Club 80-90 Forums

Morning all. In short, I've been living with a bit of a throttle flat spot for a year now. Essentially, when the engine is warm, you get a bit an initial flat spot then it pulls through. However, on returning from a day out over dartmoor yesterday, it seems to have got a lot worse. The van starts from cold fine and choke does all the right things, also starts fine when warm with no need for any throttle. As soon as you depress the go pedal, things go south and the engine will now die. If you really gently increase the revs it will just about pull through but if you give a normal blip - engine dies. Checked the fuel filter - crystal clear. Checked cone filter - clean. All vacuum hose replaced last year and visual check confirms they are all in place. Fuel pump fine. Coil is not getting hot, and I dont think it is electrical anyway as runs lovely when left alone and at high revs. Just the bit in between! Any ideas folks?

Check vac actually moves plate in dizzy.

Check the carb accelerator pump diaphragm it may have a split that is getting bigger.

Either of those or both

Thanks fellas. Had a day out with the boys today flying kites. Van got us there and back but cutting out all the time. Going to have a look hopefully after boys have gone to bed tonight. Got some spare vac pipe to check the dizzy. Is the accelerator diaphragm the one on the back (as you look at the carb) that looks a bit like the choke pull down diaphragm? How do I open it up to check?

No

Ah right. Looks simple enough to open up. I'll start with dizzy then move to this. Thanks again.

OK, so popped the dizzy cap off and with a nice new bit of vac pipe stuck on the vac advance unit gave it a good sucK! Didn't get a great deal of resistance and didnt see anything much in the way of movement. Am I right in thinking that i should be able to see some movement in the push rod which comes out of the vac unit. I've ringed a piccy below

Boom! That's your problem. Yes it should slide, however, I don't have the lung capacity go activate these, thus, a second opinion (someone else to do the sucking) is always a bonus - as long as they're not an asthmatic smoker!!!



This text cannot be taken out of context by the dirty and perverse without my permission, plus, you all missed a great opportunity the day when I innocently typed something that is shocking when read twice.

Did give a good old suck and I've been off the fags for 15 years. Ok, so is fitting a new vac unit something for the diy or do I need specialist assistance? I am thinking scribing the dizzy body and block to record position and take a piccy of the rotor arm to make sure it doesn't go back in 180 out

This is the thread you need to read. Stripping the dizzy down, polishing and oiling the plates will help in line with vac replacement if it needs it.

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Cheers again all. Suppose plates could also just be seized with gunk causing the problem so I'll give it a go. Incedentally, should there be an earth link onto the tab on the side of the dizzy body? Nothing on mine.

Not really needed. Yes could be gummed plates but it will probably be partly that and partly a lazy or dying vac unit. Its not just a flat spot ofcouse. You're also wasting fuel.

As for the carb, no point in taking any of it apart unless you have a carb kit. Undoing the top to say clean it out is ok as you can always use gasket paper, otherwise a full kit is about £30-£45. That said, its astonishing the difference new diaphrams and seals makes to an old carb. For now, concentrate on getting that plate moving easily. It should snap back sharply when you release the vacuum. Looks to be a very old vac unit.

I agree with Bigherb that a worn accelerator diaphram can give similar symptoms. If you've got that and a lazy vac unit, it really will run badly. Best to do one thing at a time, that way you can see the improvement. Just don't mess with carb adjustment screws. Once set they rarely need messing with.

Evening all again, having received the requisite bits in the post its time to dive in. Couple of quick questions please...
1. If I don't loosen the pinch bolt and just remove the the bolt into the block can i assume that the timing position should hold??
2. Is lithium spray grease OK for giving everything a coating once cleaned up?
Looked at the vac unit again today just to double check, no movement on connection when vacuum applied (new unit moves fine) so I am assuming the diaphragm is perforated (or the casing has corroded/split).
Hopefully wont drop any bits - anyone reckon i could do it without removing the dizzy or is that just silly!?

I think that you can actually swap the vac capsule without removing the dizzy, the actuating rod has a plain hole that hooks a pin on the plate inside. Worth a shot, its only two screws.