PMO Float Bowl Check Valve

[cay-ahe]

I have some bogging down when I stab the throttle that is less evident when the throttle is gradually increased. This is not as much an issue above 4000 RPM. I have used the same carbs on two different engine configurations with the same issue. I was reading some of the technical information on the PMO site and came across this bullet point.

4. Reducing Injection Quantity

We have found that race engines often need varying levels of injection quantity. Coming out of a turn, too much injection quantity can actually cause bogging. PMO has different float bowl check valves to adjust the injection quantity up or down. Rob King at S-Car-Go has cut the injection quantity down to almost nothing with excellent results. The normally installed float bowl check valves have a .5 mm side hole for bleed back. The larger the bleed back hole the less injection quantity. The valves come in increments of .1 mm up to 1 mm. We have 1.5 mm valves for people who want to almost eliminate injection quantity but still start the engine.

Just wondering if anyone here has an experience or success changing out the check valves described by Richard above.

[MBruns]

We have found that the .5mm CV's work in most cases, alot of people try to tune these like weber's and you have to throw that note book out, The idle circuit has a huge effect on the total mixture curve all the way up to about 5k, by that I mean small changes in mix screws and or idle jet sizes or IAC jet changes have a noticable effect on the AF values.
Mike Bruns JBRacing.com

[cay-ahe]

Thanks Mike. By the way we just fired up my new engine using your twin plug distributor and guidance. Beautiful, thank you.

[MBruns]

Thats Great, I spoke with Jim earlier and will be glad to help you with the jetting etc...
Mike Bruns JBRacing.com

[cay-ahe]

We spent about 2 1/2 hours on a chassis dyno and feel good about the overall A/F results. I'm headed to the track in the morning, I will know more after that.

[Eagledriver]

I ground down the cams on the injector pumps. This gives me a much smaller injection and can be adjusted with the adjuster nut. Before that I had to disconnect the injector pump to keep from bogging. That made it hard to start the car of course. I get about half the movement of the pump arm with the new cam profile.

-Andy

[cay-ahe]

Thanks for the help. Any other performance change other than getting rid of the bogging? Did you need to do any jet change after doing the injector pump mod?

[Eagledriver]

The injectors only work as you open the throttle. There are no effects on the idle or main circuits so no need to change jetting. The idea of the injectors is to prevent a temporary lean condition as the butterfly valves are opening. If you had no injectors you'd notice a little stumble due to this lean condition when you open the throttle.

-Andy

[cay-ahe]

Gotcha, thank you.