26 replies to this topic

[Omnomsan]

1990 Rover Mini

Engine Specs:

• 1310 A+
• Swiftune heritage pistons
• EVO001 camshaft (I'm told this is similar to SW5)
• Big valve head from 7 Mini Enterprises (1.4"/35.56mm intake valves)
• 3.1 diff
• standard rockers
• MED ST1 lightened flywheel
• LCB + RC40 DTM twin box exhaust
• Alloy intake (standard from Minisport, heater line isn't connected for preheating... hello Texas)
• HIF44 w/ BDK needle, 80w90 gear oil (also tried standard 20w SU oil in dashpot with worse results), Yellow spring
• 59D4E distributor
• Gold coil
• electric fuel pump
• filter king regulator/filter

I went on a 4000 mile road trip from Dallas, Texas over to Virginia/D.C./North Carolina for a camping driving trip on the Snake and Dragon's Back (very curvy, amazing roads and definitely recommend) and my old 1293 performed great! But! I blew my head gasket on the way back from a local Cars and Coffee lol. Thankfully not on my trip. But that damaged my pistons, scored my bores severely so I rebuilt it with a new block.

I've since upgraded my block/pistons/etc from 1293 to 1310. The initial run in went perfectly with a great tune and AFR. HOWEVER! As soon as I changed my oil and filter (and topped up with new fuel) my tune/AFR is completely out of wack... the jury is out as to why my tune suddenly changed with a simple oil change, but thoughts from friends are that during run-in the fuel can contaminate the oil to a degree and alter the mixture enough. I'm not sure though. It's been a flat out mystery.

Running with 93 octane fuel (American MON) = ~98 octane (UK RON) from the same station as always. Fuel level in carb and regulator glass are perfect. Filters are all clear and flow is excellent. Nothing else was touched when I did the oil change so nothing makes sense.


Idle AFR 11-12
Low Speed Cruise AFR ~14
High speed Cruise AFR 15-16
W.O.T. AFR 13
Coasting AFR ( not sure on this, will update after my next drive)


Timing has been ran through a couple times just to make sure it's in the right spot and that's good.

Carb was "new" before my 1293 roadtrip, and shows no signs of wear on the dashpot damper, nor the carb piston. The carb piston, when the holes are plugged, has a nice even drop rate when doing a drop test similar to how DS3Shooter demonstrates in his YouTube vids.

I've got the following needles to try, but by the readings I already have, I would either need an even RICHER needle than BDK, or there may be something wrong:

• BDK (current needle in HIF44 w/yellow spring & 80w90 gear oil... red spring and/or 20w SU oil performed WORSE with extreme bogging/leaning issues on acceleration)
• BBW
• BDL
• AAK
• ADF
• BFY

I've also attached a comparison chart from https://www.classicm...hnical/needles/ as well as a recommended list from WinSU, though the recommendation calls for an HS8 or twin HIF38/HS4 instead of my current HIF44 for the 1310, so the recommendations are probably based on that carb configuration and thus N/A toward my setup


Thoughts? If I can't figure this out I might reach out to AC Dodd and see if he has an idea.

Attached Files

•  needle-comparison-chart.jpeg   26.45K   3 downloads
•  Screenshot 2022-09-23 120459.png   14.1K   2 downloads

Edited by Omnomsan, 24 September 2022 - 07:53 PM.

[Omnomsan]

I'm aware that I had a similar issue with my 1293 until I adjusted the fast idle screw, but in this instance, that has not solved anything.

[ACDodd]

Heck that idle AFR is bore washing your engine!!

Ac

[Omnomsan]

Pulling the choke gets me into good AFR territory for running around town at higher speeds (a lot of highways in Texas) but I'm really not a fan of running around like that, so I've been using Uber where I can until I can figure this out.

 

Any ideas why the tune/AFR values would swing so far into lean after an oil change? Is there any truth to what my friends have mentioned in regards to fuel contaminating oil during run in? 

[whistler]

My wife's 1330 has same cam and head. Started it off with the MG Metro needle, the BDL. Took it to a rolling road session and the needle was perfect, no adjustment/thinning necessary. They did find a small hole in the vacuum advance/retard plastic pipe though.

Just adjusted timing and mixture. 90bhp at flywheel.

[Omnomsan]

My wife's 1330 has same cam and head. Started it off with the MG Metro needle, the BDL. Took it to a rolling road session and the needle was perfect, no adjustment/thinning necessary. They did find a small hole in the vacuum advance/retard plastic pipe though.

Just adjusted timing and mixture. 90bhp at flywheel.

Do you know if it's using a yellow or red spring? My vacuum line is new and shouldn't be any holes, but can't be sure until I double check so I'll do that as well. Thanks for the needle recommendation though!

[KTS]

Pulling the choke gets me into good AFR territory for running around town at higher speeds (a lot of highways in Texas) but I'm really not a fan of running around like that, so I've been using Uber where I can until I can figure this out.
 
Any ideas why the tune/AFR values would swing so far into lean after an oil change? Is there any truth to what my friends have mentioned in regards to fuel contaminating oil during run in?

No, but as AC has pointed out, you need to sort out the fueling at idle before you do anything else

[Pigeonto]

That was brave,, trying an A needle in a 100 thou' jet !!

Difficult understanding what the oil change has done but you have to work with what you've got.

I can't see where it lists which air filter you're using?? Are the 2 engine breathers in use or is it blanked off at the carb?

I think I'd try going back to more normal .

See what happens if you fit the BDK, Red spring. SU damper oil

I assume you have an AFR guage on board with probe fitted somewhere close to the engine?

[Omnomsan]

Timing cover vented into rocker cover. Transfer case vented into rocker cover. Rocker cover vented into under wing catch can (MED kit). Been running that way for months perfectly fine.

 

Running an MED foam filter on the back of the HIF44, have been for 7000 miles. I've cleaned it just in case with no change.

 

 

That was brave,, trying an A needle in a 100 thou' jet !!

Not sure what you mean here. All of the needles I've used are the swinging/sprung needles meant for the HIF/HS carbs. Granted, maybe there are some that are more A vs A+ and I'm not well versed in the differences, but regardless, it ran perfectly with the 1293 for 4000 miles and then some, and during run in up until the oil change with the 1310, so :shrug:

 

Changed it to BDL, red spring, 80w90 gear oil. Got my idle up to 13.4-14AFR so that's much better.

Accelerating lightly causes AFR to jump to 16-18... much too lean obviously. Could be a case of damper oil, needle, etc. I'll continue messing with it this weekend by changing one variable at a time and recording results.

 

I've got an AFR under dash with a bung welded into the y-piece of my LCB exhaust.

[Pigeonto]

All the other needles on that list are B prefix for use with the 100thou jet of a 44 / HS6. They are 95thou diameter at station 1 whereas A prefix needles for the 90thou jet in the 38/HS4 carbs are 85thou at stn1 and steadily decreasing in size along the length hence the over rich result shown. You show one of the weaker 'A' needles so it wasn't quite as drastic. Probably needed the jet adjusted very high up. You'll have to carry on using needle charts to find one that's richer at the needle stations where you're weak or profile one that you have.

[whistler]

 

My wife's 1330 has same cam and head. Started it off with the MG Metro needle, the BDL. Took it to a rolling road session and the needle was perfect, no adjustment/thinning necessary. They did find a small hole in the vacuum advance/retard plastic pipe though.

Just adjusted timing and mixture. 90bhp at flywheel.

Do you know if it's using a yellow or red spring? My vacuum line is new and shouldn't be any holes, but can't be sure until I double check so I'll do that as well. Thanks for the needle recommendation though!

 

I think it's the standard red spring. The dashpot currently runs on 20w50 quite happily. I think your choice of 80w90 gear oil seems excessively thick.

[Omnomsan]

Decided to take the filter off and look down the throat of a carb. I can't tell if it's not rising due to a lack of vacuum or because the oil is too thick, but I'll switch back to 20w SU oil for a comparison.

video of carb while revving

Edited by Omnomsan, 24 September 2022 - 07:20 PM.

[Omnomsan]

Just swapped over to SU oil from 80w90 gear oil and it's much much worse. So! Current thoughts are...

 

Previous configuration:

BDK, yellow spring, 80w90 gear oil, LZX1509 (damper that came with the HIF44)

- still some bogging but it's something I can still drive kind of if I make use of my choke which obviously isn't ideal

 

Current Configuration:

BDL, red spring, SU oil (20w), LZX1509 (damper that came with the HIF44)

- bogging is absolutely awful and I can not rev higher than mid throttle before it stumbles and dies

 

After chatting with Mini friends, it's been suggested that my damper is incorrect for my setup. LZX1509 is providing too little resistance for the dashpot oil which is causing an erratic tophat response which is disrupting the venturi

 

Proposed fix is to upgrade damper to LZX2085 to increase resistance to dashpot oil and stabilize the venturi and reduce/eliminate sudden onset bogging. From there I can work with different needles to achieve proper mixture.

 

For now, until I find the correct damper, I'll run with thicker oil, richer needle, and stiffer spring to keep the damper stable as much as I can. Basically reverting to my old setup with BDK, yellow, 80w90 gear oil.

 

Is this train of thought correct? Also, recommendations for where to get the new damper are appreciated as most places I've looked are sold out (I'll do Minispares if I must but shipping gets pricey to the US).

Edited by Omnomsan, 26 September 2022 - 10:24 PM.

[Omnomsan]

Swapped back to the BDK, yellow spring, 80w90 and it's much better with some bog at light throttle. Hopefully a new damper sorts things out. I'll report back when I have that sorted with some new data

[sonscar]

I am sure that you know how acceleration enrichment is dealt with on SU carbs but research it again.Too rich is easily confused with too lean.Gasping and popping thro the carb is too lean,burbling and exhaust popping is too rich.Is your timing working correctly to light off the mixture with the changing vacuum?
I say this because I find that sometimes it is better to ignore everything you have already done and start again.Have fun,Steve..