HPC on 45's overfuelling, poor idle and progression

[stevefoster]

I have had a problem of poor idle and progression at low speeds during the very hot weather or when the car has been run through town for ages.

 

Perhaps all this is beginning to make some sense.

 

Last night on advice that the carbs may be brimming I set the fuel pressure reg to 2.5. I had run it on 3 normally but a while ago Nigel (why do I take any notice of what he does) had his on 3.5 (2.0L Zetec)... Thinking aha mine might need some of that, I set it to 3.5.

 

This was before the re-jetting, re-choking, weber alpha upgrade or there abouts.

 

Since then and with all the hot weather and the not so hot on Saturday... I have had this 'try to stall' at idle problem when hot.

 

Well last night it was not so hot but I crawled around the estate twice until the fan came on and everything was good and hot. Tickover perfect.

Throttle progression is better too.

 

This morning, cool air. Very much nicer to drive off low revs. Better progression.

I reckon the poor carbs have been brimming as DVA put it.

This spoils tickover and good progression.

Even at 2000 rpm in 5th and with virtually no throttle needed everything feels tidier, both constant running is cleaner and pick up better.

 

The Weber Alpha 3d ign has always been run in the suspected over fuelling state.

 

I have had the same problem with the MBE 2d ign. Initally because the car had no pressure reg and then come the warm weather and just before the Haggis run I

had the thing set to 3.5!

 

I am a little worried about running lean at sustained high rpm with the pressure reg on 2.5.

I could set it to 3 for the track, it always ran happily on this with the MBE ignition all last year!

 

Even the RKE XF I had was set to 3 with the same pressure reg. I wonder if the fuel pipe diameter is bigger on the HPC cars? I can't remember the dimensions now.

 

My XF started life as a 1600 XF and had the original fairly narrow plastic fuel piping.

 

DCOE 40's on the XF, 45's on the HPC.

 

I really need some very hot weather again to confirm all this of course.

 

Then there is a problem at very low RPM with lots of boot that I get pre-ignition.

It clears above 1400 rpm or as soon as the boot is removed.

Super or LRP solves this problem totally. I am assuming too agressive advance on the map at higher throttle positions and low rpm. But could this problem also be related to the over fueling...?

A refill 95 octane would test it.

[deanteam]

Is this possibly due to the problem being discussed by Chris Flavel with respect to progression holes?

[stevefoster]

I have 4 prog holes. This was best practise for a 16V then. Now it's 5!

Could go to 5 even perhaps...

You get the problems using 'old' carbs on 16V engines since they only have 3 prog holes.... fine for an 8V'er but not good for an efficient at low rpm 16v'er.

 

I am quite happy now.

 

I measured the flow output of the fuel pump through the pressure reg and got the following.

 

Pressure reg setting:

 

2 = 1 pint of fuel in 28 sec

2.5 = 1 pint of fuel in 26 sec

3.5 = 1 pint of fuel in 25 secs

 

I am not under fueling with this and flow at least....

 

The pressure reg with no resistance seems to make very little difference...

As the float valve comes in it does seem to reduce the pressure enough to stop the brimming.

 

Based on this data I will try it on 2 and see if it's even better!