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Post by tommydp on Oct 3, 2012 20:27:14 GMT
Had a look at the carb setting again this afternoon, as I'm pretty sure everything is ok, ie ignition, vacuum leaks etc.
What it boils down to is: the base setting of the carb is most crucial. You can make it run at various setting but it won't necessarily be good throughout the range. At least I think so, and I believe lots of my trouble earlier and now have been due to a mis match between the jet adjustment and throttle adjustment.
Well, I've set the base setting before but I believe I've always ended up with too little a throttle opening and too weak setting of the jet ie jet adjusting nut too far up. I suppose this can explain why it would stumble at idle after a while, because of too little air entering. At this stage I guess it makes sense it will be very hard to tune correctly, as the throttle opening will be too small.
To make a long story short I now turned the jet adjusting nut 12 flats down and turned the throttle adjusting screw 1.5 rotation open from fully closed. This is the base setting.
I let it warm up fully and turned the throttle screw down to a decent idle speed. The lifting pin now made sense, revs going up and staying there. I repeated this numerous times and it gave the same result. I then turned the jet adjusting nut one flat at the time up, by 3-4 flats. Mixture fine judging by the lifting pin. I'll try it on the road and check. Perhaps the lifting pin works after all?
It idled sweetly throughout this session, and there was no smoke or unpleasant smell from the exhaust.
Quite optimistic now! Although I won't say I've had serious problems, so I believe I've been close to a good tune. I'm pretty sure the mis match of jet and throttle setting have been a major cause for my previous headaches though.
Tommy
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Post by indianajones on Oct 3, 2012 23:26:34 GMT
Let us know how you get on Tommy. I'll try and see if I can take a look for air leaks in my crab this weekend, but fear I might not get a chance until late November  -Andrew |
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Post by dave1800 on Oct 4, 2012 2:16:16 GMT
Tommy I'm still trying to get my head around what you are saying. If the throttle opening was too small - you were able to compensate with the mixture adjustment and still get the correct idle speed - interesting. Anyone else observed this phenomenon, you could be on to something here - an odd reaction of the SU outside the designed running criteria. Andrew Are we not going to hear from you for a while? regards David You can make it run at various setting but it won't necessarily be good throughout the range. At least I think so, and I believe lots of my trouble earlier and now have been due to a mis match between the jet adjustment and throttle adjustment. Tommy |
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Post by indianajones on Oct 4, 2012 5:46:16 GMT
Na mate, I'll still be around, but this design tender for 16km of new state highway is keeping me very busy at work and tech is keeping me busy in the evenings and weekends.
Tech will end mid November, then I have my holiday till early December and then the tender will close out.
So getting busy with the crab is gonna be hard I think.
-Andrew
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Post by tommydp on Oct 5, 2012 15:55:13 GMT
Had a look at it from scratch now.
Started with the valve clearances, and was rather amazed to find the inlet valve on cylinder two quite tight. The others were a bit on the loose side. So why has the gap become smaller on one valve? Strange, as I always adjust them very accurately.
After setting the clearances I adjusted the timing by strobe. With advance pipe disconnected I set it at 12 degrees BTDC at 600 rpm, the factory setting. I'll take it from there and retard it a bit if it pinks. It wil run quite evenly as low as 500 rpm, so I suppose it can't be far out of tune..
Idling at 600 rpm I checked the lifting pin, and it was spot on for correct mixture. A slight increase in revs, then falling. I set the idle speed to around 750, as the revs will fall when clutching and turning the headlight etc.
At 750ish rpm the lifting pin wil make revs fall. Natural, I suppose, as it's getting more air?
We'll take it from here and see. Yes, I'm very picky when it comes to engines...
Regards, Tommy:-)
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Post by dave1800 on Oct 6, 2012 2:20:40 GMT
Tommy
If the lifting pin is OK at 600rpm but indicates too weak a mixture at 750rpm then I would adjust the carb at 700-750 rpm (idle for Mk11 = 700rpm). You certainly don't want to risk running too weak.
I am still trying to understand your earlier post about there being more than one setting for the carb. I can understand with twin carbs you could achieve this where one carb compensates for the other, but for a single carb maybe what you have now found answers the question (brain hurts!)
Strange that No2 inlet valve gap has closed but the others are loose. After checking the obvious like the head torque, just keep an eye on it. Usually it is the exhaust valve that suffers this way through overheating, knock etc.
regards
David
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Post by indianajones on Oct 6, 2012 5:00:44 GMT
What's a sure way of telling the car is weak?
-Andrew
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Post by dave1800 on Oct 6, 2012 5:42:40 GMT
In the context of the lifting pin check - if the engine revs fall or fail to rise then it's too weak. You can also hear a splashy exhaust - but you need to experience normal and rich to appreciate the difference. Symptoms of running too weak a mixture can range from running a little hot, being down on power and at the extreme burning out exhaust valves and engine destruction! Of course nothing is simple in life and these symptoms can be due to a range of causes, eg retarded ignition. If you read Chris' thread you will see he got hi engine to run at the correct temperature by richening the mixture a little. It can be quite critical. Glad you've got time to read the forum! Regards David What's a sure way of telling the car is weak? -Andrew |
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Post by indianajones on Oct 6, 2012 7:42:01 GMT
Hmmm sounds a bit worrying lol
Well I took her for spin today, plugs looked pretty normal to me, still not keen on hills it seems. but that might just be me expecting too much perhaps (A lot of hills in Auckland as it is built on around 40 volcanoes!).
She's never ran hot in the time I've owned her, the dial on the dash only ever seems to get into the lower end of the 'N' area.
-Andrew
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Post by dave1800 on Oct 6, 2012 11:15:48 GMT
Yes, I recall those hills but they shouldn't be too much of a problem for the low down torque of the 1800. As far as the temperature gauge is concerned you should look for any CHANGE from where it normally settles once warmed up. The normal position can be just below the N, just above or in the centre. It depends on the bi-metallic voltage regulator on the instrument cluster, the sensor and the wiring. The only way really is to calibrate the gauge/sensor. I wouldn't worry too much if the plugs look OK especially with your low compression on 1 cylinder that will impact on the power especially if it's head related. Regards David Hmmm sounds a bit worrying lol Well I took her for spin today, plugs looked pretty normal to me, still not keen on hills it seems. but that might just be me expecting too much perhaps (A lot of hills in Auckland as it is built on around 40 volcanoes!). She's never ran hot in the time I've owned her, the dial on the dash only ever seems to get into the lower end of the 'N' area. -Andrew |
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Post by tommydp on Oct 6, 2012 15:04:54 GMT
Yes! It seems the lifting pin test is still valid, even when running unleaded. Case closed! Perhaps I've been running a bit too lean then. Anyway, after checking the valves and setting the ignition as descrived earlier I followed Dave's advice and enrichened the mixture so the lifting pin test would work at 700 rpm. Seems spot on now, perhaps a tiny bit too rich now, as the revs stay up a bit when doing the test. Anyway, better than too lean. I'll take it for a longer drive and check it then. I'll upload a video to show it idling as I do the test at around 700 rpm. Temperature gauge is always in the lower part of the scale by the way so seems fine. You'll also notice from the video the crankcase breather system works, as the revs rise when opening the oil filler cap. As you may spot the tachometer is a bit unsteady as it idles. I notice the dwell is not totally stable, I guess my new distributor solves that. It's almost rebuilt by no according to Distributor doctor. Anyway, I supoose I'll have to be satisfied now! As you notice it starts instantly, without touching the accelerator. Sounds quite healthy too, only on a video these engines really sound like a diesel/ old tractor! Here's the video! Click on the picture and enjoy.-)  Regards, Tommy |
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Post by dave1800 on Oct 7, 2012 1:36:07 GMT
I don't know why these engines sound so tappety on all the videos I have heard so far, the microphones must emphasise the particular frequencies, other than that it sounds as sweet as a B series engine gets! I agree you may now be a little rich at idle, maybe worth rechecking after a longish run when the engine is thoroughly warmed through. With winter not far off maybe it won't be rich for long! I assume I was looking at the RPM scale on the meter as the needle appeared to rise and fall with what sounded like small changes in engine speed. If the dwell is fluctuating then I agree wait until you get your rebuilt distributor before investigating this further. Regards David Yes! It seems the lifting pin test is still valid, even when running unleaded. Case closed! Perhaps I've been running a bit too lean then. Anyway, after checking the valves and setting the ignition as descrived earlier I followed Dave's advice and enrichened the mixture so the lifting pin test would work at 700 rpm. Seems spot on now, perhaps a tiny bit too rich now, as the revs stay up a bit when doing the test. Anyway, better than too lean. I'll take it for a longer drive and check it then. I'll upload a video to show it idling as I do the test at around 700 rpm. Temperature gauge is always in the lower part of the scale by the way so seems fine. You'll also notice from the video the crankcase breather system works, as the revs rise when opening the oil filler cap. As you may spot the tachometer is a bit unsteady as it idles. I notice the dwell is not totally stable, I guess my new distributor solves that. It's almost rebuilt by no according to Distributor doctor. Anyway, I supoose I'll have to be satisfied now! As you notice it starts instantly, without touching the accelerator. Sounds quite healthy too, only on a video these engines really sound like a diesel/ old tractor! Here's the video! Click on the picture and enjoy.-) Regards, Tommy |
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Post by tommydp on Oct 7, 2012 4:30:40 GMT
The changes in engine speed were when I used the lifting pin, did this while filming the rev counter, as well as the carburettor. Sorry, I should have said something when I did it..
I think this will do for now! That is, until I get the rebuilt distributor back:-)
Regards, Tommy
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