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286 Merc Flathead, 3 x 97's Need Help!

Discussion in 'The Hokey Ass Message Board' started by Psychobilly Boi, Sep 21, 2010.

  1. Hi Guys,

    After the glee that comes with putting a newly built motor into your hot rod I'm begining to have some serious issues which is taking the shine off. I come to my fellow HAMBers for advice.

    ***Updated 27.09.2010 at the bottom of this post***

    ***Updated 28.09.2010 at the bottom of this post***

    ***Updated 30.09.2010 at the bottom of this post***


    A couple of great guys on the hamp Flazoz and Lowsuire helped rebuild an old race motor I had the chance to grab off another HAMBer. 1942 Merc block, 4" Merc crank, 286 CID in total. Had forged pistons, an Isky 1007LD cam and some other goodies. Basically replaced what needed replacing (kept crank, cam, resurfaced the original Johnsons) and machined everything back ready to go.

    The ignition is stock 2 bolt crab with a new coil, rotor and cap. Lowsquire said the points and timing checked out ok prior to handing it over. We did have a bit of an issle getting the motor to advance enough at idle. The bolt controling the vaccum break is wound out but the mechanism is still there.


    Click below for a video of the start up



    The motor sounded nasty on break in. The 3 x 97's a I grabbed from Dickster went on to a Harrel 3x2 manifold. All 3 carbs are operated with a straight linkage. Fuel delivered via a electric fuel pump and low pressure regulator. Break in seemed to go fine. We noticed that a couple of lifters were loose and would back off causing it to sound like a sewing machine.


    At this point the car was running like a raped ape with the motor running to 5k easily and powerfully. The sewing machine noise came back due to the lifter backinig off and it seemed to me that the issue with the way the motor ran started at this point. As the noise got worse so did the way the motor ran - it would snap and pop out the exhaust, it would stumble and generally run rough.

    We took the manifold off and tightened the lifters, even Loctiting in an effort to save the expense of replacing. After doing this the first time the motor returned to its former glory and both Lowsquire and I were kinda amazed two lifters backing off slightly would have that much of an affect.

    Driving the motor for about an hour saw the lifter rattle come back and the motor degrade in performance to the point it would struggle up hills in any gear, misfire and generally carry on.

    Lifter Replacement

    I brought a set of lifters (know good ones) and Lowsquire installed them. When I picked the car up I noticed that it was not running as good as it had and it got worse the more I drove it. There is no lifter noise although it runs like it did when there lifters had backed off.

    The Symptoms

    The car starts and idles fine. The idle is a bit lumpy at 900RPM but the cam is a big cam. It sounds like it may be missing slightly at idle but its hard to tell accuratly. The car will rev fine and relatively smothly in neutral.

    When accelerating on the road the car will do a few different things:
    • Accelerate for a about 10 seconds then slightly bog and backfire
    • Going up a hill it will bog really badly in any gear when trying to accelerate
    • It will hold an RPM relatively smoothly btrying to accelerate off that will cause issues
    • You can sort of drive through the worst of the bog sometimes into the upper RPM ranges but it is rough even then
    • The bog (especially up hill) will force me to shift down even into first in order to get some sort of acceleration. Hills that would normally be fine in 3rd now need babying in 1st.
    • In order to get through the bogging I will need to almost let speed build up with about an inch or so of throttle - previously I could boot it almost to the floor in 1st and 2nd with the thing taking off.

    My Efforts So Far

    This is what I have done in an effort to resolve the issue:
    1. Check accelerator pump works on carbs (it does)
    2. Check that carbs are synchronised using a flow guage (they are)
    3. Check that linkage operates without binding and returns to idle ok (it does)
    4. Replace condensor with a new one (slight improvement in running)
    5. Correctly gap current spark plugs (some improvement again in performance)
    6. Gap new spark plugs to '25 and replace (a more noticable improvement but still having issues)

    So that is where I'm at - I know the potential of the motor because it ran exceptionally well at one stage. However, returning it to that state is proving difficult!


    Progress Update 27.09.2010

    1. Replaced coil - no improvement
    2. Check fuel pressure again - getting a constant 2.5 psi
    3. Replaced entire distributer with a known good one - marginal improvement
    4. Checked continuity between dizzy cap and spark plug. Found one suspect lead fixed and retested. No difference.
    5. Verified timing - is 5 degrees BTDC.
    6. Verified advance - advances to + 20 degrees at RPM
    7. Checked to see if fuel was leaking into the carb throat at idle (butterflys looked ok and we couldnt see anything dripping or hosing in).
    8. Checked to see if fuel was in the bowls - fuel level check ok (even immediatly after we experienced bogging).
    9. Battery - charging circuit works, battery has good charge (spins the motor over like crazy).
    10. Put timing light on every ignition lead and all have regular flashes
    11. Checked for vac leaks and tightened all carb and manifold scews, bolts and stud nuts.

    More clarification on symptoms

    AdamF came over and helped with some trouble shooting. There just seems to be a massive flatspot between 2,500RMP-5,000RPM. Even off idle its sluggish but from 2,500 its worse. If you keep your foot flat to the floor in first it will eventually wind up to 5k. Feathering the throttle doest make any difference. Acceleration is best just off idle (so if you hold 3k in first with the accelerator pedal as close to idle as possible and just give a slight push it will have a quick burst of acceleration but will quickly hit the sluggishness again).

    Doing some more trouble shooting last night the car at idle is even worse. Without changing anything since the last test run, the idle has droppped from 950RPM to 600RPM and is rougher.

    We have replaced just about all of the ignition componants which I guess leads to fuel?

    With such a large plenum on the manifold it could be possible that if one of the carbs was not functioning properly (ie blocked jets etc) that it would still allow the motor to run but would be leaning right out?

    I guess from here I need to swap out the carbs one by one onto a stock manifold and see what happens. Or I could block of two of the carbs on the current manifold and swap each into the centre position.

    Progress Update 28.09.2010

    1. Cleaned up lead placement (not for trouble shooting but to get it tidied regardless).
    2. Started engine and let idle for 8 or so minutes to come up to 180 degrees.
    3. Gave timing another check 0 at 8* BTDC.
    4. Took car for a drive around the block a couple of times - the motor runs better then it has since we replaced the lifters but the dead spot is still there.
    5. Compression check - read 80-85 PSI on all cylinders HOWEVER aparently the guage reads low or so I was told by its owner. All cylinders are consistant. I wouldnt trust the absolute PSI reading through. At least I know none of the cylinders are down compared to the others.

    More clarification on symptoms

    With the car at least semi-drivable last night I noticed a couple of things.

    The car is better at idle and off idle but with any more then say 1/4 or 1/3 of accelerator it begins to bog. If I hold a specific rev range (say 3k) with minimal accelerator and then press it again it will accelerate before bogging higher up the rev range.

    Holding it at 3k or 4k with minimal accelerator the car runs relativly smoothly with some slight popping out of the exhaust and a very slight misfire. Its not juddery or surging but again I'm gussing at this point its either running on idle circuit or off idle circuit not main jets?

    Plan of attack for tonight.

    1. Drain oil and look for chunks of cam lobe (oil needs replacing regardless).
    2. Remove main jets on each carb and examin for blockage, debris, issues etc. Check fuel draining out for anything suspect.See below for results
    3. Block of end carbs with block of plates and run each carb in turn in the centre. See if any one carb plays up.
    4. Run outside carbs only to see if over carbed (however it really ran well with all three originally).

    Well discovered alot of this sort of thing when I drained the fuel from one of the carbs:


    So, where to from here? The jets looked ok from what I could see there was no debris in the jets themselves but I'm guessing this stuff is throughout the carb. Complete disassemble, clean and reassemble? Partial rebuild? Blow through carb cleaner and hope for the best?

    Progress Update 30.09.2010

    Went over to Lowsquire's pad with the carbs in tow to blow apart and rebuild. The carbs all had some black crap in the bottom of the bowls. One of the carbs had a stuck powervalve. All emulsion tubes were removed, carbs thouroughly cleaned and reassembled. Big thanks to Lowsquire for the help. None of the jets were plugged, none of the emulsion tubes were bent, blocked etc.

    So not exactly a smoking gun in terms of finding the cause of this issue. Maybe the one blocked PV was enough but I suspect not.


    I noticed that the linkage was a little out of alignment and felt like it was binding. Certainly the differing arm and linkage lengths/alignment was meaning carbs were opening at differing rates. I've made sure all the arms are parralelle and equal lenght and all of the linkages are equal length. Will see what that does tonight.
    Last edited: Sep 29, 2010
  2. Sounds like a Vac problem and maybe a dud power valve , try blanking off a carb hole and running just on one sucker" as for the miss under power" valve train could be to tight or bent , be hard to tell without hearing it, check your dizzy shaft driving the points is straight and fresh plugs and plenty of battery power then on to a comp test"

    Bring it around with beer" after work one night

  3. what about timing, advance curve?
  4. xadamx
    Joined: Apr 18, 2003
    Posts: 1,170


    OK, I have a mildly built flathead with 2 97's on an Eddy Meyer hi-rise intake. Fuel is delivered through a low-pressure electric fuel pump and controlled by a dial-type pressure regulator just below the fuel block. One day, I was making a new set of cloth-covered plug wires and I accidentally turned the regulator down to 2 PSI when it was normally at 3 PSI. Long story short, just that little change gave me the same symptoms you're having now. It would stumble under load, hard acceleration, or uphill. It would run smoothly at idle and at a smooth, unloaded rpm...but stumble and bog otherwise. So, maybe your fuel pressure is too low...or insufficient power valves?

    One other time, a few years back in my AV8, I had similar symptoms as you currently was insufficient spark. I went through the distributor, coil, and condensor, checked the plug gaps and wires, checked all my grounds. It ended up being some corrosion at the points. I got new points, problem solved.

    Sounds like you're getting there, slowly. Some of the little things seem to be making a little difference, like gapping the plugs and new it seems like a solution is just around the corner. Good luck, and keep us informed of your progress...

  5. xadamx
    Joined: Apr 18, 2003
    Posts: 1,170


    It does sound like it could be something distributor-related :/
  6. AdamF suggested the same. I made sure all of the manifold bolts were tight, the carb stud nuts were tight. Is there a decent way to check for vac leaks without spraying flamible gas or liquid over a running motor?

    Hi mate, I have one block of plate I'll see what I can do with that. Due to it being a common plenum manifold I would have thought things like PV issues or carbs being slightly out of synch would have a far less noticible effect then on a standard carb. I'll give it a try anyway.

    Lowsquire did the lifter install - I'm pretty confident that he would have let me know if anything was bent out of shape. I can take the manifold off and check the lifter clearance.

    I didnt notice any play in the dizzy when I had it off today. Advance plate works when I rotate it by hand. I'll pick up a comp tester tomorrow and see what it tells me.

    As long as there is no hills between me in Hawthorn and you in (where is it you live?) I'll be there with many a beer!

    Thanks Mate!
    Last edited: Sep 21, 2010
  7. Hey mate, it very well could be this. Along with a compression tester I will have to pick up a timing light as well. Pretty ill equiped garage at the moment!
  8. I have the same dial regulator inline as well. Currently set to 2.5PSI. I dont know exactly what the other reg is set to (a fuel pressure guage would be a handy addition to the motor). I could try cranking it up to three.

    PV's could be an issue but it ran brilliantly with the same three carbs at one point. I could suspect a mechanical issue with one of the PVs but not the PV rating themselves?

    If you could tell me where to buy a set of 1942 points I would appreciate it! I've not been able to find any online unless I'm looking for the wrong thing?

    Thanks mate I will keep eveyone updated. I grabbed a local Bosch condensor so am assuming this will be ok - hope its not something to do with the rating of the condensor being too low?
  9. I guess I could put the timing light on each lead to see if there is a steady and consistant spark on each? Leads are the modern cloth covered wires with some old raja terminals I had on there from another set of leads. I guess lead replacement is something I can try once I have exhasted other options.
  10. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,682

    Bruce Lancaster
    Member Emeritus

    Lifter trouble associated with loss of power...repeated...
    You MUST check your valve lift now. It could be that you have no cam lobes left! Best case, lifter screws/threads were junk and just loosened, worst case the slack was caused by junk lifter material failing at base and grinding away your cam. You need to put a dial indicator on each valve head and rotate engine through full cycle of each... no need for disassembly of actual valve train unless bad news.
    You have original crab?? Keep brake as is, parts in place, backed off to near end of travel. Look over actual advance and see that all parts move smoothly.
    And do be suspicious of could temporarily use bits of tupperware or such to get them all up from head and all blocked apart. Try to get no wire closer to another or to metal than 1/2" and see what happens.
    Do you have the removed lifters?? What do bottoms look like??
  11. blown49
    Joined: Jul 25, 2004
    Posts: 2,212

    Member Emeritus

    I believe the dwell is established by the mounting of the two sets of points on the breaker plate. Bruce Lancaster posted a while back that many aftermrket foreign made points have poor mounting tolerences that would greatly affect the dwell. First thing I'd do is to try and find a set of Echlins. (I believe fourtyfordguy here on the HAMB may have them.)

    As to a condenser I'd suggest a FA66 (12 volt) from NAPA if available there.

    I ran 3 97's on my Merc for several years prior to installing the blower but I ran progressive linkage and had few problems.

    The valves changing settings bother me the most in your post as to decreased performance from start-up. Could the valve lash be too tight or too loose??? Do you have the clearance data for that cam???

    You have changed many things but the original decay in performance seemed to start with the valves.

  12. xadamx
    Joined: Apr 18, 2003
    Posts: 1,170


    Indeed. I had a sbc that lost power and backfired because of incorrect valve lash...I just spaced rechecking it after the fresh motor had run for a while. Another fairly easy thing to look into.

    ...and I have used the NAPA FA66 condensor as well, with good results.

  13. i had a dial type regulator (like the one in your pic) fail causing no fuel flow. it was brand new, now i run a fuel pressure gauge on the fuel block after the regulator. may want to make sure your fuel pressure is really what you think it is, good luck. one more thing, how did the plugs look?
  14. Hi Bruce, always good to hear from the master. Lowsquire checked the bottom of each of the old lifters, the face looks fine. They were original Johnsons that I had the lifter face reground and rehardened before installing. The lifters that backed out had a loose adjusting screw - it was very easy to turn the adjuster.

    The new lifters are from Mike Davidson (FlatAttack) and have a rockwell hardness of 60.

    I'll have to get a dial indicator and stand and check the lift on each valve.

    Ok mate the brake currently is still in place and backed out as far as I can back it out. The advance seemed to move smoothly when I was operating it by hand. Next step is to check the timing light on the motor again and see what the advance looks like in situ.

    Is there something that would allow the motor to advance with no load but stopping the advance under load? With three carbs operating in unison and a big common plenum intake I would expect the vac to drop very quickly off idle. Is it possible the advance break isnt receiving enough vac under load and is stopping the advance from operating?
  15. Is there a HAMBer who can sells these parts? Its impossible to get those parts here - I've been trying for a while.

    We tried progressive with a primary/secondaries configuration and it ran very lean. Returned all carbs to primaries and ran progressive, still ran lean. Ran straight linkage and it ran very very well prior to the issue springing up.

    Originally it seemed related to the lifters - problem went away the first time with taking the manifold off and adjusting the lifters. Came back. Took manifold off adjusted lifters and it went away but for a shorter period. Swapped lifters for brand new, good quality ones and issue didnt go away.

    The data I have for the cam is a "13 lash. The cam is a rare one so the data isnt thick on the ground as it is for currently produced cams. I can check the lash again and see what it is?
  16. Hi Zach thanks for the reply mate.

    The plugs looked a little rich one a couple but I had put this down to the motor doing nothing essentially but run at idle. There was some light oil on two of the plugs and this corresponds to two of the bores that didnt quite clean up as well as we wanted with the hone. I'll check comrpession on all cylinders to make sure we have decent compression.

    On thing that springs to mind is that when the motor was running strong it would lock up the back wheels when shifting from 2-1st - the compression lock was really strong. Now it will shift into first easily and will just pop and bog as the revs come up as you release the clutch.
  17. bykerlad
    Joined: Mar 14, 2009
    Posts: 260

    from australia

    flat motors are like a woman,they frustrate the hell out of you,but you still love em
  18. seb fontana
    Joined: Sep 1, 2005
    Posts: 7,129

    seb fontana
    from ct

    ""Is it possible the advance break isnt receiving enough vac under load and is stopping the advance from operating?""

    In my opinion yes, of course, with all three carbs opening at once..With a hot cam your available vacuum is low anyways...I don't feel there is a need to have the brake...Remove it and see what happens; might also let you run progressive linkage..
  19. 35hotrod
    Joined: Dec 7, 2008
    Posts: 81

    from Duvall, WA

  20. andyg
    Joined: Aug 10, 2007
    Posts: 560


    do you have a resistor in the wire going to the coil? if not it will toast your points in less than 100 miles sometimes. also what kind of coil do you run? most originals are bad even if they are "NOS". There is an acidic reaction that takes place over time even if they were never used.

    Also have you turned the engine over by hand? Could it be locking up from tight bearings or something like that?
  21. Hey Dan ain't got much to add but have you tried here for points -

    Last time I was hunting they had all types covered only to find mine were later ones....

    As for checking for vac leaks using flammable liquids, best way to do it. Another trick is to spray the exhausts with water to get an idea of which cylinder is missing. Its pretty obvious as it'll be the one which evaporates the slowest. Only issue is the siamesed centre port, gonna make it trickier.

    Good Luck.
  22. 32fordroadster
    Joined: Dec 4, 2009
    Posts: 144

    from Wisconsin

    Andyg might be on to something with the coil. I had a small block Ford in a effie pichup that would miss and backfire at mid to upper rpm's but would run fine at idle and off idle. I tried everything with no change, then I replaced the coil and it revved up like it was a completely different engine. It's something that could be easily swapped out just to eliminate it from the list of possibilities.
  23. HeyyCharger
    Joined: Dec 8, 2008
    Posts: 941


    I remember the build of this motor that Corey was posting up!

    Was really interested to see how it would turn out?

    Fingers crossed it's nothing too major!

    You planning to be at Chopped?

    Good Luck.

  24. Diavolo
    Joined: Apr 1, 2009
    Posts: 817



    It would be the first thing I did and the first place I would start looking. I would have checked lift before installing the new lifters, though. You might be in for another set of lifters and a new cam by now.
  25. 4t7flat
    Joined: Apr 15, 2009
    Posts: 266


    A friend of mine had a problem similar to yours. Engine ran fine in the garage,and for a few miles,sometimes 10 miles. Then it would start to miss and backfire ,then quit. The problem was he broke the outer bearing in the distributor. He put in another dist and the same thing happened. After three broken distributors,he called Mark Kirby,for help. Mark asked him what timing gears did he use? It turns out he used 49-53 gears with a 42-48 dist,and cover. That won't work ,the gears will move the cam forward looking for a thrust surface,and press against the dist shaft. Rather than change the gears,he switched to a post hole distributor,using a add on distibutor drive gear.
  26. andyg
    Joined: Aug 10, 2007
    Posts: 560


    easy check for spark is to put a timing light on each spark plug wire and see if you have an even spark. if you don't have a timing light then you can pull plug wires and hold them off the spark plug about a 1/4 inch. gloves would be a good idea for that!

    file and check point gap again too. if points are pitted at all it may be that you don't have a good resistor in the coil circuit.

    also i have had a lot of problems lately with Champion plugs. don't know why but I bought three different sets for my banger and it never would really run like I thought it should, then I bought a set of Autolites and didn't have anymore problems.

    of course all of the previous advise from others should be concidered too.
  27. UPDATE

    I'm using a Bosch GT40R coil so I thought I would look for another one online when I came across some information. The GT40R is designed to be used with an inline resistor and the coil should only see 9V at the positive terminal. I dont have a resister anywhere in the ignition circuit so the coil will be seeing 12V at the positive all the time. The post below sparked (no pun intended) my intrest in the coil.

    There is a GT40 which is designed for 12V at the positive terminal. Will not running a ballast resistor kill the points as described below or will it be ok?

    Where abouts is the resistor designed to go?

  28. Ok mate I will add to the list of things to try.
  29. After doing some research I've discovered that I've been feeding my coil 12V instead of 9V as it is designed to have a resistor inline to the +ive terminal. This cant be a good thing and I'll bump coil replacement to the top of the list.
  30. Hey HC,

    Well for about 25kms it turned out better then I could have imagined. Really strong motor. Now its turned out not so good! I've been threatened to be chucked out of the club if I dont get the rod to Chopped this year. I'll be there but need to get this issue sorted out.


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