LB20 Swap

Need help. Swapped worn out Kuhl HH 14 for new LB20 HH. Same injector. We are running a Lenco glide. Cannot get hunt or surge out of engine. I can get it to idle smooth at 2100-2200 rpm. As soon as I try to get to idle down to 1600-1700 it starts to hunt. JBR carbon hat. 990 Enderle pump. K style metering valve. 540 big chief if it matters. Things I've checked or tried. Set blades to .007 leak metering valve at 75% 4.5lbs idle check. I have gone as low as 40% to 86% leak. No change still hunts. Lapped Blower and manifold. Its flat. Checked for vacuum leaks. If I pull fuel shut off almost closed it will stop hunting but at 2200rpm. I am open to any and all suggestions. It idled fine with old blower. It had a small hunt 1500-1700. Thanks for Looking.

 

seems like .007 is awful tight. .012 is what I have had success with at about 82% leak down. Have you increased the total fuel volume with the LB20?

 

Yes, I did increase the fuel to the motor (main jet down .110 to .90) I'm not sure how the would effect the surge/ idle issue I'm experiencing.

 

hunt

increase the diameter of tank vent

 

Have you played around with your idle check crack psi? Why do you want to idle so low anyway?

 

Yes we have tried different idle check pressure. No change. It has a Lencodrive. Trans does not want to shift with idle any higher than 1700rpm.
Ownblock, It has a #12 vent line on the fuel tank. This car with same fuel system has gone 6.8s. All we did was change blowers.
Hoping some one that has swapped to a LB20 recently would have some insight.
Thankss for your ideas.

 

I increased idle check to 8.5lbs. I leaned metering valve down to 40% leak. The engine just heated up quickly.
So far the best results I have gotten is set injector blades at .014. Leak @ 84% and it will idle decent at about 2100. It still will hunt from around 1900 to 2200.

.

 

I have a #12 vent to the tank... I guess I could try removing the cap when firing it up today.

 

Is the ignition timing stable?

Caused by too much cam endplay, something else is loose (IE cracked rollpin, sloppy pin hole, etc).

What mag and what mag drive?

 

SoDak, I have a crank trigger on it. Timing is rock solid. We have tried taking timing out when on the trans brake to no avail. MSD 10 with power grid. Racpack with flow meter and pump pressure. No nozzle pressure sensor. It has about 15lbs of pump pressure @2100 rpm idling. I have been from .4 tenths of a gallon at idle to 1.4 gallons.
Any thoughts about spacer between blower and hat being to large possible causing not filling rotors. Just a thought.

 

No to the filling the rotors question---- next question is , are the inlet and outlet spacings, pattern exactly the same ?

To me it is finding air from somewhere else when you can close down the butterflies that far and still idle high, remember the manifold has vacuum until the throttle opens up -

I would go back and check the fit of the blower to the manifold , make sure your O ring is sealing properly , etc

 

I second that motion. I think the motor is finding air somewhere you might not know about. Out of round injector blades or something else. My 526 BAE w/14-71 HH LF will idle at 1,500 if I set it that low. I usually idle about 1600-1700 (clutch car). Smooth idle with no hunt. Slow to heat up until I start closing down the fuel shut-off. 5# idle psi.
Find your air leak. Possible also is that your port check is set too low.
Just my HO.

 

Mark, I have lapped the blower manifold on the motor its flat. O-ring sits up approx. .015. Rechecked injector to adaptor its silicone. Adaptor to restraint plate has a gasket. checked and good. Restraint to top of blower is O-ringed. It is also good. Going back to work on car tomorrow. I am going to raise idle check to 20lbs and leak metering valve to 70% as Mike Canter suggested. Thanks for everyone's suggestions.