Idling query

Richard P6 · Post by **Richard P6** » Thu Aug 27, 2009 9:25 pm

v8alex wrote:Bugger - I don't have 86 jets.

So for now, I'll do a rod change to 63-47 and see how that goes with the 83 jets.

Weather permitting, I'll update tomorrow...

Alex

83 63/47 set up will give you 8% leaner than stock on cruise and almost stock settings on power - far too rich for a standard 3.5

sidecar · Post by **sidecar** » Thu Aug 27, 2009 9:48 pm

Richard P6 wrote:
v8alex wrote:Bugger - I don't have 86 jets.

So for now, I'll do a rod change to 63-47 and see how that goes with the 83 jets.

Weather permitting, I'll update tomorrow...

Alex
83 63/47 set up will give you 8% leaner than stock on cruise and almost stock settings on power - far too rich for a standard 3.5

I don't think that its far too rich.

I've worked on loads of RV8 lumps running with the eddy carb. None of them would run properly when setup any leaner than 10% leaner than the stock settings. Kevin's (CastleMGBV8) post is the only time that I've come across a 3.5 that would run any leaner than 10% off the base setting.

Richard P6 · Post by **Richard P6** » Thu Aug 27, 2009 10:08 pm

I'll bow to your superior knowledge on this Pete as I am just a novice, but I have the 86 jets and 68/57 rods and my 4L stage one engine is working well with this set up.

It's 12.6% LTS in cruise and 11.6% LTS in power.

A/F is around 14.5 to 15 in cruise at 2-3,000rpm, and 13 or so when I accelerate. Drops to 10.5 to 11 during WOT.

I might even drop the secondaries down a stage just to see what happens.

I think I might run it up over the weekend and try the gasmeter in the exhaust to check out the A/F meter. Can't be too careful

CastleMGBV8 · Post by **CastleMGBV8** » Thu Aug 27, 2009 10:13 pm

Pete,

Could be that the slightly restrictive 14" x 2" air filter we are restricted to using in the MGB could be having an effect.

The 4.35 has .086 Jets and .067 x .055 Rods with silver springs. and standard secondaries for the moment.

Keviin.

sidecar · Post by **sidecar** » Thu Aug 27, 2009 10:25 pm

Richard P6 wrote:I'll bow to your superior knowledge on this Pete as I am just a novice, but I have the 86 jets and 68/57 rods and my 4L stage one engine is working well with this set up.

It's 12.6% LTS in cruise and 11.6% LTS in power.

A/F is around 14.5 to 15 in cruise at 2-3,000rpm, and 13 or so when I accelerate. Drops to 10.5 to 11 during WOT.

I might even drop the secondaries down a stage just to see what happens.

I think I might run it up over the weekend and try the gasmeter in the exhaust to check out the A/F meter. Can't be too careful

Hi Richard,

Please don't take anything that I say as "superior knowledge" !!

At the end of the day if your motor runs leaner than 10% off the base settings then that's proof enough that at least some motors will run leaner than this setting. (Although 12% is not much leaner than 10%).

I've not managed to get my two engines to run on cruise at 15:1 but they were both tuned so that might be the reason why. My mates standard 3.5 started to go a bit 'flat' with the 86, 68-57 setup that you are running. Just a 1 thou decrease in the diameter of the cruise part of the rod made his engine respond much better.

Like I said though, if the setup works for you then that's good. I think that Alex is just going to have to try a few combinations and see what happens. The good thing is that the cruise can very easily be tested just by seat of the pants driving. The acceleration and wot is a bit more tricky, I use an Innovate LC1 to help work out what's going on.

Also using a spreadsheet with all the jets and rods entered into it helps (I suspect that you have such a spreadsheet!) The Edelbrock chart in the PDF file can not be trusted, it's got errors in it!!!

Pete

CastleMGBV8 · Post by **CastleMGBV8** » Fri Aug 28, 2009 10:49 am

The other factor in addition to filter efficiency that we often forget, is engine compartment temperature which can have a drastic effect on air density and the resultant efficiency of the carbs calibration.

This can vary substancially between different vehicles, and unless addressed by way of a cold air induction system will probably need addressing with different jetting.

For example if you were having the engine set up on a rolling road this is normally done with the bonnet open so engine compartment temps will be a lot lower than when the bonnet is closed so the A/R could still be wrong when you get it back on the road.

Kevin.

sidecar · Post by **sidecar** » Fri Aug 28, 2009 11:43 am

I've been meaning to do some experiments with the two carbs that I've got in my possession. (An Eddy 500 and an Eddy 600) I finially got round to doing it today.

The main body appears to be the same for both carbs, the extra flow of the 600 comes from the fact that the primary boosters are smaller on the 600 and therefore create less of a blockage in the primary venturies. A while ago I ran these carbs back to back on a rolling road, the 600 made around 20 ftlbs more torque down at 2500 RPM, it made no difference at the top end. Anyway I could feel the difference on the road between the two carbs so I started to use the 600. The problem with it is that if I brake quite hard the mixture goes very rich and the engine virtually stalls…..very annoying. (The float heights and everything else have been checked on the 600)

Today I removed the primary boosters, all the jets, and the rods from the 600 and fitted them to the 500 carb, the result, well I could feel the increase in torque but the bloody stalling under braking issue is back.

I’ve put the 500 back to what it was before my messing about and decided to just check out the AFR as I still had the innovate LC1 connected up. My motor does not like a lean mixture, that’s for sure, it goes all rough when the idle mixture is leaned off more than 12.5:1. (2 + ¼ turns out on the pilots). I guess running a 285 cam could be having an effect?

Its now pi55ing down so I can’t report on the other settings with regards to AFR.

Anyway does anyone think that it would be too daft an idea to fit the 600 carb onto the manifold back to front?

sidecar · Post by **sidecar** » Fri Aug 28, 2009 2:10 pm

CastleMGBV8 wrote:Pete,

Could be that the slightly restrictive 14" x 2" air filter we are restricted to using in the MGB could be having an effect.

The 4.35 has .086 Jets and .067 x .055 Rods with silver springs. and standard secondaries for the moment.

Keviin.

Hi Kevin,

That setup is quite similar to mine so your filter can't be too bad, My filter is a 14x3" jobbie!

Regards,

Pete

CastleMGBV8 · Post by **CastleMGBV8** » Fri Aug 28, 2009 3:05 pm

Pete.

Mark (MGBloke) tried a 600 on his modded 4.6 and had similar results, not sure if he had the problem under braking though. You could do a search under his user name, won't be many as he doesn't post very often.

Not sure whether fitting the carb back to front is a good idea or not, depends on whether the manifold design favours only taking the flow from the primaries from the normal position at the front.

I think I need to look at a way of getting some cold air to the carb, as this will obviously help in getting a denser charge but willalso keep the carb a bit cooler, as it doesn't like it when it gets very hot.

Alex, apologies for hijacking your thread but it's all relevent.

Kevin.

v8alex · Post by **v8alex** » Fri Aug 28, 2009 3:23 pm

I had a little play this afternoon and changed the rods to 6552 - essentially 1 stage richer both in power and cruise (according to the Edelbrock manual - position 11 on the 1404 cal chart compared to the previous setting of position 10).

Anyway, the car run much better at lower speeds particularly in the higher gears when it was bogging a little - I can now cruise at just over 1,000 rpm in 5th and the car will pull away smoothly.

Took the revs through the range, gently and with a bit more passion and it seems to be OK.

I'm not sure now if this is too rich. The engine isn't a stock 3.5 - I have Stage 1.5 heads and a fast road cam. Guess I'll do a little more fine tuning with the mixture screws and float heights, then find some way of measuring the AFR.

I did some calcs on fuel economy on the previous setting and was returning approx 24mpg - unfortunately the rain stopped me doing more than a few miles today to check what the difference will be.

So - much improved from this drivability perspective

.

With respect to the odd idle (fast, normal or conk out) I noticed the throttle cable bracket on the carb/manifold was loose so I tightened up the nut - not sure if this made any difference, but the conking out mode seems to have gone away, but still occasionally 1,500 rpm idle when fully warm. I also notice the car idling normally, then surging to about 1,300 rpm, then back to normal and so on. More thought needed...

Alex

CastleMGBV8 · Post by **CastleMGBV8** » Fri Aug 28, 2009 3:36 pm

Alex,

If you have enough under bonnet room then I would seriously consider fitting a phenolic spacer between the carb and manifold, I found when the carb gets very hot the idle gets erratic, I think the fuel is actually boiling in the float chambers.

Kevin.

sidecar · Post by **sidecar** » Fri Aug 28, 2009 3:54 pm

v8alex wrote:I had a little play this afternoon and changed the rods to 6552 - essentially 1 stage richer both in power and cruise (according to the Edelbrock manual - position 11 on the 1404 cal chart compared to the previous setting of position 10).

Anyway, the car run much better at lower speeds particularly in the higher gears when it was bogging a little - I can now cruise at just over 1,000 rpm in 5th and the car will pull away smoothly.

Took the revs through the range, gently and with a bit more passion and it seems to be OK.

I'm not sure now if this is too rich. The engine isn't a stock 3.5 - I have Stage 1.5 heads and a fast road cam. Guess I'll do a little more fine tuning with the mixture screws and float heights, then find some way of measuring the AFR.

I did some calcs on fuel economy on the previous setting and was returning approx 24mpg - unfortunately the rain stopped me doing more than a few miles today to check what the difference will be.

So - much improved from this drivability perspective .

With respect to the odd idle (fast, normal or conk out) I noticed the throttle cable bracket on the carb/manifold was loose so I tightened up the nut - not sure if this made any difference, but the conking out mode seems to have gone away, but still occasionally 1,500 rpm idle when fully warm. I also notice the car idling normally, then surging to about 1,300 rpm, then back to normal and so on. More thought needed...

Alex

Hi Alex,

The 83, 65x52 setup (point 11 on the chart) is still pretty lean so I would not worry about it being too rich, Personally I think that it's still a bit lean but without setting up some sort lambda probe it will be hard to be sure. It's 15.9% leaner than base on cruise and 10.8% leaner on the powerstep.

Infact your current setup shows just how crap the edelbrock chart is, they show it as 8% leaner in both modes yet the maths shows that my figures are correct!

You know to get the cruise AFR right you can do what Edelbrock suggest which is keep going gradually leaner an leaner until the throttle becomes bad, then go one stage richer. Like I said before, the problem is that you can not use the eddy chart! (You will need to start at some point richer than what you are on now)

If you PM me an email address I'll send you an XL spreadsheet, all you have to do is wack in a jet and rod, the spreadsheet then shows how the setup will compare to the stock base settings.

What are your pilot screws set to?

Kev, I found the post that the chap you mentioned started, I even posted in the thread myself!

Richard P6 · Post by **Richard P6** » Fri Aug 28, 2009 4:33 pm

sidecar wrote:I've been meaning to do some experiments with the two carbs that I've got in my possession. (An Eddy 500 and an Eddy 600) I finially got round to doing it today.

The main body appears to be the same for both carbs, the extra flow of the 600 comes from the fact that the primary boosters are smaller on the 600 and therefore create less of a blockage in the primary venturies. A while ago I ran these carbs back to back on a rolling road, the 600 made around 20 ftlbs more torque down at 2500 RPM, it made no difference at the top end. Anyway I could feel the difference on the road between the two carbs so I started to use the 600. The problem with it is that if I brake quite hard the mixture goes very rich and the engine virtually stalls…..very annoying. (The float heights and everything else have been checked on the 600)

Today I removed the primary boosters, all the jets, and the rods from the 600 and fitted them to the 500 carb, the result, well I could feel the increase in torque but the bloody stalling under braking issue is back.

I’ve put the 500 back to what it was before my messing about and decided to just check out the AFR as I still had the innovate LC1 connected up. My motor does not like a lean mixture, that’s for sure, it goes all rough when the idle mixture is leaned off more than 12.5:1. (2 + ¼ turns out on the pilots). I guess running a 285 cam could be having an effect?

Its now pi55ing down so I can’t report on the other settings with regards to AFR.

Anyway does anyone think that it would be too daft an idea to fit the 600 carb onto the manifold back to front?

Very strange

Mine has been running perfectly for a week or so, but this morning on the way to work it was running at 16 A/F in cruise, 16 in moderate acceleration, and 16 at idle. It drove like a pig, stalling at junctions and bogging whenever I tried to touch the throttle. 16 is the leanest the A/F gauge reads so it could have been a lot leaner than 16:1

On the way home it was perfect again - sat happily in traffic idling at 600rpm, pulled away faultlessly, and accelerated like a saturn five rocket, very weird.

Just goes to show, if you are experimenting with jets and rods, try the setting for a few days before dismissing it as no good.

v8alex · Post by **v8alex** » Fri Aug 28, 2009 4:45 pm

Alex,

If you have enough under bonnet room then I would seriously consider fitting a phenolic spacer between the carb and manifold, I found when the carb gets very hot the idle gets erratic, I think the fuel is actually boiling in the float chambers.

Kevin

Yep - did that when building the engine for the exact reason you mention. I'm not too worried about under bonnet room - the air filter sticks 3" out the top

Alex

sidecar · Post by **sidecar** » Fri Aug 28, 2009 5:11 pm

Richard P6 wrote:
sidecar wrote:I've been meaning to do some experiments with the two carbs that I've got in my possession. (An Eddy 500 and an Eddy 600) I finially got round to doing it today.

The main body appears to be the same for both carbs, the extra flow of the 600 comes from the fact that the primary boosters are smaller on the 600 and therefore create less of a blockage in the primary venturies. A while ago I ran these carbs back to back on a rolling road, the 600 made around 20 ftlbs more torque down at 2500 RPM, it made no difference at the top end. Anyway I could feel the difference on the road between the two carbs so I started to use the 600. The problem with it is that if I brake quite hard the mixture goes very rich and the engine virtually stalls…..very annoying. (The float heights and everything else have been checked on the 600)

Today I removed the primary boosters, all the jets, and the rods from the 600 and fitted them to the 500 carb, the result, well I could feel the increase in torque but the bloody stalling under braking issue is back.

I’ve put the 500 back to what it was before my messing about and decided to just check out the AFR as I still had the innovate LC1 connected up. My motor does not like a lean mixture, that’s for sure, it goes all rough when the idle mixture is leaned off more than 12.5:1. (2 + ¼ turns out on the pilots). I guess running a 285 cam could be having an effect?

Its now pi55ing down so I can’t report on the other settings with regards to AFR.

Anyway does anyone think that it would be too daft an idea to fit the 600 carb onto the manifold back to front?
Very strange

Mine has been running perfectly for a week or so, but this morning on the way to work it was running at 16 A/F in cruise, 16 in moderate acceleration, and 16 at idle. It drove like a pig, stalling at junctions and bogging whenever I tried to touch the throttle. 16 is the leanest the A/F gauge reads so it could have been a lot leaner than 16:1

On the way home it was perfect again - sat happily in traffic idling at 600rpm, pulled away faultlessly, and accelerated like a saturn five rocket, very weird.

Just goes to show, if you are experimenting with jets and rods, try the setting for a few days before dismissing it as no good.

Hi Richard, Crap in the carb? (Not as in a course of action, but as in a possible cause of the problem!

)

Just been for a spin in my car, I'm running the 500 carb, 86 primaries, 67-52 rods (one offs made from a modifed set of rods), 92 secondaries, and the pilots set to 2+1/4 turns out.

The AFR's are:-

Tickover= 12-12.5:1 (Goes a bit rough if I lean it off anymore than this)
Cruise=13.5-14:1
Acceleration=12.5-13:1
WOT=11.5-12:1