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Brand New EVERYTHING - Misfire on 3&4 - HELP


racer86

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First off: nice car!

 

I believe it has to be spark.  I know you checked 100 times, but you have one of the pics labeled  "order in image is 4-3-2-1"  just for fun reach down and swap the 3-4 plug wires so its the same firing order listed on the valve cover..cant make it run any worse.    No?  check your points gap at all 4 positions and check for slop in your dist shaft.

 

otherwise:

Did you do the comp test again after it was running badly?  Dead adjacent cylinders would make me suspect a  head gasket leak between them. Shouldn't be a problem that could hide from a simple comp test, but it is a problem that can hide at high rpm.   You can do a crude leak test by pulling those 2 plugs and have a buddy put compressed air to each of those cylinders at valves closed tdc.  See if you can detect any leakage next door.  *use the hose from your comp tester and duct tape cobble something together that will make your buddy's task easier.

 

-Hard to believe could be a single downdraft carb  issue that only shows itself on 3-4. 

-you've proven there's no booster hose leak.  BTW you're not driving it until you figure it out so just keep that intake booster port plugged for now just to be 1000% sure.

-Any other intake leak can usually be easily detected with careful targeted application of your favorite non-chlorinated flammable aerosol while the motor is running before going to the machine shop.

 

Edited by Deilke53
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Michael Deilke

Whidbey Island, Washington

206-714-3379

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43 minutes ago, Deilke53 said:

First off: nice car!

 

I believe it has to be spark.  I know you checked 100 times, but you have one of the pics labeled  "order in image is 4-3-2-1"  just for fun reach down and swap the 3-4 plug wires so its the same firing order listed on the valve cover..cant make it run any worse.    No?  check your points gap at all 4 positions and check for slop in your dist shaft.

 

otherwise:

Did you do the comp test again after it was running badly?  Dead adjacent cylinders would make me suspect a  head gasket leak between them. Shouldn't be a problem that could hide from a simple comp test, but it is a problem that can hide at high rpm.   You can do a crude leak test by pulling those 2 plugs and have a buddy put compressed air to each of those cylinders at valves closed tdc.  See if you can detect any leakage next door.  *use the hose from your comp tester and duct tape cobble something together that will make your buddy's task easier.

 

-Hard to believe could be a single downdraft carb  issue that only shows itself on 3-4. 

-you've proven there's no booster hose leak.  BTW you're not driving it until you figure it out so just keep that intake booster port plugged for now just to be 1000% sure.

-Any other intake leak can usually be easily detected with careful targeted application of your favorite non-chlorinated flammable aerosol while the motor is running before going to the machine shop.

 

 

 

He did spray flammable fluid on 3 and 4 and saw a change in RPM. I can’t see how it could be anything other than a vacuum leak... But i don’t see a lot, so ?

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'74 Verona

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He did spray flammable fluid on 3 and 4 and saw a change in RPM

Oops I missed reading that.   I guess as long as it wasn't just overspray on the aircleaner then by all means yes that's the first thing to fix.  But he re-did the gaskets..with sealant even..afterward and got the same result.

Edited by Deilke53

Michael Deilke

Whidbey Island, Washington

206-714-3379

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On 4/11/2020 at 12:54 PM, scatman75 said:

Get us a closer pic here, i zoomed in and i think i can see a defect on 3 but its hard to say. I know you said they are new gaskets but the latest video is symptomatic of a vacuum leak. The trouble with vacuum leaks is that everything can appear to be fine but a doubled up gasket or a hairline crack will cause issues

20200411_075009.jpg

 

Pics below, though I've not cleaned the mating face since taking the manifold back off...

 

IMG_20200412_104720.thumb.jpg.8f9e3e19729a89ebfb2856adda1271d4.jpgIMG_20200412_104712.thumb.jpg.cae287dca58e57a774670ee35c75ec30.jpg

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19 hours ago, Deilke53 said:

First off: nice car!

 

I believe it has to be spark.  I know you checked 100 times, but you have one of the pics labeled  "order in image is 4-3-2-1"  just for fun reach down and swap the 3-4 plug wires so its the same firing order listed on the valve cover..cant make it run any worse.    No?  check your points gap at all 4 positions and check for slop in your dist shaft.

 

otherwise:

Did you do the comp test again after it was running badly?  Dead adjacent cylinders would make me suspect a  head gasket leak between them. Shouldn't be a problem that could hide from a simple comp test, but it is a problem that can hide at high rpm.   You can do a crude leak test by pulling those 2 plugs and have a buddy put compressed air to each of those cylinders at valves closed tdc.  See if you can detect any leakage next door.  *use the hose from your comp tester and duct tape cobble something together that will make your buddy's task easier.

 

-Hard to believe could be a single downdraft carb  issue that only shows itself on 3-4. 

-you've proven there's no booster hose leak.  BTW you're not driving it until you figure it out so just keep that intake booster port plugged for now just to be 1000% sure.

-Any other intake leak can usually be easily detected with careful targeted application of your favorite non-chlorinated flammable aerosol while the motor is running before going to the machine shop.

 

 

Hi Deilke, thanks for the feedback and suggestions. 

 

I'll check the leads again when it's back together; like you say it's hard to believe it's going to be on the carb side.  Once the carb is back on, new gaskets and machined manifold I'll see how it runs and spray some more brak cleaner around.  Then I'll do the timing...after that....I'll do another comp test (the values stated earlier were ones from when it's been running badly)...

 

If none of that cures it...might be time to pull the head. WELP. 

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OK, maybe I missed   it, but did you try switching #3 and 4 plug wires with 1 and 2? And then moving #3 and 4 plugs to 1 and 2? The dist cap is seated properly?

Also, are you saying you cleaned all that black crap off the mating surface on the head?

Edited by Hans
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Do you have a spare ignition condenser to swap out? Some of the new replacement condensers from bosch are crap, I chased a ignition miss on my Porsche 912 with all new parts last summer and it turned out to be a bad new of the shelf BOSCH condenser.

 

Jeff     

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I had exactly the same on my car and it came down to vacuum leak on the new intake manifold - they 'settle' in and after re - tightening all nuts etc the problem went away.  Vacuum leak solves so many issues - there is a great weber set up article somewhere that I read and the author insisted 100 times that before touching anything on the weber at all - be ABSOLUTELY certain there are no vacuum leaks. I did this and never touched my new weber at all.

The author also insisted that most people wouldn't listen to his advice and will spend hours chasing other things. I was one of those people ?

 

However it is essential you also look at the basics of timing and coil set up (with resistor etc)

 

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Thanks all. 

 

While I wait for the manifold to come back I've been going back through the basics on the ignition timing and marking the crank pulley with white paint ready for when I can get the timing light on it:

 

I found the following: 

 

1. The points has slipped to 0.025" so I reset to 0.0016" (FACEPALM)

 

IMG-20200416-WA0010.jpg

 

2. When I set the timing static to 3 degs BTDC I had to rotate the dizzy anticlockwise a fair amount! you can see the line where is was marked on the shaft/ clamp....

 

The method I used was timing the to the 3Deg BTDC mark on the crank pulley and then rotated the dizzy so the line on the body aligned to the line on the rotor arm - sound right? 

 

 

IMG_20200417_092527.jpg

Vac chamber position looks more "right" to the Haynes manual too...

 

IMG_20200417_091509.jpg

 

IMG_20200417_091449.jpg

Ps. is the "ball bearing" on my crank pulley 25deg BTDC?  I could only find a TDC mark on the flywheel. (Note: this is a carb '73 2002). While line on the outside is TDC. Inside pulley is TDC and 3deg BTDC (I believe) 

 

 

I've also cleaned up the gasket faces on the head ready to re-fit the manifold:  Pics of it cleaned up.  I've gone for geniune BMW gaskets leaving nothing to chance!  Pricey! 

 

IMG_20200417_091339.jpg

 

IMG_20200319_190535.jpg

Thanks, Rob. 

Edited by racer86
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I need more coffee. I would pull valve cover and make sure both #1 valves are closed. Arms should wiggle. That's when you want #1 plug to fire. Well, a few deg. Before.

Edited by Hans
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