Todsters Engine Rebuild Take 2

[Todster]

Hi Alistair,
I'm toying with the idea of painting the whole of the bottom half of the van that purple colour with the metalflake..... still can't make my mind up. I know the 'purists' will be frothing at the mouth at that..... after painting the fan shroud and seeing the results (photos don't do it justice) i'm now considering that also. (thats a vauxhall metallic Anthracite with the lilac chameleon flake)
Anyways, got the oil back in today, and been for a run out tonight, but before I did, I took a trip to my local garage where I get the vans at work serviced, and got the carbs dialled in a little better using their exhaust gas analyzer.
Still got a couple of gremlins tho.

1) won't run unless the timing is 18 deg btdc at idle - (can't think it was like this before, i'm sure it was 7.5) - showing around 40 deg at around 3500. I'll be pondering this one for a while, can't think what is causing this, but it just won't run at any less. I'm wondering if the Scat crank/BMD Pulley pairing has thrown the timing marks out.....
2) got a flat spot at around 2k rpm, but, I'm only drawing vacuum from one carb, and by the look of it, that is only tapped into one barrel. I'm running the 123 dizzy with vac, so i'm thinking that its not getting enough/intermittent suction from the one pot. I'm going to try drawing vac from the other carb so got a couple of non return valves and a t piece on order to see if this makes it any better.
3) When ticking over, 1,2 and 4 all read around 3.5 on the sync gauge, but no 3 is about 2.5, and doesn't change at all when adjusting the idle screw. I'm going to have to take that one off and have a look see what is happening there. Might have to put the leakdown tester across the cylinders to see what compression i'm getting.

All in all tho, I'm happy with the results, got loads more power than before, just want to get it nearly there before I take it down the rolling road (last time they revved it to within an inch of its life, don't want them doing that before its had a bit of running in.)

All the best
Mark

 

[jonboylaw]

I don't think you put non return valves in the dizzy vac signal, it needs to read the vac changes. Putting in the NRV will just give you a vacuum but will not relate to the engine load if you see what I mean. In the megajolt install I did, I used a small plenum chamber 3inch long 1.5 bore plastic waste pipe. Fitted 5 barbs and linked them to the manifolds I tapped with the 5th barb to the MAP sensor.
For a dizzy based system you need to run from the vac port near the base of the carbs for the correct signal.

My plenum chamber:

Sent from my GX64 SatCom phone using Tapatalk

 

[Todster]

Hi Jon,
Could you post up a pic of where you have taken the vac off the carbs please?

I've taken mine off the port marked up below as Vacuum Advance Port. I did wonder if I was going to have to run a plenum.



Thanks
Mark

 

[Todster]

Hi Jon,
Thinking about it now, the non return valves will not work. All that will happen, is that once max vacuum has been reached between the valves and the dizzy, it will be held there and not released. D'oh. Didn't think that one through did I?

Cheers
Mark

 

[aogrady]

That sounds a great idea with the paint, or how about a central band running around the middle, like Evil Ben's pearl white bus?

Alistair

 

[jonboylaw]

Mark, my instal is for a megajolt and that uses the manifold vac signal, not a ported vac signal as used by the dizzy. In the picture you show for a DRLA, it is labeled the Vac Advance Port. Usually you will only have 1 per pair so back to square 1. If you tap the manifolds the signal will be wrong as the dizzy needs zero vac on closed throttle, pulling quickly to high vac just off closed throttle, then dropping back as it goes towards full throttle.
It should work fine as it is for a dizzy so suggest you look at the idle /main cross over, what idle and main jets are you using?
I run 60/130 in my 1955.


Sent from my GX64 SatCom phone using Tapatalk

 

[Todster]

Hi Jon,
I seem to think they're running 55/115, I'm away at work so can't get to have a look till the weekend, they are EMPI HMPX 40s jetted as they came out of the box. They have a vac advance port on each carb, so this weekend, I'm going to try teeing them together. Many thanks for your assistance, i'm sure i'll get it sorted. 8)

Alistair, its going to be a year or two before i'm ready for paint proper.... rolling resto. I'm going to keep doing bits at it (next job for this winter is both front arches and the bottom of the front panel) and painting it orange, till its done and ready for the full paint.

Cheers
Mark

 

[Todster]

Got a bit further with this.

Hooked up both vacs to the 123, made it a little better, but not much, then remembered that the 123 has a 16 way dial switch to change the advance curve, and with the old carb (single, twin choke weber) I had it set on 0 - one curve fits all.
I changed this to 5 - 1600 and this improved things but still had the flat spot.

So, next on the list was jets.

As standard, the HPMX come with 52 idles and 115 mains, so I ordered a set of 55 and a set of 60 idles and a set of 125 and a set of 130 mains.

Left the 52 idles in, and changed the mains to 125s and what a difference. Pulls like a train! Massive difference. Now I've still got a little flat spot, but it's just off closed throttle. As soon as you get to 1200 or so RPM it pulls clean.

Not had chance to try the 55 idles yet, but that's next on the list. I'm trying to get a session booked on the rolling road to get it spot on, but, I'm nearly there myself.

Cheers
Mark

 

[jonboylaw]

The low rev flat spot is more than likely the idle circuit so the 55s should cure it. Well done!


Sent from my GX64 SatCom phone using Tapatalk

 

[Todster]

Thanks Jon,
I'm hoping so. Looking forward now to getting a couple of hundred miles in, then second oil change, then Croyde in June. That will put 600 or so miles on, change oil again then happy days. Got to say, it's not been as scary as I was imagining. Had a few niggles, but all in all a very enjoyable and satisfying experience. Learnt a lot along the way too. Now, I can't wait to get that printout off the rolling road.

Thanks for your input, much appreciated.

Cheers
Mark