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Post by geoff53 on Oct 11, 2018 8:35:58 GMT
My newly acquired 3 litre mk2 is difficult to start especially in these approaching damp cold mornings, on full choke it fires immediately but doesn’t pick up, sometimes takes 10 or more goes to keep running. Once started it starts faultlessly all day until the next morning, and once running it purrs silently, from inside the car you have to rev it to make sure it’s running as almost impossible to hear it on tickover, so assuming that there can’t be much wrong with its tuning ? Is this common ? And is there a fix ? Almost feels like it would benefit from a glow plug in the manifold, has this been done by anyone ? Yesterday against the norm it started instantly on first try, but this was at 4pm and a very warm day , again pointing towards it’s just the cold mornings it doesn’t like. It is kept in a garage at all times so not directly outside in atmosphere. Any thoughts much appreciated.
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Post by enigmas on Oct 12, 2018 6:43:56 GMT
Is the choke working as it should(?)...sounds like the jet is not being withdrawn far enough to enrichen the mixture. Check the connection and movement at the carburettor. If you observe the cable to the choke linkage at the carburettor it's quite obvious how it works...it either pulls the lever which lowers the main jet far enough or it doesn't.
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Post by geoff53 on Oct 12, 2018 8:39:39 GMT
It looks to be working fine ? By that I mean the choke lever is being pulled to its maximum. Wether the jet is fully open will need looking at, if I adjust carb to make richer I’m concerned it will mess the tuning as is,it does run superbly once running. I was speaking to southern carburettors the other day , they say that these carbs run by vaccum and that these and early volvos didn’t create enough vaccum when cold ? Which I found strange as why it wouldn’t from cold, I wondered if anyone had heard this and if there was a cure if this was the case ? Thinking the only way this could be the problem was if the rings were worn and once warm they expanded ? As this engine has only done 9000 miles from new, couldn’t see this possible.
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Post by enigmas on Oct 12, 2018 11:34:17 GMT
I presume you're talking about a 3 litre P5 with an SU catburettor and not a Volvo probably fitted with a CD Stromberg carburettor. From what you've told me so far the advice you've received is from someone who doesn't understand the operating principles of CD carburettors either SU or Zenith Stromberg.
You won't alter the overall mixture by ensuring the choke operates to it's full extent. It simple lowers the jet which enables more fuel to be drawn from it during cold start cranking. This is the only time you would need to use the choke. If you remove the air filter paraphernalia so that the throat of the carburettor is visible, lift the air slide with your finger. You will see both the needle and jet of the carburettor. Hold the air slide up and have a helper fully pull the choke knob out. You should observe the jet lowering. That's how the choke functions. There may be slack in the cable. When the engine cranks additional fuel is drawn into the engine creating a rich mixture. It's that simple.
Whoever you're currently talking too...step away and find someone who has knowledge of and experience with English cars and typically with SUs!
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Post by Ken Nelson on Oct 13, 2018 3:16:17 GMT
Hello Geoff. I own a 1964 3-litre MkIIC Coupe and have had similar problems with my car. I can almost certainly guarantee that the problem is coming from the carburetor and has nothing to do with the engine itself. I also presume that your HD8 SU carburetor is fitted with the Economizer device that was pretty unique to this engine in that time, and that even many SU folks who deal with he usual MG and Triumph setups don't understand fully (I'm sure I still don't, but finally got mine working correctly after much head scratching). Look at some of my posts about carbs, choke, fuel starvation and also do a search under Economizer for much discussion over this. These engines are very thirsty, and I'd suspect that the pin sized venturi opening in your economizer tube on the top of the fuel reservoir is plugged. If the carb has been worked on recently, also be sure that the inlet manifold gasket isn't covering up a hole in the inlet manifold for the idle circuit. Good luck, and let us know what you think of all this.
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Post by djm16 on Oct 13, 2018 3:54:18 GMT
First, congrats on owning a very special car.
As Vince says, check that the jet in the carb is actually being lowered. I suspect it is or the engine would not even fire. What is common though is that the throttle lifter that is supposed to actuate over the initial excursion of the choke cable is not working. There is a fibre? / plastic? doughnut shaped spacer that bears on the throttle lever. It wears a flat on it, and no longer lifts the throttle.
Easy enough to check, try starting with full choke and a trace of throttle.
It is also common experience that you will need full choke for up to a minute to even keep the engine running. Attempts to push it in early invariably leading to stalling.
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Post by Phil Nottingham on Oct 13, 2018 5:54:54 GMT
All the above but just check that pulling out the choke actually gives fast idle. There is a separate L linkage on top of the carb with a screw adjuster. The adjuster may not be set or the linkage has swung aside.
Our P4 and P5 both with the HD carbs start instantly from below freezing as soon as starter turns and continue to fast idle smoothly. After a few seconds the choke can begin to be pushed part in and very soon onto fast idle only
I would not advise disturbing the mixture screw yet but check the vertical internal link is pulling the jet fully down as these part seize
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Post by geoff53 on Oct 13, 2018 8:29:31 GMT
Thanks guys for all your input, I’m sure you are all pointing me in the right direction as my thoughts have been there must be something in the carb not working right ! As it purrs once started. I am just recovering from shoulder surgery, so my tinkering is very limited at present, once two handed again I will endeavour to act on all the suggestions put forward, your knowledge and experience are very much appreciated. I have one more concern to rectify regarding the steering to which I will start a new thread, so that I can plan to have all the niggles sorted for next yr, I’m itching to get these issues sorted as never been so bored & frustrated having to rest my arm ! At least I’ll have plenty to do once fit and able again. Thanks all for your knowledgable input. Cheers Geoff
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Post by Ken Nelson on Oct 13, 2018 15:54:05 GMT
Having had two shoulders repaired myself in the past, I can sympathize with you Geoff! Once yo do get to the bottom of the carb problem as Phil says, it becomes amazing how much better the car starts and keeps running compared to your current troubles. I went through many cans of spray ether (starting fluid) until I figured mine all out!
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Post by geoff53 on Oct 14, 2018 10:29:17 GMT
Thanks Ken It’s more the frustration of not being able to do much one handed, we all take it for granted until something like this makes us appreciate what we have ! I will keep you all posted on its progress but with my commitments realistically it will be in new yr ! So will put it to bed in it’s Airchamber for a while. Regards to all Geoff
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Post by 3litrekiwi on May 3, 2019 9:06:09 GMT
Hi Geoff
This was a while ago so I'm thinking you have probably resolved the issue by now however I had a similar problem when I bought my car. Hopefully your shoulder is healed.
My engine is at the other end of the mileage spectrum and has sat for long periods unused. Mine has a carb without the economiser so my solution may not apply however others may find it interesting or like to comment.
What I found was that although the enrichment part of the choke was working ok, I wasn't getting any useful fast idle. I don't know whether the fix I did was a repair or a modification but it seems to have worked well.
The lever that drops the jet to enrichen the mixture also operates a cam that lifts a shaft to operate the fast idle. There wasn't much actual movement as there appeared to be a roller missing that may have been some form of plastic a long time ago. I removed the pin that the cam was bearing on and machined up a small roller with a new pin. Once fitted I now have much more movement on the fast idle mechanism and can adjust it so that I get 800rpm with full choke when cold. It doesn't need this for more than half a minute or so from cold but has made cold starting 100% reliable.
I couldn't find a drawing of this part of the carby to be sure that anything was actually missing but a 4mm diameter roller looked like it could have been part of the mechanism from new when fitted.
Cheers
Martin
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Post by Ken Nelson on May 6, 2019 14:59:29 GMT
Did the 3-litre P5 engine HD8 carburetor ever come without the economizer device? Do you have a picture of the car and the choke linkage?
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Post by Phil Nottingham on May 6, 2019 18:15:31 GMT
The fast idle cam was a hard nylon that degrades. Early HDs on P4s had a brass one. I do not recall any P4 or P5s without the economiser. This was a Rover specified addtion and as the carb was proprietary item from SU it may be a standard one from another make Jags used them too
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Post by 3litrekiwi on May 19, 2019 8:21:59 GMT
I think my car has the economiser if that is a banjo fitting and copper line to the inlet manifold and a rubber hose back to the air cleaner elbow, l thought it was something a bit more complex although the carby may have been replaced at some stage.
The nylon roller makes makes sense as that was what I imagined should be there to make the choke operate properly. By fitting a new roller the choke now operates as it should. This was an easy fix with a lathe at hand. cheers Martin
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Post by djm16 on May 20, 2019 14:47:54 GMT
Yes that is the correct description of the economiser. Inside the brass fitting that links the copper pipe to the rubber tube is a jet. It can be blocked (leading to rich mixture at light throttle) or oversized (causing weak mixture). Careful how you unblock it as you do not wish to enlarge the jet.
In my experience, the replacement economiser jets are too large (and visibly larger than the original worn jet). To get mine correct, I blinded the jet with solder and drilled it out again.
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Post by Ken Nelson on May 20, 2019 21:01:30 GMT
How can you tell if the economizer jet is too large? Is there a spec for the size of it?
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Post by djm16 on May 21, 2019 0:14:39 GMT
Spec for the economiser jet? I am sure there is, but I can't tell you what it is. The effectiveness of the jet is critically dependent on the jet size (flow through a tube being related to the cube of the diameter).
From memory, mine were close to 1mm. Just checked my notes, for the 3-litre, I drilled out the solder with a 1mm pin drill. YMMV.
This outcome was the result of a whole day experimenting with carb settings and checking AFR with a broad range O2 sensor while driving up and down locally.
How can you tell if the jet is the right size? Buy an AFR meter to mount temporarily up the exhaust pipe, and check your mixture while driving.
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Post by enigmas on May 21, 2019 2:44:25 GMT
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Post by geoff53 on May 26, 2019 11:22:39 GMT
Thanks all for advice Apologies for tardy reply as been working away all winter, I did sort it in December before I left, you guys were correct the problem lay within the choke of the carb, on fully dismantling it was not operating fully, cable sticking as well probably to lack of use as very low mileage etc. It starts perfectly first time even on cold damp days. Thanks again Geoff
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