14 replies to this topic

[nspr]

Hi all,

Fixed my clutch today, got the car out on the road in the nick of time for my sister's wedding tomorrow afternoon. Ran great down to the pub, into town for a top up.
Whilst returning, an issue i've had previously has returned. Car simply loses power past a certain level of throttle. That level varies depending on both gradient and whatever the car seems to fancy. Issue comes and goes intermittently but at points is so severe i'm reduced to driving in 2nd on the flat to keep moving.

Previously i've trickle charged battery and checked the earths. Also replaced sparks a couple months ago. We've toyed with the ignition timing tonight and have found we can either make the issue much worse or almost resolve it, but not completely. Using choke whilst it's happening has no effect. No part of carb / inlet manifold seems loose to permit air into the intake tract. Imagine it'll clear up on its own and then return out the blue. Any ideas? Truly stumped.

[Chris1275gt]

Setting the timing to the stated timing in the manual would be a good starting point.

[timmy850]

It could be anything really:

Bad tank of fuel

Wrong ignition coil causing overheating or insufficient spark

Spark plugs fouled from rich running, wrong gaps, deteriorated from age

Timing setting incorrect

Timing curve incorrect

Fuel filter clogged or debris in the tank

Fuel bowl setting incorrect or needle valve not controlling the level

Air filter clogged

Dashpot oil low or incorrect grade

Needle provides the wrong fueling for your engine

Carb worn

Vacuum advance unit split - insufficient advance and an air leak

Battery wont accept a charge

Loose wire on the low tension side of the coil

General parts wear and condition - dissy cap, rotor, ignition leads etc

[68+86auto]

Check that the condenser is not loose in its mounting or the connection.

[Designer]

Have the same problem, the carb has just been completely renovated, so I am slowly working through all the possible solutions.

I think it could be the coil as it does seem to me to be getting very hot. 

 

Paddy

[68+86auto]

Have the same problem, the carb has just been completely renovated, so I am slowly working through all the possible solutions.
I think it could be the coil as it does seem to me to be getting very hot. 
 
Paddy

Check your dwell. Also check that you have the correct coil fitted.

[Designer]

New coil on order just in case.

 

Paddy

[corrado vr6]

Have the same problem, the carb has just been completely renovated, so I am slowly working through all the possible solutions.
M
I think it could be the coil as it does seem to me to be getting very hot.

Paddy

I too have had my carb reconditioned and it ran great in March when I fitted it. Now it runs rubbish like the OP is explaining. I have changed all the ignition side of things so I am hoping it’s the dashpot oil being sensitive to the now warmer weather.
Hopefully will find the time this week to change it 🤞🏻

[nspr]

Thanks all for the advice; got through the weekend with a mix of perfect and awful running culminating in trying to get the car home this evening barely able to pull away in 1st. However, i tried pulling the fan knob on the dash for the hell of it and found, to my surprise, it's acting like a throttle and solved all my issues.

What on earth is it cabled up to?

[timmy850]

Perhaps you’ve got your choke and throttle cables mixed up? Or maybe choke and heater?

If you mean this “fan knob” it’s normally the choke cable
http://www.minispare...er/21A2329.aspx

[nspr]

Perhaps you’ve got your choke and throttle cables mixed up? Or maybe choke and heater?

If you mean this “fan knob” it’s normally the choke cable
http://www.minispare...er/21A2329.aspx

 

 

It could be anything really:

Bad tank of fuel

Wrong ignition coil causing overheating or insufficient spark

Spark plugs fouled from rich running, wrong gaps, deteriorated from age

Timing setting incorrect

Timing curve incorrect

Fuel filter clogged or debris in the tank

Fuel bowl setting incorrect or needle valve not controlling the level

Air filter clogged

Dashpot oil low or incorrect grade

Needle provides the wrong fueling for your engine

Carb worn

Vacuum advance unit split - insufficient advance and an air leak

Battery wont accept a charge

Loose wire on the low tension side of the coil

General parts wear and condition - dissy cap, rotor, ignition leads etc

 

I reckon the heater and choke are backwards, yeah; that gives me a good list to run through, so thanks again. Haven't had chance this week to do so yet.

 

Previously drained and refilled with fresh fuel. Plugs have been swapped for new and gaps checked.

Timing, we're going to get a light on it soon. A friend's uncle's got one, but that, filters, wear items, debris, all worth a check but confuses me that sometimes it runs sweet as could be.

Dashpot, have checked previously but best go over it again exactly per Haynes. Carb generally is pretty baffling to me.

Battery, I've previously checked earth leads (actually ordered new ones but half didn't fit), ensured good contact. I was previously convinced this was the problem, but doesn't seem to have made much difference. Battery charges ok.

 

The part that stumps me is that it's so variable. You can literally drive ten miles one way with zero problems, park for a couple mins, and the next moment, it's stumbling under a quarter throttle.

Sometimes it's first drive after it's sat for a week. Sometimes it's at random halfway through a drive. Sometimes it's only an issue past 80% what. Sometimes you can't stumble up a moderate incline in 1st. Doesn't seem weather or temp dependent, doesn't seem to be affected by fuel source... really confused.

[sonscar]

Next time it happens and if safe poke your finger into the carb to check it is not iced up and that the piston moves freely.Is the float valve working correctly and shutting off the fuel?Is it sticking and causing starvation?,Steve..

[alpder]

Next time it happens and if safe poke your finger into the carb to check it is not iced up and that the piston moves freely.Is the float valve working correctly and shutting off the fuel?Is it sticking and causing starvation?,Steve..

Icing is a very interesting thought. Would you have a photo of the engine bay, so we could see where the carb is getting its air from?

[nspr]

So, timing is sorted; was something like 16deg advanced   running far better now, except for the vent pipe on the carb touching the exhaust, welding shut, and stumping us for an hour on the way back from the local pub. Kudos to the helicopter engineer who came out of his house to help and clocked it within 30 seconds. Now rerouted through the wing, soon to be replaced with suitable fuel rated hose. Whether issue is staved off for good, we'll see.

Next job is to remove the halfords special radio and associated wiring mess under the passenger side of the dash.

[cal844]

So, timing is sorted; was something like 16deg advanced running far better now, except for the vent pipe on the carb touching the exhaust, welding shut, and stumping us for an hour on the way back from the local pub. Kudos to the helicopter engineer who came out of his house to help and clocked it within 30 seconds. Now rerouted through the wing, soon to be replaced with suitable fuel rated hose. Whether issue is staved off for good, we'll see.
Next job is to remove the halfords special radio and associated wiring mess under the passenger side of the dash.

You can get a wiring kit from wired by Wilson which gives switched and permanent live, an earth and speaker wires as needed, far tidier than the standard setup