LXguy

iTrader: (5)

This sounds like a blown power valve to me.

speedtigger

iTrader: (16)

This is a common misconception. The powervalve does not affect the idle mixture, even if the diaphragm is torn. The powervalve is part of the main booster enrichment circuits, not the idle circuit.

LXguy

iTrader: (5)

It's probably a persistent misconception because it's in the instructions...


Check it out at 2:32

Or if you prefer text...

http://www.holley.com/data/TechServi...wer_valves.pdf

Cheers,
Steve

speedtigger

iTrader: (16)

You may actually be right. My response was not correct. I am used to responding to people who state that too low a # of power valve would cause a rich idle and it will not. But, in the case of a torn diaphragm fuel would be sucked into the pressure reference port, through the base plate and into the plenum. Thank you for correcting my incorrect post and supplying that info.

LXguy

iTrader: (5)

My initial "smiley" didn't show up so my previous post came across a lot more jackass sounding than I intended. Edited. Sorry if I caused any offense!

Steve

jays78

The rich idle was from the throttle blade closed to far, sucking fuel from the idle port, pop n wood was on that one.

I am now in the middle of installing a lc1 wideband meter, its taking me a little while to finish, I removed my factory gauge cluster and removed the old clock that didn't work, to put the gauge in that hole. fits pretty good!

I should be finished by this weekend.

speedtigger

iTrader: (16)

No worries. Getting the right info out here for the guys who need it is what is important. Thank you for correcting my error.

jays78

I got the afr meter installed a few weeks ago I haven't got a decent carb yet but I thought I would share what its doing.

It idles around 13.4 in neutral, put it in gear it leans to around 15, cruises around 13.

When I lift off the throttle it goes rich around 10

Crazy!!

jays78

Just bolted on a new quickfuel 735 , right out of the box I set the transition slots at 20 thou, made no changes to the carb, still got high idle, backed up initial timing to 8 degrees flat to 1000 rpms and still had to back off front and rear idle screws to get 800 rpm idle. of course this makes the idle air screws really touchy, afr is unstable at idle, cruise afr not to bad 13.7, half throttle acceleration 11.0 wot 10.0 seems that when power valve opens carb goes rich power valve is 6.5 idle vac is 20.

And has a slight lean stumble pulling off.

Happy July 4th!!

jmortensen

I've got the eye watering rich idle problem too. I did check the linkage and transfer slots and all of that, all looks good. I have a wideband O2, and the carb is a 650 Speed Demon, mounted on a L33 5.3. This is a 2006 engine with slightly higher compression at 9.9:1. Cam is 220/224, .581 lift 112+2 LSA, and it's going in a 2200 lb autocross car with 4.11 gears running pump gas. Right now at idle with the mix screws out 1 turn I'm at about 10.7:1, if I turn them in another 1/2 turn I get to 11.5, but then it pops and hesitates and actually dieseled and backfired through the carb when I shut it off. I've only taken it around the block but AFRs while driving seemed to be all over the place. Rich down low, stumble on accel, then leaned out on top. Idles at 1200 rpm with the transfer slots showing square. No adjustable timing yet, I bought the intake with the Edelbrock module without doing my homework. Will probably replace this winter, but as for now, I'm using that setup with module 3.

I really hate the idea of sticking wires in the IFR holes. That just seems so cheesy. Thinking about drilling and tapping the metering blocks and drilling holes in 6/32 brass set screws instead. I see a lot about this online for Holleys, but haven't ever seen it for the 650 Demon. I am pretty sure it's a press in restricted orifice in the 650, although some of the higher end Demons have screw in jets.

jmortensen

I went ahead and tried the wire thing while I was doing other stuff in the shop, curious to see what effect it would have. One .012 gave me about 12.5:1 AFR. Two got me to 14.7 with 2 turns out on the mix screws and I had to open the throttles about 1/4 turn to get it to stay idling, and it won't stay lit under about 1000 rpm. In addition I'm noticing a lot of missing now that I didn't have when the AFR was super rich, and even with no load it is stumbling just revving it up. It was hesitating just a little bit previously, now it's worse. I do have a flexplate/dual 7.25 button clutch, so maybe that has something to do with the fast idle issue. New to the 4 barrel world. Any advice?

Pop N Wood

iTrader: (1)

You might have fouled the plugs with the rich idle. Clean them up before you do anything.

Don't forget the basics. Make sure all the gaskets are tight, power valve is not blown, sealing surfaces all flat, no debris in the carb etc. Many good online carb guides telling you what to check. Also make sure all the airbleeds are open and not blocked. I had that problem for awhile, noticed fuel dripping from one of the boosters during idle.

I wouldn't hesitate to drill and tap orifices on a carb. Scary the first time you do it but not hard once you figure it out.

You may need to tweak the idle air bleeds when you adjust the IFR. That was the secret to finally getting mine right. That and backing off timing at idle only. Timing can be used to set the idle speed while keeping the blades set with 20 thou of the transfer slot showing. Unfortunately will be hard to use that trick with your eddy box.

Make sure you have a MAP sensor installed. Lots of talk on here how MSD boxes dial in full vac advance if one isn't there. solution there is to zero out the vac advance, but don't know that you can do that on an Eddy box. Not sure what they do.

jmortensen

Hey Pop. Dived in today and put in some .029 IFRs and still about 11.5:1 at idle, won't idle lower than about 1100 rpm. It was still popping a little bit out of pass side exhaust. Will clean plugs and see if I need to try again with some smaller IFRs.

Used the 6-32 set screws. Man those are tiny, and the hole in the carb is actually alreadly larger than the recommended drill for tapping 6-32 (7/64ths bit is what is recommended). Still I was able to get them in and tight, so I think I'm comfortable with what I'm doing. Drilling them out is kind of a PITA. Parts are SO small.

I am running a MAP sensor FWIW.

Posted about this on the Carb LSx Swaps FB page and just got a bunch of people telling me to run a 750. Sounds to me like quite a few Demon/Holley style carbs have this same problem though. Since I'm keeping the rpms fairly low and want low end, I'm going to try and make this carb work.

jmortensen

Cleaned the plugs and AFR went up to about 12 and it does run smoother. Put a vacuum gauge on it and it says 19" hg at idle. Again, idle is pretty fast at about 1000-1100, and it dies when I try to make it slower. I know the power valve is 6.5. I don't think it's leaking because this carb has next to 0 miles, but it's tough to check because I connected the float bowl vents and drilled a bunch of holes in the tube, and I read that plugging the vent and seeing if the car dies is the test. I guess the sign of a blown power valve is super rich idle, so maybe I should replace it just in case. ???

If I were to replace, don't know if I should size the power valve up or just leave what is in there since the idle is pretty high. I guess from reading the thing to do is to go 1/2 cruise vacuum. Waiting on new rear calipers so can't cruise right now to check it.

Seems like the thing to do is swap the valve and see if that changes the idle AFR, and if not then swap in progressively smaller IFRs to get to 14.7:1, then drive and check the cruise vacuum and buy the right power valve based on that.

Thinking the squirters are likely too small also. Seems like the way to go would be power valve, THEN adjust squirter size.

jmortensen

Quick update. Checked the PV by sucking on it, held vacuum. Stepped down to a .024" IFR and got it in the 14's AFR with 1 turn out on the mix needles. I did make some .021" IFRs as well, could swap those in if there is a benefit to having the mix needles further out, but barring that I think I'm moving on to PV next. Got an 8.5 PV on order already, just didn't want to wait and ended up finding the "suck it" test online so figured I'd give it a shot.

jmortensen

Put in 8.5 PV, let it warm up, idle AFR is back in the 13.5 to 14.5 range, digital gauge is bouncing around with the refresh rate. Snapped open the throttle a few times and it's still falling on its face. Actually got it to almost die by snapping the throttle open, just totally starved for fuel by the looks of it. Trying bigger squirters next. I'm going to drill these out until I get a decent reaction in the shop, then see what happens under load. Holley vid says step up 3 sizes at a time. Might go 3 the first time around, but don't want to drill these things out huge and then not be able to use them if I can make this weekend's autox.

jmortensen

Drilled out the squirters 4 or 5 times and ended up at .037. Revs up much better, still a little hesitation but I believe in order to go bigger I need the hollow bolt. Maybe will buy a .040 and see how that works, but I want to try driving to see how it feels, still waiting on calipers which look like they're going to get here Wednesday.

jmortensen

Did the drive around today, real lean on the primaries. Like 16 or 17 to 1. Will try jetting up. Other than that, still a little stumble off idle. Ordered up the hollow bolts, will try .040 with hollow bolts and see how that works, and if it still stumbles I guess I'll just keep drilling them bigger. It's definitely better than out of the box, that's for sure.

gtfoxy

Good to hear it is getting better. I hope you get it figured out.

One thing you should be aware of, if you didn't know already, is if there is a miss, caused from just about anything, the O2 will read lean, even when it is rich. So if say a single cylinder is the culprit it will cause the O2 sensor to jump around as the pulse of the miss passes across the sensor. Now imagine how the O2 will read if multiple cylinders each doing a little stumble intermittently on a random basis.

jmortensen

Looking for some kind of baseline recommendation on jetting if anyone has any. Back into this and Pop's suggestion of larger IAB makes a lot of sense. I have been reading that the Demon metering blocks have .031" holes in the emulsion tubes too, and that is too large. This makes it rich at idle and lean off idle. My eye watering idle and stumble when cracking the throttle open bears that out. Just not real excited about going bigger and bigger on the nozzles to compensate.

Looking at my Demon carb book, the IABs are on my carb are .059 and .063, and the Road Race version of the carb, tuned for 1:1 linkage has .070 IABs. I drilled out the stock orifices for the IAB and emulsion jets and tapped all of the holes, so I will need to pick a size for everything again. I didn't mess with the high speed air bleed. Thinking going .065 on the IAB and .028 on the emulsion jets and seeing what that does. Would be nice to get it in the ballpark before taking it to a dyno. I don't want to waste a lot of money to get it in the ballpark. Also read that the pink cam has the smallest shot, so I ordered up a blue pump cam and some smaller nozzles, .028 as I suspect that all of this cam, emulsion and IAB tinkering will change the nozzle requirements.