| Author | Message | ||
     Jeff Martin Yet to post message Username: jeff_r_1 Post Number: 1 Registered: 7-2018 |
Hello all, my first post. I have a 1951 standard body Mark VI with a 4.25 liter engine. On the side of the SU's there are ports to lean out the fuel mixture, so I am assuming that's what they are doing according to what Burlen carbs told me. I read that the weakener is not supposed to affect the idle, but I find myself constantly having to change the mixture to get the idle smooth depending on the weather and if there is a high pressure ridge or low pressure system. I plugged the weakener ports off and the car runs much better and it idles smoother too. What was the point of the weakener system, some carbs have it and some don't ? | ||
| Mark Taxis Prolific User Username: mark_taxis Post Number: 157 Registered: 4-2007 |
he following is a message from Norman Gleeson explaining the use of these breather pipes, all interesting stuff, many thanks Norman As you have found the particular float chamber to jet well pipe on EPW six cylinder engines cannot be found on any other engine. The arrangement is unique to the S.U .thermo H series four bolt carburettors used on the four port intake manifold. These carburettors were first used on the early 1949 MKVI 4.5 Ltr (and subsequent 4.25 ltr) engines. A problem arose with flat spotting when accelerating during trials. Investigation found that if a small bore pipe was linked between the float chamber top and the jet well this would emulsify fuel in the jet well before it egressed from the main jet and this fix eliminated the problem. During investigation into issues with the late R Type engines it was found that temporary removal and blanking of the jet well adapter still prevented the former flat spotting. Still further trials found that the original problem had been caused because the volume of the original jet well was too small. The jet well volume had been increased by the casting in the boss for the pipe adapter. A small number of R Type Continental engines had the pipes removed to richen the mixture and dampen the exhaust burble on overrun. If the pipes are removed some extra care may be needed in selecting the main needles as in certain conditions the mixture is altered by 7%. The adaptors, which are screwed into the carburettors, are also fine jets and you would be advised not to try to remove them from the alloy carburettor bodies. The pipes are nothing to do with chamber filling, chamber breathing, and deliberate weakening or vapour venting. Parts book descriptions apart they could be more accurately described as air injectors, or jet well emulsifiers. I trust this satisfies your curiosity? | ||
| Jeff Martin New User Username: jeff_r_1 Post Number: 2 Registered: 7-2018 |
Yes, thank you ! The carburetors were rebuilt along with the engine a number of years ago now. They were removed, cleaned and inspected and put back with new fibre washers. The carbs themselves weren't in bad shape, but they did need to have new throttle plate bushings put in. | ||
| Jeff Martin New User Username: jeff_r_1 Post Number: 34 Registered: 07-2018 |
Getting back into this again Mark. I can understand what they mean by the jet well was made bigger, but what is meant by " the casting in the boss for the pipe adapter" Are they referring to the holes where the fuel flows from the float bowl to the jet well ? Or the overall jet bearing was increased in size to allow more fuel to flow into the main jet when needed ? | ||
| Norman Geeson Unregistered guest Posted From: 81.99.138.38 |
Jeff I understand that you do not quite understand my comments in a previous post in this thread, as follows:- " the casting in the boss for the pipe adapter" “What does the word “boss” refer to as well as “pipe adapter” ? (Answer) The small bore pipe that connects the jet well to the float chamber top does NOT screw directly into the carburettor body. In that location a “pipe adapter” or “union “is screwed directly into the carburetter, and then the small bore pipe is screwed into the adapter. “The jet well volume had been increased by the casting in the boss for the pipe adapter” (Answer) In order to have enough space to fit a “pipe adapter” or “union “it was necessary to alter the casting local to the jet well. This was done by casting in a “boss” or “bulge” into the body of the carburetter. This boss / bulge was then tapped to accept the pipe adapter/union. As you probably realize this pipe assembly was never intended as a weakening device unlike the units fitted to Rover cars that had depression float chambers. Instead these units were intended as jet well emulsifiers. As long as both pipes and unions are not blocked, they should cause no problem. I trust this answers your query. (Message approved by david_gore) |
