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Bogging down at point of turbo engagement. Why?

Discussion in 'XJ Technical Chat' started by MADBADGER, Apr 9, 2019.

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  1. MADBADGER

    MADBADGER New Member

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    I'll try to keep this short. Bike: 1982 XJ650 Turbo. Mostly stock parts, rearranged. See pictures.

    Problem: Under load at high RPM I lose power. My boost gauge never reads boost pressure. It's as if when it is time for the boost to kick in, the engine goes LEAN. Bike runs great other than this. I can cruise in 1st at 7-8000 rpm, no problem. Medium acceleration through gears, no problem.

    Ideas?
     

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  2. Ryengoth

    Ryengoth Active Member

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    Loss of turbo power at boost could be several things. Spark blow-out from dirty/mis-gapped plugs, fuel enrichment issue or a leak in cold or hot side piping. Not knowing a lot about the fuel setup I would have to say check the plugs first to rule them out. Weak spark and turbos do not play well.
     
  3. JeffK

    JeffK Well-Known Member

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    First, welcome.....second; with your system as highly modified from stock as it is, I can only give you some "overall" suggestions. It sounds like your engine is running very well, your turbo sys, no so much. I would pay close att to the weak spark issue mentioned above....my stock spark was the weakest I'd ever seen on a running bike. I have Acells now. 28,000% improvement...lol

    Your system not making boost- IF YOU ARE POSITIVE OF CORRECT PLMG AND NO LEAKS(& good turbo)---Check actual fuel pump pressure. A failed pump will not overcome atmos press,= no boost. These are the only pressurized carbs made, they operate just a tad differently in this system.

    If you are making boost but then it cuts out, look for a disconnected or failed front knock-sensor. At the same time, test the other pneumatic/electric or PE sensor shown in the manual and it WAS located below and to the center of frame from the ICU. Typically, they begin retarding the timing very early.

    The guy that everyone recommends for parts, Chacal...is top notch. You are better to get from someone who actually knows this stuff!

    Also, the Turbo forum is over here, It's ok...we all share; https://www.tapatalk.com/groups/tmioa22687/yamaha-seca-650-turbo-f10/

    jeff
     
  4. MADBADGER

    MADBADGER New Member

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    Great info. I never considered spark. Recommended plug and gap?

    I disassembled the fuel system and checked regulator and check valve. Regulator may have been stuck cant test it because now the dang fuel pump wont operate. Whyyyy
     
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  5. Ryengoth

    Ryengoth Active Member

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    I know, right? What you really need is a hotter coil to make sure the spark won't get extinguished. As JeffK mentioned the coils on these bikes are very weak. I would think stock gap would be fine on a small turbo. Only reason I mention the spark is I did a lot of turbo engine tuning work on my Genesis project. People with boosted cars often think the misfiring and detonation are just injector or air flow issues with timing. They don't consider the fact that pressurized air flow can literally blow out a weak flame front or extinguish spark completely if it's not really hot. Racing plugs help with both detonation and bad firing issues by recessing the electrode and ground strap inside the tip. The spark is protected from swirl, the flame front has a better chance of forming on-time and the tip of the plug runs colder by being in the flame only a short period of time instead of through the entire combustion cycle.
     
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  6. JeffK

    JeffK Well-Known Member

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    Mad...., let me know via PM if you need a pdf copy of the Turbo manual...it's actually a supplement for the XJ manual, I've got both if you need them, just pm me a email addy.

    jeff
     
  7. MADBADGER

    MADBADGER New Member

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    Let the process of elimination begin.
    1) New plugs - NGK manual spec, gapped .03" from factory.
    2) I pressurized the intake, some small leaks buts it did hold pressure.
    3) I felt the original fuel pump was working properly, replaced with new pump. Zero noticeable changes.
    4) Knock sensor connected. Voltmeter jumps around when I move the sensor. I assume its working properly. All connections tight.
    5) Pressure sensor reads 2v when tested per manual which is considered a "pass". There was something strange, 3 wires to sensor - Power, Ground, signal. Both power and ground had continuity to ground. I wired a dedicated wire straight from battery + to "power" on pressure sensor... and got no changes.
    6) Checked fuel pressure regulator, it opens and closes when air is applied, sprayed some silicone lube in it, I assume its working.

    Whats next? Rode it today after everything, rpm's reach redline in first at slow acceleration, Bike runs great accept about 5-6k under load. then sudden loss of power and "spitting" noise from exhaust. back off throttle and full recovery. I can feel air being pulled into turbo at idle, and if I blip the throttle in neutral I feel a small push of air on the hose to boost guage (air taken from 2nd intake port between carb and motor. Sooo I assume the turbo is working.. well enough. I did get about 2-3 psi ish reading on gauge after one pull. Choke on only makes the bike run worse.

    Any other suggestions?

    Thanks.

    Let the process of elimination begin.
    1) New plugs - NGK manual spec, gapped .03" from factory.
    2) I pressurized the intake, some small leaks buts it did hold pressure.
    3) I felt the original fuel pump was working properly, replaced with new pump. Zero noticeable changes.
    4) Knock sensor connected. Voltmeter jumps around when I move the sensor. I assume its working properly. All connections tight.
    5) Pressure sensor reads 2v when tested per manual which is considered a "pass". There was something strange, 3 wires to sensor - Power, Ground, signal. Both power and ground had continuity to ground. I wired a dedicated wire straight from battery + to "power" on pressure sensor... and got no changes.
    6) Checked fuel pressure regulator, it opens and closes when air is applied, sprayed some silicone lube in it, I assume its working.

    What's next? Rode it today after everything, rpm's reach redline in first at slow acceleration, Bike runs great accept about 5-6k under load. then sudden loss of power and "spitting" noise from exhaust. back off throttle and full recovery. I can feel air being pulled into turbo at idle, and if I blip the throttle in neutral I feel a small push of air on the hose to boost gauge (air taken from 2nd intake port between carb and motor. So I assume the turbo is working.. well enough. I did get about 2-3 psi reading on gauge after one pull. Choke on only makes the bike run worse.

    Any other suggestions?

    Thanks.
     
    Last edited: May 2, 2019
  8. JeffK

    JeffK Well-Known Member

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    Looking over your pictures.....can you make a schematic drawing of how you have the exh/intake/turbo/carbs plumbed? I see all those K&N filters and one looks to be mounted to the impeller side of the turbo? If that's the case....it's easy to see what's going on....

    jeff
     
  9. MADBADGER

    MADBADGER New Member

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    I'll explain best I can with text and if illustrations are needed I will make them.
    Exhaust: Stock header pipes = stock 4 to 1 manifold = homemade pipe to turbo housing = turbine exhaust to homemade pipe to muffler
    Intake: Stock surge tank (BOV shimmed) = homemade pipe = K&N Filter
    Turbo 1: K&N filter on turbo compressor IN
    Turbo 2: Compressor discharge = homemade pipe = K&N Filter
    Carbs: Stock

    Motor to surge tank is all stock. What are you thinking, Jeff?
     
  10. MADBADGER

    MADBADGER New Member

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    TYPO Sorry:
    Exhaust: Stock header pipes = stock 4 to 1 manifold = homemade pipe to turbo housing = turbine exhaust to homemade pipe to muffler
    Intake: Stock surge tank (BOV shimmed) = homemade pipe = K&N Filter
    Turbo 1: K&N filter on turbo compressor IN
    Turbo 2: Compressor discharge = homemade pipe = *Surge Tank
    Carbs: Stock

    Motor to surge tank is all stock. What are you thinking, Jeff?
     
    Last edited: May 2, 2019
  11. Ryengoth

    Ryengoth Active Member

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    Is the K&N an oil media filter or one of their dry filters?
     
  12. MADBADGER

    MADBADGER New Member

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    oil
     
  13. Ryengoth

    Ryengoth Active Member

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    Does it bog down with no filter on the compressor inlet?
     
  14. MADBADGER

    MADBADGER New Member

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    I haven't tried. Anyway, are you suggesting the oiled filter is restrictive? The filter I have is probably large for its application. Got a deal so I bought them.
     
  15. ManBot13

    ManBot13 Well-Known Member

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    Is the stock boost sensor connected to the port out of the carburetor? The boost sensor must be plumbed after the carbs, as it is used to read the pressure manifold air pressure and retard timing accordingly. Are you running the stock ECU as well? Without the boost sensor functioning (and stock ECU) it won't run right on boost

    What exactly are you trying to achieve with your setup? The inlet to the surge tank is there to bypass the turbo when it's not under boost. You've replaced that with another restriction. JeffK can attest to achieving 18psi boost with the stock turbo and plumbing (some other mods necessary). Given the small displacement of the engine, and smaller volume of exhaust gases, it going to be difficult to spin up two turbos without lag, and one turbo can actually provide more boost than the motor can handle.
     
  16. Ryengoth

    Ryengoth Active Member

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    You will get better performance from dry cone media and you don't have to wash them. Try it without the filter to rule it out. With so many mods you should have as much stock as possible and add back changes one-by-one.
     
  17. MADBADGER

    MADBADGER New Member

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    1) Yes stock boost sensor is connected to port of carburetor which tee's off to boost gauge.
    2) Yes stock ECU. I'm wondering if boost sensor internal parts of ECU are damaged, fried wire or something. Rule that out last.
    3) "inlet to the surge tank is there to bypass the turbo when it's not under boost. You've replaced that with another restriction"
    I do not have issues with not under boost conditions. Anything upstream of the reed valves is not causing my problem (I think).
    4) I only have one turbo. I moved the turbo from under the bike to the middle, as kind of a show piece, among many other reasons.
     
  18. MADBADGER

    MADBADGER New Member

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    Filter can effect performance but do you believe the filter can make the difference between NO boost and 18 psi boost? It would effect efficiency, but not prevent boost conditions (I think).

    QUESTION: Suppose I had a 100% stock xj650 turbo. What would happen if the boost sensor malfunctioned? Would the bike exhibit the symptoms I'm having?
    QUESTION 2: 100% stock xj650 turbo with seized turbo. does the bike run normal with just less power (b/c no boost)?

    Work with me on this logic....
    Seized turbo seams equivalent to an induction leak, If the manifold doesn't pressurize no boost is generated, no timing is adjusted...is that right? No turbo, seized turbo, giant gaping hole in turbo, motor *should (I'm speculating) run fine just no boost..So since I'm having issues I am generating boost.... right?
    Manifold/carbs are pressurizing, my issue does not lie within the turbo, piping, induction portions but with timing, ignition, fuel.

    I don't want to sound like a know it all expert. I'm a mechanically inclined noob. I'm just explaining my problem solving direction here.

    THANK YOU to anyone trying to help. I always try to solve a problem myself before I resort to getting spoon fed ideas/solutions.
     
  19. Ryengoth

    Ryengoth Active Member

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    Yes, compressor inlet restrictions reduce intake flow, which reduces outflow which kills the turbine speed. It is not a supercharger, it's a turbo so it has to have intake air to provide turbine flow. Cold-side leaks = poor boost. A bad intake filter is just as bad.
     
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  20. MADBADGER

    MADBADGER New Member

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    I follow you on this. I agree completely. but, I feel pressure from carburetor pressure/vac hose (hose to boost pressure) when I blimp the throttle in neutral. I know the turbo builds boost under load, so if I'm getting some positive air pressure just in neutral the turbo should be breathing healthy? again, I make assumptions.

    It's just strange I'm not getting poor performance I'm getting zero performance at boost. Bike should make more power but it makes less power.
     

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