kiwicar wrote:Hi
If you cannot get the idle down and the throttle plate is fully closed it would suggest to me you have a big air leak somewhere in the body of the carb, probably one or both of the throttle shafts, a crack in the casting a dammaged throttle blade, it can't run at 1500-2000 revs without air going into the inlet, no matter how rich the carb is set, and if the air leakwas below the carb it would be very lean at idle, not what you are describing. The other possability is that the throttle peddle/ arm/ cable are sticking and the throttle is not closing for that reason. . .
Best regards
Mike
Hi Mike
I think you hit the nail on the head mate, checked the carb and cant any issue apart from a weak throttle return spring, will pick up another in the morning and try, I have a guy coming round to set up my ignition timing so hopefully we can get this sorted once and for all
Cheers Guys thank you very much for your useful posts
Evening Guys
Well had my mechinc over this morning to set the timing and the issue was with the dizzy amp hitting the PAS bracket and not giving enough advance, so hacksaw out and bracket adjusted, TDC set with a plug stop, then 14degs static dailed in with upto 36 degs at 2.5k-3k and engine running alot sweeter.
We also noticed that the carb was dripping fuel into the barrels rather then spraying, so fitted a new fuel regulator and set to 5 psi, adjusted both idle mixtures screw and got the carb to fine spray with idle set at 1100rpm with the air cleaner off, which once fitted brings it down to 950rpm, so hopefully i now have a good base setting, but the proof will be in the driving which unfortunately after completing was a little to busy with other things to test today, but hopefully tomorrow i should have time, fingers crossed and thanks for you help, cheers, Raffa
If you haven't done so already make sure your carb floats are set correctly. Simple task only takes 15 mins or so. If they are out no amount of adjusting the idle screws or jet/rod swapping will cure the problem.
DaveEFI wrote:No need to cut bits off - just remove the dizzy and move the drive round by a tooth. So you need a 'mechanic' who knows the basics.
Hi Dave
Not quite mate, its a new dizzy and the ignition module is 180degs opersite the vac, so causes an issue mate, its all sorted now and could do with some weight removed from that bracket
Evening Guys
well the bloody car is still hunting between 1 & 2k rev
Its a little better but not right and mostly happens when I am pulling away from traffic lights or on light throttle, would this be caused by a lack of fuel or overfueling please guys as this is now driving me insane, any help most appreciated and if anybody knows of a mechanic that can sort this out and is local to the Croydon/purley drop me a pm please and we can talk beer tokens
Sorry another question, what controls the curse setting on the carb please?
Raffa wrote:
Sorry another question, what controls the curse setting on the carb please?
Regards
Ralph
If you read the link that I posted up it explains how these carbs work.
The pistons, and the springs that sit under the pistons control the cruise setting along with the thick part of the rods and the primary jets. The vacuum in the manifold determines when the carb is in or out of its cruise circuit.
The hunting that you describe sounds like a lean mixture to me. The best way to set these carbs up is by having a lambda probe bung fitted to the exhaust, then using something like an LC1 exhaust gas analyizer it is just a case of driving the car on the road whilst taking note of the reading from the LC1. A vacuum gauge also helps.
Other people have had carbs setup on rolling road, personally I don't think that many RR operators know how these carbs work and/or just set them up for WOT operation which not much good for a road based car. (But thats just my humble opinion)
Raffa wrote:
Sorry another question, what controls the curse setting on the carb please?
Regards
Ralph
If you read the link that I posted up it explains how these carbs work.
The pistons, and the springs that sit under the pistons control the cruise setting along with the thick part of the rods and the primary jets. The vacuum in the manifold determines when the carb is in or out of its cruise circuit.
The hunting that you describe sounds like a lean mixture to me. The best way to set these carbs up is by having a lambda probe bung fitted to the exhaust, then using something like an LC1 exhaust gas analyizer it is just a case of driving the car on the road whilst taking note of the reading from the LC1. A vacuum gauge also helps.
Other people have had carbs setup on rolling road, personally I don't think that many RR operators know how these carbs work and/or just set them up for WOT operation which not much good for a road based car. (But thats just my humble opinion)
Hi Sidecar
I did 60 times lol, but am new to this and slowly but surely trying to understanding how it all works, so if I change the jet springs would this increase the lean mixture and stop the hunting as I read if I am correct that the springs control the cruise setting which I feel is now the issue?
OK this is briefly how the primary side of the carb works:-
The primary side of the carb delivers the mixture at low demand setting such as cruise. The primary jets controls the mixture strength but they do not do this on their own. There is a brass rod which pokes through the middle of each jet, the rod has two different diameters and this controls the size of the gap left for fuel the flow through. The thicker the rod the less the fuel can flow. The rods are attached to small pistons which are pulled down by the vacuum under the carb, springs sit under the pistons and try to push them back up. When there is a high vacuum the pistons are in the down position so the thick part of the rod in the jet, this leans off the mixture. A high vacuum exists under cruise conditions. As the throttle is opened more the vacuum drops, the springs then push up the pistons so the thinner part of the rod is in the jet, the mixture becomes richer which is what is required for acceleration. The springs determine when this changeover happens, they are for fine-tuning the system. The jets and the rods are what set the mixture ratios.
So what we need to know is what primary jets are in your carb along with what rods, once that is known we will have a base line to start working from.
sidecar wrote:I've done a shed load of work on these carbs, they generally run rich on most Rover lumps!
Here is a link to some gumph that I wrote ages ago. I have changed a few of my ideas now, I do think that the carb setup differs between engine sizes. (I state otherwise in the link)
Really the best way to set the carb up is with an LC1 or something similar to monitor the exhaust gas.
My 4.6 runs homemade rods but you can get very close to my setup using 83 primaries, 65-47 rods, silver springs and 80 secondaries. On the primary side of the carb this setup will be 16% leaner than base and the same as base during acceleration. (Please note that I can not say for sure that this is the setup for your engine!)
Muscle Manta on this forum can supply you with jets, rods and springs.
Hi Sidecar
These
OK if that is the setup that you are running and its hunting on cruise then you need to go richer on cruise. Your current setup is 16% leaner than the base setup, the problem is that without monitoring the exhaust gases it is all a bit of a guess. Anyway here are some jet and rod combos that are all richer on cruise:-
86 67-52 rod......8.3% leaner than base on cruise, 0% leaner on accel
86 67-55 rod......8.3% leaner than base on cruise, 6.8% leaner on accel
83 63-47 rod......7.9% leaner than base on cruise, 0.2% leaner on accel
83 62-52 rod......3.9% leaner than base on cruise, 10.8% leaner on accel
sidecar wrote:I've done a shed load of work on these carbs, they generally run rich on most Rover lumps!
Here is a link to some gumph that I wrote ages ago. I have changed a few of my ideas now, I do think that the carb setup differs between engine sizes. (I state otherwise in the link)
Really the best way to set the carb up is with an LC1 or something similar to monitor the exhaust gas.
My 4.6 runs homemade rods but you can get very close to my setup using 83 primaries, 65-47 rods, silver springs and 80 secondaries. On the primary side of the carb this setup will be 16% leaner than base and the same as base during acceleration. (Please note that I can not say for sure that this is the setup for your engine!)
sidecar wrote:I've done a shed load of work on these carbs, they generally run rich on most Rover lumps!
Here is a link to some gumph that I wrote ages ago. I have changed a few of my ideas now, I do think that the carb setup differs between engine sizes. (I state otherwise in the link)
Really the best way to set the carb up is with an LC1 or something similar to monitor the exhaust gas.
My 4.6 runs homemade rods but you can get very close to my setup using 83 primaries, 65-47 rods, silver springs and 80 secondaries. On the primary side of the carb this setup will be 16% leaner than base and the same as base during acceleration. (Please note that I can not say for sure that this is the setup for your engine!)
Muscle Manta on this forum can supply you with jets, rods and springs.
Hi Sidecar
These
OK if that is the setup that you are running and its hunting on cruise then you need to go richer on cruise. Your current setup is 16% leaner than the base setup, the problem is that without monitoring the exhaust gases it is all a bit of a guess. Anyway here are some jet and rod combos that are all richer on cruise:-
86 67-52 rod......8.3% leaner than base on cruise, 0% leaner on accel
86 67-55 rod......8.3% leaner than base on cruise, 6.8% leaner on accel
83 63-47 rod......7.9% leaner than base on cruise, 0.2% leaner on accel
83 62-52 rod......3.9% leaner than base on cruise, 10.8% leaner on accel
Hi Sidecar
Thanks very much, i know have a better understanding
i still have the old 86 mains and 065 x 052 rods, so i think i,ll try the rods with the 83 jets, should i change the springs to Orange? or leave the sliver springs in place
You are running 83 primaries and 65-47 rods at the moment, the important bit as far as the cruise is concerned is the 83 jet and the 65 part of the rod. (These are actually diameter's in thou of an inch)
So if you change the rod to 65-52 and still run with the 83 jet as far as the cruise is concerned it will be exactly the same setup as you are running now. The acceleration circuit will however lean off 11% from the stock settings. The springs just determine when the carb goes into the richer mode. On cruise you will be pulling enough vacuum to hold the pistons down if you have the orange or the silver springs fitted.
If you want to compare one rod and jet combo with another you can work out the jet area, subtract the two rod areas from the jet area and that will give you the two ringed shaped areas that the fuel can flow through. You can do the same with another jet and rod combo and then compare the areas. The bigger the numbers the richer the setup will be. I use and excel spreadsheet to do this for me. You can also use the Edelbrock charts but they do have some errors in them and they don't list all of the jets and rods!
I hope I'm not teaching you to suck eggs here but make sure that you are making changes to the primary side of the carb, not the secondaries when you are changing the jets. The secondary jets are used to set the WOT air fuel ratio.
