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Author Topic: Murena 2.2 with Weber 40 DCOE, "shoots" over Idle speed.  (Read 3613 times)
Dokken
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« on: August 05, 2015, 03:53:37 am »

Hello.

I have recently bought a Murena 2.2 82mod, with Weber 40 DCOE Carburetor and it want "run" over idle speed.
Does anyone have expecience with what can be wrong?

I have tuned and syncronized The carburators after standard prosedure. Still it "shoots" when touching trottle.
The valvetiming is set to 10 degrees before DTC, so I asume Its lean mixture...or leak at intake manifold, but cant find The leak. I have also read that engines with 40mm Weber are using 12-14 degrees timing. Does anyone use that on your Murena?

Do I also have to use other coil or sparks when using Weber?
I hope someone can give me som advice.

Regards

Gjermund Dokken
Norway/Valdres
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GP
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« Reply #1 on: August 05, 2015, 11:40:46 am »

Hi Gjermund,

Welcome to "Matra Madness".  Smiley

I can't specifically help you with the problem but in answer to your last questions I run my 2.2 with 45 D.C.O.E's at 12 deg. BTC.

I use standard coil, leads and plugs. The standard distributor does have the vacuum advance hose removed though and runs fine.

Hopefully someone on here will give you some further advice.

All the best,

Graham



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roy4matra
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« Reply #2 on: August 15, 2015, 07:12:24 pm »

Hello.

I have recently bought a Murena 2.2 82mod, with Weber 40 DCOE Carburetor and it want "run" over idle speed.
Does anyone have expecience with what can be wrong?

I have tuned and syncronized The carburators after standard prosedure. Still it "shoots" when touching trottle.
The valvetiming is set to 10 degrees before DTC, so I asume Its lean mixture...or leak at intake manifold, but cant find The leak. I have also read that engines with 40mm Weber are using 12-14 degrees timing. Does anyone use that on your Murena?

Do I also have to use other coil or sparks when using Weber?
I hope someone can give me som advice.

Regards

Gjermund Dokken
Norway/Valdres

Sorry but I'm not clear on your problem as the English is not quite correct.  I need to understand your problem exactly first so can you tell me if I have understood you correctly - you say first that "it want run over idle speed".  I assume you mean here that it will idle, but will not run above idle?  Is that right?  If it won't run above idle, what exactly happens?  I assume as you try to increase the throttle it either cuts-out or runs so badly that the revs simply will not increase?  Can you say which please.

You say that "Still it *shoots* when touching throttle".  This I do not understand.  What do you mean by "shoots"?

As you open the throttle does it misfire badly, or spit back through the carburettors, or what?  Will it increase revs at all?

The timing should be correct at 10 degrees before top dead centre, and it doesn't need anything special.  A standard coil suitable for electronic ignition and virtually standard plugs - I recommend NGK BP6ES - are fine.

Since 40 DCOE Webers were never a standard fitment, I would also like to know the specifications of the carbs. really. Venturi sizes, Auxiliary sizes, jet sizes and emulsion tubes, etc?  This to ascertain whether the person who originally set them up got them approximately right.  Have you checked the float levels?

Have you checked the distributor mechanical advance is working properly first - this is important.  Vacuum advance is not really necessary with Weber DCOE's so this is not important, but you don't want an air leak here so if it is connected make sure the vacuum diaphragm or piping is not leaking.

Since these cars often have a leak in the head lamp vacuum system which will weaken the mixture causing engine running problems it would be best if you blank the head light system off temporarily whilst sorting the engine/carbs.

Roy
« Last Edit: August 15, 2015, 07:21:15 pm by roy4matra » Logged

Dokken
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« Reply #3 on: August 18, 2015, 01:51:03 am »

Thanks Roy for good answers and adwice.

I'll try to explane what I ment about "shooting". You are right: The engine spits back through the carbs when touching trottle. And the engine spits back through the carbs with airfilter on and without airfilters, its the same.

The engine run quite well at Idle speed, just a few "shooting", spitting back at Idle speed. But I have to turn the Idle mix screw approximately 4-5 turn unclockwise from seated if the engine shall run at Idle speed, without spitting back through the carbs.

After your adwises I have change to new spark plugs BP6ES, new coil and leads. And after running it a while a checked the spark plugs and it was very white. So I asume that the engine Get lean mixture.

I have blanked all vacumhoses to eliminate vacum leaks.
I have also checked the Distributor and it's alright.

Here are som spesifications for the carbs: the Main jet is 145, the air jet is 180 and the Idle jet is 50. The venturi is 40. I don't know exactly what you mean by Emulsion tubes?

I have also checked the float level, and it close at 8mm.

Since the Weber 40 DCOE not where standard fitment on the 2.2S, do You know which Weber that where standard on the 2.2S?

I have read that If you have to turn the Idle mix screw more than 2,5 turn unclockwise from seated the carb have to small jets. Therefore I have ordered new main jets, 165, to eliminate lean mixture.

I also Wonder If I should change the Idle jet up to 55 too, so that I might just turn the Idle mix screw from 1,5 to 2,5 turn unclockwise from seated. What do you think? Is there some sizes at the jets that belongs together? If so which do you recommand?

Thanks again for good questions and good adwises.

Best Regards

Gjermund

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Dokken
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« Reply #4 on: August 18, 2015, 01:58:56 am »

Hi Gjermund,

Welcome to "Matra Madness".  Smiley

I can't specifically help you with the problem but in answer to your last questions I run my 2.2 with 45 D.C.O.E's at 12 deg. BTC.

I use standard coil, leads and plugs. The standard distributor does have the vacuum advance hose removed though and runs fine.

Hopefully someone on here will give you some further advice.

All the best,

Graham



Thanks for answering Graham.

Can I Ask you what jet sizes you use at your 45 DCOE?

I checked mine and the Idle jet was 50, the main jet was 145 and the air jet was 180. I'm wondering since my spark plugs were very white, so I asume lean mixture.
Do you know which jets that goes together?

Best regards
Gjermund
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northmurena
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« Reply #5 on: August 18, 2015, 07:33:31 am »

Hi Gjermund,
there was in march a similar question about the Weber 40 DCOE at the german forum. Here is the link: http://www.matraforum.de/forum/index.php/Thread/5336-Bed%C3%BCsung-Weber-40-DCOE-f%C3%BCr-Murena-2-2/

It is - of course - in german but i think the part with the needed jet-sizes is self-explaining ;-)

The Murena S was never fitted with Weber by the factory, they took Solex but that´s not a real issue. There are several Murenas what are running with 40 or 45 Weber.

Hilsen fra Danmark
Kai
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roy4matra
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« Reply #6 on: August 18, 2015, 09:56:50 am »

Thanks Roy for good answers and adwice.

I'll try to explane what I ment about "shooting". You are right: The engine spits back through the carbs when touching trottle. And the engine spits back through the carbs with airfilter on and without airfilters, its the same.

O.K. well that does seem to suggest the mixture is very lean.

Quote
The engine run quite well at Idle speed, just a few "shooting", spitting back at Idle speed. But I have to turn the Idle mix screw approximately 4-5 turn unclockwise from seated if the engine shall run at Idle speed, without spitting back through the carbs.

For Weber carburettors which have coarse threads for the idle screws, 1.5 to 2 turns out should be about correct, so if you are having to use about 4-5 turns then it is much too weak even idling.  That suggests an air leak somewhere, so you need to check this first.  The idle system provides the transitional period over to the main system and if the idle is very weak, then the transitional period is going to be poor or non-existant.

Quote
After your adwises I have change to new spark plugs BP6ES, new coil and leads. And after running it a while a checked the spark plugs and it was very white. So I asume that the engine Get lean mixture.

I have blanked all vacumhoses to eliminate vacum leaks.  I have also checked the Distributor and it's alright.

That is good and sounds correct regarding the weak mixture.  But you may have air getting in elsewhere such as the manifold joints or the throttle spindles on the carbs. or even a porous manifold casting.  The best way to check the system is to connect a vacuum gauge to the inlet and see what reading you get when idling.  It should be around 21 inches of mercury.  If it is much lower let's say 15 inches (or even lower) then you have an air leak somewhere.

Quote
Here are som spesifications for the carbs: the Main jet is 145, the air jet is 180 and the Idle jet is 50. The venturi is 40. I don't know exactly what you mean by Emulsion tubes?

I have also checked the float level, and it close at 8mm.

Since the Weber 40 DCOE not where standard fitment on the 2.2S, do You know which Weber that where standard on the 2.2S?

First the venturis can't be 40 in a pair of 40 DCOE carbs., they would have to be smaller.  Possibly 34 or 36mm?  And what auxiliaries are fitted?  4.0 or 4.5 or what?

To have 40 venturis you would have to have 45 DCOE's.

Your float level setting sounds too great.  I would suggest 7mm since these are not new carbs.  The higher float level will help richen things a little.  The other jet sizes don't sound too far off although the main and air corr. jets are for the main system and a lot depends on things like which emulsion tubes being used as it is the combination of emulsion tube, main jet and air correction jet that sets the emulsification parameters throughout the rev range which is so important.  The emulsion tubes are one of the most critical parts in getting the mixture right yet one of the most difficult items to select.  However, this will only come after you have an air tight system and good idle.

As for the Murena 'S' that had twin Solex 40 ADDHE carbs. but that is not important since you can set up Webers or Dell'Ortos to do the same job.

Quote
I have read that If you have to turn the Idle mix screw more than 2,5 turn unclockwise from seated the carb have to small jets. Therefore I have ordered new main jets, 165, to eliminate lean mixture.

No, you do not really understand these carbs. I'm afraid.  They are difficult to set up properly even for the experts so guessing sizes will just waste time and money.  You have two systems in these carbs.  The idle system and the main system.  (well there is the starting system too, but we can forget that in this discussion)

The idle system consists of the Idle jets and holders and the idle screws.  The holders are like small emulsion tubes for the idle jets and the combinations have to be correct.  The main system, as I described above, consists of the emulsion tubes, main jets and air correction jets, and again the combination is very important to get the correct emulsification of the fuel throughout the rev range, plus the pump jets and bleeds have to be right in combination with the main system to provide the enrichment on sudden opening of the throttles and also provide top end enrichment at full or near full throttle.

If you have to turn the idle screws out to 4-5 turns just to idle, all you have done is to provide more fuel mixture at idle, please note: NOT a richer mixture just more of the same, but the moment you try to open the throttle it will go weak again, as the system is still weak - all you have done turning out the screws is compensated by adding some EXTRA mixture whilst idling.  Increasing main jets does NOT alter the idle system, only the main system.  You can't richen the main system to compensate for a weak idle!  These carbs. simply don't work that way.  The main system is not in play until about 2,000 rpm upward.

Quote
I also Wonder If I should change the Idle jet up to 55 too, so that I might just turn the Idle mix screw from 1,5 to 2,5 turn unclockwise from seated. What do you think? Is there some sizes at the jets that belongs together? If so which do you recommand?

Thanks again for good questions and good adwises.

Best Regards

Gjermund

Before you start changing idle jets or any other settings you need to check the manifold vacuum reading and eliminate any air leaks, which it sounds like you still have.  When you definitely have an air tight system then you can see how it runs and whether it needs resetting.  However, these really need setting up on a rolling road, and if done well will be worth the cost as you would never achieve the same by the hit-and-miss guessing method.  What is more is that you would only get charged for the actual jets or emulsion tubes used even though he might have used several sizes from his stock before settling on the right ones.  If you tried this you would have to buy all these and the unused ones would be a waste!

One final point - what mounting system is being used?  These carbs. should not be bolted solidly to the manifold.  They should have a set of 'O' rings between the manifold and carbs. and the fastenings should be either with Thackeray washers or Cosworth mountings and the locknuts should be tightened so there is about a 1mm gap all around.  The 'O' rings do the sealing and the carbs. are flexibly mounted to help avoid fuel frothing.  Just the same as on the 'S' (or any good Lotus twin cam set up for instance).

Roy
« Last Edit: August 18, 2015, 10:56:44 am by roy4matra » Logged

Dokken
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« Reply #7 on: August 19, 2015, 02:09:17 am »

Thanks again Roy for good adwices. I'm imprest over how well you know the Webers!

And You are right again, I do not understand these carburettors  :-(  but I wont give up and luckily You are giving me many good lessons about the carbs :-)


I'll have to go back to the garage and seek for air leaks, again!
I have checked for leak between the manifold and carbs with carburettor cleaner, and cant find (hear) increasing revs when spraying carburettor cleaner on the fitting between carbs and manifold.
So I assume as You suggest that it might be a leak at the throttle spindles on the carbs. Because I have about 10-20 inches of mercury, depending og the revy. I'm wondering If it can be a leak at the inspection plate between the two throttle spindles on each carburettor?? I don't know If There is placed a gasket underneeth the inspection plate. Because that was the only thing I did not check when I disassembled the two carbs.


I have the Thakeray washers and the " O-Rings", and its a gap of about 1mm between the carbs and manifold, all around. The "o-rings" seemed in good conditions when mounting the carburettors.

I'll also have to check the manifold joints again. Do You have an adwise how to check that too?

I have blanked all the vacum fittings to the manifold. So I dont know where to look for leaks, other than spaying carburettor cleaner around the fittings?
Do You really think it is a porous manifold casting, so I have to change manifold?

I have not disassembled the manifold from the engine to check the gasket between them, but I have sprayed carb cleaner between them without getting increase revs.

Thanks again for explaning me how the carbs operate and how all the jets, venturi sizes, auxiliary sizes and emulsion tubes works together in a system.

Thanks

Gjermund




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Dokken
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« Reply #8 on: August 19, 2015, 02:21:29 am »

Hi Gjermund,
there was in march a similar question about the Weber 40 DCOE at the german forum. Here is the link: http://www.matraforum.de/forum/index.php/Thread/5336-Bed%C3%BCsung-Weber-40-DCOE-f%C3%BCr-Murena-2-2/

It is - of course - in german but i think the part with the needed jet-sizes is self-explaining ;-)

The Murena S was never fitted with Weber by the factory, they took Solex but that´s not a real issue. There are several Murenas what are running with 40 or 45 Weber.

Hilsen fra Danmark
Kai



Takk Kai.
Ja, selv på tysk var dette selv-forklarende :-)
Kan jeg spørre hva for slags forgasser du benytter på din Murena?

Hilsen

Gjermund

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northmurena
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« Reply #9 on: August 19, 2015, 11:48:33 am »

Hej Gjermund,
ja, selvføgelig må du gerne spørg ;-)

P.t. har jeg ingen Matra. Jeg syntes at jeg har overstået Matra-sygdom nu efter mere end 30 år ;-) Derfor har jeg solgt min bil sidste år i december, den stå nu i en private samling i tyskland. Men min bil er/var en Murena S og har dermed Solex-carburettor.

Hilsen
Kai
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roy4matra
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« Reply #10 on: August 21, 2015, 09:09:55 pm »

Thanks again Roy for good adwices. I'm imprest over how well you know the Webers!

And You are right again, I do not understand these carburettors  :-(  but I wont give up and luckily You are giving me many good lessons about the carbs :-)


I'll have to go back to the garage and seek for air leaks, again!
I have checked for leak between the manifold and carbs with carburettor cleaner, and cant find (hear) increasing revs when spraying carburettor cleaner on the fitting between carbs and manifold.
So I assume as You suggest that it might be a leak at the throttle spindles on the carbs. Because I have about 10-20 inches of mercury, depending og the revy.

10-20 inches of mercury at varying revs does not really tell me a lot, unfortunately.  What I need to know is the level of suction with steady revolutions.  If it is idling smoothly at say 900 rpm what figure do you get?  Or do you have a problem getting a steady idle?

Another test normally would be to open the throttle wide briefly and see what level it drops to, but in your case I don't think you can do this as it simply won't run well enough yet.

Quote
I'm wondering If it can be a leak at the inspection plate between the two throttle spindles on each carburettor?? I don't know If There is placed a gasket underneeth the inspection plate. Because that was the only thing I did not check when I disassembled the two carbs.

I have the Thakeray washers and the " O-Rings", and its a gap of about 1mm between the carbs and manifold, all around. The "o-rings" seemed in good conditions when mounting the carburettors.

O.K. that's good.

Quote
I'll also have to check the manifold joints again. Do You have an adwise how to check that too?

Nothing different really to what you have tried.  If you spray carb. cleaner around the manifold joints when the engine is running, and there is a leak, then some of the spray should get drawn in and the revs would alter; so if you have done this with no change it does suggest there is no leak there.  However, if you have no leak and yet the mixture is very lean, then I think you have to look carefully at the carburettors again.

Quote
Do You really think it is a porous manifold casting, so I have to change manifold?

It is really not very likely but not entirely unheard of, so you do need to be aware of the remote possibility; and if you have no obvious air leak or low vacuum reading then you can discount this for now.

Quote
Thanks again for explaning me how the carbs operate and how all the jets, venturi sizes, auxiliary sizes and emulsion tubes works together in a system.

Thanks

Gjermund

One final thing is that you can see from those settings on the German website that your settings are already in the right area (without knowing what venturis and emulsion tubes, etc. that you have) and yours is possibly already richer than that one which ran fine, so just putting larger jets is not going to work.  You really have to find out why it is so weak first.

Another thought has just occurred to me.  Have you checked the engine compressions and the cam timing as well as the ignition timing?  Maybe we need to make sure the basics are correct first.

Roy
« Last Edit: August 21, 2015, 09:13:06 pm by roy4matra » Logged

Anders Dinsen
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« Reply #11 on: September 02, 2015, 09:05:52 pm »

I have a similar setup on my car, and it runs perfectly. I have had it set up professionally.

While I agree completely with Roy, my first advice to you would be to read up on the carbs. Carbs are actually very interesting devices, and the DCOE's are really something special. A classic book is the Weber Carburettors books by John Passini published in the early 1970's. I have volume 2 Tuning and Maintenance. Volume 1 explains the principles of the Weber carburettors.

My second advice is to have your engine set up professionally on a rolling road - once you have found your leak.

I have kept a record of all my tuning and experiments, and here are the jets and venturis I'm running now on my 40 DCOE's with Holbay cam and standard 2.2 head:

SummerWinter
Venturi3636
Aux4.54.5
Idle jets45F945F9
Idle Screws (L to R)5/85/8
Main jets130135
Emulsion tubesF9F9
Air correctors200200
Float level (mm)   7.57.5
Fuel  press (bar)   0.150.15
Pump jet4545
Pump bleed4040
Static idle adv (deg)1515
   
Good luck!
   
/Anders
« Last Edit: September 02, 2015, 09:09:53 pm by Anders Dinsen » Logged

'82 Murena 2.2 prep 142
'01 Grand Espace 24v
'08 Smart Fortwo 0,8 cdi
roy4matra
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« Reply #12 on: September 04, 2015, 09:09:05 am »

I have a similar setup on my car, and it runs perfectly. I have had it set up professionally.

While I agree completely with Roy, my first advice to you would be to read up on the carbs. Carbs are actually very interesting devices, and the DCOE's are really something special. A classic book is the Weber Carburettors books by John Passini published in the early 1970's. I have volume 2 Tuning and Maintenance. Volume 1 explains the principles of the Weber carburettors.

My second advice is to have your engine set up professionally on a rolling road - once you have found your leak.

I have kept a record of all my tuning and experiments, and here are the jets and venturis I'm running now on my 40 DCOE's with Holbay cam and standard 2.2 head:

SummerWinter
Venturi3636
Aux4.54.5
Idle jets45F945F9
Idle Screws (L to R)5/85/8
Main jets130135
Emulsion tubesF9F9
Air correctors200200
Float level (mm)   7.57.5
Fuel  press (bar)   0.150.15
Pump jet4545
Pump bleed4040
Static idle adv (deg)1515
   
Good luck!
   
/Anders


That's the first time I have seen anyone quote different summer and winter settings for Weber DCOE's, Anders! Smiley

Do you really find it too rich in summer or too weak in winter without that small change in main jets?

Roy
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« Reply #13 on: September 04, 2015, 07:48:40 pm »

That's the first time I have seen anyone quote different summer and winter settings for Weber DCOE's, Anders! Smiley

Do you really find it too rich in summer or too weak in winter without that small change in main jets?

Absolutely, Roy. It was set up on the rollers with a 140/200/F9 in the main jets, but we ran out of jets and it was still to rich in the high end and produced only 130 hp. But this showed that I was in the right "ball park", as they say. This was with 50F9's in the idle jets, but these cogged the plugs. 45F9's turned out to be right there by plug inspection (inspecting the plugs always shows the idle system, unless you master the "plug cut" described by Passini).

So when I had the idle right, I set off to find the right mains and settled on the 130/200/F9's where it was very free over the whole rev range. But during winter (10 deg C and below), it hesitated in 5th at 110 km/h, which turns out to be motorway cruising speed, so I upped to 135 and that cured this Little problem. This is the transition area around 2000-2500 rpm. So I decided: Let's have two different setups :-)

The car is off the road at the moment, but looking at my spreadsheet now a few years later, I think I'll put it on rollers again or buy a lambda meter to make absolutely sure it's not too lean in the top.

/Anders
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roy4matra
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« Reply #14 on: September 05, 2015, 10:24:11 pm »

That's the first time I have seen anyone quote different summer and winter settings for Weber DCOE's, Anders! Smiley

Do you really find it too rich in summer or too weak in winter without that small change in main jets?

Absolutely, Roy. It was set up on the rollers with a 140/200/F9 in the main jets, but we ran out of jets and it was still to rich in the high end and produced only 130 hp. But this showed that I was in the right "ball park", as they say. This was with 50F9's in the idle jets, but these cogged the plugs. 45F9's turned out to be right there by plug inspection (inspecting the plugs always shows the idle system, unless you master the "plug cut" described by Passini).

So when I had the idle right, I set off to find the right mains and settled on the 130/200/F9's where it was very free over the whole rev range. But during winter (10 deg C and below), it hesitated in 5th at 110 km/h, which turns out to be motorway cruising speed, so I upped to 135 and that cured this Little problem. This is the transition area around 2000-2500 rpm. So I decided: Let's have two different setups :-)

Since it works it is certainly one way of curing the problem but most owners would not want to keep having to switch back and forth, and the problem then could be that if you had a few warm days in winter or cold days in summer as an example, you could end up on the wrong setting.

When it is set to the smaller main jets, you say it hesitates in the transitional area, and I would have thought the better way to cure that is to increase the pump jet delivery as it suggests it is too small.  So I would have thought that reducing the pump bleeds, and maybe increasing the pump jet size too if closing down the bleeds does not cure it.

The pump jet system is meant to add the richness at the top end where generally things start to get a little weak, and you may be running a bit lean whilst cruising in 5th and that needs the extra richness that the pump jet system should be able to provide.

The other thing is that since you are running quite a bit extra ignition advance, you may need the timing to drop back when you open the throttle, so you need to make sure the vacuum advance retard is working correctly.  In fact I would be tempted to try 12 degrees rather than 15 and see what difference it makes.  Costs nothing except a bit of time.

Worth thinking about anyway when you get the car back on the road.

Roy
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