Author Topic: Calling on the tuning experts, pls help tune 67 250SL  (Read 656 times)

Challenger_7

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Calling on the tuning experts, pls help tune 67 250SL
« on: June 08, 2022, 20:03:03 »
Hello everyone
On my recently restored 67 I am still having issues with fuel tuning.
Everything there is new and well, but I am still having issues. Let me explain.
I read many posts on this forum and saw a very informative and simple video on Youtube (https://www.youtube.com/watch?v=F6sxlOFmoYw) which explained things very easily, and I applied the knowledge on tuning my car.

Initially, the car was running seemingly well from power point of view and as long as I am driving on the highway, but would soon foul up the plugs after 2 or 3 sorties, and my mechanic was not getting it right until I decided to have a go myself.

The warm Up valve is working very well and when warm, there is practically no suction there, and when I stick my finger in, the rpm would not change, as explained by the posts and the Youtube video.
Hence I embarked upon leaning the pump by turning 3 notches at a time with the car off, then starting again. (BTW, how come we can only do 3 notches at a time?)
On my pump, screwing anticlock leans the fuel, and clockwise enriches it.

So, I kept leaning, then adjusting the air flow screw to go back to 750 rpm until I got to the desired setting which as explained in the video, under such a setting, no matter how much you opening up the air flow screw, the rpm will not go beyond around 900 or so.
Took the car for a drive and it really felt weak especially when taking off from standstill.
Came back and checked the plugs, they were quite white, fair enough as it was too lean.

I then went ahead and enriched the fuel setting on the pump and kept doing so until I could "feel" the power is up to normal again, and the way I did that is by stopping, adjusting and taking off and if the car was still hesitating, I would enrich it 3 more clicks.
So whilst the power of the car was getting better, now it would always stall on Neutral.

I decided to go back to my cave and adjust again using the split lever method, i.e. leaning out or giving more fuel to the pump until if u move the pump lever, the car will die, or if you move the throttle lever very slightly, the car will also die.

At that point, I gave the pump 3 more clicks to enrich it and took it out for a drive and it was a disaster. Kept dying out, backfiring from the engine occasionally and very poor power, could barely move from a stand still point without "help".
(HELP: My mechanic had connected a button under the dash to energize the fuel squirting when starting as the unit responsible for this was bad, had it fixed but kept the button. So when the car was unable to move freely, I would give it a squirt or two and it will immediately jump up and move)

So, having followed both methods, the video's or the group's split connector method of checking for the right setting, and both failed miserably, can I please get some advice on what to do before I mess up further?

I also noticed that I have W8DC plugs on, that also had an "RO" stamped before the number. SHould I stick to these or change?

Sincere apologies for the long write up and would appreciate any advice.

Cheers
« Last Edit: June 08, 2022, 22:35:16 by Challenger_7 »
1961 190 SL, 1962 190b, 1967 250 SL, 1977 450 SL, 1979 450 SLC 5.0, 1990 500 SL and a few Classic collectibles

Jonny B

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Re: Calling on the tuning experts, pls help tune 76 250SL
« Reply #1 on: June 08, 2022, 20:13:24 »
To clear something up. I take it you mean a 1967 250 SL, not a 76 250 SL??

Using three clicks (or two or one) is to allow you to take things slowly and stay able to keep track of where you started from.

The clicks you are doing at the back of the injection pump will only affect the low range of RPM.

Beyond that, I will back out and let FI folks jump in.
Jonny B
1967 250 SL Auto, DB 568
1970 280 SL Auto, DB 904

ja17

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Re: Calling on the tuning experts, pls help tune 76 250SL
« Reply #2 on: June 08, 2022, 22:29:44 »
Clicks at the IP will only adjust low range mixture up to 1700 rpms. Start by doing a split linkage test on your warm engine at low rpms and mid range (about 2400 rpms). Your plugs may be ruined at this point, might want to start off with a fresh set.
Joe Alexander
Blacklick, Ohio
1969 Dark Olive 280SL
2006 Mercedes Sprinter Van
2002 ML55 AMG (tow vehicle)
2002 SLK32 AMG (350 hp)
1982 300TD Wagon turbo 4spd.
1963 404 Mercedes Unimog (Swedish Army)
1989 flu419 Mercedes Unimog (US Army)
1998 E430
1974 450SLC Rally
1965 220SE Finback

Challenger_7

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Re: Calling on the tuning experts, pls help tune 67 250SL
« Reply #3 on: June 08, 2022, 22:36:47 »
 :o Sorry about that, 67 indeed  ;)
1961 190 SL, 1962 190b, 1967 250 SL, 1977 450 SL, 1979 450 SLC 5.0, 1990 500 SL and a few Classic collectibles

Challenger_7

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Re: Calling on the tuning experts, pls help tune 76 250SL
« Reply #4 on: June 08, 2022, 22:57:01 »
Clicks at the IP will only adjust low range mixture up to 1700 rpms. Start by doing a split linkage test on your warm engine at low rpms and mid range (about 2400 rpms). Your plugs may be ruined at this point, might want to start off with a fresh set.

Thank you Joe, to understand what you are suggesting:
I do the Split Linkage test at idle, then keep checking & adjusting as need be using the clicks at the IP upto 1700 rpm, right?

Then I check at 2400 if it is still good?
If that is what I should do, but I need to adjust further at 2400, do I still use the clicks?

Thanks
Farouk
1961 190 SL, 1962 190b, 1967 250 SL, 1977 450 SL, 1979 450 SLC 5.0, 1990 500 SL and a few Classic collectibles

ja17

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Re: Calling on the tuning experts, pls help tune 67 250SL
« Reply #5 on: June 09, 2022, 12:22:35 »
No clicks used on the thumbscrew at higher rpms. However if your mixture is off at all speed ranges you may have a different problem or will need a different adjustment. If you can check at idle, check at 2400rpms and even 3200rpms with warmed engine.
Joe Alexander
Blacklick, Ohio
1969 Dark Olive 280SL
2006 Mercedes Sprinter Van
2002 ML55 AMG (tow vehicle)
2002 SLK32 AMG (350 hp)
1982 300TD Wagon turbo 4spd.
1963 404 Mercedes Unimog (Swedish Army)
1989 flu419 Mercedes Unimog (US Army)
1998 E430
1974 450SLC Rally
1965 220SE Finback