230SL Stalling and lack of power

[RoyB]

Greetings everyone
I have posted other questions in this forum, all somewhat related to the issue I am about to outline here.
The car is a 1963 230SL, mostly rebuilt in the late 90's.  I have owned it for about 4 years, and am continually going through it to make it run and drive better.  It has always had a burbling or stuttering through the exhaust and a slight backfire when accelerating over 3000 RPM.
I have flushed the tank (it was clean), tested the full pressure and lines, tried electronic ignitions - giving up and going back to points.  The plugs and points have less than 200 miles on them now, and the plugs look good.  No build up, no fouling, displaying a nice tan color.  Here is the issue of the day.  I decided to flush the radiator and install a new thermostat.  After reading the forums and troubleshooting to ensure I was not missing anything, I performed the process.  I took the car out for a drive, and everything is good.
Upon returning and allowing a cool down, I top off the tank, then squeeze each of the radiator hoses to ensure I am moving the 50/50 solution by looking inside of the overflow tank.  All good.  Before getting ready to take a little trip up the into mountains, I take the car to run some errands.  The car runs good for about 20 minutes, then stalls repeatedly, exhibiting very little power off idle.  At higher engine speeds, it runs OK.  I nurse it back into my garage and let it cool down.  I verify that no antifreeze got into the distributor.  I covered the distributor prior to the flush - as this appears to be ignition or fuel delivery.  Clean and dry, but i still spray it with WD40 and wipe it clean.  Pulled plugs - clean.  I start the car again with difficulty, and even with no load, the engine stumbles when the linkage is moved to increase RPM.

So here is my question.  Is there some connection to flushing the radiator and a possible air bubble in the coolant line at the injectors that could cause this, or has my burbling fuel injection system just give me its final warning that it needs attention?
I was hoping to keep this running well enough to attend the PUB2017 session in Virginia, but it looks like I will have to fix this before I get there:)  As always, thanks for the feedback.

[RoyB]

Lets take this in a slightly different direction.  I was looking on the Mercedes Source site and saw the pump that Kent and his crew developed for testing the injectors.  If one or more of the injectors were bad, I would have the stuttering and slight miss throughout the entire range of engine speeds, not just at 3000 RPM, correct?  The idle is very smooth, and the engine accelerates nicely until 3000 RPM when it begins to stutter and slightly backfire.  This indicates fuel delivery in my mind.  The compression is very good at 155 psi on each of the cylinders, with 125 psi on the first rotation of the engine.  The fuel pump delivery conforms to the testing guidelines. I have installed a new fuel filter after flushed the tank.  With all of that said, here is my question.  Is there any definitive method to test the Fuel Injection system to very that it is delivering fuel correctly at all engine speeds? 
Thanks

[ja17]

Double check your points.  They may have settled-in. Check your ignition timing. Ignition coil can cause similar problems. Check the intake screen on the electric fuel pump. You can also watch the  fuel pressure when the problem occurs for hints.

[RoyB]

Thanks Joe.  Checked point gap and dwell today, along with the timing.  Everything is right on.  I installed a Beru Blue Coil last year as this burbling issue has been constant since owning the car.  I am still getting a popping when listening to the exhaust, and the stutter continues anywhere between idle and higher RPM's.  I still have the thought that I may have a partially clogged fuel line(s), bad injector(s), or a injection pump that is not working properly.  While I have lots of specialty tools here, I am hesitant to order the Injector Tester that Kent has on the Mercedes Source site as it would only be used once. 

[RoyB]

I have ordered the injection tester from MercedesSource and will remove and test the injectors shortly.

https://mercedessource.com/store/bosch-mechanical-fuel-injector-mfi-tester-and-cleaning-kit

After removing the injectors, I will verify that the fuel lines are clean.  If the injectors and fuel lines work as expected, then I will have the pump rebuilt.

Has anyone had recent experience with a pump rebuild?  Location, time required, issues with removal or installation, etc.
Thanks

[Bonnyboy]

Roy, I am not a mechanic  or anything like that but am thinking electrical.   

Thins I would check in order are   

Is your coil good (for sure) - have you swapped out a known good coil?
Are you using NGK plugs?   
Are your points floating? 

Good luck.

[RoyB]

I had the same thoughts when diagnosing this, but everything continues to check out properly.
The original coil checked out using an Ohmmeter, I felt the spark was weak.  I put in the Beru Blue Coil and saw a big difference when grounding the plug to the block and looking at the spark.   Ohmmeter verifies resistance is good on the primary and secondary is an improvement than the original coil.
The Points are new, and gapped at 0.012.  Timing is at 2 BTDC and 40 BTDC over 3000 RPM.
The plugs are NGK BPR6EGP, gapped to .030.  I tried .035, but the plugs were a little black.

All of this was just verified a few minutes ago, followed by a test drive.
Engine still hesitates, stutters, and pops slightly through the exhaust.
Not un-drivable, but not as much fun as I hear that stutter and wonder when something is really going to go wrong.
There is another 230SL locally that I have looked at and driven.  The compression on my engine is much higher, and even across the cylinders. The other car burns oil, so fouling of the plugs is an issue around 2000 miles.  While the other car has some driving issues, it is much more responsive when driving than mine.  No popping through the exhaust or hesitation when accelerating.

[Benz Dr.]

Which distributor are you using? Something isn't right because you have far too much advance if you are 2 BTDC at idle and 40 degrees at 3,000 RPM.  I've always thought that the blue coil was for CD ignition systems so it may not be the right one for your car. I use BP5ES plugs which are a bit hotter and tend not to foul out as easily. Make sure that there isn't any carbon core in your spark plug wires.

[RoyB]

Distributor number is 0 231 116 046.  Chassis number: 113 042 10 000211
The Engine number appears to be: 127 981 10 000801. 
You are correct in the these values do not align with anything I read in the forums, or in the 4 workshop manuals I have for this car.
The engine seems to run the best when the timing is set at 3000 RPM and higher somewhere in the upper 30's.
I have tried countless variations with little success in eliminating this stuttering and burbling.

[Benz Dr.]

According to those VIN numbers you should have a very early 230SL with what should be a correct  230SL engine. This set up uses a VA distributor. Check to see if the  vacuum port on the throttle body is on the top or bottom of the housing. It should be on the top with vacuum signal increasing as you throttle up. 

[RoyB]

I have the rear facing distributor with the vacuum port on the top.
If I disconnect the vacuum and plug the line, I see a slight retard in the timing.

[Benz Dr.]

It sounds like you have a complete VA system. You should  not have a vacuum signal at idle.

[Naj ✝︎]

"The Points are new, and gapped at 0.012.  Timing is at 2 BTDC and 40 BTDC over 3000 RPM.
The plugs are NGK BPR6EGP, gapped to .030.  I tried .035, but the plugs were a little black."

The Bosch '046' is a vacuum advance distributor. Ensure you have the correct throttle body to match. Also the timing should be set with the vac line disconnected. The vac advance gives you nearly  8 degrees of further advance at 3000 rpm.
The BP'R" plugs may be causing you an issue.
In my view the .012 point gap is too small. I prefer .014 to .016.

Just my £0.02

naj

[Benz Dr.]

I set everything with vacuum lines connected. Disconnecting the vacuum line is really only for checking if the system is working and since the engine will be used in driving mode with everything hooked up, I see no reason not to check it that way. Vacuum advance values are slightly different for every unit but in general early ones should be set to 10 degrees. I agree that .012'' is a bit close but the best way to check is with a dwell meter which should be around 38 degrees.

Some of the early 230SL distributors have a very quick advance - the curve is almost straight up. This makes setting them very difficult to do because a bit too much spring tension on the the flyweights  and they won't open soon enough. Too loose and they're fully advanced at 1,500 RPM. It's tedious, time consuming work.

[RoyB]

Latest update.
I installed the NGK BP5ES plugs, gapped to .032.
The car runs ever so slightly better, but still has the popping / slight miss / slight hesitation and can be heard through the exhaust.
At a steady speed, the popping is still there, but is far more noticeable when accelerating past 3000 RPM.
I will verify the timing again - this time with the Vacuum Advance disconnected.
I wil try anything at least 5 times or more:)

I am curious about the "right throttle body" comment Naj.
As stated earlier, there is another 1963 230SL locally, and some of my engine components are different.
According to the VIN, the build date on mine is earlier than the other car.
The engine SN indicates that this is a 230SL engine.
Note the radiator overflow tank and the throttle body shown in one of the photos differ from the other car.
Compression is very good - 155 psi after three turns.  125 on the first reading.

[Benz Dr.]

You have a VA system for sure. The rad overflow tank was changed to a later version which is not important right now.

 Set your timing to 8 degrees BTDC and then see what your highest advance value is - throttle up until it doesn't advance any more even if you have to go above 3,000 RPM to see a final value. If you end up with something like 50 degrees the problem is in your distributor where a lot of running problems  can be found.

[Naj ✝︎]

Hi, Roy,

"
I am curious about the "right throttle body" comment Naj "

If thats the picture of your throttle body, its the correct one for a vacuum advance distributor with the vac pipe coming off the top of the throttle body.

naj

[RoyB]

Todays update:)
Accessed the timing marks and verified that I have white paint on 8 degrees BTDC, 30 degrees BTDC and 40 degrees BTDC.
Adjusted the points, increasing the gap from .012 to .014.
Removed the vacuum line to the distributor and reset the timing.
8 degrees BTDC at idle, and 30 degrees BTDC over 3000 RPM.  When I put the vacuum line back on, the timing stays at 8 degrees BTDC at idle, but jumps to almost 50 degrees BTDC over 3000 RPM.

Engine runs a little better each time, but still pops through exhaust and you can feel the hesitation or stutter while accelerating.

[Benz Dr.]

It sounds like you have a problem with your distributor.  I think the vacuum portion isn't set up properly and it's giving you too much advance.

[RoyB]

Assuming the Advance mechanism is adjustable, how much Advance should I see with the Vacuum line attached over 3000RPM?

[Tyler S]

Roy, does your vacuum advance pod have a large cap nut on the front side of its housing? The rod length can be adjusted behind this cap. You should see about an 8 to 10 degree difference between having the vacuum line attached or not attached when checking timing at 3000 rpm.

[RoyB]

Yes it does.  I will give that a try.

[Benz Dr.]

I always adjust the pull rod but the vacuum cell needs to be removed first to do that. The more you turn the rod out, the more advance you get. I agree that you should have about 10 degrees of advance but I set them up so that I get 30 degrees of total distributor advance by adjusting the pull rod which is the only place you can fine tune.
Different units ( distributor numbers )  produce different amounts of total advance but our early engines like 30 degrees of total distributor advance and about 8 degrees of initial timing such as the 051 set up. These units produce about 20 degrees of mechanical advance and about 10 degrees of vacuum advance.

Late engines with the 062 aluminium units have about 10 degrees mechanical advance and about 22 degrees of vacuum.