[gtorich]

Ok, guys could use a little help here............got the new engine back, carbs were re-done by Mike Wasson......455, 290cmf Kre heads, 4 speed. Cant get this thing to idle at all for some reason.

Jets are 65/66 center, 74 ends, don"t have the paperwork here in front of me, but its close.

Started with the mixture screws out 1 1/2 turns, vacuum is around 8-10 there

Then went to 2 turns out, vacuum is around 10-11 there

Then went to 2 1/2 turns out and vacuum is around 11-12 there.

After turning mixture screws i always adjusted the idle screw back down to about 850-950.

One issue i had is even at 1 1/2 turns out, it seems to be rich, pulled plugs and they had a black power soot ring on them. Don"t know for sure how rich it was, but my eyes were burning a little.

Now i had this set up on my old motor which was the same except 6X heads and a 60919 cam...........now the cam is a roller 235-246 OF from sd and the alum heads.

Just wondering where you guys with similar set ups are setting your tri power .

If i keep the idle at 850-950, that mother is shaking like John Travolta in there........seems to run a little smoother at 1000 or so...........just nervous im out of the idle circut there.

Any help would be appreciated.

As for vacuum leaks, i checked the manifold with a propane torch seems ok, around all the bases of the carbs, ok.................only thing i noticed if i cupped my hand some over the center carb, that picked the idle up some.

Also forgot the idle tubes were opened some.........

Thanks, Rich

[mwritter]

Been there, done that. There is a long thread I started about my similar troubles with my 421.

I'd start by making block-off plates for the front and rear carbs to eliminate them from the equation.

[tripwr1964]

http://forums.maxperformanceinc.com/...r+idle+circuit
is matt's thread. there are others....

[old66tiger]

You are on the transition circuit and you need to get the throttle blades shut some to get off the transition. An engine will idle like crud (especially a rochester 2bbl) if you are too far off the idle circuit.

The only way you accomplish this is by adding bypass air, opening up the idle discharge ports in the base and playing with the idle tubes. Without an O2 meter, it is all trial and error. Blocking the ends makes tuning the center much easier. You can replace all of the lines with one single rubber hose. look for my past posts, there is some really good how-to information there. Stuff i learned from Mike Wasson, Jon Hardgrove and Cliff Ruggles.

[Cliff R]

What are the specifics on the new engine, compression ratio, cam specs, etc?

More than likely you just need some bypass air and a little bit more idle fuel to get it happy on the idle curcuit.

The "rich" condition happens when there isn't enough idle fuel available from the idle curcuit. The throttle plates are too high in the bores, and there isn't full control of the idle mixture with the adjustment screws.

One key to the solution, is that as you back them out, vacuum improves. The engine wants more idle fuel.....Cliff

[gtorich]

Originally Posted by Cliff R

What are the specifics on the new engine, compression ratio, cam specs, etc?

More than likely you just need some bypass air and a little bit more idle fuel to get it happy on the idle curcuit.

The "rich" condition happens when there isn't enough idle fuel available from the idle curcuit. The throttle plates are too high in the bores, and there isn't full control of the idle mixture with the adjustment screws.

One key to the solution, is that as you back them out, vacuum improves. The engine wants more idle fuel.....Cliff

Thanks for the replys guys.........the CR is about 10.5..cam is the "Old Faithful from SD..alum heads from SD..KRE 290 cmf

Idle tubes were opened years ago, about 3 thou i believe.............the carbs were just redone by Mike Wasson this last year, guess i have to check with him as far as the throttle blades.

I have a mds dist, with no vacuum advance on it.

[carbking]

At first blush, I think Cliff nailed the answer.

However, as Mike did the carbs, why not give him a call; as he will know about any bypass air he may have added, or any enlargement of the idle tubes; and he may have another idea.

Jon.

[gtorich]

Originally Posted by carbking

At first blush, I think Cliff nailed the answer.

However, as Mike did the carbs, why not give him a call; as he will know about any bypass air he may have added, or any enlargement of the idle tubes; and he may have another idea.

Jon.

Hey Jon, just wanted to say thanks for taking the time to talk to my dumb a$$ today.......i didn"t think you could took take another stupid question from me without going nuts, but you hung in there. LOL

Still trying to get hold of Mike W............i found some old bits i saved from doing the idle tubes years ago, they range from .031 to .035, im pretty sure i used the .035 one.

Gotta get the block off plates and do this right, because im tired of just winging it.

Thanks to everyone for the tips

Rich

[old66tiger]

When I was running the tri-power on the 455, i believe that i had the idle tubes at 0.036 or 0.038", the idle discharge ports at 0.090" and i had 0.125" bypass holes in the plates. I could run with the blades almost closed and had full control over the idle with the idle screws. Once the center is running good, you should only introduce 1 end carb at a time to make sure if you have a leaker, you can diagnose it pretty easily. you don't have to hook up the fuel, just throw it on the intake.

[gtorich]

Originally Posted by old66tiger

When I was running the tri-power on the 455, i believe that i had the idle tubes at 0.036 or 0.038", the idle discharge ports at 0.090" and i had 0.125" bypass holes in the plates. I could run with the blades almost closed and had full control over the idle with the idle screws. Once the center is running good, you should only introduce 1 end carb at a time to make sure if you have a leaker, you can diagnose it pretty easily. you don't have to hook up the fuel, just throw it on the intake.

Bob, thanks for the info, i had my brother in law knock out some plates last nite........

1 1/2 tuns out from lightly seated........idle-975-1000......vacuum at 12-14

2 turns out.....................................idle-975-1000.......vacuum at 14-15

2 1/2 turns out................................idle 850-900........vacuum at 11-12

3 turns out.....................................idle 975-1000........vacuum at 13-14

This was done with the engine warm............checked for leaks around the manifold, couldn"t find any.

On all of these i can lower the idle some more, but the engine shakes extremly bad....sidways ..........worried about snapping off a motor mount.

Vacuum is a little tough to read, because its jumping around quite a bit........problem im having now is this engine won"t do the same thing two times in a row with the same settings........meaning if i adjust the idle screw to say 900 while running, then turn the car off it starts up at 850 and stays there...........turn it off again and restart its at 900.

The only good thing i have to say is that Robb Mc starter is kicking butt, fires instantly everytime i start it..............no hot issues at all.

Almost forgot, another thing i couldn"t duplicate from the previous nite with all the carbs on...............while just running the center and i cupped my hand over the carb, idle didn"t pick up......................when the other two carbs were on, it did.

Still trying to get hold of Mike W, since he did the carbs.............want to make sure of everything before i start my off shore drilling of the carb.

Rich

[Cliff R]

A "rough" idle is certainly not a characteristic of that combination of parts. I use the same set-up at 11 to 1 compression, and it idles nearly smooth at 750rpms with 13.5" of vacuum. The idle speed and vacuum gauge barely move when you put the trans in gear.

With Tri Power carburetors, the outer carburetors throttle plates must seal off tightly in the bores. Mike knows this more than anyone, so I would not thing that would be an issue here.

2GC carburetors are extremely easy to open up for more idle fuel, but not all that easy if you go to far to put smaller tubes back in them. Same deal with drilling throttle plates for idle bypass air, so tread softly in those areas......Cliff

[Tom Vaught]

Measure the idle tubes again.

With the size of the 455 engine you have, you will typically need a idle tube orifice in the .036"-.038" range. A engine of a given size needs a certain size of idle fuel and air by-pass to run properly. 750 Holley carbs come stock with .036" idle feed restrictions. 850 Holley carbs come stock with .038" idle feed restrictions. The size of the idle blade means little because it is designed to be almost closed in the bore. The idle air bleed holes in the plates for a Holley 850 are typically .110"-.120" in diameter. The engine will not know if it has a Holley 850 or a Rochester 2BBL at idle with the right idle circuit and air by-pass holes.

It is shaking because at lower speeds the idle circuit and air by-pass air is not sufficient to support the engine.

Tom Vaught

ps I won a bet one time that I could make a 473 cid engine with a big set of heads, big roller camshaft, and a 1050 Dominator idle smoothly at 650 rpm and start up with the turn of the key. I WON (:>). It was all in the idle fuel circuit and idle air settings.

[gtorich]

Hey Cliff & Tom, and the others, thanks for the tips, i got hold of Mike today and he said to open them up .037-.038. Also to maybe open the idle mixture screws to .073.

Im gonna do the first one tomorrow & see what happens there...........had a spare venturi i fooled around with tonite...........little pratice drilling. I think im good to go.

I had these carbs done last winter by Mike, still trying to find the paperwork, Couldn"t expect Mike to remember that far back...........i can"t remember where i put the paperwork. LOL

Just hoping they are not already opened to .038...........i know i opened them up about 6 yrs ago when i was running the 60919 cam.........im thinking i had them at .035 seeing i have the drill bit here with that #.

Hard to believe just a thou or two is gonna make that much difference..........im hoping for the best here.

Thanks

Rich

[grandville455]

Rich
u would be surprised what a couple thous will do... we have pretty much the same engine , but i have a little more comp and a holley, my car idles at 800 in park and 750 in gear! stock idle tubes, but i have 4 holes drilled in the throttle plates for bypass air runs perfect!

[gtorich]

Originally Posted by grandville455

Rich
u would be surprised what a couple thous will do... we have pretty much the same engine , but i have a little more comp and a holley, my car idles at 800 in park and 750 in gear! stock idle tubes, but i have 4 holes drilled in the throttle plates for bypass air runs perfect!

Darby, i only have two little holes in my throttle plates, you would think it would run half as good as yours. LOL

One of these days i gotta get up in your neck of the woods..........take the car down the track............although im a little worried about my power steering pulley flying off and killing someone. LOL

Im almost scared to put the new one on...............i don"t care im red locting that mother on for life.

Rich

[grandville455]

Yea Mine are 5/32? maybe can't remember.....
yes get up here and lets do some racing! the muscle car race on the 22nd or the one in sep?

[Blue1967GTO]

Hey Rich

My center carb idle tubes are drilled out to 0.038 and my mixture screws are opened up to 0.075 and set at 1.5 turns out right now. You know what I have but for everyone else it's a 463 with KRE heads and Comp's biggest hydraulic roller cam. 10.4:1 compression.

It idles great at 850 rpm. At first it shook like crazy but that's because the new motor mounts were floppier than grandma's arm fat. We modified the mounts by installing two 3/8" grade 8 bolts through the rubber of each mount to hold the metal/rubber sandwich together better and that worked slick ( just like a Mity Mount but cost $3 instead of $100). Engine idles nicely and doesn't flop around.

[Tripower455]

I've got nearly the same setup, only with a smaller HR cam (for now..... I've got an Old Faithful STILL sitting on the shelf waiting to be installed one of these days).

As the others have said, the idle tubes need to be opened up. Mine are at .038 and can probably go another thousandth or so. I have a Jet "500 CFM, Circle Track" 2gc in the center FWIW. I've also got holes in the throttle plates. I can control the mixture with the screws, and it idles at 750-800 with almost 20" vacuum (with vac advance).

Once you get your center carb figured out, I'll bet that you're REALLY rich on the end carbs with 74s in them.

I also changed from 6X to the 290 KREs. With the 6Xs, 73s were a little rich at WOT (11.9-12.3ish AFR on the LM-1). When I went to the KREs, I also installed a CVM ported aluminum intake and ported end carbs. My AFR went down below 10 at WOT, blowing huge clouds of black smoke all the way down the track. I am down to 65s now (my carbs are set up for Holley Jets). I am assuming the the far more efficient chamber of the KREs is the reason, but I was stunned at how small I had to go.

The car also lost that hesitation when the ends opened up that it had running so rich!

[gtorich]

Originally Posted by Tripower455

I've got nearly the same setup, only with a smaller HR cam (for now..... I've got an Old Faithful STILL sitting on the shelf waiting to be installed one of these days).

As the others have said, the idle tubes need to be opened up. Mine are at .038 and can probably go another thousandth or so. I have a Jet "500 CFM, Circle Track" 2gc in the center FWIW. I've also got holes in the throttle plates. I can control the mixture with the screws, and it idles at 750-800 with almost 20" vacuum (with vac advance).

Once you get your center carb figured out, I'll bet that you're REALLY rich on the end carbs with 74s in them.

I also changed from 6X to the 290 KREs. With the 6Xs, 73s were a little rich at WOT (11.9-12.3ish AFR on the LM-1). When I went to the KREs, I also installed a CVM ported aluminum intake and ported end carbs. My AFR went down below 10 at WOT, blowing huge clouds of black smoke all the way down the track. I am down to 65s now (my carbs are set up for Holley Jets). I am assuming the the far more efficient chamber of the KREs is the reason, but I was stunned at how small I had to go.

The car also lost that hesitation when the ends opened up that it had running so rich!

Glen, wow 65"s on the ends, whats ya running on the center now.........another thing i have to look into.

Also a little more info for those following this thread.

Today, i opened the idle tubes to .038 & the mixture screws to .076, the throttle blades already had holes in them, they were .0125

Ok with this set up i could get the idle somewhat decent at 825-875 ish, still somewhat rough with the engine shaking............but like Blue 67 said, the motor mounts might not be up to snuff. This was done with 1 1/2 turns out on the mix screws, vacuum was about 11-12................nothing much changed going out 2 or 2 1/2 turns, idle seems to always stay around 850-950 range, vacuum really never changes much, maybe 12-13 but thats about it.

The only thing different i tried was i had the power piston spring kit that i got from Carb King many years ago, at that time i installed the green spring recommende for a cam similar to a 041 cam..................on my last test tonite, i put on a yellow spring he has in his kit, that one is a 6 oz one.

Don"t know if that had anything to do with came next or what, but after shutting the car off, i had fuel dripping out of the venturi cluster pretty good..............

So after fooling with this thing for over 8 hours today, i threw in the towel, took the carb off and called it a nite.

Problem is , there isnt really much more adjustment i can do one way or the other.........

your guys have any ideas. ?????

I have a spare venturi cluster here, im temped to drill that mother to whatever, i don"t care and see if that makes a difference.

Have a good day boys

Rich

[Tripower455]

Rich, I am running 68s in the center in the summer, and 69s in the winter. These are Holley sizes btw.

Let me chew on the idle thing for a while. I spent a ton of time getting mine to run right, and since it's been a while, I have to sort out in my mind what worked. Even after you get the idle right, you're gonna have fun eliminating the annoying off idle stumble. For such simple devices, these 2 barrels can be a PITA to dial in on a modded engine.

The fuel drip is either the float, or just boil over from the heat with the urine that passes for fuel nowadays. The float setting is not too forgiving on these things. You definitely have to set them a bit lower than factory specs, or they'll drip, but go to low, and you get the engine stopping every time you slow down.