Hey guys,

I just installed a freshly rebuilt 650 double pumper (4777) on my 350, but its acting funny. Everything about the way it idles says its running lean... white plugs, off-idle stumble under load, dieseling when I shut it off, etc... but when its sitting and just idling, it reeks of raw fuel. I can't figure it out? I was able to tune out some of it today. The dieseling issue is mostly gone since boosting the timing another 4*.

This is how I have it set up right now:

- 71/80 jetting
- Idle screws 1.5 turns out
- 6.5 powervalve (front only)
- White acc pump cam on primary
- Orange pump cam on secondary
- 30cc pumps on both ends
- Secondary idle-speed screw closed (Secondary throttles are closed completely - NO 4-CORNER IDLE)
- Idle speed about 800 rpm
- Electric choke
- Floats set to the bottom of the sight plug hole

It never used to act like this with the 750 VS Holley I had before the double pumper, and nothing else has been changed. I only changed the carb.

 

dieseling is due to retarted timing/lean. i'd richen up the mixture screws some to fatten up your idle circuit, try 1/8 to 1/4 turn more on each of them, then drive it again. Sounds like you might have to play with squirters as well for the stumble, although I'd try the mixture screws first.

 

Ok, well, today I played with the carb a bit.. richened up the idle a little bit and that helped the dieseling problem. Thats pretty much cleared up now. Also, the stumble is now gone too... its a little lazy, but no more than it was with the VS carb, so I think that might just be the cam (XE274) at work.

It is running alot better now, but still smells like fuel? The choke is opening fully, I checked that again today, and there are no fuel leaks anywhere. Is there anything aside from running overly rich that could cause the smell?

 

with that cam it would want a 3000-3500 stall, so if you're trying to beat on it, you'll want to keep the rpms up that high for the launch. It's always going to act lazy down low since it's more a midrange cam. Try advancing timing more at idle while still keeping 36-ish total to get rid of that rich fuel smell at idle. The duration of that cam would cause unburnt fuel to get into the exhaust unless you give it more timing lead in. I'm running a bigger cam, but locked out my timing and that cleared up the richness problems at idle. For you though maybe 20-something initial and 36 total would help, keep advancing it and playing with the advance slots until it gets where you want. You'd have to weld up the advance slot to limit the mechanical advance to where you want it.

 

I was thinking about that as well, actually (not enough timing, lots of unburned fuel). If this is the case, would this actually be hurting anything except my eyes? I mean, is it actually running too rich, or does it just stink because it doesn't have enough timing in it? Know what I mean? It seems to run just fine with no smell at any other speed (cruise, WOT, warmup fast-idle, etc) but not on a regular hot idle.

 

plugs "could" foul out, but the extra timing at idle might clean it up, but if you have no other issues I wouldn't worry. I have a "funk" smell like a bonfire after I drive my car around for a while and I wouldn't have it any other way.

 

Sounds good... I "fixed" the manifold vacuum port tonight, so I'm going to hook up the vacuum advance to that after I get my fuel line finished tomorrow. Thats how I always had it set up before (now that I think about it, I should have mentioned that earlier) so I can run more timing at idle w/o a load on the motor. Maybe that will clean it up some.

 

Even thou you have a "two corner idle" carb, it still must idle on all four barrels. Idle fuel flows from all 4 barrels at idle. There are two channels in the base plate to transfer fuel from the primary side idle to the secondary side. The secondary barrels must be slightly open, exposing the idle transfer slot a bit. if there is no fuel flow from the secondary side idle ports you have the wrong base plate gasket. The secondary metering block or metering plate has a fixed non adjustable idle system that mixes with the primary fuel that arives thou the channels in the base plate. If you've replaced the stock channeled throttle base plate with one that doesn't have these idle fuel transfer channels you will have trouble getting a good idle until you convert the carb to a true 4 corner idle carb. ( rear metering block, rear idle bleeds)

 

a pic

 

Thanks... I didn't know about that (idle on all 4 throttles). I set the secondary idle set screw to snug + 1/4 turn, as the instructions in the kit suggested. This sound like a good way to go?

 

thats only a rough starting point. You want to balance the throttle blade opening front and back to get a even fuel flow and best idle.