Bogging down on Webers

[RobFrost]

Any idea why my 2.2T (on Webers) is bogging down badly below about 2,500 revs? It really flies once as it hits higher revs. It would stand to reason that it's lean because pumping the accelerator seems to fix it and enables you to get some revs. And I guess that means the enrichment pump mechanism is working. But Chris68 and I tuned the carbs by listening with a pipe and thought we had "idle" mix pretty good - little or no inlet backfires, and going richer gives exhaust backfires. Any suggestions how to stop it bogging down (other than stay at high revs)?

[911hillclimber]

Don't guess on the enrichment 'squirt' from the pump. Remove the filter housing and stare down the carb ports and move the throttle cross bar quickly and see if a good (and equal) shot is delivered. There is a spec for the amount discharged, but I don't know what it is. Obviously don't do this too often without the engine running or a serious flooding will result, best done engine running.
Might be a good call to the people who are selling the new Webers for that info.?

iirc it is quite an amount that gets ejected from the jets.
It's been 30 years since I messed with my webers on my 2.2, so hope I remember correctly!

[chris68]

Hi Rob,

As well as more carb fine tuning it's a good idea to check the timing and that the advance mechanism is following the factory curve. Found my distributor to be way off when I eventually realised it was the cause of poor acceleration on my car.

Cheers

[RobFrost]

Hi Rob,

As well as more carb fine tuning it's a good idea to check the timing and that the advance mechanism is following the factory curve. Found my distributor to be way off when I eventually realised it was the cause of poor acceleration on my car.

Cheers

Ok will check that too but I'm pretty sure it's lean at low revs because a slow press of accelerator doesn't work but a few pumps gets it going.

[RobFrost]

Hi Rob,

As well as more carb fine tuning it's a good idea to check the timing and that the advance mechanism is following the factory curve. Found my distributor to be way off when I eventually realised it was the cause of poor acceleration on my car.

Cheers

p.s. how do I check that? Other than clean and oil the distributor mechanism I wouldn't know where to start.

[RobFrost]

Hi Chris, actually I know I need a strobe on lead one... It's the rest of the rev range I'm not sure about.

[chris68]

Hi Rob,

A couple of options here I guess. Strobe on lead 1 and plot dynamic crank advance at increasing rpm intervals. Convert crank advance values back to distributor advance then compare with factory curve.

Where, (measured dynamic crank advance - static crank advance) / 2 = distributor advance

Or, get the distributor on a test rig and measure its advance directly. I lashed up a rig a few years ago that hooks up with an optical sensor and into an oscilloscope. The bottom of the distributor shaft was driven via a flexible coupling up to 3000rpm. A bit of a faff but accurate.

As you say, it might not be the distributor at all. Just worth checking out if all else fails.

As 911hillclimber rightly says, have a look down the carb throats to see that you're getting a squirt of fuel from each accelerator pump nozzle when you press the throttle. Also worth running the car up and down the lanes with the engine nice and warm to progressively dial in the weber idle mixture settings. It's a bit of an iterative process.

I'm sure you'll get it sorted. Give me a shout if you think I can help (although I'm no expert )

All the best

[RobFrost]

Hi Rob,
Or, get the distributor on a test rig and measure its advance directly. I lashed up a rig a few years ago that hooks up with an optical sensor and into an oscilloscope. The bottom of the distributor shaft was driven via a flexible coupling up to 3000rpm. A bit of a faff but accurate.

This is the electronic engineer solution.

I'll get a timing light and check the base advance and at a few revs. I should probably have done it already.

[chris68]

my neighbours preferred the test rig method

[911hillclimber]

If the stock distributor is clean and the weights are free to move, not slack and the springs ok, then the timing advance should be fine?
I'm assuming all the ignition parts are ok, points etc.

[chris68]

On mine the bakelite?? plate in the base of the distributor was breaking up. It was impeding movement of the advance mechanism. There are two advance profiles on my Bosch distributor and the low speed mechanism was particularly affected causing poor low speed acceleration. I wasted a long time chasing down what I'd wrongly assumed to be a carburation issue. Having said that, setting up the carbs is a game in itself.

Doesn't mean it's the same issue on Rob's. Why wouldn't you rule it out though?

[RobFrost]

If the stock distributor is clean and the weights are free to move, not slack and the springs ok, then the timing advance should be fine?
I'm assuming all the ignition parts are ok, points etc.

It seems to run too well at revs for the ignition to be substantially off. if advance wasn't working, given it runs well at revs, it would have to be pinging at low revs which I don't think it is.

Somebody has been in the ignition recently... new leads, plugs, points etc. It's hard to imagine they didn't set the timing. The carbs on the other hand are more specialist and involved to investigate. They could also be off a different car and have completely wrong jets in for all I know.

[chris68]

Many have found this site very helpful http://www.performanceoriented.com/troubleshooting

[RobFrost]

Many have found this site very helpful http://www.performanceoriented.com/troubleshooting

"...engine tuned with the air filter removed..." Is that what we did? I can't remember if we replaced the air filter covers before tuning.

Also slightly amusing: "...as the result of an off-road excursion..."

[chris68]

It's a good site and he's a very knowledgeable and helpful bloke. Exchanged a few messages with him when I was going round in circles myself.

Yes, did the quick tuning with the filters off because you need access to the inlet trumpets.

It's recommended in general not to run without filters though, to minimize fire risk - and nobody likes that! Think it's something to do with harmonic inlet pressures at certain engine speeds giving rise to a petrol vapor cloud outside the carburettor inlet. Fuel standoff is it?? Hopefully someone smarter will intervene here because I'm out of my depth - again .

Cheers