Low revs torque

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philipmasonfrance
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Low revs torque

Post by philipmasonfrance » Sat Jun 27, 2020 5:22 pm

The GTC has never been good at low rev take-off or lugging. I always need too many revs and too much clutch slipping for my liking. It seems totally out of character with the nature of the car. Once moving, no problem at all. I'm running a reasonably new 38DGMS with a K & N filter. She starts from hot or cold no problem and petrol consumption is "reasonable". Did I read somewhere that there's a hole (at the back of the carburettor?) which I should have blanked off?



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scimjim
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Low revs torque

Post by scimjim » Sat Jun 27, 2020 5:49 pm

Do you know for certain that it has the original diff ratio? The cologne got the 3.54 because it felt a bit sluggish at low rpm with the Essex 3.31. If the balance pipe wasn’t blocked the mixture would be very weak (or set very rich to compensate).


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Low revs torque

Post by philipmasonfrance » Sat Jun 27, 2020 5:57 pm

No idea about the diff ratio, Jim. But I would think it's original. Apart from a recon engine when I bought her, I would think she's pretty well standard. What's this balance pipe? i thought that was something you find on twin SU's! :oops:



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Low revs torque

Post by scimjim » Sat Jun 27, 2020 9:28 pm

The one behind the quadrants. Basically any unused takeoff needs to be blanked off.


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SECURE DRY STORAGE FOR YOUR SCIMITAR

Current: SE5 (8Ball), 1400 1600 1800 Zetec ST170 powered SS1 (G97), 2.5TD SE5a (diesel 5a), 6 x random other SS1s.
Previous: SE5, 3 x SE5a, 2 x SE6a, 3 x SE6b, GTC, 2.9i GTC, 3 x 1600 SS1, 1300 SS1, Mk1 Ti Sabre, Mk1.5 CVH Sabre, TI SS1 (snotty), 1600 SS1 (C686CCR).
Chief mechanic for: 1400 K series SS1 (Megan3), 1400 CVH EFi SS1 (Grawpy), 1300 SS1 (Number One) & Sarah's coupe.
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Low revs torque

Post by philipmasonfrance » Sun Jun 28, 2020 8:51 am

Thanks, Jim. It's "Drive it day" today in France, so up to the lavender fields for a run in a gentle 31° of heat! I think I can see the hole in question by the quadrants (although I didn't realise it was an actual hole right into the carb). Dare I just stick some Blu-Tac in it for the moment - or could that be ingested? Or just a piece of sticky duct tape as a temporary measure?



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scimjim
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Low revs torque

Post by scimjim » Sun Jun 28, 2020 9:49 am

I’m not sure that it does go all the way through on all carbs - I think it may be either used during production, or only used on some models. Check by putting your finger over it when the car’s running. I wouldn’t use blu-tac, a small bit of pipe with a self tapper in the end is best.


Jim King

SECURE DRY STORAGE FOR YOUR SCIMITAR

Current: SE5 (8Ball), 1400 1600 1800 Zetec ST170 powered SS1 (G97), 2.5TD SE5a (diesel 5a), 6 x random other SS1s.
Previous: SE5, 3 x SE5a, 2 x SE6a, 3 x SE6b, GTC, 2.9i GTC, 3 x 1600 SS1, 1300 SS1, Mk1 Ti Sabre, Mk1.5 CVH Sabre, TI SS1 (snotty), 1600 SS1 (C686CCR).
Chief mechanic for: 1400 K series SS1 (Megan3), 1400 CVH EFi SS1 (Grawpy), 1300 SS1 (Number One) & Sarah's coupe.
CURE THE FAULT - NOT THE SYMPTOMS

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philipmasonfrance
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Low revs torque

Post by philipmasonfrance » Sun Jun 28, 2020 10:20 am

OK, finger in the hole it shall be - initially! I bought the new carb off Gower and Lee (back in 2009 - doesn't time fly?) and when I rang them to point out that there were no set-up instructions, I was informed by the young whipper-snapper that it was a "plug 'n' play" item ...



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Low revs torque

Post by AJL Electronics » Sun Jun 28, 2020 11:00 am

The port between the quadrants is for the original air cleaner's vacuum motor. If left open it will give all sorts of running issues. A piece of 4mm ID tube with a screw in it as Jim says, is the answer if not running the original air cleaner.


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Low revs torque

Post by philipmasonfrance » Sun Jun 28, 2020 11:22 am

Just dug out the old carburettor to compare it with the newer. Is the brass tube sticking out of the older carb the balance tube you were referring to, Jim? If so, on the new one there appears to be a plastic cap on it. The other holes appear to be blanked off on the old carb, so hopefully I can assume they are on the newer carb too. Perhaps I'll take the filter off to allow better visibility and, looking at the photo, a little clean-up around that area wouldn't go amiss ... !
Old carb.jpg
Old carb.jpg (141.13 KiB) Viewed 667 times
New(ish) carb.jpg
New(ish) carb.jpg (176.11 KiB) Viewed 667 times



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Low revs torque

Post by Steve_S » Mon Jul 06, 2020 12:44 pm

Remove the carb and check the bottom is not bent and dragging air in common fault folks getting excited tightening the carb down



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Low revs torque

Post by AJL Electronics » Mon Jul 06, 2020 1:03 pm

The brake cleaner test will show that up without dismantling.


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Low revs torque

Post by philipmasonfrance » Mon Jul 06, 2020 2:11 pm

Should be OK as that's exactly what happened with the previous carburettor and I have relied on two lock-nuts on each stud (see photo) rather than just keep tightening and re-tightening each time it worked loose. But what's the brake cleaner test? The engine idles and accelerates well when not under load, so will the test show up a leak somehow?



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Low revs torque

Post by AJL Electronics » Mon Jul 06, 2020 2:39 pm

Get yourself an aerosol or spray bottle of brake cleaner. Then you direct it at all the joints and spindle holes etc in the manifold and carburettor. When you hear the engine note change, you have found your leak.


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Low revs torque

Post by AJL Electronics » Mon Jul 06, 2020 2:40 pm

You should have a spring washer under each nut. Correct torque is reached when the spring washer is flat.


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Low revs torque

Post by mustang429 » Wed Jul 08, 2020 8:09 am

I had similar issues with my Essex engined 6A and found increasing the idle jets by 5 thou improved things considerably. No idea if this works with the 2.8 although two jets cost only a few pounds and fitting takes a couple of minutes.



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