tdturk Posted August 28, 2014 Report Share Posted August 28, 2014 Hello My Fellow TR6ers... My car is a 1972 TR6, rebuilt about 10 years ago. Engine completely rebuilt with new SU carbs. I've got a quandry regarding how to property hook up my manifold vapor / vacuum hose. When i purchased this car, it had a leak that I could not stop around the back of the valve cover. I decided the simplest fix would be a aluminum valve cover. I did notice when I installed the new cover that there was no baffle over the vacuum tube opening - but there was one on the old cover. A couple of months prior to swapping out the valve cover for the new aluminum one, I swapped out the air filters and I noticed that the rear filter was covered with oil. That was concerning - but I really didn't have an explanation. NOW, after I swapped out the valve cover for the aluminum one, the oil has really gotten bad in the rear air filter... and it loses a lot of oil when running at highway speed. The car has SU carbs that were installed when the engine was rebuilt about 10 years ago. The original air cleaner assembly was re-used - the inside of the filter assembly was turned upside down to accommodate the holes in the SU carbs vs. the original carbs. This is where I think the problem comes in. The vacuum hose from the valve cover goes directly over to the breather intake assembly - landing INSIDE the breather element, putting it directly into the throat of the rear carb. I realize this vacuum connection to the air filter assembly is the original configuration, but I feel like the carbs are creating too much vacuum and are sucking in oil from the valve cover - especially at high revs. I have removed my spark plugs, they all look just fine. The rear two were a little black due the excess oil going through the rear carb - but not bad. The front 4 were a nice brown color with no oil residue whatsoever. I plan to do a compression test - but i really don't suspect that is my issue at this point. I've researched this all over the internet to the point that I'm totally confused now. I have seen several configurations that connect the vacuum hose from the valve cover over to the vacuum inlet connections on the SU carbs. Mine are unused and have the original rubber grommets attached. Also - most of these configurations I've seen also involve a carbon canister - which I do not have. I suppose I could get one, but do I really need to? So - what is the advice from my sage TR6'ers that have been down this path? My car is exempt in my state on emissions, so I don't have to worry about that. If I hook the vacuum line from the valve cover directly to my SU carbs, do I need to install a canister or some other type of receptacle? What about a PCV valve in the line - would that help? I am creating a baffle to go over the opening in my aluminum manifold. I'll post a photo of that once I'm done. I'm just not sure what the best way is to hook things back up. I really don't want to be injecting oil into my carbs like it has been doing! Thanks for any input... Trent Quote Link to post Share on other sites
poolboy Posted August 28, 2014 Report Share Posted August 28, 2014 The only reason you would need a carbon Canister is so you'd have a place to vent the fuel tank vapors. If your SU carbs have an evacuation port like the ZS carbs do designed to relieve crankcase pressure via the valve cover, then those nipples would be the places to connect a hose from the valve cover using a "T" fitting so that each carb would be sucking on the valve cover relieving crankcase pressure Quote Link to post Share on other sites
Peter Cobbold Posted August 28, 2014 Report Share Posted August 28, 2014 (edited) Trent, welcome to the forum, The air filter will not creat any depression to speak of - or it should not. The oil is being blown out of the crankcase pressurised by piston blow-by. Easiest solution is to fit a catch tank and simply run the hose into that. The other is to fit the hose to an SU between the piston/dome and the butterfly- but not all SUs have the right bore pipe fitted there. That ensures the oil gets burned. Peter In the hose there should be a small in-line canister about 1 inch diameter - a 'flame trap' supposedly. Edited August 28, 2014 by Peter Cobbold Quote Link to post Share on other sites
RonA Posted August 28, 2014 Report Share Posted August 28, 2014 Hi Trent I have twin SU's and an aluminium rocker cover, the vent from the rocker cover goes via a short piece of 1/2" hose to a home made connection in the top centre of the rear plate of the original Stromberg air filter box, (ie it enters the filter box between the two paper filters), I don't have any problems with excessive oil use with this configuration. RonA Quote Link to post Share on other sites
tdturk Posted August 31, 2014 Author Report Share Posted August 31, 2014 (edited) Hey TR Friends - thought I'd post a follow up to my post above to let everyone know how I have solved my problem and my conclusions about this issue: First - I created a small baffle to fit inside my new aluminum rocker cover to fit over the vent hole. I may post a photo of it if I can figure out how to post photos. Had to drill a hole and use a small screw and lock nut with gasket material to keep it from leaking. Nobody was willing to weld it on for me... so I drilled it. No leaks yet. Second - I replumbed the valve cover vent hole vacuum pipes to go to the inlets on the SU carbs vs. inlet on the breather cover. Third - I swapped out the spark plugs. Results - ASTOUNDING! The car runs like it has never run before. It no longer idles roughly and it no longer burns any oil at all. It also does not 'stink' after I park it. I could not be more pleased with the results. Conclusion 1 - even though Triumph did plumb the vent opening on 72's over to the breather assembly when the car was built, I don't like it and I think it is a bad idea. This way of plumbing the gases from the engine over to the throat of the carb is a terrible idea and messes up the mixture of air and gas the carb is trying to produce. By using the inlets on the SU's this problem is solved. I guess may be the original Strombergs did not have this connection? Conclusion 2 - it is an even worse idea to put an aluminum valve cover with NO baffle on the car and plumb it over to the breather assembly. This just sets up a vacuum cleaner to actually 'suck' oil out of the top end of the engine right into the throat of the carbs. Anyway - she is purring like a kitten now and is even more fun to drive than before. Thanks to all of you for your advise! Trent Edited August 31, 2014 by tdturk Quote Link to post Share on other sites
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