Edelbrock 500 jets n stuff

Richard P6 · Post by **Richard P6** » Mon Aug 31, 2009 7:45 pm

Been on the 86 68/57 for a while now and apart from one day when the A/F needle sat against the stop on 16, it’s been running perfectly.

Out in the Peak District yesterday, didn't miss a beat. Tick over at 13-14 and cruising at 14 or so. Plenty of power, and very tractable.

So why when I start it today does the tick over bend the needle on 16 again? The A/F meter only reads to 16 and it stays there, although it does bob down to 15.5 now and again.

I have taken the carb to bits and blasted every little hole, jet, and crevice with carb cleaner. You can eat your dinner off the inside of it now. (not with petrol in though).

I have fitted the 67/55 rods (still with 86 jets), a full stage richer on both cruise and power; no difference.

The A/F meter is fairly new so I do believe it, especially as the car is running like a pig now which does suggest it really is running leaner than 16.

I have checked the timing and that is still at 8 BTDC as it has been for ages.

Completely baffled by this – any ideas anyone?

I have changed some other things but can't see why these should make any difference.

I have put the pink springs in now and changed the secodnaries for 392s.

sidecar · Post by **sidecar** » Mon Aug 31, 2009 8:51 pm

Richard P6 wrote:Been on the 86 68/57 for a while now and apart from one day when the A/F needle sat against the stop on 16, it’s been running perfectly.

Out in the Peak District yesterday, didn't miss a beat. Tick over at 13-14 and cruising at 14 or so. Plenty of power, and very tractable.

So why when I start it today does the tick over bend the needle on 16 again? The A/F meter only reads to 16 and it stays there, although it does bob down to 15.5 now and again.

I have taken the carb to bits and blasted every little hole, jet, and crevice with carb cleaner. You can eat your dinner off the inside of it now. (not with petrol in though).

I have fitted the 67/55 rods (still with 86 jets), a full stage richer on both cruise and power; no difference.

The A/F meter is fairly new so I do believe it, especially as the car is running like a pig now which does suggest it really is running leaner than 16.

I have checked the timing and that is still at 8 BTDC as it has been for ages.

Completely baffled by this – any ideas anyone?

I have changed some other things but can't see why these should make any difference.

I have put the pink springs in now and changed the secodnaries for 392s.

It's a complete 5hit bag when things go wrong for no apparent reason!

How is the big vac tube connected up to the rest of the engine? maybe the tube has as a split in it or something?

Do you run a regulator? someone on the Cobra forum had bad problem which turned out to be a regulator which was restricting not only the pressure but also the volume.

Try running the fuel pipe into a conatiner for 1 minute then measure how much fuel was delivered (in CC). Divide this figure by 4.7 and that is the maximum BHP that can be made with that fuel flow. If it turns out to be something really low like 50 BHP then you have a fuel sarvation issue.

If it is something like 1500cc then the issue is either in the carb or an air leak somewhere. (Manifold maybe)

I've now dropped the secondaries to 83, the AFR is now 12.5:1 at WOT.

Have you cleaned out the gauze filters that are behind the float valves? (I think from memory)

BTW, you will get a shed load more low down and top end power if you up the static to 14 degrees, (3.5) 12 degrees (4.6) change the dizzy springs to get the all in by 2700-3000 RPM (36 degrees on a 3.5 lump). You will need to ditch the vac system which does not work too well with the Eddy carb anyway!

Keep us informed!

Pete

Richard P6 · Post by **Richard P6** » Tue Sep 01, 2009 9:03 pm

I lifted the top of the carb and found both float chambers at the correct level (What I assume to be the correct level).

I took the feed pipe off and put it into a 5L bottle, then ran the pump for 1 minute. 2040cc of fuel - so divided by 4.7 I should have enough for 434bhp - plenty methinks.

As there is plenty of fuel in the float chambers, I have discounted any problems with the feed to the carb, e.g. blocked fuel filter in the regulator, or whatever.

I removed the primary jets again (did this yesterday and fired some carb cleaner down them) and then removed the primary venturi boosters. The idle jet (I think that is what it is) had a small piece of plastic wrapped around it

It is the piece in the red circle below.

Now this piece of plastic (It looks like plastic) had somehow found its way deep into the primary well.

I haven't finished putting it back together so don't know if this was the problem, but I am hopeful now.

You do have to wonder how on earth it got there though.

sidecar · Post by **sidecar** » Wed Sep 02, 2009 8:23 am

Well done for finding that, I'm sure that you have found the problem!

Where the hell the lump of plastic came from is anybody's guess!

I believe that the primary circuits feed fuel to the engine all the time, the fuel that they supply is added to the other circuits as you open the throttle more and more. Therefore if the primary circuit is blocked the AFR across the whole range will go weak. (That's my theory anyway!)