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Post by tommydp on May 3, 2014 21:36:20 GMT
Thanks, Chris! I know it's the original setting, but I've used it without any obvious problems. I run 98 unleaded. Perhaps I'd try 10 degrees BTDC instead.
I just can't help thinking this is down to fuel, "feels" like fuel starvation to me. If it was some degrees advanced it wouldnt' feel as hesitating and jerky as it does, imo. Occasionally it will improve when I pull the choke, but not all the time. Perhaps it's just down to the revs going up rather than mixture enrichment.
BTW the carb is correctly adjusted. 12 flats down, then up for the best idle. New carb this means 10 flats down, which I'd say is correct.
Waiting for Dave to wake up:-) Apologies for another head ache, Dave!
T
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Post by Penguin45 on May 3, 2014 23:47:41 GMT
Basic carb setting on the HS is jet level with "bridge", then 2 full turns - 12 flats. It shouldn't need to move much from the base setting.
Chris.
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Post by dave1800 on May 4, 2014 1:33:40 GMT
Think I'll go back to sleep again! You seem to have covered almost everything by substitution apart from the fuel pump and the quality of the fuel itself - any chance the fuel has deteriorated? I definitely think there is a clue that the pump wouldn't prime itself and the problems occur mainly under heavy load. Did you establish why it wouldn't prime itself, lack of sufficient suction or a partial maybe intermittent blockage (rust?) somewhere in the tank / feed? Have you tested the fuel pump pressure on the suction side as well as the output? I would think it highly unlikely that there is a vacuum occurring in the tank given the filler cap seal. If you drive up a long steep hill in third gear (or second)at high rpm it should show up as the level in the float chamber gradually falls faster than the pump fills it if the output is low. If you have a spare fuel pump I would try this and check the throw on the pushrod is within spec. Remember gasohol can damage the diaphragms either making them softer or causing them to rip. The fact that it also hesitates at steady speed is curious. It is not impossible there are more than one fault and steady speed hesitation is frequently down to ignition timing or too weak a mixture. You can check this out quickly by removing and blocking the vacuum advance pipe - retarding the ignition under light load /steady speed. You have already checked the mixture by pulling the choke out, but could turn the adjusting nut temporarily by 3 flats (richen). If you are using contact breakers check the distributor body is making a good earth connection (a long shot) and the ignition coil current with the engine off, ignition on and cb closed is correct. Finally, have you tried Chis' trick of using some old real Champion N9Y plugs? Frustrating, maybe exorcise that little Norwegian elf from your barn  regards David Thanks, Chris! I know it's the original setting, but I've used it without any obvious problems. I run 98 unleaded. Perhaps I'd try 10 degrees BTDC instead. I just can't help thinking this is down to fuel, "feels" like fuel starvation to me. If it was some degrees advanced it wouldnt' feel as hesitating and jerky as it does, imo. Occasionally it will improve when I pull the choke, but not all the time. Perhaps it's just down to the revs going up rather than mixture enrichment. BTW the carb is correctly adjusted. 12 flats down, then up for the best idle. New carb this means 10 flats down, which I'd say is correct. Waiting for Dave to wake up:-) Apologies for another head ache, Dave! T |
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Post by tommydp on May 4, 2014 8:19:45 GMT
Thanks Dave and Chris!
I drive it quite a lot, filling up every 8 days or so lately, so think the fuel can be ruled out.
I didn't measure the suction of the pump. I've got a NOS pump so think that will be the first thing to try. I use Champion plugs now.
It definitely struggles going up hill, so the pump could have trouble delivering the fuel. It also looked to me as the fuel level in the float bowl was lower than it should be (on both carbs I tried, so not float related). I blew up all the fuel pipes so don't think there should be any blockage. There was some rust etc in the pump filter, but not that much.
Regards, Tommy
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Post by dave1800 on May 4, 2014 10:06:17 GMT
It does sound as though the fuel pump may have a problem. I guess that if the diaphragm is damaged it could possibly let fuel into the sump - definitely not good . I can't remember are you running a filter before the pump - advisable with gasohol loosening deposits from the tank. regards David Thanks Dave and Chris! I drive it quite a lot, filling up every 8 days or so lately, so think the fuel can be ruled out. I didn't measure the suction of the pump. I've got a NOS pump so think that will be the first thing to try. I use Champion plugs now. It definitely struggles going up hill, so the pump could have trouble delivering the fuel. It also looked to me as the fuel level in the float bowl was lower than it should be (on both carbs I tried, so not float related). I blew up all the fuel pipes so don't think there should be any blockage. There was some rust etc in the pump filter, but not that much. Regards, Tommy |
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Post by tommydp on May 4, 2014 21:25:53 GMT
Ok, fuel pump changed and...
no big improvement... Oh dear.. Tried enriching by 3 flats, not better. Detached vacuum line and blocked it. This made the stumble/ hesitation even worse.
It stumbles, and has loss of power both uphill and at steady speed. The new pump made it slightly better perhaps, but there's still something very wrong. It's like driving without oil in the dashpot, or having a vacuum leak.
Next thing will be checking the PCV valve. Perhaps it plays up when the engine is under load, working as a vacuum leak. There's some oil in it. I'll block it off and guide the oil vapour hose to the carb, as the NOS carb I'm using now has a connection for the oil fume hose as on later cars.
Well, this really got me sad and down. Will have to take the Rover to work tomorrow..
Regards, Tommy:-)
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Post by dave1800 on May 5, 2014 1:01:02 GMT
Hi Tommy Sorry to hear your car's problems are not sorted. I guess you have double checked the valve clearances and there isn't a tight tappet clearance? I also assume that as you are using a carb with a constant vacuum connection for the breather that this is blocked off as you are using the PCV valve? If not it will be drawing in air. Strange it got worse disconnecting the distributor vacuum pipe this suggests the timing may be too retarded. Are you 100% certain your timing mark on the harmonic balancer really is at TDC and it hasn't shifted? You could try advancing the ignition very temporarily by 10 degrees, but don't drive for long. Good luck regards David Ok, fuel pump changed and... no big improvement... Oh dear.. Tried enriching by 3 flats, not better. Detached vacuum line and blocked it. This made the stumble/ hesitation even worse. It stumbles, and has loss of power both uphill and at steady speed. The new pump made it slightly better perhaps, but there's still something very wrong. It's like driving without oil in the dashpot, or having a vacuum leak. Next thing will be checking the PCV valve. Perhaps it plays up when the engine is under load, working as a vacuum leak. There's some oil in it. I'll block it off and guide the oil vapour hose to the carb, as the NOS carb I'm using now has a connection for the oil fume hose as on later cars. Well, this really got me sad and down. Will have to take the Rover to work tomorrow.. Regards, Tommy:-) |
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Post by tommydp on May 6, 2014 21:10:28 GMT
Hi again! Yes, the vacuum connection was blocked, Dave. I have now removed the PCV valve, blocked the manifold connection and connected the oil fume hose to the carb connection.
I made some progress yesterday, when I found the vacuum advance vernier was almost fully retarded. Judging by the pattern on the rotor and the cap terminals the spark has occured late, or the vacuum advance is not working as it should, strange as the distributor is overhauled by distributordoctor. I now set the vernier exactly in the middle of fully retarded and fully advanced. I then turned the distributor body for correct static setting.
I have checked that TDC mark is correct. It's now better at steady speed, but still stumbles up steep hills, especially when accelerating hard. Pulling the choke does not help.
I'll check the vacuum advance with the strobe later. When idling at fast idle revs don't fall much when I detach the advance pipe. I find that a bit strange.
So, an overhauled distributor, a brand new carb straight from the SU box, a brand new SU fuel pump, excellent compression...
I'm lost on this one.. I'll check the valves later too. Some of them have tightened up on their own earlier. No idea why that happens.
Updates to come.
Tommy
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Post by dave1800 on May 7, 2014 7:37:33 GMT
Hi Tommy Always worth asking the obvious question about the car vacuum take of even though I knew you would have done that . The reason I suggested disconnecting the vacuum pipe from the distributor was to determine whether it may be sticking. As you know there is no vacuum advance climbing hills under load so if there is evidence of the spark occurring late it is a phasing issue within the distributor /drive. When you say late is it possibly trying to spark back to the terminal after the rotor arm has just passed it? Turn the distributor to set the ignition timing to max, ie around 40 degrees and see how the rotor arm and post align and compare with the static setting. The other clue would appear to be the valves closing up. This can be caused by valve seat recession which normally only affects the exhaust valves and could cause loss of compression / power when hot under load. So even if your compression is good with a cold engine it may not be when under power. To prove this leave the valves slightly loose and test the car. regards David Hi again! Yes, the vacuum connection was blocked, Dave. I have now removed the PCV valve, blocked the manifold connection and connected the oil fume hose to the carb connection. I made some progress yesterday, when I found the vacuum advance vernier was almost fully retarded. Judging by the pattern on the rotor and the cap terminals the spark has occured late, or the vacuum advance is not working as it should, strange as the distributor is overhauled by distributordoctor. I now set the vernier exactly in the middle of fully retarded and fully advanced. I then turned the distributor body for correct static setting. I have checked that TDC mark is correct. It's now better at steady speed, but still stumbles up steep hills, especially when accelerating hard. Pulling the choke does not help. I'll check the vacuum advance with the strobe later. When idling at fast idle revs don't fall much when I detach the advance pipe. I find that a bit strange. So, an overhauled distributor, a brand new carb straight from the SU box, a brand new SU fuel pump, excellent compression... I'm lost on this one.. I'll check the valves later too. Some of them have tightened up on their own earlier. No idea why that happens. Updates to come. Tommy |
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Post by tommydp on May 7, 2014 22:48:07 GMT
Had a look at the valves after it cooled down. I was not able to get the 0.015 gauge in without force on valves 1 and 8, which are exhaust valves. So, they have tightened up again!
I'll adjust them once again. I can't se that I'm setting them to tightly, I tighten the screw only until there's the slightest drag on the feeler gauge. I'll re torque the cylinder head nuts first, in case something has changed after the cylinder head removal.
I didn't notice anything strange with the valves when I had the head off, and there was no obvious sign of recession, as far as I could see.
If no progress with this, I'll cut a hole in a distributor cap, and try to watch the spark.
I'm afraid I didn't quite understand, Dave, sorry. Do you mean setting the engine to around 40 degrees BTDC on cylinder one, and then turn the distributor to the points open and then I'll see how the rotor relates to the terminals at max advance?
Regards, Tommy
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Post by dave1800 on May 8, 2014 0:58:04 GMT
The valve clearance issue is very odd. Tightening the head would probably close the gap. Did you do anything to the valve seats and guides when the head was off other than lapping them in? You do seem to have an ongoing issue with the valve clearance(s) closing up which does suggest to me a problem with the exhaust valve seats. Is the head modified for unleaded fuel? In an earlier thread you noted that there was a noisy tappet - is this still present - quite common on these engines. Did you check the valves for straightness and possible sticking. Anything show on the vacuum gauge when the engine is hot? Sorry I didn't make it clear about the rotor arm and the distributor cap terminal posts. If you have an old cap into which you can cut a window it would help but not essential. I meant take off the distributor cap and note where the rotor arm points in relation to the terminal post at both 10/12 degrees BTDC idle and at max mechanical advance plus static - say 40 to 45 degrees BTDC to see if the rotor arm is still opposite the terminal post. If not it is out of phase then the spark will have to jump further and could misfire. I have experienced this with a non Lucas copy contact breaker and MG forums have reported this problem with some of the after market electronic trigger ignition systems. I think this is less likely to be the problem than the valves but it is a quick and easy check to be able to discount it. Regards David Had a look at the valves after it cooled down. I was not able to get the 0.015 gauge in without force on valves 1 and 8, which are exhaust valves. So, they have tightened up again! I'll adjust them once again. I can't se that I'm setting them to tightly, I tighten the screw only until there's the slightest drag on the feeler gauge. I'll re torque the cylinder head nuts first, in case something has changed after the cylinder head removal. I didn't notice anything strange with the valves when I had the head off, and there was no obvious sign of recession, as far as I could see. If no progress with this, I'll cut a hole in a distributor cap, and try to watch the spark. I'm afraid I didn't quite understand, Dave, sorry. Do you mean setting the engine to around 40 degrees BTDC on cylinder one, and then turn the distributor to the points open and then I'll see how the rotor relates to the terminals at max advance? Regards, Tommy |
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Post by foglaursen on May 9, 2014 8:30:31 GMT
Could it be that the vacuum advance diaphragm has split? This could account for both air leak and wrong timing. Just a thought. Peter  |
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Post by tommydp on May 13, 2014 22:58:53 GMT
Well, I've done some research again and I believe there are more than one single thing playing up. Not easy to diagnose, but I try to substitute one thing at the time.
Biggest improvement came from going back to the old distributor, rather than the one overhauled by DD. Strange in deed, but I'm starting to believe there's something not right with the rebuilt one. There were identical problems when using it on the blue car, too. Not sure what to to about it. No use of a rebuilt one that's not working as it should.
Other things I've found:
The car, or perhaps rather the NOS carb, does not like the original SU dashpot oil. It seems too thin. Far better response and less jerky with 20w50.
Quite a lot of rust/ debris has collected in quite a short time in the float chamber bottom. It's very fine, sand like stuff. If I stirr the petrol in the chamber, it will get all rust coloured. You'd think it would end some time, I've driven it every day for over a year..
Anyway, Ive installed a filter right after the tank and even after a short trip a visible collection of the debris was trapped in the filter..
Will get back later..
Tommy
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Post by Penguin45 on May 13, 2014 23:15:47 GMT
I think you've got there with the filter, Tommy. Without a filter some of the very fine particles will try and get through the jet(s). If you have bought one of those little clear plastic filters, get a couple of tanks of fuel through, then throw it away and by another one.
Chris.
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Post by threelitre on May 14, 2014 7:58:18 GMT
Oh, I remember I once fitted a new out of the box carb that had an occasionally sticking piston! What fun I had on the road until I found the culprit!
But with these filters I have had my fair share of experience: On my blue Maxi the last owner fitted such a filter between pump and carb (so the mechanical pump would push through it). I had plenty of problems, always due to the filter clogging up. Basically the car would run fine up to 80kph and light load in 5th, but all the way up to 110kph in 3rd. The lower revs in 5ht must have resulted in a lower fuel pressure, not able to feed enough fuel through the clogged filter. As the tank was rusty inside (at the very bottom) and it did not improve I needed to change these filters quite often. Possibly every 1000-2000kms. I am sure the fine debris would not have done the SU any harm. Since changing the tank it obviously improved - the old one was rusted through at the lowest point eventually.
Regards,
Alexander
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