Re: Zel's Fleet Blog...Jag, Citroen, Mercedes, Sinclair & AC Model 70
Posted: Sun Aug 02, 2020 11:14 pm
Following the experiment yesterday I had cobbled together a link to the throttle control...which went *ping* the first time I tried applying full throttle.
Version 2.0 was quickly put together.
This actually worked surprisingly well.
Unfortunately actually on the road this carb didn't work as well as it looked like it might. On wide open throttle it feels like the engine is really bogging down at lower revs. However it has very much highlighted how well the original one isn't behaving in some circumstances. The throttle response here is far more linear, the original one felt that there was far more of an off/medium/high sort of throttle. This one is also far happier to sit on a very light throttle at a set speed - 30mph for example can be maintained without needing to continually adjust.
Being able to just bring the revs up till the clutch starts to bite and then being able to just roll it on as you move off makes things so much smoother and pleasant.
At higher revs it felt more lively so long as you didn't go beyond about 70% throttle.
I think I might be seeing a reason that it feels like this engine is holding back a bit at the top end. Here's what I saw when I got back from the test.
Not maybe obvious in the photo but the whole outer of the carb was swimming in fuel.
Doing some testing with the air cleaner off showed an interesting effect - when the throttle is opened anywhere beyond about 50% there is a tendency for a fine mist of fuel to want to hover about 2" above the carb throat - I'm guessing suspended there by pressure waves caused by resonance within the inlet manifold.
I'm sure I recall hearing of folks using dual carbs on air cooled VWs (so each carb feeding two cylinders exactly like this) having trouble with exactly this phenomenon with certain carb setups. Pretty sure I've heard this referred to as "fuel lift" on a couple of occasions.
That's where the fuel that I've been seeing running off the carb has been coming from though, it's nothing to do with a leak. It's literally been getting sprayed over the inside of the air cleaner housing, then running down over the carb. The air cleaner is just a metal-on-metal join so isn't hermetically sealed or anything like that.
I'm getting the feeling that's putting a theoretical limit on how much charge we can get into the engine, and why it has always felt like the last 30% or so of the throttle travel really doesn't seem to do anything.
I think it's a combination between this effect and the carb being better to run slightly lean (according to the manual) which might together account for the sneezing habit.
What to actually *do* about it though I've no idea. Applying some brainpower and maybe ask thoughts from folks who do more engine tuning etc for a living may be the answer. Will let you know if I get anywhere.
In the meantime though I will put the original carb back...after further cleaning. I'd obviously failed to shift the offending gunk last time around so it was dismantled again and chucked back in the ultrasonic cleaner.
My cleaner wasn't quite big enough to fully submerge the whole carb though which was always rather limiting.
However someone on another forum presented an idea which was a stroke of genius and effectively made my ultrasonic cleaner more than big enough.
Plenty big enough to thoroughly submerge it now.
It was left in there with the cleaner running for a full two hours. It *definitely* shifted a lot more crud this time round...both based on the sludge left behind when it was removed from the cleaner and just how it looks.
I'll get it out back on the car tomorrow and see where we are. Setup procedure will be done by the book too.
So while this carb experiment might not have been an immediate fix, the behaviour when bumbling around at 30mph or below, starting etc has very much highlighted that the existing carb wasn't allowing the engine to perform as well as it could. Whether that's down to this carb being in need of a professional service or just limitations of the combination of this carb and this engine is something I've yet to confirm. One thing I will be doing is rechecking the valve clearances. I did check these when I first got KPL, but that was a long time ago. 0.15mm is the correct cold clearance for both inlet and exhaust valves. It will be a lot more of a faff now the engine is in TPA because she has intact wheel wells...
Will order in a new set of rocker cover gaskets first though. I was incredibly lucky to get them to seal properly when I reused them the first time round, expecting them to survive being taken off and refitted twice is a bit of an ask...
Also on the subject of carburetors I'm glad to report that the scruffy roadside find lawn mower is working like new again with the new carb fitted.
Might even treat it to a clean as a reward for living to fight another day. While it looks like hell it is mechanically well looked after though...the oil is a lot cleaner than the outside. I have tried four times now to buy a new grass box for it, every time I get an email several days after the order saying "sorry we don't actually have one in stock."
I noticed yesterday that the offside tailpipe on the Jag was buzzing again. Turned out it had managed to rotate and was touching the underside of the cutout under the bumper. Five minute job to tweak the alignment and clamp it a bit more securely.
This is how the tips now sit.
Know a few of you wanted to know why I'd spent time faffing with it. This is why. Sorry, didn't want to make too much noise as our neighbours were having lunch in the garden opposite.
YouTube Link
I'll try to get a proper driving video shortly.
That however is why I was messing with the exhaust. Sounds a bit more purposeful now I think...
Oh, and the leather has been treated a further two times today. It's almost getting to the stage where the conditioner actually sticks around for more than two milliseconds before being absorbed now.
More excuses to play with the wide angle mode on the camera too.
Looks like this car was really well looked after in a lot of ways but the leather had been quite neglected.
Something I really need to do as a matter of some urgency is get some floor mats. I keep meaning to but keep forgetting.
Version 2.0 was quickly put together.
This actually worked surprisingly well.
Unfortunately actually on the road this carb didn't work as well as it looked like it might. On wide open throttle it feels like the engine is really bogging down at lower revs. However it has very much highlighted how well the original one isn't behaving in some circumstances. The throttle response here is far more linear, the original one felt that there was far more of an off/medium/high sort of throttle. This one is also far happier to sit on a very light throttle at a set speed - 30mph for example can be maintained without needing to continually adjust.
Being able to just bring the revs up till the clutch starts to bite and then being able to just roll it on as you move off makes things so much smoother and pleasant.
At higher revs it felt more lively so long as you didn't go beyond about 70% throttle.
I think I might be seeing a reason that it feels like this engine is holding back a bit at the top end. Here's what I saw when I got back from the test.
Not maybe obvious in the photo but the whole outer of the carb was swimming in fuel.
Doing some testing with the air cleaner off showed an interesting effect - when the throttle is opened anywhere beyond about 50% there is a tendency for a fine mist of fuel to want to hover about 2" above the carb throat - I'm guessing suspended there by pressure waves caused by resonance within the inlet manifold.
I'm sure I recall hearing of folks using dual carbs on air cooled VWs (so each carb feeding two cylinders exactly like this) having trouble with exactly this phenomenon with certain carb setups. Pretty sure I've heard this referred to as "fuel lift" on a couple of occasions.
That's where the fuel that I've been seeing running off the carb has been coming from though, it's nothing to do with a leak. It's literally been getting sprayed over the inside of the air cleaner housing, then running down over the carb. The air cleaner is just a metal-on-metal join so isn't hermetically sealed or anything like that.
I'm getting the feeling that's putting a theoretical limit on how much charge we can get into the engine, and why it has always felt like the last 30% or so of the throttle travel really doesn't seem to do anything.
I think it's a combination between this effect and the carb being better to run slightly lean (according to the manual) which might together account for the sneezing habit.
What to actually *do* about it though I've no idea. Applying some brainpower and maybe ask thoughts from folks who do more engine tuning etc for a living may be the answer. Will let you know if I get anywhere.
In the meantime though I will put the original carb back...after further cleaning. I'd obviously failed to shift the offending gunk last time around so it was dismantled again and chucked back in the ultrasonic cleaner.
My cleaner wasn't quite big enough to fully submerge the whole carb though which was always rather limiting.
However someone on another forum presented an idea which was a stroke of genius and effectively made my ultrasonic cleaner more than big enough.
Plenty big enough to thoroughly submerge it now.
It was left in there with the cleaner running for a full two hours. It *definitely* shifted a lot more crud this time round...both based on the sludge left behind when it was removed from the cleaner and just how it looks.
I'll get it out back on the car tomorrow and see where we are. Setup procedure will be done by the book too.
So while this carb experiment might not have been an immediate fix, the behaviour when bumbling around at 30mph or below, starting etc has very much highlighted that the existing carb wasn't allowing the engine to perform as well as it could. Whether that's down to this carb being in need of a professional service or just limitations of the combination of this carb and this engine is something I've yet to confirm. One thing I will be doing is rechecking the valve clearances. I did check these when I first got KPL, but that was a long time ago. 0.15mm is the correct cold clearance for both inlet and exhaust valves. It will be a lot more of a faff now the engine is in TPA because she has intact wheel wells...
Will order in a new set of rocker cover gaskets first though. I was incredibly lucky to get them to seal properly when I reused them the first time round, expecting them to survive being taken off and refitted twice is a bit of an ask...
Also on the subject of carburetors I'm glad to report that the scruffy roadside find lawn mower is working like new again with the new carb fitted.
Might even treat it to a clean as a reward for living to fight another day. While it looks like hell it is mechanically well looked after though...the oil is a lot cleaner than the outside. I have tried four times now to buy a new grass box for it, every time I get an email several days after the order saying "sorry we don't actually have one in stock."
I noticed yesterday that the offside tailpipe on the Jag was buzzing again. Turned out it had managed to rotate and was touching the underside of the cutout under the bumper. Five minute job to tweak the alignment and clamp it a bit more securely.
This is how the tips now sit.
Know a few of you wanted to know why I'd spent time faffing with it. This is why. Sorry, didn't want to make too much noise as our neighbours were having lunch in the garden opposite.
YouTube Link
I'll try to get a proper driving video shortly.
That however is why I was messing with the exhaust. Sounds a bit more purposeful now I think...
Oh, and the leather has been treated a further two times today. It's almost getting to the stage where the conditioner actually sticks around for more than two milliseconds before being absorbed now.
More excuses to play with the wide angle mode on the camera too.
Looks like this car was really well looked after in a lot of ways but the leather had been quite neglected.
Something I really need to do as a matter of some urgency is get some floor mats. I keep meaning to but keep forgetting.