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Jim.Walker
Joined: 27 Dec 2008 Posts: 1229 Location: Chesterfield
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Posted: Sat Jun 27, 2009 10:33 pm Post subject: Triumph Vitesse Mark 2 - Anyone got an answer for this? |
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The car accelerates like the proverbial "bat out of ****", up to 50 mph and then the engine begins to feel rough (unhappy) and will not accelerate any further.
Fuel starvation was the original thought, and though the mechanical fuel pump tested out ok a new one was tried with no improvement.
The ignition timing is spot on and the centrifugal advance is what the book says it should be. Substitute coil etc. have been tried, all with no effect.
The twin SU Carbs are original fitment and correctly balanced and tickover is smooth and even at the recommended 900rpm. Throttle spindles are not worn. The pistons move freely with the needles correctly centred in the jets so that they bottom correctly. The throttle butterflies open fully. Removing the air filters has no effect.
The valve rockers are correctly set and the valve timing is correct.
The exhaust is not restricted (blocked).
I can think of nothing else to check!
Any ideas gratefully considered.
By the way - the car is a twin for my Gentry in my Avatar, but belongs to my son. He is cross because he has trouble keeping up with me even when I am towing my caravan! _________________ Quote from my late Dad:- You only need a woman and a car and you have all the problems you
are ever likely to want". Computers had not been invented then! |
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Penman
Joined: 23 Nov 2007 Posts: 4757 Location: Swindon, Wilts.
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Posted: Sat Jun 27, 2009 10:38 pm Post subject: |
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Hi
What gear?
If you have a rev counter, does it happen in lower gears at the self same point in the rev range? _________________ Bristols should always come in pairs.
Any 2 from:-
Straight 6
V8 V10 |
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Jim.Walker
Joined: 27 Dec 2008 Posts: 1229 Location: Chesterfield
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Posted: Sat Jun 27, 2009 10:48 pm Post subject: |
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That is the curious thing Penman.
In fourth gear the limit seems to be just over 2000rpm, but the engine will exceed those revs, still accelerating hard in the lower gears. _________________ Quote from my late Dad:- You only need a woman and a car and you have all the problems you
are ever likely to want". Computers had not been invented then! |
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victor 101
Joined: 03 Apr 2009 Posts: 446 Location: East Yorkshire
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Posted: Sun Jun 28, 2009 9:01 am Post subject: |
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It might be worth checking the flexible fuel line that connects to the inlet side of the pump, some of the older woven covered rubber pipes can become porous and allow air to be sucked into the pump instead of fuel. |
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Rusty
Joined: 10 Feb 2009 Posts: 204 Location: Bunbury, Western Australia
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Posted: Sun Jun 28, 2009 11:02 am Post subject: |
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I like the idea of the air leak from a hose or maybe a small rust hole in the steel pipe.
Something else thats unlikely but easy to check is a blocked fuel tank breather in the fuel cap or wrong unvented cap fitted causing a vacume buildup in the tank ?
Just take the cap off and give it a run, that will soon eliminate that as a problem. |
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Scotty
Joined: 23 Nov 2007 Posts: 883
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Posted: Sun Jun 28, 2009 12:51 pm Post subject: |
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Jim.Walker wrote: | In fourth gear the limit seems to be just over 2000rpm, but the engine will exceed those revs, still accelerating hard in the lower gears. |
So why, I ask myself, does the engine run ok in higher gears, yet in fourth it has running issues above 2k?
Have you run the car through the gears to establish for certain its only fourth that the roughness appears and acceleration is compromised?
Is the car fitted with an "overdrive" unit - could it be it's engaging the moment you select fourth without you knowing it and the roughness you're experiencing is actually due to the unit causing the engine to "stall" because the unit needs higher revs to run smoothly?
Scotty. |
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Jim.Walker
Joined: 27 Dec 2008 Posts: 1229 Location: Chesterfield
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Posted: Sun Jun 28, 2009 4:43 pm Post subject: |
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Thanks Victor 101, Rusty and Scotty.
For starters, the car will sustain over 3000 rpm in any gear but top.
An overdrive is fitted, but it is not engaging when it should not. Using my car as a benchmark, I can easily accelerate from 1500 rpm with overdrive engaged in top gear. The only significant difference between my son's car and mine is that he has 14" wheels while mine are 15", which makes mine slightly higher geared. The engines and transmission etc. are identical. I think the transmission can be eliminated.
The fuel lines are clear and the fuel pump delivers enough to empty the fuel tank in a few minutes. The fuel cap has already been checked and is not the problem.
Perhaps I should have made it clearer about the "unhappy" engine. The engine definitely has a slight roughness at 3000rpm in top, not at all in keeping with the wonderful smoothness normal in the Triumph 6. It does feel as if the engine is trying to fire normally on all cylinders, but is not quite getting enough fuel to succeed. I can hardly be called missing or mis-firing. Oh, and there is no air leak in the induction.
I have met similar symptoms on cars with a siezed centrifugal advance in the distributor and also a pinhole in the diaphragm of a Stromberg carb, but neither fit the bill here. _________________ Quote from my late Dad:- You only need a woman and a car and you have all the problems you
are ever likely to want". Computers had not been invented then! |
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peter scott
Joined: 18 Dec 2007 Posts: 7118 Location: Edinburgh
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Posted: Sun Jun 28, 2009 5:03 pm Post subject: |
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I know that you don't think it's missing but having pretty much covered the fuel and exhaust systems it just might be an ignition fault.
Perhaps bad earthing of the contact breaker plate. Loose screws into the distributor body perhaps.
Might be worth trying another coil or condenser too.
Peter _________________ http://www.nostalgiatech.co.uk
1939 SS Jaguar 2 1/2 litre saloon
Last edited by peter scott on Sun Jun 28, 2009 9:04 pm; edited 1 time in total |
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Jim.Walker
Joined: 27 Dec 2008 Posts: 1229 Location: Chesterfield
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Posted: Sun Jun 28, 2009 5:10 pm Post subject: |
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I like that one Peter. Though that often shows up on startup (and hasn't), it is something I have not checked.
I will do voltage drop tests across points, points to baseplate, baseplate to distributor body and distributor body to engine block.
You have also brought to mind the condition of the pigtail lead. And the coil to distributor lead.
I'll keep you posted.
Coil and condenser have both been checked by substitution.
Thanks. _________________ Quote from my late Dad:- You only need a woman and a car and you have all the problems you
are ever likely to want". Computers had not been invented then! |
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victor 101
Joined: 03 Apr 2009 Posts: 446 Location: East Yorkshire
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Posted: Sun Jun 28, 2009 10:29 pm Post subject: |
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Its certainly looking more like an ignition related problem, if it revs at 3000 rpm whilst stationary for more than ten or fifteen seconds or can stay in a lower gear on the road for the same sort of time, maybe your spark plugs are breaking down under load which might explain the roughness you describe. |
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Phil - Nottingham
Joined: 01 Jan 2008 Posts: 1252 Location: Nottingham
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Posted: Sun Jun 28, 2009 10:41 pm Post subject: |
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Whilst I think it is likely may be ignition related (especially the distributor earthing problem if it relies on teh baseplate screwes rather than a lead which canb eeasily checked) I had a very similar problem on my Rover P5B (V.
Tried everything including fueling problems and was suspecting camsahft or head gasket problems - it turned out to be a failing UJ which when replaced I discovered that it cured completely this "engine" roughness at higher revs.
Until I got the more familar loud metallic tinkle after another copuple of thousand miles and interior mirror vibration there were no other symptons. No play was apparent until prop shaft was disconnected either. _________________ Rover P2
Rover P4
Rover P5 & P5B
Land Rover S2 & S3
Morris Mini Traveller Mk2 |
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Jim.Walker
Joined: 27 Dec 2008 Posts: 1229 Location: Chesterfield
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Posted: Tue Jun 30, 2009 5:52 pm Post subject: |
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Thanks for all the interest everyone. Sorry I have not responded sooner, but I have had my hands full with other things for the last day or two.
Sadly all the suggestions came to nought.
Voltage drop test across the entire distributor from the coil connection to earth on the engine gave 0.1volt. As I remember the acceptable limit is 0.2volt. Scratch that one. We did find though that the pig-tail lead only had two or three intact strands which could possibly limit larger current flow (high hopes here), but changing that had no effect. (Carbon) plug lead resistance was well within the 25k Ohms per metre everywhere, but the cap, copper leads and rotor arm were substituted from my car with no improvement.
Compression test showed rather low pressures hovering around 100lbf/sq. in., the highest being 107. I don't feel that would cause this problem.
Jumping straight from the battery to the coil to eliminate the ignition switch and its associated wiring did nothing either. Nor did tearing hair out!
I'll keep trying. Thanks for the suggestions. _________________ Quote from my late Dad:- You only need a woman and a car and you have all the problems you
are ever likely to want". Computers had not been invented then! |
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PAUL BEAUMONT
Joined: 27 Nov 2007 Posts: 1281 Location: Barnsley S. Yorks
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Posted: Wed Jul 01, 2009 1:07 pm Post subject: |
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I am surprised at the lowish compressions. I would begin to suspect valve issues. Do you know the history of the car? Has the situation suddenly happened, declined over a period, or always been like it in your son's ownership?
Could it have the wrong valve springs fitted which are allowing valve bounce at higher engine revs?
Paul |
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Kelsham
Joined: 18 Jan 2009 Posts: 349 Location: Llandrindod Wells Powys
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Posted: Wed Jul 01, 2009 5:31 pm Post subject: triumph vitesse |
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Hi, recently suffered a loss of performance on my 1932 BSA Trike. it turned out a new rotor arm restored performsnce. I couldnt see any tracking.
I agree the compressions seem low. Was the throttle fully open when you took them. regards Kels |
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Jim.Walker
Joined: 27 Dec 2008 Posts: 1229 Location: Chesterfield
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Posted: Wed Jul 01, 2009 6:04 pm Post subject: |
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Perhaps I did not tell the whole story of the compression test.
The engine was hot, the throttle fully open and was the result of the same number of compression strokes each time - as it should be.
A squirt of oil in each cylinder to reduce ring leakage raised all pressures to acceptable levels, showing that low compressions are due to ring leakage and not valve problems.
By removing the dampers and placing pieces of light dowel in the tops of the pistons we found that after about mid-throttle the back carb. piston started to lag behind the front one and never lifted more than about half its travel. The reason was traced to a dodgy clamp on the transverse rod connecting the throttles which was slipping round as the return spring tension went up. When the throttle was closed the clamp returned to its normal position. A new clamp cured that AND THE PROBLEM! Not the piston rings of course, but they are now standing dosed in Redex in case carbon is to blame. Oil consumption is very low and performance is good, so I think we can live with the compression problem for a while at least even if the Redex does nothing.
Oh my! What do I say now? Except thanks everyone! _________________ Quote from my late Dad:- You only need a woman and a car and you have all the problems you
are ever likely to want". Computers had not been invented then! |
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