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Redmax ebz7500/ebz8500 overheating

Discussion in 'Mechanic and Repair' started by Billsz28, Dec 4, 2013.

  1. Billsz28

    Billsz28 LawnSite Member
    Messages: 70

    Ok so I have a question for you 2-stroke guys. There has been an issue with the 7500/8500 model blowers that is a lean condition and pre-ignition/overheating that develops as a result. This is a self-admitted problem from redmax.

    The solution is a no charge shortblock replacement as well as a larger main jet being installed on the 8500s only.

    Between the overheating and the crank-case mount problem, I have already R&R'd 12 shortblocks this fall and have 7 more waiting on backordered parts.

    Now heres my question. Every blower I have inspected that has the overheating issue has large amounts of what appears to be straight 2-stroke oil collected on the bottom inside of the air intake elbow as well as in the intake mouth closest to the engine. Any ideas on HOW this is happening?

    The air filters on these are PAPER and are NOT oiled so that is ruled out. I have attached photos. This symptom is present on EVERY blower with overheating/lean condition problems...




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  2. BigFish

    BigFish LawnSite Platinum Member
    Messages: 4,068

    Sure... ya mix OIL with the gas.... ya choke the chit outtta the units to start...
    the excess fuel mix runs out the carb...... the gas evaporates.....
  3. Billsz28

    Billsz28 LawnSite Member
    Messages: 70

    That was my first guess but after cleaning the elbow and running the blower for a while the same thing occurs... No choke.

    The blower pictured is actually one of the cleanest ones
    Posted via Mobile Device
  4. Jeff in AL

    Jeff in AL LawnSite Senior Member
    from Alabama
    Messages: 762

    Has the unit in the picture been shortblocked?

    It doesn't look like the plug in the first picture appears to have been subjected to a lean condition... Looks like an over rich or carbon fouled problem?

    The last pictures shows a fair amount of dust/dirt in the air filter base... Perhaps said unit has ingested enough dust/dirt to wear the rings/cylinder to now have excess spitback?

    Agreed that any fuel spit back would leave only oil after the fuel evaporates.
  5. Breezmeister

    Breezmeister LawnSite Bronze Member
    Male, from South Jersey
    Messages: 1,739

    Has this solved the problem ?

    Back in the late 80s, Tanaka had a similar probelm with over heating. The solution I believe (getting old and my mind can be like swiss cheese) was to go to a colder (?) spark plug.
    It solved the problem....

    Looking at this, I'm thinking excessive blow back....Since these are new units, I doubt it's carbon build up at the exhust port. What I would do is run the unit with out the muffler.
    If the problem goes away, then you have found the problem in the muffler..... I think the EPA has some thing to do with this.......:rolleyes:

    If the restriction is not in the muffler, and the carb is not putting out to much fuel (Flooding ? You mentioned that there was a change in jets) then it has got to be in the jug.
    Maybe in the machineing something didn't get done correctly..... Do you have an older jug to compare the new one with ?

    And one more thing, what is the compression on one of these right out of the box ? The reasoning for the question, is that to much compression can be a bad thing.

    My thoughts on the first picture. It looks like hot gases are leaking pass the spark plug gasket.....

    If the crap on the plug tip is not from stuff getting pass the air filter, then either there is something in the fuel or mix oil that is getting so hot that it melting to the tip....
    Or that is metal from the pistion, crank or jug.......Is this why you are short blocking them ?
    ericg likes this.
  6. ArTurf

    ArTurf LawnSite Platinum Member
    Male, from Ark
    Messages: 4,268

    Is it possible the oil in the air intake is dripping/draining out of the carb when the unit is not running? I have a hedge trimmer that does this. I assume the float is stuck. Runs fine otherwise and I drain the fuel out after use. I've had string trimmers that did this from time to time.

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