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fitted to GT6
From the 1300, 1500, front or rear wheel drive, to the Toledo, Dolomite and Sprint - chat about it here!
Section : Engine
Engine, cooling system, fuel system, exhaust system.
Posted By : Jonathan Parsons, 18-May-2005,
09:18pm
I have a Mk2 GT6 which has at some time been fitted with twin HS6s, I think from a Dolomite Sprint. Driving home one night I suddenly noticed a raspy noise
coming from the engine a bit like a blown exaust. With the engine running the noise would seem to come from the front carb which when is sucks in air makes
a kind of rasp or rattle as compared with the rear which is smooth and even. This is accompanied by a misfire and backfiring when driven. The noie becomes
more of a rattle at speed.
I have changed the manifold gasket and checked the pistons in the carbs but there is no obvious fault. I have had a number of cars fitted with SUs but have
never seen or heard of this before. I would be grateful if anyone could shed some light on this.
Many thanks
Jonathan
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Posted By : David Rumens, 22-May-2005,
08:35am
If you are happy it is the carbs I would first check the piston on the front carb is not sticking and then dashpot is seating correctly. Check the
piston rise and drop for sticking.
The next point to check is to ensure the fuel is getting through to the jet in the front carb by working from the feed pipe through the float chamber
valve finally to the jet itself. WD40 is quite good for blasting out muckite!
A final point is to swap over the pistons, with needles from one carb to the other. This can produce two results. Clear the problem, mainly due to the
pistons being swapped over in the near past and not matching the wear in the carb. Or if the piston or needle is at fault the problem will reapprear on
the rear carb.
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Posted By : Jonathan Parsons, 23-May-2005,
01:09pm
Thanks for that Dave. It now seems that the problem is most likley to be mechanical rather than carb related, possible burnt valve. I will check as
advised anyway though.
The carbs seem good, the only thing I noticed when I removed them was that someone had attempted to solder closed the non return spring valve
things on the throttle discs. They had however, broken through the solder. Why would anybody want to do this and what is the puropse of the valve
anyway?
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Posted By : David Rumens,
24-May-2005, 06:37pm
The valves in the throttle discs have a habit of leaking and cause running problems. Most people these days remove them and fit plain throttle
discs without these valves. However, the old trick was to solder them shut and this what you have found. I would remove them and fit plain
disc. They are readily available from the normal SU carb parts companies.