25 replies to this topic

[klivins]

I am worried how to do it right. A year ago I finally after loads of trials and errors managed to get my 1275 up and running. Got it thru local equivalent of MOT, and did good 4000 kms (incl IMM in Hungary). Then I dicovered I had the problem of bore wash and hence glazing. I had used Gunsons CO meter as a reference point to polish my needle, and also plug colour did not give me concerns of rich mixture. Nor was fuel consumption above mini's average - on par with a SPI mini anyway.

Well, the engine was dismantled again, a honing is done, and with new set of rings it is in the car again. Few thing to finish, and then Im ready to fire her up. Now - how not to make the same mistake again? Last year I had used the HS 4 carb, what was said to be too small for my build (stage 3 head, 9.5:1 CR, kent 266 cam). now I have got a HIF 44 carb. The question is - what can I do to ensure lean(er) mix besides a BDL needle and two turns down the bridge?

 

Cheers!

[elanbaby]

@ mini mad: "The question is - what can I do to ensure lean(er) mix besides a BDL needle and two turns down the bridge?" There´s no "two turns down" on the HIF. To lean out the mixture you turn the adjustment screw anticlockwise.

 

 

I read about "problems" about lean mixture after rebuild only here in the Mini Forum actually. And wonder why? I guess all Minis left the factory with standard mixture setting when new. Ever heard of "bore glazing" then? You probably DO have to start the engine using the choke anyway.

 

Personally I don´t think this should be a problem at all. When rebuilding an engine I would apply plenty of assembly grease and/or oil all parts generously. On initial start-up don´t let the engine idle too slow, better immediately rev up to 2000/2500rpm to ensure good and fast oil pressure to all bearings.

Edited by elanbaby, 18 May 2013 - 06:01 AM.

[Dan]

There´s no "two turns down" on the HIF. To lean out the mixture you turn the adjustment screw anticlockwise.

 

  The initial position in an HIF is exactly the same as in an HS.  2 full turns rich from the jet being flush, which on the HIF means 2 full turns clockwise, which winds the screw down.

 

  If anything running lean is more costly than running rich.  It takes quite an excessively rich mixture to get serious bore wash but a very lean mix leads to localised overheating to the point of melting through piston crowns, among other things.

 

  The initial position is safe for the engine, it should put the mix right about the middle of the plateau.  The method of finding the proper tune listed in Haynes (the plateau method) is good enough for a normal everyday car and will be safe enough for a car in a more developed state to run, until you can get it to someone who does know how to tune it if it's something you aren't familiar with.

[Carlos W]

There´s no "two turns down" on the HIF. To lean out the mixture you turn the adjustment screw anticlockwise.

 
  The initial position in an HIF is exactly the same as in an HS.  2 full turns rich from the jet being flush, which on the HIF means 2 full turns clockwise, which winds the screw down.
 
  If anything running lean is more costly than running rich.  It takes quite an excessively rich mixture to get serious bore wash but a very lean mix leads to localised overheating to the point of melting through piston crowns, among other things.
 
  The initial position is safe for the engine, it should put the mix right about the middle of the plateau.  The method of finding the proper tune listed in Haynes (the plateau method) is good enough for a normal everyday car and will be safe enough for a car in a more developed state to run, until you can get it to someone who does know how to tune it if it's something you aren't familiar with.

Thanks for clearing this up!

[ACDodd]

On the hif carb set the jet flush with the brass jet bearing. Fit a know lean needle BEJ is a good start for hif 44. Put 2 squirts of engine oil down each plug hole just before the engine is started. Fit a co meter up the tail pipe and start the engine with choke. As soon as it starts push the choke fully home and run the engine on the throttle. Keep the fuel mix below 1.0%. It is critical that during run in the mix is on the weak side. No engine damage will result as the engined is not running in high load high speed conditions during run in. It is as simple as that.
I am sorry but the statement above is simply wrong. Running an engine rich during run in is the quickest way to ensure that new rings need to be replaced. I get tired of diagnosing engines due to this fault by people who like to run things rich during run in. Don't do it, it'll cost you a rebuild.

Ac

Edited by ACDodd, 18 May 2013 - 07:59 AM.

[elanbaby]

 

There´s no "two turns down" on the HIF. To lean out the mixture you turn the adjustment screw anticlockwise.

 

 "The initial position in an HIF is exactly the same as in an HS.  2 full turns rich from the jet being flush, which on the HIF means 2 full turns clockwise, which winds the screw down."

 

 

 

The setting´s  the same on HS and HIF, but the method is different.

HU richer: turn (nut below the jet) anticlockwise

HIF richer: turn screw (adjustment screw close to the fuel inlet) clockwise 

 

Getting the engine started safely that´s just what I meant. The stardard setting should be ok. Choke not longer as absolutely necessary, no excessive load, no excessive (but also not too few) revs,

 

Edited by elanbaby, 18 May 2013 - 08:00 AM.

[Dan]

But that's why I wrote it as 'down' instead of clockwise or whatever, because winding the screw clockwise from the top winds it downwards and in that way it's 'down' for both types.  Makes it easier, and I think was done intentionally by SU for that reason.

 

  However, please disregard what I said about the first start as AC is far, far more qualified than I to talk about carb tuning.  I'm only going by the book and the things I have done that have worked, AC has setup many hundreds more engines than me.

Edited by Dan, 18 May 2013 - 07:59 AM.

[klivins]

Thanks AC, much appreciated!

[colinu]

AC - can you clarify something for me. You said "set the just flush with the brass jet housing". SU manual says to set it flush to the bridge. What if the jet housing isn't flush with the bridge (like mine... where the housing sits approx 2.5mm low of the bridge)? Do I set to the bridge or the jet housing?

[ACDodd]

Set it flush with the jet bearing not the bridge on an hif44. Then you must adjust again with the engine running. You must ensure lean running. A flooding carb will also damage a new engine.

Ac

Edited by ACDodd, 19 May 2013 - 04:43 PM.

[Ethel]

I'd say jet bearing. The fact it's not flush makes little difference, it's the fit of the needle in the hole that matters.

 

Ring bedding can also be affected by oil, don't use anything fancy, just cheapo mineral based stuff.

[colinu]

Good - 'because I'd set to the jet bearing when bedding my cam in (with AFR showing mid/high-15s).
I just wanted the experts to confirm what was correct so it gets "documented" on TMF for other to use on future.

[klivins]

So far so good. The engine is in the car, and the mini has passed MOT. The Gunsons CO meter at home told me I have 2% of CO, 30 mins later MOT station printout told me its 0.11 %. Is it not too lean? Am I using Gunsons wrong way round? The car runs fine, only slight detobation after stopping the engine. havent revved it very much yet.

Just concerned about running it too lean.

[Captain Mainwaring]

 

There´s no "two turns down" on the HIF. To lean out the mixture you turn the adjustment screw anticlockwise.

 

  The initial position in an HIF is exactly the same as in an HS.  2 full turns rich from the jet being flush, which on the HIF means 2 full turns clockwise, which winds the screw down.

 

  If anything running lean is more costly than running rich.  It takes quite an excessively rich mixture to get serious bore wash but a very lean mix leads to localised overheating to the point of melting through piston crowns, among other things.

 

  The initial position is safe for the engine, it should put the mix right about the middle of the plateau.  The method of finding the proper tune listed in Haynes (the plateau method) is good enough for a normal everyday car and will be safe enough for a car in a more developed state to run, until you can get it to someone who does know how to tune it if it's something you aren't familiar with.

 

 

I'd agree that really excessively rich mixture might wash the bores and dilute oil, but I wonder how we got on years back. I had a lovely rebuilt lotus twink, mixture was set up completely normally, but the run in was controlled - I did 150 miles first trip out, never laboured it, and didn't cane the revs, next day the timing was advanced a couple of degrees closer to standard and a little more work done. 

Changed the engine oil at about 1200 miles (no synthetics then), and the engine was fine 65000 later with normal maintenance - 

 

There were never the issues years back with glazing, and mixture was never set as accurately as it is now, are engine oils just too good now, or is the honing too good? If anything the running in back then was softer than it is now.

 

I'd expect problem with the choke left out for the duration of the run in, but not for running a bit rich. Aircraft engines don't have these issues - I've flown aircraft with new barrels and pistons, and especially on those aircraft with manual mixture, they are frequently run heavily rich from time to time - and never glaze up, but then maybe they aren't treated so softly as a car engine, purely because of a respect for the ground.

[Captain Mainwaring]

I am worried how to do it right. A year ago I finally after loads of trials and errors managed to get my 1275 up and running. Got it thru local equivalent of MOT, and did good 4000 kms (incl IMM in Hungary). Then I dicovered I had the problem of bore wash and hence glazing. I had used Gunsons CO meter as a reference point to polish my needle, and also plug colour did not give me concerns of rich mixture. Nor was fuel consumption above mini's average - on par with a SPI mini anyway.

Well, the engine was dismantled again, a honing is done, and with new set of rings it is in the car again. Few thing to finish, and then Im ready to fire her up. Now - how not to make the same mistake again? Last year I had used the HS 4 carb, what was said to be too small for my build (stage 3 head, 9.5:1 CR, kent 266 cam). now I have got a HIF 44 carb. The question is - what can I do to ensure lean(er) mix besides a BDL needle and two turns down the bridge?

 

Cheers!

 

 

Do you think your mistake was mixture, a problem with bad honing, too sedate run in, or too "good" an engine oil during run in? I personally don't think it was mixture -