TR4A revving at idle

[harley50]

I have a 1966 TR4A.  Recently my car doesn't seem to want to idle properly at tick over. I have looked at everything but nothing appears to be sticking on the throttle mechanisms.  I even took off the SU carbs to check if the throttle butterfly's were not closing properly. The idle screws are backed off completely and it ticks over at 10,000 revs.  The only way to bring it down is to adjust back the distributor a tad and it then idles at 8,000 but I am unsure if retarding it like this is good for the health of the engine.  This is only a recent issue but otherwise the car runs lovely and nothing was changed or interfered with to cause this.  I did fit new throttle brass shafts and butterfly's with new screws and proper gaskets from Turner Carbs but that was some time ago.  Anyone out there with any suggestions of help on this one.   Cheers Toddy

[Lebro]

Have you tried a drop of oil on the spindles where they pass into the carbs ?

Bob.

[RobH]

Er - I assume you actually mean 1000 and 800 revs?  It's possible you have a manifold gasket air leak.  There must be air leakage past the butterflies too else there would be no fuel reaching the engine to allow it to run, so perhaps the fit of the butterflies is not as good as you think?

This thread discusses something similar from about half-way down page 21 :- 

 

Edited August 6, 2020 by RobH

[EliTR6]

Have you checked all around the inlet manifold for leaks with wd40 or similar? 

[AlanG]

I had a similar problem and like yourself changed the worn looking spindles and the butterflies without success. I found that a very light finger press on one of the spindles reduced the tick over although I could not feel any play. So I fitted an oversize spindle. This has completely cured the problem so it would appear you only need a small amount of wear of the spindle bores to effect the tick over. 

Alan.    

[ctc77965o]

Bad brake servo? Or manifold gasket leak?

[John Morrison]

Welcome to the forum Toddy,

as you see, we'll soon sort you out.

John.

[Tr4aJim]

Don’t the butterflies have a bevel, that if reverse mounted, can cause an “open throttle” condition?

Jim

[Lebro]

Yes, but the car has been fine untill now, with nothing changed as I understand.

Bob

[Tim Carr]

If the car has a PCV it could need a new diaphragm.

Tim

[John L]

Check the diaphragm in the distributor, do a suck test, on the tube to the distributor, it should hold a vacuum, if its not holding, extra air is entering the manifold via the tube, you could blank off the tube to try if it makes a difference.

John

[harley50]

Hi,  Thank you all for your quick and helpful replies to my fast idle issue.  Sorry about the wrong rev number's quoted  as you are correct 800/1000 is what I meant.  I did initially think it was an inlet manifold leak and I did check that but it was fine.  I also did a check on the vacuum pipe because my mechanic friend showed me this trick himself and that was fine also.  I also had a another look at those bevels on the butterfly just in case and those are fine too and are closing as I checked them against the light in a darkened area.  I did check these over a period of time.  I only fitted new butterfly discs and shafts as the old shafts were badly worn and drawing in air and causing a run on when switching off the ignition.  I now have the distributor timing set just between the fast and slow setting for present.  With the two idle screws totally wound back and not touching, the car now idles at 800 on the rev counter.  However I am not happy about it being like that so further investigation is needed.  If anyone else came across this issue and its not any of the aforementioned and maybe something else then could you please let me know.    Cheers Toddy  

[RobH]

If the butterflies really are completely closed the car shouldn't run at all as there will be no fuel supply Toddy -  so at least one of them isn't shutting off fully. You could try blanking off each carb in turn when idling, which will tell you which one is supplying most of the flow; that might provide a clue as to what is going on.

Is the fuel level in the jets correct?

[Lebro]

Is the link rod between the two carbs causing one butterfly to not fully close ? try slackening the clamp bolt. or, listen to the air intake of the carbs using a short hose, are the hissing at the the same volume ?

Bob.

[stuart]

Have a read of this thread, albeit for a TR7 its mostly still applicable for SU HS6 carbs

https://www.tr-register.co.uk/forums/index.php?/topic/72880-su-hs6-tick-over/

Stuart.

[harley50]

Hello All,  As regards my car not ticking over at a normal rate and from your replies to my issue I found one which was worth a try as I had already gone through the normal checks as suggested by others previously.   That thread one was new parts don't sometimes work out !!!!  I took off my carbs again and I reused my old butterfly's but left the new shafts.  I maintained that one of the new one's was not seating properly but which one.  While I had them off I cleaned and polished the interior of both dash pots and pistons.  I found that one of them was sticking so I was happy to find something wrong.  After I had finished I tested both by dropping in the piston's into their dash pots as I kept them separate so as not to incorrectly re-install them.  It was a controlled vacuum drop in one but still sticking on the rear one.  I returned to my polishing and eureka it dropped nicely into the dash pot in a controlled vacuum.  I was happy now with both.  I had fitted new butterfly shafts as my old one's were worn and as a matter of course also fitted new butterfly's as well.  With the old butterfly's and dash pots re-fitted I fired her up.  I noticed there was a change from the running of the engine .  I use 3 in one oil in my dash pots and used that oil years ago when these Triumph's were my daily drivers with no issue back then and using it past 17yrs in my present TR.  I took her for a test drive and boy was there a transformation and it ran great but was running rich.  The test was that fast tick-over and if it was still there.  As a result of my fast tick-over it had also developed running on when trying to switch off which necessitated turning it off using both brake, clutch and key coordination.  Think everyone is familiar with that trick.  I found after a bit of tuning it ticked over just below 1000 mark which I was most pleased about and my running on was almost gone too.  I stopped at my friends house during my test and did further tuning by ear but on odd occasion it did come up in revs so I used my screwdriver to pressure lightly on the throttle linkage's and found the rear was still not fully closing off.  There was no reaction with this pressure test with the front carb which was ticking over fine.   This now leads me to the conclusion that the rear new throttle shaft area needs more detailed scrutiny so off it will come again.   I have a color tune kit which I use but I usually wait till dark to use it but with that shaft issue I will wait till I find that sticking fault before tuning it further.  It now starts first time , pulls without pinking or any snatching or slightly missing as I set the timing by ear so I am happy with my effort so far.  That thread that new parts don't work is quite possibly true as where are these new parts coming from and quality control they have with them.  The only thing that runs through my mind as regards the old butterfly's is I did not mark their position and which carb I took them off so I possibly have put them back in their not worn into positions but I will never get them back to that and because I thought new parts were the fit and forget answer.  You learn all the time.  So thank you for that.  Cheers Toddy    

[AlanG]

Have you tried gently pressing on throttle spindle to see if this has any effect?

Alan.