Static, mech and vac advance set-up RV8 + Weber 500

sidecar · Post by **sidecar** » Tue Aug 09, 2011 4:13 pm

mk1storm wrote:Ok, cool. Will take a look in the next day or two and let you know what I’ve got in there.

Mike – To try and sort the transition between the idle circuit to the primary main jets (without fiddling with the accel pump – currently on outer most of the three holes by the way, was initially on middle hole) would I tweak the idle mixture screws or would the change of primary main jet (or both) sort this?
For additional info, the idle CO figure measured recently during the IVA test for my car (kit car) measured 2.7% ish on both banks I think it was (limit of 3.5% due to engine age)… I went for the rule of thumb 2 turns out on the idle mixture screws I think it was. Sound like they’re set too lean?

I have described a good way of setting up the pilot screws in the link that I sent to you, it has worked well on every engine that I've done. (Checked with a lambda probe)

The transition circuit is not adjustable on the Eddy carb, the pilot screws will have very little effect on this circuit although they may be feeding a very small amount of fuel into the venturi when the transition slots are also delivering fuel. The actual order of the flow of fuel is the curb idle circuit first which is adjustable via the pilot screws then to the transition circuit which is not adjustable. It then goes to the primary main jets with the rods in the low position. It then goes to the primary jets with the rods in the up position. The finial circuit to start delivering fuel is the secondary jets. There is an overlap between the circuits.

I have found that the accelerator pump can dump in too much fuel into a 3.5, when I was running a 3.5 I made an extension to the pump arm to reduce the shot. Two turns out for the pilots is in the ball park but is probably a bit lean, this would cause the pickup to be a bit jerky.

If your issue is that the car surges and does not respond to the throttle well say at 40 MPH and the fault is in the carb it will be the cruise circuit that is too lean.

At the end of the day you need to get the carb and the ignition sorted out if you want to get the maximum performance out of the engine! You need to know what jets and rods you have got fitted and what the critical figures of your ignition system are.

mgbv8 · Post by **mgbv8** » Tue Aug 09, 2011 9:09 pm

mk1storm wrote:Sidecar - If I were to bother with fiddling with a tee piece on the vac line and play around with some hole sizes (I guess it wouldn't actually take that long to mock stuff up) can I check my advance curve first without vac to set the baseline mech advance curve and then reconnect the vac, run the engine back up (at no load of course) to see what the vac addition is?

mgbv8 - For the engine's you've done for the MG mates, do you mean you've perm disconnected the vac system or just did that for the timing set-up? Are these running webers too?

Cheers for the info so far guys.... keep it coming!

Yep!
Ditched the vac alltogether and made sure the dissys were working as best they could. 2 of them eventually gave in and bought mallory dissy's.

mk1storm · Post by **mk1storm** » Wed Aug 10, 2011 8:40 am

Yes thinking about it, it is at speeds of around 40mph ish where it’s worst.

Regarding the accel pump, I’d seen the extension arm photo so for a few mins of the last drive I did I decided to take the linkage off the accel pump just to see what it was like without any accel pump fueling at all but it didn’t have an influence over the hesitation. My original thinking was that I might be getting a rich bog type issue due to the accel pump being too aggressive, of course the last run might have gone too far the other way without the accel pump connected. Anyway will get the rest of it sorted (ign, carb etc) and come back to look at the accel pump setting/mods.

Anyway bear with me and I’ll check the rods/jets and let you know what I’ve got, prob after the weekend.
Cheers for the help so far!

kiwicar · Post by **kiwicar** » Wed Aug 10, 2011 9:01 am

Hi
Sorting out the idle/transition to main jets also involves ensuring you are idleing on the idle cct and not on the transition slot, there is a description of what to do on David Vizard's book on carburetors and inlet manifolds. what it comes down to is ensuring you are not opening the throttle too far at idle by drilling air pilot holes in the butterfly, it then lets you set the idle mixture on the screws without compromising the action of the idle slot, then jetting the mains has far less effect on the idle mixture and the three components do the job they are intended to do.
Best regards
Mike

mk1storm · Post by **mk1storm** » Fri Aug 12, 2011 4:07 pm

Right, then.... some interesting findings this afternoon. Here are the rods and jets fitted to my carb:

Rods are 6252 and primary jets are 380.

I couldn't make out what was written on the secondaries.

So, looking at your spreadsheet on your link sidecar, that means my set-up is 19% leaner on cruise and 21% leaner on power step than the stock carb!!! Am I right? I double and triple checked the rods and especially the jet numbers.

So, what's the thinking regarding the best rod/jet combo to have a go at first? I honestly wouldn't now take any notice of my comments regarding how the car drives because as we already know, unless my dizzy has already been sorted it's highly unlikely to be particularly optimised.

Hopefully tomorrow or Sunday I'll get to look at the mech timing and I'll let you know what I have.

sidecar · Post by **sidecar** » Fri Aug 12, 2011 4:21 pm

mk1storm wrote:Right, then.... some interesting findings this afternoon. Here are the rods and jets fitted to my carb:

Rods are 6252 and primary jets are 380.

I couldn't make out what was written on the secondaries.

So, looking at your spreadsheet on your link sidecar, that means my set-up is 19% leaner on cruise and 21% leaner on power step than the stock carb!!! Am I right? I double and triple checked the rods and especially the jet numbers.

So, what's the thinking regarding the best rod/jet combo to have a go at first? I honestly wouldn't now take any notice of my comments regarding how the car drives because as we already know, unless my dizzy has already been sorted it's highly unlikely to be particularly optimised.

Hopefully tomorrow or Sunday I'll get to look at the mech timing and I'll let you know what I have.

I was going to post up a 'guessimate' of what the settings would be, what you have posted up looks like one of RPI's 'load of cobblers' settings.

I'm surprised that you can even drive the thing with it being that lean! (your percentage figures are correct)

I bet the secondaries are standard which are rich at WOT, they will be 395 (95's) The jets that are hard to read are the ones that are fitted as standard, if the jet in question is not fitted to any of the Eddy range as a STANDARD jet then the number stamps are much clearer.

Anyway a good setting to try would be 86 primaries (these are the standard ones) 67-55 rods, silver rod springs and 83 secondaries.

I've run the above settings on several 3.5 lumps and checked the settings with a lambda probe. The AFR figures were good for all modes of operation. Obviously every engine is different but I'll guarantee that your engine will run 10 times better than it does now!
Whilst your carb is in bits you should set the float heights, they can be miles out!

Jim of JRV8 can supply the jets and other bits, if Jim does not have them then Muscle Manta on this forum can also get hold of the stuff. There is no point in buying a calibration kit because it does not have 86 jets in it.

One other thing, I was working on an Eddy carb the other day, it would not respond to the pilot screws which had to be turned out loads of turns before the engine would run. We stripped the carb including removing the primary and secondary boosters, it all looked clean. In the end we totally stripped the carb and blasted every hole with compressed air, it was fine after doing this. In other words it all needs to be spotlessly clean!

mk1storm · Post by **mk1storm** » Fri Aug 12, 2011 8:44 pm

Yeah I went trawling back through the past posts and it does seem that those rods/jets are (or were) the set-up supplied by RPi.

By the way, my lump is a 3.9, do you reckon I should still try the set-up you suggest?

Yep float heights were checked this afternoon, both spot on.

Forgot to mention, springs were orange too.

Good point about not getting the calibration kit. Will indeed contact Jim, got some bits from him before.

As I said, if you still think that set-up is a good starting point for a 3.9 I'll go ahead and get that and give it a go (hopefully after also sorting the timing).

Thanks for the great help.

sidecar · Post by **sidecar** » Fri Aug 12, 2011 9:30 pm

mk1storm wrote:Yeah I went trawling back through the past posts and it does seem that those rods/jets are (or were) the set-up supplied by RPi.

By the way, my lump is a 3.9, do you reckon I should still try the set-up you suggest?

Yep float heights were checked this afternoon, both spot on.

Forgot to mention, springs were orange too.

Good point about not getting the calibration kit. Will indeed contact Jim, got some bits from him before.

As I said, if you still think that set-up is a good starting point for a 3.9 I'll go ahead and get that and give it a go (hopefully after also sorting the timing).

Thanks for the great help.

The orange springs are standard, they are a bit soft which means the rods stay held down in 'lean mode' when they would be better off being in 'rich mode' during medium to hard acceleration.

The 3.9 engine is not one that I've messed about with much, hopefully over the next month or so I will have a better idea how to set one up with regards to the carb.

I have done a couple of 4.6 lumps and the carb setting are not the same as the 3.5 settings even though the AFR does end being the same as the 3.5.

The 3.5 settings are 8.3% and 6.8% leaner than the base settings for cruise and acceleration.
The 4.6 settings are 16.9% and 0% leaner than the base settings for cruise and acceleration.

So maybe if you stick the 3.5 setting into your carb it won't be lean enough on cruise and will be too lean on acceleration. (But not as bad as the settings that you have now!)

I know that with a 4.6 running on the 3.5 settings the cruise is not as lean as it could be, this does not affect the way the car drives but the acceleration mode is too lean and I could tell that it was not as good as the base setting. My 4.6 runs 77 secondaries, but I have not seen much difference in the AFR with 80 or 83 secondaries.

Really it's a bit tricky to suggest settings for your 3.9.

The other thing is that you only want to be running 32-34 degrees advance with a 3.9

Edit...

I've been thinking! I reckon that the 3.9 will need percentage leaner figures somewhere in between the 3.5 and the 4.6. So you will want a cruise figure around 12% leaner and an acceleration figure around 2-3% leaner.

I've fed all of the rods and jets into my spreadsheet, unfortunately I can not get those percentages using any combination.

The best I can find is:-
86 68-52....12.5% and 0%
83 63-47.....7.9% and 0.2%

That is why in the end I made my own rods!

At a guess your secondaries will need to be around the 80 size.

I suspect that someone will suggest getting the engine setup on a dyno. This is OK as long as the dyno is a brake dyno because the part throttle and cruise can be setup whilst the revs are held constant. I don't think you can do this with an inertia dyno, the engine revs are always rising. Also the bloke running the dyno need to know his stuff AND have the rods and jets for the carb. I'm not sure rolling roads are anything other than inertia dynos.

I think that buying an LC1 or something similar and then doing the carb yourself is cheaper and more satisfying in the long run. Just my humble!

mk1storm · Post by **mk1storm** » Tue Aug 16, 2011 6:45 am

Cheers for the extra info sidecar.

Sorry for the delay in replying, Fri evening Mr Lurgy turned up and have been feeling rough ever since!

Yeah in the long run will need to go down the route of a RR session or buying some gear to have a play myself, but would like to get things a little closer in terms of set-up for the time being so I can enjoy driving the car before the summer is over... I can then look to do some proper tweeking in the new year.

Might see what rods/jets I can get for what money and maybe see about getting a couple of combinations to try if they don't end up being too much.
I suppose I could use my primaries for the secondaries (80).

Right, best get on and order some up and see what I get!

Still not done the mech adv check yet, that was planned for the weekend until it got scuppered! Will have to leave until this weekend now. Hoping my set-up is std, therefore meaning I have some good potential gains available with an optimised adv curve

Thanks.

DEVONMAN · Post by **DEVONMAN** » Tue Aug 16, 2011 8:43 am

mk1storm wrote:
Still not done the mech adv check yet, that was planned for the weekend until it got scuppered! Will have to leave until this weekend now. Hoping my set-up is std, therefore meaning I have some good potential gains available with an optimised adv curve

Thanks.

When you remove the baseplate to fit different springs, check out the marking stamped on the weights. (Difficult to see). It will be either 9 ,11 or 13 degrees. This is the max that the mechanical advance has been set at in distributor degrees. So double this gives engine degrees 18, 22 or 26.
For a 3.9 you are looking for about 32-34 degrees max mechanical advance, so if the dizzy is marked 9 degrees (18 engine degrees) then your static advance needs to be 14-16 degrees to achieve 32-34 total degrees advance.

Even though the dizzy is marked the total advance should also be checked with a timing light.

Cheers Denis

mk1storm · Post by **mk1storm** » Tue Aug 16, 2011 9:15 pm

Yeah I'll have a good look at the dizzy once apart (well after the strobe checks).

Regarding the rods/jets, found this.... quite interesting. Shows what RPI are currently proposing (83 jets, 65-52 rods).

http://www.ebay.co.uk/itm/Jet-needles-j ... 2c5e37c5ab

mk1storm · Post by **mk1storm** » Tue Aug 16, 2011 9:24 pm

Ah, but this is what they have for a 3.5 (80 jets, 62-52 rods) - this is what I have... which is what I was told when I got the carb 2nd hand...

http://www.ebay.co.uk/itm/Weber-Carter- ... 27bd662b8c

So 80 62-52 for a 3.5 and
83 65-52 for 3.9 and 4.6's....

sidecar · Post by **sidecar** » Wed Aug 17, 2011 4:55 am

mk1storm wrote:Ah, but this is what they have for a 3.5 (80 jets, 62-52 rods) - this is what I have... which is what I was told when I got the carb 2nd hand...

http://www.ebay.co.uk/itm/Weber-Carter- ... 27bd662b8c

So 80 62-52 for a 3.5 and
83 65-52 for 3.9 and 4.6's....

Basically I would not take a blind bit of notice what RPI recommend, their setups do not work very well at all. Muscle Manta (Paul) phoned them up and gave them settings for the 3.5 and 4.6. Chris at RPI just did his usual....Tried to sell Paul a black box ignition amplifier!

The 83 65-52 setup is 16% leaner on cruise which is OK on a 4.6 but it is 10% leaner on acceleration which is no good at all.

The 80 62-52 setup is just too lean everywhere for any engine.

Paul and I worked on a 3.5 for a bloke the other day, it had RPI settings in it (I guess the 3.5 settings), the car was not nice to drive. After we had sorted the carb the bloke has spent the following weekend just driving around for the hell of it because the engine actually responded to the throttle! We are now building him a stage II 3.9.

In answer to your other post, yes you can use primaries in the secondaries, they are the same type of jet. You can use any rod and any jet even if they are not listed in the 500 calibration kit.

I can send you the spreasheet that I use for calculating the precentages if you like, You just whack in a jet and rod combo and it will compare it to the reference set at the top of the spreadsheet if you want it you will need to PM me an email address.

You can even get to the stage of modifying rods, I have done this by turning them down but you do have to be very accurate, one thou out and the rod is scrap! My 4.6 runs with a 69 thou cruise just fine, I then made a 70 thou cruise rod, I could not drive the car at all!
Another method which is described in Vizards book on Carbs and Manifolds is to file 'flats' on the rods as in some ways this is easier to do.

Obviously if you start modifying rods then you need some method of actually checking the AFR. (apart from on cruise which you can do by 'seat of the pants')

mk1storm · Post by **mk1storm** » Wed Aug 17, 2011 6:28 am

Yeah don't worry I shall not be taking any notice of their recommended settings!.... I've seen enough posts from enough people on this forum to be sure of that.

Right, emailed Jim ref supply of rods/jets, lets see what he comes back with.... Want to get this sorted now and get driving about!

sidecar · Post by **sidecar** » Wed Aug 17, 2011 6:38 am

mk1storm wrote:Yeah don't worry I shall not be taking any notice of their recommended settings!.... I've seen enough posts from enough people on this forum to be sure of that.

Right, emailed Jim ref supply of rods/jets, lets see what he comes back with.... Want to get this sorted now and get driving about!

Just added a load more 'gumph' to my last post as you were writing yours, let me know if you want the spreadsheet.

It does look like I'm on a witch hunt over RPI which I'm not but really they should not say crap like the following..

"The Weber Edelbrock 500 (1404) is not a jet fussy carb"

I'd say a one thou difference in rod size messing up the carb as being quite fussy.