Close



Page 3 of 3 FirstFirst 123
Results 51 to 68 of 68
  1. #51
    FEP Supporter Broncojunkie's Avatar
    Join Date
    Jan 2015
    Location
    Barboursville, WV
    Posts
    1,148

    Default

    Mrriggs, I missed your comment earlier. Yes, I reset the timing. It will run with the timing advanced and actually sound ok until driven.
    79 Pace Car - 331, t5
    79 Cobra - working on 351w, t5
    86 coupe - rotbox roller
    86 coupe - working on 408w, c4
    88gt - 302 efi, t5

  2. #52
    FEP Member
    Join Date
    Dec 2016
    Location
    Grand Rapids, MI
    Posts
    467

    Default

    Without rereading the entire post. I am assuming the cam has been constant throughout this whole ordeal?
    '89 XR-7 5 Speed
    '95 SC 5 Speed
    '91 Crown Vic P72 351W
    '97 Thunderbird
    '85 Ford LTD Squire

  3. #53
    FEP Supporter Broncojunkie's Avatar
    Join Date
    Jan 2015
    Location
    Barboursville, WV
    Posts
    1,148

    Default

    Quote Originally Posted by KevinVarnes View Post
    Without rereading the entire post. I am assuming the cam has been constant throughout this whole ordeal?
    Yes sir. I was going to say it's the only thing that has been constant, until I started tearing it down this evening (still in the car). I noticed what I would consider excessive slack in the timing chain. I verified tdc and it doesn't appear to have jumped time, but could the slack in the chain cause my problem? It is excessive for having less than a couple hundred miles on it, but I've seen high mileage engines with the same amount. I would say just under a half inch of slack.
    79 Pace Car - 331, t5
    79 Cobra - working on 351w, t5
    86 coupe - rotbox roller
    86 coupe - working on 408w, c4
    88gt - 302 efi, t5

  4. #54
    FEP Supporter Broncojunkie's Avatar
    Join Date
    Jan 2015
    Location
    Barboursville, WV
    Posts
    1,148

    Default

    Pulled the cam and there's no damage...what lifters are accessible look fine. I didn't degree the cam, but I'm installing a new x303 and Cloyes double roller timing set. Pushrods, cam bearings, dog bones, etc look fine as well.
    79 Pace Car - 331, t5
    79 Cobra - working on 351w, t5
    86 coupe - rotbox roller
    86 coupe - working on 408w, c4
    88gt - 302 efi, t5

  5. #55
    FEP Supporter Broncojunkie's Avatar
    Join Date
    Jan 2015
    Location
    Barboursville, WV
    Posts
    1,148

    Default

    Well, backfire is still there. Timing was much easier to set. Seems to be running a little better, but I still have the backfire on deceleration. Actually, it's changed a bit. It will backfire after goosing the gas pedal. A little on deceleration, but not quite as bad. Did some cleaning up of contacts on the rotor (msd distributor), ohmed the cap/rotor contacts, wires, etc. I'm going to revisit carb/fuel again, I guess.
    Last edited by Broncojunkie; 04-11-2020 at 08:42 PM.
    79 Pace Car - 331, t5
    79 Cobra - working on 351w, t5
    86 coupe - rotbox roller
    86 coupe - working on 408w, c4
    88gt - 302 efi, t5

  6. #56
    FEP Supporter Broncojunkie's Avatar
    Join Date
    Jan 2015
    Location
    Barboursville, WV
    Posts
    1,148

    Default

    Cleared up some more after a good drive to clean out the lungs. Still quite a bit of excessive popping and occasional backfire on deceleration, but only after decelerating after getting in the throttle. Not right, but getting better. I spent some time retuning the carb and she's starting to sound healthier, but it's raining and I haven't been out for a drive. If it clears up tomorrow, I'll see how she does.
    79 Pace Car - 331, t5
    79 Cobra - working on 351w, t5
    86 coupe - rotbox roller
    86 coupe - working on 408w, c4
    88gt - 302 efi, t5

  7. #57

    Default

    How much vacuum does your cam make ? Does it have a lot of duration ?
    It not uncommon for an aggressive cam to need a lot of base timing. I’ve had motors that needed 25* of base timing. Try limiting your distributor to about 10* of mechanical advance. No vacuum advance. Set timing to be 34-35 total advance revving till it stops advancing. Forget about base timing for now.
    Most durasparks come out of the box with 36* of mechanical advance. Your msd is easy to limit the mechanical advance. Also some light springs are probably in order to speed up the advance curve. You probably want full advance by 2800 rpms.

    Do you have a ground strap on the motor ?

  8. #58

    Default

    Have you considered where your coil is getting power from? Have you considered adding a relay and hooking up a direct from battery run for power and ground just as a precaution?

    The ground straps can go bad. Try adding a heavy ground from the engine to a clean spot on K member. Sure cleared up a lot of insanity on my sonís 86.

    Ive seen hella slop on a Ford timing set run not only just fine but horsepower wise even great. Especially if the timing set it had initially advanced the cam or ran it straight up. That 3-4 degrees of retard that ends up there is good for building more horsepower up high. Pretty sure thatís why my old worn out 1/2 million mile beater runs as hard as it does. Iíve rode in head/cam/intake cars that did not run like my cam/intake car. Itís always a humorous conversation if there are rides in both cars involved.

    Anyway - Iím curious how your cam is ground and where the cam timing is at.

    Have you considered stuff like exhaust leaks or maybe a valve or two with some crap on it thatís not letting it close and seal properly?

    Grasping at straws. I sure hope you get it sorted!
    Last edited by erratic50; 04-13-2020 at 12:56 AM.

  9. #59
    FEP Supporter Broncojunkie's Avatar
    Join Date
    Jan 2015
    Location
    Barboursville, WV
    Posts
    1,148

    Default

    Quote Originally Posted by 4idfox View Post
    How much vacuum does your cam make ? Does it have a lot of duration ?
    It not uncommon for an aggressive cam to need a lot of base timing. Iíve had motors that needed 25* of base timing. Try limiting your distributor to about 10* of mechanical advance. No vacuum advance. Set timing to be 34-35 total advance revving till it stops advancing. Forget about base timing for now.
    Most durasparks come out of the box with 36* of mechanical advance. Your msd is easy to limit the mechanical advance. Also some light springs are probably in order to speed up the advance curve. You probably want full advance by 2800 rpms.

    Do you have a ground strap on the motor ?
    It is an x303 cam. Fairly aggressive. It has around 15 inches of vacuum at idle (5 speed).

    I played with it some more today and got most of it cleared up. Still a noticeable stumble and occasional backfire. I advanced the timing quite a bit. The last few adjustments, I made without the timing light...so I'm not sure where it is at this point. I'm going to try and address the slight misfire before playing with the timing any more. I put a cheap set of plug wires on it after some weird symptoms. I hooked up the timing light and moved the pickup cable around to each plug wire and watched the pulse. I noticed there's an occasional dead spot. That is, the pulse would skip every now and then. I swapped wires thinking the Accels had a couple bad ones, but the new wires didn't make a difference. Miss could just be something as simple as carbon buildup on the plugs. I did have it jetted up yesterday, but I swapped jets a few times and got it leaned back out. Idle mix leaned out as well. It seems to clear up with the secondaries opened up, though. Ran like garbage with larger jets in primary (75ish). Lowered to 64, it runs way better at part throttle. Secondaries still jetted up with 78's and it seems to do great at WOT. Power valve is a 4.5. I may need to go back up in size, according to my vacuum reading. It has a single power valve (none in secondary). I'm definitely no expert in tuning carbs but what little I do know seems to have gone out the window with this car. It likes a small primary jet and large secondary with a pv that seems too low. Carb is a 650 quick fuel brawler. Seems to me it would want more fuel, but maybe I'm looking at it wrong. It's a 331 stroker with aluminum heads (185cc) and 58cc chambers....compression should be around 10.5:1 and running premium pump gas. Maybe I should have gone with a 750 carb for more air?
    Last edited by Broncojunkie; 04-13-2020 at 11:01 PM.
    79 Pace Car - 331, t5
    79 Cobra - working on 351w, t5
    86 coupe - rotbox roller
    86 coupe - working on 408w, c4
    88gt - 302 efi, t5

  10. #60
    FEP Supporter Broncojunkie's Avatar
    Join Date
    Jan 2015
    Location
    Barboursville, WV
    Posts
    1,148

    Default

    Quote Originally Posted by erratic50 View Post
    Have you considered where your coil is getting power from? Have you considered adding a relay and hooking up a direct from battery run for power and ground just as a precaution?

    The ground straps can go bad. Try adding a heavy ground from the engine to a clean spot on K member. Sure cleared up a lot of insanity on my son’s 86.

    Ive seen hella slop on a Ford timing set run not only just fine but horsepower wise even great. Especially if the timing set it had initially advanced the cam or ran it straight up. That 3-4 degrees of retard that ends up there is good for building more horsepower up high. Pretty sure that’s why my old worn out 1/2 million mile beater runs as hard as it does. I’ve rode in head/cam/intake cars that did not run like my cam/intake car. It’s always a humorous conversation if there are rides in both cars involved.

    Anyway - I’m curious how your cam is ground and where the cam timing is at.

    Have you considered stuff like exhaust leaks or maybe a valve or two with some crap on it that’s not letting it close and seal properly?

    Grasping at straws. I sure hope you get it sorted!
    Good point about the 12v supply for the coil. The coil is ran directly from the spark box, which gets power from the battery (and also has a switched power source from the harness). At one point, I tried wiring the switched source straight from the battery, as well (fused, of course). Didn't seem to make a difference.

    As for a ground strap, I do have a 4 gauge cable going from the front of the block to the frame rail. Car has solid motor mounts, so it should (in theory) ground through there, anyway.

    I'm about as certain as I can be that there are no exhaust leaks, at least, not around the headers or collectors. The exhaust is dumped just before the rear axle.

    I have recently had the heads off. Valves were clean and no issues that I could find. I swapped valve springs and checked all guides and seals.

    Hopefully, I'll get it sorted with a little more tuning. I'm definitely better off than I was.
    79 Pace Car - 331, t5
    79 Cobra - working on 351w, t5
    86 coupe - rotbox roller
    86 coupe - working on 408w, c4
    88gt - 302 efi, t5

  11. #61
    FEP Power Member qikgts's Avatar
    Join Date
    Jan 2010
    Location
    Rockledge, FL
    Posts
    1,098

    Default

    Do you know the P/N of the Brawler? A listing I have shows several 650 mechanical secondary models with differing set ups from the factory.

    Are your metering blocks adjustable with 3 emulsion jets? Have you changed anything on the blocks or air bleeds yet?
    '85 GT

  12. #62
    FEP Member
    Join Date
    May 2016
    Location
    Lake City Pa 16423
    Posts
    445

    Default

    You said that you have changed everything under the sun so far, but yet it still back fires through the exhaust. Your last post is the first time you mentioned what kind of exhaust you have on it. Sounds to me that the short exhaust system you just mentioned, might be your problem.

  13. #63
    FEP Supporter Broncojunkie's Avatar
    Join Date
    Jan 2015
    Location
    Barboursville, WV
    Posts
    1,148

    Default

    Quote Originally Posted by dynodon64 View Post
    You said that you have changed everything under the sun so far, but yet it still back fires through the exhaust. Your last post is the first time you mentioned what kind of exhaust you have on it. Sounds to me that the short exhaust system you just mentioned, might be your problem.
    I'd say you have a good point here. I don't believe it's the cause, but probably does make the problem much more noticeable. But just so we're clear, I'm not talking about some crackling like you hear with a set of glass packs. This is a full-on load-up backfire that has the neighbors ducking for cover. ��
    79 Pace Car - 331, t5
    79 Cobra - working on 351w, t5
    86 coupe - rotbox roller
    86 coupe - working on 408w, c4
    88gt - 302 efi, t5

  14. #64
    FEP Supporter Broncojunkie's Avatar
    Join Date
    Jan 2015
    Location
    Barboursville, WV
    Posts
    1,148

    Default

    Quote Originally Posted by qikgts View Post
    Do you know the P/N of the Brawler? A listing I have shows several 650 mechanical secondary models with differing set ups from the factory.

    Are your metering blocks adjustable with 3 emulsion jets? Have you changed anything on the blocks or air bleeds yet?
    Here's the carb I'm running.
    https://www.summitracing.com/parts/qft-br-67199

    I've had a couple other Holley 4150's on it, as well. Same problem. So far, I've only changed out the main jets and power valve.
    79 Pace Car - 331, t5
    79 Cobra - working on 351w, t5
    86 coupe - rotbox roller
    86 coupe - working on 408w, c4
    88gt - 302 efi, t5

  15. #65
    FEP Supporter Broncojunkie's Avatar
    Join Date
    Jan 2015
    Location
    Barboursville, WV
    Posts
    1,148

    Default

    I also am running Accel wires. I've watched the engine running, at idle, in a dark garage and can't see any rogue sparks. I can't help but think that maybe they're not quite up to par, though. I do currently have a strong spark coming from a Blaster 2 coil. I just wonder if the healthy ignition system isn't taxing my so-so wires. The reason I'm considering them suspect is because I threw a cheap set of plug wires on and problem got worse. I ordered a set of MSD wires just for peace of mind.
    79 Pace Car - 331, t5
    79 Cobra - working on 351w, t5
    86 coupe - rotbox roller
    86 coupe - working on 408w, c4
    88gt - 302 efi, t5

  16. #66

    Default

    I would suggest returning the carb back to the stock jets for now.
    How much total timing are you getting ? It should be somewhere around 34-35. You need to limit mechanical advance.
    Set timing for total advance not base timing.
    No vacuum advance.

  17. #67

    Default

    As for the carburetor, QFT's come new in the box with three inherent problems for correct/proper/safe function, ironically, since they are obviously aimed directly at performance combinations, they are especially badly calibrated for anything with more than a stock/mild camshaft in it... all of the problems they come with are guaranteed to provide "stupid rich" in most cases, wildly varying air:fuel mixtures, and the worst case scenario of going dangerously lean at the top end rpm of whatever engine they're on.

    Problem number one is a calibrated wide open throttle fuel "curve" that starts out blobbing stupid rich and then veers lean up top of the rpm limit of the engine... the very WORST case scenario for engine safety... speaking of that, ALL of the "new and improved" carburetors and their calibrations are very stupidly and dangerously rpm-dependent as to their wide open throttle air:fuel ratio... air:fuel ratio should be load-dependent, and as constant as possible for wide open throttle regardless of rpm, NOT rpm-dependent. Problem number one is too big/many main well "emulsion" bleeds, and that always coupled with main air bleeds too big to counter the main circuit's tendency under such calibration to continue to go stupid rich up top of the rpm range. The SOLUTION is a return to traditional Holley 'booster air correction bleeds', blocking some and resizing others, and then also installing something like 0.028" or 0.026" main air bleeds, to establish a main circuit that functions like they were supposed to.

    Problem number two is transfer slots in the base plate that are machined too wide and/or too long. Transfer slots' area always were a very important part of correct and efficient calibration/function for MOST off-idle driving conditions... "they" seem to have forgotten this fact. The SOLUTION for this is modifying for and installing 0.081" (for starters) transfer slot feed restrictions, so that every mode of throttle opening off idle is not ridiculously rich (read - fuel mileage)...

    Problem number three is up-high located (especially primary) idle feed restrictions... most especially with more than a stock/mild camshaft, up-high located primary idle feed restrictions will always provide a widely varying idle/off-idle air:fuel mixture, because the intake manifold vacuum pulsations, especially with a mildly-lumpy to radical camshaft, allows idle air bleed air to variably get in front of and behind such up-high located idle feed restrictions. Idle feed restrictions are most beneficially located SUBMERGED in fuel and only metering fuel, where idle air bleed air can never get in front of and behind them, therefore never affecting their metering of idle/off-idle FUEL. Bottom line - idle feed restrictions should (and will) consistently meter fuel (if submerged) - and idle air bleeds should meter idle/off-idle air... no mish-mash nonsense crossover of the two functions... all functional modes of idle and off-idle is magnificently and consistent and efficiently taken care of when these initial Holley design parameters are stuck to, returned to.

    Wide band AFR's are a great tool, in my opinion most importantly for monitoring/establishing safe wide open throttle AFR... but they are just a tool... ANY misfire (rich, lean, ignition) will always indicate lean in the O2 sensor sniffing the output in the exhaust, because there's far more oxygen than fuel sent out the exhaust with misfires... so don't get too hung up chasing certain numbers with the AFR gauge... the engine will tell you what it wants, and the very best tuning and outcome and function results from instead listening to what the vehicle tells you...

    ... as to gunshot exhaust backfiring... after breaking in the cam/lifters in my car, shut off provided a spectacular, neighborhood-shaking gunshot backfire out of the exhaust... I even ducked, LOL!... because of a defective power valve that had been providing far too much idle/off-idle fuel the whole time. So, your issue is either far too much fuel existing in the exhaust at all times and/or upon deceleration (idle/off-idle), or I did not see mention throughout the whole of this thread that proper valve timing (both valves closed, the compression stroke) was also verified when true TDC of #1 was verified, therefore bringing question to correct initial ignition timing...
    Last edited by Walking-Tall; 04-17-2020 at 04:03 PM.
    Mike
    1986 Mustang convertible ---> BUILD THREAD
    Past Fox-chassis "four eyes":
    1983 Mercury Cougar LS
    1986 Ford Thunderbird ELAN
    1980 Capri RS Turbo

    Work in progress website ---> http://carb-rebuilds-plus.boards.net/

  18. #68
    FEP Supporter Broncojunkie's Avatar
    Join Date
    Jan 2015
    Location
    Barboursville, WV
    Posts
    1,148

    Default

    Walking-Tall,
    Thanks for the detailed description of the problems with these carbs. I was literally going through your explanation on my original post and using it to try and learn a little more about it. I have had a couple older Holley carbs on it, which is what originally prompted me to get this one. The problem persisted through all 3 (actually, 4...I just recalled borrowing a buddy's from down the street). I'm definitely not ruling out carburetor issues. I plan on addressing all three issues you pointed out.

    As for the timing, yes...I have verified compression stroke, both by watching the valve events while turning the engine by hand AND by removing #1 plug and feeling compression (using a small rubber hose inserted to "ride" the piston to the top of the cylinder). The dial on my timing light shows somewhere in the 34-36 range on total timing. I have since advanced even more, where it appears to be running much better. It is a mechanical advance distributor only (MSD), so no vacuum advance to deal with. It has the stock heavy springs and bushings that bring advance in late and total isn't reached till, iirc, somewhere in the 4,000 rpm range (I don't currently have a tach hooked up, but I seem to recall total timing wasn't reached until it was in that neighborhood). Could the slow advance be causing my issue? Coming out of the throttle with too little timing may explain it. Although, I've never had that happen before. I've always adjusted mechanical advance only for better performance....not to fix something like a backfire. Not saying it can't. I just wasn't considering it until now.
    79 Pace Car - 331, t5
    79 Cobra - working on 351w, t5
    86 coupe - rotbox roller
    86 coupe - working on 408w, c4
    88gt - 302 efi, t5

Page 3 of 3 FirstFirst 123

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •