What should fuel pressure be?

[Bruce Edwards]

Yes you need to get the pressure done to 5 or 6 at the carb. As for a good temp?? if the mix is right it will find it own best. Every engine will be different the trick is not melting the top of the piston. A cast iron head will run hotter than a aluminum one so for me temp is not that much of a factor.
The idle bleeds should not see any effect from a jet change. The idle is not dependent on the jet size. The idle system gets it fuel mix from bleed holes in the air horn and the slots at the bottom of the bore just in front of the plates. Your idle screws change the air to fuel mix between these two areas and the way to see big changes here is to change the bleed jet size and as all but race carbs are not set up for this type of thing you have nothing to worry about.
If you want to know what I am talking about take off the air cleaner and look down the throat of the carb. See those little holes made out of brass on the sides? Should see two on each bore one small and one larger.

[blykins]

Thanks for your help, Bruce. I appreciate the input.

I like learning all of this stuff. I've always been a gearhead....and I've usually spent time on Mustangs....swapping rearends, clutches, working on this and that.

I bought my Cobra and went hog-wild.....Built the engine myself, built the tranny and setup the rearend. I love getting my hands dirty. Unfortunately, setting up a carb is something I don't know much about at all. I had to get my dad to help me on that since he grew up in the muscle car era.

It was a big learning experience though.....and Dad told me that he was proud of me for all that I have done and learned....so that makes it all worth while.

[Bruce Edwards]

Did you say Mustang?? My sister site is www.PonyCarStore.com
Shamless plug.

[blykins]

Yep. I'd like to have a buck everytime I've set up a set of 4.10 gears for my Mustang buddies.....Well, on second thought, I'd probably have about $5. hehehehe

One of my other buddies has an '03 Cobra....so I did his mechanic work for him....changed a clutch for him....did his upgrades for him....I think he put down around 450 to the wheels last time he had it dyno'd. Not too shabby......

[Bill Wells]

Bruce, not to hijack this thread, so briefly..I checked out your shameless plug site. i have a relative serving in Iraq , 2nd tour over there, who is restoring a 70 Cougar XR7 convert when he is in the States and is need of rocker panels. I told him I would look around for him while he is overseas, as 'puter time/Hemmings and swap meets dont seem to fit into his current job assignments...I did not see any listed on your site, but suspect it might not be all inclusive. do you have any ? reply offline if you wish . thanks. bill.

[Bruce Edwards]

Bill,

Sent you an email.

[Bruce Edwards]

Blykins,

Just went over this again and saw your post about 15" or 16" on your gauge. If you have that kind with that cam your timing must be set pretty high at idle. Still the 6.5 should be fine if that is your reading.

[Bill Wells]

Bruce, got it . thx. I replied to it offline..hope ya get it.

now, back to fuel pressure talk. Bill

[rblong]

Wow - this is a great topic. I won't hijack the thread, but I have been playing with my 750 demon on a 428CJ based on what some dyno guys told me. I am running 76 and 87. I will investigate some more and may jump in with some questions.

Bruce

[Bruce Edwards]

Your set up sounds more realistic as far as jet size goes.

[blykins]

RB.....I'm thinking you may have the right setup. I'm gonna go home this weekend and lean it up some with the jets.

Your setup and mine should be pretty close....

Bruce, I'd say I was wrong on the vacuum.....I'd say it's not that high. For some reason that number was in my head, but it doesn't really make much sense now that I think about it.

Initial timing is at 12 degrees.....

[rblong]

I started with 76/83 and the dyno guys said I was lean at WOT. I went to 79/87 and it was too rich at lower end, so I went back to the 76 on pri. I am getting a little popping as Bruce mentions, but I think I just need to tweak mix some. I have a new set up pipes I am putting on it so I am waiting to see what they do before I call it done. I will check fuel pressure though since I think mine runs higher than recommended.

[blykins]

Alright....I stuck a vac gauge on the carb today....it was around 12 inches.....

So the stock power valve that comes with the Demon (6.5) is probably close.

I also changed the jets back down.....put 78's in the front and 88's in the back...Still got a pop or two.....so may contemplate going a little lower. It's definitely not as rich as it used to be....but I hate to get it on the lean side. Just may keep it the way it is now....until I can get it on a dyno.

Also seeing the fuel pressure hit around 7 - 7.5 psi....too high?

[Bruce Edwards]

It is a bit on the high side but if the carb does not overflow you should be ok. Check your timing and plug wires for cross fire. Open the hood and start it up at night in a very dark area. Look around the plug wires for a stray spark.
What kind of plugs are you running?
A sigh you may be on the right track is that the plugs should look cleaner and you may see a small rise in the water temp due to better combustion at lower speeds as well as better take off.
Any pinging under load?
Is the vacuum nice and steady? 12.5 is pretty good and 6.5 would be pretty close. May want to go to 6 to be on the safe side.
Let me know what you find out.

[blykins]

Timing is 12 degrees initial.....

I'm running Champion plugs....can't remember the part # off the top of my head, but running the plugs recommended by Edelbrock for the cylinder head.

Plugs were looking a lot cleaner the last time I changed out idle air bleeds. Pretty impressed for a car that has been sitting and idling a lot.

No pinging that I know of.....of course I couldn't hear it if it did over the sidepipes.

The vacuum is pretty steady....it bounced between 11.5 and 12.

[blykins]

Oh yeah.....not popping as much as it did before I changed jets.....I can see a relation between the popping and the smaller sizes....probably just need to go down a hair more...

[Bruce Edwards]

The bounce could be a soft valve spring or a sign that it may wish a bit more timing. Try moving it up a touch and see if smoothes out. Sounds like you are on the right track.
So does it run better on the street?

[blykins]

To be honest Bruce, it's never really been "driven". I've had it out on the road in front of the garage a few times....but it's never had a good drive.

I changed jets and tinkered with the air bleeds again today.....checked it with a vac gauge....then took it out in front of the garage. The thing starts and idles like a champ.....and when I got into it a little bit on the road, it had really crisp throttle response.

Soft valve spring? I used the valve springs that Comp cams recommended with the cam. Not too soft.

It may not have had a good vacuum connection......Dad had the vacuum gauge line in his hand while I read the gauge.... I think he pulled the PCV line off the valve cover and shoved the vac gauge line up inside it....probably not the best of seals.

[Bruce Edwards]

Valve springs can get over stressed when installed if they are "stacked" to get the retainer in place.
Just a thought, I am not saying that is the problem. Take a good read off the carb to be sure you have a nice steady reading.
Of course if your cam is really tall and has lots of overlap you will have a low reading.
Again sounds like you are on the right track. A test drive will tell you a lot more than a run in the driveway.

[blykins]

It's thumpy, but not too radical.....230 degrees, .544" lift, 110 LS