Mopar Muscle Association UK

Well I copied most of the settings from the old carb.
Fitted the loudest pump cam in the primary (brown for you anoraks) and upped the secondary to green.
Replaced the leaking float bowl with one pinched from the old carb.
Binned the sight lenses and refitted the brass screws and set float levels.
No leaks, started up instantly, idled cleanly and revved lovely

Out for road test and tuning tomorrow

Must say Paul.
You look rather femanine to be playing with a Mopar race car !

That's my personal mechanic

So I went out for a couple of hours with my box of jets, pump cams and tools to try and get the carb to run right.
It started really well, but as soon as it started to warm I realised it was very rich. In fact it wouldn't start again once hot.
I started with:
77 main jets, idle screw 2 1/4 turns, 31 shooters, brown (loudest!) pump cam. AFR showed 12 at idle, 10- 11 part throttle (secondaries disconnected). Except for the pump cam, these are the same settings I ran in the vac sec carb.

I worked my way down in stages to:
68 mains, idle 1 turn, pink (base) cam.
IT STILL shows rich on the AFR- idle 13.8, part throttle 11- 12!
Nothing seems to make much difference, I'm thinking there must be a leak or a fault

What size power valve are you using? and make sure the accelerator pump is not sticking

PV is 4.5, same as I had in the vac sec. To be honest I didn't try changing that.
Vac at idle is about 5, light cruise about 15.
I tried a 6.5 and a 2.5 in the other carb but the 4.5 seemed to work best. I guess that doesn't mean it's right for this carb tho...

The pump seems fine. It squirts every time I pump the throttle. You can even see the difference between the steep curve of the brown cam and the milder pink one

Yea those cams get me in trouble , I dont have to pass any regs here so I get it driveable with out fouling the plugs ,or a rough idle , these Hollys can be very tempermental ,do you have a cam somewhere in the middle? they have several ,I have the milder pink one on mine works pretty good, and the idle mix screws need constant adjusting when the fuel here changes, stick with it ,you will get it

With a cruise vacuum as high as that I'd be trying an 8.5 power valve for faster enrichment. If that works, you might be able to lean off the idle circuit and cut back on the pump shot.

Thanks. I've a 6.5 so I'll try that for starters.

Some good news... MOT PASSED

I've raised idle speed to around 900 which is a bit steadier and gives an idle vac around 7, AFR is now 14-ish at idle so that seems good.

I didn't have chance to give it a decent run this morning but I'll change the PV up and see what it cruises like later.


When we had it over the pit for the MOT I had a good luck underneath. LOADS of oil everywhere again
Luckily we spotted a split O-ring on the neutral switch (my fault, It did have a fibre washer which leaked. I couldn't find one the right size so used an O-ring. Wrong!)
Also the rocker gaskets are getting worse- should have my new one's from Hausers soon.
Axle's still oil-tight though! And I've replaced the crappy breather with and adaptor and run a length of pipe into the trunk and into a little bottle.

But if the vacuum at idle is "about 5" then the power valve is probably opening at idle.

You need to go the OTHER way. 3.5" valve.

db wrote:Thanks. I've a 6.5 so I'll try that for starters.

I've raised idle speed to around 900 which is a bit steadier and gives an idle vac around 7, AFR is now 14-ish at idle so that seems good.

There you are then. You raised vacuum above the PV level and it leaned out. Stick with the 4.5 valve or a 5.5 may be better.

I forgot I'd put the 2.5 in at the same time I raised the idle vac, I'll put the 4.5 back in, that should still be fine now vac is up.
I've also gone to the orange pump cam (midway between pink & brown )

It has a massive stumble off-idle, almost stalling as the AFR briefly hits 18-20, then as I level off the throttle AFR drops to 12-13.
Is this likely to be pump cam or pv? Or something else entirely?

Make sure the power valve channel restriction is drilled out to around 50 thou. Just to be sure you get enough enrichment when the power valve does open.

I'll check that ta.
I made good progress tonight, the bog has virtually gone but there's still room for improvement.
Though I guessed my work was being messed up by the secondaries- I'd removed the linkage but not fixed them. I reckon air was getting sucked past the butterflies as I hit the throttle and that's what was giving the momentary weak spot.
Current settings:
Idle screws 1 1/4 turns
Idle 900, vac 7, AFR 14
4.5pv
66 mains
31 shooters
Brown pump cam (lumpiest)

At a steady 3000rpm, vac is 15, AFR is 13.8, though this is around 12 under acceleration

That is nice, with some adjustments it looks like you are on the road

Dave wrote:Make sure the power valve channel restriction is drilled out to around 50 thou. Just to be sure you get enough enrichment when the power valve does open.

I did a search for more info on this Dave and came up with this from a Cobra site:
http://www.clubcobra.com/forums/holley- ... rcuit.html

It suggests spending some time tuning the holes for best. Do you think that's worthwhile or should I just drill them as you suggest?

I quite like this quote I found on there...
"There is nothing nice about a Cobra. It is stripped down to the essentials- a big engine, a small car, and four wide tires to keep the whole business on pavement. Its loud, smells like gasoline, and shakes, shudders, and bucks. It makes your arms tired and your feet hot. You nearly crash about once every 10 minutes. Its so damn wonderful that you cant believe it" Automobile Magazine 2004