HELP; Mystery: Wont pull away after head/cam change.

[beavy69]

Problem:

Idles (roughly) and revs ok in neutral but cant pull away unless I do a good race start and floor it, but as soon as I come off the gas its like it can't pull at all and doesn't even sound like its running at idle speed let alone what it should be at.

I have:

- Weber 32/34 - 1.3 engine - Ported head and AST2 cam (just fitted) -

Background:

* After I fitted the head and cam (last Fri) It was working fine but got progressively worse by Monday.
* My cam belt is a little loose as I cant shift the water pump to tighten it. I thought this was the problem but LongLiveTheNova seems to think it can't be that as it stays on and must have been the same tension before the head change.
* I just went round the block a miniute ago and when I got to the bottom of my hill and revved a bit I heard a squeeling sound. Did that twice before I pulled away and the noise went.

I have checked:

* Taken carb off and dismanteled etc
* Cam timing fine (aside from the belt being loose)
* Spark plugs and leads swapped n checked - fine
* Every idle speed n mix combo under the sun tried.
* Vaccy advance is fine (holds pressure on the tougue)
* All these were also fine before the head change.
* Head seemed fine (although I didn't get it pressure checked - but then surely things would be much worse if it leaked) plus I gave it the works; polished and lapped in the valves etc.

Ignition timing:

When I adjust this with the timing light (and the Vaccy advance hose off) I can set it fine but in adjusting the idle speed and/or mix of the carb, it changes position. In other words the timing could appear to line up in quite different dizzy positions so how do I know what its absoultely right to complete rule out the ignition timing as the problem?

Thanks for reading - any help/ideas grately appreciated - I'm at teathers end!

[Adam]

I'd wip the waterpump out and replace it, get the cambelt tension spot on.

The squeeling could of been the alternator belt..

First thing i'd try is another carb

[beavy69]

OK havn't had a chance to change the carb yet as have been working.

But it was working perfectly yesterday until I went over a big bump and then went ****ty again!

I will change the fuel pump and maybe try the coil. Anyone have any other suggestions from this new info?

[Adam]

WTF?
So it was running fine, and you hit a bump and its fooked again?

[beavy69]

yeah weird isn't it!? It worked fine all the way to work and back someone's house whom I was giving a lift and then I hit a large bump and it was like it again!

[Adam]

Perhaps the cambelt jumped a tooth or two...

Hmm, but how could it jump back to stop working again,Lol.

[beavy69]

Don't think it could when you compare the weight of the belt Vs the engine which is sprung a little from the mounts anyway. I'm determined to get to the bottom of it. I'll post an update 2morro when I swap/check the carb, fuel pump and coil (so glad I have another sh!ttier, older Nova lol)

[beavy69]

Swapped coil and took carb off for a look again. Power valve diaphragm is in tact but looks a bit lame as if there may have been an ingress of petrol?

Refitted with new coil seemed fine but now and then (bout 30min test drive so far) progression is not quite good enough.

I think (and am hoping) that the carb's power valve diaphragm needs replacing. Possibly the bump caused it to become stuck like a backward umbrella causing the problem.

I have ordered a new one and hopefully that will be it.

[beavy69]

Hey LLTN sorry I thought I'd posted the conclusion.

It was the power valve diaphragm on the carb, I hadn't noticed the ingress of petrol as I had left it disassembled the first time and the fuel evapourated so it seemed fine.

Thanks for your help anyway.

[Adam]

Whats the power valve diaphragm?
Something do with accel enrichment?

I aint too clued up on the various bits of carbs,Lol.

[SRlew]

yeh i also wouldnt mind knowing what the power valve diaphragm is.

might come in handy knowing, as im getting a 32/34

glad you got it sorted any way mate!

[Stuart]

if it wont play at low load, low speed. Usually an IGN timing issue.
dont use a sodding timing light, time it by ear ffs.
Its possible that the dizzy has got its advance mechanism fecked in the swap of cam etc.

plus the fact your fuelling will be gash as youve not had it setup for the new cam and head. Dont use the "its jetted the same as my mates 1.6" as a comparative answer as it would just infer a total lack of thought and common sense.


edit*** power valve diagphram, its the accelerator jet effectively.

[Adam]

I learnt on mine that timing lights are utter ****e, and the haynes ign timing at idle is also ****e on my engine too.

[beavy69]

if it wont play at low load, low speed. Usually an IGN timing issue.
dont use a sodding timing light, time it by ear ffs.
Its possible that the dizzy has got its advance mechanism fecked in the swap of cam etc.

plus the fact your fuelling will be gash as youve not had it setup for the new cam and head. Dont use the "its jetted the same as my mates 1.6" as a comparative answer as it would just infer a total lack of thought and common sense.


edi*** power valve diagphram, its the accelerator jet effectively.

Fair enough I didn't really think that through with the jets. Interesting you should say about the timing light because when I was doing it I was rotating the dizzy away from me thinking, hmm this sounds good. But then I was looking at the line and questioning it thinking that the "worse sound" that the better sounding setting was due to the fact that they tell you to take the vacc advance hose of the diphragm - so I need to sort that by ear and get it RRed or new jets for the poor hot starting.:thumb: