Sticking Throttle Mechanism - CR TR6

[Chilp3]

Good Afternoon,

I have had my original CR series TR6 throttle bodies rebuilt by Prestige Injection Services and re-fitted together with an under-slung Prestige linkage kit. The quality of work is excellent and the assembly has all gone together very well. I have covered approximately 2,000 miles since.

 

I have a problem when the car gets hot (not overheating) that the throttle sticks open and doesn't allow the car to return to idle. When this happens if you push the linkage manually from under the bonnet normal tick-over is resumed. Once the engine cools the throttle return works perfectly so it would appear to be a heat related problem.

 

I have removed and re-adjusted the mechanism many times but have yet to be successful in curing the problem. There is a degree of 'adjustment' on the throttle bodies themselves as well as the linkage where the brackets bolt up to the bodies.

 

I will contact the ever helpful Malcolm Jones next week but for now I was wondering if any other forum members may have experienced similar problems.

 

Thanks for reading this post and taking the time to share your thoughts and advice.

 

Best Regards, Peter

[snowric]

Peter - you will get many suggestions on here.

 

One clarification. Did your car always do this after the kit was fitted or has the fault appeared.

 

have you checked the air flow and balance at idle when coldish and after the fault happens so you can see which butterfly or pair is causing the problem.

 

Finally when it is warm and idling high, if you disconnect the throttle rods does the problem carry on.

 

ie is it a throttle body problem or the linkage?

 

Good luck.

 

Snowy

[barkerwilliams]

Peter,

 

If all else fails, get a can of freezer spray from your local screwfix / toolstation etc and whilst the mechanism is hot and stuck open and the engine off, work you way around the metalwork without touching, just cooling individual components, until the linkage releases.

 

That should point you to the component causing your problem.

 

 

Alan

[TRsixchris]

I realise this is an old post but I am experiencing the same issue. I have just balanced the throttle bodies on my CR equipped TR. I have the prestige underslung linkage. Everything seems OK and the car drives well but I can't get the throttles to shut reliably. The car sits at 1500 - 1800 RPM untlil I either flick the throttle pedal or manually push the throttle linkage.

 

I have removed cleaned and lubricated the linkage and assembled one piece at a time ensuring everything is aligned and free including the throttle butterflies. Everything seems fine but once all connected up the throttles refuse to close without a bit of help.

 

​Its a shame as the car generally drives better with the throttles balanced.

 

Any ideas?

 

Regards

 

Chris

[john.r.davies]

This has happened to me twice, once about eight years ago at Zandvoort, and the other last autumn at Oulton Park.

Each time, disassembly found that there was scoring of one spindle, which must have seized.

 

My first solution was to fit return springs to each throttle arm, which worked well for the last eight years. Now, I've fitted Oilite bushes to the throttle bodies, but delays in this work meant that I had to reassemble a spare set of throttle bodies and fit those - which on the first test drive, stuck, wide open! My next race (Thruxton, I hope) is too near to fit the modified TBs, so I've retensioned the return springs, and crossed my fingers.

 

Let you know what happens, and eventually how the Oilites behave.

And alternative would have been PTFE bushes.

 

John

[TRsixchris]

Hi John,

My thoughts are the throttle bodies themselves. I will remove them today and strip out the spindles and butterflies and make sue the spindles are free and the butterflies shut properly. I did notice quite a discrepency in the flow on the 5&6 pair so all may not be well on that one.

Regards

Chris

[DaveN]

Before you do that, are the TB's properly aligned?

[TRsixchris]

They were not particularly well aligned but as I am using the Prestige throttle linkage which has effectively an independent link to each TB the alignment should not be too critical. However the TB have all now been rebuilt and I will ensure they are correctly aligned when reinstalled.

 

Chris

[Chilp3]

Hi Chris,

A good way of aligning the throttle bodies when you re-fit them is by using a long engineers steel rule played across the machined flats. This will give you a good start when you come to balance each of the throttle bodies with the flow meter.

 

As a matter of interest I have now replaced the Prestige under-slung linkage kit with an overhead type from RTR. I have found that the RTR kit provides much finer adjustment across each throttle body/ butterfly. As my car is a CR series I have also fitted the RTR cam mechanism which utilises part of the original mechanism. This provides a smoother and more progressive throttle opening avoiding the 'snap' that can sometimes be evident due to the higher vacuum created on the CR cars. The RTR kit is also necessary if you have fitted an extractor manifold I believe due to clearance issues.

 

hope this may be helpful and good luck setting your car up.

 

Best Regards, Peter

[john.r.davies]

Mmmmmmmmmm. I seem to be accumulating a number of my own goals recently.

 

Found the cause of my newly sticking throttle - a butterfly screw that I recently reassembled had fallen out, and no doubt been ingested by the engine. The butterfly was wobbling about on the spindle.

To find that, I took the old TBs off, so now to install those with the new Oilite bushes.

And yes, I have been over their b'fly screws to be sure they are tight!

 

John

[stuart]

Hi Chris,

A good way of aligning the throttle bodies when you re-fit them is by using a long engineers steel rule played across the machined flats. This will give you a good start when you come to balance each of the throttle bodies with the flow meter.

 

As a matter of interest I have now replaced the Prestige under-slung linkage kit with an overhead type from RTR. I have found that the RTR kit provides much finer adjustment across each throttle body/ butterfly. As my car is a CR series I have also fitted the RTR cam mechanism which utilises part of the original mechanism. This provides a smoother and more progressive throttle opening avoiding the 'snap' that can sometimes be evident due to the higher vacuum created on the CR cars. The RTR kit is also necessary if you have fitted an extractor manifold I believe due to clearance issues.

 

hope this may be helpful and good luck setting your car up.

 

Best Regards, Peter

FWIW You seem to be missing a split pin on your clevis pin BTW.

Stuart.

[TRsixchris]

Thanks all.

Peter,

Yes as you suggest I will use a decent straight edge to get things lined up.

John

I was surprised on stripping my TBs down that the screws were just a normal items. When I have rebuilt carbs previously the butterfly screws are usually designed to be peened over - not always easy to without bending the butterfly spindle. I have seen screws for the Lucas butterflies which are split so that the ends can be spread to prevent the screw falling out if it comes loose.

I will use some medium strength loctite when I reassemble.

This won’t be for a week or so as I had one of the spindles on the bench and a box fell off the shelf above bending the spindle which when I tried to straighten snapped in two.

A new spindle is on order from Malcolm at Prestige as they are non-standard conversion items.

Chris