Distributor adjustment

[Largeowner]

Hi Folks,

I have a 1967 230 SL.  Even though I run 93 octane in it, there is slight knocking when I accelerate hard.  The distributor is an 051 with the bolt and pointer for adjusting when using a "lower octane" fuel (early system).

  My question is: How does this adjustment work?  When I loosen the bolt, the pointer just moves freely and does not seem to be attached to anything.  I set the marker to 2 notches off of "F", but the knocking persists. 

Large

[thelews]

You would first need to loosen the hex bolt holding the distributor in place.  Then the pointer gizmo might work, but it sounds like yours is not.  To correctly check and set the timing you should have good timing strobe light and tachometer.  You want to check it at idle, 1500, 3000 and 4000 rpm.  You need to check the manual for your proper specs.

[jameshoward]

Large,

If you are going to set the timing to spec (start there and then adjust again if it doesn't sound right) then first check the dwell of the points on the 051. It's not complicated, but you will need a dwell meter. Many automotive amp meters have a dwell function, and they also tend to have an RPM function also. If you buy one with both functions you'll be able to do the job properly using a strobe gun. It's not a hard process at all, and very satisfying. There is a lot here on the site about such adjustments, and the Haynes manual has a pretty good section. The kit isn't expensive at all.

Of course, before doing the points, you might like to take a look at the linkage tour first to ensure that everything is set up properly if you haven't already done so, then a gross error check on the points gap (using a feeler gague), then check dwell, then do timing last. You can also check things like resistance in your spark plug leads and other fun things with the amp meter! (I found a problematic lead that way; wish I'd started with the leads as it would have saved me a lot of time).

If you don't have the haynes manual, or the BBB (both worth getting) let us know and I'll post the specs for dwell, etc.

JH

[Largeowner]

I was hoping for a quick and easy fix for a very minor problem, but it is always better to "DO SOMETHING THE RIGHT WAY".  Looks like I am buying a dwell meter today!

Thanks for the replies!

Large

[ja17]

Hello Largeowner,

Make sure you are using high octane fuel.

[Largeowner]

Hi again,

This reply is a bit delayed because I had to special order a Dwell Meter and Timing Light. 

My Dwell is now set correctly to 39 (range 38 plus 2 minus 1).  However, a new problem has emerged...

When I set the timing to the correct 2deg BTDC (plus or minus 2), the warm idle RPM is a whopping 1500 RPM!  I can adjust the timing to bring the idle down to 800 RPM, but this retards the timing to 8deg ATDC.  I ran the car around the block at this setting and it REALLY seems to like it!  The hard-acceleration knocking is gone, and the engine pulls strong with no hesitation.

So, my new question is:  Is this a safe setting to use or am I risking calamity?  Do the members of this group recommend returning the timing to spec and dialing down the idle RPM instead...and if so, how do you do that?

Thanks again for all the answers,

Large

[thelews]

Hi again,

This reply is a bit delayed because I had to special order a Dwell Meter and Timing Light. 

My Dwell is now set correctly to 39 (range 38 plus 2 minus 1).  However, a new problem has emerged...

When I set the timing to the correct 2deg BTDC (plus or minus 2), the warm idle RPM is a whopping 1500 RPM!  I can adjust the timing to bring the idle down to 800 RPM, but this retards the timing to 8deg ATDC.  I ran the car around the block at this setting and it REALLY seems to like it!  The hard-acceleration knocking is gone, and the engine pulls strong with no hesitation.

So, my new question is:  Is this a safe setting to use or am I risking calamity?  Do the members of this group recommend returning the timing to spec and dialing down the idle RPM instead...and if so, how do you do that?

Thanks again for all the answers,

Large

Did you disconnect the vacuum line to the distributor before timing?  Follow the plastic line from the distributor to where it connects on the passenger side and pull it off.  Then plug the hole where you pulled it off from.

I just reset my timing on the 250 SL and defer to the 3K -4500 rpm value, 30 degrees btdc.  After setting there it fell close to the values specified for idle and 1500. 

[Largeowner]

John,

The specs on this site say to keep the vacuum connected for all settings on the 051 distributor.  So that is what I did.

Large

[Naj ✝︎]

At idle, does connecting and disconnecting the vacuum line make any difference?

With vacuum disconnected, when you set the timing at 30 degrees btdc at 3k rpm, then your timing reading will be around 8 degrees btdc at idle. When you reconnect the vacuum, it should retard to atdc.

Have a look in the wiki to ensure you have a matching 'retard' throttle body with the vacuum line connecting below the 'throat'.

naj

[glenn]

Sounds like too much fuel.  Cut back CCW on the FIP knob(engine stopped).  You want 800 RPM with right amount of air to burn the minimum amount of gas necessary for 800 at correct timing.  Then cut back air 50 RPM to get 750 slightly rich.

   And rotating the distributor a couple degrees(to retard) should end the pinging. 

[thelews]

Not sure what you're reading, but with my 051 distributor, the specs are to disconnect the vacuum.  Leaving it connected would produce the type of issue you are having.  NAJ response agrees with my experience.

P.S.   Wiki is a nice thing, but I will always defer to the MB owner's manual and MB service/tech manuals

[Naj ✝︎]

Not sure what you're reading, but with my 051 distributor, the specs are to disconnect the vacuum.  Leaving it connected would produce the type of issue you are having.  NAJ response agrees with my experience.

P.S.   Wiki is a nice thing, but I will always defer to the MB owner's manual and MB service/tech manuals

On the vacuum retard system, its rather academic whether you disconnect the vacuum or not. As soon as you open the throttle, the vacuum falls away, and should not affect the advance at 3k rpm. Now, with vacuum advance, its a whole different matter.

Disconnecting/reconnecting the vacuum line does let you ensure that the vacuum retard is working.

naj

P.S: I am glad this debate is taking place as we need to make the Tech Manual accurate and dependable.

naj

[thelews]

But, if his is working, and he's trying to set his timing at idle (which I wouldn't), then, ve gotta prrrroblem.  Otherwise, what you say is true and he can eliminate the issue on the 051 dist. by setting the timing at 3k-4500 rpm at 30 degrees.

[Largeowner]

Dear All,

I just checked the distributor setting spec column out of the Tech Manual again to make sure that I had not goofed.  My car is a 1967 230 SL and has the cast iron distributor with the allen screw clamp.  It is marked JFUR6 and is an 051.  The vacuum enters at the front side of the distributor.

The tech manual says that this is a retard distributor, and the specs say to set timing with the vacuum attached (w).  I did not want to use the specs in the manual (green book) because it applies to the older vacuum advance distributors of the early 230 SLs.

I agree that setting the timing at 3000 RPM takes the vacuum issue away, but this is a "one man job" for me.  I was attempting to set it at idle, and check it at 3000 RPM.

Other than the idle mixture set screw, is there any other way to slow down the idle via fuel?

Large

[thelews]

It's easy to set the timing at 3K plus.  Just rev the engine via the linkage while looking at the timing and make the adjustment to 30 degrees depending upon what you observe.  I have no helpers.  When the timing no longer advances as you rev, you've hit the limit of the mechanical advance and that is 30 degrees spec.  Your dwell meter has a tach also, so you can glance at your rpms, no?  Then you can recheck the 12-19 spec at 1500 and your idle spec with and without vacuum.  But, I would still defer to the high end spec.  Did you check the max advance when you were experiencing the 1500 rpm idle? The reason for the various specs is to verify the timing curve and that your distributor advance is functioning properly.

As Glenn suggests, if the timing specs at the various (especially max) rpms check out, then there's another issue affecting your idle speed.  You only gave us idle timing spec, so you have not ruled out timing as a possible issue.

I would still time with the vacuum disconnected, even though there is a spec for it connected, in order to rule out any issue that may be related to vacuum and be confident that the timing is correct.

[waqas]

Are you suggesting one should set timing at 3000 rpm (30 degs) and then work backwards? Maybe I should try that.

My technical data book (issue 1969) gives the 230SL/250SE/250SL/280SE/280SL data for the IFUR 6 (0 231 116 051) distributor as:

(1) Adjusting value at 4500 rpm. without vacuum and without load: 30 degrees

(2) Inspection values during measurements with stroboscope:

• Starter speed and screwed-in spark plugs: 8 degrees BTDC w/o vacuum
• Engine w/o load, idle speed, with and w/o vacuum advance: 2+/-1 degrees ATDC with vacuum
• Engine w/o load, 1500 rpm, w/o vacuum advance: 12-19 degrees
• Engine w/o load, 3000 rpm, w/o vacuum advance: 30 degrees

Yesterday, after I replaced my points and set the dwell (closest I could get was 39 degs), I started to set the timing. As specified, I set the idle timing at 2-3 degs ATDC with vacuum. When I disconnected the vacuum line, the idle went up to 1100 rpm. I than raised the idle to 1500 and measured the timing as ~16 degs BTDC. However, the max advance I could get was 27 degs BTDC (at >3000 rpm).

Am I supposed to start from setting the max advance timing value and work my way back to measure the 1500 rpm and idle settings?

[glenn]

Dear All,

I just checked the distributor setting spec column out of the Tech Manual again to make sure that I had not goofed.  My car is a 1967 230 SL and has the cast iron distributor with the allen screw clamp.  It is marked JFUR6 and is an 051.  The vacuum enters at the front side of the distributor.

The tech manual says that this is a retard distributor, and the specs say to set timing with the vacuum attached (w).  I did not want to use the specs in the manual (green book) because it applies to the older vacuum advance distributors of the early 230 SLs.

I agree that setting the timing at 3000 RPM takes the vacuum issue away, but this is a "one man job" for me.  I was attempting to set it at idle, and check it at 3000 RPM.

Other than the idle mixture set screw, is there any other way to slow down the idle via fuel?

Large

'idle mixture set screw'  --if you mean the  air screw on the manifold-- that's not how to reduce the idle rpm.  Idle gas flow is determined by the idle knob on the back of the FIP(fly weights), the CSV on the inlet manifold, atmospheric pressure on the lever inside the FIP, and the temperature compensation on the lever inside the FIP.  If the outside lever on the FIP has been rotated on the shaft from the factory setting, idle gas could be altered.  Adjust the FIP knob CCW to lower idle.  Then adjust the air screw to max rpm.  Repeat until rpm is 800, then cut til rpm is 750- i.e. 50 rpm rich.

[thelews]

Are you suggesting one should set timing at 3000 rpm (30 degs) and then work backwards? Maybe I should try that.

My technical data book (issue 1969) gives the 230SL/250SE/250SL/280SE/280SL data for the IFUR 6 (0 231 116 051) distributor as:

(1) Adjusting value at 4500 rpm. without vacuum and without load: 30 degrees

(2) Inspection values during measurements with stroboscope:

• Starter speed and screwed-in spark plugs: 8 degrees BTDC w/o vacuum
• Engine w/o load, idle speed, with and w/o vacuum advance: 2+/-1 degrees ATDC with vacuum
• Engine w/o load, 1500 rpm, w/o vacuum advance: 12-19 degrees
• Engine w/o load, 3000 rpm, w/o vacuum advance: 30 degrees

Yesterday, after I replaced my points and set the dwell (closest I could get was 39 degs), I started to set the timing. As specified, I set the idle timing at 2-3 degs ATDC with vacuum. When I disconnected the vacuum line, the idle went up to 1100 rpm. I than raised the idle to 1500 and measured the timing as ~16 degs BTDC. However, the max advance I could get was 27 degs BTDC (at >3000 rpm).

Am I supposed to start from setting the max advance timing value and work my way back to measure the 1500 rpm and idle settings?

In answer to your question, that's how I do it, which doesn't necessarily make it right.

You will notice in your instructions, #1 says adjusting value 4500/30  #2 says inspection values and gives ranges for various rpms.  So, it seems that MB's priority is that you get proper and full advance above 3k rpm, which is where I spend much of my time.  The >3k rpm is a fixed amount whereas <3k rpm is a range.  So, once I've set the high value and confirmed the range values, I get a sense of how the engine is running.  I might just tweak the timing a degree or two and run the rpms up and down from idle to 4500 and see how smoothly the engine is running to and through the rpms.  I like to set it where things seem smoothest while still respecting the specs.  Then, of course, is the road test and how it feels under light load (surging? smooth? etc.), sharp demand (hesitation?  strong smooth pull? etc.) and how it feels at high rpm and speed (that nice effortless glass smooth feeling at 90 mph, yeah baby!).  I'm thinking one might find a timing that works best for their specific car that might differ slightly from spec due to gas, wear and interaction of other engine components.  Obviously, if you're way off spec, ve've got prrrrrroblems!

BTW, my distributor is a JFUR 051

[waqas]

Thanks John. That makes sense now.

[graphic66]

'idle mixture set screw'  --if you mean the  air screw on the manifold-- that's not how to reduce the idle rpm.  Idle gas flow is determined by the idle knob on the back of the FIP(fly weights), the CSV on the inlet manifold, atmospheric pressure on the lever inside the FIP, and the temperature compensation on the lever inside the FIP.  If the outside lever on the FIP has been rotated on the shaft from the factory setting, idle gas could be altered.  Adjust the FIP knob CCW to lower idle.  Then adjust the air screw to max rpm.  Repeat until rpm is 800, then cut til rpm is 750- i.e. 50 rpm rich.

What effect does the CSV on the manifold have on the idle speed?

[glenn]

CSV(cold start valve) could stall the engine if it opens at 750rpm idle on a warmed up engine.  Probably speed up a cold starting engine with additional air coming in air passage on the temperature tower.

[Largeowner]

OK,  I have removed the vacuum on the car and set the timing at 3000 rpm.  I ALSO could only get 27 degrees at 3000.  I took a chance and briefly reved to 4500 rpm, but 27 degrees seems to be the limit.  However, the 1500 rpm setting is bang-on and curiously enough, when I reattach the vacuum it retards about 14 degrees (as it should) to 2 degrees which agrees with the wiki.

In other words, the timing is just right.

In the above stated condition my idle in gear is 800 rpm, and 1100 rpm in neutral and idle.  I checked the adjustment at the venturi and the butterfly is fully closed in idle.

I adjusted the idle mixture knob 6 clicks toward lean (which was the limit of my bravery) and the figures remain unchanged.

Any suggestions?

Thanks,

Large

[thelews]

Suggestions?  If the car is running great and the specs look good and the plugs read well with no pinging or knocking...leave it alone.

Why could you only get 27 at 3K?  Is the distributor stuck and won't turn any further or did you not try to advance it more?  If the distributor is stuck, or being limited from turning in some way, you may want to address that...you should be able to go past 30 and have a full range of movement.

You are not "taking a chance" revving the car to 4500 to check the advance mechanism.  The specs call for it and for the short period of a timing check there's no damage being done.

[JimVillers]

Large ... Just to support what John said, if it runs good and you are happy, leave it alone.  On the other hand, you may not be driving with the engine RPM over 3K so you might not realize the benefits on a correctly tuned and running engine. 

Tune the engine to how you like to drive.  I have a manual transmission and use the higher RPMs so I prefer my ignition set with more advance, similar to Johns.  But again, tune it to the way you like to drive.

[Largeowner]

This thread started because I was experiencing pinging while hard-accelerating.  I am now satisfied with the timing on the car since the pinging is gone.  My only concern now is the 1100 rpm warm idle while in Park.  It results in quite a jolt when selecting a drive gear so I would like to decrease it.

My owners manual says to adjust the idle mixture no more than 3 clicks lean or rich of the factory setting.  I have no idea if the PO left this car at the factory setting, however, 6 clicks in the lean direction has not lowered the idle RPM a single bit!

I checked plug condition and gaps before I began this operation, and they showed a light formation of black soot rather than brown or tan.  My sense is that the car has been running a bit rich prior to my adjustments.

I am now contemplating adjusting the idle mixture progressively leaner until the idle is correct, or the car stalls due to fuel starvation.  Is there any reason I should not do this?

Large