Loss of power

[Mad Moose]

Hi,
Could anyone shed any light on an intermitent fault I have with my van? It runs and starts fine but when you try to pull away the revs drop and you need to dip the clutch to prevent it stalling. When travelling along it will suddenly loose power for a bit almost like it is running on 3 cyclinders it will also back fire. This generally happen for a few miles then it sorts itself out and is OK. The engine is a 1.9 petrol DG. I've checked the timing, dizzy cap and rotor arm, its got a new coil, fuel and air filer, the plugs and leads seem fine.

Has anyone and ideas??

[kevtherev]

it does this when cold or warmed up or both?
Fuel filter OK? for a quid I'd change it
air leak giving a weak mixture causes a backfire.
check vacuum hose connections to airbox and carb, for perished rubber, check braided servo hose for air leaks (from inlet manifold to one way valve)
carb manifold gasket leak

any water in the petrol/fuel filter?

does it stutter if you blip the throttle?

[Aidan]

vacuum and/or mechanical advance issue ? backfire is timing related I think
was timing/idle speed checked with engine warm ?

[boatdog]

have you checked plugs and leads sounds like a cylinder going down hence loss of power then kicking back in and causing the back fire (unburnt fuel in exhaust)

[Mad Moose]

Only does it when warmed up. Filers changed. Vac hoses have been changed recently. Will check servo hose and carb manifold.
Timing checked when warmed up.

Cheers.

[kevtherev]

Filters changed.

should only be one petrol filter visible next to the tank.. the other one is inside the carb search this forum for that.

I'm sure it's weak mixture related if you have trouble when warmed up.

[Madmoose]

Hi, Just spent afternoon investigating my lack of power and I've got a few more details:

Its Intermitant
Only happens once warmed up
If you hold the throttle half open the engine will stutter and stall when there is no load
When there is load the engine will run ok at high revs but at lower revs when a torque is needed it stutters and feels like it will not go and when it does it back fires.

I was looking at it out on the drive and it was doing all of the above, it stalled and when I restarted it, it was fine???

So I took it out for a run and it was OK. Then I tried to re-create the problem:

Removed a plug lead- Less power but did not run as above
Removed vac advance hose - ran lumpy at tick over but still not the same as above

Any Ideas welcome!!

Cheers Mike

[jason k]

spray some wd40 round the base gaskets to see if it takes any in

you will hear the motor note change.

it sounds like an air leak to me.

[Aidan]

accelerator pump failure ? the diaphram may have a hole in, when you press the accelerator the pump adds in more fuel to ensure pick up, perhaps on choke the mix is ok, but once choke is off mixture becomes weak ?

with the inlet off you should be able to observe if the pump is adding extra fuel when pushed

I can't illustrate it cos I don't ahve a DG

diaphram is part of carb repair kit I think, but I've not changed one myself