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Mira Bogs Oh Well Back To The Lotions And Potions!


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#21 oldtuckunder

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Posted 11 June 2017 - 02:17 PM

That comment from kas on your link was what I mentioned some time ago.  I never explored it but I recall Kas said they added a second vent hole on the other side.  

 

Was going to say fuel surge in the float bowls.....  Fuel temp might also be a factor as modern fuel boils awfully easily and if it's warm you might gets some unexpected effects just from sloshing it around.

 

Triumph day at Prescott a few years ago I had comment that mine was among the few cars that picked up cleanly accelerating out of Pardon and when we thought about it, it was mostly the injected cars (Mike Bestards Spit 6 was another) than could do this and the carb cars that were fluffing......

 

 

Curiouser and Curiouser said Alice.......................

 

Well have spent the last two weeks trawling the internet for any hint of a mention of Stromberg's and left hand corners, I think I have inspected half the contents of the internet, and come up with only a handful or possibly relevant postings, funnily enough most of which date back a decade or two and usually include somewhere a posting from GT6Steve :yes: on the topic, and of course the great GT alternatively supplying an interesting fact, interspersed with outright condemnation of anyone else!

 

The extra vent drilling came up a couple of times but no details as to how where, the best (again a GT6Steve post) indicated that a former ASC competitor told him about the fix back around 2000, but was at a point where I think Steve had given up and gone Webbers.

 

The other problem with the Left Hand Turn Stromberg problem, is that from reading there appears to be two not one problems. There is the long left hand turn where the explanation of the fuel surging blocking the vent, the float dropping on the fuel angle but no fuel incoming due to blocked vent. And there is the very short sharp left turn stutter, where that just doesn't make sense, and the problem I had.

 

A few theories and suggestions thrown up over the years. 

 

Scrap the Stromberg's

Seems to have been a reasonably popular choice over the years, however countered by some really experienced racers in the US who have never had a problem with them! 

 

Raise the float level 1-2 mm 

Increase Fuel pressure 0.5-1 psi

Both these seem to leave the carbs on a knife edge of flooding

 

Change the Needle valves from 1.75 to 2.25  

I have managed to find a pair! but haven't tried them yet

 

Don't swap the 150's for 175's but get the 150 counter bored so that they are actually 1.5" right the way through rather than 1.25" at the inlet.

This is similar in concept to me playing with reducing the 175's which I haven't got any further with. NB if anyone has a pair of GT6 MK3 150 strombergs for sale please let me know as I don't want to experiment with my almost new ones, and the other sets of 150's I have are the earlier ones with the lifting bridge choke that aren't suitable.

 

So as they say an ounce of real experience is worth a pound of theory, and we had the Abingdon Sprints this weekend. Great event 8 runs on two courses in one day.

 

I also as you will see from this thread had two problems to resolve, the Start Line bogs from Mira (and a couple from Shelsley) plus the stutter out of the left hander at Shelsley. So what did I do in preparation? Nothing!  Well to be honest all I did was drop the float bowls and check the float heights, they were perfect to spec 16mm.  And decided to revert to a 75w90 synthetic dash pot oil and standard springs.

 

I didn't make any other changes as I'd run out of time, and had reached a point where I didn't know what to try.

 

Abingdon is an airfield course, flat but with long fast G pulling corners (left and right) plus some nice sharp left and rights where you exit at full throttle etc, so should be ideal to data log and find out what was happening.

 

So I now have some great data logs of the problems, to work on?   NO!

 

I have some great data logs, but everything was dam near perfect.

 

No bogs off the line (I think this may be as I have now adapted the launch technique so that instead of bringing the revs up, holding, dropping the clutch and going WOT as I could with the 150's, of just bringing the revs up at the last moment, dropping the clutch and then gently squeezing the the throttle open as we pull away)

 

Not the slightest hint of any stutter/stammer during or coming out of any long or short left hand bend.

 

In fact if I look at the logs the AFR's are almost perfect everywhere, and you cant watch the CD carbs responding perfectly to every throttle/rpm input/change. In fact I'd go far as to say you have to be a genius to program EFI to respond as nicely, and as the carbs are doing it based entirely on a single input of airflow its quite remarkable. I'll try and put together an annotated log later so you can see.

 

So I couldn't a test road anywhere to replicate the left turn problem (which was one of the reasons I hand't changed anything) and Abingdon where I thought I had every chance of doing so also turned up nothing.

 

So I'm a bit stumped, if I can't replicate the problem then its pointless changing anything as I cant test if it works. Well I could test if it makes things worse but that seems a bit pointless.

 

Anyway back at Shelsley next Sunday, so can see if the problem(s) are still there, and will take new float jets etc, so if it appears in morning practice I have a chance to make some changes lunch time before the timed runs. Seriously wondering if I can replicate GT6Steve's old suggestion of making the float bowl securing bolts into wing nuts so that they can be dropped quickly!

 

Alan

 

Oh PS. On Nicks suggestion that is could be heat in the float bowls causing this modern crap fuel to boil/vaporise, I went equipped with laser thermometer so after a couple of runs where I knew we had idled for a fair time before the start, at the end of the run I flipped the bonnet and checked. Inlet manifold circa 88deg (about right) Carbs 45deg and felt cool, as a comparison Master Cylinders on bulkhead 43deg, so phenolic spacers and the huge heat shield I have that keeps carbs in cool inlet flow seem to work. So I'm going to park that suggestion. However worth noting the difference between inlet manifold temp and carb temp, if the carbs were bolted direct to manifold without spacer I think they would have been way hotter!



#22 oldtuckunder

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Posted 19 June 2017 - 11:07 AM

Wow I just won my first Motor Event (well Class) in about 35 years (and in the same car!)

 

Shelsley came good for me! Have I broken my Jinx?

 

Come Saturday night when I went to refuel, I wasn't sure if we were going to make it :unsure: started the car and had what sounded like a sort of rumble or rather like something rotating at about cam speed knocking/tapping. Bit hard to identify where its was coming from (as exhaust a bit noisy from header collector to pipe joint (dam little 13" wheels means I clout the exhaust on virtually everything)  Anyway took it for around 15 mile refill run and when I got back noise was worse  a bit, but I still couldn't identify, seemed worse when listening from RH rear. Tightened manifold bolts and it got a bit worse! So started hoping it may just be either a manifold gasket blow, or a blow from a cracked header joint. It was too late to start stripping, and to be honest I thought my Shelsley Jinx had just struck again!. So decided sod it will drive to Shelsley in the morning (drive because I have decided to stop trying to fight the odds and dropped into pure road going  for a few events) Thought it might go bang on the way, but it drove like a dream (country lanes early morning with the hood down are just fun!) and also with the bonnet down and the main exhaust blowing a bit I couldn't hear the new noise anyway. Did notice that the popping on over run (which it always does a lot) was actually getting quite bad! By the time we got to Shelsley and lifted the bonnet the new noise was now quite bad, but I still couldn't locate if it was manifold gasket or break in the header somewhere.

 

Decided sod it just continue and see if it holds together. Took first practice gently really just practising the correct line, second practice thought go for it a bit (as it had been pulling well on the first) and starting nudging towards by new bogey time (but could see that others were doing better) Opted out of a third practice run that everyone else took (for UK getting hot 30C air, and under bonnet?) thinking I'd save the car for at least one competition timed run in the afternoon (noise was getting loud now, but engine still pulling well) First run after lunch engine nice and cool (had had a longer rest than most!) just warmed the engine up enough to get oil over 60 (oil water heat exchanger meant I could do this quite quickly) and just went for it! (expecting a load bang or total loss of power at some point) bug.er me as I crossed the line saw the clock and spotted I had beaten my bogey by just under a second!

 

And that at the end of the day was enough to win the class (did do one further run, not as quick, slightly slower than my bogey).

 

So what happened to the Start Line bogs, and fast left hand stutter problems I had been battling?

 

Don't know, just disappeared!, despite the new problem it went like a train all day. No, as in previous reports I hadn't changed anything as I didn't know what to change.

 

What was interesting was that by afternoon runs (real hot under bonnet temps), a lot of other people running on SU's were complaining about gutless engines, loss of power, apparent misfires, and changing plugs, coils, removing filters etc, to try and resolve with no effect. Whilst my unfashionable Strombergs (admittedly in the cooler air chamber I have created) behaved as though they were having the time of their life.

 

Did the higher temps actually help with my problem? Has it mysteriously gone away? Or is it waiting to bite somewhere else?

 

Anyway well pleased with the car and the weekend!

 

Alan  



#23 Nick Jones

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Posted 19 June 2017 - 12:38 PM

I think your careful development and preparation re. the heat shielding was paying off yesterday.  Fuel vaporisation is a huge problem with current fuels in carb cars.  We built Spitty specifically with this in mind - electric pump at the rear, fuel pipes well clear of anything hot, several gaskets between manifold and carbs - but still it gets issues in hot weather.  Chris just invested in a rather nice SS heat shield.  We only fitted it Friday so I guess I hear if it worked or not later.  Today will be a fairly severe test - it's hot here.

 

I also wonder about fuel variation.  Usually I'm a shameless (inverse) rate chaser and buy the cheapest crap I can find.  Typically this has been Morrisons or Asda, though recently a local BP station has been running them close on price and is more convenient being directly on my route to work.

 

However this weekend I needed mower fuel and went to Texaco 'cause it's much nearer than the really cheap ones and much cheaper than the really near one (gouging b'stard Esso station on A303).  So the Vitesse was carrying the mower can and got a drink too - just plain ordinary Texaco 95.  Possibly unrelated but seems to be running extra sweet right now.......  Maybe Texaco put the expensive stuff in the wrong tank by mistake......?

 

Nick

 

PS.  Your strange noise sounds (indirectly obviously) like it could be a manifold blow either due to a crack, leaky gasket or leaky joint.  Fits in with the popping on the over-run too.



#24 oldtuckunder

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Posted 22 June 2017 - 11:15 PM

THERE SHE BLOW'S! 

 

Had to have most of the day off travelling and visiting aged relative, where my body had been promised to fix a broken curtain rail, whilst everyone else sat around drinking and saying how nice it was to be able to sit outside.

 

Now its easy to change a curtain rail isn't it! And as a good boy scout I had taken about every tool I could conceive I might need (knowing no tools at destination) Plus a complete new Rail Kit longer than required (took what I was told and added a couple of feet on for good luck).

 

Old rail brackets had been nailed up by some "Master Craftsman" with masonry nails into plaster, so as I took it down I had chunks of plaster falling of the header rail! Also discover when I tried drilling header rail for new brackets that the dam thing had been formed by some other Master Craftsman out of solid plaster no inner timber or anything. So now have to go off hunting in strange town for a DIY store to buy Wooden Batten, Polyfiller etc.  3 hours after I started finally have repairs done, solid wooden header rail, and new rail and curtains hung!   So now its a journey back cross country in the rush hour, and finally get home around 7pm.  Had originally thought 5 ish and then I could get on with stripping the tunnel, starter, and headers to find the blow. 

 

Bug.er it normally takes me at least an hour to get all the electrics disconnected and the tunnel out (plus and hour and a half at the end reinstalling), just so I can get at the two nuts on the bolts holding the starter motor on. Look again is there anyway I can get at those nuts from engine bay side? Nope impossible!  But what if I cut a chunk out the Transmission Tunnel?

 

startercover (Large).jpg

 

Easy!  10 mins later starter off!  OK I will have to make some jointing plates when putting it back, but from now on removing the starter is going to be a walk in the park!

 

So now all I have to do is break the joints between the collector box and the two header pipes and I can get the headers off. Bug.er the engine doesn't seem to be burning as much oil after this years rebuild, in the past the joints have all been a bit oily and have come apart easily, this time they are rusted solid (and they were only refitted 3 months ago) and it takes half an hour just to pull/bash/cajole/threaten the two parallel joints apart. But finally they come and the headers can come off! All done by about 8.30 (just about clawed back the lost curtain rail time)

 

BlownHeaders (Large).jpg

 

Whoops look like they started mating and have burnt a hole through each other where they touch so they can exchange bodily fluids gasses! 

 

Now I know that all the header wrap looks tatty, but that stuff is the dogs bollocks, after two wrappings in the best I could buy in the UK which just turned to powder in less than a year, this stuff an American friend into drag racing sent me, and its survived two and a half seasons so far, sure its brittle, but it hanging in there!. My point? Loads of people say don't use header wrap on mild steel as it attracts damp and starts the steel rusting between the wrap and the header, but 1) I'm sorry but I'm a bit anal about under bonnet temps and I want that heat out and away and 2) as the rest of the headers inside the wrap are solid its the bits that weren't wrapped that have rusted/burn't through.  Why aren't they wrapped there? because with wrap between them I couldn't fit the headers. OK pondering that with wrap on lot more heat trapped and going down the pipes (just what I wanted) but maybe heat focused on the touching faces that aren't wrapped causing steel to burn? rust? away.

 

So what to do?  I have a new set of stainless headers in a box that I was saving for a rainy day, and maybe (if I didn't think it may be snake oil) get zircon coated before fitting. But by the time I have beaten them into shape and fitted them (New Headers Never Fit) then pulled them again, then got the sensor bungs welded in, and then either get them coated (£££!) or get some more header wrap from the States (£!) the season will be almost over! Certainly won't make Castle Combe on the 28th!

 

So I think I'm going to cut some plates in the morning and see if a clever friend can weld them for me!  Having seen the video that either John or Nick posted a few months back about how beating headers in all sorts of ways seemed to make virtually no difference, what I think I will do it beat these two points in when welded, so I can actually get some wrap in between them, and hopefully stop it being a high heat transference point!.

 

But at least problem found!

 

Alan 

 

PS. Was the engine running so well at Shelsley because the headers could cross breath? Darn wish I hadn't asked that question! 

 

 



#25 Nick Jones

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Posted 23 June 2017 - 07:24 AM

Well, that's fairly ugly....... and certainly explains the odd noises. I was imagining cracked welds in the "armpit" of one or two joints, not damn great rot holes!  I imagine it's because they've actually been in contact some of the time and there's been fretting.

 

Looks like a 6-2-1?  Is the stainless one a 6-3-1?  No idea whether "cross-talk" has been affecting performance but looks like hole enough for cross-talk to have been happening!

 

Good luck with the repair!

 

Nick



#26 oldtuckunder

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Posted 24 June 2017 - 02:36 PM

Well, that's fairly ugly....... and certainly explains the odd noises. I was imagining cracked welds in the "armpit" of one or two joints, not damn great rot holes!  I imagine it's because they've actually been in contact some of the time and there's been fretting.

 

Looks like a 6-2-1?  Is the stainless one a 6-3-1?  No idea whether "cross-talk" has been affecting performance but looks like hole enough for cross-talk to have been happening!

 

 

Wow back already!

 

platedheader1 (Large).jpg

 

And the nice man decided that even though I had only cut plates for the holed side

 

platedheader2 (Large).jpg

 

That he would cut some more and plate the other, so I now have completely new collector boxes, and all for £20 in the beer fund! 

 

Just have to hope that the wrap I ordered yesterday (even though I know it will be rubbish and will probably be in the bin by Christmas) actually turns up on Monday so that I can get it wrapped (sorry too hot under bonnet not to wrap) and get all assembled in time for Castle Combe on Wednesday.

 

In the mean time I think I'll do a trial fit of the Stainless System (Yes Nick its a 6-2-1, with a 2ltr competition car I think I want top end not mid range) That way I can do any bashing required and mark up the sensor bung positions and maybe have it ready to fit when this one finally expires.

 

Interesting had a few comments elsewhere that Stainless Systems should be Wrapped and Mild Steel Coated, so maybe thoughts of getting the stainless system Zircon coated are rubbish anyway.

 

Alan



#27 oldtuckunder

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Posted 25 June 2017 - 06:46 PM

Idled away a couple of hours today doing a trial fit of the spare new stainless headers, so now all I have to do is decide if its coating (looks like I may be wrong about not coating stainless, but still not sure if its snake oil) or wrap, and get some sensor bungs welded in (do I need stainless bungs?)  Then it can be ready to fit at some point in the future if the MS one gives up without needing any work.

 

Not too bad a fit out the box (unlike the MS one was) Bolted to the head the collector box actually connected to the two down pipes, and the outlet pipe was bang in line for the main exhaust pipe.  Had to fettle/open out all the bolt cut outs where the clamp bolts go, and had to grind away some weld around some of the pipes so that the clamps would actually seat, and a few little taps with a hammer on the collector boxes and down pipes so they weren't tight together, so now have enough clearance room for coating or wrap.

 

Nice job to have in the bank as it will save a lot of hassle if I have to fit in a hurry at some point. If I decide on wrap they can just sit there, if I start selling my body on street corners to get it coated I may be tempted to fit, as who can resist a little bit of bling if you have it! :P  



#28 GT6Steve

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Posted 25 June 2017 - 08:31 PM

Alan, I perceived a significant underhood temp reduction when I coated my extractors.  I later coated the inlet manifolds to further inhibit heat transfer.  Many have poopooed the results as IR heat guns don't show a reduction but I am a believer.  In fact, I was pondering two days ago what had reduced the horrid interior temps I used to experience.  many small things  and I consider the ceramic coating to be a contributor.



#29 oldtuckunder

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Posted 25 June 2017 - 10:40 PM

Alan, I perceived a significant underhood temp reduction when I coated my extractors.  I later coated the inlet manifolds to further inhibit heat transfer.  Many have poopooed the results as IR heat guns don't show a reduction but I am a believer.  In fact, I was pondering two days ago what had reduced the horrid interior temps I used to experience.  many small things  and I consider the ceramic coating to be a contributor.

 

"but I am a believer"   Whilst not a great Monkeys fan, it was amazing the number of people humming that tune when Davy Jones died a couple of years back!

 

Interesting comment on coating, did you use wrap before? and find the coating better? what coating did you use? inside and out?  (sorry many questions)

 

I can understand why race teams use, lighter, less messy, lasts longer, just at the moment I'm struggling (other than supplier claims) that it actually is better, mind you I'll admit its way prettier  :wub:  

Alan






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