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Post by Nick RS on May 20, 2013 20:19:37 GMT
Hello David, Noted about the timing, Won't get much car time in the next week or so but I now have all the equipment to get it done so watch this space.
I am not aware of any internal engine modifications. The previous owner kept a list of the things he knew about and passed that on to me but he also said that the owner before him did not keep records of any changes made. I am surprised that the one obvious modification was not made, namely to go to the twin carb S spec.
Is there any way for checking for air leaks in the vacuum pipe, would this affect the rpm?
Nick
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Post by dave1800 on May 21, 2013 2:45:29 GMT
Hi Nick If you want to check the vacuum advance pipe, disconnect it from the carb end and suck - not too hard. It connects to a MAP (pressure) sensor inside the 123 distributor and there should be no leak. You could start the engine and get someone to suck on this pipe while you watch to see if the ignition advances. It may or may not at idle depending on the 3D timing program map inside the 123 but should as you raise the rpm to say 1500. As the car is running well I think this is not very likely as without the proper vacuum advance you would get some hesitation and loss of low end pick up. At idle with the carb butterfly closed there should not be any vacuum in the pipe because the outlet is the air cleaner side of the butterfly and not exposed to the manifold vacuum. If there was a leak in this pipe it would affect the rpm a little as the throttle was opened exposing the vacuum pipe orifice to the manifold depression. If you detect a vacuum in this pipe at idle (disconnect from distributor end) this indicates the carb butterfly isn't properly closed. I t should be possible on these engines to slow the idle progressively using the throttle adjusting screw until the engine stalls at say 500rpm or less. If it is not possible to reduce below 1000 rpm this would almost certainly be due excess fuel and not an air leak.
The most likely cause of excess fuelling is the butterfly not closing fully or if it has been replaced with a later version which has an overrun valve then this valve could be stuck partly open. To check, disconnect the throttle cable and manually open and close the butterfly feeling it close. You can inspect this with a torch and mirror with the air cleaner removed and the piston lifted if any uncertainty. If there is an overrun valve on the butterfly it would mean removing the carb to inspect it unless you could see anything obvious with the mirror. Of course it is always good practice to check for air leaks. I still think it's worth checking the speedo v the tacho to ensure the 123 isn't giving any odd results. It shouldn't but... Regards David Read more: landcrabs.proboards.com/index.cgi?board=talk&action=display&thread=408&page=4#ixzz2TtDPN8JtHello David, Is there any way for checking for air leaks in the vacuum pipe, would this affect the rpm? Nick
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Post by Nick RS on May 21, 2013 17:02:07 GMT
Forgot to mention that I did take a look inside the carb at the weekend using a mirror. The throttle butterfly looked like a plain disc with a band or join across the middle. It did appear to be opening and closing properly.
I also got the digital tachometer (ACE Parts, service OK) and compared it to the tacho in the car. When the tacho was 1000rpm the digital device read 950. On the road I recorded about 28 mph at 1500 revs in top and just below 60mph at 3000. Given a bit of speedometer error I think the tacho in the car is about right.
Nick
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Post by dave1800 on May 22, 2013 0:19:17 GMT
Yes it looks as though you have an accurate tacho reading so you are now trying to diagnose a real issue. Now you have the engine speed down to 1000 instead of 1500 rpm it would be worth, when you have time, taking an ignition advance reading so at to be able to discount this. Given your reading at 1500 or so rpm was correct, unlikely but I never discount anything with electronics systems! If you undo the throttle screw so far that it no longer engages and loosen or disconnect the throttle cable what is the engine speed. Can you reduce it my manually trying to close the butterfly further (gently!!). Forgot to mention that I did take a look inside the carb at the weekend using a mirror. The throttle butterfly looked like a plain disc with a band or join across the middle. It did appear to be opening and closing properly. I also got the digital tachometer (ACE Parts, service OK) and compared it to the tacho in the car. When the tacho was 1000rpm the digital device read 950. On the road I recorded about 28 mph at 1500 revs in top and just below 60mph at 3000. Given a bit of speedometer error I think the tacho in the car is about right. Nick
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Post by Nick RS on May 31, 2013 16:52:40 GMT
Great advice to get a timing light with a dial, it made the job much easier. My father in law is visiting at the moment and he kindly did the footwork inside the car while I grubbed about underneath.
Vacuum connected 1,000 20deg 1,500 22deg 2,000 28deg 2,500 36deg 3,000 40deg 3,500 50deg 4,000 52deg
Vacuum disconnected 1,000 20deg 1,500 24deg 2,000 30deg 2,500 30deg 3,000 34deg 3,500 38deg 4,000 40deg
Still idling at around 1,000
Nick
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Post by dave1800 on Jun 1, 2013 1:45:02 GMT
Hi Nick Some interesting data. Here is my analysis - I would greatly welcome input from others on the forum. Vacuum advance Your unit is showing a maximum of 12 degrees at 3,500 rpm no load and 2 degrees at 2,000 rpm. The vacuum advance unit as fitted to the Mk11 engine has a maximum advance of 16 degrees at 12" Hg and starts at 4" Hg. To establish a true comparison would require connecting the pipe to a vacuum gauge. However, my observation is that the 123 is giving too little advance (maybe up to 6 degrees) in the range 1200 - 2000rpm under light load and cruising and up to 4 degrees from 2000- 3200 rpm. Above that rpm the vacuum falls off rapidly except on over run with the throttle partly opened. Initial advanceYour setting of 20 degrees at 1000 rpm is around 5 degrees over advanced. The factory setting is 12 degrees BTDC at 600 rpm to which you must add 3 degrees for the advance between 600 to 1000rpm. This compensates reasonably well for the under advance of the vacuum as described above, but is a potential issue for high speed running. Maximum settingThis is probably the most crucial as this is when the engine is under load and most at risk of damage from being over advanced. First, you can ignore the 3500 rpm and above readings of 52 degrees as the engine wasn't under load. At these rpm under load the vacuum advance would fall off rapidly to zero. This leaves the 40 degrees at 4000 rpm reading to consider. With the normal 45D4 distributor 41234 the total advance at 4000 rpm should be 12 degrees initial setting at 600rpm plus 24 degrees distributor advance ie a total of 36 degrees. This suggests your 123 unit is 4 degrees over advanced at 400 rpm (and above). ConclusionIt would appear that the previous owner(s) set the timing over advanced to compensate for the vacuum unit giving less advance than required; this would ensure better driveability in the low to mid engine ranges. BUT if your readings are corrrect (worth double checking high rpm readings) could lead to engine damage above 3500 rpm. The question is what to do next. Here are my suggestions: Check whether you have a standard 123 distributor or a 123 Tune version. If the latter you can reprogram the vacuum to the standard distributor spec ie start 4" Hg end 16 degrees at 15" Hg. If it is a standard 123 unit set up for the MGB you can check which of the 16 curves 0-9, A-F is selected. You can then check which curve would give a max total of 36 degrees at 4000 rpm and more advance at the lower end. I think curve F looks like a good starting point. hereThen set the distributor so that you achieve 36 degrees advance at 4000 rpm and this should also reduce the idle advance and the idle speed as well. (Disconnect and plug the vacuum advance when you do this.) Before you do anything, double check your figures and ensure you can set the distributor back to its current setting, mark it and note the reading for the led light shining through the disk. You have commented earlier that there is no pinking. While this is easy to detect at lower rpm, above 3000 or so it becomes more difficult. Hope this makes some sense, sorry the post is so long. However, I am still baffled by why you cannot adjust the idle speed lower. Even with over advanced ignition it should still be possible to close the butterfly so far that the engine stalls. Are you certain nothing is stopping it from fully closing? Regards David Great advice to get a timing light with a dial, it made the job much easier. My father in law is visiting at the moment and he kindly did the footwork inside the car while I grubbed about underneath. Vacuum connected 1,000 20deg 1,500 22deg 2,000 28deg 2,500 36deg 3,000 40deg 3,500 50deg 4,000 52deg Vacuum disconnected 1,000 20deg 1,500 24deg 2,000 30deg 2,500 30deg 3,000 34deg 3,500 38deg 4,000 40deg Still idling at around 1,000 Nick
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Post by Nick RS on Jun 1, 2013 21:55:08 GMT
Really tried to adjust the distributor today but just couldn't get it to budge. I may well be missing something but I thought undoing the clamp bolt would be enough to allow it to move. Plan was to back off timing by 5deg to see what effect that had on the idle. Incidentally it is not the programmable version of the 123 so my guess is that it is the generic 4 cylinder British cars model or the MGB specific.
My attention then turned to the carb. It was running a bit rich so I backed it off a couple of flats and got the rpm down to 800. Pushing one of the throttle levers reduced it further so I am pretty much at normal revs though it doesn't return to that point later. I need to take a photo of the part I was pushing on to reduce the revs further as I don't want to go charging in and messing it up. It is difficult to pinpoint on the exploded diagrams in the manuals but with a bit of photo editing and arrows I should be able to point it out. Will post back as soon as able.
Some progress I think, the timing is a bit frustrating though. If i ever do loosen it i'll probably take the whole thing out and find out what curve is set. i don't understand why you have to remove the 123 to do this. I don't normally go above 3500 revs so am not losing sleep over engine damage. I did hear high rpm pinking when I ran on 95 octane for a few days so I know what to listen out for.
Thanks for all the advice so far - Nick
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Post by Penguin45 on Jun 2, 2013 0:12:59 GMT
I'll leave David to the techy stuff - he's much better at than me! Getting the dizzy to actually move is more my sort of level.........
You'll have realised that there is a clamp plate holding the dizzy in place. Slackening the clamp bolt should allow it to move; obviously yours doesn't. There are two bolts holding the clamp plate to the block - slacken these and back the actual clamp bolt right off. Using a big straight bladed screwdriver, see if you can prise the jaws of the plate apart. Dizzy might come free - if it doesn't, you will now be able to apply KiGas/Duck Oil/WD40 to the joint at the block.
On my old engine, the clamp had been tightened to a degree such that the clamp bolt had actually bowed and I had a helluva job getting it to release. I did replace the plate with a new one from Moss and the dizzy is now just nicely nipped into place.
Chris.
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Post by dave1800 on Jun 2, 2013 1:29:01 GMT
Hi Nick Sorry you're having trouble with moving the distributor, Chris has given some good advice. Just some quick advice before you post the photos. You should never weaken the carb mixture to reduce the idle speed. The safest mixture setting is to find the point at which the revs fall off when weakening the mixture. Then richen the mixture until the revs fall off again. The safest point is half way between the two. You will find the revs fall away faster when weakening and at a slower rate when richening the mixture so this is a little less easy to determine. If in doubt go to the point where the revs just start to fall away when weakening and then enrichen 2-3 flats. Remember to do this at normal running temperature and to rev the engine at 1500 - 2000 rpm for about 10-15 seconds between adjustments to clear any unburned fuel which would give misleading or confusing results. By weakening the mixture with a potentially over advanced ignition you are increasing the chance of damage. It sounds as though the carb problem is mechanical in a linkage. Regards David My attention then turned to the carb. It was running a bit rich so I backed it off a couple of flats and got the rpm down to 800. Pushing one of the throttle levers reduced it further so I am pretty much at normal revs though it doesn't return to that point later. I need to take a photo of the part I was pushing on to reduce the revs further as I don't want to go charging in and messing it up. It is difficult to pinpoint on the exploded diagrams in the manuals but with a bit of photo editing and arrows I should be able to point it out. Will post back as soon as able. SThanks for all the advice so far - Nick
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Post by Nick RS on Jun 2, 2013 15:41:23 GMT
Chris, I managed to ease the plate apart but still no joy. I noticed the two other bolts but I'll need some shorter spanners to get access to them. Since Coventry Machine Mart now know me by name I am going to leave that one for a bit. Will keep going with WD40 though. Re-tuned the carb according to David's advice and went on the side of caution and left it a touch rich. The lifting pin test showed a small steady increase in revs before heading for a stall and I checked with a mirror so see that the piston was lifting by the required amount. If anyone else is a complete beginner like me then I can recommend the Pitman book of the 1800 by Staton Abbey which gives a lot explanation around the routine maintenance tasks as opposed to just saying how to take something to bits and put it back together. Usually yours for an opening bid on eBay as there seem to be far more copies around than there are cars extant. It's a nice day here in Leics so I went for a drive to make sure that the performance was still good and no pinking - all OK up to 70 on an incline - good (I think). Couldn't resist a pic. Next post will hopefully show the carb. I'v e done the pic just need to try an edit an arrow on. watch this space. Nick
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Post by Nick RS on Jun 2, 2013 16:34:54 GMT
Here is the close-up of the carb The arrowed lever is the one with the black button showing. Pushing it down just above where the button is allows the revs to drop to normal and they stay there until the throttle is activated again after which the revs only drop to around 800-900 again. There seem to be a lot of interconnected levers. For reference the throttle butterfly closes properly. I tested it gently yesterday and it was fully home. The fast idle screw is also now clear of the cam. Nick
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Post by dave1800 on Jun 3, 2013 2:37:47 GMT
Hi Nick Difficult to tell but it looks to me as though the throttle cable is too tight. It should have a little slack. Also oil all the linkages. The car looks great! regards David Here is the close-up of the carb The arrowed lever is the one with the black button showing. Pushing it down just above where the button is allows the revs to drop to normal and they stay there until the throttle is activated again after which the revs only drop to around 800-900 again. There seem to be a lot of interconnected levers. For reference the throttle butterfly closes properly. I tested it gently yesterday and it was fully home. The fast idle screw is also now clear of the cam. Nick
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Post by Nick RS on Jun 9, 2013 18:09:45 GMT
Idling now correct, thanks for all the advice. The throttle cable was too tight and things are a lot better now. Last tank of fuel has given me 28.4MPG which included a lot of time revving and idling while I checked the timing and the carburettor. There is one thing has been cropping up a bit more frequently and that is a tendency for the car to refuse to engage 2nd gear. It will either jump out straight away or will protest with the sound of teeth and not go in at all. It doesn't happen all the time which is making me hope that it isn't something that's suddenly broken, more an adjustment. I've started at the cables and had a go at adjusting them. On a very short test run things seem OK but as I say it doesn't happen all the time. In case it's not the cables is there anything else I should look at should this start again? All the others gears work fine all the time. Nick
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Post by dave1800 on Jun 10, 2013 0:14:20 GMT
Hi Nick If it is intermittent, and you are happy with the gear change cable adjustment, it may be worth looking at the clutch hydraulics to ensure there isn't a slight air leak. I've found that this type of problem seems to afflict 2nd gear more. Next time it occurs (if it does!) try pumping the clutch pedal up and down several times; if this improves the change then the clutch needs bleeding and any leak resolved. Good to hear the idle is sorted out. Regards David Idling now correct, thanks for all the advice. The throttle cable was too tight and things are a lot better now. Last tank of fuel has given me 28.4MPG which included a lot of time revving and idling while I checked the timing and the carburettor. There is one thing has been cropping up a bit more frequently and that is a tendency for the car to refuse to engage 2nd gear. It will either jump out straight away or will protest with the sound of teeth and not go in at all. It doesn't happen all the time which is making me hope that it isn't something that's suddenly broken, more an adjustment. I've started at the cables and had a go at adjusting them. On a very short test run things seem OK but as I say it doesn't happen all the time. In case it's not the cables is there anything else I should look at should this start again? All the others gears work fine all the time. Nick
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Post by Nick RS on Jun 10, 2013 20:22:48 GMT
Thanks David, I wouldn't have thought of that. If it happens I'll update with a post Nick
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