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Loss of power when engine hot


tonyl999
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Can anyone help with regard to a problem I cannot resolve. I have a 1972 GT6. Apart from sports exhaust and K&N filters the engine is pretty much standard. The engine has developed a problem when it gets to full operating temperature. Starting up and running while warming up it is fine. After about 10 to 15 milles and under load the engine looses power and runs very roughly. I have to ease of the throttle and allow the car to accelerate very slowly and even then it is constantly missing. If I stop and allow it to cool a bit it runs smoothly again until it heats up.

 

The carbs were replaced about two years ago and colourtune shows them to be set correctly. The timing is correct. I have fitted new HT leads, coil, distributor cap and rotor arm. All made no difference. The car has electronic ignition. I have just set all the valve clearances and although the car then started running better the old problem came back after 30 or 40 miles.

 

I am running out of ideas and getting fed up of buying new parts that make no difference.

 

Anyone got any ideas where I should look next?

 

Thanks.

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What make electronic ignition do you have?  

 

 

I had exactly those symptoms when I first fitted electronic ignition. I purchase a cheap Accuspark system which was found to be the cause. From my investigations I have found that the cheap versions are fine for 4 cylinder cars and not good for six cylinder.

 

My solution was just to buy and fit a quality system.

 

A cheap way to check is to revert back to points and condenser for a short time to see if it solves the problem. They are always useful as a backup!

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Fuel starvation? It may not be at the engine end! If so, suspect something blocking the fuel lines, so remove, flush and replace, and maybe fit an inline filter; make sure all breathers are unblocked. Something is building up to breaking point as the car drives, but then after a period of sitting idle - draining back? - it works again. Try that angle and see if things improve.

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Sports exhaust and K+N's will upset the mixture.

 

Yes, at idle the mixture will be correct, but at higher rpm it will be too lean, only way is to swap the needles, though tricky with strombergs, a trip to a rolling road may help by reprofiling. However, probably not the cause of your symptoms (though not helping, lean running will get the engine hotter than normal)

 

However, Colin has a fair point, could be fuel supply. Is the tank suffering with a vacuum? Not sure if there is a breather system for the tank?

 

Also, there are some dreadful new ignition parts on the market. Notably rotor arms, condensers and coils. Good condition old parts are usually fine. 

 

Try a meeting, see if you can "borrow" some known good parts??

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Check the coil polarity is correct neg coil to dizzy pos to white ignition.

does yor car have a ballasted coil, electronic ign generally need a 12v supply ,not a balasted 6-8v

 

then the coil must match

ballasted primery 1.5 ohm or 12v = 3 ohms

 

remove the carb fuel pipe and pump into a jar , this could be the dreaded floating slivers of rubber hose that float until load james them up behind the float needle

its quite common, need to remove the float and take the needle out to be sure

 

make sure no green stuff is in the coil ht terminals

 

may not need it , but see that the dizzy earth to the moving plate is sound

is a filter fitted, isnthe pump body full of debris !

 

pete

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Thanks for the latest posts. There's a lot to go through so I'll crack on and see how it goes. The electronic ignition was fitted over 10 years ago by the previous owner and has never been a problem. The recent coil change was like for like so should be a correct match. I think I will start with the fuel suggestions first.

Thanks again.

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Quick update in case anyone else has a similar problem. The fuel delivery all checked out ok. Good pressure and petrol crystal clear. Managed to 'borrow' an accuspark system my son hadn't used yet and swapped it for the existing Newtronics Systems electronic ignition. Took for a 20 mile and no sign of the power problem. Didn't have time for a longer drive but it seems to have done the trick.

Now need to look for perhaps a better quality system. Anyone got any recommendations?

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Beware of cheap kits especially for 6 cylinders. The Aldon from the club shop is specifically for Delco distributors and GT6 ballasted systems. It needed no additional wiring, on mine anyway, others kits do. Reassuringly expensive but, it works. My car runs very much better since fitting it.

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The Piranha / Newtronic ignitions are fairly easy to fix,. they are just a couple of transistors and discrete components.

 

If you are not up for fixing it (probably a dry joint) then leep your eye out for a replacement box, they come up on Ebay occasionally.

 

The Piranha is a far superior system to most of the modern ones.

 

Cheers

 

Colin

 

p.s. do not throw it away, give me a shout if it need rehoming!!

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Happy to support the club shop but I see they are out of stock at the moment.

The Aldon web site supply what looks like the same system for nearly 20 pounds less (including vat and postage). Is the club shop one different?

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I've been pleased so far with the Simonbbc electronic ignition kit on my 1973 GT6 (Mines a 2.5 PI. Not sure if this is a different distributor to the standard GT6)

 

It's a lot cheaper too.

 

http://www.simonbbc.com/index.php?main_page=advanced_search_result&search_in_description=1&keyword=triumph+gt6

 

You pay your money and roll the dice I guess...........

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Don't think anyone has mentioned it and just in case you were not aware, the dizzy number is on the outside case usually hiding opposite the battery. Mine was covered in black paint originally, useful to let them know the number if you are emailing.

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