Loss of power/revs pulling away

[MidLifeCrisis]

Just driving back from weekend away.

Everything fine at first then got that sixth sense feeling that the acceleration didn't "feel right" - felt like there was a flat spot, or bogging down while cruising along ...
Then having stopped at junction, pulling away there is initial power, then revs/power just drops away, and acceleration stops; remedy was to rev and slip clutch to get away but feels that there is just no torque at all.

Better in higher gears but still a feeling that the revs/power isn't responding to throttle as it usually does?!?

Anyone got any starters to consider?
Just changed out fuel filter (4 weeks ago)
Seems to rev ok out of gear (but it's difficult to tell)
Cheers for any help/pointers??

[CovKid]

Faulty lead/s will do that too.

[BOXY]

^^^WHS

Check all four plugs are firing. One not firing will stand out when pulling away, but once up to speed you'll hardly notice it.

[kevtherev]

I read it like the timing isn't advancing.

[MidLifeCrisis]

Thanks

Assume check leads by measuring resistance? Or pulling one by one and see if there is any change? Or see if a plug will spark onto engine block?

Any easy tests for timing advance working correctly?

Thanks again

[CovKid]

To check timing advance, with engine off, go to pipe between dizzy and carb, remove from carb end and suck on pipe. With dizzy cap removed, plate inside should move. However, if it was running ok, more likely to be lead I'd say. They can break down and will cause those symptoms.

You could try lead removal but the problem may not occur at some temperatures, or indeed at idle.

[MidLifeCrisis]

They can break down and will cause those symptoms.
You could try lead removal but the problem may not occur at some temperatures, or indeed at idle.

Is the best option to replace them then?? Or is there anything that can be done to test/diagnose?

[300CE]

As Covkid has said symptoms could possibly be a sticking plate - dizzy would really need a strip down and clean (I'll find the thread on how to do this), but to test this for the time being, where you can see the plate spray it up with a good dose of WD40 & take her for a run.

[MidLifeCrisis]

As Covkid has said symptoms could possibly be a sticking plate - dizzy would really need a strip down and clean (I'll find the thread on how to do this), but to test this for the time being, where you can see the plate spray it up with a good dose of WD40 & take her for a run.

Will do - thanks all.
That's tomorrow's job list sorted!

[CovKid]

If you haven't changed leads in living memory, I'd change them.

[MidLifeCrisis]

If you haven't changed leads in living memory, I'd change them.

Changed all five HT leads out and took for a drive.
All seemed fine but 10 mins in the problem returned as before.

Note that sitting on the drive after test drive, engine running, out of gear; if I press the accelerator just a touch, revs drop and it feels like it's about to stall (but doesn't)?? Give it a boot of accelerator and it surges back to life??

Checked vacuum advance on dizzy and that certainly moves the plate when you suck on the vac hose
I've not disassembled the dizzy further than taking the cap off but as I say I can see movement when the vacuum tube is sucked and I can also feel the spring resistance of the centrifugal advance when the dizzy shaft is rotated (this probably doesn't prove its working correctly but it's not obviously sticky/stuck??)

Anyone got any thoughts or tests I can do??
Or should I get the dizzy out and disassemble (I need to go get some good circlip pliers first too?!?)

Are there any carb problems that would cause this??

[kevtherev]

Engine off..
Take the duct off the top of the carb
Get someone to press the accelerator
Look down the carb throat. (Open the choke flap if you have to)
You should see a squirt of fuel going into the throat

This is the accelerator pump, it help the transition from partial to open throttle.
If it is not working the symptoms are like you describe.
But is increasingly reading like an air leak into the manifold

[MidLifeCrisis]

Engine off..
Take the duct off the top of the carb
Get someone to press the accelerator
Look down the carb throat. (Open the choke flap if you have to)
You should see a squirt of fuel going into the throat

This is the accelerator pump, it help the transition from partial to open throttle.
If it is not working the symptoms are like you describe.
But is increasingly reading like an air leak into the manifold

Thanks - yep, have had a play with the carb in the past so I'm aware of the accelerator pump - I'll take a look;
Ok - then also have a trawl over the various vacuum pipes looking for leaks .......
Cheers for the input ....

[MidLifeCrisis]

Shameless attempt to keep this post near the top .....

Well - checked for accelerator pump output and its spitting out a good healthy squirt of fuel when accelerator is pushed.
When I push accelerator rapidly to about half I get a short lag in revs before it bursts into life and revs away??
Could the progression slot in the primary venturi be blocked ?? How would I unblock it??
Is there anything else it could be??
My natural inclination is to assume it's carb related - but could it be something else (bearing in mind that it idles fine and it has new HT leads) but seems to be worse when engine is warm??
If it's an air leak wouldn't thus show up during idle too??

[kevtherev]

Shameless attempt to keep this post near the top .....

Well - checked for accelerator pump output and its spitting out a good healthy squirt of fuel when accelerator is pushed.
When I push accelerator rapidly to about half I get a short lag in revs before it bursts into life and revs away??
Could the progression slot in the primary venturi be blocked ?? How would I unblock it??
Is there anything else it could be??
My natural inclination is to assume it's carb related - but could it be something else (bearing in mind that it idles fine and it has new HT leads) but seems to be worse when engine is warm??
If it's an air leak wouldn't thus show up during idle too??

During warm up the choke may well be employed albeit briefly in the current warmer climate, so any air leak would be negated by the richer fuel charge.
As the choke comes off it leans out and an air leak will lean it out even more, too lean and the engine will falter.

Does the coil ever get hot?
Is the choke pull down in good order ?(does it work, is it leaking air)
Does the secondary throttle open when you suck its pipe?
Has your mixture been checked recently on a gas analyser?