'71 PI engine doesnt run well on low revs

[mortenh]

Hi

 

This is my first post here, and I'm quite new to the TR6 as well, so this might be a rookie question for you folks out there. I'm not even going to pretend to now a whole lot about mechanics, but I have spend enough hours working on the TR6 this last half a year for my wife to give the car a suitable name;)

 

I bought a US '73 Triumph last fall, with a '71 PI engine fitted. This runs quite well idle, as well as on high revs, but between 1000 and 2500, it has big problems under acceleration. Particularly if cold. It looses power and it runs really uneven, jumping and coughing. It actually seems like it pushes too much petrol. I get a similar effect when I pull the choke when driving.

 

I've checked the injectors, they seem to be fine, I've changed the coil, checked the distributor, changed the lead and spark plugs. No help. I haven't changed the injector pipes, though. I'm thinking that if it gets too much fuel, it might be the metering unit. Also I've been advised not to mess with the metering unit - buy a new one or send the one I have in for a check.

 

Any ideas?

 

Btw: It has a Bosch fuel pump, spin-on oil-filter.

 

Best regards

Morten

Edited May 12, 2010 by mortenh

[Mike Collins]

Are the butterflies balanced and synchronised? There should be roughly equal airflow through each intake at idle, quick check by listening to the intensity of hiss at each.

 

Do all three groups of butterflies start to open at exactly the same time when the accelerator is depressed? The linkage may need readjusting.

 

Mike.

[88V8]

Hello Morten, welcome to the forum.

 

I agree with Mike, it sounds like the butterflies need synchronising. Poor running up to 2,500rpm, and on trailing throttle, is a classic sign.

 

You can try listening to the hiss, but it's easier to buy a Uni-syn.

Here's one

 

http://cgi.ebay.com/...=item5d28e966a9

 

It's like balancing multiple carburettors. Needs to be done pretty accurately. After a few years you'll be able to do it in your sleep, so I'm told.

Balance them at 1200rpm, not at idle. It's when they just start to open that the balance is most crucial.

 

Before you start on this however, check the butterfly spindles for wear. If they're worn, you'll get air leaks, it will never run properly. But fear not, there are people over here who can refurbish them.

 

I don't know what resource there is in the US for Lucas injection, not a lot I guess, but if you're a 6-Pack member it will be worth asking in there. There are a few members with Lucas PI.

 

Two other things you might look at, although I don't think they're the problem.

#1 check that the fuel control lever on top of the metering unit returns fully to its stop when you push in the choke knob.

#2 check the vacuum hose - from the inlet manifold to the metering unit - make sure it's not leaking. That hose tells the metering unit how much petrol to send, if there's a vacuum leak it will send too much petrol.

 

This website has the Lucas reference cards which you may find useful to download.

http://picasaweb.goo...feat=directlink#

 

This site has some info on fault finding.

http://www.lucasinje...20page%2015.htm

 

Ivor

 

[mortenh]

Thanks Ivor and Mike

 

Sorry for not replying earlier - I've been kind of stuck with putting on a new exhaust manifold..and since I was "down there" I found some other things to fix, resulting in pulling most of engine apart. Anyway, I'll have it all back in place tomorrow. Then I'll check the butterflies and air leaks The fuel control lever on the metering unit seems to be returning fine.

 

Thanks for your help and tips, I really appreciate it!

Morten

[mortenh]

Hi

 

Just to let you know - the problem was the not syncronized butterflies; after a bit of looking, listening and adjustments the engine now runs (close to) perfect

Thanks for the tip Ivor and Mike!

 

Morten