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New Engine Struggling Under Load


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#1 AndrewT

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Posted 29 November 2020 - 04:06 PM

I've got my newly rebuilt engine into my car but am having problems getting it to run properly under any sort of load or fast throttle movement and am now getting worried that unless I can sort it soon I won't be able to run the engine in properly.

 

Spec:

HIF44

Maniflow LCB and RC40

MG Metro cam

Electronic ignition

K&N cone filter (but see below)

Modified MG Metro head with 35.5/30 valves

BEJ needle

 

Symptoms:

It starts fine but won't idle below about 1,200 rpm.

In neutral, if the accelerator is pressed sharply it will bog down and stutter before revving up.

When trying to pull away, unless given a bootfull of revs it will stutter and stall.

Once moving, anything more than very gentle acceleration causes revs to drop and cut out.

Once up to constant speed it runs along ok.

 

Things checked/tried so far:

Put a standard air filter back on.  Not much change at all and just makes it harder to adjust the carb.

Blocked off half the surface area on the K&N to restrict airflow.  No noticeable difference.

Checked dashpot and needle drop - lifts smoothly and takes about a second to fall back with a light clunk.

Static timed at 6 degrees.

 

Once it's run in I'm going to take it to a rolling road to get properly set up but at the moment that seems a long way away.

 

I'm at a complete loss now.  I'm sure it's fueling related rather than ignition.



#2 richmondclassicsnorthwales

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Posted 29 November 2020 - 04:35 PM

Just an idea, is the gasket on correctly between the air filter and carb, you've not got it upside down blocking the air venting holes on the carb?

 

You have not said how you have set up the mixture ratio - just need a bit more meat on the bones with that one too

 

There is oil in the dashpot ?



#3 AndrewT

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Posted 29 November 2020 - 04:42 PM

Gasket is on the right way round.

Oil in the dashpot and it's moving at the right speed so I'm fairly sure that's ok.  I did have SAE 20 in per SU website but that was creating too much resistance so I swapped it out for 3in1 and it seems fine now.

Mixture was originally set with the jet 2 turns below the bridge.  Adjusting this helps at tick over but doesn't sort the main problem. 



#4 cal844

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Posted 29 November 2020 - 04:50 PM

Sounds like the piston is rising too fast to me, possibly the wrong needle or fuel settings.

What size of engine?

Edited by cal844, 29 November 2020 - 04:50 PM.


#5 AndrewT

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Posted 29 November 2020 - 04:52 PM

1275



#6 richmondclassicsnorthwales

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Posted 29 November 2020 - 05:43 PM

OK

 

Now, I had this scenario with a 44 on a Mini. I had rebuilt it, jetted it with a correct needle corresponding to the actual tag spec.

 

Long story short, I sold it on, and the new owner contacted me a couple of weeks later, with the problems similar to yours.

 

He swore black and blue that it was a faulty carb, so as he was only about 20 miles from me, I went to the garage who was "Fitting and tuning it !!!!"

 

I opened the bonnet and straight away, I could see someone had had the carb pot off - lack of lock washers !!

 

I took it back off, took out the needle and someone had changed it.

 

I put another needle in - relevant to the tag spec - and bingo - Job done.

 

If you have the tag number, I will give you the needle spec which it was built with,   that much I can help you with



#7 AndrewT

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Posted 29 November 2020 - 06:10 PM

Sounds promising. Just checked and the MG one should be BDL but mine is BEJ. The tag is:

FZX 1524
4 WK 901

#8 richmondclassicsnorthwales

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Posted 29 November 2020 - 06:59 PM

BEJ is the correct needle for that specification tag

 

Other 44 needles are 

 

BDL,  BFY,  BGX,  BDD,  BFA,  BFZ,  BER,  BFA

 

The turbo Metro used a BDD and BFA.  Metro Sport, MG & VDP used a BDL

 

I know you can't just go and buy 8 needles at £12 a pop,

 

I'm drawn to the mixture and needle being the issue, hopefully some others members could give some input and help



#9 AndrewT

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Posted 29 November 2020 - 07:14 PM

That's very helpful, thanks. Looks like someone has replaced the carb at some point previously.

I'll try a BDL and see if that solves the problem as it only needs to be close enough to get it running well enough to run in properly before rolling a road tune up to get it spot on.

Out of interest, have you any idea how the coding works as I assumed A would be richest or leanest and then it would move up as you go along the alphabet. However it seems a bit random with for example some charts showing (for the third letter) it going J, L, C in order of increasing richness.

#10 minidave54

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Posted 29 November 2020 - 07:33 PM

I am running a fairly new built engine with 700miles on the clock and a spec fairly similar to yours, differences being;

 

1293cc

Cam, mini spares Evolution 001

Mini spares dizzy to match above

Standard airbox and filter

Mini spares head with 35.6/29.3 valves.

 

The carb has a BDL needle and the static timing i have set at 12 degrees ( i noticed yours is set at 6 deg which may be a little retarded). I have found these settings to be a good starting point to get it running.

To get the mixture set i used a colour tune.



#11 minidave54

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Posted 29 November 2020 - 07:33 PM

I am running a fairly new built engine with 700miles on the clock and a spec fairly similar to yours, differences being;

 

1293cc

Cam, mini spares Evolution 001

Mini spares dizzy to match above

Standard airbox and filter

Mini spares head with 35.6/29.3 valves.

 

The carb has a BDL needle and the static timing i have set at 12 degrees ( i noticed yours is set at 6 deg which may be a little retarded). I have found these settings to be a good starting point to get it running.

To get the mixture set i used a colour tune.



#12 AndrewT

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Posted 29 November 2020 - 07:40 PM

Sounds like the needle swap to a BDL is definitely the first step and then have a look at the timing.

Actually, thinking about it I could't set the genuine static timing so could only do it at starter motor turnover speed so it's probably a little retarded from 6 anyway.

#13 PACINO

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Posted 29 November 2020 - 07:54 PM

Hi. I had a similar problem years ago. 1275 engine, Hif44 carb in show condition, BER needle, K&N air filter. The car was not going well and I almost went crazy. I spoke with everyone and nobody gave me the solution. Until one day someone told me, remove the K&N and put the original filter inside the case. Well, it was to put it and the car was perfect in all ratios.

* The oil that I put in the shock absorber chamber of the carburetor piston is: or the specific for S.u. carbs or the thin (light) of a sewing machine.

Good luck!

#14 AndrewT

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Posted 29 November 2020 - 08:14 PM

Yes, I thought the K&N might be letting through too much air so tried blocking half off thwn resorted to a standard airbox and filter but it made no real difference.

I'll try the new needle with the K&N and then the standard if necessary.

Already got the thinner oil in the carb piston too.

There are so many variables that you can end up going in circles.

#15 cal844

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Posted 29 November 2020 - 09:47 PM

Personally I wouldn't touch the timing until its on the rolling road. In the mean time if you can set the CO appropriately for the year of car (use an MOT emissions test machine in non official mode, it shouldn't take long to set that, then the idle. Once you do that you can play about with the needle without needing to alter mix too much.

Then finalise the timing.

You need a KnN element type (that sits in the standard box) filter if you have a stage one kit, it'll just lose power with a cone or paper element filter. You could also try a spare filter housing with the holes drilled in to see if you get any gains there.

Edited by cal844, 29 November 2020 - 09:50 PM.





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