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Thread: Mikuni Carb and Modern Ethanol Gas?

  1. #1

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    Mikuni Carb and Modern Ethanol Gas?

    I have been having an issue when trying to start my truck when warm and sometimes when cold where it just wants to spin and not fire aka its "hard starting". This hard starting issue has only nearly left me stranded once but I hate it when I go somewhere and return to start my truck and have to run the starter for about 3-7 seconds before it finally takes off. once it starts running it will run a little rough but if I give it some throttle it will even out and run fine. I've replaced the coil with a new Bosch unit and have a new set of Denso wires and cap and rotor are fairly new so that stopped the crappy idle/running I had when first driving the truck after getting it back on the road. I also set the timing according to the service manual. I was wondering if these Mikuni carbs have issues with these modern high ethanol fuels on the market today, I have heard of certain carburetors where modern fuels will boil in the bowl due to the lower boiling point of gas with ethanol in them causing hard start issues when warm and other problems. If this is the problem are there any ways of stopping this like fuel additives etc? If this isn't the problem what could it be? I'm new to carburetor's for the most part so I'm sure there could be something I'm missing?

  2. #2

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    Food (or in this case, fuel...) for thought - http://www.mightyram50.net/vbulletin...d-Fuel-Quality

    I would try altering your ignition timing and regap the plugs to see if you can improve starting and running (trial and error - maybe wind out the air/fuel mixture screw as well) Technically the carb would need bigger jets to run E10. I am not a fan of this stuff. I wouldn't recommend using an additive to E10 either. Although the ethanol added fuel has a higher RON, it has an unpredictable combustion pattern. Increasing the RON/octane with an additive is not going to help and IMO is risky.
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  3. #3

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    Thanks for the reply geezer! I went to check out the spark plugs and realized they were ash fouled. I have only put about 8k miles on them but I guess the oil consumption issue my truck has had wore them out sooner than expected. My old coworker at the parts store recommended slightly hotter plugs to help the issue. I guess time will tell how this fixes the hard start issue but so far it starts fine.

  4. #4




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    Use Sta-bil marine ethanol fuel treatment in your gas - it negates the effects of ethanol blended fuel and will clean out the fuel system and intake valves as well. It is a must for our trucks if you want them to run - I have been using it for years in all my vehicles.
    Pennyman1
    The best Dodge that Dodge never made
    Living the D-50 lifestyle since 1980

  5. #5

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    Ill have to try that. On an related issue I just had the other day I came out of the doctors office and tried to start my truck when it was about 100 degrees out and it would start and run for a split second and then quickly die. I tried several times before opening the hood and pulling the main lead going to the distributor and resting it above the ground lead on the battery (bad idea I know due to the explosive gasses a battery produces but it was the only place i could see it) I then noticed when I would turn the key it would arc a couple times then stop even with the starter still going. I thought I was going to have to call AAA for a tow but I put the cable back to the distributor and waited a minute with the hood up and tried it again and it fired right up and didn't give me any more problems after my next 2 stops that day. Could this be a issue with the new coil overheating or is the ECU or Ignition module killing power to the coil? I guess the ECU only monitors the ignition signal right? Its an 87 so it was built before the capacitor plague of the 90's and I've had it open before and it seemed like I checked the ESR on them and they were good, how reliable are the ECUs and Ignition modules in the older 2nd gen trucks?

  6. #6

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    Grab the ballast resistor on the coil when the engine conks out - if it's red hot, it's dead. Tell tale sign of an issue - engine runs, dies. Won't start. Try again in 10-15 mins, starts and runs but does it again.
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  7. #7

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    Thanks I didn't even think of the resistor for some reason. I will do that next time the truck dies.

  8. #8

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    Grab the ballast resistor on the coil when the engine conks out - if it's red hot, it's dead
    sure u wanna do that? sounds painful Mist some water on it or somethin

  9. #9

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    Quote Originally Posted by dash View Post
    sure u wanna do that? sounds painful Mist some water on it or somethin
    Hmm, spraying water around a gadget that emits 40kV ish. Sound entertaining. I think you'll figure out of the resistor is cooking long before you burn yourself on it. Anyway you're a man! You have nerves of steel and hands of granite What could go wrong...
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  10. #10

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    what 'gadget emits 40kV ish' after "it conks out" ? Better use holy water instead then.... because its possesed
    didn't say spray it, just dip fingers in water n flick it on the (hot)resister

  11. #11

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    Dirt cheap Infra red temp gun is ideal for these situations

  12. #12

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    Quote Originally Posted by dash View Post
    what 'gadget emits 40kV ish' after "it conks out" ? Better use holy water instead then.... because its possesed
    didn't say spray it, just dip fingers in water n flick it on the (hot)resister
    The coil will if the ignition is on and you actually get the engine running. And you won't forget the first time you get buzzed by an ignition coil - funny to watch some other poor fool take one for the team but stings like a biatch when you've on the receiving end. Especially with the transformer type coils. Fun times... also if the resistor is hot and you try hitting it with a spot of water, the sudden change in temp could cause it to crack (if it wasn't already) Basically, you will know if the resistor is baked by touching it long before you singe yourself unless your reflexes are glacial-like.
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