Leadership Team SLR No.77 Posted April 15, 2014 Leadership Team Share Posted April 15, 2014 It's been discussed plenty about the difficulties in getting the RBTB's to give smooth running at low throttle openings and certainly I've achieved a lot by taking as much play out of the throttle cable as is practical, but I want to get it perfect and it's not there yet! 😬 Having done a couple of hundred miles at the weekend with the LBBB I had plenty of time to think about what I can change ..... - the throttle cable needs swapping to something much shorter, it's ridiculously long and will reach as far as the front wishbones in the loop created when fitted. All my research has suggested that this is the "correct" cable ... but not really the best one for the job! Half the length would be more appropriate! - I intend to fit a bicycle style "barrel adjuster" in-line in the cable to give minor adjustment possibilities without faffing around at the cable end below the TB's. - the plastic plug where the cable enters the pedal box is a pretty poor arrangement and can easily be improved to give more stability at that end of the cable. - and lastly, and this is where I'm looking for anyone who may have done it ... I'm convinced the RBTB's would benefit from a stiffer throttle return spring? Is there one available? Could a second spring be added to "piggyback" the first? Only when I'm happy that I have more accurate throttle control am I going to address any mapping issues that might be resulting in hunting between sites at low throttle openings. Stu. Link to comment Share on other sites More sharing options...
jackb_ms Posted April 15, 2014 Share Posted April 15, 2014 I'm keeping a eye on this thread... Jack Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted April 15, 2014 Member Share Posted April 15, 2014 Yes, "Before" and "After" photos please. Jonathan Link to comment Share on other sites More sharing options...
Mark Durrant Posted April 15, 2014 Share Posted April 15, 2014 Stu If you want a bespoke cable made to your specification I can recommend Venhill who made me a clutch cable for my Busa conversion . I believe they also make cables for Radicals. Link to comment Share on other sites More sharing options...
Leadership Team SLR No.77 Posted April 15, 2014 Author Leadership Team Share Posted April 15, 2014 Thanks Mark Stu. Link to comment Share on other sites More sharing options...
Jon Stewart Posted April 15, 2014 Share Posted April 15, 2014 Would this here work for the cable? Link to comment Share on other sites More sharing options...
Guest Posted April 15, 2014 Share Posted April 15, 2014 Stu, Do you think your barrels are set up ok at idle? I got a good result after balancing the pair,resetting the idle speed and correcting the throttle pot voltage. Graham. Link to comment Share on other sites More sharing options...
Leadership Team SLR No.77 Posted April 15, 2014 Author Leadership Team Share Posted April 15, 2014 Pretty sure the setup is good. I spent a lot of time getting the balance right and it idles really nicely, in fact it drives very well but on very gentle throttle openings it can have a tendency to jump around a little. Trimming the throttle cable has a major effect on reducing this but getting it right without the cable becoming the throttle stop is a real challenge! This is one of the reasons why I wonder whether a slightly heavier return spring might help? Stu. Link to comment Share on other sites More sharing options...
Guest Posted April 15, 2014 Share Posted April 15, 2014 Hi Stu, I am about to make my own throttle cable from parts purchased from Venhill as previously mentioned by Mark. Every cylinder takes a different volume of air hence a perfect balance between all the cylinders would be difficult to achieve would it be possible to run a balance tube between the tracts? Dave Link to comment Share on other sites More sharing options...
Leadership Team SLR No.77 Posted April 15, 2014 Author Leadership Team Share Posted April 15, 2014 Hi Dave, yes I like the look of the Venhill cable also. I think the ideal would be to send them my "Rover" cable to have one made with all the appropriate adjusting pieces but a much shorter length and maybe an in-line adjuster as well. The plastic piece at the pedal box end may not need replacement but possibly just some stabilising to ensure it's position is consistent 100% of the time. My opinion is that between the pedal and cable fitments there's just too much variable "slop" in the setup to get it sweet. A balance tube would be possible (I assume you mean post-RB) but would obviously mean modifying the bodies - this was one good feature of the old KV6 bodies. I'm going to attack everything else first though! Stu. Link to comment Share on other sites More sharing options...
Guest Posted April 15, 2014 Share Posted April 15, 2014 Yes I know what you mean about low speed drivability,I found the best result was with a slightly higher base idle speed of around 1050rpm. This was higher than I would have liked but it seems to help with small throttle angles when you are not picking the revs up from a lower point. I also fitted a throttle pedal top stop. This made cable adjustment more effective with close to zero slack easier to achive. A full travel stop is also a good idea if you have not already got one. Graham. Link to comment Share on other sites More sharing options...
Leadership Team SLR No.77 Posted April 15, 2014 Author Leadership Team Share Posted April 15, 2014 A pedal stop makes sense The bit I'm trying to improve is around 2200-2500rpm where it's tricky to hold a steady throttle without getting some serious diff-slap .... I'd have never believed previously that taking up throttle pedal slack would make a difference but it does! If I can I'd like to eliminate the slack in the system completely. Stu. Link to comment Share on other sites More sharing options...
Guest Posted April 15, 2014 Share Posted April 15, 2014 If getting rid of the slack is your mission then I think a pedal top stop will be the way to go. Sounds like the running issue at 2 -2.5k revs will require a different fix. Graham. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted April 15, 2014 Member Share Posted April 15, 2014 Does the loop of the cable change shape when you push the pedal? Can you detect the same instability when revving in neutral or only when driving? Does it occur if you open the throttle by hand? Or operate the pedal end of the cable by hand? Thanks Jonathan Link to comment Share on other sites More sharing options...
Leadership Team SLR No.77 Posted April 15, 2014 Author Leadership Team Share Posted April 15, 2014 The issue is only there when driving and only in a defined rpm band, I think there's jumping between to map sites but slack in the system makes it massively worse. The ideal would obviously be fly-by-wire but that's not possible with my ecu (Emerald K3). The whole throttle pedal setup is pretty crude and I think the RBTB's are just a step too far, this is why my thoughts are to start by overhauling the system and improve where practical. Stu. Link to comment Share on other sites More sharing options...
Guest Posted April 15, 2014 Share Posted April 15, 2014 I've been down the scrap yard and collected rover 25 throttle cables the pedal end is different apart from that all the other fittings are the same. The inner cables i found to be in good serviceable condition. Venhill supply the outer and various solder-less nipples that combine well with the throttle pedal. I find a throttle pedal stop is essential with my big feet and cables that stretch. hope this helps Dave Link to comment Share on other sites More sharing options...
Leadership Team SLR No.77 Posted April 16, 2014 Author Leadership Team Share Posted April 16, 2014 I can see the first job is going to be a pedal stop! Stu. Link to comment Share on other sites More sharing options...
TomB Posted April 16, 2014 Share Posted April 16, 2014 I was looking into this after our GTKY7s session on Saturday. I took the pedal off and bent it a bit (tricky without a vice) which has helped with a bit of slack in the cable. I also looked at a pedal stop, and while I haven't done any disassembly yet, it looks like a longer bolt for one of the coil attachments on the outside of the pedal box, with suitable washers and nuts, may be a way of making one. The problem I found early on Sunday morning was that as there is no slack to take up when I press the pedal, applying the power smoothly was tricky as I shot out of the drive making a racket! Link to comment Share on other sites More sharing options...
jackb_ms Posted May 2, 2014 Share Posted May 2, 2014 Something I have discovered on Sunday, fitting an air box smoothed out the issue I had at low throttle opening. The car is now very nice to drive in town at low throttle opening The "lumpiness" is only there if you look for it. The air box I have is a modified Bernard Scouse with an inlet between cylinder 2 and 3 Jack Link to comment Share on other sites More sharing options...
Slipper man Posted May 3, 2014 Share Posted May 3, 2014 I have an R500 with the same TB's. There are three things I did to get the car from where it was (fine on high throttle openings, but not great when pooling around gently): 1. Adjust the angle of attack of the throttle pedal so the first opening of the throttle was less abrupt (this made a big difference). The adjustment was by bending the end of the pedal 2. Make sure the bodies are balanced, just as you would a carb car. They are adjustable, just like carbs 3. The two Steves then transformed it by getting the mapping right It is now really smooth at low revs and easy to drive. And you can hold a constant RPM A further thought: mine had a real problem holding (say) 2,500 rpm when I went to get it MOT'd. When Steve plugged it in, he could see the TPS was faulty. Link to comment Share on other sites More sharing options...
Leadership Team SLR No.77 Posted May 6, 2014 Author Leadership Team Share Posted May 6, 2014 Quoting Slipper man: 1. Adjust the angle of attack of the throttle pedal so the first opening of the throttle was less abrupt (this made a big difference). The adjustment was by bending the end of the pedal Can you elaborate? I've adjusted the throttle cable so that the cable acts as the "stop" rather than the stop itself with the result that the tickover is different every time the throttle is closed ... proving in my mind that the cable setup is compromised. nb. Airbox fitted already. Stu. Link to comment Share on other sites More sharing options...
Slipper man Posted May 7, 2014 Share Posted May 7, 2014 If you think about it, when the end of the throttle pedal is at right angles to the cable you will get the maximum TB movement for each degree of throttle movement. With mine I bent it forward so the the cable is at right angles to the pedal at wide open throttle. This way, the initial response is tamed a bit and you get sharper response at wider throttle openings. Mapping will solve a lot of problems though. The way you have described your issues, it sounds like the idle speed is partially set by the cable, which may well be throwing out the TPS and causing some rougher running at slow speeds. By coincidence I was at the two Steves yesterday getting mine tweaked and got a right roasting for balancing the throttles and idle speed! Apparently that throws all sorts of things out and the only way to adjust this stuff is via a laptop and the application of something Steve Greenauld seems to think I lack - skill! I think you should just take it to the Steves (having made sure the cable/pedal angles are appropriate) and I am sure they will sort everything else out for you Link to comment Share on other sites More sharing options...
Leadership Team SLR No.77 Posted May 7, 2014 Author Leadership Team Share Posted May 7, 2014 Quoting sforshaw: I've adjusted the throttle cable so that the cable acts as the "stop" rather than the stop itself with the result that the tickover is different every time the throttle is closed ... proving in my mind that the cable setup is compromised This was purely a temporary setting to get an idea about what's happening with the cable and certainly the cable pull has proven to be inconsistent. As you suggest adjusting the "attack angle" may soften the response at low throttle openings which would definitely be better, I just need to modify the cable so that the action is consistent every time! Stu. Link to comment Share on other sites More sharing options...
Leadership Team SLR No.77 Posted July 4, 2014 Author Leadership Team Share Posted July 4, 2014 Update ... new throttle cable received from Venhill Engineering . I firstly cut the old one down to a more suitable length using a solderless nipple to get the setup something like, and then sent the whole lot to Venhill and they've copied it re-using any original bits that they needed to. The result is a cable that fits nicely and feels taught and positive in it's action, plus I can get virtually all the play out of the cable and still have the TB's return to there own "stop" every time. In retrospect I could probably lose a further 6" from the cable but having already lost 12" to 18" I was a little nervous about going too short! The drive of the car is a lot smoother and I can now hold a much steadier throttle in the rev range that was previously a nightmare (2000-3000 rpm). In fact the throttle response feels crisper which I wasn't expecting. Another owner has suggested that with a long cable run the sideways play of the cable inside it's conduit (the official term for the outer) may have been adding to the problem ... my cable went all the way to the front suspension then back in a large loop before entering the TB's from below! Now I'm going to rebalance the TB's, but I'm probably 80% to where I want to be. Stu. Link to comment Share on other sites More sharing options...
Mr Locust Posted July 4, 2014 Share Posted July 4, 2014 Stu, what you need is a variable rate lever/cable guide to give a large effective radius at small throttle openings and a small effective radius at large openings. I made my own setup for Jenveys to utilise the standard Rover throttle cable. Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now