Slightly rough running at 1500rpm

[grumpy2]

Went on a very nice organised run with one of my clubs today. Lots of very old cars (1930s) etc. trouble with the oldies is that they drive slowly and keeping such a slow place wasn't easy for my TR. At 1500rpm it's quite rough almost misfiring type of running yet at idle and above 1700 it's excellent. Also when not with the oldies, acceleration is smooth and strong from 1000 all the way through.

 

Any ideas chaps?

 

Thanks

 

Gary.

[TriumphV8]

Maybe throttle sync.

Would test that first.

[grumpy2]

What's that?, same as balancing carbs? And how's it done? Same again?.

 

Thanks

[RogerH]

Hi Gary,

have you cruised at this speed before with the same results or is this new?

Some sporty cams don;t like low speed!!

 

Roger

[grumpy2]

It's never liked cruising at 30 in 4th which is 1500 rpm but not quite the same running feeling. Definitely worse today but not driven under these conditions before. Lots of 10-20 mph light throttle driving.

[Beachie]

With colder conditions, any rough running will be enhanced as the engine naturally wants to perform a little better. As already suggested, the throttles may be slightly out of sync. This means that the butterflies in the throttle bodies are not opening equally at the same time. Thus two or more cylinders are getting their charge air at different rates to the other cylinders. This will result in a lumpy engine at low power/low revs. Not so noticeable at higher power settings.

[TriumphV8]

The difference between carb and PI is that some out of sync at the carbs causes that they get a little more or less mixture.

The PI calculates for all cylinders the same fuel amount and so unequal setup leads to different quality between cylinders.

Some run rich and some go lean. If that becomes to much the range where the mixture can't be fired safely will be reached

and that gives the lumpy behaviour.

 

Setup should be done by shortening the throttle cable that idle is at 2000 and than with a flow meter

each manifold is checked and set to equal flow.

[Guest ntc]

It's never liked cruising at 30 in 4th which is 1500 rpm but not quite the same running feeling. Definitely worse today but not driven under these conditions before. Lots of 10-20 mph light throttle driving.

It never will it's a cp car.

[grumpy2]

so can I surmise the above as lumpy running on light throttle is a characteristic of the CP injection but it can be minimised by correct throttle body balancing, and that this is similar in principle to balancing carbs.??

 

cheers

 

sort of hoping that this was the answer as the car runs so well otherwise and I've only noticed the lumpiness today with the oldies

 

Gary

[TriumphV8]

 

 

There is no fixed limit what the engine does or not.

CP is 40 years old and already ex works

had some space for improvement.

Now more or less worn out things turn worse.

 

Modern spindles like used in Weber DCOE have proper

sealing and ball bearings for precise movement.

 

Just fit those bearings from model cars and things improve.

I also rebuilt the complete linkage in neddle bearings and

the problems are history.

 

 

[grumpy2]

thats a proper bit of engineering there, within my capabilities but I'd prefer to do something like that on a 'spare' set up not the one I was using. perhaps I'll have a look for a used set of throttle bodies. May also have a check for spindle wear but in my experience this has usually shown itself as inconsistent idling

[TriumphV8]

For idling the CP manifold has an interconnection between the runners.

That is the reason why the idle screw can be positioned at one end of the line

and still they all get the same amount of air.

 

When the rpm is raised more air is needed and the interconnection fails to compensate.

If one throttle should open too much it can not get rid of the air sucked in

because the holes in the interconnections are too small.

 

That is done because the runners should not interfear at low revs because the

cam does not fit for these revs and causes unwanted pulsations in the manifold.

If they are limited to one runner they do not do much harm.

 

So it is just enough for equal air at idle but separated good enough that with part throttle

it does not interfear.

 

At higher load the mismatch of the throttle plates does not make that difference in percent.

So the whole disadvantage of this system is definitely that a good setup of throttle plates

is required for small openings.

 

So mild cams like in the BMW 320 can be used with a single throttle,

the runners do not disturb each other but the wilder cams in the M3

require 6 individual plates. Motorbikes also benefit from individual plates.

[RogerH]

Hi Gary,

thinking about it why 30mph in 4th gear. Why not 3rd or 2ndOD!!!

 

Roger

[Guest ntc]

Triumph changed the cam spec later so the ladies could drive it.coat on

[mike3739]

Good one Neil

 

Cheers

 

Mike.

[Nigel Triumph]

Triumph changed the cam spec later so the ladies could drive it.coat on

 

My good lady enjoys driving our CP-series TR6, and does so more than competently!

 

Back on topic, I'm betting the problem is throttle synchronisation, been there and had the same symptoms described here. A well-fettled CP- or CR-series 6 should pull smoothly from around 1,000rpm in direct top. It's also worth checking the throttle linkage for wear. I've fitted the ball-jointed throttle link rods from Moss, as the old trunnion-type connectors on the link rods were badly worn.

 

 

Nigel