Greg.H

I've got a lean stumble when going from primaries to secondaries, gauge goes to 17:1 or thereabouts for a second and then back to normal. The secondary transition slot is not showing, and I'm pretty sure (like 100%) that this is the problem.

If I open the secondaries up so that I get .020" showing, the engine idles at ~1400 rpm, and definitely needs more fuel from the mixture screws. At this position, with both blades closed, looking down the bores I can see that the secondary side is clearly more open (I can see more light through the cracked open blades) than the primary side. It's as if the transition slot is not deep enough, or the throttle blades are not wide enough.

I haven't changed anything on the baseplate, but I got the carb secondhand. It's a 650 DP 4777-3. Primary blades are marked 172 and secondaries are 173.

Anyone have any ideas how to remedy this or have at least had the same problem? Thanks.

Doug G

I would look at the cam/pump shot and squirters before anything.

The transfer slots (how much showing) isn't going to do anything but maybe cover your issue and create another....IMO

Greg.H

I would have thought that no transition slot would be the cause of the problem.

It's got a green cam and a .033 nozzle. I can bump up to a .035 and see what happens.

Pop N Wood

iTrader: (1)

That has to be the first thing you have ever said that I disagree with.

Getting my transfer slots right made a huge difference in getting rid of off idle stumbles.

Two things: double check for vacuum leaks and if none found lower your idle timing.

I had the exact same problem, stock cam LS2 wanting to idle at 1200 or so. The idle speed screws were all the way out causing the blades to rest on the stops. Put primary and secondary at 20 thou, squared up the idle mixture screws, than lowered the 500 RPM timing mark to something like 5 degrees and brought the idle speed down. Between that and some IFR and IAB adjustments it smoothed out the AFR at idle, got rid of off idle hesitation and allowed me to go multiple sizes smaller on the accel shot.

Doug G

Maybe it's my carb ?
Closed my secondarys, IAB screws out only 1/2-3/4 turns from seat, played with the cams some.

Idles at 900-1000
AFR 13.7-14.5 cold..............14-15 warm
Cruise AFR is 14ish
WOT AFR is 12.5-13.5

I have a way to record, but never hooked it up yet

Another thing to add on to the list

Greg.H

Thanks for the help you guys. I've tested for vacuum leaks several times for various other things, and never found any. So this weekend I set My Daytona module to the lowest setting and unplugged the vacuum advance and it helped a lot. So I think the solution here is to get the adapter and take out some of the vacuum advance from 500-1000 rpm.