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Thread: 2500M Carb Conversion

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    2500M Carb Conversion

    Need some add'l opinions on this. I've got the opportunity to switch out my 175CD ZS carbs on my stock 2500M w/ a set of HS6 SU's. My ZS carbs are fine, but I'm a fan of SU carbs and understand them. Is there any performance gain to be had w/ the switch to SU's or am I wasting my time & money?
    I do have other places to waste my T&M if this doesn't work out....lol
    1971 MGB GT
    2004 C4 Corvette Convertible

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    Re: 2500M Carb Conversion

    I don't believe there is any performance gain with switching to the HS6 carbs. I'm a fan of the 175s and the Stroms have proven trouble-free. Any clearance issues with switching to the SUs?
    Nigel
    TVR 2500M
    TVR Vixen 2500
    Triumph TR3B

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    Re: 2500M Carb Conversion

    Good question on clearance. I think I'm OK, but need to verify, thanks. I'm more partial to SU's but haven't had issues w/ the ZS carbs.
    May just leave well enough alone and not fix it if it ain't broken. But as I need to pull off the carbs to get the exhaust manifold jet hot coated was just thinkin'........
    1971 MGB GT
    2004 C4 Corvette Convertible

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    Re: 2500M Carb Conversion

    Speaking of carbs, I have thought about switching to SU's to try and cure a starting problem I have.

    When I start my 2500M from cold, it starts right up. When it's up to temperature and I shut it off and wait about 5 minutes or so it is very hard to start and requires a lot of cranking to get it going. If it sits long enough (30-40 minutes) it starts right up. Once started, runs strong and smooth.

    Determined that fuel seems to dribble out of the main jets after switching off and puddles by the butterfly, thus, I believe causing a slightly flooded situation when warm. I've tried:
    - Carefully adjusting the float levels
    - Carefully adjusting the temperature compensator valves
    - Pinched off fuel line after shutting down to make sure it's not residual fuel pressure
    - Installed aftermarket heat shield with additional heat shield material added
    - Completely replaced carbs with a set of non-emission 175CD's that I bought at a flea market and throughly rebuilt (carefully adjusting float level) - absolutely no difference.
    - Replaced coil (just to make sure it's not the coil getting too hot)
    - Replaced plugs, wires, cap, cond. etc.
    - Obviously, adjusted valves, timing, the usual stuff.

    Has anyone else ever experienced this?

    Incidentally, I understand the float bowls on SU's sit at a slightly incorrect angle when used on the TR-6 engine to permit smooth functioning of the float and must be modified slightly or a set of SU's from a certain Triumph sedan used. Anyone have experience with this?


    '73 2500M

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    Re: 2500M Carb Conversion

    My '74 2500M has HS6 installed by a former owner. I did rebuild them over the winter and I'm running BAE needles now.

    Your symptoms do sound like vapor lock induced flooding but you sure have gone through almost all the right diagnostics I can think of. Is there any possibility that the venting of the float chambers is plugged. I'm guessing that those would normally be routed to the charcoal canister. Might pay to leave those lines open for a test.

    If you go with HS6's, check out a post I made a while ago that you'll want to be aware of. You really must use the SU Insulator Block or risk a vacuum leak. Go here to see what i'm talking about.


    https://www.britishcarforum.com/bcforum/u...trom#Post771993

    I fixed the float chamber leveling problem by installing SU part numbers AUD1071 and AUD1070 float adadpters. I forget which one was on the front carb and which one was on the back carb but they're both level now.

    By the way, ordering from SU in England was a breeze and the parts came within a couple of weeks.

    Oh, and one more thing. I was able to install a standard TR6 air cleaner assembly to the HS6 setup. I had to make some small adapter plates which are almost invisible. Makes the installation look very factory. If you're interested, I can post some photo's.


    Gregg
    '74 2500M 3111TM

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    Re: 2500M Carb Conversion

    Thanks all for the info. I think I'll keep the ZS carbs on the car as there is nothing to gain by a swap. I'll save the $$'s for the jet hot coating on the manifold.
    1971 MGB GT
    2004 C4 Corvette Convertible

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