Doolittleraider

My Feedback: (72)

I have quadra 75 in a ziroli corsair has a Menz 22-14 prop and the highest rpm's I am getting is about 6500. I have flown this plane seven times and everytime it flew after 4-5 minutes it dropped RPMs/power in the air and I landed it. I just changed the fuel tank and all the lines. It now has a simple two line system with a vent and T-line. The fuel tank is wrapped in foam. I also checked the screens and the diaphragm. After running on the ground for 1 minute it surges for a second, a couple times like its getting air bubbles in the line? The transition is flawless. It also has plently of cooling in the cowl.

The needles right now are 3/4 high end and about 2 low end.

Any suggestions???

Thanks
Peter

Truckracer

My Feedback: (19)

see my post in the gas engine forum.

Rebel Flyer

Prop is probably too big. Try a 24-12 pitch. Use whatever prop that gets you around 7300 rpm's. You will never get the air bubbles out of a tank that a Quadra 75 is shaken...Not stirred. Make sure your Fuel lines are not too big. Zip tie all the connections. They need to be tight.

Good luck.

Rebel

Truckracer

My Feedback: (19)

Q75s do shake but no that bad. I do mount tanks in foam behind them though when most gasser tanks can be more solidly mounted.

G-Pete

Sounds to me this engine runs too lean...

Don't worry about a higher pitch prop, they unload in the air - static RPM's are only for reference.

What is the spark plug heat range and what color is it?
How is the compression on that bugger?

Doolittleraider

My Feedback: (72)

Compression is great. Spark plug, when I last checked it was light sandy brown.

G-Pete

That means the fuel is good until she dies/surges, the motor is strong. About 6.5HP. What about the vent line?

Doolittleraider

My Feedback: (72)

The engine has never quit just dropped power in the air. On the ground after running it will get this quick one second surge about every 30 seconds. I have a simple two lone system....the vent is a brass tube in the top on a sulvan tank and exits out the cowl.

G-Pete

Now I'm running out of ideas without laying hand on it. I ask about the vent line because it just sounds like the carb can't pull gas in the chamber. When the vent stuck on the roof of the tank, it takes a little time then the engines almost dies and fresh air gets pulled in because of the immense vacuum. Then the cycle starts from the beginning.
Sorry, that's it from my side. If the carb is older then 2 years you need to replace the diaphragm because of the ethanol contents in the fuel.

Ham639

My Feedback: (13)

I had a G-62 that did the same thing. The carb block was leaking. It only did it after the engine got hot and would warp the block just enough to suck air. The engine would never die, just go lean. Once I put a new carb block on I never had a problem again. BTW, this happened twice, both on NIB G-62's.

Just my 2 cents, best of luck

Ham

crashproof

You say it has plenty of cooling but a better question might be is it baffled correctly. You know the cowl is covered except for a cut out directly in front of the fins, then atleast 2 times as much for exit. If the entire front of the cowl is open that could be the problem causing it to get hot and sag. Just a thought. Kevin.

Doolittleraider

My Feedback: (72)

Crash proof thanks for that suggestion...I have a feeling it is sucking air from somewhere..

Meschmidt

My Feedback: (15)

I see your problem. Only 3/4 turn on high end? Start over on needle settings to 1 1/4 low end and 1 1/2 high end. Set high end to top rpm first, then set low end for good transition. Quadra's are torque motors rather than rpm motors. They like big lower pitch props best. Card tuning tips at http//tech.flygsw.org/walbro_tuneup.htm Paul

Doolittleraider

My Feedback: (72)

Ran the quadra 75 today with the 24-10.
I set the low end at 1 and had the high end from 3/4 - 1 1/2 best RPM was 6200. The surge/quick 150-200 drop occured every 45-60 seconds when ran wide open but would last for a second. The engine fired every time, never stumbled or cut out. I did not see any air bubbles in the line or see any fuel around the carb. What is a strange is the low end was just as good at 1 turn than at my orginal setting of two it never seemed to make a difference the transition was still flawless...