Low speed jerkiness

[Wangler]

I’m trying to get rid of a moment of jerkiness when for example gently joining traffic at a roundabout from low rpm. It doesn’t always happen, but it often does. I’m happy that the ignition timing is pretty well spot on.
 
I have already replaced the 47 idle jets with 49 ones and that has made a small but helpful improvement.

I’m tempted to go up to 51 or 52, but wonder if plug fouling in traffic queues is likely to be an issue due to the increase in fuel/air ratio. I could go for hotter plugs which might help if there is a problem, but that might perhaps affect things at high revs. Any thoughts welcome.

[Spider2]

I experience a bit of the same and put it down to modern petrol. I might try bigger idle jets as well although I should get around to fitting a pair of 40 DCOE 31 Webers I have in my workshop. I may try and sell the Webers if anyone is interested and try and locate a pair of dellortos as they are simpler to fit

[dhla40]

I am using 50 jets with 120 air and response off the line is good but I still have a vague flat spot around 3000 rpm on light throttle which feels like engine braking, may be due to air leak but is not too bad so I live with it.

Sean

[lancialulu]

I am using 50 jets with 120 air and response off the line is good but I still have a vague flat spot around 3000 rpm on light throttle which feels like engine braking, may be due to air leak but is not too bad so I live with it.

Sean

Which version of PHH?

[dhla40]

PHH E3 which originally had 52.5 jets and 200 air, I tried 55 and 57 jets but finally fitted 120 brass air sleeves and 50 jets to get closer to the old PHH settings.

Sean

[Spider2]

I have been trawling through old threads about the solex carb and came across a post by David Wheeler in Feb 2013. He said fitting 55 idle jets made the engine pull smoothly from 1000 rpm. Do you remember that David?

[lancialulu]

I have been trawling through old threads about the solex carb and came across a post by David Wheeler in Feb 2013. He said fitting 55 idle jets made the engine pull smoothly from 1000 rpm. Do you remember that David?

That was a 1600 with 42 DDHF's iirc

[lancialulu]

PHH E3 which originally had 52.5 jets and 200 air, I tried 55 and 57 jets but finally fitted 120 brass air sleeves and 50 jets to get closer to the old PHH settings.

Sean

The air correction jet is fixed at 120 but the emulsion tube is the one with 175/180/190/ or 200.....

[Spider2]

I have no idea what idle jet size a 42 DDHF would have had originally fitted but I assume a 55 is larger. The point I was making was even 10 years ago people were experimenting with fitting larger idle jets to improve smooth pick up. Back in the 70's and 80's when old style 2, 3,4 & 5 * was the norm I assume people did not have this problem.

[dhla40]

The emission carbs have different idle air bleeds, E2 is 80 E3 is 200.

Sean

[lancialulu]

I thought I would update recent experience with a pair of PHH E3's fitted to a 1400 (yes one I built). First stage was to overhaul the carburettors and get the butterflies to close. These E3s have ball bearings on the shaft so wear is minimal. You have to fully dismantle though if using an ultrasonic bath as this will ruin the small ball bearing races. Then I chose to up the main jet from 115 to 125 (anticipating more fuel requirement of the  larger engine). The engine was ran for c 200 miles but tickover was erratic and it stalled when the electric Radiator fan ran. After checking (and rechecking) synchronising of the 2 carbs, balancing the 2 channels in each carb and finely adjusting the idle mixture screws with no improvement I replaced the 52.5 pilot jets with 60. Yes it was a big jump but I was suspicious that this larger engine needed more fuel in transition. Well bingo the engine had a solid tickover (did not die when the fan kicked in) and the previous hesitation completely disappeared. As the engine is still running in (max 4000rpm) it is impossible to say if any more adjustments will be required but clear evidence that upping the pilot jet removes the hesitation during slow speed acceleration.

[Wangler]

I thought I would update recent experience with a pair of PHH E3's fitted to a 1400 (yes one I built). First stage was to overhaul the carburettors and get the butterflies to close. These E3s have ball bearings on the shaft so wear is minimal. You have to fully dismantle though if using an ultrasonic bath as this will ruin the small ball bearing races. Then I chose to up the main jet from 115 to 125 (anticipating more fuel requirement of the  larger engine). The engine was ran for c 200 miles but tickover was erratic and it stalled when the electric Radiator fan ran. After checking (and rechecking) synchronising of the 2 carbs, balancing the 2 channels in each carb and finely adjusting the idle mixture screws with no improvement I replaced the 52.5 pilot jets with 60. Yes it was a big jump but I was suspicious that this larger engine needed more fuel in transition. Well bingo the engine had a solid tickover (did not die when the fan kicked in) and the previous hesitation completely disappeared. As the engine is still running in (max 4000rpm) it is impossible to say if any more adjustments will be required but clear evidence that upping the pilot jet removes the hesitation during slow speed acceleration.

That’s most interesting. Did the much larger jets cause any plug fouling at low revs or tickover?

[lancialulu]

I thought I would update recent experience with a pair of PHH E3's fitted to a 1400 (yes one I built). First stage was to overhaul the carburettors and get the butterflies to close. These E3s have ball bearings on the shaft so wear is minimal. You have to fully dismantle though if using an ultrasonic bath as this will ruin the small ball bearing races. Then I chose to up the main jet from 115 to 125 (anticipating more fuel requirement of the  larger engine). The engine was ran for c 200 miles but tickover was erratic and it stalled when the electric Radiator fan ran. After checking (and rechecking) synchronising of the 2 carbs, balancing the 2 channels in each carb and finely adjusting the idle mixture screws with no improvement I replaced the 52.5 pilot jets with 60. Yes it was a big jump but I was suspicious that this larger engine needed more fuel in transition. Well bingo the engine had a solid tickover (did not die when the fan kicked in) and the previous hesitation completely disappeared. As the engine is still running in (max 4000rpm) it is impossible to say if any more adjustments will be required but clear evidence that upping the pilot jet removes the hesitation during slow speed acceleration.

That’s most interesting. Did the much larger jets cause any plug fouling at low revs or tickover?

No and they wont if the idle mix can adjust within range. The car travelled back c150miles and report was no problems at all

[Spider2]

I think most 35 PHH were originally specked with 47.5 pilot jets for the 1300 engine but now it seems a larger one now works better. I assume It must be the modern fuel.

[Scott]

This is a really interesting thread.

My Fulvia has hesitation under normal throttle on starting off; not great in stop-start traffic. It's fine otherwise.

When I took my car for a tune-up to a specialist a couple of years ago they did a good job ... but said there was only so much they could do as the "carburettor spindle(s) are worn". From this I'm taking it to mean this: https://www.pieces-fulvia.com/pair-of-original-shafts-for-carburettors-solex-35-phh.htm

The carbs had a rebuild several years ago which was with a standard 'service kit' ... I can't recall if that would have involved new jets but I suspect so.

Is the 'worn spindles/shafts' analysis plausible and/or should the jets be the focus?