KJL

I am trying to dial in my carb and can't seem to get around a rich condition when when under light throttle, light load high vacuum condition.

It seems when I am in a light throttle condition with lower load, the high vacuum sucks to much fuel and my LM-1 AF ratio will dip into the low 11's to high 10's. This is not persistent but annoying. I have reduced the main jets, increased the idle air bleed diameters, dialed in the idle mixture screws to lean out the idle as much as possible.

My engine like to idle at abut 1100 rpm. This produces about 9" of vacuum.

It seems the high vacuum low load condition is causing unneeded fuel to be drawn into the engine. My initial guess was through the idle circuit.

My carb is set up as noted below:

950 cfm w/mechanical secondaries
pri jets 79
sec jets 88
Pri vac adv. 6.5
Sec vac adv 5.5
Idle air bleeds 075
Hi speed air bleeds 035
pri squirt 21
sec squirt 32
Secondary blades are open just a tad at idle (now 100% closed)
Primary and secondary blades have been drilled approx 1/16" diameter (holes have been filled)

lars

Here's an easy thing to do and check: Pop a couple of staples out of your office stapler. Most staples are about .017" diameter. Straighten them out except for the one 90-degree bend and stick the short end of the bend into your IFR holes in the primary metering block, sandwiching the staples in place with the gasket. This will lean out the transition circuit, which is where most of the fuel comes from under the described conditions. If this affects it in the right direction, you'll know where to start tweaking the carb.

Lars

KJL

Thanks Lars, I will give it a try. I have included a diagram of the primary metering block and jet diameters and number sizes for reference. This carb could have been initially set up for a marine application.

Jebbysan

AED makes a three circuit billet primary metering block that will give you control over the transfer circuit.....

http://www.aedperformance.com/compon...roduct_id,114/

Jebby

KJL

I have looked at several diagrams showing the IFR holes at two different locations. On my metering block, the lower holes do not have a pressed restriction. They are very large in diameter. The upper holes have screw in jets and measure 0.037" in diameter.

PAmotorman

yes those are the IFRs at the top. you can get .015/.018 dia wire by taking apart some stranded electrical wires

lars

That's correct - the IFRs are at the top. As noted in my earlier post, standard office staples are .017" diameter, so you can just pop a couple of staples out of your office stapler, leave one bend in them, pop them in the holes and sandwich them with the gasket to retain them. This may not give you the exact results you desire, but it will make a significant change - you can then evaluate if the change went in the desired direction so you'll know if you're on the right track. If so, since you have screw-in bleeds and IFRs, you can then order some orifices in the correct size range: You can calculate the area reduction induced by the .017" diameter wire and use that as a guide for selection.

Tip:
When tracing down circuits to determine what orifice goes with what, you can use a can of WD40 with the skinny plastic tube extension on it. Remove an idle mixture screw and squirt the WD into the hole that the mixture screws goes into. The WD will come out the idle circuit holes, including the IFR. You can then reverse the flow to re-verify. This is also a good technique to use when checking to see if any circuits are plugged.

Lars

KJL

Ran it with the staples and found it was too lean just off idle. I found some wire with a smaller diameter(0.013") to see where this puts me. Will try and track down some screw in orifices and use my pin drills to dial it it. I was amazing how much using the staples affected the system. The car would not even start until I opened up the idle screws a tad.

lars

Good job. As noted, using the staples is just a troubleshooting tool to see if it moves things in the right direction. If you use some 5th grade arithmetic and calculate the cross sectional area of a .017" diameter staple, and then calculate the cross sectional area of the IFR metering hole, you can subtract one from the other and run that as a percentage of the IFR cross section to see how much of a percentage drop in area you produced. You will see that it's rather significant - usually over 20%. Obviously, when fine tuning a carb setup, you don't want to be making 20% changes, in most cases. But if the staple trick leaned out the transition, light cruise and idle circuit, even if it was too much, you know you can then tune it where you want it by tweaking that percentage reduction a little - always work in cross sectional area and not diameters when calculating how much change to make (keep changes in the 5-10% range). Good luck the with tuning!

Lars

KJL

As a follow up I have discovered what I believe to be a contributing issue with this carb, all 4 butterfly plates were drilled. This forced me to run an extra rich idle circuit to compensate for all that air bleeding by at idle and also caused the car to idle too high when I tried to lean out the idle which in turn resulted in the throttle blades to be almost 100% closed which in turn resulted in the idle transfer slot being completely covered which in turn also resulted in a lean flat spot when accelerating off idle. Long story short, I filled the holes with solder and now I can properly set up my idle and throttle blade position and have an idle speed around 1000 rpm. My vacuum at idle has also improved. My guess is now I can lean out my idle to where it needs to be and still have a good idle speed. This should also take care of the rich low load cruise issue. I also went to smaller IFRs. Test drive today weather permitting.

New specs:
950 cfm w/mechanical secondaries
pri jets 79
sec jets 88
Pri vac adv. 6.5
Sec vac adv 5.5
Idle air bleeds .073
Hi speed air bleeds .035
pri squirt .032
sec squirt .032
Secondary blades are open just a tad at idle (now 100% closed)
Primary and secondary blades have been drilled approx 0.01" diameter (holes have been filled)
Primary IFR was 0.037, now 0.035
Secondary IFR 0.036
Idle screws about 1 full turn out each and idle is about 1100 rpm with correct amount of idle transfer slot exposed.
Idle vacuum has increased from 9" to 11'' at approx 13.5 AFR

fishslayer143

why did you drill all 4 throttle blades? and what Power Valve are you using? with 9 inhg you should have a 4.5 PV

KJL

My vacuum is running at about 10-11 in hg now. The car seems to respond well under acceleration with the primary power valve coming in at 6.5 but that may change now that I have filled the holes. Rule of thumb is 2" lower than idle vacuum to start with.

As stated in my last email, I did not drill the plates. It was sold to me that way.

fishslayer143

drilling blades is old school, usually when a carb is too big to begin with.. .. not necessary ,Air bleeds are replaceable now.. I had not read the whole thread yet.. good luck

KJL

The carb he sold me is a marine carb and was likely setup for a boat. I wanted to buy my own carb but he insisted that I purchase the "custom" carb from him. He would have the carb specifically built for my application and it would work out of the box. This shop has a good reputation and has been building race engines for many years for pros and also done stuff for magazines. I had no reason to doubt him. It is clear this carb was not set up for my engine. He just probably had one he needed to off load and stuck me with it, engine dynoed it at full load and called it a day. The car was un-drivable when I first attempted to drive the car with the carb as recieved. The carb itself is high quality and completely adjustable. I have been chasing my tail around over the last year trying to get the bugs worked out. I think by filled the holes I may be able to finally dial in the primaries. Once that is done I will rent some dyno time and work on the secondaries. They are close.

One other thing that surprised me was there were no jet extensions on the secondaries.....I thought that was typical on all street/strip carbs? Still on the fence regarding the secondary PV. May plug and increase the secondary jet sizes but so far the car seems to do OK with it.

To be honest I don't even trust he dyno numbers at this point..... the car was dynoed with 95 primary jets and 96 secondary jets and yes that was with 3.5 PVs in the primary and secondary circuits.

fishslayer143

yeah, always be skeptical of the guy who has the part for sale telling you.." this is PERFECT part for you"... now if he is telling you to buy a specific part somewhere else, that he doesn t sell, I might be more convinced ... hope you get it dialed in.. sounds like you are getting closer with those holes plugged.. ...I went Quickfuel on my build, was a breeze to dial in.. doesn t need constant tinkering like some ...9 yrs, runs just like the day I installed it .

btw, what kind of numbers did it dyno? or should I say did he "say" it dyno'd

KJL

My settings are looking more and more like an out of the box Quickfuel 950 every day. I am just very disappointment with this guy... finding an honest shop is very difficult. This is my second time around and my first shop was no better. I really want to give this guy a honest review on his web page but if I do, I can kiss any future support goodby but I am not sure if I would ever go back there regardless. There are other things with the engine that don't seem right for a custom built engine like leak-down values ranging from 6 to 14% and two oil changes into the new engine, only about 2000 miles...maybe...I am still finding metal flecks in the oil filter. Some of that I think was from a bronze distributor gear that was self destructing. He should have known that was going to happen with this cam.

695hp at 6500 & 600ft-lbs at 4800 I was there when he tested it and saw the numbers with my own two eyes but still.....I can't trust anything from him at this point. I am eager to chassis dyno but want the carb dialed in and to stop seeing metal in my filter first.

Haggisbash

Seems no matter how small the pool, you can find a shark swimming in it. I wish you luck in getting your engine sorted. Did you test the flecks you found with a magnet?

KJL

Yes, most of the larger flecks were not magnetic. I am interested to see what filter # 3 looks like. I have kept all the filters for comparison. The second was better thank the first engine dyno filter.

MotorHead

Have you tried reducing the jets a couple of sizes. When I got my 406ci dynoed the operator put in huge jets to get max power and make me happy but he didn't tell me.

I got home and put the engine back in and it ran OK but stunk of gas in the garage. I noticed that the gas gauge was going down way faster than before.

I honestly thought I had I had a gas leak somewhere and spent some time with a flashlight under the car looking for one.

Looked in the carb and found the huge jets and went down about ten sizes front and rear IIRC.
That fixed the problem and got me back up to my normal 8mpg Only kidding I got pretty good gas mileage out it.

PAmotorman

if the dyno room was pulling in outside cold air and if you are pulling in 200 degree under the hood air you will need a big jet change