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MG MGB Technical - Is this Part 'Needed'
| I have a 1979MGB that the "emmision" parts have been removed. Weber Carb/Cannon Header/Peco Exhaust installed. Runs GREAT.... but now that I am retired and have the time to clean-up the engine bay I have a few questions before I remove any more parts (if it runs good leave alone, I know, but I want to make it look better). What, if any, of these parts could/should be removed "or" just cleaned and replaced: Anti Run-on Valve Carbon Canister (2) Hose to nothing? Goes from the Anti Run-on valve to the front of the engine... but not connected to anything? I still have the hose from the valve cover going to the canister?? is this needed? Also, I want to "clean-up" the area where the fuse box, wiring clips etc. What is a good way to make sure all wire contacts are clean... and is there any thing I can do when I put these back together to help keep them clean (prevent possible corrosion). All I want to do is "tinker and clean" and use the same parts where needed. Note: I have kept all of the original parts, the PO kept everything that he changed too... just in case the urge to return to original (sic). Looking forward to your responses. Have a great holiday. Don |
| Donald Wheeler |
| The anti- run on valve does nothing if it is not connected in some way to the carb. Its function is to create a vacuum in the carb and suck out any remaining gas vapor when you shut off the car, thus no dieseling. The valve closes when the car is shut down. Again, if it is not connected to the carb, and since you have a Weber and it doesn't have a fitting for the anti run on valve plumbing, I believe it is not needed. Since the Weber is probably not connected and the anti run on valve is not performing the way it should, then the carbon cannister is not performing its entire function. The carbon cannister also runs on engine vacuum to suck in and capture the unburnt fuel vapors. This holds them in the carbon until the engine is running again, the anti run on valve opens and allows fresh air to be drawn through the cannister and back into the carb. The hose from the rocker cover to the cannister also is part of the emmissions control. It also helps in engine ventilation. I also have a Weber conversion but have left most of the valve, cannister etc., plumbing in place, I don't know why, but it runs well so I don't want to disconnect anything and jinx it. I would say clean and replace. |
| John |
| The carbon canister should also be connected to the fuel tank vent through a vapor separator. Clifton |
| Clifton Gordon |
| Donald, leave the vaccumn switch mounted on the top of the pedal box in place. Make sure the vac line from the Weber runs to it and then over to the distributor. It is designed to give you full vaccumn advance in fourth gear only and if the dist is connected straight to the carb you will have full vac advance even at idle. The electrical wires should be kept in place as well. It does matter which direction the hose goes into and out of that switch. You can check it for operation by shifting the car into fourth gear at idle. The idle will increase a couple of hundred rpm. Fusebox would be good to remove it and solder the rivets in the back to the spades where they connect so that corrosion between the two doesn't cause later electrical failure. A dremel tool with a wire brush can polish up the brass contacts and will last a long time. You can leave the cannisters in place or remove them and just let that pipe vent to atmosphere. I have never experienced any fumes coming back thru it. Run your crankcase vent hose from the pipe from the left front tappet cover to the bottom of the Weber air filter. |
| mwhitt |
| The plumbing between carbs, inlet manifold, tank, charcoal cannister and anti-run-on valve can all be left in place, they detract nothing from performance, help the environment a bit, and in the case of the anti-run on valve can be a positive benefit. If not all plumbing is in place have a look at http://www.mgb-stuff.org.uk/wn_fuelframe.htm and click on 'North American Emissions Plumbing' to help you replace missing bits. If it is all removed: 1. The carb vent(s) must be directed down past the engine so as not to drip on the exhaust. 2. The tank vent pipe must be sealed and a vented filler cap fitted. 3. The rear port on the rocker cover must be sealed and a vented oil filler cap fitted. Unless the Weber has a suction port for crankcase venting connecting connecting the front tappet chest breather pipe to the air filter will only result in minimal crankcase ventilation, you should keep an eye out for condensation and scum in the rocker cover. If you get this then I recommend fitting a PCV valve and connecting the tappet cover breather to that. 4. Unused ports on the inlet manifold must be plugged. 5. The slate/something wire to the anti-runon valve must be insulated, it is live when the ignition is switched off, albeit via an in-line fuse. If you remove the inline fuse remember that the slate wire feeding it will be *unfused* and live when the ignition is off. The other wire on the valve just carries a ground from an oil pressure switch when the engine is running, nevertheless it should be insulated from coming into contact with anything else. BTW the anti-runon valve actually sucks the liquid fuel out of the jets when the engine is turned off to prevent running-on, not vapour. The valve on the pedal box restricted vacuum advance to 4th gear only on late model cars to prevent surging caused by other emissions features. If you remove the emissions controls you should not suffer from that surging and so bypassing the valve (i.e. running the vacuum pipe direct from inlet manifold to vacuum capsule) will restore vacuum advance in all gears which all previous cars (and those that never had emissions controls) always had. One of the wires is live and unfused in 4th gear and the other is a ground so if you remove the valve make sure you insulate the wires *from each other* as well as from everything else. |
| Paul Hunt 2 |
| Paul, still, if you run that vac line straight to the dist he will absolutely go to full vac advance at idle! |
| Mwhitt |
| FWIW, my '78 (with a DCOE and earlier cast iron exhaust manifold) has everything removed - since none of it was operational when I got the car. As Paul says, the cannisters and their plumbing do not detract from performance - but, like you, I wanted a cleaner engine bay. Two comments about what is said above, and one of my own :-) I'm not so sure you have to plug the inlet on the rocker cover and install a vented cap, but maybe Paul can explain why (he certainly knows way more about these cars than I do!). It would seem that doing so would just trade one restricted inlet for another. Maybe they're different size holes? At any rate, I installed an alloy cover and vented cap anyway to improve the looks... My vac advance is run directly to the dizzy (25D) (from the manifold) and the valve by the pedal box is removed. It certainly does NOT go to full vacuum at idle! You will get some vacuum advance at idle, but not full advance - the engine is not producing full vacuum at idle! If you're getting full advance at idle, you have another problem that needs addressing, such as weak advance springs. The timing light verifies that the advance increases with RPMs, and I have no problems with pinging, run-on, etc., at all. I originally vented the crankcase to the air filter and found that inadequate, so I came up with another solution I haven't seen elsewhere. I'm sure others may find fault with it, but I've used it for the last year with no adverse effects. I placed a generic 90 degree PCV valve from AutoZone atop the pipe from the tappet cover and connect the two with a short piece of rubber hose. Then, I installed a "T" fitting where the brake booster hose attached to the front runner of my intake manifold...put the booster hose on one side of the tee...and ran a hose from the PCV valve to the other side - after installing a restrictor in that side of the "T". If you try this without the restrictor, you'll lose your brake boost and #1 and #2 will be way too lean since it'll suck way too much air from the crankcase. With the restrictor installed, I get just enough crankcase suction, brake boost is unchanged, and driveability is not impaired. The plugs on #1 and #2 still look perfect, and neither the idle jet nor the idle adjustment screw needed to be altered on the front carb throat. |
| Joe Reed |
| Whew! Thanks for the feedback. Ok, here is a little clarification... need more data to insure that I am on the right track "BEFORE" I do any thing. The valve on the pedal box is not in use (never was when I got the MG) just sitting there like a soar thumb. The original vac line to the dizzy was old. cracked. Replaced this and it is conected directly to the dizzy per procedures provided from Brit Tech when I installed the Weber set-up. (Timing etc. per their specs). So, I quess I can remove this needless pc from the engine bay. I like the idea of removing the canistors, changing then to use a vented cap... but could I plug the valve cover hose (use small rubber plug). I want to keep the "look" of the basic engine, plus not have the expense of buying a new valve core (retired, need to watch my pennies). Paul, do you also mean I should switch to a vented gas tank cap too, and seal-off the vent? Please provide direction. Also, when I polish/clean the wire terminals I read someplace about lightly coating the terminal end with ?? forgot what it was...any body? The anti-run valve... is it safe to just seal'wrap these wires and remove the valve? My "wish" is to eliminate clutter... but not hinder how great my MGB is now running. And as long as this really is not used any harm? I'll tinker and clean other spots and parts until I receive your replies. Have a GREAT Holiday, Don |
| Donald Wheeler |
| Yes you can remove the TCSA(?)valve - it's useless now...you rarely see one hooked up anyway. No reason to have to change rocker covers if you want to keep the original. If you use a vented oil filler cap, you'll need to plug or fill the hole in the "spout" on top of the cover. When I got mine, it had the original cap and the hose was simply removed from the cover. Maybe Paul will chime in here soon about why you shouldn't just do that. Your fuel tank is originally vented via a line running to one of the carbon cannisters. If you remove the cannister and plug that vent line, you'll have to vent the tank some other way. My car originally just had a piece of hose dangling underneath the back from the vent tube exiting the tank near the right taillamp. I plugged that - and drilled a couple of small holes inside the sealing portion of the original gas cap to vent the tank. The stuff you want to put on the wiring terminals is called dielectric grease. Probably the best way to handle any disconnected wires is to seal the ends with shrink wrap, then either wrap them inside the harness or zip-tie them to the harness - whichever is possible in that location. |
| Joe Reed |
| Thanks Joe for your fast reply! The dielectric grease I'll see if the local auto zone/part store has on hand. I have a vented oil filler cap that was purchased by mistake... now I'll be able to put it to use. At one time I was getting a "gas" smell only to fined out the hose going to the canister in the trunk was old and cracked where the clamp held it. replaced the hose and the smell cleared-up. I can see where it would be very easy to run a hose outside by the right tail light. You said you drilled a couple of holes in the gas cap... did you drill through the gasket but not the cap? Just enough to prevent a tight seal? Any wires that will not be in use, I'll follow your suggestion and shrink-wrap then tuck away when I re-wrap the wire harness. Again, thanks very much, extra help is nice to get! Don |
| Donald Wheeler |
| (Warning -- the following is a rant. I know I'm bound to offend folks, but here goes...) I don't agree with removing pollution control devices in general, and especially not for the reason of making the engine bay look "nicer." To me, that's one of the most arrogant, selfish, inconsiderate reasons I can think of. Only you will see your engine bay, but I and everyone else have to breath your pollution. It's the same as saying, "I don't like the way garbage cans look in my back yard, so I'm just going to throw all my trash in your yard." Removing pollution control devices for performance reasons isn't much better. The smog pump has a little parasitic drag associated with it, but I know from experience that it's nothing you'll feel seat-of-the pants. The gulp valve ONLY operates when the throttle is closed, so it cannot affect performance. The charcoal cans and associated evaporative emissions devices have absolutely no effect on performance and do help keep the air cleaner. The same goes for the PCV valve (or other closed crankcase ventilation system). EGR helps cool the combustion event and allows you to run more compression and/or ignition advance without danger of preignition, so it can HELP performance rather than hurt it. If you want more power, make sure engine is in good repair and properly tuned. Make sure your ignition curve is right (that's probably the single biggest gain you can get without serious engine work -- you'd be amazed how much a tired distributor can kill performance). Keep your tires properly inflated. Put in a hotter thermostat -- Smokey Yunick says that running an engine at 180 vs 200 can reduce power 2% - 3%.... MGs are not the cleanest cars around, so I think that we owe it to ourselves and other to maintain them so that they are as clean as they can be. (Rant over -- thanks for reading!) |
| Rob Edwards |
| Rob, I am all for clean air etc. but the MGB was already 1/2 "de-toxed" when I purchased it 6 years ago. Still had the Zenith (sic) carb, I got about 16-18 miles per gallon, plugs fouled up every 100 miles. A lot of parts not connected to anything (the purpose of my wanting to "clean-up" the engine bay. By putting the Weber carb/header etc on the MGB on a recent trip to Watkins Glen and back (slightly over 650 miles round trip) I got 29 MPG vs. 18 MPG the year before .... now that's less gas, less polution. I only drive about 1,500 - 2,000 miles per year (retired now so this may rise to as much as 2,500). I know the comment about making the engine bay look nice is a little silly, but I did get this MGB for fun and enjoyment and if cleaning 20+ years of dirt/grease/grime gives an old retired person something to do.... I might, just might, want to raise the hood and show it to my neighbor. So, enjoy the fresh air... I am able to go further on less gas. Plus, this old retired man is off the streets and in the garage out of harms way. PS: just think, the time I am spending "playing" cleaning up the engine bay, I am not driving my 2005 Grand AM... |
| Donald Wheeler |
| Don, It sounds like the bulk of your car's problem was not the emissions control but rather the DPO. ;-) A ZS-eqipped car with everything in good nick should not have the problems you were having.... I certainly wasn't saying that you shouldn't clean the grease and grime from your engine bay. I was taking issue with people removing emissions gear because the extra plumbing is unattractive to them. I'm also not saying everything must be kept stock. If there is a modification that someone is considering that makes the car cleaner (or at least no dirtier), then I say go for it if you want! I'm also not saying we shouldn't enjoy our cars, I just think we should enjoy them responsibly. :-) Cheers! |
| Rob Edwards |
| Rob, Maybe I'm a little dense but what good does a smog pump do on a pre catalitic converter car? My 68 MGB had one installed but no catalitic converter.. My understanding of a smog pump is that it simply injects extra air into the exhaust. This being the case the PPM of hydrocarbons and CO goes down but the car still creates the same amount of polution and expells the same amount. Now if the car has a catalitic converter, the thinning of the hydrocarbons and CO allows the converter more opportunity to absorb the polution. If this is the case, a smog pump pre catalitic converts is simply an energy steeling device that was introduced to please the buracrats by reducing the PPMs but not cleaning the exhaust at all. If I'm wrong can someone please tell me how it improves the environment? Cris |
| Cris DeYoung |
| The theory is that by injecting fresh air into the exhaust stream, you're introducing enough oxygen into the exhaust to allow unburned hydrocarbons to finish combusting. In practice, it may indeed just dilute the exhaust -- I don't know. But since the power it consumes is so small that I cannot feel the difference with it versus without it, I choose to keep it, if for no other reason than that it might be doing some good, and that makes me feel better.... |
| Rob Edwards |
| The comment on the vacuum advance is not correct. The engine is producing near max vacuum at idle. (an engine with a modified 280 degree cam will produce a lot less vacuum at idle) A direct connection from the manifold to the distributor will produce max vacuum advance at idle which is exactly the opposite of what is desired. The vacuum advance port on the carb is ported so that it is closed at part throttle. Slightly off throttle the vacuum advance comes in. Under heavy loads the vacuum drops and the ignition is no longer advanced by the vacuum canister and the timing is controlled mechanically by the distributor weights and springs and centrifugal force. The fine dance between vacuum and mechanical timing adjustments when set up properly makes a more responsive, powerful and economic ride. Barry |
| Barry Parkinson |
| "exactly the opposite of what is desired" Well, it may be, but emission regulations demanded that the vacuum pick-up point be moved from the carb port to the inlet manifold in 1971 for North American spec cars and 1977 for UK cars. This does result in maximum vacuum advance at idle, which is why the vacuum pipe on these cars must be removed and the inlet manifold port plugged when dynamic timing. Removing the vacuum has the effect of reducing the idle revs, so these may need to be tweaked up a bit at the carbs (both carbs by the same amount in the same direction remember) then put back again afterwards. The only exception to this is on cars fitted with the valve that limited vacuum advance to 4th gear only. This happened in late 76 on North American cars only i.e. they had the pick-up point on the inlet manifold. If a PO has moved the pickup point from the inlet manifold to a carb port (UK HIFs had the port, North American's didn't) then of course it won't have maximum vacuum at idle, whether or not it also has the 4th gear only valve. It was all a cn anyway, the only reason the vacuum was moved was that at maximum vacuum and advance at idle you get higher revs, so the butterflies can be closed a bit to reduce the idle back to normal, so you are using less fuel for the same revs, hence less emissions. Of course, off idle it goes back to the 'normal' level of emissions. And max vacuum at idle makes starting a bit more difficult. The carb port is closed at idle (strictly speaking the throttle is part open I suppose, otherwise the engine wouldn't run), opening rapidly to give maximum vacuum as the throttle is opened slightly. From this point both carb and inlet manifold vacuum operates the same i.e. as the throttle is opened further the vacuum, and hence the amount of advance, gradually decreases. Centrifugal advance is operating independantly of vacuum advance, and at part-throttle high revs you will be getting advance from both, potentially as much as 50 degrees of *extra* advance. The two are dealing with different characteristics of the engine. As revs increase the advance can be increased as there is less tendency to pink at higher revs, and if you didn't advance the timing more and more of the mixture burn would occur further down the expansion stroke, losing power and increasing waste heat, and this is what centrifugal advance compensates for. Vacuum advance takes account of the fact that at wider throttle openings (not necessarily higher load) there is a bigger charge in the cylinders, a bigger bang, so higher cylinder pressures, which increases the chance of pinking, so the reducing manifold vacuum with increasing throttle openings compensates for this. OTOH at light throttle openings the timing can take much more advance without pinking, so high manifold vacuums are used to advance the timing. The engine runs with the greatest power *and* economy just short of pinking, and in the 80s there were BL engines with closed-circuit systems that detected knocking and used electronics to back off the timing until it stopped. One half of the electronics was continually but slowly increasing the advance, whereas the knock sensor would rapidly back it off a few degrees if pinking started, the first half th4en slowly increaisng it again. When suddenly accelerating in these cars you could hear pinking easily, rapidly backing off. I'd love to get this system onto my B. You can get the electronics, but the difficult bit is the knock sensing. Modern engines use open-circuit system that adjust mixture and ignition according to a set of fixed maps. I think this is for a couple of reasons - the closed loop system 'might' take things outside safe parameters for the engines, and pinking might be detremental to catalytic convertors and emissions. |
| Paul Hunt 2 |
| Paul, The system you describe sounds interesting! What is the difficulty with the knock sensor in that setup? Is it an odd-ball proprietary item? Or does it need special mounting? About 10 years ago I installed fuel injection on an old V8 Camaro, and the FI system needed a knock sensor. I ended up screwing it into one of the block drain holes (the thread size happened to be the same), but as I recall placement was not critical. I think some people install them on motor mount brackets. Anything that can conduct the sound waves effectively (i.e. anything metal that is rigidly attached to the block) will apparently work. On the Camaro at least, it was easy to tell if the knock sensor was working -- put a timing light on it and then hit the engine with a small hammer, breaker bar, etc. If the spark control system is working properly, the timing will momentarily retard then return to normal.... Cheers! |
| Rob Edwards |
| Rob - it is sourcing and placement of the sensor(s) I'd like to find out about. Chopping a distributor to fit a stepper motor in place of the vacuum capsule should be pretty easy, the only source of the electronics I found at the time was J&S - http://www.mustangworks.com/articles/poweradders/KnockControl.html In an email they said they had a customer with one on an MGA but no MGBs they were aware of. My specific question to them was sourcing and placement of the sensor, but they avoided that. Love the test to check it is working :o) |
| Paul Hunt 2 |
| I Went to the J&S website -- not much part-specific info there, but they do mention one of their kits using a GM sensor. GM likes to share parts amongst models, so I'm sure it's a readily-available part (at least here in the colonies. ;-) I'm sure we could arrange for one to find its way to you, if you were at the point of needing one. As for placement, if you don't have an electric oil pressure gauge, I'd think that you could tap one of the bosses for the sender plate out to 1/8" NPT and it would work just fine.... HTH! |
| Rob Edwards |
| Here's a thought, tough. Would tappet noise confuse it? I don't know.... |
| Rob Edwards |
| I use a knock sensor on my Twincam race car. http://tinyurl.com/9tepo at the rear under the oil line fitting. |
| Bill Spohn |
| Have to be a pretty heavy tappet ... :o) I couldn't find a price on that URL I posted, but have since seen references to $400-500 just for the electronics. Not sure I want it that much. I've also seen statements that J&S are the only manufacturer of a knock retard system short of full EFI engine management, which maybe explains the high price. If I could find the exact year and model they were fitted by BL I could probably get all the stuff out of a scrapyard. |
| Paul Hunt 2 |
| >Have to be a pretty heavy tappet ... :o) Maybe not -- I had Rhoads lifters in that Camaro and they seemed to affect the timing. If you're not familiar, Rhoads lifters are hydraulic lifters that are designed tame aggerssive cams. They are built to leak a little so that at lower RPM, they leak down and you don't get the full cam profile and thus better idle, better vacuum, etc. At higher RPM, they don't have the time to leak down so you get the full benefit of your cam. The side effect of this is valve clatter -- enough to annoy the EFI ECM I was using. Whether or not the J&S electronics are as sensitive would be hard to know without trying. And at $500+, I think I'll let someone else find out! ;-) Cheers! |
| Rob Edwards |
| Rob Thanks for the rant--saved me the trouble. when I got my '80, the emissions were a mess--the engine bay was a mess. The wiring was a barn job. Cleaned up real nice and pretty. Everything functions and runs much better, mileage is improved and I know I'm putting less garbage into the air. Could have gone the other route--I figure it would have sost about the same, and would have taken about the same amount of time. If you want the clean, unobtrusive look of an early car--get one. The stink and pollute quite nicely. I also own an MGA and the diference between the exhausts is very noticeable. The A only gets out for special occasions. The B is driven. |
| R. L Carleen |
| I can sympathize with both sides on this. When there used to be a certified British Leyland dealer in my town in the 70s, all the mechanics advised owners to leave the emissions controls alone. The engines were built around it. My 1970 ran full emissions and was faster than any B I've ever been in. However, like some of the comments above, I got an 80 LE totally gutted of emissions and no parts from the previous owner. If you look in Moss or Victoria British, you'll be out hundreds to refit it all. There has to be several of these systems laying around garages around the country. I would refit it to my 80 LE and expect it would compromise power very little, but I'm not certain that I'm ready to dole out all the money to refit it at new prices. |
| Rick Penland |
This thread was discussed between 22/11/2005 and 05/12/2005
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