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DOHC Carb engine running poorly
Jon Bradbury - 10/6/05 at 11:41 AM

hi

Just got back from my pre SVA MOT and the engine has been misbehaving.

Basically it is running OK on full throttle but with moderate loads it cuts out momentarily before kicking in again. Holding the throttle about half way causes the engine to hunt in regular spurts, so it cuts out, then revs, then cuts out, then revs (and so on), with the frequency of each cycle being regular.

I think the ECU is trying to compensate for something, but I don't know what it is. It's similar to fuel starvation.

The kind of things I will check are

- air leakage on the inlet manifold
- blocked jet in the carb
- a blockage in the fuel system before the carb

Does anyone have any other ides? I couldn't get the emission test done because of this, it wouldn't hold steady idle or intermedite engine speed (2500 RPM was what the tester wanted).

All ideas welcome!

Thanks

JonB

PS, Apart from that the car performed well. Got up to 90mph on the dual carriageway <ahem> private road and it's going well (on full throttle). After getting the wheels aligned I have self centering too!

TTK77 - 10/6/05 at 12:12 PM

Propably needs different kind of emulsion tubes.
To get more fuel to middle rpm's.
Which number tubes do you have in them?


[Edited on 10/6/05 by TTK77]

awinter - 10/6/05 at 01:14 PM

what carbs are you running?

Could you not richen up the idle mixture to increase the fueling on part throttle. Just a couple of turns of 4 screws on DCOE or DHLA carbs

Jon Bradbury - 10/6/05 at 01:27 PM

It's a Weber 2V TLD, standard fitment to the Ford 8v DOHC engines (well the ones that aren't injection that is!).

I don't expect there's anything non stock about it as it came straight out of the donor with the engine as-is.

This problem manifests itself once the engine is warm, after a few miles.

[Edited on 10/6/05 by Jon Bradbury]

TTK77 - 10/6/05 at 01:38 PM

My mistake...I read DCOE instead of DOHC. I thought you had twin webers...

Jon Bradbury - 10/6/05 at 04:41 PM

Not on that engine. No one makes a manifold for it

Jon Bradbury - 10/6/05 at 04:42 PM

quote:
Originally posted by awinter

Could you not richen up the idle mixture to increase the fueling on part throttle. Just a couple of turns of 4 screws on DCOE or DHLA carbs


Don't think I can be doing that as it's going for SVA next Thursday. Fiddling the mixture will spoil the CO2 + HC readings.

big_wasa - 10/6/05 at 10:16 PM

I had a Fiesta that would do that.It was just crap in the jets from me always running it with bugger all petrol...You used to have to pull the choke out to richen the mixture to get you home..

The carb on those is servo controled from the ecu,are they working ok? on mine it sticks from time to time and you have to dab the loud pedal

What air filter do you have, again I have this engine in my donor car and I fitted a piper cross jobie which leans it of a bit to much.Great induction sound from it