Satisfying day in the garage today.

[ldtopham]

Whilst I'm waiting for some steel plate to turn up to finish my harness brackets I thought I would spend a bit of time tuning the engine.

Ford 351C Holley 750V/S, MSD ignition.

I originally had a double pumper on top but hopefully made the correct decision to swap it for a vac secondary with Ken from EDA. He said it had only seen dyno time but was unsure as to why it never left the shop? This in no way is a slur as Ken did promise to swap it for another unit should it prove faulty.

I basically had it running with base carb and timing settings but driving on private road proved a little disheartning. It idled ok but felt real flat up to 2000rpm sometimes needing double clutching to clear the fuel delivery. It was also proving difficult to start, sometimes backfiring through the intake. Lean and timing possibly retarded.

I increased the timing to 16 BTDC from 12, limiting total to 34 at 2950RPM. Idle is now 850 and it starts to advance at 1100rpm.
Starts real smooth with no excessive compression nor any run on after turning it off. I used the black MSD bush (+18 mech) and 1 silver light and 1 silver heavy adv spring. The Vac is connected to timed port.

I then checked the idle bleed screw settings and found that I could screw them all the way in (lean) and the engine would continue to run. It actually idled real smooth at this setting but something was wrong as it should have cut out. I wondered if I had a reverse idle Holley but there isn't a 750cfm version listed so needed to investigate further. I use an Innovate wideband sensor to check A/F ratio but it wasn't playing ball. It works for about 10 seconds after starting up before reading above max readable lean (6 lambda!) and was oscillating all over the place. I checked for vacuum/ intake/ exhaust leaks but all seemed ok. I may have the sensor bung in too hot a location this I need to check out.

I decided to tune using the vacuum gauge method on full manifold vacuum and manged to get 13" of vac. It would still run with the bleed leaned right out so I wasn't happy. I pulled the carb and got to stripping it down. With the backfiring I also wondered if I had blown the power valve as I didn't know at this stage whether it had blow out protection.

Even though it had stood for 2 years there were no signs of gummy petrol inside. More worrying was the small amounts of swarf still attatched to the tiny drillings in various places of the metering block and plate from manufacture
I removed all these, took note of jet/ power valve and metering plate sizes and generally gave it a clean up/ inspection. The primary idle transfer slots were showing 60 thou below the primary butterflies and holley reccomends a max of 40. This would be the reason for idle being too rich as the idle transfer was feeding the idle A/F instead of the curb idle. A quick tweak of the secondary idle transfer slots to allow the primary to be adjusted by means of the idle speed screw and fingers crossed. I also noticed that the gasket between the venturis and base plates was slightly in the airflow down the venturis so trimmed it back with a scalpel.

All back together, a quick tap of the accelerator pump showed too much clearance. Adjusted so that as soon as the throttle moves it tips in (even got the lingo down now!) and idle screws set 2 turns out, it fired up fine. I checked the float levels, both levels at the base of the sight hole, tweaked the idle bleed screws both the same amount and got 15" of vac. It does now stall if I lightly seat the screws no leaks and idles nice with the odd skip at 850rpm due to the mild 270H cam.

Bonnet down into 1st and whoa what a difference. Very responsive and very smooth with no puff of smoke on initial acceleration, happy as a pig in muck. I can now shift into second without it wanting to die. Having never driven a big V8 before I initialy thought I might have gone daft with the cam choice or something. It was the first time I have dabbled with a holley and found the whole day very satifying. I can thoroughly recommend ISBN10:1845840062 'How to Build & Power Tune Holley Carburetors' by Des Hamill.

Now need to suss out why my o2 meter isn't working as it should so I can data log fueling through all rpms

Must sort small leak from sump pan gasket too as I am leaving trails on my test ground! SVA might be an idea too.

For anyone who has a holley and it needs tweaking I would buy the book and have a go, 1/2 a days work has made such a difference!

Cheers.

[Clarkson]

Well done mate good write up, I have spent all week finally tweeking my double pumper with squirter jets and pump cams,that it runs so well I am now getting very high teens in MPG!!

[ldtopham]

Originally Posted by Clarkson

Well done mate good write up, I have spent all week finally tweeking my double pumper with squirter jets and pump cams,that it runs so well that I am now getting very high teens in MPG!!

As engineers do I tend to jump staight in and take it from there. I read the instructions this time and blimey they helped! Quite a lot to them but once you have got your head around which circuits are in play all becomes clear.
Do you have to adjust on them a regular basis or they pretty much stable once set?

[Clarkson]

Originally Posted by ldtopham

As engineers do I tend to jump staight in and take it from there. I read the instructions this time and blimey they helped! Quite a lot to them but once you have got your head around which circuits are in play all becomes clear.
Do you have to adjust on them a regular basis or they pretty much stable once set?

No,it's set for life! Maybe check it once a year,just keep the carb clean and use a good fuel filter.

There is much more you can do,but sounds like your learning fast.

I got lots of help and support from Tim Adams with lots of late night phone calls.

What jets and P/V have you got fitted??

[Clarkson]

Oh re your lambda probe,where have you fitted it??sounds like the locition is not hot enough or a exh leak!!

[ldtopham]

Originally Posted by Clarkson

No,it's set for life! Maybe check it once a year,just keep the carb clean and use a good fuel filter.

There is much more you can do,but sounds like your learning fast.

I got lots of help and support from Tim Adams with lots of late night phone calls.

What jets and P/V have you got fitted??

Currently on 70H jets on the primary, the secondary is a metering plate for which I made note of the pt number but haven't referenced yet.

The power valve I think is a 6.5. Nothing stamped on the flats but on the body. clockwise from top 6 then 5 at 3 o'clock, 2 at 6 o'clock and 0 at 9 o'clock???? I will go with 6.5 for now. I'll run my vac gauge inside the car when I'm tuning the p/v and that should be a good pointer. I wondered if it was a 2 stage type but it isn't. It a high flow type with the 2 cut outs and correct gasket. I did notice 2 gaskets fitted. With one the p/v doesn't seal, I could see no problem with with running 2.

The book mentions leaning out 2 jet sizes for evry 2000ft of alt above sea level, I'll go with what I have for now and see how the data logs come when I have the chance to get it on the road proper.

Bumping the timing up and sorting the fuel has lowere the exhaust noise considerably too

[Clarkson]

Originally Posted by ldtopham

Currently on 70H jets on the primary, the secondary is a metering plate for which I made note of the pt number but haven't referenced yet.

The power valve I think is a 6.5. Nothing stamped on the flats but on the body. clockwise from top 6 then 5 at 3 o'clock, 2 at 6 o'clock and 0 at 9 o'clock???? I will go with 6.5 for now. I'll run my vac gauge inside the car when I'm tuning the p/v and that should be a good pointer. I wondered if it was a 2 stage type but it isn't. It a high flow type with the 2 cut outs and correct gasket. I did notice 2 gaskets fitted. With one the p/v doesn't seal, I could see no problem with with running 2.

The book mentions leaning out 2 jet sizes for evry 2000ft of alt above sea level, I'll go with what I have for now and see how the data logs come when I have the chance to get it on the road proper.

Bumping the timing up and sorting the fuel has lowere the exhaust noise considerably too

Yeah 6.5 sounds right,but you can change it later on when you have your car on the road. They say rough general rule on p/v setting is half your total engine vacuum. As for your primary jet is maybe alittle small at 70 as I have 75 in mine, but only a dyno/your lambda probe can tell that.

Your going the right way about it.

[ldtopham]

Originally Posted by Clarkson

Oh re your lambda probe,where have you fitted it??sounds like the locition is not hot enough or a exh leak!!

The bung is 1.5" back from the 4 primaries as they gather into the collector just outside the body. I checked for leaks the other night and there are no signs of any blow by on the slip joints as the x4 1 3/4" headers slip into the 2" side pipe tubes? I have been re-checking the manifold flanges after every start up and again no signs of leakage? It reads ok intermittantly maybe once a minute at correct A/f 13:1 at idle then goes bonkers. Same both sides. I checked to see if my MSD CD unit was causing interferance on the power supply but all seems well. I going to let it get well up to temp and try again, hopefuly with the heat the pipe slip joints will seal up if they are leaking. Short of that I need to borrow a heat/ thermo gun to see exaclty how hot that area is getting as the sensor stops reading around 500 degrees.

[Clarkson]

Originally Posted by ldtopham

The bung is 1.5" back from the 4 primaries as they gather into the collector just outside the body. I checked for leaks the other night and there are no signs of any blow by on the slip joints as the x4 1 3/4" headers slip into the 2" side pipe tubes? I have been re-checking the manifold flanges after every start up and again no signs of leakage? It reads ok intermittantly maybe once a minute at correct A/f 13:1 at idle then goes bonkers. Same both sides. I checked to see if my MSD CD unit was causing interferance on the power supply but all seems well. I going to let it get well up to temp and try again, hopefuly with the heat the pipe slip joints will seal up if they are leaking. Short of that I need to borrow a heat/ thermo gun to see exaclty how hot that area is getting as the sensor stops reading around 500 degrees.

It sounds like it's in the right place.You could try wraping the power wires in tin foil and the MSD wires too,but I still think its not getting hot enough.

[wilf]

Lee - good work - a sensible, logical approach to carb tuning (doing just one change at a time) will always result in a better running engine. I would bet that probably 75% of carbed engines out there could be made to run better/more economically with some sensible tweaks - after all, you can really only set WOT AF ratio on a dyno.

Hope you sort your Lambda meter out - one omission I made during my build that I regret. And these days I am too fat/lazy to take the manifolds off just for that.