308 GTS Carb high speed miss | Page 2 | FerrariChat

308 GTS Carb high speed miss

Discussion in '308/328' started by bl10, Nov 1, 2020.

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  1. bl10

    bl10 Formula Junior

    Jun 8, 2011
    377
    Chatsworth, CA
    Full Name:
    Barry Leavengood
    I'll find out today if the increase in fuel pressure fixed/helped the problem. Since I live in Los Angeles I have to wait until the traffic dies down.

    Kcabpilot Yes I replaced the filter with the same cartridge type.

    Tony No vacuum leaks I can find. Idles perfect at 1K, all carbs synced great and respond to idle screw (rich/lean) as expected. Float settings triple checked. Jets 60 idle and 130 main which is what I ran before. Tried 55 and 125 (stock) and problem got worse. Coils are new 6ohm Pertronix but they didn't change anything over the stock coils without ballast resistors.

    Aaron I don't believe rotor phasing could be off in the rear distributor unless the Pertronix setup is phased wrong which I have no control of. The front bank on the other hand could be out of phase, however, I moved it the full advance / retard range (adjusting slots on distributor mount) and it didn't change anything. If it was out of phase I would think it would drop the whole bank.

    BigTex The grounds are fastened to a common bolt on the oil cooler mount. Here is diagram of North American fuel system. Item 59 is the regulator or at least appears to be. Note item 60 is a fuel line that connects the output side of the fuel pump to the regulator on the input side of the pump. When I checked fuel pressure with the stock fitting it was only 2psi(not enough). When I blocked the return lint it pegged my gauge at 6+ psi (to much). So I put a restrictor in the return line to get it to 4.9 psi which is what I going to test today. I think, however, I need to reinstall the factory pressure regulator at the pump as the tank head pressure changes the system pressure to much.

    In thinking about it I wonder if the purpose of the regulator is to minimize pressure change due to head pressure created by the fuel tank pickup exiting the bottom of the tank. I know on mine with half full tanks the pressure went from 3psi drawing fuel out of a gas can from the top to 6 + psi when installed in the car. It looks to me like the head pressure (pressure created by fuel in tank) is added to the pressure created by the fuel pump and they use the regulator to control that. I haven't calculated it but I would expect to see a 4 or 5 psi difference between full and empty tanks.

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    Thanks for all the input.

    Barry
     
  2. ATSAaron

    ATSAaron Formula 3
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    Jun 1, 2004
    1,120
    Shady Shores, TX
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    Aaron Bunch
    Earlier you said it was popping. Fuel problems don't pop. They "gasp" or "bog"

    I don't think fuel pressure is as critical...because the fuel regulated by the float/needle and seat before it gets to the metering parts of the carburetor. As long as you aren't over powering the needle and overflowing the bowl nor sucking the bowl dry you should be OK.

    Are you sure you have the Pertronix dual pickups wired to the right banks?

    Try playing with ignition timing. Run an initial of 0 degrees and see what happens, then do the same thing with an initial of 12 degrees. I want to know if the problem gets better or worse or happens at a lower or higher rpm.

    Aaron
     
  3. bl10

    bl10 Formula Junior

    Jun 8, 2011
    377
    Chatsworth, CA
    Full Name:
    Barry Leavengood
    The saga continues
    Just took it for a test drive with the fuel pressure up from 1.9 lbs to 4.9. It made a world of difference. It now pulls hard to 6500 which is far as I wanted to take it albeit with some missing above 4500 but nothing like before. No more popping (back) which I think was it going lean (ever see a supercharged engine pop back due to lean condition. Really nasty).

    Aaron your correct. If it actually was running out of gas as in empty or fuel line blockage and so on it will gasp. I think in my case the gas flow was so low due to low fuel pressure it would go lean and pop back.

    Fuel pressure is still not right as pressure continues to rise a little the longer I run it. After the test drive this morning it went from 4.9 to 5.75 psi. I'm going to reinstall the fuel pressure regular at the pump and see if that stabilizes the fuel pressure.

    I do think the remaining relativity small miss is ignition related.

    Last night (dark in garage) I ran it a bid to check for arcing, all looked good.
    Next up is rechecking the timing on both banks both for initial and advance at 5k now that it will relativity cleanly rev that far. I'm shooting for 34 degrees at 5k no matter what the initial is so long as its close to 7degrees BTC. I think its Ok but ill check it again.
    Assuming the timing is close enough Ill check the plug and coil leads resistance. One thing I'm not sure about is the plug extenders. I'm currently running 4 of the original brown/black extenders and 4 new ones from Superformance. I thought the Superformance extenders were OEM duplicates as far as function goes but it turns out they have virtually no resistance while the OEM extenders have 11.4 on the 200K scale. I think I'll try bypassing the original extenders to see if it makes any difference. I will also check the resistance on the 4 original extenders I'm running to insure they are OK.

    Thank for the help everyone. It's actually running pretty well now.

    Barry
     
    ATSAaron likes this.
  4. Nuvolari

    Nuvolari F1 Veteran
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    Sep 3, 2002
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    Rob C.
  5. bl10

    bl10 Formula Junior

    Jun 8, 2011
    377
    Chatsworth, CA
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    Barry Leavengood
    Thanks I'll take a look at it. The reason I using a different pump is as you surmised cost and I had switched out the pump 30 years ago for a Stewart Warner with pressure regular (pump is no longer available) when the original Corona died and never gave it another thought. It worked great The Stewart Warner rotted from the inside while sitting and had to be replaced. Is your car the North American version? I ask because mine has the pressure regulator piping per the drawing above and I noticed yours in the link doesn't. The drawings show it both ways with and without which is why I didn't reinstall it. I'm going to measure the calibration hole in the banjo bolt today to see what size it is. I suspect it's larger than the 60 thou the manual references which is actually for a GT4 with no year mentioned that I can find but it does show the fuel pump both with and without the regulator.
    Thanks
    Barry
     
  6. Nuvolari

    Nuvolari F1 Veteran
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    Sep 3, 2002
    6,370
    Toronto / SoCal
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    Rob C.
    Mine is a 77 USA 308GTB. There is no regulator from factory. Fuel runs from the tank to the filter to the pump and straight up to the carbs. I've never had any fuel starvation issues and the car pulls full to redline no problem.

    Thinking about the fuel system I am reminded that the tank does have a strainer on the inside that is part of the outlet nipple. If the car sat a long time this strainer could be clogged so it may be worthwhile to unscrew the nipple from the tank and check to see how clean it is. Of course you need to empty the tank and take all the necessary precautions with the fuel fumes but it is a worthwhile thing to check given everything you have done so far.
     
  7. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    Jan 11, 2001
    25,040
    30°30'40" N 97°35'41" W (Texas)
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    Steve Magnusson
    #32 Steve Magnusson, Nov 4, 2020
    Last edited: Nov 4, 2020
    The F documentation (the 1977 North American 308GTB OM Addendum) shows that they did come with the regulator (but very easy to remove and adopt the euro layout):
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    My impression is that the "regulator" is more of an "over-pressure relief valve" (in case the fuel line gets blocked/kinked) rather than something that actively regulates the fuel pressure (note the English description is "anti-downflow valve", not "regulator").
     
  8. bl10

    bl10 Formula Junior

    Jun 8, 2011
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    Chatsworth, CA
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    Barry Leavengood
    Steve
    After really searching the web I believe your correct. Its mentioned over and over that its a "safety" device. I cured most of my problems by putting a restrictor in the return line to keep the pressure up. (I'm not using the "regulator") However the way I'm doing it now is kind of mickey mouse so I ordered another fuel pump today identical to the one I ran for 5 years with no problems. What I thought the "regulator" was for was to stabilize the fuel pressure fluctuations due to fuel tank head pressure but I guess thats not the case so I will leave it out of the new pump plumbing and remove the restrictor from the return line and every thing should be rainbows and lolly pops. What lead me down this path was very low fuel pressure (1.8psi) with my new 3.5psi 42gpr pump which was causing most of my problems. When I blocked the return line it pegged my 6psi gauge so I figured the half full tanks were adding to the pressure because I wasn't using the "regulator". Some of the stuff is really weird. The "calibration hole" in the banjo bolt on the last carb is supposed to be a little under 60thou according to the manual. So I measured mine and its 71 thou. which makes a big difference in how much fuel gets routed back to the tank.

    Anyway I hope putting the carter P4070 vane pump (same as I used to run) on will solve the fuel problems. Its quiet and about the same specs as the HARDE 18872 or Facet type pumps.

    Thanks for your input.

    Barry
     
  9. bl10

    bl10 Formula Junior

    Jun 8, 2011
    377
    Chatsworth, CA
    Full Name:
    Barry Leavengood
    Nuvolari
    Sorry missed your post. My strainer fell apart when I pulled the tank fitting to check for crap in the bottom of the tank so I just left it out. Even after sitting since 1992 there was still gas in the tanks and it smelled pretty much like gas. The tanks were very clean inside much to my amazement. Probably because they are alum. There has been no debris in the filter. (I've checked it several times).

    Thanks
    Barry
     
  10. bl10

    bl10 Formula Junior

    Jun 8, 2011
    377
    Chatsworth, CA
    Full Name:
    Barry Leavengood
    Its been a while but I'm still fighting the same high speed miss.
    So you don't have to reread the 1st part of this here is what I've done so far.

    So here's what I've done so far.

    1. Changed out points for Pertronix Igniter II in rear dizzy. Lubed both advance mechanisms.
    2.Changed all valves in rear head with new valve seals. Lapped valves, no leakage.
    3.Changed engine related seals.
    4.Changed outer cam drive bearings.
    5.Changed to Hill tensioners.
    6.Changed water pump.
    7. Switched to Derek Whites's cam pulleys with round tooth belts.
    8. Adjusted valves. In at 22-23 Ex at 32-33 .
    9. Degreed Cams Intake at 106 CL Exhaust at 109 CL (1 degree retarded.)
    10. Synced Carbs a bunch of times.
    11. Verified timing was advancing in both dizzys. (34 degree marks line up)
    12.Changed to 6 ohm Pertronix coils. (It got a little better)
    13.Changed plug wires to Accel SS per Birdman. (It got a little better)
    14.Changed plug extenders. Also tried it without extenders, no change.
    15. Changed from Champ N9YC (what I always ran in the old days) plugs to NGK BPR5IX Iridium then to NGK PBR6IX then back to Champ N9YC. (all new) (Virtually no change) Gaped at 24 thou, even tried 30thou.
    16. Changed from 130 main jets back to 125 and accelerator nozzles back to 30 from 40 (both stock) got much worse.
    17. Blew out all jet passages and put 130 jets and 40 accelerator nozzels back in. (much better)
    18. Moved front Dizzy the full range available with no change (spark controlled by read dizzy but maybe set out of registration, not the case)
    19. New fuel pump (cheap from ebay) then 2nd new Mr Gasket fuel pump as 1st cheap one stopped working.
    20. Along the way I completely dissembled and cleaned all 4 carbs.
    21. Although dizzy caps and rotor are old they appear to be in great shape.
    22. Soldered fuse panels across top to eliminate intermittent electrical problems. (did this early on)
    23. Verified TDC marks on flywheel.
    24 Changed Dizzy caps and rotors.
    25. Rebuilt Carbs again in case of something plugged up.
    26. Verified voltage to coils 12+ even tried jumping coils directly to battery.
    27. Per Pertronix verified distributor ground resistance at .04 ohm even ran jumper directly from the distributor with the Pertornix units to the neg post of battery.
    28. 3rd new fuel pump (vane type like stock) and set and verified fuel pressure at 4psi at full throttle under load going through the gears.

    Stopped worrying about this as I had to get it through Calif smog which meant putting the cats and air pump back on and adjusting the idle on the carbs until I was blue in the face. It passed although not as clean as last time when it had the original factroy R1, R2 points with retard switch.

    The thing that mystifies me about this is that it passed smog without a hiccup but runs like crap above 4K. It will run to 65 hundred but with a major miss (like fouled plugs but the plugs look great). When I run it up with a good tach on it, it just goes flat at about 4500 and I really have to force it to get to 5000 or 5500.

    After the smog test I removed the cats and smog pump primarly because I don't want to screw up the cats by running it two much as I will need them again in two years and Calif is really picky on after marked cats. While I had it apart I went ahead and put some Heatshield armor on the rear header as I had removed the factory head shields and even though I painted the header with "ceramic" header paint and cured it per the instructions the heat generated by the header was extraordinary. While adjusting the carbs the hot air off the headers was unbearable. Anyway the Heatshield armor really cooled it off. Way better than stock.

    So it's back to the miss.

    I've decided to reinstall the stock point type ignition with both R1 and R2 points along with stock coils, ballast resistors and retard switch. If this doesn't do it I'll find a shop with a dizzy machine and double check the advance curves even though the rear dizzy (with the Pertronix units) looks fine with a timing light.
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    I have a couple of questions about the coil and condenser wiring.

    The picture is of a stock coil. I just want to verify the wiring.

    The yellow wire, not in the picture, is hot from the ign switch and goes to the positive post of the coil. (full 12 + volts to the coil)
    The red wire goes from the negative post of the coil to the ballast resistor.
    The black wire goes from the other side of the ballast resistor marked D to the R1 points.
    The Radio noise suppression capacitor goes from the negative post of the coil to ground.

    Condensers

    There are two condensers on each distributor. One has a single wire out while the other has a wire out of each end (two wires)

    My documentation indicates that the single wire condenser goes to the R1 points along with one of the wires from the dual wire condenser with the other wire from the dual wire condenser going to the R2 points. So you end up with two condenser leads on the R1 points and one on the R2 points. Does this sound correct?

    Thanks in advance

    Barry
     
  11. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    25,040
    30°30'40" N 97°35'41" W (Texas)
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    Steve Magnusson
    Yes -- see Fig 66 on page 74 of the 150/78 OM.
     
  12. bl10

    bl10 Formula Junior

    Jun 8, 2011
    377
    Chatsworth, CA
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    Barry Leavengood
    Steve
    Thanks, I wasn't absolutely sure about the coil wiring as the point type ignitions on cars I've worked on had the ballast on the positive side of the coil between the 12v supply and the coil.

    Believe it or not I looked at the OM but the page 74 was stuck to 75 and I skipped right by it. Also looked at my repair manual (L 13) but don't see ballast resistors.

    Just out of curiosity on mine only one of the coils has a radio noise suppression capacitor. Is that stock? It's not a problem as the new plug wires have some resistance built in. Just in passing there is also a radio noise suppression capacitor on the fuel pump.

    Barry
     
  13. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    Jan 11, 2001
    25,040
    30°30'40" N 97°35'41" W (Texas)
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    Steve Magnusson
    The 161/78 SPC says that each coil should have a noise suppression capacitor, but it's not a huge deal, and I wouldn't worry about it unless you have some specific radio noise issues.

    BTW, page L13 in the 308GT4 WSM is for a 1975 euro version 308GT4. Page O7 for a 1975 US version 308GT4 is closer to what you have, but the 150/78 OM is the exact reference for your 1978 US version 308GTS.
     
  14. bl10

    bl10 Formula Junior

    Jun 8, 2011
    377
    Chatsworth, CA
    Full Name:
    Barry Leavengood
  15. bl10

    bl10 Formula Junior

    Jun 8, 2011
    377
    Chatsworth, CA
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    Barry Leavengood
    So I finally got to the bottom of my high speed miss. I decided to pull the Pertronix out and put the original points, coils and micro switch back in. Keep in mind it was running well enough with the Pertronix to pass Calif smog.

    I did the front dizzy without the Pertronix first and still had the miss. No change. So I pulled the rear dizzy and discovered the new SF rotor was burned on one corner from arcing. So I put the points back in and what do you know after setting the timing per the manual on both banks and resetting the idle mixture (It changed a lot on the rear bank) It now runs strong to 7K never missing a beat. Its a little sluggish probably because I had put 135 mains in it thinking it was to lean. I put the 130's I had been running when it was my daily driver 20 + years ago today but haven't had time to take it out.

    My question to anyone who knows about the Pertronix Igniter II MR183 (both modules in one dizzy) is can the modules be wired to the wrong bank and the engine still run. Mine clearly has a phasing problem with the rear dizzy (the one with the Pertronix modules in it. The front rotor looked fine. (The SF rotor contact area in narrower than the stock rotors which probably explains the arcing).

    As mentioned before the miss was at 35K and above.

    With the points it starts great with virtually no popping back through the carbs when cold and the idle is easy to set due to the r2 point retard which requires more throttle blade opening to maintain the idle. I had have the carbs completely closed and even put a extra throttle spring on the rear bank to get a 1K idle with the Pertronix due to no R2 retard. I idles now at 975 rpm with the AC on and 985 with the AC off.

    I will speak to Pertronix tomorrow about this unless someone out there indicates the modules were wired backwards.


    Thanks
    Barry


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  16. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #41 Steve Magnusson, Jan 17, 2021
    Last edited: Jan 17, 2021
    Looks more like a phasing issue to me (modules-to-housing) -- causing the rotor tip end to not overlap the contacts in the dist cap when the spark occurs so the spark jumps off the side of the rotor tip (and the Pertronix has a strong enough spark to jump the huge distance at low RPM but misses at higher RPM).
     
  17. bl10

    bl10 Formula Junior

    Jun 8, 2011
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    Barry Leavengood
    Yep I agree. But you can only install the Pertronix mounting plate and modules one way. It uses the existing point mounting holes. At least I think it can only be installed one way. Anyway I'll talk to Pertronix tomorrow to see what they say.

    Barry
     
  18. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    Jan 11, 2001
    25,040
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    Steve Magnusson
    Using the wider 124288 rotor shown in post #2 would give you some improvement -- but it still seems like something else is wacky (I think having the wrong module going to the wrong bank would add a 45 deg error in the rotor to the cap relationship -- but it should affect both, and you indicate one is OK?).
     
  19. Miklas

    Miklas Karting

    Dec 10, 2018
    79
    Luxembourg
    Can the distributor shaft be moved one tooth in relation to the camshaft in order to fix the phasing issue?
     
  20. bl10

    bl10 Formula Junior

    Jun 8, 2011
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    Chatsworth, CA
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    Barry Leavengood
    Miklas.
    It doesn't do any good as it affects the ignition timing so the whole distributor has to be rotated to compensate for moving the shaft. I'm going to look at it again to see if there is another way to install the Pertronix unit but I don't think so.

    Barry
     
  21. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    [QUOTE="Steve Magnusson, post: 147682261, member:...(I think having the wrong module going to the wrong bank would add a 45 deg error in the rotor to the cap relationship -- but it should affect both, and you indicate one is OK?).[/QUOTE]
    I should've said: "I think having the wrong module going to the wrong coil/bank would add a 45 deg error in the rotor to cap relationship in the distributor with the pick-ups, but the slave distributor could still be OK (if the 5-8 dist was wrongly installed with the 5-8 rotor pointing at the red notch in the 5-8 dist housing when the crankshaft was at the cyl #1 firing position).
     
  22. bl10

    bl10 Formula Junior

    Jun 8, 2011
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    Chatsworth, CA
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    Barry Leavengood
    Steve

    Sorry I missed your post. Actually the original (stock) rotor distributor terminals are wider which is why I probably didn't see the arcing before. You are correct I didn't see any arcing in the front dizzy which leads me to believe the rear cyl bank module is out of registration. The mechanical advance could factor into ii as the mechanical advance moves the rotor in relation to the cap plug terminals. While the front dizzy's mechanical advance is not used to control spark advance it does move the rotor the same as the rear.

    Your right about the spark with the Pertronix. Since I was using the low ohm coils to it had a huge spark.

    I'm not sure how I would even check the location of the Pertronix modules for correctness. I remember a thread that mentioned one of the modules was out of registration maybe I'll look for it.

    At this point it seems to be running fine and I expect the jetting change will perk it up a little. I'm not interested in absolute HP, just that it runs and revs as it should. When I let the boy racer out I have a 670 hp ZL1 Camaro parked next to the 308 that is scary fast.



    Barry
     

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