8 replies to this topic

[mrbrightside]

Hi lads, i've got a terrible stone cold start problem with my 1289cc 5-port Skoda 130. If any of you are running a tuned 5-port with a single DCOE then we've basically got the same engine just by different manufacturers and i'd really like to hear from you. All other avenues have been exhausted, Skoda OC, tuners shops etc. and according to Webcon UK i'm the only person in living memory to ever have had such an acute problem of this type.

 

All ancillaries are fine and it's been dyno run to set the carb and ignition up properly, ignition is by distributor and contact breakerless setup. The starter jets are 85F9 emulsion tube and 150 air corrector, though the air corrector has been drilled out to 200 which didn't make a blind bit of difference, the chokes are 28mm. The carb is a 40DCOE 151, brand new and rebuilt by Northampton Motorsport just for good measure. The problem does not happen with smaller downdraught carbs, just the DCOE.

 

I've tried all combinations of choke, throttle pumps, throttle trim etc. but still it won't go without a lot of pedal work and repeated attempts, 10 attempts to get it firing is not uncommon if the ambient air temp is around 5c. When it eventually splutters asthmatically into life at least 2 cylinders are flooded and you're banging away at the pedal to keep the other 2 going, it takes about 5mins of running on 2 to get the others cut in and it up to all 4. Previous tests have concluded no plug fouling before the key is turned or after a 5sec crank with ignition supply isolated, and it doesn't flood plugs common to the same carb barrel- any plugs can get soaked and all have been in the past. It only needs to fire on all 4 for a matter of minutes before the whole problem vanishes into thin air like a virgin on prom night, and it has to be stone cold for the problem to occur ie- left overnight/all day.

 

Here's the setup...

 

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There have been comments made about the inlet manifold being a worst case scenario.

[nicklouse]

Don't like the look of the inlet at all. It looks like it will want to put all the fuel to the outer cylinders. Does not look like it straightens up anywhere.

I would have it over the exhaust and have it straightening up well before the head.

Then there is the filter. Running any stacks in there?


Finally what is the engine spec? Road of race? As that will have effect on what is a suitable inlet length.

[mrbrightside]

Don't like the look of the inlet at all. It looks like it will want to put all the fuel to the outer cylinders. Does not look like it straightens up anywhere.

I would have it over the exhaust and have it straightening up well before the head.

Then there is the filter. Running any stacks in there?


Finally what is the engine spec? Road of race? As that will have effect on what is a suitable inlet length.

Good input, thanks.

 

The filter has short trumpets inside. Full fast road spec- high comp pistons, 265/270 cam, ported/gasflowed head, Grp A valves, CC'd head chambers, tubular manifold with matched headers (Czech rallycross)...fully rebuilt lump. 2 and 3 are the rich running pots on these engines.

[nicklouse]

What is the firing order? As for a Mini I would have expected 1 and 4 to be rich.

Longest inlet we would use on a Mini is about 7" and would have a straight shot into the head as the inner two cylinders tend to get robbed of fuel/air.

My thoughts are the engine is not pulling enough volume for such a long inlet.

Is the starter up to the job?

[Ivor Badger]

I don't like the inlet manifold, too long, too many bends. I suspect you have the aircraft rich cut problem. The fuel instead of remaining atomised in the inlet air, seperates out and gathers on the inlet manifold walls and then enters the cylinder as neat fuel.

 

Can you not move the carb to the other side of the engine with shorter manifold like a mini?

[mrbrightside]

The starter is a recon replacement and as good as i'm going to get, firing order is standard 1-3-4-2. The aircraft rich-cut problem sounds interesting, i'll look into that, the problem worsens exponentially as the temperature drops- whether that has anything to do with it i don't know. I've commissioned a custom manifold to sit over the exhaust, but it'll be a while as i've specified servo take-offs and mounting tabs for anti-vibration stay bars.

 

The temperature was about 10c when i left work today so it fired on the first crank with no trouble. Thing is you have to work the pedal to keep it going, even if it fires strongly like it did it'll die suddenly and not be able to sustain itself on the idle and starter jets alone, it's this furious throttle work that floods any cylinders that did not fire strongly first time around. There's a frosty morning or two coming up and they're always the worst as the battery (brand new Bosch Silver ) is weaker the colder it is, good job i live on a hill really.

 

Cheers for the input gents, there seems to be a pattern of comments about the inlet. All the rally 130LRs had these 180deg over the back inlets, but they won't have given a damn about cold starting trouble...

 

[nicklouse]

Yeh but look how short the inlets are there.

Mini 45 DCOE on a 7" manifold, get in. Pump the pedal a couple of times and then start. No problems. And that is with the choke not connected or used. Same goes for Minis with shorter inlets.

[mrbrightside]

Yeah, true. It's a taller head than the 5 port too, the inlets are really high up, i would walk bare-arsed to Barnsley to get my hands on one of those.

[nicklouse]

Yeah, true. It's a taller head than the 5 port too, the inlets are really high up, i would walk bare-arsed to Barnsley to get my hands on one of those.

Now that is a brave thing to suggest.Your biggest problem would be getting out of Leeds.