Please Help. Rear Engine Is Stumbling.

Discussion in 'Friction Drive' started by 5-7HEAVEN, Apr 18, 2009.

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  1. 5-7HEAVEN

    5-7HEAVEN Guest

    I have a problem that started about a week ago. On my morning rides both TLE Mitsubishi 43cc engines on "The Dragon Lady" perform flawlessly. The temperature is in the mid-70's.

    On the afternoon ride home both engines start out okay. Temps are in the low-80's. Everything's fine until I reach and maintain top speed AND 8900RPM. This is where maximum hp is attained. Then slowly the rear engine starts sputtering like it's running outa gas. If I floor the throttle the engine falls flat until I let up. If I give it part-throttle it'll struggle and catch itself. Then I can go full bore for a few seconds before it falters again.

    Both engines have their 24oz tanks being fed by a single Happy Time 2-liter tank. Fuel/oil ratio is 50:1.

    The loss in performance is only when top speed is above 34mph and 8500rpm. Any speed lower and both engines respond beautifully.

    Both engines have ADA S1 expansion pipes. The front engine has 39" exhaust tubing connected to the bleed port and exits below the crankset. It has no muffler/silencer.

    The rear engine has the standard silencer and four inches of connecting exhaust tubing.

    I washed both air filter elements but that didn't help. Tomorrow I'll replace both sparkplugs. Then I'll replace the expansion pipe's silencer.:idea:

    Can anyone figure out what this problem is? It doesn't seem to happen in the morning:sweatdrop:
    Last edited by a moderator: Apr 18, 2009

  2. grouchyolfart

    grouchyolfart Member

    Ooops. Never mind.
    Last edited: Apr 18, 2009
  3. jg767

    jg767 Member

    Check for an intake leak. And the fuel line and filter. Good luck.
  4. Mountainman

    Mountainman Active Member

    just wondering if your lean mixture of 50:1 has caught up with you ?

    but then again a simple thing such as the new plug you have planned may be a fix

    ride that thing sideways
  5. 5-7HEAVEN

    5-7HEAVEN Guest

    Well Mountainman, 50:1 is the recommended gas/oil mix. I'm pulling the plug soon to replace it. The old plug will show if it's lean.

    I just got a WYK-58 Walbro carb. I'm gonna try that soon.

    jg767, I'll look for intake leak. Come to think of it, I removed the carb a few weeks ago to check measurements. And lately the engine HAS been idling erratically. In fact sometimes it'll die while idling.
  6. Happy Valley

    Happy Valley Active Member

    Sounds like the engine is fuel starved at high demand.....or an air leak which is the same thing. Since you had the carb off I'd start there but check fuel lines and filter too. How many hours are on this engine? If it's fairly new I wouldn't think the problem to be electrical.

    As an aside, while I doubt fuel mix ratio is causing a problem if cylinder compression is still good, I'm convinced the rec on 50:1 is to pass emissions. I broke mine in at 40:1 and have kept it there, produces a tan plug and good looking piston wash.
  7. 5-7HEAVEN

    5-7HEAVEN Guest

    Happy I believe you're right about fuel delivery causing the stumbling.

    BTW, both engines have less than 1,000 miles on them.

    In the morning the tanks are partially full. After 1.5 miles of travelling at 25mph, I hit the highway for two miles of full speed. Engines are fine, lots of fuel. Two more miles of 25mph riding.

    The bike sits for nine hours in covered parking. The engines' fuel levels are low. Although the Mitsubishi engines are identical, each has a different tank design. They also have a different configuration of fuel lines to the reserve tank. The front and rear engine also sit at different heights as compared to the reserve tank, which is slightly higher than both tanks. This might explain why sometimes the rear engine runs outs fuel. On other occasions the front engine runs out of gas.

    On the way home it's about two miles of riding 25mph or less, then two miles of sustained high speed. On the third mile the rear engine starts to stumble. Flooring it makes it worse. If I drop speed down to 30mph the engines runs fine.

    Well I replaced both sparkplugs and they look lean. I also removed the carb to look for broken gaskets or loose bolts or fuel lines. Carb looks fine.

    I have a new WYK-58 high-performance carb, so I tried to bolt it onto the dual-port(air/gas) manifold. No luck, the carb's larger port does not match the Mitsu's intake manifold. The carb bolts directly on, but ports don't match.

    Need to find a matching intake manifold.

    I'm willing to bet that if I fill both engines' tanks via siphon hose then my problem will disappear. If the rear engine does NOT stumble at sustained high speeds, then I need to come up with a more efficient fuel delivery system that feeds from reserve tank to BOTH engine tanks.

    :idea:I think the final solution will be a low-pressure electric fuel pump and a small Whizzer-type battery.

    Then of course I must also solve the engines' lean conditions, probably with HP carbs and filters.
  8. kerf

    kerf Guest

    Check the fuel screens inside the carb diaphragm fuel pump.
  9. 5-7HEAVEN

    5-7HEAVEN Guest

    Well today was a blast. The roads were wet, the tires slipped constantly and it took a bit longer to reach work. Both engines ran well with no stumbling.

    This afternoon's ride home went very well. Traffic was extremely congested, but I managed to get home in 19 minutes, a great time.

    Both engines' tanks were full and the rear engine never missed a beat, even after two miles of sustained high speed.!!!

    I checked fuel level when I reached home. Both tanks were quite full, so some fuel WAS being delivered from the reserve tank.

    SOLUTION: I need to keep spending 30 minutes daily manually priming the fuel lines or siphon fuel directly from reserve tank to each engine tank...

    or install electric fuel pump with small battery.
  10. 5-7HEAVEN

    5-7HEAVEN Guest

    Electric Fuel Pump Being Installed!

    A comedy of errors dictated that today was the day to begin installing a low-amp/low volume/low pressure fuel pump.

    Yesterday the fuel line from reserve tank to rear engine got punctured. Today I went home during my lunch hour to repair it. After doing so, I filled the reserve tank and motored to work. A mile away the rear engine started stumbling at 30mph. This problem had gotten worse over the months. Once either engine starts stumbling, it's because of low fuel level at the engine tank. The carb's primer bulb cannot pull fuel from the reserve tank. Tanks are only slowly filled by siphoning effect that takes hours.

    So I ride home to siphon fuel from reserve tank to rear engine. Forgetting myself, I take a deep suck to prime the siphon line...and get a mouthful of gas!:ack2::ack2:

    Then I spill gas on my workpants.:ack2::ack2:

    That's it! Workday is over. I call my secretary to let her know I had car trouble. She laughs because she knows I ride my "putt putt" to work.:whistling:

    Fuel pump mounts on the studs of the Happy Time tank. Brass fittings and cutoff valves are installed. Tomorrow I'll run 1/4" fuel hose. The Whizzer 12volt/1.2amp/hour battery will not be mounted on the bike, but carried in my backpack.

    This should PERMANENTLY resolve my fuel-delivery issues.

    It is the same fuel pump I used on my modified VW Bug engine 25 years ago. :detective:
  11. DetonatorTuning

    DetonatorTuning Active Member

    is that pump internally regulated for pressure, or do you have an inline adjustable regulator ?

    when i was running dual Delorto 2 barrel carbs on VW's with electric pumps we had to cut down the pressure to avoid a forced flooding situation.

  12. Hawaii_Ed

    Hawaii_Ed Member

    Had the same thing trying to run a holley blue pump without a regulator. I have no idea what PSI these carbs could take, I doubt even 5, but I think he is just going to transfer fuel from the reserve tank to the engine tanks, not full time while moving.
  13. 5-7HEAVEN

    5-7HEAVEN Guest

    Ed, you are correct.

    Steve, the pump flows 4psi. HOWEVER, I'm gonna install a pushbutton switch to control its operation.

    The electric fuel pump will only be turned on for a few seconds. That should be enough time to fill the engines' tanks.

    Therefore, a fuel pressure regulator should not be needed for this situation.

    Individual shutoff valves will control which tank gets filled.

    I don't believe there will be any natural siphoning action, due to the pump being in series with the main fuel line.

    The pump will not have power untill I decide to add more fuel to the engines' tanks.
    Last edited by a moderator: Jun 20, 2009
  14. 5-7HEAVEN

    5-7HEAVEN Guest

    It's In!

    Okay, I installed the pump.:detective:

    It works fine, except a little loud.

    Sounds like the frame being whacked by two sticks. I'm glad the pump will only be on for a few seconds every day.:sweatdrop:
  15. duivendyk

    duivendyk Guest

    This fuel (oil) starvation is potentally serious, esp with your 50:1 ratio.Go to 40,that would be safer.IMO.
  16. 5-7HEAVEN

    5-7HEAVEN Guest

    JJ, with the pump installed, methinks my stumbling issues are a thing of the past.

    Unsure if the siphoning effect works with fuel pump inline. I might just leave both fuel valves open while riding.

    For example, what if I forget to fill the engines' tanks and one engine begins to stumble while riding?

    I pull over and connect the 12v/1.2ah battery to the pump. If the rear engine had stumbled, I shut off the front engine fuel supply valve. After the pump fills the rear tank in a few seconds, I disconnect the battery, open the front supply valve and motor on.

    All this is done with both engines idling.

    If I permanently install the battery on the bike and one engine stumbles for lack of fuel at 35mph, I can push the "FILL" button for a few seconds. Both tanks are sufficiently filled while motoring down the highway without losing speed.

    If it is safe enough to do so, I can reach for the shutoff valve, push the "FILL" button for a few seconds and motor on without losing speed.

    Time will tell which technique works best.:detective:
  17. duivendyk

    duivendyk Guest

    You could pressurize the main tank with a hand bicycle pump.Could work if pressure not too high but might flood engines.Probably too risky.
  18. 5-7HEAVEN

    5-7HEAVEN Guest

    Pressurized Tank?

    Possible, but I REALLY like my idea!

    Reminds me of back in 1964 when I had a V-8 engine in my 1951 Chevy sedan. I pull into the gas station; car had a rumpity-rump cam in it. The owner pops the hood and exclaims...

    "Hey, you got a 12-volt battery in this car!"

    Hey, I got a 12-volt battery ANNND an electric fuel pump on my bicycle!:jester:
  19. Hawaii_Ed

    Hawaii_Ed Member

    Met up with 5-7 this morning for a little breakfast converstaion this father's day. His system looks pretty cool! I also got a shot of his friction drive tensioner mod. :cool:

    Attached Files:

  20. 5-7HEAVEN

    5-7HEAVEN Guest

    Upon leaving Mcd's in Ewa Beach, my front engine quit at the third traffic light. Strange, because its tank had sufficient fuel.

    I used the electric fuel pump and filled both engines' tanks anyway. The rear engine was still running; when I opened the shutoff valves, I could sense it run smoother, like it gave a sigh of relief.

    This led me to believe that both engines STILL needed to vent THROUGH the fuel pump TOWARDS the keyhole in the Happy Time locking gas cap!

    The keyhole is the vent hole for BOTH engines!:detective:

    Then I realized that the front engine had died for lack of ventilation (I had plugged both engines tanks' vented caps to keep fuel from spilling).

    Upon leaving Ed, I joined my sister's family at a restaurant near Pearl Harbor. My family wanted to pick me and the bike up. There was no reason to, because the restaurant was on the way home.

    Next stop was Sears, where I ordered a roller tool chest for Father's Day. Happy Time reserve tank was bone dry; luckily I had carried a gallon container of gas. I filled the reserve tank and used the electric fuel pump to top off the engines' tanks.

    My family followed me home and clocked me with the van. On the highway both of us were cruising at 35mph until "The Dragon Lady" began pulling away. Final cruising speed for van and bike was at 40mph.

    My son stated that "The Dragon Lady" accelerated very strongly from the traffic lights.
    Last edited by a moderator: Jun 22, 2009