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Vitesse 1600 spluttering when hot


george

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Hi all first time posting here. I have a Vitesse 6 that runs fine at low RPMs (up to 3.5K) or when cold. Once the car warms up or the revs exceed 3.5k or so the car develops an aggressive misfire/ splutteing and refuses to rev any higher. The misfiring continues to get worse as the car warms up to operating temperature, eventually causing it to stall even under no load at idel.

To try and diagnose this issue:

I have set the timing at idle with a timing lamp to 10° BTDC. Both the mechanical and vacuum advance work.

I’ve also checked the mixture on the carbs (Stromberg 150CD without emission control); with the lifting pin, the revs increase briefly and then go below idle speed, but the misfire still persists. To see if the misfiring was caused by a lean mixture; whilst the car was misfiring I pulled out the choke, but this only made it splutter harder. Checking if the misfiring was caused by a rich mixture I made the mixture intentionally lean but this had no impact on resolving the misfire. I then moved onto the plugs, I found that they were sooty so I cleaned the soot off but the problem still persisted so I retried making the mixture richer or leaner, but had similar results.

Thinking the problem was fuel related I took apart the fuel pump to see if the diaphragm or valves were clearly damaged, they weren’t. I have also checked the operation of the fuel pump when hot by lifting the priming lever, but fuel still came out of the pump. I then checked if fuel was getting into the bowls, expecting it to be a vapour lock issue on the carbs I removed the brass mixture adjuster on the bottom, there was plenty of fuel in the bowls, which were also cold. I then wondered if the misfire was caused by some kind of blockage between the fuel tank and pump so I ran the car off a fuel cell that used the cars mechanical fuel pump but the problem still persist.

I then wondered if the problem was caused by a head gasket failure (at this point I’m clutching at straws) but there wasn’t any oil in the radiator or water in the oil.

At this point I am stumped so would appreciate any help from anyone.

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To me it sounds more electrical like the coil or an electrical breakdown somewhere. You could try running it in the dark, carefully, to look for sparks and/or spray WD40 on components but substitution of items might be the only solution (they are always useful to have as spares)... 

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I had a similar problem eg it’s my Sprint it has graphite or something ht cables and the distributor end the cable is held/connected with little pins/needles these burnt around there connection point cut the cable and traffic all ok for a few days then again.

solution was some new cables made by the local ignition people

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I would change the condenser first. That has always been my first point of call since my first motor bike. 90% of the time since, this has always been the cause. The condenser works when cool but breaks down as it heats up. Tell tale sign is blackened points.

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31 minutes ago, Peter Truman said:

I had a similar problem eg it’s my Sprint it has graphite or something ht cables and the distributor end the cable is held/connected with little pins/needles these burnt around there connection point cut the cable and traffic all ok for a few days then again.

solution was some new cables made by the local ignition people


Good to know someone else has had a similar problem, I’ll definitely try new leads if the dizzy cap/rotor arm doesn’t change anything. 

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I had not realised that you had electronic ignition. Inside the module, there will be a solid state switch. many components including capacitors. (Called Condensers prior to 1960's) These do not last for ever. I always arrange to be able to convert back to a points operated system if possible when using electronic ignition units. They are not all what they are cracked up to be and you cannot 'See' symptoms easily.

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Not my experience, johny. I've seen a fair few electronic units develop intermittent or partial faults. Misfires are not uncommon. There was a Vitesse at the start of the 2004 RBRR which revved cleanly up to 3000RPM then cut out completely; putting it back to points solved the problem.

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Would have thought it unusual with micro electronics used in Accuspark types as any failure is normally catastrophic. The older remote type electronic ignition units with circuit boards can have tracking or components breaking down to give intermittent problems...

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49 minutes ago, NonMember said:

There was a Vitesse at the start of the 2004 RBRR which revved cleanly up to 3000RPM then cut out completely; putting it back to points solved the problem.

2004, quite a while ago now plus I imagine the electronic system was a few years old when it failed. Twenty year old technology, surely even the cheap Accuspark systems have better technology now.

My 13/60 has an Accuspark unit in the distributor, fitted in February 2015. Yes one day it will fail but with all the comments on forums about the poor quality of condensers I'll fit the same again.

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19 minutes ago, Chris A said:

2004, quite a while ago now

I've worked in automotive electronics - specifically engine control - since 1990. Very little has changed in how ignition coils are driven. I doubt the aftermarket has changed much, either. And a well designed EI should last - my GT6's Lumenition is over 20 years old and still going strong.

Anyway, that's all irrelevant. Electronics does fail and NOT always catastrophically. It can go in surprising and weird ways. An intermittent misfire - especially one that's temperature and revs related - could well be a failing EI unit.

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This is a slight drift, so apologies. My antique Sparkrite SX1000 electronic ignition unit died the other year as some of you will remember and the car is running with it still incircuit but set to conventional. Now, obviously this unit is old skool electronics, so the question is, has anyone opened up one of these and repaired it? I don't want to go inside without having a chance of fixing it. I did try the modern Sparkrite 4000 unit without success. 

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On 04/04/2022 at 08:57, johny said:

Would have thought it unusual with micro electronics used in Accuspark types as any failure is normally catastrophic. The older remote type electronic ignition units with circuit boards can have tracking or components breaking down to give intermittent problems...

I am a retired Electrical and Electronic Engineer. Believe me, Potted or Integrated circuit components still fail AND it is not possible to find out which component is faulty without access to every NODE. At least one can fault find a points system in a layby. I made my first system with descreet components and could fix that, but only on the bench.

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29 minutes ago, Badwolf said:

I think that I'll just leave it as it is, but thanks for the observations. I was hoping that I might be able to replace a fried capacitor or something but no, I'll just leave it as it is.

There is a simple piece of test equipment you could try.

Hammer-gross-2_2048x-1024x686.thumb.jpg.3341ee954e3fed4c289a0dd8eac931b0.jpg

It may not work but it might make you feel better

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