Post by tommydp on Apr 7, 2016 6:49:32 GMT
As mentioned before I have, of all things, an ancient CO meter. It's old, but it seems to work well and accurately. It's a Riken, top of the range in its days and cost a fortune back then. So it's a workshop machine and originally not one for mr home mechanic.
Anyway, I've been using it to investigate and (try to) learn and understand more. The main thing is that I want to make damn sure that the new rebuilt engine for the blue car does not get to much petrol. The only reasonable explanation why the last one wore out so quickly, is that it was "washed out" with petrol.
So, just for testing, I installed the carburettor I intend to use on blue into the white car. My first discovery is that two tight valves, one inlet and one oulet (no idea how that happened) made the co level very high and made it impossible to have the engine running evenly at idle with a decent co %. Once valves were fine, it made more sense. I also noticed that changes in the float level make drastic changes to the co. As far as I could tell, viton tipped float needles made a difference here. Even though the original type needle and seat are almost new.
As you adjust the mixture with the meter you should rev the engine to above 2000 rpm for a while if the setting can't be done within 3 minutes. Well, I've had to do that a few times... At the staring point for mixture, 12 flats down, the mixture is far too rich. On all carbs I've tried. CO will be around 8 %. The carb for the blue car is all new btw. Then weakening, one flat at the time until the revs just go down on the weak side, the engine wil start spitting and the CO goes below 2%. Too weak in other words. Then it's a matter of richening, the smallest amount, until the idle speed catches up again. At this point, which should be the correct spot, the CO will be somewhere between 3 and 4,5% which is correct (stated for the Princess 1800, never seen it mentioned for the crab) I ended up with around 3.5% on the "new carb" and just below 4% on the one I use on the white car. The car is then idling at around 700 rpm.
As far as I can tell, there is no obvious difference between fixed and biased needles. I now only used fixed needles, as the idea of the needle rubbing against the jet makes no sense to me. A properly centred fixed needle must be best. Small variations on the carb can make quite big differences on the mixture, according to the CO. Any wear on jet and needle will contribute to this. I found the new carb less sensitive, than the one I use on the white, which possibly has a mis match of jet and needle too..
Looking back, I might have been too obsessed with the lifting pin test, and had the mixture too rich. At the correct setting using the CO meter, the lifting pin test does not work as the book says. The revs will drop a bit. I believe this is down to modern petrol, but stand to be corrected. I think I'd rather aim for a setting at the point where the engine starts to run evenly when enriching from the too weak point (engine spitting) and using the CO meter. Then again, the micture must not be too weak (I know Dave) as it will ruin the engine.
Now, question time:
What's supposed to happen with the CO at higher revs/ driving? I assume it should go down a bit? At least the new carb does that when holding the rpms up steadily, and then returns to the original setting. The white car's carb seems to have a more steady CO, even going up a bit at steady, high rpm. I believe this is due to a possible mis match and worn needle and jet. I'll get replacements and see if it changes. On both carbs the Co will go up a bit instantly as you rev it, which is normal I guess as the carb damper/ oil works as an accelerator pump.
Another question: Thepoint where the choke arm is fixed to the jet, by the screw. Is this point supposed to pivot? I would think so, but at least one, new, choke arm does not allow this. I could only imagine that this could lead to wear on the outside of the jet, inside of the jet bearing. Remember they went from the choke arm with the screw, to the angled iron which is just pushed into the hole in the jet and does in deed pivot.
Anyway, I feel assured that at least the carb intended for the blue car is Ok and will not allow more petrol than it should. Remember, I tried both carbs on the same car. I'll also order a new bearing, jet and needle for the white car to see if it makes any difference.
OK, a lot said... Perhaps out of interest, but at least a good way for me to sum up what I've done.
Tommy
Anyway, I've been using it to investigate and (try to) learn and understand more. The main thing is that I want to make damn sure that the new rebuilt engine for the blue car does not get to much petrol. The only reasonable explanation why the last one wore out so quickly, is that it was "washed out" with petrol.
So, just for testing, I installed the carburettor I intend to use on blue into the white car. My first discovery is that two tight valves, one inlet and one oulet (no idea how that happened) made the co level very high and made it impossible to have the engine running evenly at idle with a decent co %. Once valves were fine, it made more sense. I also noticed that changes in the float level make drastic changes to the co. As far as I could tell, viton tipped float needles made a difference here. Even though the original type needle and seat are almost new.
As you adjust the mixture with the meter you should rev the engine to above 2000 rpm for a while if the setting can't be done within 3 minutes. Well, I've had to do that a few times... At the staring point for mixture, 12 flats down, the mixture is far too rich. On all carbs I've tried. CO will be around 8 %. The carb for the blue car is all new btw. Then weakening, one flat at the time until the revs just go down on the weak side, the engine wil start spitting and the CO goes below 2%. Too weak in other words. Then it's a matter of richening, the smallest amount, until the idle speed catches up again. At this point, which should be the correct spot, the CO will be somewhere between 3 and 4,5% which is correct (stated for the Princess 1800, never seen it mentioned for the crab) I ended up with around 3.5% on the "new carb" and just below 4% on the one I use on the white car. The car is then idling at around 700 rpm.
As far as I can tell, there is no obvious difference between fixed and biased needles. I now only used fixed needles, as the idea of the needle rubbing against the jet makes no sense to me. A properly centred fixed needle must be best. Small variations on the carb can make quite big differences on the mixture, according to the CO. Any wear on jet and needle will contribute to this. I found the new carb less sensitive, than the one I use on the white, which possibly has a mis match of jet and needle too..
Looking back, I might have been too obsessed with the lifting pin test, and had the mixture too rich. At the correct setting using the CO meter, the lifting pin test does not work as the book says. The revs will drop a bit. I believe this is down to modern petrol, but stand to be corrected. I think I'd rather aim for a setting at the point where the engine starts to run evenly when enriching from the too weak point (engine spitting) and using the CO meter. Then again, the micture must not be too weak (I know Dave) as it will ruin the engine.
Now, question time:
What's supposed to happen with the CO at higher revs/ driving? I assume it should go down a bit? At least the new carb does that when holding the rpms up steadily, and then returns to the original setting. The white car's carb seems to have a more steady CO, even going up a bit at steady, high rpm. I believe this is due to a possible mis match and worn needle and jet. I'll get replacements and see if it changes. On both carbs the Co will go up a bit instantly as you rev it, which is normal I guess as the carb damper/ oil works as an accelerator pump.
Another question: Thepoint where the choke arm is fixed to the jet, by the screw. Is this point supposed to pivot? I would think so, but at least one, new, choke arm does not allow this. I could only imagine that this could lead to wear on the outside of the jet, inside of the jet bearing. Remember they went from the choke arm with the screw, to the angled iron which is just pushed into the hole in the jet and does in deed pivot.
Anyway, I feel assured that at least the carb intended for the blue car is Ok and will not allow more petrol than it should. Remember, I tried both carbs on the same car. I'll also order a new bearing, jet and needle for the white car to see if it makes any difference.
OK, a lot said... Perhaps out of interest, but at least a good way for me to sum up what I've done.
Tommy
