will rev too 6000 when the car is stationary and not under load but when driving it starts to miss fire at 4000. Is it possible 'push through' or does the loss of power prevent this?Richard Link to comment Share on other sites More sharing options...
Roger King Posted March 9, 2021 Share Posted March 9, 2021 Is the engine a Caterham supplied Supersprint?Does this problem occur exactly the same whether you are on large or small throttle openings?Did you drive the car with the new carburettors and parts before the rolling road? If so was it reasonable to drive then and did the problems only occur after the rolling road?Does your invoice show you what was changed and what your current choke and jet settings are?Do you know what advance curve is in the new dizzy?You should check the following -Bypass the new filter and see if that improves fuel delivery to the carburettors (you're looking for more than a dribble, but not a fire hose squirting across the room).Check float levels.Check that the aux vents are in their correct positions; if you look down the barrels the aux vents are the circular aluminium tubes that are held in the centre of the barrels by two arms - the aux vents should all be in the same position as each other (just to be clear, the barrels adjacent to each other on the same carburettor are actually mirror images of each other, so you need to allow for this when I say "same position"). Photos would be useful. Link to comment Share on other sites More sharing options...
Weavie Posted March 9, 2021 Author Share Posted March 9, 2021 Hi RichardThe engine won't go past 4000 revs and just gets slower as you go along at the same throttle openingSteve Link to comment Share on other sites More sharing options...
Weavie Posted March 9, 2021 Author Share Posted March 9, 2021 Hi RogerI bought the kit car Q plate in 2009 from the second owner. It was built in 1997 and the paperwork looks like the engine was supplied by the first owner, not Caterham. The recent fault has always been on acceleration up to 4000 rpm so large throttle, I guess. It will not accelerate beyond 4000rpm and just goes more and more slowly due to the misfiring. The carbs were fitted before the rolling road and there didn't seem to be a problem. They were set up properly on the rolling road the first time but the original distributor was a non-vacuum advance version. The guys at the rolling road suggested that it would be better if I fitted an vacuum advance distributor, which they fitted and drilled the inlet manifold for a vacuum pipe from each inlet (4 in total) which were combined and fed back to the new distributor. Choke and jet settings were as before. They reran the car on the rolling road and it all seemed okay. No details of the advance curve given to me. The only other comment is that sometimes, the tone of the engine changes just before the fault starts i.e. the engine seems to "hammer". I also fitted a new fuel pump as part of the problem solving exercise.I can bypass the filter and check the aux vents but I'm not sure how to check float levels?Steve Link to comment Share on other sites More sharing options...
David Brown Posted March 9, 2021 Share Posted March 9, 2021 Could it be a blocked air bleed into the fuel tank? If you stop when yo have a problem and immediately remove the filler cap, is there an inrush of air? Link to comment Share on other sites More sharing options...
harrebe Posted March 9, 2021 Share Posted March 9, 2021 The dizzy that came loose? Link to comment Share on other sites More sharing options...
Roger King Posted March 9, 2021 Share Posted March 9, 2021 Loose dizzy and blocked fuel tank breather are possibilities too, but please check the fuel filter and the aux vents first. If the aux vents have moved this will block fuel from one or more of the main jets and can cause symptoms exactly as you describe. I was asking about how much throttle you were giving it to try and determine if your problem was on the main jets or the slow run jets. From your original post I get the impression that you can rev to 4000rpm + if the engine is under no load. Is this correct?It is not usual to fit a vac advance with dcoe carburettors. Having said that, they seem to have gone about it the correct way if there are interconnected tubes from each inlet tract. The vac advance should help with part throttle response and fuel economy if set up correctly in much the same way that a 3D ignition system will. Just to be sure, pull each hose from the inlet manifold, plug the resulting hole in each inlet tract and try the engine again (you do not need to plug the dizzy or the tube leading to it since it does nothing if it sees atmospheric pressure). If you have excess hose you could cut four small lengths of that and wind a screw into each one to plug it; make sure nothing can get sucked into the engine. Link to comment Share on other sites More sharing options...
Weavie Posted March 9, 2021 Author Share Posted March 9, 2021 Hi DavidGood idea and one that I wouldn't have thought of. I will try it and let you know.ThanksSteve Link to comment Share on other sites More sharing options...
Weavie Posted March 9, 2021 Author Share Posted March 9, 2021 Hi RogerYou're right in that the engine revs freely up to 6000rpm with no load.When they fitted the vacuum system, they said it would help with economy but, more importantly, cure a significant hesitation on pick up at 2000 rpm. I will try the idea re blocking off the vacuum pipes and let you know what happens.It would just be great to find a solution which is incredibly frustrating. The car is great up to 3500rpm but, bad news if you are in the middle of overtaking!Steve Link to comment Share on other sites More sharing options...
David Brown Posted March 9, 2021 Share Posted March 9, 2021 #9 Happened to me twice. Once with a Morris 1000 which led to me resolving the same issue with my father in law to be's one day old Austin Princess. He was so impressed with my instant diagnosis that he welcomed me marrying his daughter. Also lay in the boot of his brand new Rover 2600 to diagnose slack suspension bolts. Note BL/Rover theme. Link to comment Share on other sites More sharing options...
Olgawld Posted March 9, 2021 Share Posted March 9, 2021 Could it be when you replaced the Weber carbs you've overtightened to manifold, there should be slight play so fuel doesn't froth up. Did you use new misab plates? Could it be the o rings are crushed/damaged causing a leak? Carbs balanced up? Would've thought it would have shown up on the rolling road though. Link to comment Share on other sites More sharing options...
cobaltcodd Posted March 10, 2021 Share Posted March 10, 2021 Restriction in the exhaust (collapsed or shifted packing materials)? Link to comment Share on other sites More sharing options...
Colin Cooper Posted March 10, 2021 Share Posted March 10, 2021 I had a similar problem. It took ages to sort, but James Whiting eventually traced the problem to an occasional fault in the fuel pump. A new £20.00 pump sorted it.Col Link to comment Share on other sites More sharing options...
Colin Cooper Posted March 10, 2021 Share Posted March 10, 2021 I had a similar problem. It took ages to sort, but James Whiting eventually traced the problem to an occasional fault in the fuel pump. A new £20.00 pump sorted it.Col Link to comment Share on other sites More sharing options...
cobaltcodd Posted March 10, 2021 Share Posted March 10, 2021 When you said the engine runs to 6000rpm when stationary, is that a sustained 6000rpm, or just a throttle blip that shows 6000rpm for a fraction of a second? Link to comment Share on other sites More sharing options...
Area Representative Andrew Gilbert Posted March 10, 2021 Area Representative Share Posted March 10, 2021 Smoke? what colour? I'd be tempted to get it back on the RR and have them replicate this under load whilst looking for signs of a problem.Hows the alternator and connections? They do tend to get hot under the primaries. Link to comment Share on other sites More sharing options...
HendrixsWhiteStratReturns Posted March 10, 2021 Share Posted March 10, 2021 AndrewI have a 1700 SS Xflow and had a similar issue, nearly drove me mad. Replaced everything you had done and even had a hole drilled in the fuel cap in case of an airlock. Problem eventually traced to dodgy igniter in the (Aldon) distributor...worth a look.My car would run fine for 10-15 mins then same issue as you, refused to go past 4k revs, die and then 20 mins later run fineThread can be found under 'XFLOW WOES - FINALLY SORTED'.Good luck Link to comment Share on other sites More sharing options...
orangepeel61 Posted March 10, 2021 Share Posted March 10, 2021 I have experienced issues with the auxiliary venturi when I inserted one of them slightly out of line, on the road car ran fine at light throttle setting but if given the beans it would pull back like it was being strangled, ease off and it would be ok again, when stationary (no load) it would rev fine. So I would say that's worth checking. Link to comment Share on other sites More sharing options...
orangepeel61 Posted March 10, 2021 Share Posted March 10, 2021 Additional Just read HendrixsWhiteSt post and concur, I have recently had the same problem with the Aldon Ignitor! Link to comment Share on other sites More sharing options...
7 wonders of the world Posted March 10, 2021 Share Posted March 10, 2021 Did you check the Aux venturis for location and security, seen the lock screw come a drfit on the rollers before... Link to comment Share on other sites More sharing options...
Weavie Posted March 10, 2021 Author Share Posted March 10, 2021 Probably 10-15 seconds at a time Link to comment Share on other sites More sharing options...
Weavie Posted March 10, 2021 Author Share Posted March 10, 2021 Hi AndrewLight grey smokeSteve Link to comment Share on other sites More sharing options...
Weavie Posted March 10, 2021 Author Share Posted March 10, 2021 Hi AndrewGreat tip. many thanksSteve Link to comment Share on other sites More sharing options...
Weavie Posted March 10, 2021 Author Share Posted March 10, 2021 It's on my list of "to dos" from an early commentThanksSteve Link to comment Share on other sites More sharing options...
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