the turbo is back.. this is a long one

[rspector]

End of last season I picked up an 1978 gs750 , with the atp (american turbo pac) turbo kit on it. Now that it is nice around here again, I figured time for another shot! Since last season I had removed the turbo and cleaned it out, didn't remove the fins. I had a turbo guy take a look at it , and he said it seemed fine. This bike has a zenith carb on it, and when you try and open the throttle it falls on its face, with no boost. At about 8k rpm it feels like its starting to spool, but never quite gets there. After repeated plug checks she seems to be dialed in pretty well. So I was wondering if 1) any one knew where a good place to start on the carb settings was?i.e where do you want your mixture screws set at. 2)Would the carb tuning cause a no boost situation?

I also pulled apart and cleaned the waste gate. I noticed that there is a small machined hole in the side of the waste gate, upon further inspection it appears that the hole goes all the way to below the piston in the gate. And there is a ball bearing inside it? Any ideas on what this could be? Also whats a good way to test the waste gate and make sure its not leaking? I did poor some paint thinner into the top of the valve and checked for leaks on the bottom and didn't find anything. The same way you would check a valve lap job on a head. So I can onyl asume that its not leaking?
any way , if the turbo is the problem I would gladely replace it or get it rebuilt , I just want to rule everything else out first

Thanks
Rob

 

[lecroy]

Ah, the bent fin turbo is back....

I guess I am a bit lost. Your last post talked about it making 20 lbs of boost.

i got the thing running pretty well, pulled turbo apart removed excess carbon, soaked carb, tuned it to the best of my ability, went and bought some 110 octane and off I went, the bike is almost too much to ride, at 7k its almost pushing 20 lbs of boost. Would love to get it out to a track and find out what it can do. So far I have put about 100 miles on it, with no ill affects. Thanks for all your help guys

If there are no air leaks in the system (exhaust or intake, this means you have gaskets on everything!) then it could also be the wastegate. It could be a weak spring, blown seal, wrong screw.....

There may be nothing wrong with it. The turbine uses the heat from the exhaust to turn. The only way to get heat is to load the engine. The only way to load the engine is to keep it running in the torque curve. So, for example just driving down the road, there is not a lot of load on the engine, so your not going to make a lot of boost. Depending on the size motor, motor setup, turbo setup and gearing, it may very well not make boost over 8000 but could still make 20 lbs at 7000 RPM.

Get some help from your turbo guy on this.

 

[rspector]

turbo

turbo

it just never really develops any power, at any rpm and really only makes boost every once and a while, if I plug the outlet from the manifold to the waste gate, you think I will have time to kill the power to the bike asuming that the waste gate is leaking and after I do that it develops boost ? None of the plugs are running lean at all, rich if anything.

 

[jgordon]

it just never really develops any power, at any rpm and really only makes boost every once and a while, if I plug the outlet from the manifold to the waste gate, you think I will have time to kill the power to the bike asuming that the waste gate is leaking and after I do that it develops boost ? None of the plugs are running lean at all, rich if anything.

Don't plug off your wastegate. If it makes too much boost you'll melt your pistons. I don't know about the little motor but I am running a HSR42 on mine and it has an accelerator pump so I don't get the lag. Also the turbo likes to be under a load like Lecroy says so you may want to change your gearing. You have Rayjay W/ water injection for cooling at 20# of boost?

Ask Chef1366, He has a buddy that is running a turbo bike that can probably help you.

 

[lecroy]

So, even at 20 PSI it doesn't make any power? BTW, hope your running some good fuel at those levels. I have been going rounds with fuel problems and made the switch to VP C16 from Torco Mach 118 NOS. Big difference.

I would not (LOL typo) block off the wastegate. If you do, you better be fast on the draw! If it can make 20 PSI, I'm thinking the problem is not the wategate. Can you post a few close ups of the plugs?

Have you had it on a dyno to get an idea of how much power it is putting out?

Again, the boost is not so much based on the engine RPMs as it is the heat the engine is putting out. No load, no heat. It sounds simple, but a picture is worth a 1000 words.

These plots are right off my bike. Top two graphs are engine RPM and output shaft speed. Bottom graph is boost. Notice that even at 8000 RPM, I make under 3PSI boost. Whats wrong??!! The key is the RPM graph. Every time it drops, the boost starts to rise, then falls right back off again.

In this next set of plots, blue is the torque curve. Notice that the torque is pretty much flat above 8000 RPM. This means above 8000 RPM the bikes does not accelerate as much. It's not working as hard and it's not making as much heat. Notice this is not HP, but torque.

Now look again at the to curves. When the RPM just starts to drop, this is where I am shifting the bike. Notice it is over 8000 RPM.

So what happens if the only thing I change is I move the shift point down just a few hundred rpm?

Notice now that the engine stays in its torque band and the boost pressure continues to rise.

So, my point is that there may be nothing wrong with your engine. Hope this helps.

 

[Frankenzuki]

turbo

turbo

I'd jhave to agree about blocking off the wastegate. If it makes that much boost you can't get of the gas quick enough before something bad will happen! I would think you have something wrong with the turbo. It's not going to make any boost by just blipping the throttle, but under a load, say 3rd or 4th gear a good turn of the throttle and you should be making something unless you have severe leaks between the exhaust and the turbo. And then you should be hearing some of that.

 

[rspector]

the problem with me trying to give it full throttle, below say 8000 rpm is that the motor just falls on its face, (I will get pics of the plugs tomorrow in the daylight). And thats why I ask if the carb could make that big of a diff, if its so off that I can't open the throttle up enough to build good heat and pressure that would probably prevent proper spooling. I spent 3 hours today checking gaskets. And running the bike with my head right next to all the exaust waste gate and manifold gaskets, I can't hear any leaks nor can I feel any either. So my next question would be, where do I start with my carb settings, the zenith was popular with the turbo kit so there has to be docs some where for at least a good base line. Also I am running race fuel (took your advice from last time) I have done many 4 carb bikes and have an idea how to tune those, but i'm not sure where to start on a 1 carb turbo 4 cylinder, as I don't want to create a really lean situation. Can you explain why the wastegate has a ball bearing in the bottom of it in what look sto be two channels drilled out of the bottom of the gate? also shold I be able to put some air pressure (from a compressor) to the waste gate and not have it leak at all at say 2 to 3 pounds? Because I get a small about of air bleeding threw the little machined hole in outside underneath where the piston sits? Doesn't make much sense to me why ou would want to bleed pressure slowly out of the waste gate all the time

and thanks for the graphs
Rob

 

[lecroy]

The wastegate has some type of sealed chamber that moves the valve as it expands and contracts. This hole is a vent. Sounds similar to my old valve that has a piston in it. The piston is not a perfect fit and will leak past it and out the vent. This is normal.

I doubt it could leak enough to not see any boost. The compressor can flow a LOT of air! Way more than a small leak like this would cause.

Not sure what race fuel your using, but that Torco is a real race fuel and I just want to be clear that even though the specs. for the two fuels are very similar, the VP is based on MON and behaves VERY different. Of course its $12.78 a gallon here compared to $8.00 or so for the Mach. Cheap considering the price of a motor. 20 lbs would be no problem (with correct jetting) with the VP. I was doing some crazy jetting with the Mach to get it to work at 12 PSI. So, use VP C16 and be happy, or limit the boost.

You should be able to see black from the carbon around any exhaust leaks. Ok, to your point, yes the carb could be so far out of wack that the motor would not make power. Before getting into that, what is your cranking pressure? I am not sure what a good number is for your bike, but would hope your at least in the 150 PSI range. Post your numbers. Remember to use a good gauge with a valve in the tip and do it with the throttle wide open. This will tell us a LOT about your motor.

Also post what the ignition timing is set to, what type of ignition you have and how you measured it. Post what plugs your using too, brand / part number.

I have never had a Zenith carb in my life and know nothing about them. If everything else looks good, I would want to see pictures of the plugs. It would be funny if the choke were on. In my case, when I switched to the VP this year, I had also increased my main and needle jet. The bike ran rich enough that it was difficult to get it to heat the tire. Heat line, what heat line?! So, sure it could be jetted fat enough to not run right.

Start with the compression numbers.

 

[AOD]

Can you explain why the wastegate has a ball bearing in the bottom of it in what look sto be two channels drilled out of the bottom of the gate?

Is this the linkage to the wastegate you are talking about?

I'm a turbo guy (engineer at a turbocharger company) so I think I may have some ideas of what's going on. I need you to take a picture of the process you describe above to detect a leak, but what I'm leaning towards is if the wastegate is not allowing it to seal properly (stuck open) or it's a vaccum system and it never seals properly. With the wastegate open you need lots of energy (engine speed and load) to build boost...which is why your system is flat until 8000 RPM.

Is your turbo a vacuum operated wastegate or boost operated, for starters?

Thanks,

~Adam

 

[rspector]

ok all cylinders are just about exactly 120psi , one is off 1 lb and that is with a very nice snap on compression testing kit. That does seem low does it not? But the fact that they are all the same I think is a good thing. It doesn't use any oil, nor does it smoke.
So now we are back to the carb or the turbo?, the racing fuel I used I believe is 118 octane, now I know you guys are gonna yell at me when I say this.. but I used a jic cap to plug off the waste gate (I'm sorry I had to try) still no boost, but I still can't open the throttle up all the way until I am at at least 6.5k on the tach.. Any one in southern NH that would come check this out and give me a second opinion.
Thanks
Rob

 

[rspector]

also the plugs are b7es, the ignition has been converted to solid state(no points) and its running red coils with yellow plug wires(has to be after market)I don't know wha tthe ignition timing is set to, how would I measure that?

 

[lecroy]

So, as suspected it's not the wastegate. I really have no idea about your engine but could believe the 120 PSI. Do you know which cams and pistons you have and what they are set to? I want to know the lobe centers and the deck height. If the pistons are stock and your at zero deck height I suspect the cams are out of wack.

The Torco is based on RON, the VP is MON. There is also more lead in the VP than the Torco. How is the fuel your using measured? What exactly are you using for fuel anyway?

For the ignition, Terry had told me some different numbers. The one he said to remember is 3030. I remember this as a common rifle cal. in my area. Anyway, this means your safe with 30 lbs of boost and 30 degs. timing.

You did not tell me what ignition you have, so I can't tell you how to set it. If you have a Dyna SP-4000 or an MSD unit, you can NOT use a timing light to set the timing. It must be done with a degree wheel. The red coils could very well be from MSD, but we need to know what box is driving them. Let me know what ignition and advancer you have.

Yes the carb could be a problem, but you need to start some where. Post some closeups of the last plugs. Do you know what your looking for on the plug reading? If so, you don't need to post pictures, just tell me what you see.

 

[rspector]

yes the plugs to me look like a rich condition(black and sooty), the 1 and 4 coil/cylinders cut out when you dump the throttle as they are blacker then the rest. Tonight I will take pics of the ignition, and plugs and the cdi, I have not removed the valve cover on this motor, nor did I install the cams so I have no way of knowing if they are off, I will of course check them out if we can't find any other problem. What I do know is the man who owned the bike before me (unfortunately he died) was winning trophies with this bike, so it ran correctly with this configuration at one point. and I believe the gas i'm using is 118 octane, not sure of the brand.

 

[lecroy]

You can buy some jets and start drilling. The problem is this. More boost means more HP which means more fuel needed. If the engine can't make boost, it does not make power and doen not burn as much fuel. I will normally take quite a few jets with me (for any engine) when I set them up.

The only way to use the color is to bring the engine up to full power then shut it off. No idle, nothing. Of course, this is after you install new plugs. Obviously if you run the motor at all after the peak point, the plugs color will change. Mine are normally black as you describe because I run it VERY rich when there is no boost.

With a turbo bike, like yours, the Rajay has an oil bearing. You turn off the motor like this under power and the oil supply stops while the turbin is spinning. Very bad. I know you don't like to listen, so I am sure you will want to try this at some point. LOL. So forget the color. What you want to do is look at the heat line, period.

Not to kick a dead horse, but if you don't know what your putting in the fuel tank, drain it and put it in the lawn mower.

How did you ever get it to 20 PSI boost?

Get those pictures up and lets have a look at this thing.

 

[rspector]

lol I don't know, i'm starting to think it was a guage malfunction, another thing I would like to add is if I put alot of load on the motor the boost gauge bounces it usually is it zero boost, but when the needle is moving into the +side of the gauge its not smooth, its bouncing. Dunno if that says anything... pics to come soon, I have big pics of the whole bike up at
http://www.hinsdalegreyhound.com/bike/bike1.JPG
http://www.hinsdalegreyhound.com/bike/bike2.JPG
http://www.hinsdalegreyhound.com/bike/bike3.JPG
http://www.hinsdalegreyhound.com/bike/bike4.JPG
http://www.hinsdalegreyhound.com/bike/bike5.JPG
http://www.hinsdalegreyhound.com/bike/bike6.JPG
http://www.hinsdalegreyhound.com/bike/bike7.JPG
P.S do you think that a Rajay Model # 302B25 Part # TC85-99 would work?

 

[lecroy]

It could be a gauge problem, but you wrote:

""went and bought some 110 octane and off I went, the bike is almost too much to ride, at 7k its almost pushing 20 lbs of boost. Would love to get it out to a track and find out what it can do. So far I have put about 100 miles on it, with no ill affects. Thanks for all your help guys""

What I want to know is what you changed from when you wrote this! Too much to ride, to no power? 20lbs to 0? What gives?

 

[AOD]

Probably off topic here, but how do you guys go about retarding the ignition timing as you make boost? Or...do you still continue to run advanced timing and use the higher octane to prevent detonation?

~Adam

 

[rspector]

i honestly dont know, I got one ride in and put it up for the winter, I roll the bike back out and get basically nothing.
also do you think that turbo I mentioned will work?

 

[lecroy]

I have no need for any of the B parts. Way too small for my needs. I don't know anyone with a 750 turbo so I am not sure what a good match would be. What compressor and turbine is on the bike now?


Adam, if you go back to the early days of F/B, they were running fixed timing. There was none of this fancy electronics we have now. Just a mag. But they were running 6's. Way quicker than I plan to go (for now).

With the MC-4, I can retard about any way you can think of. I just run fixed except during the take off while the bike is still in 1st. I use a Star advancer which is just a solid aluminum part.

And yes, again in my experience the fuel is key! VP C16 only! (Of course we are not talking about a street bike). Besides retard, you can also cool the charge with a little methanol and water. I have heard guys using a small shot of N2O (10HP sort of numbers) just for the cooling effect. Methanol is a great fuel for this as well if you can get it to work.