Carb'd 308 - sticky throttle

I fully expect that I will be removing the air box and either fiddling around with the linkages or having to poke around with the butterflies but I am always happy to benefit from other's experiences!

In 23 years of ownership I have never had this - but the car hasn't been driven an awful lot over the last 2 summers, I guess this may be a contributory factor. This started happening a month or so ago and was intermittent, it is now more frequent.

A simple example; I parked up today for 5 minutes, hopped back in the car, fired it up and it sounded a bit flat and the revs were quite low on tickover (i.e. 500/700 as opposed to 1000rpm). I pulled away and I had to check that I was actually in 1st gear, it felt like I was in 3rd. I started to accelerate and the car was very sluggish. This is quite disorientating when you can see cars getting larger in the rear mirror. And then boom! The revs leapt and I was on my way, presumably as the mechanism freed up.

I'll need to fix this before I drive it again as it's quite dangerous or it will strand me somewhere!

As I said at the outset, I'm sure once the airbox is off the problem may be evident but any advice is welcome.

 

Hi Steve,
Yes, that's a very good point.
I have the single distributor with electronic ignition (Marelli SM805A). So this could be one of the coils or one of the amplifiers etc.? To be honest, I can't remember how the 2 banks are split from the dizzy onwards.
Glad I asked!

Thanks

 

Thanks for this. I decided to start the hunt with the distributor. It all looks clean inside barring some slight deposits on the 8 pins that I can clean up.
The centre carbon brush slides easily enough. When fully pulled out it is 5/16" long.
I can't see any problem with the actual distributor. The 8 plug leads and the 2 king leads were all shiny and firmly inserted.

I'll pull the rotor next. My thinking is that the way that the issue manifest itself, it points at something mechanical as the issue.
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Thanks Steve,
I'm probably getting the wrong end of the stick but the Coils connect to the dizzy using the same connectors that go to the plugs. (see picture).
The rotor itself shows some signs of wear (see pictures) but I don't think it's excessive and I can't believe that this wear would cause an intermittent fault? Happy to be corrected. My instinct is to clean them up and put them back rather than replace them.

Your understanding of the spark from the coil jumping from the ring to the rotor - and then from the rotor to the plug is correct. The ring has marks where the spark has been jumping to the rotor (see picture).

Edit...
Looking at some online stuff, the distributor cap contacts may be past their best - i.e. they have carbon build up etc.
I'll try and measure the resistances from the coil to the dizzy next time I'm under the hood. I'll be in that area in any case as my next step is to check that the king leads are connected securely to the coils.






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I took a change of tack and removed the airbox.
As soon as I pulled on the throttle cable the problem was evident, the cable was slipping through the clamps that connected to the carbs...
But all has not been in vain, I went through my records and found that the Distributor and Rotor are actually 7 years old. Very little mileage but quite mature. In two minds about whether to clean them up or replace.
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Ah!
Yes, of course. Back to the drawing board. Thanks again.
My only excuse is that the car has been ignored for 2 years and I've forgotten everything!

 

Sorry, an long overdue update...

Due to other commitments & frustration, progress has been very slow.
1. Bit by bit I replaced the entire ignition system (Plugs/Leads/Distributor/Rotor/Ignition Modules/Sensors). All to no avail.
2. I've had the airbox off more times than I care to count. This combined with my efforts underneath the car confirms that the right foot connects to the carburettors without interference.
3. I've checked all the mechanisms of the carbs and everything moves as it should. I rebuilt them in 2013/2014, so I am confident with this.
4. The dizzy and advance/retard mechanism have been dropped off at a specialist - simply to run up and confirm that all is well. They are so busy that I have no idea when I'll get it back. Had they been capable of turning things around quickly I would have dropped it off before buying all new bits.

My latest theory is that the fuel pump has an intermittent fault and is not delivering enough fuel. However, I spoke to a very seasoned vintage car restorer and racer - he suggested that fuel is problem.
The main thrust of complaints about Ethanol in fuel is that it rots rubber etc. in classic cars. But leaving fuel in tanks for moderate periods (i.e. infrequent use of a classic car) is the bigger problem in older cars. His main points were that the modern fuel now absorbs water and also Ethanol reduces the energy in fuel. The combination of these 2 points is fine in a modern car with electronic sensors that constantly monitor and adjust the mixture but carbs simply can't cope. His race car is 1930's Riley and if he uses regular pump fuel he empties the tank and carb bowls after every meeting. He is absolutely positive that this is essential to get the best out his race car.
So once the dizzy is back, I plan to empty the fuel tanks etc. flush the car through with fuel (ethanol free) and then run thereafter with ethanol free fuel - which is still available but not at every garage.

Whatever the outcome, I've missed an entire summer of driving my car, which is a real shame. On the upside, my golf is a lot better!

 

No rubber worries here!
All my rubber bits have been replaced in the last few years.