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Thread: Please Help With My Backfiring/Stumbling/Stall Problems

  1. #1
    Hallett19
    When I start my motor up, it runs like an animal, after it starts warming up, it starts backfiring, poping then ultimatley dies and has difficult starts and once started, still runs shitty with backfires and pops. Now, take note of this.... it runs fine for about 30 - 45 min, then has problems, then, once it cools off, it runs just fine all over again which makes me want to rule out anything mechanical other than maybe lifters, but there is no chatter or anything coming from the motor. At martinez this weekend I changed my coil, voltage regulator and made sure my balast resistor was up to par in the ohms (0.8) So the only electric problem I need to fix now is the distributor, which I bought a new pro billet msd dist. and will put it in this week with an msd 6A. What else would cause this problem ? Fuel starvation ? I run a mech fuel pump, edelbrock victor, big ass pump. Isnt it timing that causes backfires though ? that has always been my assumption. At certain temps, maybe the dist is advancing the timing so high that the thing falls on its face, who knows, I'm at a loss and now am trouble shooting with my wallet. Also, does a voltage regulator need to be grounded to the block, or can I mount that thing anywhere ?

  2. #2
    78Eliminator
    Aaron,
    Sounds like you're overheating big time. Are you sure that you're cooling the motor? Your water temp gauge might be deceiving if NO water is going through your system. Water temp senders will actually read cool if they are dry. Did you check the plugs? They'll show lean if they're hot. If you got hot enough they might show signs of melting.
    The second thing I would check is your carbs. If you can have someone control the boat and look down and make sure fuel is coming out ALL the venturis, that would be good to check. An excessive lean condition will get your motor hot just like no water. Anyway, I'd check those things to begin with.
    Justin
    [ July 13, 2003, 10:13 PM: Message edited by: 78Eliminator ]

  3. #3
    Moneypitt
    What is the history of the heads? any chance the exhaust guides are tightening up hot. this WILL cause popping in the intake, and run shitty. after cooling off it'll run good for a while, until the valves start to sieze in the guides again....my .02...Moneypitt

  4. #4
    LeE ss13
    This is kind of rare, but I have seen it happen twice in 40 years. (yea I know, I'm old) Back when I owned a shop, a car came running the same way you have discribed. It didn't take long for me to find water in the gas tank. I drained the tank and flushed everything our and put new gas in it and a little water remover. The car had new spark plugs in it because some one thought that might me the problem. When I got all done it ran the same way. I worked on that car for 8 hours straight. No change. The next day I started in again. This time I replaced the spark plugs and it ran perfect. I seems when water runs through an engine, it leaves mineral like deposits on the porcelin of the plugs. When they heat up enough, they short out. Just a thought.

  5. #5
    Hotcrusader76
    Here's the drill.
    We changed three different carbs on this set-up, both being stock 3310s and a warmed over 3310 from TPC. It obviously ran best and idled better again with the TPC set-up. We originaly thought that the loose shafts and sloppy linkage was causing some vacuum leaks which is why we opted for the new carb.
    Now after the new carbs was installed she ran extremely strong up to a new 4900RPM, idled great, very responsive, maintained positive fuel pressure throughout the RPM band, but just when the oil temp hit ~240'F (150'H20 temp) it would send a black pop through the carb.
    Out of pure curiousity we replaced the coil (about 3 years old), checked the ballast resistor, and checked the distributer for any contamination, and replaced some other electrical components. Plugs read very light brown to clean color.
    It's not a wiring issue at this point either, since Froggystyle engineered the layout and all grounds were tight.
    Now this popping/dieing consistently happened once the temps were up and about 30 minutes of run time. Once she cooled down it went away, the motor fired up and we were back in business.
    The timing was originaly at 20'Initial, which we both backed down to 10-11'. We didn't get a test run after that change, but my assumptions lead me to believe that might have fixed it. Only another test run will show.
    Hope this cleared up any confusion.
    ~Ty

  6. #6
    LeE ss13
    Hotcrusader76:
    ... Plugs read very light brown to clean color... I guess my question is, have you installed new spark plugs since the problem began? If so, here is a once in a life time similar problem. I had a customer with a Buick station wagon that everytime he went up a long hill it would start popping back through the carburetor and missing etc., but only when the engine got hot enough. It wasn't until I ran it on a chassis dyno, that I could load it down and see the spike firing line on one cylinder come down lower and lower until it started popping and missing. Something was prematurely setting off the fuel mixture before the spark plug was. So I pulled the head off and found a cast iron stelagmite (sp) type casting flaw in the same cylinder. It would heat up like a glow plug and fire the fuel prematurely. Just a thought.

  7. #7
    Hotcrusader76
    LeE ss13:
    Hotcrusader76:
    ... Plugs read very light brown to clean color... I guess my question is, have you installed new spark plugs since the problem began? If so, here is a once in a life time similar problem. I had a customer with a Buick station wagon that everytime he went up a long hill it would start popping back through the carburetor and missing etc., but only when the engine got hot enough. It wasn't until I ran it on a chassis dyno, that I could load it down and see the spike firing line on one cylinder come down lower and lower until it started popping and missing. Something was prematurely setting off the fuel mixture before the spark plug was. So I pulled the head off and found a cast iron stelagmite (sp) type casting flaw in the same cylinder. It would heat up like a glow plug and fire the fuel prematurely. Just a thought. That could very well be a posibility. What ever is causing the issue is heat/time related. Hallet19 said the plugs were fairly new, I didn't see any tiny specs that would clue me otherwise to pre-detonation, but new plugs might have alleviated any curiousity.
    It is my honest opinion that his old points sytle distrubitor is junk. It was converted to a electronic pick-up from his engine builder but this piece looks ancient, hence the reason he's upgrading to an MSD set-up.
    ~Ty

  8. #8
    Hallett19
    When I initially had this problem right before the rebuild of the carb, I changed my plugs. The old ones looked great, but I figured, what the hell. Wires are about a year old and they are Bosch 8mm wires. The gas is fairly new, fresh tank at the end of May. But I think if the problem was bad gas, the problem would be much less consistant and probably run like crap all the time. I have had water in the gas before and it runs like shit, very similar to how it is acting now, but I remember when I did have water in the tanks, it ran like shit all the time and not only when it got hot.
    And LeEss13, the motor was gone through about a year ago, new bearing and head gaskets and new oil pump, this is a very new problem, I have had the boat run for hours at a time while wakeboarding with friends and have never had problems. I have thought of a spark spike, that is why I'd love to get it on a scope and see if anything like this is happening. What do you think about the dist. being a problem ? My gut tells me that its an electric problem, but you have some great input.
    [ July 14, 2003, 09:46 AM: Message edited by: Hallett19 ]

  9. #9
    Froggystyle
    I suspect a vapor-lock condition of some sort. If the motor is getting hot enough, and with a block-mounted pump you could be getting quite a vapor lock in the pump.
    My real guess is contaminated gas, or a problem created by past contaminated gas. I think that the 35-45 minutes is an indicator of what is being picked up by the fuel system at the time, and he has a very recent history of a lot of water in the fuel, and no history of totally, deliberately removing it. In fact, as of a month or two ago, when this problem first reared it's head, he had not really run it since getting it back from Barney's after nearly sinking it, and mentioned that he was not sure if the tanks had ever been fully emptied and filled. One tank for sure had old gas in it. Add this to the fact that it has never run right since nearly sinking it.
    My wager is on corrosion in the fuel pump, corrosion in the lines, corrosion in the tanks/pickups from the water-down segment of our program.
    There is only one way to solve this problem though. Remove the pickup, inspect. Clean the tanks, inspect. Clean the hoses, remove or replace, inspect. Remove pump, disassemble, inspect. Remove the filters, inspect and replace as neccessary.
    Then, you start changing ignition components.
    BTW, a competent boat mechanic probably could have removed, cleaned, installed new pickups, and re-installed your tanks for close to the $200 spent on the distributor. Just a thought...
    But, at least you will have a new distributor and coil now.
    I have said this a hundred times. A wallet makes a poor troubleshooting tool.
    [ July 14, 2003, 12:14 PM: Message edited by: Froggystyle ]

  10. #10
    James'SS-24
    How about the fuel tank vents? are they open? That will cause the time related thing!

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