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Misfiring Sprint Engine

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Beans
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Misfiring Sprint Engine

Postby Beans » 10 Oct 2014 13:07

During the Border Raiders in August the car developed an engine problem (Sprint engine on DCOE Webers and optical ignition module from Newtronic). Symptoms were lack of power especially at higher revs, running rather lumpy at idle. But running fairly well in higher gears at about 3000 rpm. So since then I have been checking various things;

• The contacts inside the distributor cap were showing signs of corrosion as were some earth wires;
• The spark plugs from cylinder 1, 2 and 4 looked OK, but number 3 was literally washed clean;
• Removing spark plug caps one by one reveals that number 3 is not working on idle;
• Measured the spark plug leads but the measurements were the same as a (new) spare set.
• Ignition timing is spot on (in this case 11° BTDC, checked both static and dynamic);
• Changed dizzy cap, spark plugs, spark plug leads and coil, no success;
• Checked the compression to see if there was anything wrong with number 3.
Should have done it on a warm engine but I just wanted to rule out any issues with cylinder number 3:
o # 1 - 8,0 kg/cm² (114 psi)
o # 2 - 10,0 kg/cm² (142 psi)
o # 3 - 9,7 kg/cm² (138 psi)
o # 4 - 9,4 kg/cm² (134 psi)
Clearly nothing wrong with number three, but number one's too low.
But I don't think that's causing the problem
• Checked the carburettors but nothing visibly wrong there.
• Same applies for the in line filters and the electric fuel pump;
• With the ignition switched on and the dizzy's chopper disc in the correct position
I got a reading of approximately 6 Volts. So the ballast wire is OK;
• Checked valve clearances, though not spot on, they didn't need immediate adjustment.
Al the above have had no effect whatsoever, so has anyone suggestions as to a solution for this problem?

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<font color="blue"><i>1976 TR7 FHC (needs some TLC ...)
1980 TR7 DHC (my first car, a.k.a. Kermette)
1981 TR7 FHC (Sprint engined a.k.a. 't Kreng
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FI Spyder
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Postby FI Spyder » 10 Oct 2014 13:47

You may have more than one problem. Re: #1 cylinder what is compression of it when warm? When you squirt oil in the cylinder to help seal rings? It's going to have to be addressed sooner than later.

#3 is a conundrum. By washed clean I assume you mean white. That would indicate it's running lean (don't see how this can be on just one cylinder without having one carb per cylinder) or sucking in coolant (head gasket). If the spark is failing on this cylinder and all else was good it should be black/sooty.

Sounds like engine work needed.

What kind of spark plug wires are you using? resistance/carbon silicone, straight wire, magnetic core wound wire?

I have used carbon silicon wires back in the day and have found that they can measure good but still be bad under operating conditions, I just don't trust them.



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Beans
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Postby Beans » 10 Oct 2014 14:59

With washed clean I mean no deposit and wet with fuel.

Coolant level hasn't dropped so far.

I use Magnecor Electrosports leads on my cars.


<center>Image
<font color="blue"><i>1976 TR7 FHC (needs some TLC ...)
1980 TR7 DHC (my first car, a.k.a. Kermette)
1981 TR7 FHC (Sprint engined a.k.a. 't Kreng
</font id="blue"><b>[url="http://www.tr7beans.blogspot.com/"]<u><b><font size="3"><font color="red">My full Blog</font id="red"></font id="size3"></b></u>[/url]</b></i></center>

jclay (RIP 2018)
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Postby jclay (RIP 2018) » 10 Oct 2014 15:10

I had a simular problem with my 7. I turned out to be a hole in the intake gasket between pistons 1 and 2. It was along the bottom edge of the gasket where it couldn't be seen with out removing the intake system. It sure acted like burnt or bent valves.

Clay

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Postby jeffremj » 10 Oct 2014 16:47

If you don't have fitted the distributor's Flash/Spark Guard RTC316 (and IIRC I didn't with my Newtronic) this might cause problems. I eventually used the Luminition Magnetronic, which is very low profile (so the guard fits) and the wiring is the same as for points (I then went to Megajolt - another story). I sold my old Newtronic on ebay and got reasonable money. See what a recent sale got:

http://www.ebay.co.uk/itm/291230776027

which is a good deposit on a new £100 Magnetronic MKT007 (also on ebay).



It might be worth swapping spark plug 3 with 4 to see if the problem moves (or not).

Otherwise, is it possible that the carb is giving too much fuel down one 'track' - a jet fallen out (is this possible?)?

FI Spyder
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Postby FI Spyder » 10 Oct 2014 19:43

<blockquote id="quote"><font size="1" face="Century Gothic, Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Beans</i>

With washed clean I mean no deposit and wet with fuel.

Coolant level hasn't dropped so far.

I use Magnecor Electrosports leads on my cars.

<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">

That makes more sense. Should have no problem with Magnecor wires. Dolly Sprint people have used sets of them for 20 years with no problems. The only thing you haven't replaced is the electronic stuff in the distributor, doesn't make sense but what else is left?

Interested to find out the cause of the low compression on #1.


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Postby dursleyman » 10 Oct 2014 21:45

<blockquote id="quote"><font size="1" face="Century Gothic, Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by jeffremj</i>

I sold my old Newtronic on ebay and got reasonable money. See what a recent sale got:
http://www.ebay.co.uk/itm/291230776027
<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">

I bought that Newtronic set off Ebay, all I wanted was the amplifier box as a spare. I obviously don't want the distributor unit because its for a Delco.

Russ

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dursleyman
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Postby dursleyman » 10 Oct 2014 21:52

Beans, my first thought is that if you have changed all the electrical stuff (plugs, leads, cap etc) with no result and the problem stays on No.3 then the only thing still to look at the carb. Is there any way something in that rear Weber is causing it? Can't think of anything but you have tried everything else so must be worth a look?

Russ

1981 TR7 Sprint DHC
Dursley
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http://tr7russ.blogspot.co.uk/

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FI Spyder
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Postby FI Spyder » 10 Oct 2014 23:34

If it were the carb it would beg the question, why isn't #4 also affected? He did say #3 didn't have spark.

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sonscar
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Postby sonscar » 11 Oct 2014 06:16

With Webbers there is effectively one carb per cylinder so one of the venturies could be blocked/maladjusted without affecting the other.Lot of work but you could swap front front to rear carbs and see if the symptoms move.Steve..

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Postby dursleyman » 11 Oct 2014 08:18

<blockquote id="quote"><font size="1" face="Century Gothic, Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by FI Spyder</i>

If it were the carb it would beg the question, why isn't #4 also affected? He did say #3 didn't have spark.
<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">

He is running on Webers so there is effectively a separate carb for each cylinder.

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Postby TR Tony » 11 Oct 2014 08:59

Theo,is the advance mechanism working correctly?

Tony
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Postby reychris » 11 Oct 2014 11:59

Theo,
I also think its something in that Webber.Sounds similar to brother-in-laws recent problem on a webber equipped zetec. Thought it was an ecu issue but turned out to be a loose choke in the carb.
Chris

Beans
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Postby Beans » 11 Oct 2014 16:22

Thanks for the input so far, some interesting lines to investigate further ...

<blockquote id="quote"><font size="1" face="Century Gothic, Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by jeffremj</i>

If you don't have fitted the distributor's Flash/Spark Guard RTC316 this might cause problems ... <hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">
That indeed didn't fit over this ignition kit so I stored it in the attic. It just might be that the ignition module is on the way out and number three (sitting closest to the optical sensor) is affected most. Will see tomorrow, I will use the strobe light to check if there's a pulse going through number three lead.

<blockquote id="quote"><font size="1" face="Century Gothic, Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by reychris</i>

... I also think its something in that Webber.Sounds similar to brother-in-laws recent problem on a webber equipped zetec. Thought it was an ecu issue but turned out to be a loose choke in the carb ...
<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">
Good you mention that. the day before the event I found one of the two bolts that hold the choke in place was coming loose. So better to investigate that a little further.

<center>Image
<font color="blue"><i>1976 TR7 FHC (needs some TLC ...)
1980 TR7 DHC (my first car, a.k.a. Kermette)
1981 TR7 FHC (Sprint engined a.k.a. 't Kreng
</font id="blue"><b>[url="http://www.tr7beans.blogspot.com/"]<u><b><font size="3"><font color="red">My full Blog</font id="red"></font id="size3"></b></u>[/url]</b></i></center>

Howard722
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Postby Howard722 » 11 Oct 2014 16:25

How about trying a Coloutune plug in number 3 and `see` whats happening?

Enjoy& regards Image

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