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Got the lemon running

Discussion in 'HPI Savage Octane' started by F-Type, Mar 20, 2018.

  1. F-Type

    F-Type Well-Known Member

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    Hi guys, I'm back!

    Did you miss me? Ha-ha, bet you didn't even notice I was gone :)

    Is there anyone around here any more, or is Octane stone dead now?

    In any case, as you may remember. I was fighting a lot with my octane engine trying to get it running. Checked everything about the engine, compression, carb pump pulses, etc, only to conclude it was in mint condition. Same thing with the carb, checked everything, did leakage tests, pressure tests and stuff, tried it on another engine (bigger leafblower engine) just to conclude that it was in mint condition. Still, the engine wouldn't run.

    So now, the engine has been put aside for quite a while. In the end my conclusion was that there really isn't anything wrong with either the engine or the carb. It is the combination of the two that is all wrong, and that is why so many more than me have problems. With a bit of luck, you get it running, for a while, sometimes, -ish.

    Too big a carb on too small an engine. Simple as that. The Walbro WT-668 used on the Octane has a 15.88 mm bore, which is big even for an engine twice the size of the octane, and in general recommended for 50cc+ engines. Bigger bore/venture gives more power, people say, but it's not like there are no other differences, otherwise everyone would use bigger carbs, no doubt. It comes with the drawbacks of flooded engines (check) and extremely sensitive on carb tuning (check) for instance.

    In any case, if this is the problem, somehow somewhere I should be able to get my Octane running with this carb, even if it is tough finding the tuning that will work.

    One other thing I have been on about before is the air restrictor in the filter, or between the filter and the carb. Why on earth would anyone wanna restrict the air? Well, if you put on an oversized carb ... ... ... (yeah, it is really so incredibly stupid, what where they thinking?)

    Also, what I noticed, by chance, when experimenting with limiting the airflow even further, was that the air restrictor is not symmetrical, it can be put in no less than four different ways, add to that the two different ways you can put the little t-shirt shaped sorry piece of plastic "fly" under the restrictor, you get 8 different ways of putting it back. I wonder how many Octane owners managed to get that back in the correct position every time. Because, what I noticed was, that it makes a difference, a difference of go or no go, one way or the other. How many of you realized that, 8 different ways, only 1 correct. Yup.

    And, in the end, funny enough, I managed to get my engine running, when the low speed needle was set to 1 & 1/10 turn out, not 2 & 7/12 or whatever the updated manual stated.

    Now, the problem I had, and still to some extent have, is to get idle speed down. I am probably running a bit lean, and if I turn the low speed out further, the engine stutters and stops. However, when the engine heats up, I can adjust out / down a bit to what seems like a more normal idle rpm. And guess what, the low speed needle then ends up close to 1 and 1/4 turn out. Now, go read the original manual, not the updated one. Yup, there we go again, recommended low speed needle setting 1 & 1/4 turn out. It's in the f*cking manual. But not the updated one, that HPI said you should use if engine won't run. But it'll only work in that setting once the engine is hot. Cold, 1&1/10 is what works. On my engine, yours could be different!

    The combination of this engine and this carb, band-aided with a f*cking air restrictor on the air intake, is probably the worst piece of poop engineering I have seen in my entire life. And I have seen a few things. Now, the engine is fine, and the carb is fine too. But not the two together, and the air restrictor confirms that.

    Well well. You might say, if you, against all odds, remember that I have said several times before that I found the problem and got the engine running, so why believe me this time? Well, first of all, I didn't jump to conclusions this time. It's been three days. Ever since I got the engine running the first time three days ago, it hasn't failed me one single time. Not one. Also, there is no "magic", no odd additions or changes. Back to basics. Everyting back to original, everything at factory setting, properly fitted. Only carb adjustments, nothing else.

    Cold it starts after 3-4 pulls. Once started from cold, it will start again on the first pull, every single time, without exception. I've been through half a tank in three days, (not much I know) but running on the bench half a minute - minute a time, it makes a hell of a difference compared to before when a long run was 5 seconds, and rare. Now I can stop and re-start, with confidence.

    Now, my main recommendation to anyone with an octane on the shelf, get a smaller carb, I'd recommend a Walbro 9,5 mm. I haven't had the chance to test one myself, but I bet it will be a hell of a lot easier getting that to run with the engine, than the stock WT-668 which is made for a lot larger engines. (LIke my leaf blower which runs a lot better with the octane walbro carb than with its own china-crap-carb I can tell you).

    Well, that's all for now! If there is still someone out there, listening on the "Octane"-channel, at least say Hi, so I know you're there! :)

    Thanx!
     
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  2. NightFlier X4.6

    NightFlier X4.6 Well-Known Member

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    I'm happy you found a band-aid big enough to fit the octane lol. Never owned one I've heard tooooo many horror stories. If I ever found one for a steal I might give her a try but doubt it.
     
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  3. F-Type

    F-Type Well-Known Member

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    If one is given to you, you could give her a try, or if you are up for a real challenge. ☺

    On the other hand, following my example it should be easy getting any octane to run now :rolleyes:
     
    #3 F-Type, Mar 21, 2018
    Last edited: Mar 21, 2018
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  4. F-Type

    F-Type Well-Known Member

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    Ok, so, today I did what I have been thinking about for a while. I replaced the carb for one with a smaller bore/venturi, a Walbro WT-300A. The engine started right away and was easy to adjust to a nice and stable idle. BIG DIFFERENCE.

    I have only tested on the workbench so far, so have no idea how it will run in the car, though.

    But in any case, using a carb that is more of a matched size for this size engine definitely made a huge difference. Certainly something to try for anyone having start-stall issues.

    THough the WT300A is not the best choice, no primer, no choke and gas lever on wrong side. I just tried that one because I had it. There are other alteratives that would be a better choice to replace the stock WT-668 straight on.

    And of course, no air restrictor or anything alike was needed ;)
     
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  5. desertbasher

    desertbasher Member

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    So with the 300A not being the best , what would you recommend? Anything off the top of your head?
     
  6. Mark Walters

    Mark Walters Well-Known Member

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    Hi I'm still here. I'm going to try what you did to your. I'll let you know how it goes
     

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