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Author 1989 vfr 750 fg engine
cpcrampton
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Registered: 16th Feb 07
Location: Stirling
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13th Mar 12 at 19:25   View User's Profile U2U Member Reply With Quote
Basically I have a vfr 750 (v4 engine) that will choke on full throttle although it will rev to the red line under partial throttle. Everything has been stripped down and checked and I cannot seem to find the problem. Any ideas?

Noticed the front banks plugs are suity! So front bank running rich but the carbs have been set up properly using gauges. Could a exhaust restriction in the front manifold being removed cause this? Ie no restriction allowing more fuel being pulled through allowing the front bank to run rich?

Note ; it is a new front manifold and it looks alot more free flowing at the ports than the old one. The old style is on the rear bank btw.

Any views appreciated.
Tiger
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Registered: 12th Jun 01
Location: Leicestershire Drives:Astra VXR
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13th Mar 12 at 19:36   View User's Profile U2U Member Reply With Quote
Is it in a Corsa?
harrisp
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Registered: 15th Dec 07
Location: Derbyshire
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13th Mar 12 at 19:37   View User's Profile U2U Member Reply With Quote
quote:
Originally posted by Tiger
Is it in a Corsa?


Is it in a the corsa section?
Tiger
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Registered: 12th Jun 01
Location: Leicestershire Drives:Astra VXR
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13th Mar 12 at 19:38   View User's Profile U2U Member Reply With Quote
quote:
Originally posted by harrisp
quote:
Originally posted by Tiger
Is it in a Corsa?


Is it in a the corsa section?


Are you Italian?
cpcrampton
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Registered: 16th Feb 07
Location: Stirling
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13th Mar 12 at 19:38   View User's Profile U2U Member Reply With Quote
No it's in a bike.
Tiger
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Registered: 12th Jun 01
Location: Leicestershire Drives:Astra VXR
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13th Mar 12 at 19:40   View User's Profile U2U Member Reply With Quote
quote:
Originally posted by cpcrampton
No it's in a bike.


Checked the float bowls?
cpcrampton
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Registered: 16th Feb 07
Location: Stirling
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13th Mar 12 at 19:45   View User's Profile U2U Member Reply With Quote
Checked, all carbs have been stripped down to nothing cleaned and rebuild. Gaskets replaced , needles all set.
Tiger
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Registered: 12th Jun 01
Location: Leicestershire Drives:Astra VXR
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13th Mar 12 at 20:00   View User's Profile U2U Member Reply With Quote
Check your coils, valve clearance. Are the jets ok? Can you check the Igition module?
cpcrampton
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Registered: 16th Feb 07
Location: Stirling
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13th Mar 12 at 20:09   View User's Profile U2U Member Reply With Quote
Coils and leads are new, haven't checked valve Clearance, jets are new low speed jets are set and the high speed ones cannot be adjusted. The ignition module is new, the rectifier is new. I have a replacement engine and loom and now it's just a case of elimination. I thought maybe the free flowing manifold on the front bank could be the cause.
Tiger
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Registered: 12th Jun 01
Location: Leicestershire Drives:Astra VXR
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13th Mar 12 at 20:12   View User's Profile U2U Member Reply With Quote
Any breather hoses blocked? Fuel/breather hose pinched under tank maybe?
cpcrampton
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Registered: 16th Feb 07
Location: Stirling
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13th Mar 12 at 20:18   View User's Profile U2U Member Reply With Quote
You sound as if this has happened to yourself before?

Yes iv checked the breather on the tank, it was capped but the rubber had dried and cracked. Now running the newer style filter. It is free flowing though.

When looking at the fuel filter (clear plastic) you can see its full of fuel under partial throttle but half full under full throttle. Is this normal? Possible pump or tank breather problem?
Tiger
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Registered: 12th Jun 01
Location: Leicestershire Drives:Astra VXR
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13th Mar 12 at 20:27   View User's Profile U2U Member Reply With Quote
I used to strip and build bikes for fun when I was about 13 and I did a bit of motocross, I just used to watch my dad do stuff and pick it up real easy.

Try your fuel tank breather hose, blow through it in case its blocked. if its accesible its not uncommon to get blocked with bugs/flys.
cpcrampton
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Registered: 16th Feb 07
Location: Stirling
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13th Mar 12 at 20:30   View User's Profile U2U Member Reply With Quote
I will give it a go tomorrow, if I open the tank filler cap I should be able to blow freely through the hose ?
Tiger
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Registered: 12th Jun 01
Location: Leicestershire Drives:Astra VXR
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13th Mar 12 at 20:30   View User's Profile U2U Member Reply With Quote
Your filter level will change with flow and demand, if it were totally empty or totally full i'd investigate maybe.
Tiger
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Registered: 12th Jun 01
Location: Leicestershire Drives:Astra VXR
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13th Mar 12 at 20:31   View User's Profile U2U Member Reply With Quote
quote:
Originally posted by cpcrampton
I will give it a go tomorrow, if I open the tank filler cap I should be able to blow freely through the hose ?


Yeah but because its a small diameter dont be surprised if its a little restricted, just have to use your judgement. maybe try getting something through it like a bit of welding wire perhaps, or something like it.
cpcrampton
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Registered: 16th Feb 07
Location: Stirling
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13th Mar 12 at 20:34   View User's Profile U2U Member Reply With Quote
Il have a play tomorrow.

What's your thought on the restriction on the exhaust?
Tiger
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Registered: 12th Jun 01
Location: Leicestershire Drives:Astra VXR
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13th Mar 12 at 20:38   View User's Profile U2U Member Reply With Quote
If its set up like you say it should be a problem, if you tuned it after adding the manifold then you will have balanced the minor difference in exhaust gases out, i'd recheck the valve clearance though on the front bank and maybe adjust as your exhaust gases will be leaving the cylinder faster than before.
cpcrampton
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Registered: 16th Feb 07
Location: Stirling
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13th Mar 12 at 20:42   View User's Profile U2U Member Reply With Quote
Ok, thanks for all of your input. You've been a great help. I will update tomorrow or Thursday.

Tiger
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Registered: 12th Jun 01
Location: Leicestershire Drives:Astra VXR
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13th Mar 12 at 20:44   View User's Profile U2U Member Reply With Quote
No worries.

 
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