Hi,
I've been battling poor running for some time and I'm most of the way there, my issue is locating poor running. Here are the symptoms:
Using the throttle to accelerate is fine, in fact good, the car pulls well with any amount of throttle.
Coming off the accelerator the engine pops and bangs from any high rev to around 2k.
It idles ok although you can hear a splutter.
The car will drive fine on occasion without a problem however it has been doing it most of the time recently.
The engine is a 3.5 Rover V8 with 9.75 compression and hurricane cam. The carb is:
Primary Jet - 80
Needles - 62 52
I've replaced most of the ignition, been around with the multimeter, checked fuel flow and nothing shows up. Is there anything I'm missing?
Edelbrock 1404 - poor running 3.5 V8 Rover
Moderator: phpBB2 - Administrators
your setup sounds like the sort of setup the RPI recommend, they don't know their arse from their elbow!
I've worked on loads of these carbs, on the 3.5 engine you can go around 8-10% leaner than the base (out of the box) setup on cruise, your current setup is 19% leaner. On the bigger RV8 you can jet the carb a bit leaner on cruise, maybe 16% leaner. This does not mean that the mixture is actually leaner because larger engines pull more vacuum, the result is that on cruise both engines run at about 14.5-15:1 Air Fuel Ratio. (AFR)
By the same token the secondary jets end up being smaller on larger engines compared to the 3.5 lump, the AFR at WOT needs to be around 12.5-12.8:1
As a rough starting point the standard 86 jets can be used with 67-55 rods, this setup will be 8% leaner than base on cruise and 6.8% leaner when on the power step. Be aware that the proper way to set the carb up is by use of an exhaust gas analizer!
I've worked on loads of these carbs, on the 3.5 engine you can go around 8-10% leaner than the base (out of the box) setup on cruise, your current setup is 19% leaner. On the bigger RV8 you can jet the carb a bit leaner on cruise, maybe 16% leaner. This does not mean that the mixture is actually leaner because larger engines pull more vacuum, the result is that on cruise both engines run at about 14.5-15:1 Air Fuel Ratio. (AFR)
By the same token the secondary jets end up being smaller on larger engines compared to the 3.5 lump, the AFR at WOT needs to be around 12.5-12.8:1
As a rough starting point the standard 86 jets can be used with 67-55 rods, this setup will be 8% leaner than base on cruise and 6.8% leaner when on the power step. Be aware that the proper way to set the carb up is by use of an exhaust gas analizer!
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Rossco
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Some excellent advice there from Sidecar.
A lot of suppliers think that as the carb is set up for a Chevy 350 or similar then it will be "a bit rich for a Rover but alright". This is nonsense, as Sidecar points out larger engines pull much more vacuum so when you put one of these carbs on a Rover then surprise surprise it runs lean as well as having poor atomisation.
A lot of suppliers think that as the carb is set up for a Chevy 350 or similar then it will be "a bit rich for a Rover but alright". This is nonsense, as Sidecar points out larger engines pull much more vacuum so when you put one of these carbs on a Rover then surprise surprise it runs lean as well as having poor atomisation.
To be honest I don't have much faith in rolling roads, I'm sure that a few of them are good but many of them just thrash the pants off your car which does look impressive, they then tell you that the jetting is alright. The reason that they do this is because they don't understand how these carbs work and therefore don't want to take the lid off the carb, they don't have the jets or rods anyway!. Changing the primary jets on one of these carbs will always result in a big change in the AFR, the jets go up or down in 3 thou of an inch in diameter, the change may well be far too big. You usually need to change the rods at the same time. The numbers on the rods are also just thou of an inch. It is the ring shaped area that the rod and jet forms which determines the fuel flow. You can actually richen the mixture by fitting a SMALLER jet and a THINNER rod! The rods have two diameters, when the vacuum is low the springs push the rods up so that the thinner tip is poking into the jet, this richens the mixture the fat part of the rod will be in the jet when cruising with a high vacuum, this leans the cruise mixture off.
Anyway, rolling roads...Its the cruise circuit that you are having issues with so the rollers need to be able to hold a steady load which is equivalent to around 30-50 mph on the road with the throttle 8/10 shut. Your acceleration circuit and WOT may also be wrong but that's a different story. Many rollers can not hold the engine at a steady load, they can only allow the car/engine to accelerate.
I set these carbs up using an Innovate LC1 in conjunction with a 'real' road and a box full of jets, rods, and springs! It can take a few hours!
BTW you can buy a calibration kit for a load of money, it seems like good value but it isn't, if you are lucky one set of rods might be near what you need but not spot on, all the other rods will be no use at all and that goes for the jets too!
My mate can supply you rods and jets on a return basis, in other words you can try a setup, if its no good you can return the stuff to be swapped out for the next combination that you want to try. (Muscle Manta on this forum). Over the years we have collected many jets and rods, loads that you don't get in the 500 calibration kit. Also the chart that Edelbrock use is wrong, they quote jet and rod combinations that are not leaner or richer by the percentage on their chart! I use an XL spreadsheet which will compare any jet and rod combo with any other. These days I have made or modified rods because sometimes you just can not get both the cruise and acceleration circuits sorted out to give the correct AFR figures with any of the standard rods. The combo can be critical down to one thou of an inch. I have worked on cars where it was undriveable on the cruise circuit but just taking 1 thou of the diameter of the rod richened the cruise up by 2 or 3 percent and the car was perfectly driveable!
As a rough guide the AFR figures that you need to aim for are below:-
Tickover......12-14:1 (This depends on many things, your engine will tell you what it wants when you twiddle the pilot screws, you just have to learn how to listen to your engine!) My engine has a fairly hot cam, my tickover AFR needs to be 12.2:1, if I lean it off to 12.5:1 it runs rough!
Cruise.........14.5-15:1. (Basically you want this as lean as you can go before the throttle response goes bad. I have never manage do go leaner than 15:1. I'm sure that you can go much leaner with EFI but not with one of these carbs!
Acceleration....12-12.5:1
WOT............. 12.5-12.8:1 (You don't want to see '13's flicking up on the AFR gauge, 12.8 is what most engine make best BHP on, running say two points richer at 12.6:1 may cost you 2 BHP, running two points leaner at 13:1 could cost you 10 BHP. (The bell curve on the graph is lob sided, you lose loads more on the lean side). This is despite 13:1 still being classed as a rich mixture, i.e. richer than the 'magical' 14.7:1 that people bang on about!
Anyway, rolling roads...Its the cruise circuit that you are having issues with so the rollers need to be able to hold a steady load which is equivalent to around 30-50 mph on the road with the throttle 8/10 shut. Your acceleration circuit and WOT may also be wrong but that's a different story. Many rollers can not hold the engine at a steady load, they can only allow the car/engine to accelerate.
I set these carbs up using an Innovate LC1 in conjunction with a 'real' road and a box full of jets, rods, and springs! It can take a few hours!
BTW you can buy a calibration kit for a load of money, it seems like good value but it isn't, if you are lucky one set of rods might be near what you need but not spot on, all the other rods will be no use at all and that goes for the jets too!
My mate can supply you rods and jets on a return basis, in other words you can try a setup, if its no good you can return the stuff to be swapped out for the next combination that you want to try. (Muscle Manta on this forum). Over the years we have collected many jets and rods, loads that you don't get in the 500 calibration kit. Also the chart that Edelbrock use is wrong, they quote jet and rod combinations that are not leaner or richer by the percentage on their chart! I use an XL spreadsheet which will compare any jet and rod combo with any other. These days I have made or modified rods because sometimes you just can not get both the cruise and acceleration circuits sorted out to give the correct AFR figures with any of the standard rods. The combo can be critical down to one thou of an inch. I have worked on cars where it was undriveable on the cruise circuit but just taking 1 thou of the diameter of the rod richened the cruise up by 2 or 3 percent and the car was perfectly driveable!
As a rough guide the AFR figures that you need to aim for are below:-
Tickover......12-14:1 (This depends on many things, your engine will tell you what it wants when you twiddle the pilot screws, you just have to learn how to listen to your engine!) My engine has a fairly hot cam, my tickover AFR needs to be 12.2:1, if I lean it off to 12.5:1 it runs rough!
Cruise.........14.5-15:1. (Basically you want this as lean as you can go before the throttle response goes bad. I have never manage do go leaner than 15:1. I'm sure that you can go much leaner with EFI but not with one of these carbs!
Acceleration....12-12.5:1
WOT............. 12.5-12.8:1 (You don't want to see '13's flicking up on the AFR gauge, 12.8 is what most engine make best BHP on, running say two points richer at 12.6:1 may cost you 2 BHP, running two points leaner at 13:1 could cost you 10 BHP. (The bell curve on the graph is lob sided, you lose loads more on the lean side). This is despite 13:1 still being classed as a rich mixture, i.e. richer than the 'magical' 14.7:1 that people bang on about!
Thanks for the replies 
I found the issue this morning, there is something wrong with the idle jet on the left side of the carb. I can move the idle mixture on the right and it works perfectly but on the left it barely does anything. On idle it is only the left bank spluttering.
I've booked it in with Airey Tuning which is near me to have it sorted, he has all the jets/rods in stock and does it for a fixed price. I'm really surprised none of the three garages I've been to with it have not noticed it but I supposed they're used to laptops and efi. I'll update the thread when I'm done, I can't wait to get it running properly, it'll be a first since I bought it last October!
I found the issue this morning, there is something wrong with the idle jet on the left side of the carb. I can move the idle mixture on the right and it works perfectly but on the left it barely does anything. On idle it is only the left bank spluttering.
I've booked it in with Airey Tuning which is near me to have it sorted, he has all the jets/rods in stock and does it for a fixed price. I'm really surprised none of the three garages I've been to with it have not noticed it but I supposed they're used to laptops and efi. I'll update the thread when I'm done, I can't wait to get it running properly, it'll be a first since I bought it last October!
MX5 4.6 V8
Previous of many SD1's back in the day!
Previous of many SD1's back in the day!
As Sidecar says..
I also use an Inovate LC1 system to calibrate carbs.
Resulting in several rolling road sessions with differend cars to be spot on.
Have three onboard systems and one system converted to be swapped between cars to calibrate cars, only a sensor bung has to be welded on those cars.
Indeed rolling roads mostly look at WOT power and so on WOT A/F ratio. Cruise conditions are mostly overlooked at those sessions as its hard to simulate.
I also use an Inovate LC1 system to calibrate carbs.
Resulting in several rolling road sessions with differend cars to be spot on.
Have three onboard systems and one system converted to be swapped between cars to calibrate cars, only a sensor bung has to be welded on those cars.
Indeed rolling roads mostly look at WOT power and so on WOT A/F ratio. Cruise conditions are mostly overlooked at those sessions as its hard to simulate.
'73 Ford Capri. 3.5 RV8, Magnacharger 110 Supercharger, Merlin F85 Heads, Water/Methanol Injected
'73 Ford F250, 6.7ltr V8
Building a GT40 mk2
'73 Ford F250, 6.7ltr V8
Building a GT40 mk2
Update
Thought I'd give an update as too many threads show no resolution!
Took the car to Airey Tuning near Winchester this morning. Within less than a minute Tom said the carb was running way to lean. He upped the jetting by 4 sizes before it started running properly. It's made a huge difference, more important than the performance is the heat from the engine has dropped dramatically. In fact from Winchester back to Southampton the fan didn't kick in once and the cabin is a lot cooler.
Performance wise is the drivability, it's been pretty poor performance since I bought it, today it felt and drove like a V8. Overall very happy, the power went from 150bhp to 200bhp which is more than enough for me
Took the car to Airey Tuning near Winchester this morning. Within less than a minute Tom said the carb was running way to lean. He upped the jetting by 4 sizes before it started running properly. It's made a huge difference, more important than the performance is the heat from the engine has dropped dramatically. In fact from Winchester back to Southampton the fan didn't kick in once and the cabin is a lot cooler.
Performance wise is the drivability, it's been pretty poor performance since I bought it, today it felt and drove like a V8. Overall very happy, the power went from 150bhp to 200bhp which is more than enough for me
MX5 4.6 V8
Previous of many SD1's back in the day!
Previous of many SD1's back in the day!
Re: Update
So just out of interest what jet and rod combo is it running on the primary side now? Also what secondary jets are fitted?southernd wrote:Thought I'd give an update as too many threads show no resolution!
Took the car to Airey Tuning near Winchester this morning. Within less than a minute Tom said the carb was running way to lean. He upped the jetting by 4 sizes before it started running properly. It's made a huge difference, more important than the performance is the heat from the engine has dropped dramatically. In fact from Winchester back to Southampton the fan didn't kick in once and the cabin is a lot cooler.
Performance wise is the drivability, it's been pretty poor performance since I bought it, today it felt and drove like a V8. Overall very happy, the power went from 150bhp to 200bhp which is more than enough for me
I told you that RPI are a bunch of dimwits!
LOL, no worries! The rods have three diameters, the main (longest) bit of the rod is just the rod its self, it does not have any control over the fuelling.southernd wrote:I'm a bit green in this area, he changed the rods in the centre part 4 sizes up, I can get the exact size if you like? I was a bit like a child when it was working, hand over the keys and I'm outta here
There is a section of the rod which is 5mm from the end of the rod down to about 15mm (i.e a 10mm length) which controls the cruise. Then the last 5mm of the rod controls the acceleration whilst running on the primary side of the carb. So really there are two important diameters for any given rod.
The rods don't really have stages, not like the jets which go up or down in size in 3 thou steps, 92, 95, 98, 101. (Apart from one-off jets which are factory fitted to some carbs, like the 100 jet).
On the cruise side of things for the rods the diameters go up in thou's of an inch....37, 42, 47, 49, 52, 55, 57. I can't see any pattern to how the diameters increase.
Anyway no worries, I'm pleased that your engine is running well now.
Interesting, just seen our threads running side by side...
Sidecar - Just out of interest how do I check(measure) what needles/jets are in place?
I notice there is maybe a number on the side of the jet? what does this relate to?
For the needle do I measure just past 5mm from the thin bit at the end with a vernier to get the size?
Sidecar - Just out of interest how do I check(measure) what needles/jets are in place?
I notice there is maybe a number on the side of the jet? what does this relate to?
For the needle do I measure just past 5mm from the thin bit at the end with a vernier to get the size?
The numbers on the jets and rods are a total pain in the ass to read but it is possible with a jewellers loupe....moppit wrote:Interesting, just seen our threads running side by side...
Sidecar - Just out of interest how do I check(measure) what needles/jets are in place?
I notice there is maybe a number on the side of the jet? what does this relate to?
For the needle do I measure just past 5mm from the thin bit at the end with a vernier to get the size?
http://www.ebay.co.uk/itm/LED-Jewellers ... xyCepScWvN
The numbers on the jets depend on the 'series' of the jet. the '3' series go from 377 up to 398. A 377 is 77 thou in diameter, the next being a 380, then a 383, then a 386...... Once the jets go over 100 thou in diameter they become a 4 series jet. 401 is 101 thou, 404 is 104 thou,..... 407, 410, 413.
The rods have two diameters, you can measure the tip and then you can measure about 10mm back from the tip. The tip diameter is the acceleration or power step diameter, the thicker diameter further back is the cruise diameter. a 62-52, has a cruise diameter of 62 thou, it has a power step of 52 thou. The rods are mega accurate, most vernier gauges are NOT good enough to measure them, a decent micrometer can measure them. The rods do have their diameters stamped on the side of them and as long as you can read the stamping then there is no need to measure them. (Unless they have been modified, which I do but then I always file off the number stamps if I have done this!)
Brilliant! Just what I need...sidecar wrote:The numbers on the jets and rods are a total pain in the ass to read but it is possible with a jewellers loupe....moppit wrote:Interesting, just seen our threads running side by side...
Sidecar - Just out of interest how do I check(measure) what needles/jets are in place?
I notice there is maybe a number on the side of the jet? what does this relate to?
For the needle do I measure just past 5mm from the thin bit at the end with a vernier to get the size?
http://www.ebay.co.uk/itm/LED-Jewellers ... xyCepScWvN
The numbers on the jets depend on the 'series' of the jet. the '3' series go from 377 up to 398. A 377 is 77 thou in diameter, the next being a 380, then a 383, then a 386...... Once the jets go over 100 thou in diameter they become a 4 series jet. 401 is 101 thou, 404 is 104 thou,..... 407, 410, 413.
The rods have two diameters, you can measure the tip and then you can measure about 10mm back from the tip. The tip diameter is the acceleration or power step diameter, the thicker diameter further back is the cruise diameter. a 62-52, has a cruise diameter of 62 thou, it has a power step of 52 thou. The rods are mega accurate, most vernier gauges are NOT good enough to measure them, a decent micrometer can measure them. The rods do have their diameters stamped on the side of them and as long as you can read the stamping then there is no need to measure them. (Unless they have been modified, which I do but then I always file off the number stamps if I have done this!)
