Jer82Z28

I think my carb is messed up.

Since I put my new carb in it's been running rich, the stock jet/rods made the car seem like a coal burnin steam engine.
I have the smallest primary jets and largest rods in out of my jet kit and it still runs on the rich side, but not too bad.
I took it for a ride tonight.
cool night, humid, higher than normal pressure
I started it up and the driveway was a cloud of smoke, smelling of gas. oh well I take off and moments later i notice on my a/f guage the engine is running normal! I give it gas and the guage goes further lean, almost off the scale lean and I feel a missing cylinder.

I drive around like that, normal driving and it was dancing around lean/normal, as the rpm's got past 3000 on part throttle it would move its way back to the rich side.
I go to race a punk and i take off easy and go wot, I get a couple real bad misses, the engine sounds like it wants to die (at 4500rpm) the tach was dancin around pretty bad. I let off and it ran normal after that. I tryed to repeat the lean spot on a backroad, but it never came back.

the thing is, the engine runs pretty damn good when the guage is showing extreme lean. I wasn't watching the guage when i was racing though.

It's acted up like this before, but not the massive lean spot like tonight. I'm trying to find a connection with environment conditions but so far, only on cool nights only sometimes

anyone experiance something like this??



PS- the punk still lost

F-BIRD'88

Put the stock rods and jets and power step up spring back in. Even at Alberta's elevation you don't need to go that lean.
Check fuel pressure at idle, 6psi max.
Check float level and drop
Check to see if the rods are moving up and down in the jets
and that the jets are screwed in tight.
Should only neede to go 1 or 2 stages leaner from stock to
correct for altitude.
Check fuel flow and pressure at Wot.
Wouldn't trust that A/F guage. if you have a tiny exhaust leak it can suck in O2 and give a false reading.
CHeck for a vacuum leak..... Ignition problems look like
carb problems.

ronterry

I disagree to a point. Edelbrock 750's come rich as **** out of the box for a SB350.

I live at 6300 feet, and gave up on jetting with the 1407 chart with my 750, and started using the 1405/600 chart.
The baseline on the 1405 chart is .100Pri/.095Sec @ sealevel vs. .113/.107 for the 1407/750.

I'm down to .098/.092 - 73x52, and still seeing a little sout on my plugs. My plugs foul quick on anything bigger than .104 (remember that in my case the sugested setting on the 1407/750 chart @ 6300 = 8% lean. That would have been .107/.101 ??? yea right !!!)

I also had the same lean spot your talking about, and I solved with the silver springs. My performer RPM Cam pulls 16PSI @ idle @ 6300 feet !!!
You'll need to see what you vacuum is at idle, and just devide by two, and pick the spring closest - this is good enough.

I would agree by double checking your fuel pressure, and set to around 5.5
...and since you where running very rich for a while you might pull a plug, and make sure there not all carbon fouled with fluffy black ****.


Ron (Still not done tuning my Edelbrock 750)

Jer82Z28

I pulled a few plugs and ithey've been showing me the same that the guage has so far.

trust me when I say stock jets/rods is waaaaaay too rich

maybe I'll get a jet kit for 1405?

I think I'll search again for some vaccum leaks and check my pressure.

thanks

F-BIRD'88

Select the power step up spring to a value that is lower than what
you see on a vacuum guage while idling in gear(not neutral)
If you have a manual trans do it while rolling along slowly in gear with the clutch out.
With a performer rpm cam that would be 4" or less
which is the yellow or blue spring.
If you just take the vacuum reading in neutral and divide by 2
you will still be in power rich (rods up at idle in gear)
This will cause you to have a rich idle. When you try to lean down the jetting to correct the idle, the full throttle jetting will be too lean.
Do this first, before you start jetting away from stock.

ronterry

4" off the full vacuum port on the driver side, right? I checked it in gear, and it dropped a whole 1" to 15". I might be able to get 4" off the part time vacuum on the driver side.

I still get a little stumble on part, but it pulls hard from bottom to top end. My G-Tech is on dope, cause I think it peaked at 138 or so, but It pulls harder than my Vette. I might just bight the bullet, and get one of those pro units. BTW: It showed my Impala going 120 HP driving at 20MPH in a parking lot. I must of dropped it to many times

...also the stumble might be my fault since I took a little material off the sec. vacuum plate

Remember the Lobe sep. on the RPM cam is 112 deg.

Ron

Sitting Bull

I can tell you that Alberta is definitely MUCH more humid than normal this summer. And wretchedly HOT too

The jet stream has shifted, as per usual when el nino is showing up, and we are getting the moisture in the air that is normally seen 1000 - 1500 miles south of here.

We are usually around 30% humidity. This summer we are at twice that.

This is probably messing with our carbs. I know mine is acting funny too, and I just had it rebuilt in May. Right now it is sometimes stumbling in the 3000 rpm region, like there isn't enough fuel coming through. Prior to this humidity I had no problems.

F-BIRD'88

I have the funny feeling that your cam is/may be a bit milder that 234/244@.050 an .488/.510" lift 112 LCA. (performer RPM cam)
I have the 214/224 .442/.465" 112 and I don't think that I pull that much vacuum in gear. Unless you have High bleed down Variable lifters Like Rhoads. Wouldn't be the first time a cam was miss-labeled.

I wonder what effect the altitude has on your vacuum guage?
It is calibrated for Sea Level. "O" being 14.7psi
At significantly higher elevation there is less air pressure
and weight to act on the guage (at rest) so it will always start out low, and not act on the spring (mechanizm) in the guage in the same way. That would explain your high vacuum readings
on cam that is known to be fairly low vacuum and marginal on power brakes on a lot of cars.
This could cause you to select the wrong step up spring
based on what you see on the guage.

At any rate there are two things that don't jive.
You're getting more vacuum at idle that you should normally see for that cam. and your having more trouble that you should have
tuning your carb. Even at the high altitude and hot summer weather.


Anyways.... are you saying you shaved some material off the sec air valve counter weight? That would defeniatly cause a
flat spot as the air door would tip in too quick.

F-BIRD'88

Something else is causing the problem.
Your tuning or something else is affecting the way your car is running. Cause most people never have to adjust their carbs for the weather. Ever. Higher humidity displaces oxygen, which makes your carb seem richer so a lean stumble whould tend to disappear on hot days. You may still be getting "Winter Gas"
that is too volitile for hot summer weather. That will definatly give you drivability problems. And your carb would seem way too rich.
especially when the motor was hot. Try going to a different brand of gas station.

This makes sense. If I was a gasoline refiner/ wholesaler
and knowing the 3 week summers that you experience
in Albertia, I'd sell "Winter Gas" all year around cause you'd onlly get a few little complaints from a few insignifgant hot rodders.
Most people (with EFI) (the majority) would never notice. And then It would snow again.
I'd save a lot of money and less headaches.

HUMMM....

ronterry

You have summarized something I have suspected for more than a year now. This engine only has 200-300 miles on it, and when I assembled the engine - in my profound wisdom, I did not degree or double check markings. I bought the cam at a Checker super shop, and the box was opened, so I always suspected that it was a performer, and not the RPM. It also feels flat at 5400!!!
But feels awfuly strong for a mild grind, unless this is a testiment to the Eddie RPM heads?

I went out to the garage and put a vacuum hand pump and the gauge head to head. They had identical readings all the way up to 15".


Ron

ronterry

I found this on Edelbrock website.
"With 10 to 12 inches of manifold vacuum at idle, Performer RPM cams have more lift and duration than most street camshafts."

I guess that cam does pull some vac! Still don't understand why I have 15. I would think that at this altitude(24"@6300) it would be lower than "10 to 12"?

I need to degree my cam, and double check no less.

Ron

Jer82Z28

I get 12... PSI? on the vaccum guage in gear
so i put in the orange springs the carb still runs lean on part throttle and I have inconsistant part throttle miss.
the vaccum guage was twitchin on me while I was testing though, is that normal for a higher lift cam? otherwise maybe I have a bit of an ignition miss.. perhaps a plug is beginning to foul.
the guage would twitch and the engine lopes uncharacteristically..
perhaps a manifold leak also...

If I give it just the right amount of gas it goes off the scale lean, yet drives fine. no stumbling or lean spots.

F-BIRD'88

Yes a twitching guage means one cylinder is not working.
Could be an ignition problem, a vacuum leak or a
a problem with one of the valves (sticking or leaking or a bad spring). But definatly a problem, the guage should be nice and steady at idle.

F-BIRD'88

I would go along with 10/12" vacuum in neutral (less in gear)
for the performer rpm cam with normal hyd lifters.
It would be some what rough at idle too.
You may be right about getting the wrong cam in the right box.
That happened to me when I bought a BB LS-6 cam for my 454
and got a Marine hydraulic instead. I only found out after trying to adjust the lash to no end. (Solid cam). GM took it back and supplied a new cam and lifters.

You might want to check the cam lift to see if it is in spec.
You could mark a push rod at the guide plate (valve closed) then open the valve to full list and mark the pushrod again.
This dimention X 1.5 is valve lift.
Lifter bleed down may sqeuw the measurement but try it.

You car would still perform strong with a milder cam with
your performer RPM heads. The RPM cam is only better above
say 4500 compared to milder ones.

ronterry

I'm going to go out there and try that on both the intake & exhaust.

Add roller rocker to the twitchy gauge reading. I had one come off last week. I was able to mellow it out with the idle screws before I discovered it. The damn thing came off with the valve cover, & the nut/lock fell on the floor. The 2 intake showed no carbon, & a little oil leading up to this, plus no power the day before. Compression check was inconsistant, and never went over 40#.


If I had some oil deflectors I probably could just use like a dull knive, and while the engine running put flat against one of the guide plate and allow it to scatch the lift on the push rod ???



Ron

Jer82Z28

Would a sticking valve or bad spring show up on a compression test?

I did a test and they are all 150psi on the dot.

I'm going to check my plugs for fouling, I can feel an inconsistant miss at part throttle, not enough to be an ignition prob I don't think.

any other symptoms that I can look for to determine if I have valve probs or weak springs?

ronterry

I stumbled across this http://www.iwemalpg.com/Vacuum_gauge.htm
It might help.


BTW: I pulled the cam yesterday, and the markings resembles a crate motor cam I had sitting around. It had no references to a RPM cam, so I ordered what I hope is a real RPM cam!!! Last time a buy a cam in an opened box. I also ordered a degree kit!!!

Ron

F-BIRD'88

I would look real good at the whole ignition system.
New parts or not. This is usually where the problem lays.

Any thing that would cause a valve to not seat properly would affect a compression test. But if you have 150 in all cylinders
that would only leave the possibility of a bad valve spring.
A bad valve spring shows up as a rapid jumping guage when you
rev up the motor. You might want to check for a wiped cam lobe too. Just start the motor up with the valve cover off and watch the valves moving, a bad lobe will be easy to spot.
Other than that I'd look for a vacuum leak or ignition problem.

F-BIRD'88

Ronterry:

The dirty rotten buggers eh! Giving ya the wrong cam.

I'm curious,

What cam lift did it turn out to be anyways?

You can just measure the major and minor diameters of a lobe
with a mic or dial caliper,to get a rough idea of cam lift on mild cams.

Jer82Z28

Yea, I looked over my ignition components, didn't find anything until I took a pyrometer to my headers, fouling plug.
less than 5000km on the buggers too.
all my plugs were pretty dark, it runs really rich on idle, it doesn't like to run nice with anything leaner. I'm going to check my idle transfer slots. maybe my primaries are open too much on idle.

ronterry

Hey F-BIRD'88 over here~~~

I created a cam WTF thread over here, I'm sorry 'Jer82Z28' that my problem took over the thread, but I would rather have been in a simple A/F situation instead of being set back 350 bucks for cam. & degree set.

https://www.thirdgen.org/techbb2/sho...hreadid=121140

I'll be back on the A/F issue as some as I get the right ****ing cam.
BTW: This cam might require more fuel, so I'll have to adjust my figures.

Ron