engine and drivetrain Car Wont Accelerate past ~4000 RPM Under Full Throttle

[Simeon]

Issue with the power valve in your 32/36? Interesting that it only occurs during low vacuum / WOT(but then you have swapped the carb).

[Utah02]

Here are the first two threads on this problem

 

http://www.bmw2002faq.com/topic/165901-car-chokes/

 

http://www.bmw2002faq.com/topic/166190-car-bogging-troubleshooting-stumped/

 

I have reread them and sort of like the "fly stuck in the fuel line" theory... seriously.

I would pull the line at the tank and the firewall, then let it drain back into a jar, or bottle.

Then I would use compressed air to blow out the line (very carefully, of course) and see if any insects come out.

 

In one of your earlier posts, you mention the carpet limiting pedal travel.  I am wondering whether you have inspected/adjusted the pedal travel yet?  There is an arm that clamps onto the throttle pedal shaft, on the outside of the pedal box.  On my car, the clamping portion of the arm had distorted and the two sides were touching, before sufficient clamping could occur.  I removed a little metal between the tabs and it has stayed put since.  This is not likely to be the source of your problem, but it is an important step in setting up the carb; to make sure full pedal equals full throttle... with no slipping.

 

It is a little weird that you can achieve higher rpm as long as you do not give it full throttle.

 

You have replaced the fuel pump in the trunk and one of your early photos showed nice new fuel lines, so old cracked lines are not likely the problem.  Is the plastic sleeve intact (not cracked) on the outlet nipple of the fuel sender (at the tank)?

I can easily clean the fuel line and I'll do that tomorrow or Wednesday. The carpet travel has already been fixed since the post but that you for mentioning it again. It was something I needed to fix. I Have indeed replaced the pump and fuel lines. I checked and the sleeve is there but has a small crack in it on the end, though the crack doesnt run through the whole sleeve.

 

can you adjust your valves first. then set your ignition timing correctly based on the distributor model for a base line setting. generally 1600rpm vacuum advance disconnected and plugged to the ball or 2400rpm with a centrifugal advance only distributor to the ball. If you do not know how to do this to achieve a base line for your timing can you please use the search function and learn. timing the ignition at idle will not give you the correct advance at higher RPM. then double check your best lean idle carb settings. put in new spark plugs(which ones are you currently using?) gapped correctly and report back. when doing so, show us a picture of the spark plugs

Spark plugs have been replaced with new one that are gapped correctly. Not sure exactly what model but they are NGK and i got plugs recommended by forum members and gapped them to the gap they told me to. Valves were adjusted about a month ago but I have actually done an advanced time. Just realized with your rpm explanation that the timing i did was actually advanced.

[Guest_anonymous]

great!

so what did you set the timing at?

Can you confirm crank to cam timing please

Edited January 5, 2016 by dar_on_

[LimeySteve]

Have you checked for a hole /crack in the fuel line between the carb & the firewall connection, sucks a little air & not enough fuel at hi rpm. My first car in England I had the same problem , sat still & rev all day long but not under load, there was a long streamer like raffle tickets someone had dropped in the tank & at load the paper was sucked down & stuck on the pick up tube then floated away when not under load, odd to say the least !

[AlanM]

Just to add something a little more out there.  Is the cam timing correct? If the cam were 1 tooth advanced it would also have no top end power.  If you pull the tappet cover and bring the engine to no.1 TDC  on compression, with both exhaust and inlet having clearance, then no.4 will be on overlap, meaning both valves will have no clearance and both will be partially depressed a bit under 2mm with a standard cam. If one valve has clearance then the cam timing is out.

 

If the motor had a big cam fitted it would have been having valve to piston clearance issues if it were out by a tooth. While you are at it, checking the tappet clearances wouldn't be a bad thing to do whilst you have the cover off.

[Roland]

Please disregard the following if it has already been asked and/or answered.

 

Can you confirm that your throttle linkage is properly adjusted so that when your foot "floors" the accelerator pedal, the carb throttle plates are opening fully?    I did read where you changed carbs and you corrected something with the carpet that might limit pedal travel.    However, if the throttle linkage is not adjusted to obtain full wide open throttle, you are figuratively "spinning your wheels."    My point is that changing carbs will not necessarily overcome improperly adjusted linkage.    Also, you may not realize this but the connecting/pivoting arm toward the bottom of the firewall has been known to loosen and strip, and in turn, prevent full movement.  I believe someone else referenced this and when you see it you will know it.     Again, please have someone put the pedal to the floor while you look at the carb with air filter removed - and confirm the throttle plates are fully opening.

 

I am also confused about swapping distributors.    If either or both distributors functioned well in another M10 engine, then that probably ends this inquiry.  Is it possible that both test subjects have a  problem with their respective centrifugal advance mechanisms?    I doubt it, but if you are swapping 40+ year old parts for equally old equipment, it may still be possible.    I am assuming you can feel the tension of the advance springs when twisting the top of the shaft where the rotor sits and the bottom where the drive gear is located.    If there is no movement or little tension there is likely a problem.    On that subject, it is worth exploring whether you have the correct rotor and cap combination.    This is not a question about a rev limiting rotor that has reached its limit, but rather could you be using a rotor that is not appropriate for the cap.    There are a great number of different aftermarket rotors and caps that all seem to fit bosch 4-cylinder distributors, but "seems" is not always acceptable.    The differences are not always that obvious, but comparing rotor tip lengths is probably not a bad idea.

 

Your reference to occasional misfire is slightly off putting.  This may be typical for an M10 engine that is set to run on a very lean mixture to pass an emissions test, but it is hard to say that an occasional misfire is generally acceptable.  Assuming everything is mechanically sound, i.e., decent compression and valve timing is set correctly and valves properly adjusted cold (not too tight or too loose ~.008")  then you are left with mixture, ignition timing  and possibly spark plug heat range or improper gaps.  BP5ES~BP6ES.   If you have the information handy, what jets are in your carburetor?  (Most important for this exercise are probably the main fuel, air correction and idle jet.)    You have been asked to provide ignition timing settings.  I'll go one better and merely ask, what happens if you manually advance/retard the ignition by turning the distributor and tuning by ear?  Any difference???

 

BTW, someone mentioned a plugged/restricted exhaust.    This should be fairly easy to detect, especially if you notice either reduced tailpipe flow or reduced sound.  Problem could be a bent or kinked pipe, or a malformed muffler with a collapsed baffle, or a misplaced pet boa constrictor.    I doubt this is your problem, but long distance diagnostics are not my strong suit.

 

Since you are adept at posting a video, consider posting a quick tour of your engine bay with the air filter removed.  Perhaps there will be something obvious that you are overlooking.

[Utah02]

Please disregard the following if it has already been asked and/or answered.

 

Can you confirm that your throttle linkage is properly adjusted so that when your foot "floors" the accelerator pedal, the carb throttle plates are opening fully?    I did read where you changed carbs and you corrected something with the carpet that might limit pedal travel.    However, if the throttle linkage is not adjusted to obtain full wide open throttle, you are figuratively "spinning your wheels."    My point is that changing carbs will not necessarily overcome improperly adjusted linkage.    Also, you may not realize this but the connecting/pivoting arm toward the bottom of the firewall has been known to loosen and strip, and in turn, prevent full movement.  I believe someone else referenced this and when you see it you will know it.     Again, please have someone put the pedal to the floor while you look at the carb with air filter removed - and confirm the throttle plates are fully opening.

 

I am also confused about swapping distributors.    If either or both distributors functioned well in another M10 engine, then that probably ends this inquiry.  Is it possible that both test subjects have a  problem with their respective centrifugal advance mechanisms?    I doubt it, but if you are swapping 40+ year old parts for equally old equipment, it may still be possible.    I am assuming you can feel the tension of the advance springs when twisting the top of the shaft where the rotor sits and the bottom where the drive gear is located.    If there is no movement or little tension there is likely a problem.    On that subject, it is worth exploring whether you have the correct rotor and cap combination.    This is not a question about a rev limiting rotor that has reached its limit, but rather could you be using a rotor that is not appropriate for the cap.    There are a great number of different aftermarket rotors and caps that all seem to fit bosch 4-cylinder distributors, but "seems" is not always acceptable.    The differences are not always that obvious, but comparing rotor tip lengths is probably not a bad idea.

 

Your reference to occasional misfire is slightly off putting.  This may be typical for an M10 engine that is set to run on a very lean mixture to pass an emissions test, but it is hard to say that an occasional misfire is generally acceptable.  Assuming everything is mechanically sound, i.e., decent compression and valve timing is set correctly and valves properly adjusted cold (not too tight or too loose ~.008")  then you are left with mixture, ignition timing  and possibly spark plug heat range or improper gaps.  BP5ES~BP6ES.   If you have the information handy, what jets are in your carburetor?  (Most important for this exercise are probably the main fuel, air correction and idle jet.)    You have been asked to provide ignition timing settings.  I'll go one better and merely ask, what happens if you manually advance/retard the ignition by turning the distributor and tuning by ear?  Any difference???

 

BTW, someone mentioned a plugged/restricted exhaust.    This should be fairly easy to detect, especially if you notice either reduced tailpipe flow or reduced sound.  Problem could be a bent or kinked pipe, or a malformed muffler with a collapsed baffle, or a misplaced pet boa constrictor.    I doubt this is your problem, but long distance diagnostics are not my strong suit.

 

Since you are adept at posting a video, consider posting a quick tour of your engine bay with the air filter removed.  Perhaps there will be something obvious that you are overlooking.

Thanks for the advice! That's a lot to look over and check but I'll make sure to do all that and get back to you. As well as post a video in the engine bay.

Thanks again!

Colby

[Utah02]

Here is a quick video of the car. I tried to show everything but likely could have missed things. If anyone would like a better video or pictures of specific things feel free to ask.

Colby

https://youtu.be/4SjXeZo6SKQ

[avoirdupois]

The video is instructive, but it might help if you slowed the shots a bit.

 

The throttle linkage seems okay when you operate it by hand.  However, what about operation at pedal from inside the cabin?  That may be the weak link!  (Or it may not be?)

 

At 1:07 I see a loose electrical connection.

 

Hard to tell about that fuel pump setup.  I am not familiar with that pump and wonder why you need it as opposed to the stock mechanical pump.  As a few have suggested, I would want to establish that it continuously feeds that carb at least 2-3 lbs/in2.

 

Distributor advance is still a question mark.  Is that a vacuum advance setup?  Or could it be a vacuum retard?  If I recall correctly, the Weber vacuum port is not the same as the original Solex 2bbl.  It draws vacuum further above the throttle plates - delivering a different vacuum signal.  Could this be restricting maximum ignition advance?    Have you tried running with the port plugged?  How about a topless shot of the distributor with the cap removed?  Twist that rotor on the shaft to demonstrate centrifugal advance function?

 

At this rate, it probably couldn't hurt to pull a plug or two and provide a look at the electrodes and gap.  A video with the engine running might also be of help.

[Turkistornado]

At  0:15  I  see two different colored auxiliary venturi tubes.    The secondary is gray.    The primary is brass colored.    Is the brass colored tube loose or worn?  If either is loose it may cause a fuel delivery issue generally felt during acceleration.

 

At  0:51  I see an unconnected  ballast resistor.   I probably missed this but I am confused by coil wiring.   I do not think this is likely, considering your symptoms,  but could the polarity of the coil be reversed?

 

Ignition timing?    Total advance?    

[Utah02]

The video is instructive, but it might help if you slowed the shots a bit.

 

The throttle linkage seems okay when you operate it by hand.  However, what about operation at pedal from inside the cabin?  That may be the weak link!  (Or it may not be?)

 

At 1:07 I see a loose electrical connection.

 

Hard to tell about that fuel pump setup.  I am not familiar with that pump and wonder why you need it as opposed to the stock mechanical pump.  As a few have suggested, I would want to establish that it continuously feeds that carb at least 2-3 lbs/in2.

 

Distributor advance is still a question mark.  Is that a vacuum advance setup?  Or could it be a vacuum retard?  If I recall correctly, the Weber vacuum port is not the same as the original Solex 2bbl.  It draws vacuum further above the throttle plates - delivering a different vacuum signal.  Could this be restricting maximum ignition advance?    Have you tried running with the port plugged?  How about a topless shot of the distributor with the cap removed?  Twist that rotor on the shaft to demonstrate centrifugal advance function?

 

At this rate, it probably couldn't hurt to pull a plug or two and provide a look at the electrodes and gap.  A video with the engine running might also be of help.

I'll get a video of the car running in just a few minutes and demonstrate the throttle linkage from the cabin. The pump is a low pressure carter full pump made to put out 3 psi and is brand new. I switched from another full pump that came with the car that was putting out 6 psi, far too much. In the same video I will show the cap taken off and show the dizzy better. Then I will pull a plug and show that as well.

 

Colby

[Utah02]

At  0:15  I  see two different colored auxiliary venturi tubes.    The secondary is gray.    The primary is brass colored.    Is the brass colored tube loose or worn?  If either is loose it may cause a fuel delivery issue generally felt during acceleration.

 

At  0:51  I see an unconnected  ballast resistor.   I probably missed this but I am confused by coil wiring.   I do not think this is likely, considering your symptoms,  but could the polarity of the coil be reversed?

 

Ignition timing?    Total advance?    

The secondary is dirty and was brass. I have tried cleaning it with carb cleaner and it wont return to the original color. But I recently rebuilt the carb and its all okay. 

I was also told with the newer fuel pump to bypass the ballast resistor as it might have too much resistance causing a weak ignition system, I did that to see if it would help the issue and it did not. 

I still need to do ignition timing and advanced timing but haven't had the time in the last two days.

 

Thanks for the help

 

Colby

[Utah02]

Here is a video of the car running. Sorry it's a little long. I let it warm up for a few minutes but it's not totally warm yet. I wasn't smart and cold revved. I caught a misfire on film too.

https://youtu.be/mu8XK4JwM9s

I was a little stupid and cold revved it a bit. There is oil on the spark plugs and I'm assuming that's the cause. Amateur mistake. My spark plugs are black though. Here are a few pictures of plug #1 and #3

And here is a distributor video. I have shaft play but the other distributor I switched to for a little came off a perfectly running 2002 and I still had the problem. It can rev past 4 when in neutral which makes me think it's not linkage.

https://youtu.be/lQnCbGYTCEk

Edited January 6, 2016 by Utah02

['76mintgrün'02]

The Pertronix ignitor module comes with optional spacers, to raise the height, if needed.

(I did not need two of the spacers when I installed mine).

It looks like you have them all installed, which makes it sit too high.

It should be down even with the magnetic ring on the shaft.

The gap between the ignitor and the ring should be around .030", if I recall correctly. 

From that angle, it looks closer than that.

 

That does not seem like a problem which would be throttle sensitive though.

Have you looked at the arm that is attached to the throttle pedal shaft on the side of the pedal box?

 

The R in the plug number stands for Resistor.

You do not want that type...

As stated in post #5 of your "Bogging" thread

 

Also could be weak ignition- at WOT at high rpms, your spark needs to be at its best and brightest.  I had trouble with Jenn's car with a blue coil, resistance wires, resistance rotor and resistor plugs.  Remove one level of resistance, and the misfire under heavy load disappeared.

 

There will also be a number on the bottom of your rotor, indicating its resistance.  The one I have like that is R1, but I have also see R5.  Lower is better, I believe.

 

Try taking the vacuum line off at the base of the carb and watch the points plate inside the distributor while you suck on that line.  You should see the plate rotate counter clockwise, if the diaphragm in the pod is intact.  This is just a "while you are in there" thing to check, to know it is still good.  There are two nipples at the base of the carb.  You want to attach that vacuum line to the upper one and put a cap on the lower one..

Edited January 6, 2016 by '76Mintgrun'02

[Roland]

Thanks for the video efforts.  In my mind it excludes several possibilities, including the operation of the distributor centrifugal advance and fuel delivery.

Two things remain  "somewhat"  unresolved.  First, you do not need to run the engine for this, but can you get someone to step on the gas pedal while you watch the carb to ensure the throttle plates are fully opening.  This is different from you turning the throttle linkage by hand.  It may be properly operating based upon the video, but it might help to allay any remaining concerns that you are not getting the same results from actually depressing the accelerator pedal.

The other big question for me is your total ignition advance.  The timing light is great for documenting the exact measurement and having a base line.  Still, even without the light, what happens if you time the engine by ear and advance it to the point of pinging?  I am not exactly sure why, but others on this board have called this the "Big Dog" method.   Don't wish to sound unnecessarily difficult but judging from the plugs alone it looks like you are running too rich a mixture.  Again, this could simply be due to the engine not having reached normal operating temp.  OR,   the carb's jets are too big, or  the ignition timing is slightly retarded.     When you blipped the throttle, I thought I heard a bog that suggested the engine might be happier with more ignition advance.    Also, consider disconnecting the vacuum advance to eliminate it as somehow limiting total advance.  Its value  is generally derived at part throttle anyway. 

 

A strange observations?   Your choke plate seemed to be strangely vibrating, making me wonder about its linkage.  To be sure, it was fully opened, but is it somehow engaging when you have the bogging situation?   I can't really see this happening, but maybe someone else can see a connection.