Jackshaft Engine max went from 34mph to 25mph? with a jackshaft and tuned pipe

Discussion in 'Transmission / Drivetrain' started by StrontiumEthics, Oct 9, 2009.

  1. StrontiumEthics

    StrontiumEthics Motored Bikes Sponsor

    I have a jackshaft kit, tuned pipe, and a dax 70cc engine. However today my engine started to act weird. Before it could hit 33-mph fairly easily. Now its struggling to hit 26-mph. What do you think the problem is? Chains adjusted right, bearings are good, just did a tuneup yesterday, and it was ok.

  2. Pablo

    Pablo Motored Bikes Sponsor

    What does your plug look like after a hot, hard run? (and kill and glide)
  3. StrontiumEthics

    StrontiumEthics Motored Bikes Sponsor

    It looks dark brown not to dark, more like a tanish dark brown.
  4. Pablo

    Pablo Motored Bikes Sponsor

    Sounds OK. Something basic is not correct. (pardon the brazzilion questions).

    What plug, what wire?
    Have you widened and matched your intake gasket with manifold and port?
    Have you widened and matched your exhaust gasket with header and port?

    What is your head torqued to? Any leaks? Checked compression?
  5. StrontiumEthics

    StrontiumEthics Motored Bikes Sponsor

    No no its ok, I dont mind the questions. I actually like them.

    1. The wire im using is the high performance wire from sickbikeparts, im using NGK B6HS.

    2. No I haven't widened and matched my intake gasket with manifold and port. I used the stock intake mani and gasket, and use the copper gasket for my exhaust port.

    3. Not to sure what "matched your exhaust gasket with header and port" means.

    4. I don't have a torque wrench to torque my heads, but there aren't any leaks as far as I can tell. How can I check Compression?What should the heads be torqued to? Im going to check at my local automotive shop for a torque wrench

    Also, I have been hearing a rattling sound but It didn't just happen it was happening for a while now, before I didn't see a decrease in power. Its just one day my top went down from 35-mph to like 26-mph or so. thats what I find very weird. Also I use motor oil for oil in my gas mixture. I recently found out that it really hurt my engine and could be the culprit for the rattling..
  6. Mountainman

    Mountainman Active Member

    simple compression test may tell a story
    all information may be found here in search
  7. Pablo

    Pablo Motored Bikes Sponsor

    Also borrow a compression tester.

    Torque should be around 10-12 ft lbs, but go easy if you use those silly stock acorn nuts. It's probably not your porting if you suddenly lost power.
  8. Hawaii_Ed

    Hawaii_Ed Member

    My guess would be a leak somewhere. Do you have oil seeping at the base of the cylinder? The base gasket can go, or the head can be loose. I snug my head down every week or so, but I ride pretty hard. I have a bit of mechanical experience, and these engines do not seem to be built to super high tolerances, so I use the German torque spec of gutentight. (good 'n' tight!)
  9. Fabian

    Fabian Well-Known Member

    Yes, i agree with Paul - something is clearly wrong with your engine setup.
    I have a SickBikeParts Jackshaft kit with a totally stock standard muffler and only a modified intake tube.

    My bike easily cruises at 25 miles an hour and has no problems hitting 30 miles an hour with a verly light tail wind.
    With the optional 11 tooth Jackshaft sprocket fitted and an 11 tooth smallest gear on the 9 speed cassette, my bike sits on 3500rpm at 30 miles an hour.

    You can use ordinary motor oil in your engine but it must be at 16:1 oil/fuel ratio and you must increase the size of your main jet to compensate for the lean air/fuel mixture caused by using so much oil in the fuel.
    You must also use the highest (non alcohol fortified) fuel you can get at the petrol pump to compensate for the octane lowering qualities of excessive oil in the 2-stroke mix.

    Basically, using ordinary motor oil in a 2-stroke engine at 25:1 or greater is a recepie for engine disaster

    Last edited: Oct 11, 2009
  10. StrontiumEthics

    StrontiumEthics Motored Bikes Sponsor

    What do you mean by this?
  11. Fabian

    Fabian Well-Known Member

    Petrol (otherwise known as gas) is not designed to have oil mixed with it - Petrol is designed to be used as petrol.

    Adding oil to petrol reduces the performance parameters for the fuel as designed by the manufacturer.
    To try and compensate for octane reducing effects of adding oil to the fuel, you must use a higher octane fuel to prevent detonation, especially when mixing fuel at 20:1

    Alcohol increases the octane rating of the fuel but it attracts water from the moisture in the air.
    When the engine cools down the remanants of any water vapour will also cool down and condense into fine water droplets on any of the parts inside your engine, and the potential for light surface rust on precision machined surfaces is a real possibility, roller bearings being the worst possible place you would want any water vapour to condense.

    Seems quite simple really.

  12. Pablo

    Pablo Motored Bikes Sponsor

    Unfortunately many places in the USA, petrol without EtOH is not to be found. In my state for example. The only thing you can do is mix fresh, and when you store the engine, run a good oil with anti-rust and other preservatives, plus fog the engine.

    As far as oil reducing octane rating you are quite correct. However these engines (stock) have a static CR of about 7:1, so the octane reducing effects of oil are not even perceived by the engine, so in the quest to get higher octane fuel - sometimes power is lost because the anti-knock compounds used to make fuel "higher octane" (EtOH for example) don't actually add any energy to the petrol. I know for a fact my engine with stock CR ran much better on regular fuel 87 (R+M/2) (not "premium" 92). My high compression slant head, it's a wash. Either fuel is about equal as far as I can tell in that one.
  13. motorpsycho

    motorpsycho Active Member

    you must use gasoline with as little alcohoal added to it as possible. if you look on the gas pump it will say"X % alcohol") you want to steer away from gas that has alcohol in it.
    why not just use regular 2 stroke oil instead of motor oil? it would make things alot easier.
    by using motor oil, you may not have enough oil in the fuel/oil mix, and you MIGHT have cause premature ring wear, which would cause you to loose compression, which would cause a big loss in power.
    It would be like running a 4 stoke engine low on oil in the crank case. it woudl cause premature brearing and ring failure and a huge loss in power.
    when the rings wear, the compression goes down causing "blow-by". in other words, the compression "blows past" the rings. the more compression you have, the more power an engine will make you can never really have too much compression, but if you build a high compression motor you will have to go to a higher octane fuel for it to run right.
    Last edited: Oct 11, 2009
  14. Skyliner70cc

    Skyliner70cc Active Member

    quote: "rust on precision machined surfaces"

    Hahahah, I laughed so hard when someone refered precision machined surfaces on the HT engine ...hahahahaha:tt1:
  15. StrontiumEthics

    StrontiumEthics Motored Bikes Sponsor

    Hey guys strange enough I actually got hold of the possible problem. It was my gasoline to oil mix. Previously the only 2 stroke oil that I used was the one from Autozone:
    Sta-mix 2 stroke oil. But I decided to pick up some motorcycle 2 stroke oil: Honda GN2 2 stroke oil, and accuratly mixed it at 32:1 ratio adding 120ml of 2 stroke oil to one part of gas. And surprisingly, when I started it up and let it warm up for about 20 mins so I could get all the old fuel out the system, it went back up to about 30-31mph. I didnt really max it out yet, but it felt like before but a better. I learned from the situation that 2 stroke oil quality is very very crucial, and adding motor oil to gas is a recipe for engine malfunction!!!! Im sorry I ever done it.
  16. AussieSteve

    AussieSteve Active Member

    32:1 is still pretty light on. It wouldn't hurt to try a little more oil and see if performance improves even more. (Say, 25:1 or even 20:1) The extra oil will help the rings to seal and possibly bring the compression up a bit, as well as slightly improve cooling.
    More compression = better high and low end power.
    It certainly won't do any harm. If power is better or the same, the extra oil will ensure a longer engine life.
    If it runs better, but the plug gets a bit dark, try going from an NGK B6HS to a B5HS. (Hotter)

    ... Steve