Big hesitation.

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cahootchey
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Big hesitation.

Post by cahootchey »

Looking to hear if anyone can give me advice on what to check out on the 1.6 laser. The engine starts good, but on pressing the accelerator there is a big hesitation, do it slowly and it will rev ok. Out on the road i can drive it but if there is a hill it gets quite hard to get to the top. Timing is right, electronic ign, carb seems in tune but smells rich going up a hill. New filters all round. Going for the MOT saturday 2nd april, hopefully will pass even if not running properly.
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Re: Big hesitation.

Post by Supercharged Nat »

What carb is fitted? If the weber dgav from the 2.0l, then it could be float valve not sealing, or dodgey power valve diaphram making rich mixture...
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Re: Big hesitation.

Post by [email protected] »

It sounds like it could be an ignition or timing issue, are you sure that the vacuum advance is free and working? Was it timed static or running with vacuum detached? What is it set to BTC? I assume all the ignition components are in good order, dizzy cap and rotor arm and plugs still need to be in good nick with electronic ignition.
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Re: Big hesitation.

Post by Jasonmarie »

Gaps in plugs ? Leads ? But as they say what carb are you running ?
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Bug
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Re: Big hesitation.

Post by Bug »

I think the rich fuel smell is the giveaway here.
Too much fuel getting into the carb so when you accelerate and it adds even more then its moving the mixture outside of a combustible range.

However, if the above answers don't cure it then this is also a classic symptom of a failing accelerator pump diaphragm.
When you push the throttle down, the flap opens which suddenly dumps the low pressure by reducing the venturi effect (Check out Bernoulli's Theorem). Therefore the carb temporarily cannot suck the fuel through the jet.
The accelerator pump exists to cover this temporary loss of low pressure by firing fuel straight into the carb mouth.
If you open the throttle slowly the engine is able to keep up and keep pulling the air through fast enough to create a low pressure area in the carb, thus sucking in fuel.
The accelerator pump is basically a diaphragm with a big spring behind it. The spring forces the diaphragm across to allow room for a small reservoir of fuel to accumulate behind it.
When you push the accelerator open a long way, the linkage acts on a plunger on the other side of the diaphragm, overcoming the spring and pushing the diaphragm across, forcing the accumulated fuel out through a jet into the carb mouth.
If the diaphragm splits the fuel just nips to the other side of it and doesn't squirt in.

Simple check. Take of the air filter, look down the carb and open the throttle right up. Don't need the engine running. You should see a squirt of fuel.
On the assumption that you have a 32/36 DGAV fitted then there is a Y-shaped nozzle below the choke flaps. If the carb came off a lower spec (GL or similar, you may well only see fuel squirt into one barrel as the other side is blanked off. On a 'S' model, it should squirt into both barrels.

You may also have a blocked Y-nozzle. Simply remove the top of the carb, undo the screw in the middle and lift it out to clean it. Beware there is a very small ball bearing underneath the nozzle body, which acts as a valve to stop the carb sucking fuel through in normal operation.

Probably not your issue, but always handy to know a bit more about how the carb works. ;)
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Re: Big hesitation.

Post by Not_Anumber »

If yours still has the standard single barrel VV type carb as fitted to most non S 1.6 Capris then this isnt worth fixing. An opportunity to swap to a good used 32/36 Weber & manifold. Better reliability and bhp for very little money.
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Re: Big hesitation.

Post by D366Y »

Not_Anumber wrote: Mon Mar 28, 2022 3:58 pm If yours still has the standard single barrel VV type carb as fitted to most non S 1.6 Capris then this isnt worth fixing. An opportunity to swap to a good used 32/36 Weber & manifold. Better reliability and bhp for very little money.
Second this swap!
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Re: Big hesitation.

Post by STEVEW »

If yours still has the standard single barrel VV type carb as fitted to most non S 1.6 Capris then this isnt worth fixing. An opportunity to swap to a good used 32/36 Weber & manifold. Better reliability and bhp for very little money.
:cool:

This sounds like a good fix to me.
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Re: Big hesitation.

Post by pbar »

Bug wrote: Mon Mar 28, 2022 12:13 pm I think the rich fuel smell is the giveaway here.
Too much fuel getting into the carb so when you accelerate and it adds even more then its moving the mixture outside of a combustible range.

However, if the above answers don't cure it then this is also a classic symptom of a failing accelerator pump diaphragm.
When you push the throttle down, the flap opens which suddenly dumps the low pressure by reducing the venturi effect (Check out Bernoulli's Theorem). Therefore the carb temporarily cannot suck the fuel through the jet.
The accelerator pump exists to cover this temporary loss of low pressure by firing fuel straight into the carb mouth.
If you open the throttle slowly the engine is able to keep up and keep pulling the air through fast enough to create a low pressure area in the carb, thus sucking in fuel.
The accelerator pump is basically a diaphragm with a big spring behind it. The spring forces the diaphragm across to allow room for a small reservoir of fuel to accumulate behind it.
When you push the accelerator open a long way, the linkage acts on a plunger on the other side of the diaphragm, overcoming the spring and pushing the diaphragm across, forcing the accumulated fuel out through a jet into the carb mouth.
If the diaphragm splits the fuel just nips to the other side of it and doesn't squirt in.

Simple check. Take of the air filter, look down the carb and open the throttle right up. Don't need the engine running. You should see a squirt of fuel.
On the assumption that you have a 32/36 DGAV fitted then there is a Y-shaped nozzle below the choke flaps. If the carb came off a lower spec (GL or similar, you may well only see fuel squirt into one barrel as the other side is blanked off. On a 'S' model, it should squirt into both barrels.

You may also have a blocked Y-nozzle. Simply remove the top of the carb, undo the screw in the middle and lift it out to clean it. Beware there is a very small ball bearing underneath the nozzle body, which acts as a valve to stop the carb sucking fuel through in normal operation.

Probably not your issue, but always handy to know a bit more about how the carb works. ;)

That's a super post.
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Bug
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Re: Big hesitation.

Post by Bug »

pbar wrote: Mon Mar 28, 2022 9:14 pm That's a super post.
Thanks mate, and on the face of it, probably bugger all to do with the OPs problem :xd:

I did forget to add that a sneaky minor mod if you have the 'GL' spec 32/36 is to find the Y-nozzle from an 'S' and fit that.
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Re: Big hesitation.

Post by pbar »

Bug wrote: Tue Mar 29, 2022 6:50 pm
I did forget to add that a sneaky minor mod if you have the 'GL' spec 32/36 is to find the Y-nozzle from an 'S' and fit that.

Martin, tips like that are pure gold dust. I mean, how would anyone know about that, unless you hear it from someone who was there back then doing all these things.
cahootchey
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Re: Big hesitation.

Post by cahootchey »

Thanks to every one that replied to my question last sunday. I work away from home, came home early with cover, just got round to checking reply. So, its 32 weber manual choke. Timing was done running, vacuum disconnected and block off. New cap, rotor and leads. Timing set at 6 % btdc. Not outside yet but will check the suggestions by you all. Thanks again.
cahootchey
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Re: Big hesitation.

Post by cahootchey »

Should have read COVID.
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Bug
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Re: Big hesitation.

Post by Bug »

Are you getting anywhere with this?

Or still hesitating? :xd:
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Re: Big hesitation.

Post by Bug »

C'mon now. That's another month gone by.
The biggest hesitation seems to be fixing it. :xd:
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Re: Big hesitation.

Post by D366Y »

If it helps Bug I had a big hesitation as well, set the points again and problem solved!
Only thing is that I also seem to have fiddled with the timing as the auto now changed up gears way too early and I can't seem to sort it again :roll: :lol:
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Re: Big hesitation.

Post by Mr B »

Bug wrote: Mon Mar 28, 2022 12:13 pm I think the rich fuel smell is the giveaway here.
Too much fuel getting into the carb so when you accelerate and it adds even more then its moving the mixture outside of a combustible range.

However, if the above answers don't cure it then this is also a classic symptom of a failing accelerator pump diaphragm.
When you push the throttle down, the flap opens which suddenly dumps the low pressure by reducing the venturi effect (Check out Bernoulli's Theorem). Therefore the carb temporarily cannot suck the fuel through the jet.
The accelerator pump exists to cover this temporary loss of low pressure by firing fuel straight into the carb mouth.
If you open the throttle slowly the engine is able to keep up and keep pulling the air through fast enough to create a low pressure area in the carb, thus sucking in fuel.
The accelerator pump is basically a diaphragm with a big spring behind it. The spring forces the diaphragm across to allow room for a small reservoir of fuel to accumulate behind it.
When you push the accelerator open a long way, the linkage acts on a plunger on the other side of the diaphragm, overcoming the spring and pushing the diaphragm across, forcing the accumulated fuel out through a jet into the carb mouth.
If the diaphragm splits the fuel just nips to the other side of it and doesn't squirt in.

Simple check. Take of the air filter, look down the carb and open the throttle right up. Don't need the engine running. You should see a squirt of fuel.
On the assumption that you have a 32/36 DGAV fitted then there is a Y-shaped nozzle below the choke flaps. If the carb came off a lower spec (GL or similar, you may well only see fuel squirt into one barrel as the other side is blanked off. On a 'S' model, it should squirt into both barrels.

You may also have a blocked Y-nozzle. Simply remove the top of the carb, undo the screw in the middle and lift it out to clean it. Beware there is a very small ball bearing underneath the nozzle body, which acts as a valve to stop the carb sucking fuel through in normal operation.

Probably not your issue, but always handy to know a bit more about how the carb works. ;)
I think your spot on here Bug, had the same problem with a 390 Holley carb, on the the Holley you can adjust when the accelerator pump does it's thing, on mine I had it set too late, crack the throttle, big rush of air into engine, no fuel to go with it = big hesitation until it catches up with itself.

Great Post explaining how it all works, wish you had wrote this about 2 years ago!

Wayne
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Re: Big hesitation.

Post by Mc Tool »

I have found 3 holley 390's now that have had the wrong accelerator pump diaphragm assy fitted. The difference being the length of the linkage rod . These may have been part of an incorrect overhaul kit but whatever it sure gave problems getting the thing to run right.
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Re: Big hesitation.

Post by Mr B »

Mc Tool wrote: Wed May 04, 2022 10:04 am I have found 3 holley 390's now that have had the wrong accelerator pump diaphragm assy fitted. The difference being the length of the linkage rod . These may have been part of an incorrect overhaul kit but whatever it sure gave problems getting the thing to run right.
Good call, got a Holley on a V6 Essex, took a lot of fucking about to get it dialled in - as you know there are loads of options for tuning it to your application which can be a headache but once it's done it certainly let's the Essex breathe and along with big valve heads it ain't far behind triple webbers and no where near the price of the triple carb set up.

Wayne
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Re: Big hesitation.

Post by Bug »

Mr B wrote: Wed May 04, 2022 9:26 am
Bug wrote: Mon Mar 28, 2022 12:13 pm I think the rich fuel smell is the giveaway here.
Too much fuel getting into the carb so when you accelerate and it adds even more then its moving the mixture outside of a combustible range.

However, if the above answers don't cure it then this is also a classic symptom of a failing accelerator pump diaphragm.
When you push the throttle down, the flap opens which suddenly dumps the low pressure by reducing the venturi effect (Check out Bernoulli's Theorem). Therefore the carb temporarily cannot suck the fuel through the jet.
The accelerator pump exists to cover this temporary loss of low pressure by firing fuel straight into the carb mouth.
If you open the throttle slowly the engine is able to keep up and keep pulling the air through fast enough to create a low pressure area in the carb, thus sucking in fuel.
The accelerator pump is basically a diaphragm with a big spring behind it. The spring forces the diaphragm across to allow room for a small reservoir of fuel to accumulate behind it.
When you push the accelerator open a long way, the linkage acts on a plunger on the other side of the diaphragm, overcoming the spring and pushing the diaphragm across, forcing the accumulated fuel out through a jet into the carb mouth.
If the diaphragm splits the fuel just nips to the other side of it and doesn't squirt in.

Simple check. Take of the air filter, look down the carb and open the throttle right up. Don't need the engine running. You should see a squirt of fuel.
On the assumption that you have a 32/36 DGAV fitted then there is a Y-shaped nozzle below the choke flaps. If the carb came off a lower spec (GL or similar, you may well only see fuel squirt into one barrel as the other side is blanked off. On a 'S' model, it should squirt into both barrels.

You may also have a blocked Y-nozzle. Simply remove the top of the carb, undo the screw in the middle and lift it out to clean it. Beware there is a very small ball bearing underneath the nozzle body, which acts as a valve to stop the carb sucking fuel through in normal operation.

Probably not your issue, but always handy to know a bit more about how the carb works. ;)
I think your spot on here Bug, had the same problem with a 390 Holley carb, on the the Holley you can adjust when the accelerator pump does it's thing, on mine I had it set too late, crack the throttle, big rush of air into engine, no fuel to go with it = big hesitation until it catches up with itself.

Great Post explaining how it all works, wish you had wrote this about 2 years ago!

Wayne
Cheers Wayne,
I just did it to prove I can still remember, not having had a Capri for quite a while now.
Reckon I could still set up an auto choke though. ;)
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