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Ocassional miss fire on Mk1 vitesse


iana
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Been following Paul H's thread about engine not happy cruising. Just returned from a trip out 70 mile each way with a stop on the way up and the car miss fired once on an incline but other than that fine, cruised up at 60mph. Coming back the car miss fired 3 times, twice on an inclined, the other time on the flat. The miss fire is random but only occurs when the car is fully warmed up after say a 20 min drive.

The car starts fine, tickover at idle maybe a little fast at 1000rpm.

Any pointers where to start looking? Im thinking spark plugs, coil or possibly fuel getting too hot over the carbs. The car has twin Su's and the fuel feed to the carbs is as the photo - Im wondering if this is causng a fuel vaporisation issue (can someone describe the syptoms) as when I got home an put the car away I lifted the bonnet to check all ok,and the carb to carb fuel feed was very warm but not hot.

D08BB1C4-7F28-44B4-9702-2FB2C5A6C21B.jpeg

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Couple of things in the photo, to  start with SU were never used on the small chassis 6 cyl cars, those have breather tubes direct to the 

Carb venturi , piped together to presume seal,them off  the  pipe under the smiths valve looks squashed and restricted

Question  is  with out the breathers and with pancake filters what on earth needles are fitted to a hybrid set up like you have

? Pete

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Anglefire, thanks, Ill source a couple of 'P' clips and re-route similar to your layout.

Pete - I had clocked the pipe under the breather and have 2 new pipes waiting to be fitted (ran out of time before todays run) What effect would a restricted breather have?

On a GT6 Mk3 I owned in the past a previous owner had fitted SU carbs and it ran really well (albeit HS6's), and now you commented on the carbs being piped together Im struggling to remember how they were connected but I vaguely remember a setup more like that in Angelfire's photo - Ill have to have a trawl through my old photographs to see if I have any of under the bonnet. 

I think I have the original invoice for the carbs as recommended by STS to the PO, I think this also detailed there recommended needles, so I will see if I can remember how to check whats in place.

 

 

 

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STS recommended and fitted AAQ when they worked on the car, Im assumimg these are still there but will check whats in the car now in the week.

Rightly or wrongly I'd discounted the carbs as its intermittent rather than a constant issue. Its usually at 50-60mph going up an incline and always when the car is hot so Id assumed something breaking down.

The car has electronic ignition, intermotor coil, iridium spark plugs.

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Stick to BP6ES ,   nothing with an R in it .

certainly a hard drop out under load is looking plug related 

Weak would give a more general misfire , rather than a kick

You,could if   the needles suit dump the smiths valve and   pipe the rocker to the SU breather stubs  as in the Su carbed 2000

Worst thing about any pancakes is the loss of nice cold air , hot air is rarified ,   less bang for your bucks , 

Pete

 

On all make sure the oil filler cap seals ok.

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Pete thanks, Ive googled the su carbed saloon and that looks like how I remember the setup on my GT6.

I'm going to swap the smith valve hoses tomorrow and move the fuel hose to infront on the filters (i was surprised how warm the fuel hose was)

Is there a preferred make of spark plug? (Not sure I understand the benefits of iridium plugs so Ill revert to standard plugs) Im also going to order a spare coil is a Lucas 12V sports a good option.

I wouldnt have picked K&Ns but they came on the car. I need to see if theres an air box that will fit and then it can revert to a standard setup and take advantage of cooler air to the carbs.

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Lucas have not made anything for several years, it is all outsourced so probably best avoided.

Bosch 0221119027 is a good choice, a 12V (non ballast) coil from a proper brand. Have a search, but should be available for about £20.

Good call on the airbox, use a std vitesse one. 

I have used NGK BP6ES for years, though I am led to believe quality is becoming an issue and lots of fakes are being sold (lfe should not be this hard) so buy from a reputable source. Others like the Bosch multi-prong plugs, but I have no idea on part number. Denso are another reliable, japanese, plug.

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11 hours ago, Pete Lewis said:

Worst thing about any pancakes is the loss of nice cold air , hot air is rarified ,   less bang for your bucks , 

I keep meaning to put some data loggers on mine to see what the temperature difference between the area where the air would get picked up from if using the OEM airbox and the air that is around the K&N filters. 

When I get the car running again, I must dig them out!

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Re airbox, I wonder about using the std airbox with no filters inside (but short stub stacks would be good) then flex hoses to a K+N cone filter with "twin outlets"

https://www.knfilters.co.uk/search/univdualtapoval.aspx

 

Or a dcoe type filter, weld 2 short stub pipes on the backing plate?

or even a single outlet, using something like an exhaust Y piece. Would need a little thought/effort, but not a lot and would achieve good/efficient filtration and a cold air feed. Win-win 

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i echo some concerns about current ngk's once sooted bin them .

R sufix is a suppression idea but best suited to higher HT than we have , any with them that i come across have misfires , bin and use std and solves the hic ups

std air box for SU on a six pot is only available on 74 /75   2000 mk2 saloons   where they fitted the dreaded SU's and lost 10 bhp.

the stromberg air  box looks similar but centres and hole piercings all very different .........  wont fit without serious mods.

have had 2  local  Vitesse with SU fitted and lots of running issues, returned to strombergs , set up correctly and it made a new world of difference..  true there are more needle options with SU but in reality they are pretty hopeless compared to what Triumph developed ...and we all have a dyno in the shed to test results dont we........guesswork ...doesnt 

Pete

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https://www.sparkplug-crossreference.com/convert/NGK_PN/BP6ES

5 or 6 are close , champion eg   revised to a dual  range plug   N7/9Y  to cover the same range

As you read on here some are leaving ngk and moving to bosch plugs 

In all my years  I relied on champions but less these days ,  who makes what , nothing is what it used to be 

And all my years in warranty bosch were hapless to deal  with or accept their own problems  .

There was a youtube film of a plug manufacturer in china     ...OMG.

Pete

 

Pete

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6 minutes ago, Pete Lewis said:

And all my years in warranty bosch were hapless to deal  with or accept their own problems 

Yep, that sounds like the Bosch I know. It's a slightly different psychology to the Japanese one. The Japanese would be so devastated at being seen to fail that they'd have to fall on their sword, so they do everything they can to hide problems. Bosch just don't care - they will be able to persuade the punters that their product is top quality as long as they blame all the problems on somebody else.

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Thanks, so either will do, I will try the bp6es as they’re in stock.

Things have definitely changed in the 10 plus years I’ve been away from classic cars, and not necessarily for the better.

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The problem of who makes what, who owns who, and the quality of what is made by who for whoever has raged on this forum since I joined it. Buy something today and it works fine, buy it next week.. who knows. No one knows these days if the product (say NGK) has ever seen the factory where it is supposed to have been made. Fleabay is rife with counterfit products with no way of knowing what is good, bad or genuine. You simply pays  you money and hope for the best.

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Hi 

After reading all the above, what plugs other than NGK, which I have found to be unreliable, would people suggest? and Where to buy from?  Club shop would be my first port of call but they only sell NGK

 

Aidan

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On 29/04/2019 at 17:53, AidanT said:

I've fallen out with NGK! Clive, it's interesting you have had the same issues with them as I.  I've moved on to these and so far so good. (Ad picture does look odd!) 

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F291831106471

 

Aidan 

 

Plugs £16, postage £14.95? Must be a cheaper way....

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8 minutes ago, Colin Lindsay said:

Plugs £16, postage £14.95? Must be a cheaper way....

That's Changed from when I got them Colin!  I'm sure there must be a better way plus now this article has scared me somewhat! Hence the Q  above  - where else to buy from?

Not sure if I have the real thing or good fakes or what  - its a minefield!

 

Aidan

 

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