Heavy Throttle

[hugepiece]

ive always thought my throttle cable was buggered as its really heavy, but last night i tool the bonnet lock mechanism apart to tighten it and had a feel of the throttle engine side. I noticed how heavyweight the throttle spring was. Could I have the wrong one on there? I'd rather swap this then go down the new cable route as thats more hasstle and quite pricy all in.

Edited by hugepiece on Thursday 28th June 14:38

[Mars]

From what I can see, the external throttle spring (AJP?) is only there "just in case". The throttles themselves are sprung internally.

Some racing classes insist on external throttle springs but I think this is only for carb'd cars.

You could first try removing the external spring altogether and see if the amount of effort required is more acceptable. Then you could either anchor the spring closer to the linkage (assuming the spring gets harder to pull the longer you stretch it - not an assumption that's true for many springs but it *does* tend to happen as a spring is extended near to its max stretch) ir replace with a softer spring.

Or, if the tension without the external spring is adequately strong, leave the external one off altogether. Seems redundant on mine but it's not obtrusively strong so I've left it on.

Edited by Mars on Thursday 28th June 12:39

[Kerberos]

My throttle is also very heavy and when I mentioned it to the place I bought it from, he told me that was TVR's version of traction control! Seemed a fair answer at the time.

[hugepiece]

thanks, will try disconnecting as a test. Does anyone have one lying around or could measure for me? If the diameter or length is different then maybe that will give me an incling I have the wrong one. Leven did put a note when they serviced that the throttle was heavier than normal so don't think its just me..

[marcus1970]

hugepiece said:

thanks, will try disconnecting as a test. Does anyone have one lying around or could measure for me? If the diameter or length is different then maybe that will give me an incling I have the wrong one. Leven did put a note when they serviced that the throttle was heavier than normal so don't think its just me..

You measure yours and I'll measure mine - then we'll find out who has the hugest springy piece.

MB

[JensenA]

The 4.5 does have a heavy throttle, I thought there was something wrong with it the first time I drove it.(after being used to the 4.2) I suppose it is possible that you have a non-standard stronger spring fitted, But make sure the cable is lubed well - squirt loads of WD40 into the cable using the plastic straw thingy the new cans come with. There have been some reports on here where the driver has pushed the clutch in and the engine has tried to rev itself to destruction - the problem was traced to a snapped throttle spring, so be careful, I wouldn't remove it!

[Mars]

You would have to be extremely unlucky for a snapped throttle spring to have caused that. You have springs in *each* throttle body set, plus the external spring... 3 in total. And they're all linked together by the throttle linkage.

Un-tensioned, my external spring is about 5 inches long and a little over 1/4 inch wide but that tells you nothing about it's performance.

[JensenA]

Mars said:

You would have to be extremely unlucky for a snapped throttle spring to have caused that. You have springs in *each* throttle body set, plus the external spring... 3 in total. And they're all linked together by the throttle linkage.

Un-tensioned, my external spring is about 5 inches long and a little over 1/4 inch wide but that tells you nothing about it's performance.

OK sorry, silly me - yeah go ahead and remove the spring, it'll be fine.

[Mars]

Are you interested in understanding how things work or do you just prefer to spout scare stories? Nothing in what I previously wrote contradicted what you said but your tone implies I have slighted you. I have recently had the throttle bodies off my car, and have serviced the throttle linkage during which time I noted that each throttle body is self-sprung and that the external spring is not intrusive yet you state that the "4.5 does have a heavy throttle" as though they all do when this is plainly not the case.

Additionally, your scare story does not qualify how on earth a single snapped throttle spring, out of the 3 present, could cause the runaway situation you described so I only noted how unlucky you'd have to be to experience such a condition. Your sarcasm was unecessary.

[julian64]

I think your both right. In a fully working Cerb the two springs wound round the throttle arms themselves should be enough. They certainly are when you have them on the bench.

I think the final spring is an addon, and the cars that I have seen not only have different lengths but also connected onto different places.

I think the springs round the throttle arms get broken and are not replaced, relying on the one big spring to protect from disaster.

One final point. I found that I set the throttle bodies up perfectly on a bench, they would have had no need for a seperate spring. Then when they were bolted to the engine, the very small amount of flex that must have crept in siezed both throttles to the point they were both quite stiff and the butterflies where slightly out. This took a whole lot more sorting and I nearly reverted to the 'just bung the big spring on' technique.

[hugepiece]

i'm going to measure the spring later, from memory though the coiled part is about 25mm wide at its widest point. When I saw it I instantly thought it looked a bit heavyweight for what it was for! I'll measure it properly and post on here tomorrow to get some comparisons. When I opened the linkage by hand it felt like there was more resistance then expected due to the spring, so i'm assuming maybe my cable is ok???

Thanks for the wd40 suggestion, I'll try pumping some down the sleeve to lubricate too.

[JensenA]

Mars said:

Are you interested in understanding how things work or do you just prefer to spout scare stories? Nothing in what I previously wrote contradicted what you said but your tone implies I have slighted you. I have recently had the throttle bodies off my car, and have serviced the throttle linkage during which time I noted that each throttle body is self-sprung and that the external spring is not intrusive yet you state that the "4.5 does have a heavy throttle" as though they all do when this is plainly not the case.

Additionally, your scare story does not qualify how on earth a single snapped throttle spring, out of the 3 present, could cause the runaway situation you described so I only noted how unlucky you'd have to be to experience such a condition. Your sarcasm was unecessary.

re: my Scare Story

http://www.pistonheads.com/gassing/topic.asp?h=0&a...

[Mars]

I must be missing something. That page doesn't mention spring failure. It states "the engine had spun up under no load, the air pressure going in keeping the throttle butterflies open and it finally going bang at 14,500 rpm according to the ECU".

I'm curious how that could happen given that the butterflies are hinged in the middle anyway, specifically designed to prevent this mode of failure. The air pressure against both sides of the butterfly are intended to cancel out any differences.

Regardless, I remain sceptical that one broken spring could cause a failure of this type given that the linkage holds all throttles together.

I can see how throttles may not close 100% because of insufficient springing to overcome deformation of the throttle body as described by Julian, but this is the sort of problem that exists upon reassembly and doesn't simply *happen* while racing.

[julian64]

Well, if I were looking for a scenario, I would say that the amount of stiction of the throttle rod is dependant on its rotation.

Personnally my throttles were very free and easy at full open and started to stick as they closed shut. I initially thought this was the butterflies fouling on the barrel but it turned out to be that the throttle rod was ever so slightly bent.

I could see a scenario the other way round where the throttles were fine for normal driving but at WOT became stuck by a slighty bent throttle rod.

There is a lot of insensitive power under your foot on full throttle, therefore if there was a problem at WOT the throttle could easily be forced under power of your foot into a position the spring couldn't bring them out of.

[Mars]

But you'd check the full rotation of the throttle upon completion of assembly, meaning it shouldn't catch you out on the road.

Surely?

[JensenA]

Were talking about a friggin spring here !! You can theorise all you like about what might happen if..... and How it shouldn't happen if.....
But it's a spring on the throttle, and I would imagine it's there for a reason. And if you have all got wimpy little sparrow legs and the spring is too strong for you, then by all means remove it. Just thought I'd be helpful and point out a possible risk to the original questioner, that I had read on this forum.
I hardly think that is worth a stupid accusation that I am "Spouting scare stories"!

Edited by JensenA on Friday 29th June 18:37

[DonnyMac]

JensenA said:

I am "Spouting scare stories"!

OOOH... JensenA you spring hater!

[Mars]

So who are you havin a go at now then with your "sparrow legs" comment? The chap who asked the question at the top of the thread? Isn't that what the forum is about... to discuss issues? If you think his original queiry was stupid why'd you jump in then?

You mentioned "reports" - plural, which when questioned, you could only point to one which mentions nothing about the spring failure.

You stated the "4.5 has a heavy throttle" when it doesn't necessarily.

And yours was the first stone cast with your sarcastic reply so don't get all moody because you were caught out spouting scare stories.

[JensenA]

FFS mars - chill out! Me posting a thread to another article isn't spouting scare stories, it's just pointing a fellow Cerb owner to another article that might be relevant, or it might not be, you want to take the spring off, then take it off.