Idle too high on new engine break-in

I finally started my new engine to break in the cam. Break in went fine but afterwards when I tried to adjust carb idle, it will not run well under about 1500 rpm. Engine specs are as follows:

-200 six, essentially stock short block rebuild but with ARP fasteners, 0 decked, double roller timing set, and H264/274 cam with 112 lobe center, advanced 4 degrees.
-Rebuilt OZ-250 head and intake, ported with 1.8" back-cut intake valves and 1.5" exhaust valves, 3 angle valve job, 302 valve springs.
-1.6:1 Adjustable roller tip rockers.
-Classic Inlines header (rest of exhaust not yet installed).
-Post 68 Pre DS1 dizzy with mechanical and vacuum advance (currently un-hooked and plugged), Pertronix Igniter II, Flame Thrower II coil, Pertronix Wires with 0.040" plug gap.
-Rebuilt 1.02 245cfm Autolite 2100 with manual choke, 48F jets.
-0.048" compressed head gasket with 6.5CC stock dished pistons for CR of approximately 9.4:1.

I decreased the idle to 1200 rpm and with the engine running rough, set the base timing to 12 degrees BTDC. Vacuum is also about the best at this setting but is between 16 and 17 with a shaky needle unless rpm is increased. Lifters were adjusted following procedure on this forum. Idle mixture screws will not completely stall engine when turned all the way in (one at a time). Once they are about 1 turn out, they seem to have no effect at all.

I do not believe it is a vacuum leak since the idle increased and smoothed out when I created one by disconnecting a hose to attach the vacuum gage. I believe the engine is running way rich from the following observations:

-Exhaust smell and effect on eyes.
-After turning the engine off and then when trying to restart, I get a white cloud coming out of the carb.
-I removed the top of the carb and float is not full of gas-logged and is about 3/8-1/2" below gasket line.

I suspect that the float is either set too high or that the power valve is bad.

Does this sound likely to anyone else??

check the throttle blade shafts for wear or a gasket on the carb itself. check timing first.

I have the same cam installed straight up.
Similar issues although it's running acceptably smooth at this point.
Idles comfortably at around 1100rpm, and about 750 or so in gear with the brake on.
I'm not getting as much vacuum as you are, and it seemed to have dropped even more with the below freezing temps we now have.
Carburetor idle speed screw can be backed all the way out closing the butterfly, and the mix screw has little effect on rpm. I think there is a sweet spot though.
My timing is also set @ 12°BTDC. I can lower that but the idle gets lumpy.

power vlavle blown is a possiblity if it backfired even one time.

When its "idling'" look down the carb throat and see if gas is coming out any of the passages. Gas *should* be going out the idle port, which is below the throttle plate. So you shouldn't see any gas at idle...

I agree with your power valve assessment.

CobraSix":2jnz3n3t said:

I agree with your power valve assessment.

Click to expand...

8) X2

i was having a problem similar to that for a while. replacing the power valve helped, i also adjusted the float level a little bit. Both things helped but didn't fix the problem for me because it ended up being something wrong with the 2100 carb that i could never figure out. just my luck i guess. i went with a holley 350 afterwards and everything is great now.
still planning on rebuilding the 2100 and trying it again though.

X3 for the power valve for now

ozconv
I decreased the idle to 1200 rpm and with the engine running rough, set the base timing to 12 degrees BTDC. Vacuum is also about the best at this setting but is between

16 and 17 with a shaky needle unless rpm is increased.

Lifters were adjusted following procedure on this forum. Idle mixture screws will not completely stall engine when turned all the way in (one at a time). Once they are about 1 turn out, they seem to have no effect at all.

Click to expand...

You could also look closer at your vacuum needle movement.
A good place to start is here:
Vacuum Testing

Down at bottom of page…

Howdy Oz and All:

Is the throttle linkage hooked up? If so verify that it is adjusted properly and not hanging the throttle from closing all the way.

Have you backed off the fast idle cam? It could be hanging up and not allowing the throttle to close.

It is possible that the butterfly valves in the carb are not seating completely. If the valve plates were removed from the shaft during the rebuild and not reassembled properly that's a possibility. Your rich idle is partly caused by the engine idleing too high. A 1,200 rpms, on a 1.02 you are leaving the idle circuit and into the transition circuitry.

I doubt that you've blown the power valve. that is way less likely to happen on a 2100 than on a 2300 because of internal porting. You did say that your carb is "rebuilt". Was it rebuilt by you? Or bought that way? Did you use the power valve from the rebuild kit? It could be faulty. You can use a Holley power valve as a replacement for a comparison.

The shaky vacuun needle causes me to ask- Have you adjusted the valves since start up? Is it possible, with the high lift of the new cam plus the 1.6 rocker arm ratio that a/the valve/s is/are not closing completely? A shaky needle reading might indicate a valve leak. A not completely closing valve or two fits with your exhaust smell and white cloud symptoms.

IIWY, I'd start by readjusting the rocker arm adjustments, by backing off the adjustments to no contact and then retighten to contact and a half turn more. My second mission would be to completely reassess the carb- linkage, both choke and throttle, and butterflys first, then internals.

Your build sounds great. You're going to enjoy this engine. keep us posted.

Adios, David

The carb has a manual choke that I operated by hand during break-in. I also backed the fast idle cam all the way off for the cam break-in and turned in the slow idle screw to keep it at 2000 rpm for 30 minutes. At that point I had the choke completely open and backed off the slow idle screw but couldn't get a steady idle below about 1500 rpm. The engine didn't seem to get very hot (160 degree t-stat, aluminum water pump and radiator, 6 blade mechanical fan). My inffrared gun showed a max of about 170 degrees at the back of the block.

The carb was an eBay purchase by a guy with a website called "gone fishin" out of Oregon who has a constant supply of rebuilt 2100s. The add did say that the carb was for a truck engine (I guess they were the ones that got a manual choke). The carb looks really good inside and out but I have never bought anything from the guy before. I need a manual choke for clearance with the shock tower and OZ head.

Before the initial start up, I adjusted the valves cold by setting #1 at TDC just after the intake closed and running the oil pump with a drill till I got a pressure of 50 psi (mechanical gage). I then adjusted the valves specified on this site by loosening the rocker and then tightening it until the play was gone and then went another 1/4 turn. I primed the oil pump in between each valve adjustment. I then rotated the crank one revolution and followed the same procedure on the remaining valves. After the break-in, I redid the adjustment warm but the adjustment screws pretty much ended up back in the same location.

The other issue I suppose could be the cam timing. I did degree the cam, I could never completely convince myself that it was right. I first took measurements with the timing set straight-up and got an intake center-line of 108 and an exhaust centerline of about 112, When I advance the timing set +4 degrees, I got an intake centerline of around 105. I decided to go back to the +2 setting. My final measurements were 106.5 intake centerline, 113.5 exhaust centerline. The cam is marked as a 264/274 with a 112 lobe center so my understanding is that when advance 4 degrees, I should have gotten an intake centerline of 108 and an exhaust of 116. My cmeasurements seem to indicate a 110 lobe center advance 3.5 degrees. Since I never got the measurements I thought I should, I left it at +2 figuring that I either had a measurement error of +1.5 degrees on the intake and -2.5 degrees on the exhaust or I had a 110 lobe center advanced 3.5 degrees. Either that or I have the right cam advanced somewhere between +2 and +6. I tried the other method too and even called Clay Smith but never could get the numbers to come out the way they should.

I am putting the exhaust on now but will give it another try in a couple weeks when that is done.

I'm not intimate familiar with the carb you are using, but did you adjust the idle mixture screw to try and get the idle lower? Your problem is very similar to mine, but I'm trying to use a 1bbl YF. The best I can figure is the idle circuit isn't functioning right, so I have to open up the throttle blades to get gas from the main/transition circuit. I can get mine down to about 1200 rpm before it won't idle (but that's in gear). I'm pullin' for ya!!! keep up the troubleshooting!!

Don't have the idle problem fixed yet but I finally have the exhaust on the car so I will try again this weekend. I custom fit a universal X-pipe along with a V-8 system and Flow-master 40s. I thought about buying Mike's starter kit but it didn't look to me like it would work with the extra convertible floor pan structure.
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Ozconv, I have a similar problem with not being able to get my idle lower than 1000rpms. Its with a 4100 autolite. I'm curious to see how you go about fixing your problem.

-Curtis

I drilled a hole in the throttle plate on my 1bbl.
I can now set it down farther, and has a much smoother low end response.

I have worked with similar problems. My experience comes from a dirt car that was restricted by a vacuum rule. I have found that the idle circuit is inadequate for most performance applications. Think of it this way, this carb has to feed more engine, with less vacuum. The larger cam will pull less vacuum, and will pulse more than a stock cam. That lope comes at a price. The factory carb may not be able to feed a modified engine without some help.
You need to be able to feed enough air and enough fuel while maintaining a quality mix to get the best idle.

Most performance engines can't get enough air past the butterflies to idle on. This results in the butterflies being open far enough for the pulses to pull some fuel from the boosters. This results in a poor mixture quality.

The next problem is some carbs not getting enough fuel to feed the engine at idle. By enough fuel, I mean enough to have a proper ratio. You should be able to make it too lean or too rich. Most carbs will lean out, then when you try to richen it up, it gets sort of okay and makes no difference how far you turn the screws out. If I can't make it too rich, I'll rework the idle circuit to get more fuel.

Take the carb off make sure the butterflies close properly. Then bench set it and keep track of where it is. If you have to open very much at all, you should consider getting more air somewhere else.

The pcv valve port is part of the idle circuit. Remember, the engine needs this air also. This air bypasses the butterfly. Some carbs like rochesters have another passage that bypasses the butterflies. On my racing Quadrajets, I have been known to make a 5/16 needle valve from a brass tee and use this for idle speed adjustment, leaving the butterflies at their optimum setting. This is why some carbs have a hole in the butterflies. However, if the holes are too large, they will allow enough air to pull from the boosters.

I'm just giving some food for thought.

I know you said your idle was too high. The mods I described help get the proper mix. This results in being able to idle it down where it needs to be.
Carbs have become an obsession with me. They used to intimidate me. Then I built a max effort purestreet engine for a friend. He had to pull 16in of vacuum at 850 RPMs. I did it with a 286AH8 Comp racing hydraulic cam. The key is to get enough air and fuel and have a quality mix. This will allow you to get the best idle quality and the MOST vacuum. Use your vac gage to tune it. You can expect it to bounce, that is reversion in the intake. Some gages are dampened. They don't bounce as bad, but the engine is still pulsing some.

Well unfortunately or fortunately, I have more information. Last weekend I started the car again with the exhaust on to try to get the idle working. This time, however, there was white smoke coming from the exhaust. After it came up to operating temperature, the exhaust started to smell sweet and I noticed coolant dripping from the head gasket on the passenger side of the engine between the header pipes for cylinders 4 and 5. I shut the engine off and checked the oil which was changed after the 30 minute break-in. Both the oil and the coolant looked normal and the engine never overheated and had an oil pressure of 50 psi. I haven't done a compression check yet but the head gasket is a Felpro and I reused it from the engine mock-up (actually the head had been on and off and torqued 2 or 3 times but never started). After the initial break in I did re-check the head bolt torques and they were tight. I think I will go ahead and pull the head off and have the machine shop that rebuilt it re-check it for cracks and make sure it is still flat. I also have one of Mike's Corteco head gaskets that I can use when I re-assembly it. I re-used the Felpro gasket because I saw in the Falcon Handbook that I could as long as the engine had not been started. Has anyone else done this successfully? Has anyone had any luck with the Corteco gasket? Hopefully the head and block are not cracked and maybe the head gasket has something to do with idle issue.

Went out today to get a closer look at where the coolant leak was coming from now that the header is cool and noticed evidence of a second one. Both are directly below two of the freeze plugs in the head. Not sure if they were replaced at the first shop I took the head to a year ago. He was supposed to have cleaned it, magnafluxed it for cracks and mill the head 0.030" to get the combustion chambers down to 51cc's from 56 cc's. After I got it back I painted it.

Later, I decided to have the valves and guides replaced at a different shop that did the block work for me. Not sure if the freeze plugs were ever replaced. Since I am also getting some leaking at the radiator cap I am still suspicious of the head gasket. I guess I'll go ahead and pull the head back off this weekend. Better safe than sorry.

In reference to the butterflies.IF they were removed at rebuild time,the best way that I know of to properly align them is this.
With carb on bench,loosen the screws holding the butterflies just enough to let them move a little bit.Then,close the throttle completely to align the butterflies with the carbs bore.
Hold the throttle snugly and them retighten the butterfly screws.That should properly align them in the bore.
This method was tought to me by an old time mechanic,and has saved me a bunch of headaches over the years.
Then,reinstall and retune the carb.
Good luck.
Leo