Welcome to our resource for MG Car Information.
MG MGB Technical - 77 MGB carb conversion?
|I have a 77 MGB with the dreded Calf. smog! Short of buying a new intake and exahust manifold can I just remove all the smog equipment and retune the SU?, I have a webber but just cant afford the manifolds, unless anyone has some inexpensive ones... been out of work for a while now and need this as transportation again , truck only gets 8 mpg and is no where near as fun...|
|Absolutely not legal in California!|
I am not from there, but I would be if I had started there! They not only must pass emissions, but also "visual checks" to ensure that everything that came on the car is still there and working, and CHP knows because their computers show what every car came with. There are some pricey alternatives that have been issued CARB acceptance numbers, but you do not have the shekels.
And it is not an SU, but a Zenith-Stromberg.
Learn to fix it or buy a pre 65 car, or at least a pre 75 one (twin SU stock, no cat, better cam, all around win).
|Thanks for your reply FRM, I understand the laws here but after passing smog I have two years to run it and I will re-install it at the next smog check...smog is due in November so any advice would be helpful. All cars run crisper and with more power without this garbage on them.Learned to drive in a 62' TR3, dont want the sync issues with twin carbs even though they started my wrenching masichisim.I do have a webber but it has the wrong manifold and understand my car needs to be switched over to the seperate intake and exhaust manifold if I use it so was wondering if I can just remove all the air pump and such and re-tune the Zenith stromberg, (I stand corrected there.) One other question,my distributordoesnt have the flash sheild,what problems does this cause?|
|Removing the air pump has no effect whatever on drive-ability; if it works leave it, except then it will be dead at smog time! |
No air pump or no cat would be an immediate major fail in a roadside check, They could have discontinued these for economic reasons, or they might accelerate them to make cash for the state, hmmm...
Lots of cars are missing the flash shield - I suppose there might be some arcing issue, but probably only in damp weather on cars that have bad wires and plugs - never noticed any ill effect.
Very little retuning possible or necessary. You can advance timing a bit, and fiddle with mixture for minor gain, maybe, I have heard that using a SU HIF6, a direct bolt on to your horrid manifold, is better, but I doubt it and have never actually seen one. Much fiddling may kill the cat, so then you buy that for smog.
Big thing is to get the ZS working correctly, and the distributor advance, and the EGR stuff.
The big issues are the horrible manifolds, low compression, and castrated cam timing.
I would guess that exactly where you are might influence the rabidity of enforcement, aka, Redding might be better than LA. A good friend somehow got away with replacing his ZS's with HIF's on his Lotus Elan, and filling it with methanol from the sprint car racers at smog time, in Mill Valley.
|Anything before 1976 in Ca., avoids the "dreaded" smog compliance. Why not just tune what you have. Replace the ZS rubber diaphram as they always micro crack: unscrew it and hold it up to the sun while stretching it. Bet you see sunlight. If you spiff the car up tune wise, you should get a driver worth 18-23 mpg. Cheers, VEM|
|thanks for the feedback guys, yea hate smog cars,low comp 120each cyl.I have to agree that I have started on the ignition first. New plugs, cap,rotor,coil |
(MSD Blaster)Think thismight be thewrongchoice but I'm broke and it was all I had. Timed at 10 degrees @ 1500rpm per sticker on car. it starts at 5 at idle and advances to 10 as I reve it. Starts easy idles more or less @ 900 to 1000rpm but revs slow and not much past 3000rpm. I removed the vac advance from the stupid 4th gear switch and directly to the manifold and it advances, as soon as I try to drive it wont rev and bogsdown. definatly not drivable. Thanks for letting me know about the flash sheild. it has a Lucas ab 14 amplifier but it wasnt hooked up,the distb was connected directly to the old lucas coil that was bad.Does the 12v starting and droping to 6 volts at the coil cause the MSD to drop spark? Ilookedfor amplifier wiring diagrams but couldnt find any. it has a w/b with female connector and a w with a male connector coming out the bottom. On the side pointing to the front it has a small .187 male connector and a .250 male connector tucked inside a rectangle hole.it looks like a plug went in there. wish I had the money just to swith to points. but of course Smog will be due this november so you guys are right and I should keep all that smog crap on it!!!I have a MSD 6 (thats where I got the coil butitsays Ihave to use the wire from the amplirier. Well there it all is, figured I would give you everything I could so you might be able to help better Im out of work and cant put gas in my truck...Dodge v-10 8-10mpg and need to start driving this to look for work,any help will be appreciated
|Your description of the distributor makes no sense. Can you take a picture with the cap off? Show the wiring or make a drawing. It must have something to replace the disconnected Lucas amplifier. Cars with cross connected different systems do very odd and unpredictable things.|
Did you check the ZS diaphragm as VEM suggested? That is the most usual cause of no acceleration and terrible gas mileage.
After you check the carb and sort the distributor, it is worth trying a few degrees (+5-8) more advance. These things often work better that way, and the LC engine doesn't seem to know there is such a thing as too much advance. On a smog check that may give high NOx, so you may want to back it off for smog, but it usually gives better power and mileage.
|Thank you FRM, I havent checked the Diaphram as I like to work one problemat a time but I will check it today. I can draw a scematic as it would be clearer than a picture. I thought there should be an amplifier or somthing between the distb.and coil also. I have the lucas AB14 one but dont know how to wire it in. I have "The complete official MGB 1975-1980 drivers handbook and workshop manuel". its not socomplete as it doesnt show the AB14 anywhere. it is a fix for the amp on the dist. that failed often so I thnk that is the original scematic. I will also take a picture of the distb. thank you for your help, I am greatful. TF Fullmer|
|Diaphragm is always the first check on a ZS car with these symptoms, and I recommend people carry a spare and a PoziDrive #2 screwdriver to change it. Big problem is that while it is causing poor running, it is also dumping your gas into the crankcase, there to kill your bearings.|
I want the pic so we can see what is inside the distributor. A pertronix or similar is usual now, but other systems were formerly common - any finned boxes scattered about?
|Good Morning FRM, There are no pinholes or rips in the diaphram. Luckily my oil is clean and clear also, have had that problem in some of my bikes...It might be a little low on oil? would that cause this problem? it doesnt stutter just wont rev. There are no finned boxes anywhere,just the AB14 that was mounted under the coil with no wires connected to it.I'mattachingpictures so youcan have a look at the Distb. and wireing. hope their clear enough? I have run it at 15 degrees butitdidnthelp either but I like a little more advance also normally. My Harley has a 40DCOE Delorto and twin Morris Magnetos with duel plug heads lightened Flywheels short stroke big bore cylinders @ 76 hp. so I'm pretty good with older systems but electronics being less maintenece are a pain when not working right.Man, with points and a webber this would be soooo easy to tune!!! Better manifolds of course! PS I received this car in this condition and wired like it is and have no idea where the extra wires go yet.
|Whoops,wrong pic.AB 14 was mounted under coil on fender well. heres the inside of distb, both wires go to coil,red + white - cant upload a second pic, ill start another thread with this pic, called inside of Distb,77MGB|
|Here's the inside of the Distb... it finally let me upload...
|here are the x-tra wires, the single w/blu with stock connector comes out of the harness where the 2 W/bla tach wires come out connected to one added white to the - coil.not connected|
the black plug has 2 W/G not connected
the after market plug has 3 wires W/blu, W, W/bla also not connected
This thread was discussed between 30/07/2012 and 24/08/2012
MG MGB Technical index
This thread is from the archive. The Live MG MGB Technical BBS is active now.