8 replies to this topic

[mini_mad69]

1380
286 cam
stage 2 head
alloy inlet (heated)
hif44 carb
foam filter



Recent carb modifications from the vizard book. The car wouldn't run very well, so enriched the mixture and it seemed better.

Now when I drive the car at slow speeds around my village it seems ok, anything above 3000rpm and more than half throttle, it just dies.

When I got out, the carb was realy realy cold, i mean freezing. The weather here is very hot at the moment aswell by the way.


Im not sure if it's icing, but somethings not right, I can't drive the car at the moment, much above 40mph and it just starts to die.

Any ideas? I've replaced the dashpot with some 5w40, no difference.

[Dave33]

its obvious the mods to carb will effect the mixture,so if you have just richened it up on the adjuster (i.e raise and lowering the jet) you wont get the fuelling right throughout the whole throttle travel and rev range.
You need a different needle,or if yours is too lean(which it probably is),then reprofile it as described in the vizard bible.
Out of curiosity and as it might help us to help you,what mods have been done to carb?
Im hoping you didnt touch the bridge.....
Also what needle is currently being used?
Did it run well before the mods and was anything else changed at the same time?
How many turns out from fully in is the mixture screw?generally with a correct profile you want the jet about 1.5mm down from the bridge,around 2 to 3 turns out.
dave

Edited by Dave33, 23 June 2010 - 01:18 PM.

[BGB]

I had sometign very similar on my 998 and even though the heating matrix was plumbed into the manifold it still did it.


Eventually tracked down to the fuel system, Filter was clogged, some pipes were split (not enough to leak untill under pressure) and wrong needle on Carb


all replaced and the car goes perfectly

[mini_mad69]

I realise that just adjusting the jet won't sort the fueling, im just mentioning it.

I leaned it out a bit on the adjuster and it got better, but still the problem is there.

I need it to be running somewhere close to get it to the rolling road.


I've fitted a HIF abundument plate which has the heat sheild on it, I did have a HS one on there before, which did not have the heat sheild, so will change that back.


I drove it and it cut out, I got out and the carb was freezing, I pulled out the plunger and pushing it back in I felt the piston drop back down, so the piston is sticking.
It's fine and smooth if left to warm up
.

It currently has a modified BDL needle, which richened the top end.


The carb has had rough casting marks cleaned up, screw threads filed off. Bottom of the piston smoothed. Butterfly spindle shaft halfed and filed, and cap head bolts used to retain it.
Bridge is left alone, I was going to just smooth the edge a tiny bit, but didn't in the end as vizard explained not too.






Oh and BGB, the filter is brand new as fitted at the same time as the mods to the carb.

I need a new needle, but would have thought that it would be close, just a bit lean.


I've got a new lambda probe coming, so I re-wire my AFR gauge and see where the fueling is.
Just wondering what the cause for the icing could be?

[bmcecosse]

The carb will always feel 'freezing' - the evaporating fuel does that! Look for another reason for the engine dying - but lack of fuel supply does look like top suspect. However you say the piston is sticking - so get that free'd off anyway. It MUST slide up and down really smoothly.

[Dave33]

Lik bmc says the carb will always feel cold to touch when you remove it,try putting petrol on your finger and you will see.
your carb is not icing up,it would be impossible to in this weather.
You also have the water heated manifold connected,this is not really needed in this country unless your maybe in the highlands during a febuary blizzard!
The sticking piston will be causing all sorts of fuelling problems,so until this is sorted you wont be able to tune the carb.
The BDl needle should be a good starting point,and with a bit of patience and testing you should be able to get it very near spot on with needle reprofiling,you could also try a BDK if you have no luck.
Dont remove the Heat shield,you dont want fuel evaporation caused by the heat from the exhaust manifold,its there for a reason.
Just noticed you say you have smoothed the bottom of piston?is all thats required is a chamfer either side where it protrudes into the venturi at full lift.I dont see this mod in the vizard book,so maybe this is causing your probs.
Dave

Edited by Dave33, 23 June 2010 - 10:12 PM.

[bmcecosse]

I only ever rounded the in-going side of the base of the piston - just a nice radius. Wizard does warn about not modifying the piston too much........

Edited by bmcecosse, 23 June 2010 - 10:37 PM.

[mini_mad69]

The carb will always feel 'freezing' - the evaporating fuel does that! Look for another reason for the engine dying - but lack of fuel supply does look like top suspect. However you say the piston is sticking - so get that free'd off anyway. It MUST slide up and down really smoothly.

It slides perfectly fine when warm, but when cold it seem a little sticky.


And yeah it's just a chamfered edge of the piston. I can drive the car fine, at half throttle and below 3000 rpm or so.

Although when I go past this, it starts to rev up and then just starts to die, sometimes cutting out and not restarting, fiddling with the damper or piston it starts up again fine.


I'll take it apart again and check it all over again, maybe theres some swarf in there making it stick or something.

Although it only does it when the engine has been run and carb is cold. If left for a couple of minutes it starts up again.

[CPC]

Holy thread bump!!

But how did you cure this mine is doing the same!