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Engine -missing under load
https://www.ausmini.com/forums/viewtopic.php?f=2&t=97495		 Page 1 of 2
Author:  JEA [ Sat Jul 14, 2018 10:50 pm ]
Post subject:  Engine -missing under load
I’m hoping someone can help myth bust an issue I’m having with my Mini.
The car starts and idles really nicely, but under load it runs extremely roughly (back firing and sounds like it’s running on 2 cylinders). It feels like you’re driving around with the choke on full.
This is not the first time that it has done this. To remedy it in the past I’ve;
* changed the plugs
* changed the ignition coil
* changed the ignition leads
* changed the fuel
* changed the fuel filter.
Taking it out this morning, it ran like sh1t but it would come good for a split second and then pull the same caper again. I managed to only just limp around the block.

Needless to say, the problem only crops up when you need to take the car somewhere and it finds a way to embarrass you.

The engine is;
* 1100 with twin 1.25 SU’s. The carbies have been refurbished.
* The distributor was recently rebuilt, recurved and converted to an electronic ignition module.
* the car was recently tuned.
* I’ve pulled the air filters off and taken it out for a spin, hoping that it was starving for air. It made no difference.

What else am I missing? Surely it has to be something simple.

Thanks in advance,
James.
Author:  gtogreen1969 [ Sat Jul 14, 2018 11:17 pm ]
Post subject:  Re: Engine -missing under load
Did it do this before you went to electronic ignition. Do you have the old points and condenser to put back in just to discount the electronics?
Author:  timmy201 [ Sun Jul 15, 2018 8:01 am ]
Post subject:  Re: Engine -missing under load
A couple of thoughts:
Are the carb fuel bowls filling to the appropriate level, is the fuel pump working ok
Loose or damaged low tension wire on the coil
Incorrect coil ohms
Low voltage at the battery
Vacuum leak near the carb or manifold
Check cylinder compression values
Tappet adjustment

Do you have a tachometer? How does the needle react?
Are you sure the timing and mixture are spot on?
Author:  SlipperyGypsy [ Sun Jul 15, 2018 12:55 pm ]
Post subject:  Re: Engine -missing under load
Sounds like you have the same problem as i had. I changed my fuel pump and got the car re-tuned by a pro. Also my car atm only gets going when its warm, when its cold i it doesn't run smooth.
Author:  JEA [ Sun Jul 15, 2018 5:54 pm ]
Post subject:  Re: Engine -missing under load
Hi, sorry for the delay in getting back to you all.
Since moving to the electronic ignition, I don’t have a set of points and condenser on hand.

Fuel pump; as far as I know it’s working fine. I can hear it ticking away, but that doesn’t always mean that it’s delivering fuel. I’ll check that over the next few days.
Compression; this is good at 145 psi on all 4 cylinders.
Battery; I know that this is low as she does labour a bit first thing in the morning.
Coil; this should be okay as it’s a brand new one.
Vaccuum leak near manifold; I could understand this if was all the time, but this issue seems to be intermittent.
Tappet adjustment; okay 12 thou.

I’ll charge the battery, check the fuel pump and also look at the fuel levels in the carb bowls.

Thanks,
James
Author:  Willkog89 [ Mon Jul 16, 2018 7:55 am ]
Post subject:  Re: Engine -missing under load
Sometimes pays to go back to basics, and check your cap and rotor for hairline cracks and rotor, make sure everything is sitting where it should be. I had a failing electronic ignition module that caused my car to behave very similarly, I had a lot of people tell me that electronic components generally fail outright and don't slowly/intermittently work, well that electronic ignition module changed all that for me - that thing died a slow and painful death! The fact that it comes good suddenly, is very suspect of something electronic. If it were me, I would ask someone nicely for a spare and swap out the distributor for another and try that to rule it out next, as you've done most of the rest of the ignition.

Other easy and cheap few checks you could try is get the mini to act up again - check your float for acceptable fuel level. Check your carb needle is rising and falling freely. Check the oil in the dashpot (that would generally rule out the carb, unless you fiddle with it). Go over your LT and HT wiring. I like to wipe a little smear of vaseline on the electrical spade ends to discourage any corrosion on them while I'm there.

My mini is now starting to misfire very briefly when it's got hot an turned off for a while, after I restart it. I'm very suss on the ignition module again.
Author:  PAT [ Mon Jul 16, 2018 1:29 pm ]
Post subject:  Re: Engine -missing under load
Had the same problem with our 1100 with single 1 1/4 carby Replaced all items as you mentioned and it started doing the same. Spoke with my mini mechanic and he said some of his customers were having a lot of problems with using 98 fuel and spark plugs. At the time we were running 98 fuel so I changed the plugs again and swapped to 91 fuel and it I have not had an issue since. Wasted money on replacing all the other parts.
Author:  AWOODY [ Mon Jul 16, 2018 3:55 pm ]
Post subject:  Re: Engine -missing under load
What fuel pump do you have ?
Author:  Scoop [ Mon Jul 16, 2018 8:18 pm ]
Post subject:  Re: Engine -missing under load
PAT wrote:
Had the same problem with our 1100 with single 1 1/4 carby Replaced all items as you mentioned and it started doing the same. Spoke with my mini mechanic and he said some of his customers were having a lot of problems with using 98 fuel and spark plugs. At the time we were running 98 fuel so I changed the plugs again and swapped to 91 fuel and it I have not had an issue since. Wasted money on replacing all the other parts.

I have been told that 98 fuel is designed for fuel injection. It needs the pressure and injector to be atomized properly. Not sure how true it is but the bosses big block hotrod goes heaps better now NOT on 98...
Author:  deluxe67 [ Mon Jul 16, 2018 10:37 pm ]
Post subject:  Re: Engine -missing under load
"I have been told that 98 fuel is designed for fuel injection. It needs the pressure and injector to be atomized properly. Not sure how true it is... "
- Not true at all, someone is telling you porkies...
Author:  JEA [ Tue Jul 17, 2018 4:24 pm ]
Post subject:  Re: Engine -missing under load
Last night I changed the electronic module, it didn't really make all that much difference. It still ran rough. When it was running, you could hear and feel it back firing through the RH carby. I checked the oil in the dash pot and that seemed to be where it was meant to be. I checked that the main jet wasn't sticking and that too appeared to be doing what it's meant to.
I can't remember what brand fuel pump I'm running, but I've got a feeling that it's generic SU knock off. To date, I've never had a need to think that it's not performing. I can hear it ticking away on start up. Maybe that's the next step, replace the pump.

Fuel wise, I'm pretty sure that I run with standard BP 91 octane. I'm going to drop the fuel in the tanks on the off chance that its gone bad. It's probably only been in there a couple of months, but it's another thing to rule out.

Thanks for all of the ideas and thoughts on what to try next to sort this out.

James.
Author:  simon k [ Tue Jul 17, 2018 4:49 pm ]
Post subject:  Re: Engine -missing under load
have you taken the lids off the float bowls and had a look at how much fuel was in them after running it for a little while?

have you had a look at the float levels? take the dashpots off the carbs, look down the jet with a torch and you should be able to see the fuel level just below the top of the jet

JEA wrote:
you could hear and feel it back firing through the RH carby.


I reckon there's a bit of a clue in this - while it's running, take the spark plug lead off each cylinder in turn, starting with #1 - I don't think there will be any difference when you take #1 and #2 off, but it'll conk out when you take off #3 or #4

you might get a shock or two, you'll get over it, just be brave when you grab the lead, you're more likely to get a shock if you're hesitant
Author:  Scoop [ Tue Jul 17, 2018 6:21 pm ]
Post subject:  Re: Engine -missing under load
Or use plastic brake line clamps, no shock!
Author:  Morris 1100 [ Tue Jul 17, 2018 7:56 pm ]
Post subject:  Re: Engine -missing under load
Take the lead off the distributor not off the plug. That way you are holding a lead that isn't trying to bite you.
Author:  Phil 850 [ Tue Jul 17, 2018 8:05 pm ]
Post subject:  Re: Engine -missing under load
Morris 1100 wrote:
Take the lead off the distributor not off the plug. That way you are holding a lead that isn't trying to bite you.

Now that's taken the thrill out of it 8)
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