Unisynch's can be a pain to use.....the linkage should be disconnected from all carbs being adjusted and some sort of return spring on 'em to keep one from opening when ya don't want it. Adjust each carb to same....idle is going to change as you adjust, which in turn changes the level of the ball...plus with a new setup, it's tough enough keeping it running with mis-adjusted carbs, let alone holding that "tool" above each carb...hahaha!......arrrr... It definitely takes patience.... When I was dialing in my setup.....I found it easier to bolt all the carb bases to the manifold, set all the throttle blades to just be closed, then install the linkage. This way allows you to easily see how well the linkage is working and to ensure all carbs reach WOT at the same time. Once set, then install yer carb bodies. Set all the idle mixture screws to @ 2 turns out. Carbs should be really close....then just use one carb idle screw (or the two middles on a 6x2) to set your idle.....any fine adjustments to idle mixtures can be made with a vacuum gauge.
"Set all the idle mixture screws to @ 2 turns out. " Are you sure you don't mean 1 turn out? I originally started at 1.5 turns, like I'd done on every other carb I'd worked on, but was told to cut that way down. I was told to run the center 2 carbs around 1 turn on the idles and the outside 4 carbs at somewhere around 3/4 turn. I did that and it seemed to run a lot better....leaner at idle. That is until I got back from the trip this last weekend and all hell broke loose.
That's just what I did with mine.....if at startup it's WAY too rich, start again at 1 full turn out or so.....as long as all are even. Then tune with vac gauge. Getting all the throttle blades dialed in first makes tuning later much easier. But it still can be a pain in the ass.....haha....just don't give up....it'll all be worth it in the end.
I totally agree about setting the carb bases BEFORE you install bodies. I actually had mine all together and then decided to tear it all apart to adjust jets etc. When I took the bodies off I realized I could stop there, and that the linkage didn't have to come off at all. I made it VERY easy and straight forward to adjust the butterflies. By the way, should I be more concerned with where the primary butterflies are at when the secondaries engage or that all the carbs open completely at the same time? I was setting mine so the outside carbs didn't start to open until the primaries were at approximately 50% throttle, but then when the primaries are full open the outer carbs still have 30% +/- left to open. I assume that the engine doesn't NEED all that fuel anyway, but can that screw things up on the very extreme top end???
This is a great thread I have 6x2 for a 348 I am only going to run the 2 primarries for now. I am using progressive linkage. What are you useing for air filters. I have velocity stacks.
Hey man! I just noticed, yer in WA???? Where? West side?? I set my secondaries to kick in right @ 1/2 throttle....and I've got the 2:1 arm on the shaft, so all are getting WOT at same time. It shouldn't be too much of an issue for the engine itself having the secondaries not fully open, your just not getting all the HP you "could".... finding arms that will give ya a 2:1 ratio, or making something, would be better, IMO.
OK, so while I'm at it I might as well throw everything on the table. I should probably start another thread for this question, but I figure since I got some pretty savvy carb guys already on board I might as well ask this too. I have been told that you can time an engine with a vacuum gauge. Is that true? The reason I ask is because I tried it with this engine and I get less than straight forward results. Like I said originally, I do not know if the engine has an aftermarket cam. The "book" shows that a 1964 401 is supposed to be set at 2.5 degrees advance stock. I've got a fancy timing light so my buddy and I started screwing around with it. At 2.5 degrees advance I can really get the idle down low....probably almost kill the engine. It is pulling 14-15 inches of vacuum at 650 RPM but the vacuum is kinda bouncy. I have been told that you should try to achieve the highest possible vacuum reading when turning the distributor to time the engine. Well, that's what I tried and as my buddy watched the timing light I watched the vacuum gauge. I got to about 28 degrees advance before it peaked at around 19 inches of vacuum. That seems like where it should be if you go off the vacuum gauge, but the problem is I can get it to idle below 1250 RPM at that much advance. I didn't shut the engine off and try to restart it, but I assume it would be a bugger to start too. The main reason I'm throwing this on the same thread as the above is because I was wondering if my timing could be an issue with the running rich deal? Hopefully this won't muddy the water even more.....if I should start a new thread regarding this please let me know. Thanks.
I'm over here on the dry side of WA. To bad I wasn't closer to Roy.....I'd have you over for dinner this weekend. Dinner and carb tuning that is....
I tried to make air filters for my frogsmouth scoops but gave up because it just made things richer and my buddies all gave me shit for being a pussy. They did have a good point about one thing, though, and that was if the engine backfired I'd melt the foam filter element and suck the crap into my carbs/engine. I did find some filters made by The Hot Rod Company that are about the only things I can find for this kind of setup. Here's a link.... http://www.thehotrodcompany.com/shopnow/show_item.asp?product_id=md001 I don't know if they work or not so maybe someone on here can give some advice on filtration for 2 bbl's.......
Hahaha....are ya going to Billetproof next weekend? Yeah, timing can be set with a vac gauge, but if you turn to get highest vac readings, you'll most likely be to advanced and it'll be hard to crank over and/or ping/detonate under a heavy load. I'm no carb or timing "guru", believe me....as most of my "tuning" is done on the side of the road with a screwdriver and hand wrench......haha....by how the car "feels" runnin' the road, under full throttle, cornering, quickly letting off throttle, etc.........
Like I said in a previous post: They are not like a jet. They have the same size hole in them regardless of the number on them. The number dictates When they open not how much they flow.
nearly pulled my hair out setting up my 6 two;found an old hot rod mag that had rules for 94's. one power valve for every 250 cubic inches; power valve# should be about 3 inches below crusing vacume;not halve of the idle like a modern holley. this helped me alot. had some over rich problems later anyway;it turned out to be dirt in the system. whenever a piece would clog or nearly clog a jet; the carb would flow over the top and go rich instead of the lean you would expect. hope this helps good luck.
UPDATE: I just pulled that front carb that was leaking badly and the bowl under the power valve was full of fuel. I can't figure that out because I installed a new Holley PV block off in place of the standard PV and used the correct gasket. Is there some other way for fuel to get into that bowl? Do I need to use nylon tape on the threads of the block off? I also checked the needle and seat by blowing through the fuel inlet and moving the float up and down......it seems to seal fine. I was hoping for a smoking gun when I opened the first carb up but don't see anything blatantly wrong. Any suggestions????????
Doesn't the bowl under the PV just have a passage that senses engine vacuum? Shouldn't be any fuel in there... This is a great thread, I've got a 6x2 to set up for a friend this coming weekend. Good info!
Yes, that's my thought exactly. And that passage on my outside 4 carbs is leaded shut anyway, so where did the fuel come from? I tightened the PV as much as I dare to, but I didn't use thread tape on it when I installed it. Should I have done that too, or is there something I'm not getting?
Seems like it would have to be leaking around the threads. I wouldn't want bits of teflon tape in my fuel system. Seems to me I remember something about the modern manufatured PV's not seating correctly in the 94 carbs. You've got to get the correct early type.
I think you have a fuel volume problem ,where the system is building more pressure than you think . I would try running a return line back to the tank to get rid of some of the volume
I have a pressure gauge at one end of the fuel log and the line coming from the regulator at the other end. The gauge reads 2.5 lbs or so, but could I still have a volume issue? I would assume that the needle and seat should shut the fuel off to the entire carb when there was enough fuel to raise the float, but are you suggesting that the excess pressure is actually overcoming the float and forcing fuel past the needle?
UPDATE: I discovered the problem with the carb that was overflowing. When I pulled it off and was measuring the float levels, everything checked out just perfect. I was kinda frustrated because I hoped for something obvious to fix. I pulled the pin on the float to remove it and check the needle/seat and immediately discovered that the float was completely full of fuel. It took a minute, but I finally found the hairline crack along the bottom of the float. I'm not sure when or how it happened, but I know that it didn't have fuel in it when I tore everything down and rebuilt it last week. Anyway, that explains why that carb was puking fuel and even draining fuel after the engine was shut down. I checked all the other carbs and everything checked out so I put it all back together. I turned on the fuel and turned the key on to build fuel pressure. The gauge rose to 2.75 lbs., I hit the key and she fired right up and idled fine. It was idling high still so I hooked up the timing light and started to play around. We had set the timing at 10 degrees advance, but the factory setting is 2.5 degrees so I back it down to stock and it still wouldn't idle below 1150 so I started messing with the linkage. I had played with my UniSyn the last time but couldn't get the primaries matched at a low idle so I started messing with it again. This time I unhooked main linkage that goes from the back cross bar to the primary carbs, like I had done before, and I still couldn't get it to idle down. While I was standing there scratching my head I noticed that the rod that comes off the primary carbs throttle shaft and goes forward to the front carb had 2 lock collars....one that engages the secondary carb throttle arm and the other that basically pushes the secondary carb back closed (if you didn't have a return spring on the secondaries). I had synched the collars that engage the secondaries on both banks of carbs but I hadn't touched the other collar. As soon as I loosened that collar I could idle the engine down to where it would die! I know I might seem like an idiot (and I probably am) but I wanted to post this so everyone reading about my 6X2 drama would realize that anything can be overlooked and EVERYTHING makes a difference. I then was able to easily synch both primary carbs, after which I reconnected the linkage and dialed the idle in to 700 RPM. I still have a small puff of black smoke when I burp the throttle quickly a few times, but it comes right back to 700 when I let it off and idles smooth. I am going to talk to my buddies and see if anyone has an exhaust gas analyzer to try and fine tune things a little more. I'm not saying its perfect, but its a lot better than it was on Monday. I do still have a question that hopefully someone can explain. 3 of my 4 secondary carbs had the bowl under the powervalve full of gas when I pulled them off their bases. It doesn't make sense because not only are the vacuum ports that lead to those bowl soldered shut, I also installed PV blockoffs on all of those carbs. I double check the gasket fit and it seems just right, but I lightly filed the gasket surfaces to make sure. I just want to know how the heck fuel could be getting into that bowl if the PV isn't there? Thanks for everyone's help and advice on this thread. I hope it helps the next guy understand powervalves and maybe some other things about their own 6X2 setup. I'll continue to post on this thread if I make improvements or find more important information to pass on.
I was going to suggest you might have a heavy (fuel filled) float, but you beat me to it. Im not sure if later Holley power valves/block offs seal the same as the older ones, but I remember reading something about different types of Holley PV gaskets. One was a normal circular gasket while the other had little tabs on the inside circumference. The gaskets would supposedly cause problems if used in the wrong application. It was mentioned before that your secondary carb throttle plates should be fully closed...this is actually pretty difficult to do without a lot of return spring pressure. Primary carb throttle plates were never intended to fully seal (thats your idle adjustment). Actual secondary carbs have a thicker throttle plate with edges ground at an angle so they seal to the throttle bores. Put your hand over each of the secondary carbs and see if your idle speed goes down. If so, you have an air leak which could at worst be drawing fuel into the motor. If the secondaries are leaking air, your adjustments on the primary carbs are trying to compensate for this and will never be right on the money. Hopefully some of this helps.
Glad to hear it was something simple! I learned a TON from this thread! Now go drive and keep us posted!
ok i have 3-2,s on a small block chevy---it has aluminum heads---504 lunati cam---hot at idle it has 10 lbs. vac---in gear idle it has 6lb,s vac---when i rev it up i hear a poofing out the exhaust--i tried everything---jets---timming--checked for vaccum leaks---any-1 wanna give me any idea,s---Tony
Just a suggestion (not trying to be a jerk), maybe start a new thread. You'll probably get a better response instead of moving off focus from the topic at hand. Your issue is entirely different as is your entire setup.
We would stay away from using teflon tape anywhere inside of the carb as one of the others mentioned as it doesn't take much for the smallest piece to break loose and cause havoc. Having a good sealing surface is important and I see where you filed it to true it up. Also make sure you are not over tightening the power valves as that can sometimes cause internal leakage. Here's a couple other things to keep in mind with the six 2's as we have been doing some systems here lately and some dyno work using them. On our Six Deuce we are only running power valves in what we call the 2 primary carburetors like you are but all six carburetors will have some amount of idle fuel that goes through them. With our 98's we do have the adjustable mixture screws on the primary carbs but the secondaries carbs do not. Even with them set up like this though there is still a small amount of idle fuel. On some of our kits though that come with multiple carburetors we are using the mixture screws on all the carbs in those kits for just a little bit better idle mixture control . Generally we like to adjust them twice by going over them the first time for the best idle and then the second time for a little finer adjustment. With changes to the intake and different plenum and runner designs sometimes the motor will need more base timing then originally and when you tried it at 10 you were on the right track but it might need just a little bit more to clean it up where you want it. Your idle rpm at 700 now sounds like a decent range with what you believe to be a stock cam but ultimately how well/low the carburetors will idle comes down to how tight the butterflies fit in the bores in situations with idle speed of less then 1000. With our Six Deuce we will generally try to set the idle using the 2 "center" or primary carbs and close the outers down as much as possible. I know some of you guys have seen the Buick called Reslilence , it has a 500 cubic inch Cadilac motor in it with 6 of our 98's on it and it idles in the same rpm range as yours does. I do know that adding some base timing to that set up helped to achieve that so overall it sounds like you are headed in the right direction with just a little tweaking left to do. The Buick has a story coming out in the September issue of Rod and Custom if you want to look at how the linkages are set up on that one.
Now I've got a question that may sound stupid.....how the heck do you listen for "pinging" when you are running open headers? I can't tell if I'm running too rich except to watch for black smoke. Should I just expect that little puff of black smoke when I burp the throttle a couple quick times or do I need to lean it out more? I don't want to go too lean, but how the heck can I tell? Any ideas.....or do I just need to go find someone with an exhaust gas analyzer? I know I can "read" the plugs, but I was hoping there was a way to tell while the engine was running and I'm adjusting the timing.
I have 6x2 on 322 nailhead, I spent alot of time on throttle valves, I sanded them until they shut tight .It can idle at 800 RPM. On the 94s, I took end carb PV,s out with stock jets in middle and one size down for end carbs. I also use MSD to get more spark, I highly recommend MSD Did you put in new throttle valves? You can buy less angle valves, that close completely. Did you put in new shafts or bushings? Howard
Ok, I was contacted by Mr. Allan and we solved his problem. I never thought about it originally and I guess allyall didn't either. Ok, here's the senerio. He has 6-94's on his nailhead that he has tuned to idle perfect, come off idle perfect, midrange perfect, top end perfect, BUT, when decelerating, the carbies flood out. Now, with the second or third generation spray bars this cannot happen, but he has the first generation bars that sit lower in the bowl than the upper rim of the fuel well. So, here is something we call gravity taking over because we all know liquid seeks the lowest level, but I bet everyone like myself, had forgotten something so simple and again way to simple of a solution to such a technial problem. To prove this I took a freshly rebuilt 94 bowl with all the pieces installed with the first generation spray bars. Then I took the same set up, except with second generation bars. I filled each bowl until the seat shut the liquid level off and raised the air horn and removed it with the float. I then took both bowls and tipped them forward about 30 degrees, oh wait, I forgot to mention his carbies are facing backwards, at 30 degrees, which is about 1.25" form the top of the bowl well, liquid began pouring out of the first gen bars onto the throttle plates and would not cease until the carb was placed back in stock position. The bowl with the second gen bar had fuel overflow the top of the well and still no leakage from the bar onto the throttle plates, why, because it is 1/2" taller than the well wall. So, the solution here would be to turn the intake around and place the carbies forward as designed, OR, change all 6 spray bars with second or third generation spray bars.
Hi Mate, If you look at a stock Holley 94 power valve, the threaded section meets the gasket surface at a 90 degree angle. If you look at at a modern power valve or a block of plug for a holley there is a redius between the threaded area and the gasket surface. In addition the new valves have raised area on the glasket surface that does not match the the gasket surface on the bottom of the fuel bowl. Net result? You may or you may not get the power valve or plug to seat properly. The the bottom of the fuel bowl gasket surface is uneven or if, in my case, the threads the PV threads into a slightly cross threaded and the PV goes in slightly off angle, fuel will pour into the vaccuum chamber. Its easy to fix, get the PV and machin the gasket surface flat and machine the radius off the PV. Danny