adj. ZS carb needle

[69S4]

Dan, I think the throttle bypass valve is only on the federal emission set up so Stuart won't have that on his, just the temperature compensator. Have you checked the balance pipe O rings are sealing properly ? If they came with your overhaul kit they should be OK but if they are the wrong thickness material they won't seal properly. Also did you renew the throttle spindle seals ?
Apologies if all this is obvious and you've been over it already - just trying to help.

Regards,

Yes, I felt kind of shortchanged that the UK spec cars don't have the bypass valve. Something else I could have fiddled with

The balance pipe is sealed ok, that was one of the first things I did on this overhaul. The carbs had not only new spindle seals but new spindles and bearings. The jets and needles were replaced and set up according to the manual and the temp compensators were set up according to the info on the TR6 site - ie opening at 115F. However on restart the idle was unstable, reving away one minute and just about stalling the next - something that I traced to air leaks.
Sealing off the vacuum take off to try and isolate the problem helped but the real problem was the O rings. I'd used non genuine replacements that were 3.15mm diameter rather than the genuine 3.5mm and of a softer material. When they heated up I could hear a whistling sound - an air leak. Replacing them with genuine ones and taking care over fitting them made a big difference. The idle is now pretty good and I can get on to the next bit of checking the mixture. The plan is to try and come to Malvern in it at the weekend. I've managed to convince my wife to come as well so it had better work properly!

[collins_dan]

Roger, I did change all the seals, including o-rings and throttle spindle seals. I also adjusted the float levels back to spec, installed some gaskets that were missing and got thackery washers installed. Previously, the orings were completely crushed and the washers were just regular washers and everything was completely tightened down. I also changed the timing. It was at 15 degrees and I tried to reduce it, but the car ran horribly, so am now back to about 14, and its better, but still not right. My issues are the idle is really fast and inconsistent, sometimes at 1500, sometimes getting stuck at 2500, but never down at the 800-1000 that I would like to get to. I've tried backing off the throttle screw, but it's almost all the way out and still idling fast. It is also running really rich at idle and almost acting lean at higher rpms (hesitating and popping on overrun), so I have lots of things to work out. It was actually running really well before, but getting hot if sitting in traffic for long and I had some hesitation at 4500rpms. It was probably just the mix and the crushed orings and washers, but now have a number of items to work out. Its really my first time really trying to do this myself, so learning a lot by making mistakes. I need to try to isolate some of things and work through them one at a time. May just go back to 15 degrees advance, then focus on getting the carbs sorted (including new needles B1BT that will work better with my L2 cosworth camshafts), then go back and see if I can reduce the advance a little, but I'm open to suggestions on how to manage my work flow. Thanks. Dan

[oldelanman]

Stuart, sounds like you are almost there. Hope you do make it to Malvern, all the effort will have been worthwhile. Still undecided whether to go myself - if I do go it will be in a Fiat Punto as the Elan is still some way off completion.


Dan, I think your step-by-step approach is the right one and you will get there in the end if you persevere. I would leave the timing at 15 deg while you sort the carbs out. That may well be correct for your cams anyway but I wouldn't know.

Some possible causes for your high idle speed and rich idle mixture......again apologies if these are "bleedin' obvious" but maybe there is something you haven't thought of.
Air valves sticking - check they lift and drop freely with dampers removed.
Throttle cable sticking - do you have the additional return spring from the throttle shaft to the airbox?
Choke lever not fully returning - the one piece loop though cable can be tricky to adjust properly to get both levers working together - would give rich mixture and high idle speed.
Fast idle screws on choke levers not set correctly and preventing throttle lever returning to idle stop - would explain why adjusting the idle stop screw has no effect.

Hope this helps. Keep at it. Good luck.

Regards,

[collins_dan]

Roger,

Some I had thought of and checked (throttle cable), others, I had not (choke lever, fast idle screw). What do you mean air valve?

My suspicion is that the once I get the mixture right, I can back off the advance. There were all sorts of ways that air could get in before, causing the car to run lean, plus the B1G needles, all of which was compensated for by advancing the timing.

I appreciate your help. Now I just need to the time to spend working through this stuff, and tracking down a part number from Burlens for pistons for the B1BT needles.

Thanks. Dan

[oldelanman]

Some I had thought of and checked (throttle cable), others, I had not (choke lever, fast idle screw). What do you mean air valve?

Dan, Sorry to cause confusion - the air valve is the piston. The way to check they are not sticking is to take out the damper from the top of the cover then lift the piston with your finger through the intake. When you let go it should drop smoothly 'til it hits the bridge. Ideally both pistons should drop at the same rate but it is unlikely that they will be exactly the same.

As a matter of interest, you mentioned before about the throttle bypass valve, does that mean that your car still has the complete federal emission set-up with cross-over pipes to the exhaust manifold and vacuum retard distributor etc or has all that been removed?

All the best.

[collins_dan]

Roger, Let me start by thanking you for all your help. I got an email from Gower & Lee and it looks like they have what I need.

2 x B1BT metering needles @ ?10.82 each
1 x B20379 adjusting tool ?9.99
2 x New pistons @ ?69.01 each
or 2 x second-hand pistons, chemically cleaned and fitted with new adjusters & fixing screws @ ?35.00 each
Allow ?14.00 for insured shipping.

I think I save the extra few quid and go with the second-hand pistons.

As to my set up, most emissions items (crossover pipes and vacuum retard) have been removed, but the throttle bypass remains.

I'll do your check on the pistons to see that they drop smoothly. It will be a long weekend of testing I think.

Thanks again. Cheers, Dan

[69S4]

Dan, just remind me again why you've gone with the B1BT needles? To the best of my knowledge they're not std Elan needles and my Stromberg book lists them as fitted to XJ6 Jaguars. The Elan options were B1Y for 69/70 UK spec, changing to B2AR and B1G for later years and B1G for the "export" versions. I would have thought that if you've stripped all the crossover pipes etc from your car you must be close to UK spec and UK spec needles would be a good choice.

If you're taking the carbs to bits it's probably worth doing some other stuff while you're at it - spindle seals for example cost very little and my experience over the last few days suggests that some care in minimising air leaks is vital in getting a decent idle. Make sure you get some genuine O rings (and probably a few spares). As mentioned earlier I used a slightly thinner, slightly softer substitute and got a huge air leak. Replacing them with genuine ones solved it instantly.

Related to replacing the O rings has anyone got any tips for removing replacing the bottom fixing nut on the rear carb? The other five take seconds to remove but that one can take me 20 mins to undo and an hour to replace. My single most hated job on the car, I'd rather replace the rotoflexes.

[oldelanman]

Dan, another thought....as you no longer have the emission set-up why not remove the throttle by-pass valves as well ? It is another possible source of air leaks and is no longer necessary. Non-emission carbs have a blanking plate where the valve would be and I would think you could get them from Gower and Lee with your other bits.

As for undoing the bottom nut on the rear carb it is bloody awkward to say the least ! The best way I have found is to remove the front carb completely and then you can get at the rear one from the front. Also an open ended spanner with the end bent at an angle is helpful - I use an old thin cycle spanner. Still not easy though and I find a few expletives are needed as well. Reverse the procedure to refit.

Regards,

[collins_dan]

Thanks all.

Roger, I was thinking the same thing, so emailed Gower and Lee about blanking plates. I didn't realize that only the federal carbs came with them, so I will blank them off.

Stuart, I settled on B1BT's because I need a leaner mixture at idle and I richer mixture at WOT than I can get with the B1G's. I considered the B2AR's, but someone else I know prefers the B1BT's and I found that on the Golden Gate Lotus Group website, they list them as their favorite for cars with performance cams:

* B2AR: Late T/C non federal needle good performance with standard cams. Richer low end, leaner upper mid-range, rich top end.
* B1BT: T/C high performance needle. Our favorite for T/C's with mild performance cams. Richer mid/top than B1Y.

For good or bad, I have Cosworth L2 cams, which I won't be replacing right now, so I need to work with them.

All seals, gaskets, orings... have been replaced with parts from RD Enterprises, so the parts aren't to blame, hopefully the installation is OK. If not, I should be able to determine that shortly, once I got all the right parts installed.

As to the bottom nut, I got a short open ended spanner that can get it.

Cheers, Dan

[Frank Howard]

anyone got any tips for removing replacing the bottom fixing nut on the rear carb?

Stewart,

My buddy has a car in which the P.O. cut out a square under the carb to allow access from the top of the footwell. Of course, he fashioned a cover plate as well. As I have a left hand steering car and there is ample passenger foot space, when I begin my major body restoration, I plan on shortening that footwell to allow plenty of access to the rear carburetor as well as the fuel pump.