OS 91 PS Issue

[Festus1567]

I have a 7 flight old OS 91 Pumped engine in a Tempest that I'm having issues with.

At idle, it sounds as if popcorn is popping inside the engine. I know it's odd but that's the best way to describe it....

Idle needle is at factory setting and I am about two turns out on the main. On spool up and higher RPM's the sound goes away. Happens only at idle.

Figured it might be running lean so I opened the idle needle up and it still does it.

Could the pump setting be off? I did notice a slight amount of fuel collecting and dripping from the bottom of the pump during the short time this engine was running.

I am the second owner of this particular engine. Running an MP II and Magnum 30%.

I've always used YS but I'm willing to give this engine a try.

Thanks for the help.

[WillJames]

You running a Viper Head? If so you need more shims to run the Magnum. If not, you may still need an extra .004 or so to make it run good with the magnum.

The popcorn sound you describe is probably the motorgoing lean. From my experience with 4 C-SPEC PS's, the mid range is where they go lean and to get rid of the lean midrange on 3 of the 4 I had to run the bottom and top ends VERY rich. You could also get someone to cateye them, Shannon did one of mine. I am also running the extra return restrictor needles on 3 of my 4.

Also, you say you saw fuel dripping from the pump... I had one that had a very small slit in the very short tube that connects the pump to the nipple on the backplate and it caused the motor to run very lean. I replaced it with a piece of Tygon and it has run great ever since. (Thanks Dr. C-SPEC "Clintstone" :) )



Hope this helps a little. Sorry I did not see your post sooner.

Anyone else wanna take a stab at this????