[mustang 671]

hi all. happy xmas. hope you have a good new year.

just insured the mustang for the road. dyno is booked for this wednesday and mot in the afternoon. not long now and i hope to be out driving.

will post some dyno figures and hopefully get some pics and possibily a video will be nice.

bloody weather is awful though. not stopped raining here.

[mustang 671]

hi all . got to the dyno and found out why i had some issues previously , i have a weak crank sensor , we put a pitch anayliser on it and the resonation changed the sensitivity of it which meant it didnt read thed crank trigger wheel 100% at certain rev ranges , it wasnt a carb problem that i first was trying to fix, so i have ordered a more higher output senor , engine ran well and we re jetted the primarys to 65 jets from 72s , got bad weather here now so wont be back to the dyno till mid feb.

getting there now.

[F-BIRD'88]

Just don't get too carried away on trying to get it tuned too sharpe. ( best power) You need some in cylinder cooling (extra fuel) to keep it alive under boost. You don;t want to be on the edge. A bit rich er Under boost/throttle is fine. You can drill/hone the jet hole in the sec metering plates to fatten that side up if needed.

I'd use a minimum of a holley #21 sec metering plate in the 600VS carbs. These are found in the 3310 VS 750 holley carb.

Was it pig rich with #72 pri jets in it.? ( I assume that you had the power valve in.) Starting rich is the safe way to tune it in.

If its tuned on the edge with a #65 you may want to bump up to a #67ish pri jet. A bit rich is best.
The secondary metering plate matters. Its not that hard to modify/convert to replaceable holley jets.

How much vacuum did the wide open throttle carbs pull at WOT? max rpm. What is the blower drive ratio?
Indicated boost @WOT.

[mustang 671]

hi f bird . happy new year and all that

yes it was rich as hell with 72s on the primary side , i still have 78s in the secoundaries for now , but was difficult to get "wot" and see what the air fuel mix was reading from lambda senors as the crank sensor wasnt reading 100% dyno guy shut it off and said to change it as when the secoundaries kick in - if the sensor miss reads a tooth it could fire the wrong plug , so i have ordered a ford vetec sensor which pushes more lots and will compensate fot the engine resonation ( noise and movement combined )
but he had it running very smooth on primary side and idle at 925 ish , started each time fine.

pulley ratio is bottom 45 and top 51 . so -8% under driven given me around 10 lbs boost.

[F-BIRD'88]

So you have not actually make a full pull under boost and WOT on the dyno yet.
You have only tested it on partial load , on the primaries, correct.?

The 78's sound good on the sec side as a start but it may want fatter than 65's pri @WOT.

Yup the crank sensor signal matters. The air gap setting is critical.
may have seemed rich because of misfire under load, cause of the crank sensor trouble.

65's primary just seem lean for this one.

[mustang 671]

That's correct , he changed the primary 72 and went to a 65 to see the lambda sensor reading , but when started to do some pulls on wot the crank sensor error paramter box started to read some errors , we then opened up a dyagonsitics programme which works behind the scenes on my ecu and shows a graph of exactly what is happening at the engine , seems to show the sensor was struggiling to read the missing tooth at certain rpm and also as you stated the air gap being 0.8 mm was able to move under a certain load ,

So I have to make a stabiliser strap to the front of the senosr mounting arm with a adjuster nut on it so I can fine tune , he said it may be ok but as it started to read errors it shows the ecu was having to guess for a split secound which isn't ideal , even though some v12s he has done do work like that , but with my set up it cannot be run in that manner ,

I also agree with you that the 65s seem too lean , I wasn't that happy for him to jump from 72 to the 65 , but have to repect what equipment he has and also the cars he has tuned over the years , a lot of blown ones ,

[cobalt327]

I'm guessing the large jump down to 65 jets were to see that the O2 sensor was responding as it should. A small jet change might have gotten 'lost', where a big change should be easily seen. As long as he didn't run it into detonation (and I'm sure he knows better), the big change didn't hurt anything. Now, if he were to try to do a full pull that way, I'd stop him- unless it wasn't running lean jetted like that. And I have to assume he knows what he's doing. But all that said, mistakes are made- even by the best. It's your engine and your "dime", so if there's any question in your mind, you HAVE to speak up.

[F-BIRD'88]

If it turns out that there is a imbalance between how much primary jet it wants when cruisng at part throttle load just on the primaries and the jet size it needs for correct WOT AFR, then the primary power valve restriction size and the primary high speed air bleed will need work. This is not unusual when using a N/A carb on a blower motor.

Thats why screw in swappable metering block orrifices are desired. When a carb(s) is tuned right for a blower it is very responsive in all modes and throttle inputs. It takes some work to get there.

Great to hear of you progress.. and getting the little bugs worked out.

[mustang 671]

thanks guys .

points are very valuable . i do have secoundary metering block on one carb as they are back to back so can only fit one in . but he swapped them for the sec plate and wanted to have both carbs set up the same . cobalt - spot on - he changed down as when i reversed in onto the machine he smelt it and said it was too rich and put in the 65 from the 72 for a starting point but did stress he wouldnt do any dyno pulls till the lambda sensors got us somewhere near to where it was needed.

fbird . thanks for the carb advise . its a mind field isnt it . i have a fantastic tuning book just on holleys and also for use with my 671 weiand blower . and step by step on what to do if a stumble flat spot etc etc , also on boosters there is a really good section.

plugs 5 and 6 fouled , so changed them at the same time as the jets.

once i get the crank senor sorted i will get it back up . the guy knows his stuff but i feel is a bit too ols school . for eg when adjusting the float level petrol was just trickling out the sight holes . didnt put anything to soak up the fuel , maybe im being to cautious,

as a builder i just get a machine and smash things apart so im sure others may think im a bit gun ho looking at me .

i just worry especially when its been a 10 yr project

[F-BIRD'88]

You cannot determine a jet change based on the smell from the exhaust at idle.
The main jets have very little/ nothing to do with this. Thats how you blow up engines.
I suggest you go back to the richer primary jetting for testing You want to start rich @ WOT.
The plugs fouled from the ignition fault, not the jetting.

The main jets do not effect the idle. And you cannot smell a "rich" AFR. What you were smelling was unburned fuel in the exhaust. (spark misfire, late timing at idle)
You do not want to test under boost with a main jet that is too lean @ WOT.

The 72's are big but a good safe spot to start testing with.
The carbs idle circuit may need work. fine tuning the idle feed restrictions and idle air bleeds.
Thats why they make and sell "blower carbs". cause they are set up for a blower motor.

The main jets do not come into play until you are well into the throttle. Anything below that is the idle /off idle circuit.
The power valves must stay closed at idle to idle clean too.

[F-BIRD'88]

My rough hunch is the jetting will end up 67 to 70 pri (with functional power valves) and 75 to 78 sec. (or two #21 sec metering plates)
The power valve channel restriction will need work. The idle feed restrictions and idle air bleeds will need work.
And the high speed air bleeds will need fine tuning once best jetting is found.
The power valves need to be boost referenced so they operate correctly on the blower motor.
So they see the vacuum/boost signal below the supercharger and react accordingly.

The prority is to not test with a jet that is too lean. Ignore the smell of the exhaust at idle, for now.
(once the ignition fault is corrected)

If you are going to dyno test with the primary power valves plugged, start rich on the pri jet . #72+++++

Like I said before you should at minimum tear these carbs down and get them ready for the blower and dyno testing.

Boost reference the power valves
remove the chokes and the choke horns. ( do not remove the bowl vent tubes)
modify the secondary metering plates to accept standard screw in holley main jets.
blueprint the vac sec housings. (leaks)(spring)

[F-BIRD'88]

You'd best verify correct ignition timing and fireing before dyno testing.
Incorrect spark timng or scatter will smoke this blower motor in seconds.
You are supposed to start power testing @a low modest boost/blower drive ratio say 5psi and sneek up on the boost and power. Not immediatly @ 10psi boost.

a little white grease or petroleum jelly on the holley bowl/metering block gaskets keeps them from sticky/tearing for jets changes.

You need a vacuum boost gauge on the intake manifold and a vacuum gauge on the base of a carb.
and be able to watch both while testing. AT WOT under boost the carb vacuum gauge reading cannot exceed the power valve opening-closing point with non boost referencing or it will go lean and burn up under WOT.
Thats why the power valve "boost reference" mod needs to be done, first.

[F-BIRD'88]

realize and remember you cannot smell a "rich" or a lean fuel mixture.

What you smell in the exhaust is incomplete combustion/unburned fuel and or late combustion-fuel still burning in the exhaust pipe. And what you may or may not smell at idle has nothing to do with the carbs main jets.

[mustang 671]

hi all - been a while. the weather here has been awful so last weekend was the first time I have been back on it since lasts posts. ok so as we had some fuel contamination last time so I thought I would drain the tank and clear all the lines. so I stripped the carbs down and blew out any debris and rebuilt. I then tried to undo the drain plug in the tank and as I was trying a little hole appeared from the tank and rusty water started to drain out. not good !!!!! so I think I have found the reason to a lot of my problems with bad running and starting . so I have ordered a new tank which comes this weekend so for now I have cleaned all lines out and run fuel from a can of high octane fuel. so I primed it. made sure all plug leads fired. made sure all plugs fired. and started it. it started straight up and after warming up it idled at around 900 rpm.

problems I have. front plugs either side are wet but plugs to rear are black with soot and front headers aren't as hot as ones towards the rear. seems to be running on all 8 though when rev'ed . however as I was running out of a fuel can I knew exactly how much fuel I was using. working on it all day Sunday and starting and running I used 4 litres of fuel . it was running on idle for a while and I revved a few times ( but only up to 2000rpm ) so my thoughts are I either have a leak or my idle circuit is way to rich. it doesn't change note by opening the air mix screws on the sides of the primary metering blocks. I am going to take the carbs off and block up and turn my eclectic fuel pump on to see if there is any internal leak anywhere. will also check again the transition slots underneath along with the throttle blades to make sure they only expose the amounts that should be.

checked the current power valves and they are not split. as I am on the idle circuit how can I lean off the idle circuit and get a less black/sotty plug and to get a more even burn on all 8 plugs. I understand on idle the blower may provide more fuel air mix to some plugs. and have heard that once higher rpm the mix will be more equal to all 8 plugs. currently primary jets are 70s and 1x set of sec are 78 with a another sec plate ( which I need to mod to take jets )

so staring from basics what /where should I begin ? when I went to the dyno the timing is set bang on at tdc with the stobe light. 17d at start-up going to about 22d at around 1200 rpm then heading quickly up to 30 -32d all out and then mainly flat timing .

cheers guys

[metalstorm]

Keep plugging away at getting it figured out but you have had a hard time so far so I hope things get better for you soon.