edelbrock 500 jets and rods

[gd302]

would anyone with a bit of experience with these know a good starting point for re jetting to suit a 3.5 rv8?
at present the primaries have been changed to 6252 rods and 1421 jets,which are not in the calibration kit,this advice was taken from another site,its sat on an offy manifold and has a mild cam in it ,also range rover heads,i still feel its too rich as the plugs are sooty and so is the exhaust,the pump shot is also on its lowest setting,the engine is fitted to a westfield kit
just read the other thread on this and it suggests the rods and jets i have are correct

[sidecar]

You need a calibration kit from Real Steel.
The carb is fairly easy to work on but you need a torx driver.

Here's some grumph that I wrote on the cobra forum :-

Hi Chris,

I was in the same boat as you not that long ago, my RV8 was over fueling and I'd never worked on an Edelbrock carb. I also looked at the manual, in my opinion its rubbish and has at least one error in the charts

V8 Developments gave me some help over the phone, armed with that I bought a calibration kit from Real Steel and had a go at setting the carb up myself, (Any tuning shop that you go to will probably want you to buy a kit before turning up so you might as well have a go anyway).

You need to be very careful when removing the top off the carb as the gasket is very delicate, remove the air filter stud to avoid breaking the gasket, also watch out for the
clips for the choke and accelerator pump rods...they are microscopic!!

I agree with Wilf, you should either wire the choke open or remove it all together. I actually removed the choke plates but set it up to give a fast tickover when the choke knob is pulled (you need a single strand stiff choke cable if you are going to do this).

You also need some torx drivers to get the top off the carb.

Basically the carb has two modes of operation, cruise and power, the needles control the mixture strength along with the fuel jets, the needle springs control when the carb goes from the cruise mode onto the power step (the stiffer the spring the sooner this happens).

Using the following method you can compare different jet and needle combinations.

Take the two needle sizes (i.e 65x52) and subtract them from the jet size (eg 86), all the sizes are in thousands of an inch 86-65=21, 86-52=34. These two numbers are the size of the hole that the fuel can flow through, the larger number is the power step, the smaller is the cruise mode (The example that I used is what is supplied as standard with the 500 CFM carb). This setup is bad for a standard motor as it will over fuel and cause bore wash.

I found that you do not have to change the size of the holes much to make a big difference to the mixture strength (The plugs will show the change after a few miles).

I also tried 83 jets and 65x52 needles, ie 18, 31, it was as flat as a fart on cruise but OK on the step!

My motor is tuned but the following is the setup that I run with, 86 jets 67x55 needles, which is 19 cruise, 31 power mode. The pump rod is on the middle hole, the needle springs are orange (which is standard), the pilot screws are 2 3/4 turns out, which seems like a lot but it doesn't pick up quick enough if I lean them off too much (might have to turn them in 3/4 at MOT time!) The secondary jets are 94 which is standard.

It takes 5 minutes to change the needles (or rods as they are sometimes called) and it takes 15 minutes to change the jets.

I know other people have said don't mess with it and get it set up on a rolling road but IMHO if you make a note of all the settings that you have now then give it a go, whats the worsed that can happen? If you cock it all up just put it back to standard.

Check your float height before you do anything as mine were out.

When you get you kit draw up a table that gives all the combinations that you can try, remember to include the standard jet 86, and standard rods 65x55 with all the combinations. (I even bought a rod from another kit 65x52 to give me a bit more scope).



After a bit more banter I wrote this lot:-


I've had another thought about the pilot screws (which I reckon is where the immediate problem is unless its the pump over pressurizing the carb or duff float valves etc).
Before my motor had the stage three heads fitted the screws needed to be about 1 3/4 to 2 turns out, the heads effected the tickover mixture quite a bit. If your motor is more or less standard these settings maybe nearer the mark.

The way I checked was to do the following, (not very scientific but it works).

Warm the motor up with the screws set at 2 turns then gradually turn them in until you hear the revs drop slightly (the revs might even pick up before dropping, this is OK, it just the motor telling you it wants a leaner mixture) open the screws 1/2 a turn from where the revs start to drop.
Stop the motor and wind each screw fully home making a note of how many turns they were open. Wind them back out that amount.

Take the car for a drive and from a reasonable speed take your foot off the gas and allow the engine to slow the car down to maybe 30 mph, then feed in a very small amount of throttle, if the engine hesitates for a fraction of a second or does not respond at all until you press the throttle more its running lean, open each screw 1/4 of a turn and try again. Keep repeating the test opening the screws until it picks up properly. Don't press the thottle too quickly or the accelerator pump will dump a load of fuel into the manifold which will spoil the test. Basically you just need to get rid of any hesitation and not go any richer than that. (After a while you can even feel the difference with 1/8 of a turn on each screw).

Once you've got that sorted your car will run OK but heed my words with regards to the standard setup over fueling your RV8, it will damage the bores if you leave it long enough.


The carb can suffer from fuel evaporation, even more gumph!!:-

I have a dual plane manifold which has a bridge that effectively cuts the carb in two. I read in a book that it is possble to cut this bridge down to increase the breathing ability as each cylinder as gets "access" to all four barrels of the carb but without the charge robbing that can occur with a single plane manifold, some loss of power low down maybe the price you have to pay.

I chickened out of cutting the bridge but fitted a spacer with one large hole, (Cheaper than a manifold if the motor complains!). I can confirm that it still runs OK and does start better when hot with the spacer fitted.

My spacer is only about 8mm thick so maybe it isn't thick enough to make any difference to the power at the top end or bottom end!...starts better though.

cheers,

Pete.

[gd302]

what spec is your engine? it looks as if you have only had to go 1 stage lean cruise and power to sort out your problems

[Eliot]

I had heatsoak on these with a rover (and chevy for that matter) - first thing to do is fit a 1" heat-resistant spacer and the other thing i would suggest is recirculating your fuel back to the tank via a restriction (i used an old jet in the return line).

As for tuning them, get the calibration kit and then buy or borrow a wideband lambda sensor - then you can see exaclty whats going on, rather than tying yourself up in knots trying to decide whether a change has made any difference or not.

Then if you get sick to death of carbs, you can use your wideband with most aftermarket fuel injection systems too.

[Paul B]

would anyone with a bit of experience with these know a good starting point for re jetting to suit a 3.5 rv8?
at present the primaries have been changed to 6252 rods and 1421 jets,which are not in the calibration kit,this advice was taken from another site,its sat on an offy manifold and has a mild cam in it ,also range rover heads,i still feel its too rich as the plugs are sooty and so is the exhaust,the pump shot is also on its lowest setting,the engine is fitted to a westfield kit
just read the other thread on this and it suggests the rods and jets i have are correct

GD301, I've posted my jet sizes earlier in this section, if you go back a few weeks there is a whole load of discussion about it.

I also recommended moving the accelerator pump rod to the outermost hole, to squirt less juice in, else it floods the stuff in.

Eliot, I also have some starting problems after it has been shut down when hot, but it is limited to a few seconds cranking before it fires up. I bought a phenolic spacer recently but haven't got round to fitting it yet. I'm not sure if it is actually petrol evaporation that causes it, as I have an electric fuel pump that should refill the carb as soon as it is turned on.

[sidecar]

would anyone with a bit of experience with these know a good starting point for re jetting to suit a 3.5 rv8?
at present the primaries have been changed to 6252 rods and 1421 jets,which are not in the calibration kit,this advice was taken from another site,its sat on an offy manifold and has a mild cam in it ,also range rover heads,i still feel its too rich as the plugs are sooty and so is the exhaust,the pump shot is also on its lowest setting,the engine is fitted to a westfield kit
just read the other thread on this and it suggests the rods and jets i have are correct

GD301, I've posted my jet sizes earlier in this section, if you go back a few weeks there is a whole load of discussion about it.

I also recommended moving the accelerator pump rod to the outermost hole, to squirt less juice in, else it floods the stuff in.

Eliot, I also have some starting problems after it has been shut down when hot, but it is limited to a few seconds cranking before it fires up. I bought a phenolic spacer recently but haven't got round to fitting it yet. I'm not sure if it is actually petrol evaporation that causes it, as I have an electric fuel pump that should refill the carb as soon as it is turned on.

Hi Paul,

I believe in your old post you stated that you were using 6252 rods and 80 primaries. That would give a cruise figure of 18 and power step of 28 which is a lot leaner than my setup of 19,31, I doubt that my motor would run on those settings. I believe that Jim (of JRV8) uses 21, 31 but fits a 92 secondary instead of 94.

I guess every motor is going to need a slightly different setup due to different cams, exhaust, etc. The exhaust gas analyiser is a good one but I reckon that you can still get it quite close looking at the plugs and much better than the out-of-the-box setup which is way too rich.

I also run an electric pump but it only works when there is oil pressure so the fuel evaporation was a real problem for me, with the carb top off you could see the fuel boiling in the float bowls! I run an over ride switch so that I can prime the carb before cranking the motor.

Regards,

Pete

[gd302]

thanks for the input,i know its a job for the rolling road but its nice to know what others have done

[ppyvabw]

would anyone with a bit of experience with these know a good starting point for re jetting to suit a 3.5 rv8?
at present the primaries have been changed to 6252 rods and 1421 jets,which are not in the calibration kit,this advice was taken from another site,its sat on an offy manifold and has a mild cam in it ,also range rover heads,i still feel its too rich as the plugs are sooty and so is the exhaust,the pump shot is also on its lowest setting,the engine is fitted to a westfield kit
just read the other thread on this and it suggests the rods and jets i have are correct

Mate, what ignition system have you got on it, includint the leads. I had this problem, I was convinced it was running rich and no amount of jetting and adjusting fixed it, the plugs were black and it ran like complete *****. The rolling road guy said it wasn't running rich, but he put the throttle pump on the weakest setting to no result.

I've posted this before, it turned out to be the ignition leads. After contacting RPI they strongly recommended using magnecor leads with a good ignition system. I didn't believe it at first, thought it was just a selling ploy, but the leads fixed everything!!!

Change the ignition if you havn't already and put good leads on, it will fix it I suspect.

The out of the box setting were almost right for me, a bit leaner in cruise and richer with the secondaries!! with the secondaries and it runs nicely. thats on a 3.5

[gd302]

running with magnecor leads and a mallory dual point which has been converted with a pertronix ignitor

[Paul B]

Hi Paul,

I believe in your old post you stated that you were using 6252 rods and 80 primaries. That would give a cruise figure of 18 and power step of 28 which is a lot leaner than my setup of 19,31, I doubt that my motor would run on those settings. I believe that Jim (of JRV8) uses 21, 31 but fits a 92 secondary instead of 94.

I guess every motor is going to need a slightly different setup due to different cams, exhaust, etc. The exhaust gas analyiser is a good one but I reckon that you can still get it quite close looking at the plugs and much better than the out-of-the-box setup which is way too rich.

I also run an electric pump but it only works when there is oil pressure so the fuel evaporation was a real problem for me, with the carb top off you could see the fuel boiling in the float bowls! I run an over ride switch so that I can prime the carb before cranking the motor.

Regards,

Pete

Thanks for the info Pete. I'd like to get my car on a dyno sometime, just to see how close/far out the fuelling actually is, but I have little or no idea what a couple or three dyno runs would entail or cost. Or whether the dyno guy would have the jets or know how to adjust my carb.

Any suggestions? I'm in the Midlands, Stafford.

[ppyvabw]

running with magnecor leads and a mallory dual point which has been converted with a pertronix ignitor

Ok, well ile shut up then!! ile try and remember what jets i got in mine, cant remember the sizes and im not at home at the minute.

[sidecar]

Hi Paul,

I believe in your old post you stated that you were using 6252 rods and 80 primaries. That would give a cruise figure of 18 and power step of 28 which is a lot leaner than my setup of 19,31, I doubt that my motor would run on those settings. I believe that Jim (of JRV8) uses 21, 31 but fits a 92 secondary instead of 94.

I guess every motor is going to need a slightly different setup due to different cams, exhaust, etc. The exhaust gas analyiser is a good one but I reckon that you can still get it quite close looking at the plugs and much better than the out-of-the-box setup which is way too rich.

I also run an electric pump but it only works when there is oil pressure so the fuel evaporation was a real problem for me, with the carb top off you could see the fuel boiling in the float bowls! I run an over ride switch so that I can prime the carb before cranking the motor.

Regards,

Pete

Thanks for the info Pete. I'd like to get my car on a dyno sometime, just to see how close/far out the fuelling actually is, but I have little or no idea what a couple or three dyno runs would entail or cost. Or whether the dyno guy would have the jets or know how to adjust my carb.

Any suggestions? I'm in the Midlands, Stafford.

Hi Paul,

I don't know of any dyno places in the Midlands but who ever you choose will need the calibration kit and need to know how these carbs work. (They may think that its like a normal weber but it's not...unfortunately).

To be honest if you work out all the combinations of of rods and jets you can try the ones that are near what you've got now, the changes in mixture strength are quite coarse, you can easily tell when you gone too lean and you won't damage the motor if you realize that its too lean then just take it easy until you get home and change the combination.
My motor runs fine with a cruise of 19 but is flat as a fart with 18 so a small change in the number does make a noticeable difference.

A rolling road operator can only choose one of the combinations, the same as you. The problem is when you want a particular cruise setting, say 19 but you want a power setting of 30 or some other number that no needle can give you, you're stuck with the combinations that Edlebrock have decided.

Not all the combinations are listed in their mixture chart and there is at least one error in it! You are better off just working out the combinations yourself.

Anyway, good luck and post how you let on.

Regards,

Pete

[Paul B]

Hi Paul,

I don't know of any dyno places in the Midlands but who ever you choose will need the calibration kit and need to know how these carbs work. (They may think that its like a normal weber but it's not...unfortunately).

To be honest if you work out all the combinations of of rods and jets you can try the ones that are near what you've got now, the changes in mixture strength are quite coarse, you can easily tell when you gone too lean and you won't damage the motor if you realize that its too lean then just take it easy until you get home and change the combination.
My motor runs fine with a cruise of 19 but is flat as a fart with 18 so a small change in the number does make a noticeable difference.

A rolling road operator can only choose one of the combinations, the same as you. The problem is when you want a particular cruise setting, say 19 but you want a power setting of 30 or some other number that no needle can give you, you're stuck with the combinations that Edlebrock have decided.

Not all the combinations are listed in their mixture chart and there is at least one error in it! You are better off just working out the combinations yourself.

Anyway, good luck and post how you let on.

Regards,

Pete

Hi Pete,
My motor is basically bog standard apart from the manifold and carb, so that'll probably explain difference in the fuel requirements from your motor. This setup is basically what RPM (if i remember correctly) recommended but doesn't seem to get much by way of mpg. I haven't really tested it on a decent run but its looking like less than 20 to the gallon. With the 38dgas and offy I was getting a regular 23 mpg.

I'm not sure how much I've gained performance wise either as it was dialled in bit by bit as I swapped the carb settings around. Plus, the first few miles were done with a leaky carb overfuelling it, until it basically died from sooted plugs. That was gunge in one of the float needle valves. I cured that, swapped the jets over, swapped the squirt pump connection and drove again and it was better than before. I definitly recall some extra seat-of-the-pants power, but it is surprising how soon you get used to extra power.......

A mistake I almost made was trying to get the carb top off, with the airfilter stud locked down with a nut. A nut I had fitted a day earlier. Took me a few minutes to figure that doozer out. Could have resulted in £200 worth of scrap carb.

I'm offshore at the moment but I'll come back to this thread when I get home in a couple of weeks and see about having a play with needle sizes. My car is a little undergeared, which may explain the low mpg figures too. I have a 3.9:1 rear end with 28" tall tyres, so it spins the motor pretty fast. Great for squirting round town, but not too good on a longish run. Still, my Morris V Eight is hardly a practical, common-sense type of car.