Fuel system - Carburettor Air leaks - Revision history

CovKid: /* Carb Renovation - Throttle Flap Wear and Idle Issues */

2011-05-21T21:46:18Z

Carb Renovation - Throttle Flap Wear and Idle Issues

← Older revision		Revision as of 21:46, 21 May 2011
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	CovKid: Roger Ball in Clacton specialises in refurbishing throttle flaps on almost any make of carb. Carb makers tend to fit nylon bushes to throttle flaps as standard. He dumps these and fits phosphor bronze bushes which have superior wear characteristics and lube nicely. Roger will refurb worn throttle flaps via mail order, or dropped to him if local.		CovKid: Roger Ball in Clacton specialises in refurbishing throttle flaps on almost any make of carb. Carb makers tend to fit nylon bushes to throttle flaps as standard. He dumps these and fits phosphor bronze bushes which have superior wear characteristics and lube nicely. Roger will refurb worn throttle flaps via mail order, or dropped to him if local.

	You can reach him via: ~~http~~:~~//www~~.~~thephonebook.bt.com - residential numbers - R Ball - Clacton (won't put his number directly on here)~~		You can reach him via: [[Image:rogerballnumber.gif]]


	Providing ignition is in good form (and it may need investigating if the following doesn't help), in laymans terms for the engine to idle succesfully, it likes a very predictable and even 'suck' through the inlet manifold and carb body (as a unit) to ensure it recieves just the right air/fuel mix. Its finely balanced and relies on the free flow of air and no leaks along the way. At idle, its this vaccum (or suck) that pulls in a small but steady trickle of petrol through passages in the carb (carb is basically inactive at idle remember). Therefore if theres a leak below the carb (inlet port gaskets, bottom carb gasket, brake servo pipe etc), the suck through the carb is seriously reduced and the mixture goes weak - weak enough to kill the idle but possibly not when revving the engine as fuel is injected down the carb throat at that point and then the engine doesn't give a fig really. In fact this predictable vacuum is the whole basis of setting the idle speed/mixture correctly. Once set, a certain volume of air is assumed so if this is upset by a sudden change in that, for whatever reason, it can alter how much fuel is drawn in and destroy the idle speed and probably across the range at various points too with generally poor performance. A weak mixture also tends to make the engine run hotter and can cause damage.		Providing ignition is in good form (and it may need investigating if the following doesn't help), in laymans terms for the engine to idle succesfully, it likes a very predictable and even 'suck' through the inlet manifold and carb body (as a unit) to ensure it recieves just the right air/fuel mix. Its finely balanced and relies on the free flow of air and no leaks along the way. At idle, its this vaccum (or suck) that pulls in a small but steady trickle of petrol through passages in the carb (carb is basically inactive at idle remember). Therefore if theres a leak below the carb (inlet port gaskets, bottom carb gasket, brake servo pipe etc), the suck through the carb is seriously reduced and the mixture goes weak - weak enough to kill the idle but possibly not when revving the engine as fuel is injected down the carb throat at that point and then the engine doesn't give a fig really. In fact this predictable vacuum is the whole basis of setting the idle speed/mixture correctly. Once set, a certain volume of air is assumed so if this is upset by a sudden change in that, for whatever reason, it can alter how much fuel is drawn in and destroy the idle speed and probably across the range at various points too with generally poor performance. A weak mixture also tends to make the engine run hotter and can cause damage.

CovKid: /* Carb Renovation - Throttle Flap Wear and Idle Issues */

2010-07-11T01:17:15Z

Carb Renovation - Throttle Flap Wear and Idle Issues

← Older revision		Revision as of 01:17, 11 July 2010
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	Providing ignition is in good form (and it may need investigating if the following doesn't help), in laymans terms for the engine to idle succesfully, it likes a very predictable and even 'suck' through the inlet manifold and carb body (as a unit) to ensure it recieves just the right air/fuel mix. Its finely balanced and relies on the free flow of air and no leaks along the way. At idle, its this vaccum (or suck) that pulls in a small but steady trickle of petrol through passages in the carb (carb is basically inactive at idle remember). Therefore if theres a leak below the carb (inlet port gaskets, bottom carb gasket, brake servo pipe etc), the suck through the carb is seriously reduced and the mixture goes weak - weak enough to kill the idle but possibly not when revving the engine as fuel is injected down the carb throat at that point and then the engine doesn't give a fig really. In fact this predictable vacuum is the whole basis of setting the idle speed/mixture correctly. Once set, a certain volume of air is assumed so if this is upset by a sudden change in that, for whatever reason, it can alter how much fuel is drawn in and destroy the idle speed and probably across the range at various points too with generally poor performance. A weak mixture also tends to make the engine run hotter and can cause damage.		Providing ignition is in good form (and it may need investigating if the following doesn't help), in laymans terms for the engine to idle succesfully, it likes a very predictable and even 'suck' through the inlet manifold and carb body (as a unit) to ensure it recieves just the right air/fuel mix. Its finely balanced and relies on the free flow of air and no leaks along the way. At idle, its this vaccum (or suck) that pulls in a small but steady trickle of petrol through passages in the carb (carb is basically inactive at idle remember). Therefore if theres a leak below the carb (inlet port gaskets, bottom carb gasket, brake servo pipe etc), the suck through the carb is seriously reduced and the mixture goes weak - weak enough to kill the idle but possibly not when revving the engine as fuel is injected down the carb throat at that point and then the engine doesn't give a fig really. In fact this predictable vacuum is the whole basis of setting the idle speed/mixture correctly. Once set, a certain volume of air is assumed so if this is upset by a sudden change in that, for whatever reason, it can alter how much fuel is drawn in and destroy the idle speed and probably across the range at various points too with generally poor performance. A weak mixture also tends to make the engine run hotter and can cause damage.

	Insufficient air (ie through a clogged air filter) won't supply enough oxygen and again the suck through the carb is reduced, mostly at idle although it'll probably pop and bang too on deceleration. A worn throttle flap also messes up the idle since air then gets sucked in through here (often randomly) and kills off the 'predictable' vaccum I mentioned earlier and often causes a 'hunting' idle or even sudden stalling as you approach junctions. A mixture screw set too lean can also do that but I don't advocate resetting mixture if its run ok up to now - find the cause first.		Insufficient air (ie through a clogged air filter) won't supply enough oxygen and again the suck through the carb is reduced, mostly at idle although it'll probably pop and bang too on deceleration. A worn throttle flap also messes up the idle since air then gets sucked in through here (often randomly) and kills off the 'predictable' vaccum I mentioned earlier and often causes a 'hunting' idle or even sudden stalling as you approach junctions. A mixture screw set too lean can also do that but I don't advocate resetting mixture (or touching ANY carb screws) if its run ok up to now - find the cause first. If you don't you'll just be compensating and not very well at that.

	The carb itself can become full of foreign bodies too which can clog the tiny passages/jets that supply the idle mixture. The above applies to all carb engines from Type1 onwards. It also applies to 2ltres with twin carbs which technically are one carb split into two and merely act as one carb when its running correctly.		The carb itself can become full of foreign bodies too which can clog the tiny passages/jets that supply the idle mixture. The above applies to all carb engines from Type1 onwards. It also applies to 2ltres with twin carbs which technically are one carb split into two and merely act as one carb when its running correctly.

CovKid: /* Carb Renovation - Throttle Flap Wear and Idle Issues */

2010-07-11T01:15:53Z

Carb Renovation - Throttle Flap Wear and Idle Issues

← Older revision		Revision as of 01:15, 11 July 2010
Line 80:		Line 80:
	You can reach him via: http://www.thephonebook.bt.com - residential numbers - R Ball - Clacton (won't put his number directly on here)		You can reach him via: http://www.thephonebook.bt.com - residential numbers - R Ball - Clacton (won't put his number directly on here)

	Providing ignition is in good form (and it may need investigating if the following doesn't help), in laymans terms for the engine to idle succesfully, it likes a very predictable and even 'suck' through the inlet manifold and carb body (as a unit) to ensure it recieves just the right air/fuel mix. Its finely balanced and relies on the free flow of air and no leaks along the way. At idle, its this vaccum (or suck) that pulls in a small but steady trickle of petrol through passages in the carb (carb is basically inactive at idle remember). Therefore if theres a leak below the carb (inlet port gaskets, bottom carb gasket, brake servo pipe etc), the suck through the carb is seriously reduced and the mixture goes weak - weak enough to kill the idle but possibly not when revving the engine as fuel is injected down the carb throat at that point and then the engine doesn't give a fig really. In fact this predictable vacuum is the whole basis of setting the idle speed/mixture correctly. Once set, a certain volume of air is assumed so if this is upset by a sudden change in that, it can alter how much fuel is drawn in and destroy the idle speed and probably across the range at various points too.		Providing ignition is in good form (and it may need investigating if the following doesn't help), in laymans terms for the engine to idle succesfully, it likes a very predictable and even 'suck' through the inlet manifold and carb body (as a unit) to ensure it recieves just the right air/fuel mix. Its finely balanced and relies on the free flow of air and no leaks along the way. At idle, its this vaccum (or suck) that pulls in a small but steady trickle of petrol through passages in the carb (carb is basically inactive at idle remember). Therefore if theres a leak below the carb (inlet port gaskets, bottom carb gasket, brake servo pipe etc), the suck through the carb is seriously reduced and the mixture goes weak - weak enough to kill the idle but possibly not when revving the engine as fuel is injected down the carb throat at that point and then the engine doesn't give a fig really. In fact this predictable vacuum is the whole basis of setting the idle speed/mixture correctly. Once set, a certain volume of air is assumed so if this is upset by a sudden change in that, for whatever reason, it can alter how much fuel is drawn in and destroy the idle speed and probably across the range at various points too with generally poor performance. A weak mixture also tends to make the engine run hotter and can cause damage.

	Insufficient air (ie through a clogged air filter) won't supply enough oxygen and again the suck through the carb is reduced, mostly at idle although it'll probably pop and bang too on deceleration. A worn throttle flap also messes up the idle since air then gets sucked in through here (often randomly) and kills off the 'predictable' vaccum I mentioned earlier and often causes a 'hunting' idle or even sudden stalling as you approach junctions. A mixture screw set too lean can also do that but I don't advocate resetting mixture if its run ok up to now - find the cause first.		Insufficient air (ie through a clogged air filter) won't supply enough oxygen and again the suck through the carb is reduced, mostly at idle although it'll probably pop and bang too on deceleration. A worn throttle flap also messes up the idle since air then gets sucked in through here (often randomly) and kills off the 'predictable' vaccum I mentioned earlier and often causes a 'hunting' idle or even sudden stalling as you approach junctions. A mixture screw set too lean can also do that but I don't advocate resetting mixture if its run ok up to now - find the cause first.

CovKid: /* Carb Renovation - Throttle Flap Wear and Idle Issues */

2010-07-11T01:13:45Z

Carb Renovation - Throttle Flap Wear and Idle Issues

← Older revision		Revision as of 01:13, 11 July 2010
Line 87:		Line 87:

	Sudden power loss at high speeds (ie forcing it from 60mph to 40mph) is usually due to level in float chamber falling below demand, caused by blocked fuel lines, filters, a worn fuel pump pushrod or indeed a tired fuel pump. Carbs in a nutshell really....		Sudden power loss at high speeds (ie forcing it from 60mph to 40mph) is usually due to level in float chamber falling below demand, caused by blocked fuel lines, filters, a worn fuel pump pushrod or indeed a tired fuel pump. Carbs in a nutshell really....

			In fact, even an apparently knackered carb can be made to run as good as new if the throttle flap is rebushed and all seals, diaphrams and gaskets replaced. Its often significantly cheaper than buying a new carb or chancing your luck on a second hand one.

CovKid: /* Carb Renovation - Throttle Flap Wear and Idle Issues */

2010-07-11T01:10:52Z

Carb Renovation - Throttle Flap Wear and Idle Issues

← Older revision		Revision as of 01:10, 11 July 2010
Line 80:		Line 80:
	You can reach him via: http://www.thephonebook.bt.com - residential numbers - R Ball - Clacton (won't put his number directly on here)		You can reach him via: http://www.thephonebook.bt.com - residential numbers - R Ball - Clacton (won't put his number directly on here)

	Providing ignition is in good form (and it may need investigating if the following doesn't help), in laymans terms for the engine to idle succesfully, it likes a very predictable and even 'suck' through the inlet manifold and carb body (as a unit) to ensure it recieves just the right air/fuel mix. Its finely balanced and relies on the free flow of air and no leaks along the way. At idle, its this vaccum (or suck) that pulls in a small but steady trickle of petrol through passages in the carb (carb is basically inactive at idle remember). Therefore if theres a leak below the carb (inlet port gaskets, bottom carb gasket, brake servo pipe etc), the suck through the carb is seriously reduced and the mixture goes weak - weak enough to kill the idle but possibly not when revving the engine as fuel is injected down the carb throat at that point and then the engine doesn't give a fig really.		Providing ignition is in good form (and it may need investigating if the following doesn't help), in laymans terms for the engine to idle succesfully, it likes a very predictable and even 'suck' through the inlet manifold and carb body (as a unit) to ensure it recieves just the right air/fuel mix. Its finely balanced and relies on the free flow of air and no leaks along the way. At idle, its this vaccum (or suck) that pulls in a small but steady trickle of petrol through passages in the carb (carb is basically inactive at idle remember). Therefore if theres a leak below the carb (inlet port gaskets, bottom carb gasket, brake servo pipe etc), the suck through the carb is seriously reduced and the mixture goes weak - weak enough to kill the idle but possibly not when revving the engine as fuel is injected down the carb throat at that point and then the engine doesn't give a fig really. In fact this predictable vacuum is the whole basis of setting the idle speed/mixture correctly. Once set, a certain volume of air is assumed so if this is upset by a sudden change in that, it can alter how much fuel is drawn in and destroy the idle speed and probably across the range at various points too.

	Insufficient air (ie through a clogged air filter) won't supply enough oxygen and again the suck through the carb is reduced, mostly at idle although it'll probably pop and bang too on deceleration. A worn throttle flap also messes up the idle since air then gets sucked in through here (often randomly) and kills off the 'predictable' vaccum I mentioned earlier and often causes a 'hunting' idle or even sudden stalling as you approach junctions. A mixture screw set too lean can also do that but I don't advocate resetting mixture if its run ok up to now - find the cause first.		Insufficient air (ie through a clogged air filter) won't supply enough oxygen and again the suck through the carb is reduced, mostly at idle although it'll probably pop and bang too on deceleration. A worn throttle flap also messes up the idle since air then gets sucked in through here (often randomly) and kills off the 'predictable' vaccum I mentioned earlier and often causes a 'hunting' idle or even sudden stalling as you approach junctions. A mixture screw set too lean can also do that but I don't advocate resetting mixture if its run ok up to now - find the cause first.

CovKid: /* Carb Renovation - Throttle Flap Wear */

2010-07-11T01:07:19Z

Carb Renovation - Throttle Flap Wear

← Older revision		Revision as of 01:07, 11 July 2010
Line 74:		Line 74:


	==Carb Renovation - Throttle Flap Wear==		==Carb Renovation - Throttle Flap Wear and Idle Issues==

	CovKid: Roger Ball in Clacton specialises in refurbishing throttle flaps on almost any make of carb. Carb makers tend to fit nylon bushes to throttle flaps as standard. He dumps these and fits phosphor bronze bushes which have superior wear characteristics and lube nicely. Roger will refurb worn throttle flaps via mail order, or dropped to him if local.		CovKid: Roger Ball in Clacton specialises in refurbishing throttle flaps on almost any make of carb. Carb makers tend to fit nylon bushes to throttle flaps as standard. He dumps these and fits phosphor bronze bushes which have superior wear characteristics and lube nicely. Roger will refurb worn throttle flaps via mail order, or dropped to him if local.

	You can reach him via: http://www.thephonebook.bt.com - residential numbers - R Ball - Clacton (won't put his number directly on here)		You can reach him via: http://www.thephonebook.bt.com - residential numbers - R Ball - Clacton (won't put his number directly on here)

			Providing ignition is in good form (and it may need investigating if the following doesn't help), in laymans terms for the engine to idle succesfully, it likes a very predictable and even 'suck' through the inlet manifold and carb body (as a unit) to ensure it recieves just the right air/fuel mix. Its finely balanced and relies on the free flow of air and no leaks along the way. At idle, its this vaccum (or suck) that pulls in a small but steady trickle of petrol through passages in the carb (carb is basically inactive at idle remember). Therefore if theres a leak below the carb (inlet port gaskets, bottom carb gasket, brake servo pipe etc), the suck through the carb is seriously reduced and the mixture goes weak - weak enough to kill the idle but possibly not when revving the engine as fuel is injected down the carb throat at that point and then the engine doesn't give a fig really.

			Insufficient air (ie through a clogged air filter) won't supply enough oxygen and again the suck through the carb is reduced, mostly at idle although it'll probably pop and bang too on deceleration. A worn throttle flap also messes up the idle since air then gets sucked in through here (often randomly) and kills off the 'predictable' vaccum I mentioned earlier and often causes a 'hunting' idle or even sudden stalling as you approach junctions. A mixture screw set too lean can also do that but I don't advocate resetting mixture if its run ok up to now - find the cause first.

			The carb itself can become full of foreign bodies too which can clog the tiny passages/jets that supply the idle mixture. The above applies to all carb engines from Type1 onwards. It also applies to 2ltres with twin carbs which technically are one carb split into two and merely act as one carb when its running correctly.

			Sudden power loss at high speeds (ie forcing it from 60mph to 40mph) is usually due to level in float chamber falling below demand, caused by blocked fuel lines, filters, a worn fuel pump pushrod or indeed a tired fuel pump. Carbs in a nutshell really....

CovKid: /* Case history */

2010-05-03T10:41:35Z

Case history

← Older revision		Revision as of 10:41, 3 May 2010
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	'''NB.''' I must thank Roger Ball (2 Totlands Drive, Great Clacton) for the many many carbs he rebushed for me using phosphor bronze bushes. He still does carb bushes if anyone is out that way.		'''NB.''' I must thank Roger Ball (2 Totlands Drive, Great Clacton) for the many many carbs he rebushed for me using phosphor bronze bushes. He still does carb bushes if anyone is out that way.


			==Carb Renovation - Throttle Flap Wear==

			CovKid: Roger Ball in Clacton specialises in refurbishing throttle flaps on almost any make of carb. Carb makers tend to fit nylon bushes to throttle flaps as standard. He dumps these and fits phosphor bronze bushes which have superior wear characteristics and lube nicely. Roger will refurb worn throttle flaps via mail order, or dropped to him if local.

			You can reach him via: http://www.thephonebook.bt.com - residential numbers - R Ball - Clacton (won't put his number directly on here)

HarryMann at 09:44, 22 September 2008

2008-09-22T09:44:51Z

← Older revision		Revision as of 09:44, 22 September 2008
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	==~~Symptons~~==		==Symptoms==

	Poor idling, poor running generally, underpowered running, backfires, misfires... worse when engine hot, choke off; worse in cold weather sometimes.		Poor idling, poor running generally, underpowered running, backfires, misfires... worse when engine hot, choke off; worse in cold weather sometimes.

HarryMann at 22:34, 21 September 2008

2008-09-21T22:34:16Z

← Older revision		Revision as of 22:34, 21 September 2008
Line 1:		Line 1:
	==Symptons==		==Symptons==

	Poor idling, ~~pooe~~ running generally, underpowered running, backfires, misfires... worse when engine hot, choke off; worse in cold weather sometimes.		Poor idling, poor running generally, underpowered running, backfires, misfires... worse when engine hot, choke off; worse in cold weather sometimes.

HarryMann: /* Diagnosis */

2008-09-21T22:33:59Z

Diagnosis

← Older revision		Revision as of 22:33, 21 September 2008
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	'''Alternative diagnosis:'''		'''Alternative diagnosis:'''

	Heater plate under carb; diaphragm pull-down unit; idle stability mechanism; accelerator pump;		Heater plate under carb; diaphragm pull-down unit; idle stability mechanism; accelerator pump; '''All ignition problems, esp. coil.'''

	'''All ignition problems, esp. coil.'''

	==Maintenance==		==Maintenance==