Inlet Manifold query (and a story!).

[Spitfire1500]

Dear all,

I wasn't able to fit my HS2s today as I seemed to have hit a couple of stumbling blocks!

So I decided to spend some time tuning my HS4s. Big mistake!

I did a few circuits around my local area and did get my mixture, to what looked like absolutely spot on, but my idle had gone to 1,100rpm which I thought was too high. On setting my idle to 900rpm, my whole mixture got so rich that my Car was misfiring every few seconds, I had hardly any acceleration, the engine was sounding very rough and I was dreadfully embarrassed, especially when in front of pedestrians and other road users; attracting too much attention and a lot of negative comments (which I didn't want to do realy). Clearly the mixture had become so rich that the whole system was choking because the plugs were too fouled to spark.

After stopping many times, at the most convenient locations, I started leaning off the mixture 1-3 flats at a time on each Carb. Sadly, the outcome always concluded in lots of popping and banging. It wasn't going away and my patience was wearing very thin!

After losing all patience, I eventually had enough and dramatically reduced the mixture to a lean state, by making full turns on the jet needle, on each Carb instead. The popping and banging slowly died down and my acceleration was almost there. My car was finally able to go past 1500-2000 or so without the misfiring.

At this point, I don't have the time (or the patience left) to do any more adjusting of the HS4s, although I did get the mixture right once, I have no idea why something as simple as changing the idle speed would cause that much of an impact, and it only seems happy idling at 900-1000 or more, which I am not sure should be the case. I have always thought a healthy Spitfire should have a smooth idle between 750-850rpm and not a bumpy one where it wants to stall, like in my case.

So it's back to the original plan of getting the HS2s on...even trying to get the HS2s fitted wasn't really successful....

I don't have the 'hose tail', or plug/bung on my engine, nor a 'T' piece on the HS2 inlet manifold water pipe (that goes from the manifold and connects the heating system to the rest of the cooling system).

So, I have decided to go to the local Diy stores tomorrow (well, later today, once I have had some sleep) and fit my own t-piece which will allow me to connect the water pipe on the intlet manifold.

However, I had another important reason to post - as some of you may know, I have the PCV on my HS2 inlet manifold, along with the brass tubes on my HS2s as well (which both do effectively the same thing).

I also found a plug on the HS4 manifold. So my question really is this - could I take off the PCV on the HS2 inlet manifold and block it off with the plug I have on the HS4 inlet manifold? Or are they going to be different sizes?

My thinking is that this will allow me to put the PCV/Mushroom thing away in storage, block off the hole on the HS2 inlet manifold with the plug from the HS4 inlet manifold and then feed the brass tubes to the rocker cover (as is the system currently on the HS4 and inlet manifold). This will also, in some way tidy up my engine at least slightly.

Along with sorting the T-piece out, I am hoping that this will mean that my HS2s will go on (which have the advised AAQ needles in them, to match my exhaust system) and hopefully won't be such a nuisance to tune as my HS4s have been.

Many thanks and kind regards,

David

[JohnB67Spit]

Hi David. If you do away with the PCV and route breathers direct to carbs you must fit a sealed oil filler cap. The oil filler cap used with the PCV is vented, and will not work with direct crankcase venting.
If you take the oil filler cap off a direct vented engine while it is running it will try to stall, due to weakening the mixture.
Hope that helps

John

[drofgum]

David,
Is the plug from the HS4 manifold threaded? I don't think the hole where the valve goes on the HS2 manifold is threaded. I think the valve fits into a rubber sealing ring, so you may not find the plug suitable for the job.
                                                                     Good luck,
                                                                     Paul

[Spitfire1500]

Many thanks for your replies John and Paul,

The plug was too small for the PCV upon checking. I also tried my utmost to get the last nut off for the inlet/exhaust manifold, but it wouldn't come off - I tried plus gas, as well as a blow torch so I have now had to put it *all* back together again.

I'm going to test the needles out - my HS4s had ADN needles in them, however, I have put in some AAQ needles (which were meant for the HS2s and my exhausts, but I'll give them a try) and if I can't get a decent level of tuning and acceptable performance across the rev range then I'll have to try a new set of needles, because I'm convinced that a lot of the tuning problems I had might have something to do with the needles, although the carbs are a bit big really for a dolomite 1300 engine, I'll have to make do unless a miracle could get that last nut off!

Kind regards,

David

[Spitfire1500]

Okay, AAQ wasn't a good idea as it made my idle go all over the place!

So I'm going to put the old ADN needles back on and see if I can get them back to some kind of decent level, I wonder if ADN would be the correct profile for 1300/HS4/Sports Exhaust...

Kind regards,

David

[James]

David,


Changing needles shouldn't effect idle once you have adjusted them— the idle part of the needles are all very similar.


James

[Spitfire1500]

Many thanks for your reply James,

With the idle screws turned all the way up, and the idle screaming at 1500 rpm I am under the impression I might have an air leak, I'll go over all the nuts/bolts and spray the hoses to make sure they are all in properly if I get a chance tonight, otherwise at another time. I ended up leaving for work at 8am - half an hour later than normal because of my fiddling!

Kind regards,

David

[Clive]

Are the butterflys seated correctly? They can cause these issues. Take the air filters off, slacken the butterfly screws a little (1/2 turn??) and open the throttle and let it flick back. Repeat a few times and it shoyld seat the butterfly properly, then retighten the screws. Do the other carb as well, then check that both seat fully.
Of course you need to slacken the idle screws right off to start with.

Another thought, is the accelerator cable moving easily?

[Kev W]

Dave,

I seem to recall in one of your earlier threads that you had a problem with your condenser wire coming adrift. Make sure you sort this properly before you look to adjust the carbs everytime it starts to run badly! I had the same problem and had to press the connector in at least twice a journey! I glued it in place in the end and then went to electronic ignition which takes the problem of a condenser away. In my experience once the carbs are set right they normally stay set for a good long while, however, the ignition can screw up much more often!  :)

Kev

[Spitfire1500]

Many thanks for your replies Clive & Kev,

I will check the butterflies today - I was a bit concerned about them - because one side of the lever seems to move more than the other (despite the screw being at the same position both sides!) it might be that a setting has been knocked out whilst I was putting them back on - I also had another thought - because I haven't attached the 'spring' on the throttle linkage, it could well be the lack of this spring is causing the problem I have with the idle speed - although the accelerator does move freely, there is a chance it is not 'springing back' I will look at how this looks as well.

I do have an intermittent ignition light - I am thinking a bad wire might be responsible - (although the battery does still charge, whether the ignition light works or not) I have just the glue for my wires - the sticks like **** stuff by Evostick I think it's called!

Kind regards,

David

[Tom2000]

Have you checked to make sure that the dashpots have an equal/decent amount of oil in them, this sorted my brothers MKIV random idling issues out.

[Spitfire1500]

Many thanks for your reply Tom,

I'm not sure what my oil levels are, so I'll have a look at the dashpots tonight. I think ATF or 20w50 should be thick enough.

Kind regards,

David

[Spitfire1500]

Just had a good look on my carbs. Butterflies seem good, needles appear to be straight as the pistons are dropping and  there is no sign of wear. However there is hardly any oil in the dashpots! I'll fill them up tonight.

kind regards,

David

[Spitfire1500]

Dear All,

I'm not sure if this 'bump' deems another thread, so I'll stick with this for now.

If I have my HS4 mixture adjustment nuts right at the top, is this the 'richest' or 'leanest' possible mixture? I ask this, because I have yet again reset my Carbs - put the mixture enrichment nut all the way up and the idle screws are also all the way up. This results in the engine starting and dying straight away.

The reason I am asking is, I spent an hour trying to tune my carbs and didn't get anywhere at all. I'm thinking it now might be prudent to just go back to the ADN needles that were originally in the HS4 carbs, as the AAQs are just being an absolute pain. At one point, lifting up a Carb piston didn't do anything to the engine speed, almost as if my settings had 'crippled' it and it was only running on one carb.

I was looking at oil grades and the only 'fixed' grade I could find was 10w stuff which I believe will richen my mixture upon acceleration and may even be too thin - but I wasn't able to find anything thicker that was fixed - plus it was only £5.99 for a top-up bottle. At least my 5w30 and 10w stuff can be used to top up my leaky Corsa (nowhere near finding out where the leak is yet).

The only other oil I have is 5w30, which is variable and probably too thin as well. I really would have liked some SAE 20 stuff, but it wasn't anywhere to be found. I couldn't really justify a £18.99 bottle of 20w50 just to top up my dashpots as a service isn't due yet.

I don't know where to go from here. I'm happy to get a 20w50 bottle, and do an oil change and change the dashpots but I'm not sure I like the idea of using variable oil in my dashpots.

I don't believe the 10w stuff I have is causing problems either, as my fast and lumpy idle problem has gone away. I don't know where to start with my SU tuning now and I'm starting to really lose my patience!

Any help will be greatly appreciated, it's getting desperate!

Many thanks and kind regards,

David

[piman]

Hello David,

with the nut fully up you are at the leanest setting, nominal setting is two full turns down from being fully up, you shouldn't need to deviate far from that setting.

You say the throttles don't open together, they should and this is corrected by slackening the clamp on the connection throttle shaft, also the return spring will make a big difference. At this point I wouldn't worry too much about the dashpots, they only work on acceleration, to counter the natural weakening of the mixture as the throttles are opened.

Another factor, and one that came to mind on your preliminary post is of flooding, what is your fuel level when you look down the jets, it should be about 1\8" approximately down in the jet?

To summarise, set the jets 12 flats down from the top, (ensure the needle's shoulder is flush with the base of the piston), adjust the balance, you can use a piece of tube as a stethoscope to judge  for an equal hiss in each carburettor, fit the return spring, check fuel level. One other thing check the choke is not sticking on.

Alec

[Spitfire1500]

Dear Alec,

Many thanks for your reply.

I'll have a go again this evening, hopefully I can get somewhere this time around! At present my throttle is still slack and my choke will be slackened off again tonight, but provided I get the same idle on each carb and start at the 12 flats from the top setting, it should at least get my car started again. I try to throttle to 2-3k everytime I adjust anything to keep the engine warmed up. I am not sure what my fuel level is in my jets, so I'll need to check that is correct so that the engine isn't being flooded.

At present I use a bit of fuel tube to balance the air flow on my carbs. I did once have a flow meter but I got rid of it. Fingers crossed I get going tonight - I really want to be able to make it to the North London meet on Monday and be able to get my Corsa sorted this weekend as the MoT approaches.

Many thanks once again and kind regards,

David

Edit: Booked a half day off today, so it's *hopefully* going to be a productive afternoon on the Spitfire.

[Spitfire1500]

Hi all,

I got some level of tuning on my Carbs (I stress the some part!) checked my fuel level in the jets and it seemed to be okay. I think it is still running rich as the spark plugs are still dry black (although it has been idling a lot though).

This morning it started on the key with no choke or throttle (usually indicates a rich mixture) and when I backed it out, it did appear to have a rather quiet and slow idle and stalled on me once. It was choppy on the low revs but as soon as I gave it some welly it roared up the ramp to my garage with no problem.

I'm almost out of petrol in it, so I need to fill up for the fourth(!) time this month. I am wondering if the thin 10w oil I am using in the dashpots is making my mixture too rich upon acceleration on top of how rich the mixture is already - generally when I hit 3000 revs, it hesitates and misfires.

Maybe I ought to fine-tune it and consider getting some thicker oil?

Kind regards,

David

[piman]

Hello David,

thicker oil will richen the mixture, not weaken it. It does sound as though it is rich, air cleaner elements clean? If so then screw up the mixture nuts a couple of flats and try again? If it needs much more than that then possibly the jets are worn (you have sprung needles I think?)

Alec

[BarryH]

David

You have asked a couple of times what needles to use and if the AAQs are ok.  From my recollection if you have KNs and a sports exhaust then AAQs and a yellow spring are what is recommended and HS4s should give more performance than HS2s.  For dash pot oil the workshop manual recommendation is the same as the engine oil which is a multi grade (10w40 but I could be wrong) but as long as it is not too thin (3 in 1) or two thick (EP90) then it shouldn't be a problem for the reasons stated in previous responses.

One other thing that can cause patchy pick up is if the carb piston and the tube and cap it slides in have got a coating of lacquer or other dirt.  Give them a clean with some petrol or other non abrasive cleaner (e.g. Autoglym Tar Remover) and see if that smooths the movement.

It sounds as if you are almost there so don't give up.

[Spitfire1500]

Many thanks for your replies Alec and Barry,

The original air filters were in pretty bad shape - Ferny gave me a pair which were much cleaner. I also have the airbox around them (which will probably be richening things up a bit by further restricting the air intake).

I have the original ADN needles in at the moment - rather than the AAQs - I was advised that with my sports exhaust, I should use K&N air filters and yellow springs with the AAQs - but I haven't got round to purchasing either - although the yellow springs are only £5 each or something. K&Ns do seem much pricier. But if it does get my engine much happier, then I could use them and keep the HS2s as spare.

I actually found out that one of the dashpot lids on my HS2s is loose and won't seal and I have managed to crush one of the needle holders and needle spring when I overtightened the needle screw - so my HS2s might be out of comission for a while longer!

Although the jets appear to be in good working order, they could be in a bad way, I could use the new jets I have on my HS2s if I need to. I have some very good carb cleaner which certainly goes through everything (as well as paintwork!) which might be a good idea to use again as my hands do get very grubby when I'm playing with carb settings and checking spark plugs. Both the HS2s and my HS4s have spring-loaded needles.

Fingers crossed it will be much happier this evening and over the weekend when I take it round the block and change the mixture on the fly in the nearby lay bys.

It needs to come out of my garage anyway, so the sooner I get it sorted the better - my Corsa Oil leak *really* needs seeing to - I only did an oil change 3 months ago if that and it's already lost half of it's oil!

Many thanks and kind regards once again,

David

[Spitfire1500]

A further update!

I must be driving people mad, with my thread posting, but I am still fairly new to all this!

After a conversation with Ferny, I have decided that I need to get the HS2s on. I could fiddle with my mismatched HS4s all winter and still not get it quite right. However, my HS2s and AAQ needles should make for better running and easier tuning. Ferny stressed that I need to stop fiddling and get the HS2s on and they could be tuned much better. I have clearly wasted a lot of time on trying to get the HS4s working properly and I cannot spend anymore time doing that. I am impatient, it has to be said and whilst shoving on the HS4s will certainly get me going...it won't be perfect without a lot of faffing with needles and mixture settings etc.

I may have introduced an air-leak along the way - especially with disturbing a few bits and bobs on my Spitfire - however, I am also aware that the mushroom part on the Mk3 inlet manifold is quite loose, and fairly easy to remove. I don't think it should be like this. Is there anything I can do to make it tighter? I could well be introducing an air leak here if it is not sealing properly, which also will not be any good for tuning.

I aim to replace the dodgy damper in my HS2 (ptfe tape may help) as well as the needle holder - but I need to have a new manifold gasket as the one that arrived was broken. Ferny has offered to help get the nut off my manifold that I couldn't remove and provided I have everything ready (relavent pipes, HS2 carburettors, blocking off the brass bits, ensuring the emissions control mushroom is sealed properly) there is no reason why I can't swap the HS4s and manifold for the HS2s and manifold within half an hour and have it tuned within an hour.

Hopefully I'll be all sorted by this Saturday or more likely next Saturday. It may mean I can't make it to the Plough in my Spitfire this month sadly for the North London meet, but once everything is in place, it will mean a much happier car. Well that's the plan at least!

Many thanks and kind regards,

David

[Spitfire1500]

Well, it's a hell of a lot better now.

Taking it for a run did the world of good. It didn't misfire once. However, I do get backfiring when the throttle is closed or I am coasting at times. I think that indicates a weak mixture - as my spark plugs were grey -  shame as it does sound pretty cool, so I'll adjust the carbs by one flats each, as many times as I need to until the spark plugs are brown to black.

I noticed as the mixture was getitng richer through adjustment my acceleration was a lot smoother and where it used to misfire at 3-3.5k rpm it went all the way to 4k and beyond with no issues.

So getting there. But once my HS2 bits arrive, I will be putting HS2s on next weekend.

Kind regard,s

David

[rotoflex]

You're getting good at this.

[thescrapman]

Popping and banging on teh over run is unburnt fuel getting through, so could be wear in eth carbs, or its running to rich, so the engine is still pulling in excess fuel from the manifolds and buring in in the exhaust.

Lack of back pressure can cause it as well.

When i ran my Moss with no silencer it sounded like a machine gun on the over run. (Triumph 6's sound very good unsilenced.. :-) )

You have very little back pressure with those renegades from teh back of a Chav-mobile on your car.

Cheers

Colin