Holly Secondary Vac spring change

[MetaJacko]

Hi,

I'm planning on changing the secondary vac spring on my Holly 3310 this week end (assuming they arrive from Real Steel) becouse it seems like the secondaries are opening too quick coursing the engine to 'coff' 'stumble' etc. I've no idea what spring is in there at the momement.

I've got a Holly book and it looks simple enough but I havn't done it before.

Any suggestions on what to look out for IE things going 'ping' and dissapearing to the farthest corner never to be seen again

Thanks

Paul

[gwak76]

Spring kits usually have have a scrap of paper with the spring colours /strengths etc included.

When you remove the four screws holding the vac cover on the spring is right before your eyes, easy to change and not much to lose, be careful replacing the screws as you can catch and rip the diaphram.

The quick change kit is worth buying if you are going to fiddle, it's about £10 and makes the job much easier, Real Steel sell them. That info might have been more use a couple of days ago

Happy springing

[MetaJacko]

Hi Gary,

Just ordered the quick change cover since I think I will end up 'fiddling'.
From what I've read, getting the right spring is a bit trial and error.
IE put in a spring and try it!

Oh well, should be fun.
Hopefully the existing one is colour coded and will give me a starting point.

Paul

[mikey]

Unfortunately the symptom you describe can be one of 3 things.

1. Secondaries opening too soon
2. Not enough initial advance (check the initial advance and limit overall advance with bushing.
3.Too small a squirter, or too little initial shot of fuel (carb pump cam) as secondaries engage.

On a Cobra as it is a light car the advantage is to get the secondaries opening as soon as poss without getting bog.

A bit confused you have put goes like a bullit - this suggests that it has only just started happening which puts the secondary spring in question if it was OK before. If this is the case it could be some blockage that has occured.

Whichever way. it dosent necessarily mean its the secondaries.

If the bog occurs as soon as you hit the throttle from slow cruise it is more likely to be timing . If it goes and then bogs when you think the secondaries are opening it is klack of enrichment at that point
Mike

[MetaJacko]

Hi Mikey,

Yep, your right about what it could be. Basically, I'm working down the list.
I just feel that it may be due to the spring.
Why? Well I've change the air cleaner and put it in a different place.
I don't think it was breathing nearly as well before. I think that the prevoius owner
got round lack of breathing by putting in a weak spring so that the secondaries opened faster. I could be completly wrong but I think I should check that anyway.

The accellerater pump may not be quite right ether so I'll look at that next.
I beleve the timing is OK but you never know, I'll try that as well.
One thing at a time I guess.

Basically, it 'bogs' usually if I accellarate hard from under 2000rpm, above that it seems fine. It is also not such a problem once the engine has warmed up.
I guess one reason I thought about the vac secondaries was becouse the cam has changed. It now comes on cam at 2000 the one before I think ran from 1500 or less. Again, I may be completly wrong here.

'bullitt' is in reference to the film as that car had a 390FE in, yep its lame I know

Thanks for the advice

Paul

[MetaJacko]

Hi Again,

What I probably havn't made clear is that on accelarating har from about 1000rpm it picks up fine initially even in 4th (my top gear) and then seems to bog around 1800 ish

Paul

[MetaJacko]

Well,

I opened up the vac module and found the problem imidiately.
The diaphram was knackered!
You would have thought that this wolud never open the secondaries
but it was still maintaining a vaccume and was in fact opening suddenly
up to about 1/2 way and then jamming at that. It would then suddenly close.
Replacing the diaphram solved this.
I need to do some more testing, I've got the smallest spring in at the moment,
but I'm sure I'll get the spring right with a few tries.

Paul

[mikey]

Hope this is it
What cam have you got, if its coming in at 2000 RPM it may still want some increased initial timing and limiting overall. If you can cahnge the mechanical advance try setting the initial at 18 degrees and fit the black bushing to limit to 36 degrees overall.

To compiment this try using a silver normal and a silver light to speed up the advance.

Sorry the above relates to Mallory end some other aftermarket distributors which are tunable.

Worth a try if the vac secondry issue dosent resolve it.

IMPORTANT - If you do increase the initial advance make sure you limit the overall to around 36 or thereabouts - dont want you to destroy an engine
Mike

[MetaJacko]

Hi Mike,

Its a Comp Cams 282s. Its 'On Cam' 2000 to 6000 although running my 390 up to 6000 is a bit scary

If it is still misbehaving then the timing is the next thing to look at.

Paul