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MG MG Y Type - Carb needle replacement
|My Y runs very rich. The muffler shoots out soot like a cannon.|
I tried to adjust the mixture with the aid of a Colortune tool. Even when I screwed the carb's mixture adjusting nut all the way up, the engine was still turning (!) and the Colortune indicated that the mixture was still rich.
I then partly dismantled the carb. Float level was correct. But the float bowl's needle valve seemed rather worn. I tought to myself that this could be indicative of the general conditions of all of the carb's parts.
This then lead me to check the main needle & jet. Of course, with only my eyes, I can't see if the needle is thinner than it should be or if the jet has enlarged over the last half century.
I believe a carburetor master rebuild kit is the next logical step. But which one to order? My local supplier gets its wares from Moss.
Are our SU H2 carbs exactly the same as the TC-TD?
Are there subtle nuances I should know before ordering?
I made a similar decision about a year ago to re-build my YA carb (running rich - black soot etc), but upon examining both the needle and jet, they showed no signs of contact or wear. I had also screwed up the jet as far as it would go to lean the mixture (at idle).
I replaced the needle with the "lean" specification, rather than the "standard".
The car still runs a little rich, but much less soot from the exhaust, and performs much better/smoother on the road and in traffic. It could be leaner, but as my car often tows a small trailer at highway speeds, I would rather be rich than lean.
My theory is modern fuel is more dense than pool fuel of the 1940's-50's, and you therefore need less of it to get the same fuel/air ratio.
You should note that adjusting the mixture at idle (by adjusting the jet), only affects the mixture at idle. The mixture across the rev range is entirely controlled by the needle profile/jet size (fuel), and the lifting of the piston (air).
|Gilles (and Tont [aka Tony!] if you want to),|
I had my carburetors, and those on Tracey Johnson's YT, rebuilt by Joe Curto in New York. I have no idea how on earth he provides such a fantastic service so cheaply - it isnt even worth thinking about getting dirty as he provides a fantastic service. Check him out on the Links page at www.mgytypes.org.
|Order the EF-needle (and an overhaul set if you want to) from Burlen or Sumidel and you will improve the rich running. I run the EF needle and it performs nicely. The FI needle is the standard needle.|
I presume you know that the needle code is stamped on the needle shaft that goes into the piston.
I also presume that you checked the correct height of the needle? If it is to high into the piston it will be rich always.
|Willem van der Veer|
I echo Paul's sentiments regarding Joe. Have known him for too long, but I wouldn't even think of going anywhere else. His breadth of knowledge and level of skill/service are unmatched. I have given him some tough assignments and he has never failed to come through. His links around the world are equally as impressive. In short, his advice is as good as his repair services. Give him a try.
| Remove the damper cover and piston. Then turn the ign on and check the fuel level in the jet at the bridge. I find that 1/16" below bridge is right. I always check my float level that way as there are many different thickness' of gaskets that are used to mount the float body to the carburetor. Remember you can have the float level check out okay in the float bowl but if the bowl is mounted too high the level is raised in the jet.|
|Gilles, while you have the damper cover and piston off, turn the mixture adjustment nut to full lean. Count the flats so you can set it back to where you had it, if necessary. See if the jet comes up flush with the bridge of the carb and the jet guide. Many times I've seen the jet low in the guide, there is just no adjustment to bring it up flush. If this is the case, re-set the needle so that the shoulder of the needle is protruding an equivelent amount that the jet is short of the bridge. This will allow the jet to reach the maximum diameter on the needle (.089") and allow you to adjust the carb.|
This thread was discussed between 18/04/2008 and 22/04/2008
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