Big hesitation.

Please restrict your questions and replies to Capri related technical issues!
User avatar
D366Y
Donator
Donator
Posts: 2222
Joined: Mon Sep 03, 2012 2:26 pm
Car(s): 1986 Laser 1.6, daily runaround project
1981 GL Auto 2.0, Barn-Find-Resto, now also a runaround project
1980 3.0S, crash damage resto
1993 Fiesta 1.1

Currently full up and no more space but I still want a 2.8...
Location: Buckinghamshire

Re: Big hesitation.

Post by D366Y »

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. ;)
So the auto has started doing this recently as well - recs absolute fine without load, and if you squeeze the throttle she is ok (Ish) but if you plant your foot she wants to stall (or does)

I have checked points, timing and spark etc. So tried your trick earlier of looking down the carb - very interesting, you can see the first side squirt fuel and then if you keep going the second jet starts squirting too (interestingly the new (probably fake) Weber on the laser doesn't do this by I digress) - but the big hesitation when you plant your foot still occurs. It's almost like it's taking a deep breath and then tries to hold it for a few seconds before actually deciding what to do.

What is the best course of action? If this sounds like an accelerator pump I will look to change it, but to me carbs are the dark arts and I can just about get to grips with where air goes in and fuel goes in :lol:
A wise man once said... "you can never have too many capris - buy another" :beer:
It's me, I'm the wise man.
Mc Tool
Donator
Donator
Posts: 2000
Joined: Sat May 17, 2014 8:34 pm
Car(s): 1980 mk3 capri 2l ohc T9 , Toyota Blade Master 3.5l V6, Paso , 850T,rd400, 900ss
Location: Invercargill New Zealand

Re: Big hesitation.

Post by Mc Tool »

May sound like a dumb question ....but ....does it seem to run worse going uphill, or really hard to hot start when pointing uphill?
Sometimes I talk to myself ... and we both have a good laugh
User avatar
Peter-S
Donator
Donator
Posts: 7300
Joined: Mon Jul 28, 2008 7:57 am
Car(s): 1985 Capri 2.0
1983 Capri 2.8i
Location: Kent
Contact:

Re: Big hesitation.

Post by Peter-S »

D366Y wrote: Sat Sep 17, 2022 5:45 pm
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. ;)
So the auto has started doing this recently as well - recs absolute fine without load, and if you squeeze the throttle she is ok (Ish) but if you plant your foot she wants to stall (or does)

I have checked points, timing and spark etc. So tried your trick earlier of looking down the carb - very interesting, you can see the first side squirt fuel and then if you keep going the second jet starts squirting too (interestingly the new (probably fake) Weber on the laser doesn't do this by I digress) - but the big hesitation when you plant your foot still occurs. It's almost like it's taking a deep breath and then tries to hold it for a few seconds before actually deciding what to do.

What is the best course of action? If this sounds like an accelerator pump I will look to change it, but to me carbs are the dark arts and I can just about get to grips with where air goes in and fuel goes in :lol:
Sounds like something for us to do in a field next weekend - strip your carb and look for a split diaphragm 😁
ImageBanner by Peter Smith, on Flickr
User avatar
Bug
Posts: 3676
Joined: Sun Jan 04, 2009 3:52 pm
Car(s): Some

Re: Big hesitation.

Post by Bug »

D366Y wrote: Sat Sep 17, 2022 5:45 pm you can see the first side squirt fuel and then if you keep going the second jet starts squirting too
Are you saying that if you keep opening and closing the throttle then eventually the second jet starts to squirt as well?
The only point they split is at the base of the 'Y'. There is just a single ball bearing underneath that acts to stop fuel being continually drawn through by vacuum.
So to me the only issue could be a blocked jet in the second barrel half of the 'Y'.
Dead easy to whip the top off the carb, unscrew the bolt and get the 'Y' out to blow it through. Don't lose the ball bearing under it though.

Scary how after at least 12 years since my last Pinto I can still visualise exactly how to strip the carb. :D
User avatar
D366Y
Donator
Donator
Posts: 2222
Joined: Mon Sep 03, 2012 2:26 pm
Car(s): 1986 Laser 1.6, daily runaround project
1981 GL Auto 2.0, Barn-Find-Resto, now also a runaround project
1980 3.0S, crash damage resto
1993 Fiesta 1.1

Currently full up and no more space but I still want a 2.8...
Location: Buckinghamshire

Re: Big hesitation.

Post by D366Y »

Bug wrote: Sun Sep 18, 2022 2:00 pm
D366Y wrote: Sat Sep 17, 2022 5:45 pm you can see the first side squirt fuel and then if you keep going the second jet starts squirting too
Are you saying that if you keep opening and closing the throttle then eventually the second jet starts to squirt as well?
The only point they split is at the base of the 'Y'. There is just a single ball bearing underneath that acts to stop fuel being continually drawn through by vacuum.
So to me the only issue could be a blocked jet in the second barrel half of the 'Y'.
Dead easy to whip the top off the carb, unscrew the bolt and get the 'Y' out to blow it through. Don't lose the ball bearing under it though.

Scary how after at least 12 years since my last Pinto I can still visualise exactly how to strip the carb. :D
It is very impressive how you can still remember it all!
I meant that if I open the throttle from closed to fully open, the first jet squirts in, then when you keep going the second jet squirts in around the 2/3rds mark

As Peter says, looks like we could do this next weekend!!
Peter-S wrote: Sat Sep 17, 2022 8:53 pm
Sounds like something for us to do in a field next weekend - strip your carb and look for a split diaphragm 😁
As long as you can promise me I'll still get home that's fine by me :lol:

I did buy a whole carb rebuilt kit a little while ago but was so unconfident about doing it on my own I've just left it in the box

Would be a perfect to bring the GL out anyway, I usually always being Debby to CRaP so this way you can finally meet June haha
A wise man once said... "you can never have too many capris - buy another" :beer:
It's me, I'm the wise man.
User avatar
Bug
Posts: 3676
Joined: Sun Jan 04, 2009 3:52 pm
Car(s): Some

Re: Big hesitation.

Post by Bug »

D366Y wrote: Sun Sep 18, 2022 2:53 pm
Bug wrote: Sun Sep 18, 2022 2:00 pm
D366Y wrote: Sat Sep 17, 2022 5:45 pm you can see the first side squirt fuel and then if you keep going the second jet starts squirting too
Are you saying that if you keep opening and closing the throttle then eventually the second jet starts to squirt as well?
The only point they split is at the base of the 'Y'. There is just a single ball bearing underneath that acts to stop fuel being continually drawn through by vacuum.
So to me the only issue could be a blocked jet in the second barrel half of the 'Y'.
Dead easy to whip the top off the carb, unscrew the bolt and get the 'Y' out to blow it through. Don't lose the ball bearing under it though.

Scary how after at least 12 years since my last Pinto I can still visualise exactly how to strip the carb. :D
It is very impressive how you can still remember it all!
I meant that if I open the throttle from closed to fully open, the first jet squirts in, then when you keep going the second jet squirts in around the 2/3rds mark

As Peter says, looks like we could do this next weekend!!
Peter-S wrote: Sat Sep 17, 2022 8:53 pm
Sounds like something for us to do in a field next weekend - strip your carb and look for a split diaphragm 😁
As long as you can promise me I'll still get home that's fine by me :lol:

I did buy a whole carb rebuilt kit a little while ago but was so unconfident about doing it on my own I've just left it in the box

Would be a perfect to bring the GL out anyway, I usually always being Debby to CRaP so this way you can finally meet June haha
That's odd as the two jets should squirt simultaneously.
However, the second throttle only opens at the 2/3 mark, so maybe you're just not seeing it until then?
I'd suggest one of you takes a pump of some description to blast some air through.
Not sure which field you're heading to but sadly I can't make it as annoyingly I have to get on a plane to the Caribbean :D
User avatar
D366Y
Donator
Donator
Posts: 2222
Joined: Mon Sep 03, 2012 2:26 pm
Car(s): 1986 Laser 1.6, daily runaround project
1981 GL Auto 2.0, Barn-Find-Resto, now also a runaround project
1980 3.0S, crash damage resto
1993 Fiesta 1.1

Currently full up and no more space but I still want a 2.8...
Location: Buckinghamshire

Re: Big hesitation.

Post by D366Y »

With Peters help on Saturday we took the head off the carb, the Y was taken out and blown through (the scree holding it in was very loose!), And the diaphragms on both side were changed and it does run much better :D

It no longer tries to stall itself when coming off the throttle, but when you plant your foot it does still reert to running on 3 cylinders...
As Peter pointed out, it may have something to with my impeccable air filter... 👀

Will change that first, then set the timing again if still doing it

Cheers
A wise man once said... "you can never have too many capris - buy another" :beer:
It's me, I'm the wise man.
Mc Tool
Donator
Donator
Posts: 2000
Joined: Sat May 17, 2014 8:34 pm
Car(s): 1980 mk3 capri 2l ohc T9 , Toyota Blade Master 3.5l V6, Paso , 850T,rd400, 900ss
Location: Invercargill New Zealand

Re: Big hesitation.

Post by Mc Tool »

Does your carb have the anti stall diagram system fitted ......looks a bit like the accelerator pump.......pretty sure it feeds into the same y nozzles. The thing is a spring loaded diaphragm that is held back by manifold vacuum , spring and manifold vac on one side and fuel on the other. When engine is in danger of stalling low manifold vacuum allows the spring to push the fuel reserve on tother side of diaphragm into the accelerator pump circuit and engine recovers.
Might be nothing but its in the right area.🙂
Sometimes I talk to myself ... and we both have a good laugh
User avatar
D366Y
Donator
Donator
Posts: 2222
Joined: Mon Sep 03, 2012 2:26 pm
Car(s): 1986 Laser 1.6, daily runaround project
1981 GL Auto 2.0, Barn-Find-Resto, now also a runaround project
1980 3.0S, crash damage resto
1993 Fiesta 1.1

Currently full up and no more space but I still want a 2.8...
Location: Buckinghamshire

Re: Big hesitation.

Post by D366Y »

Pretty sure we changed that one too Hamish... Acceleratr pump diaphragm on the driver's side and awkward to get at, vacuum diaphragm on the other side that was much easier to get at and both were changed

Solved the wanting to stall aspect of it, just need to get it running right now!
A wise man once said... "you can never have too many capris - buy another" :beer:
It's me, I'm the wise man.
User avatar
Peter-S
Donator
Donator
Posts: 7300
Joined: Mon Jul 28, 2008 7:57 am
Car(s): 1985 Capri 2.0
1983 Capri 2.8i
Location: Kent
Contact:

Re: Big hesitation.

Post by Peter-S »

D366Y wrote: Mon Sep 26, 2022 12:23 pm
As Peter pointed out, it may have something to with my impeccable air filter... 👀


Cheers
A cool wash and gentle spin and it will be fine 😄
ImageBanner by Peter Smith, on Flickr
User avatar
D366Y
Donator
Donator
Posts: 2222
Joined: Mon Sep 03, 2012 2:26 pm
Car(s): 1986 Laser 1.6, daily runaround project
1981 GL Auto 2.0, Barn-Find-Resto, now also a runaround project
1980 3.0S, crash damage resto
1993 Fiesta 1.1

Currently full up and no more space but I still want a 2.8...
Location: Buckinghamshire

Re: Big hesitation.

Post by D366Y »

Peter-S wrote: Tue Sep 27, 2022 7:19 am
D366Y wrote: Mon Sep 26, 2022 12:23 pm
As Peter pointed out, it may have something to with my impeccable air filter... 👀


Cheers
A cool wash and gentle spin and it will be fine 😄
I've just ordered a new one so will see if that fixes the misfiring... As someone wisely mentioned - if no fuel can get to the engine it won't run right!! 😂
A wise man once said... "you can never have too many capris - buy another" :beer:
It's me, I'm the wise man.
Post Reply