12 replies to this topic

[WanaGo]

Hello,

 

Hoping someone here can point me in the right direction.

 

1978 Morris Mini 1000. Newly rebuilt engine (A series, 998)

 

HS4 carb, looks to originally have been off a 1100cc or something, but history not totally known. Its tag is AUD608. Changed the needle for a 998 one already.

 

Cleaned it up, put in new spindle bushings, spingle, red jet, needle etc, and all was pretty good. However the butterfly I didnt replace, and there was quite an obvious gap around the outside when fully closed.

Also, the butterfly was the WZX1324 type it seems, with the hole in it. Designed for Waxstat jets it seems, and is there for Antistall - based on Minispares description.

I dont have a Waxstat jet though, old one was the red type, and replaced it with a new red type.

 

Drove pretty good, was running rich until I replaced the jet, even with it turned all the way lean. Better now. However still not perfect.

 

Ended up buying a new WZX1323 kit, which is the solid butterfly, without the hole.

Installed it this evening, and now having a few issues which I am not sure about.

 

Adjusted the idle, as without the hole in there now, the butterfuly has to be opened for it to idle - that is all fine. Started up OK after that was opened a bit, but hunts a bit (not much 100-200 rpm maybe).

Let it warm up, and the hunting somewhat settled. However if you blip the throttle, it falls on its face and almost stalls, and then recovers back to an idle again.

 

The carb is also emitting a high pitch squeel, which it was not doing before changing the butterfly. It does it across the whole rev range, not just at idle.

 

Any ideas what is happening here?

Falling on its face after throttle blip, and high pitch squeel.

 

I assume, for whatever reason, this carb wants a butterfly with a hole in it, and maybe that is what the whole 'antistall' thing is about...

The WZX1324 wasnt in stock here in NZ, so I could just take the butterfly out and drill a hole in it - that is no big deal. But wanting to know what is going on before I do that.

 

I have no idea what this squeel is about.

 

Here is a video showing the squeel - ingore what the camera is pointing at, was just getting the microphone closer, but its so obvious that wasnt really needed.

https://youtu.be/zlDfAiYzyCE

 

Here is a video of a small throttle blip, and it falling on its face and recovering.

https://youtu.be/xyMNK2X95vc

 

Any ideas?

Appreciate the help

 

Thanks

[nicklouse]

Changed the needle for a 998 one already

Which one?

Edited by nicklouse, Yesterday, 02:53 PM.

[WanaGo]

 

Changed the needle for a 998 one already

Which one?

 

 

 

Currently have an ADF needle installed. This is what the SU UK guys recommended.

I had an ADE on hand which I had tried before I did the bushings etc on the carb, and that was largely OK too. The ADF is a bit richer than the ADE.

The carb came with an ABP, which was for the 1100cc (which oddly is the leanest I think).

 

These issues I cant see related to the needle though, as its at idle you see the problems as well as everywhere else, and it would appear pretty much all needles are very similar at idle.

 

The book suggest ABX, but I have no idea if that will help anything or not. The 'falling on face' and squeel, is new just after changing the butterfly only. Before that it was completly driveable.

 

 

Regards

[sonscar]

Air leak somewhere?.Steve..

[Spider]

Sounds like there's an Air (Vacuum) leak somewhere.

 

[WanaGo]

OK, thanks guys. 
i'll go over it all again and check for air leaks, and use some brake clean while its running and see if the revs change etc, and see if I can spot anything. Hopefully its something dumb and obvious.

 

What are the thoughts on the butterfly with and without the hole though - should I be using the same type as what was in there (assuming it was original), or is going to the solid plate without the hole a totally fine solution?

The lack of hole shouldnt be causing the 'falling on face' or squeel, right?

If the idle screw is set right, the butterfly must be being cracked open slightly or it wouldnt start, so it must be getting air past the butterfly anyway - so the idea of needing a perfect seal when the butterfly is closed, seems like something that is not all that important in reality, as you cant have it perfectly closed and the engine running - right....

 

Thanks

[timmy850]

If you give it a quick rev up and it gasps or doesn’t want to rev, this can be due to the dash pot oil being too thin (and potentially too thick). A common symptom of too thin or insufficient oil is the damper rises too quick and it leans out the mixture, causing it to stall. It’s less common for it to be too rich that it causes the same stalling, but it is possible.

Best way to check is by measuring with an air fuel ratio gauge. AC Dodd has lots of good videos on YouTube with SU theory and tuning info

[WanaGo]

If you give it a quick rev up and it gasps or doesn’t want to rev, this can be due to the dash pot oil being too thin (and potentially too thick). A common symptom of too thin or insufficient oil is the damper rises too quick and it leans out the mixture, causing it to stall. It’s less common for it to be too rich that it causes the same stalling, but it is possible.

Best way to check is by measuring with an air fuel ratio gauge. AC Dodd has lots of good videos on YouTube with SU theory and tuning info

 

Thanks for the reply.

 

Before I did the carb rebuild, I had engine oil in the dash pot. After the rebuild, I put the proper SU oil in it, thinking that is what it should have in it.

I have gone back to engine oil again, so I am not sure what is going on here exactly.

I think the SU oil is thinner than the engine oil is. 

 

Since I have changed the butterfly, ill start off with checking the mixture, as that likely could have changed with less air passed the butterfly now, so ill start there. Ill do the whole, 3 turns and see if revs go up or down, and 3 turns the other way, etc, and then narrow it down to the position that the revs are the highest. Then adjust the idle down to where it should be. That is still the recommended 'go to' starting point for mixture, right?

 

I dont have an air fuel ratio gauge sadly, however my plan once I get this running a bit better is to take it into a local shop who have good knowledge of minis, and they will have a AF gauge I am sure, and get them to do the final adjustments. 

I am just in a worse position than I was with the old butterfly right now, so ideally want to get back to where I was.

 

Regards

[timmy850]

If you can’t measure where the fuelling is with a gauge, it’s just guesswork

Using the idle mixture nut is the way to set the idle mixture only. If it’s too rich or lean anywhere else you need a different needle profile, or there is another fault like an air leak somewhere

[WanaGo]

Figured out the main issue. Thanks everyone.
Air leak.
Idiot me didn't do the nut up to the manifold on the driver's side very tight. Did it up and squeel stopped and so did the falling on its face.

Thanks everyone.

[WanaGo]

Figured out the main issue. Thanks everyone.
Air leak.
Idiot me didn't do the nut up to the manifold on the driver's side very tight. Did it up and squeel stopped and so did the falling on its face.

Thanks everyone.

[WanaGo]

Figured out the main issue. Thanks everyone.
Air leak.
Idiot me didn't do the nut up to the manifold on the driver's side very tight. Did it up and squeel stopped and so did the falling on its face.

Thanks everyone.

[WanaGo]

omg these forum server timeouts are frustrating!