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Flattening out and smoke?!


Cousins72
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So, I’m having an issue with my spitfire mkIV and I’m after some advice.

The issue started to develop when I took it out for the first time this year after leaving it for the winter. The car idled OK, but after a very short distance I started to notice that it flattened out under acceleration and seemed to have a bit of a misfire. I got it back home sharpish and started having a look to try and work out what the problem is…

The first thing I noticed was that the spark plugs were all pretty grot (a bit black and damp (oil???)) but they were all consistent. I had a set of new ones that I was going to replace them with anyway so popped those in and ran it out again a short distance to see if there was any improvement on the flattening out/misfire. Well, it seemed to cure the misfire but it was still having an issue with low power. I also checked the mixtures, using both a colourtune and a bit of intuition and it seems like the mixture was burning well (and the exhaust didn’t smell rich or splashy as if lean)

It was also noticed that as I pulled out of our driveway and pulled away there was an amount of slightly blue-ish smoke from the exhaust (not a smokescreen but an observable amount). Again, pulled back home and went to check the state of the plugs. After pulling cyl 1 plug a reasonable amount of smoke started coming out of the cylinder! This doesn’t strike me as normal… In addition, cylinder 1 plug seemed to be back in the same state as before while the others seemed pretty healthy.

I should also say that I’ve done a cold and warm/wet and dry compression test and they all seem pretty reasonable (no outliers and only marginal change between dry/wet). I don’t have a leak-down tester so can’t really give any more info on the compression figures.

So, I’m after a bit of help in diagnosing the problem…

Symptoms:

  • Smoke under acceleration (slightly blue)
  • Fouled plug (cylinder 1)
  • Smoke from cylinder 1
  • Reasonable compression (no outliers)
  • Can hold a reasonably steady idle

My thoughts:

Given this is the first classic that I’ve owned I’m hesitant to jump to conclusions, but I’m feeling that of ignition, compression and fuel the problem is to do with the compression side. Mixtures seem reasonable and all plugs/points etc. seem ok so it only leaves compression. From what I’ve read I know there can be issues with both valve seals/seats and also piston rings – does what I’ve described feel like one over the other or neither? Is there some test that I’ve missed that would give a better indication?

Sorry for the giant block of text, but whilst I’m happy to have a go at whipping the head off I want to make sure that I’m barking up the right tree before doing anything likewise, if I'm being a bit of a dolt and have missed something obvious feel free to call me out on it, I'd prefer to suffer that embarrassment if it means I can get the car going again! 😁

Cheers.

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Welcome to the forum. Don't worry about the post, I am probably even worse for questions. You will, I'm sure get a good response from those that know. There is a lot of knowledge here and a lot of great people willing to share it. Just wait. Sadly this is not in my league, but there are plenty here to help.

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If the rings are gone it is unlikely you will see a big difference doing a wet/dry test.

It is plausible that the rings have stuck over the layover - you might be lucky and get away with an italian tune up once its good and warm.

But blue smoke is normally rings I think - I've refurbed the top end of mine over the last few weeks and replaced the pistons (Was just going to change rings, but a set of NOS pistons came up on ebay and swapped them out. Ran it for the first time yesterday and a short run out today as it happens.

What happens when looking behind if you accelerate and then come off the throttle? I.e. high vacuum? and the accelerate again? 

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Just another check that you can do it with the oil filler cap loose run the engine and feel or hear if she is chuffing. It could be a blocked breather.

I was told of an old trick for stuck rings but never used it. It was to put a table spoon of white viniger into each cylinder when warm and leave it there for a short time rocking the crank back and forth a few times, apparently it softens the carbon and any aluminum corrosion. Then turn the engine over on the starter with out the plugs to expell the viniger and take it fir a hard run. Then give it an oil change.

As I said I have never done it but have seen it done a couple of times back in the 70's and it seemed to work.

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It's not impossible that you've actually got two problems here. The oily plug / blue smoke could be rings - possibly just sticky as Mark suggested - or breather problems as Algy said. The flat spot / refusal to accelerate could be due to crud in the fuel pump. That's easy to fix - remove the top and wash the gauze filter out - and not uncommon after a lay-up.

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Some more easy ideas.

You can get smoke from over filled dash pots the excess is ingested and burns off

Smoke from removing a plug from a hot engine is not uncommon

Make sure you plugs dont have an R in the suffix

Use engine oil in the dashpots

As said there is a gauze inside the tin rocker cover and make sure there are no air leaks from split breather hoses

Or filler caps.

Check the manifold nuts are tight .

Pete

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Thanks everyone for the responses!

I've not had chance to get it out of the garage tonight, so I'm afraid I've not got any real updates on how it runs just yet.

On 07/04/2019 at 17:08, Anglefire said:

What happens when looking behind if you accelerate and then come off the throttle? I.e. high vacuum? and the accelerate again? 

I'll be sure to check what happens behind me as I get on and off the accelerator when I can get it out next.

On 07/04/2019 at 17:36, Algy said:

Just another check that you can do it with the oil filler cap loose run the engine and feel or hear if she is chuffing. It could be a blocked breather.

I was told of an old trick for stuck rings but never used it. It was to put a table spoon of white viniger into each cylinder [...]

I've gone through and checked all the obvious breathers (hole on filler cap, hose from rocker box etc.) I don't think there are any other secret ones hiding anywhere, right? Likewise, there wasn't any significant chuffing, a little bit of pressure but not much when I removed the oil filler. I'll be sure to remember the trick with the vinegar, but I might keep mine in the cupboard for the next time I have fish and chips for now! 😁

22 hours ago, NonMember said:

The flat spot / refusal to accelerate could be due to crud in the fuel pump.

I had a look in the fuel pump and there was a little bit of sludge in the bottom - I've cleaned this out (and ordered some of those disposable filters from eBay to fit at some point). Maybe that wasn't helping...

12 hours ago, Pete Lewis said:

Some more easy ideas.

You can get smoke from over filled dash pots the excess is ingested and burns off

Smoke from removing a plug from a hot engine is not uncommon

Make sure you plugs dont have an R in the suffix

Use engine oil in the dashpots

As said there is a gauze inside the tin rocker cover and make sure there are no air leaks from split breather hoses

Or filler caps.

Check the manifold nuts are tight .

Pete

Checked the dash pots and no signs of excess oil that would be pushed into the venturi. I'm using some champion N9YC plugs in the engine, I'm sure they were the ones recommended to me or that I'd read were good for the spitfire. I inherited a bottle of "dashpot oil" from the previous owner (although I've got no guarantee it is genuine SU oil in the bottle) and it seems pretty thin, which I thought was what you wanted in the dashpots... Checked all of the manifold nuts and can't feel any obvious intake leaks or exhaust leaks around the manifolds.

59 minutes ago, Nick Jones said:

Old fuel? Have you put any fresh in yet this year?

I've not filled it up yet this season, when I get the chance to get it out next, I'll make sure the petrol pumps will be the first stop to top it up.

 

Whilst I'm not overly optomistic maybe a fresh tank of fuel and a clean out of the fuel pump might be all it needs. I'll be sure to feedback when I've got it out again - most likely later this week. But if there is anything else I could check I'm keen to know. I'm keen to check as much as possible because even if it might pop out something I've missed.

 

Cheers!

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Su specified a straight sae 20 oil in the dashpots  triumph say engine oil

This is the accelerator pump , it stops the air piston rising too quick making a flat spot on acceleration

Fill them with cats pee and they become useless

Just use  some of your 20/50  engine oil and all is fine 

If thin oil makes it run better then something else is wrong 

Pete

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