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| 2X1 troubles.... https://www.slantsix.org/forum/viewtopic.php?t=24773 |
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| Author: | BigBlockBanjo [ Mon Sep 03, 2007 6:06 pm ] |
| Post subject: | 2X1 troubles.... |
O.K., I pulled my trusty iron 1-bbl off, and replaced it with my Offenhauser 2X1 intake. To make it short and sweet.....It runs like mess. It won't idle much at all; if I punch it quick, it stays revved 10 seconds after I close the throttle blades!  Is this a vaccum leak??? Or could my setup be that far from synch? I adjusted both idle screws out 2 turns. Linkage is all good. What's the deal? Or did I answer my own problem?
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| Author: | DusterIdiot [ Mon Sep 03, 2007 6:14 pm ] |
| Post subject: | Yep... |
That's the fun part about using some of the 'other' types of intakes, sounds like you have amay have a vacc. 'leak', and check your throttle linkage for smooth operation with a good return spring upon letting go of the pedal. If all is well, you might be out of synch (even if you have two of the same type of carb with the same number 'R-48XX' etc, you might check to see if they both have the same throttle plate position, settings, jets, etc... one may be a bit off...) good luck, -D.idiot |
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| Author: | GTS225 [ Mon Sep 03, 2007 6:58 pm ] |
| Post subject: | |
Yep.....follow D.I.'s plan of attack, but get yourself a vacuum guage. I would suggest two, so that you can immediately compare vac readings on both carbs. If all seems ok mechanically, you'll have to disconnect the trottle linkage from the carbs, then start tuning individually, keeping close tabs on vac readings. This will involve idle mixture, idle speed, and even linkage adjustements. Oh, you'll need to unplug and cap your vac advance port while you're doing all this. Good luck.....Roger |
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| Author: | LUCKY13 [ Mon Sep 03, 2007 8:27 pm ] |
| Post subject: | |
The staying rev up sounds like one of them is not close right. Unhook the linkage and work with each carb individuly. That intake may not allow this but rev each carb by itself to compair to each other. It should give a idea as to which is not working right. You think with two carbs it would be rich right off. But it is a good chance it is lean. There is not as much vacume signal to the carb so it does not flow the fuel it needs. Most duel setups have to have fuel added (bigger jets). Closing the chokes off slightly will give a good indication if this is so. It would also smooth out the idle closing the chokes off some if its lean. But make sure you have no vacume leaks. Jess |
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| Author: | argentina-slantsixer [ Tue Sep 04, 2007 3:46 am ] |
| Post subject: | |
the staying up in revs is typicall when you are out of linkage sync. One of them carbs is being held open a little longer than the other when you release the gas pedal. Are you using your rod accel pedal assembly or did you uprgrade to cable? I may suggest you add on a return spring over the manifold linkage. (and upgrading to cable, but that's not 100% necessary) Also, you may want to run 1 oe 2 sizes larger main jet on the back carb. The front carb and plenum gets cooled by the fan, while the rear carb not so much, producing an artificially lean condition. |
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| Author: | Pat Dawson [ Tue Sep 04, 2007 5:30 am ] |
| Post subject: | |
It may be a mess but I bet it looks cool. Can we see? Thanks. |
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| Author: | james longhurst [ Tue Sep 04, 2007 4:26 pm ] |
| Post subject: | |
I would definitely do as Duster Idiot states and double check your carbs to be sure that everything is identical between the two. I also agree you should then check your carb synch (synching the carbs will do no good if they are physically different.) I have used a Uni-Syn for this (not the best out there but inexpensive) on the Holley carbs with success but you'll need to fab a short spacer to provide a flat sealing surface for the tool to rest on (I used an old metal can of similar diameter, but some exhaust pipe will do.) First warm up your engine and then shut it down. Make sure the throttle blades on both carbs have a return spring on them and remove the linkage from both carbs. Start the engine and let it idle. Set your synch tool up per manufaturer's suggestion and take your vacuum readings. Adjust the idle speed and mixture screws on each carb until you have similar vacuum readings and achieve the proper idle speed. All this takes a little while but you'll get the hang of it in no time. Once you feel your carbs are set properly shut the engine down and adjust your linkage rods until they fit properly on the carb's ballstuds without moving the throttle blades. Depending on what carbs you are running you may have to play with the ballstud location on the throttle arm of the carbs to make things work right and keep from binding when working the throttle by hand. Also, I would suggest using 2 light throttle return springs on each carb with this setup as heavy springs tend to cause a lot of deflection in the linkage Offy supplies with these manifolds. Hope this helps. -James |
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| Author: | BigBlockBanjo [ Tue Sep 04, 2007 5:40 pm ] |
| Post subject: | SSDan?? |
Thanks! Boatload of info to use...... To answer some of the questions: "I know everything is the same on these carbs. A pair of Economaster carbs. The number, jets, even the "Power-valve" assemblies are the same. (Would the larger idle slots in the Econo make it idle rich?)......." Hey Dan, is there anything about the Econmasters that wouldn't allow me to use them on this intake??? |
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| Author: | BigBlockBanjo [ Wed Sep 05, 2007 9:02 am ] |
| Post subject: | |
O.K., I got the intake installed, and fired it up. Runs alot better, but I believe ya'll hit the problem right on the head. It's running lean! I can feather the throttle to make it run off the accelerator shot, but it won't pull smooth. Even holding the throttle open, it tries to die as it (apperantly) leans out. The smallest jets I've found are #60....What do you guys think? |
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| Author: | SlantSixDan [ Wed Sep 05, 2007 9:20 am ] |
| Post subject: | |
Very interesting situation! If anything, I think the Economasters should be especially well suited to 2x1 usage, because their venturi design creates a good, strong vacuum signal even at lower airflow rates. What's the history of these particular carbs? New? Used? Rebuilt? I can't think of a good reason why it should be necessary to increase the carbs' jet size; I think the cause of the lean running is probably elsewhere. Come to think of it, is this a new or used manifold? I'd hate to think of a crack in the heat crossover allowing exhaust into the intake tract, and it seems unlikely because generally the Offy 2x1 is a high-quality casting, but I guess we should think of all possible causes. How 'bout the carb mounting gaskets, which ones are you using? And where's your PCV hooked up? |
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| Author: | BigBlockBanjo [ Wed Sep 05, 2007 12:58 pm ] |
| Post subject: | |
Dan, These carbs are used/rebuilt by me. I used a NAPA kit, which had everything in it, exept the float. I picked the best, used floats out of my "collection". I did discover something today: the front carb has the 3-valve economizer. The back carb also has a 3-valve, but the long arm is broke off. The plug & ball are gone from the diagonal "well".  Carbs were running lean....I didn't have jets yet, so I drilled out 2 old stockers. Carbs run much smoother. But still crazy idle, and that annoying high engine speed after releasing the throttle. Here's something I found: I can cup my hand over the back carb, and it almost dies instantly. If I cup my hand over the front carb, the idle just gets rougher. I think I might be running on the back carb. Note: The intake has a small hole to feed vaccum to the back carb, but theres not a hole for the front carb. Problem? I'm kinda stumped over this, I knew it would require tuning to get right, but I didn't know it would barely run! |
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| Author: | SlantSixDan [ Wed Sep 05, 2007 4:17 pm ] |
| Post subject: | |
Quote: Dan, These carbs are used/rebuilt by me.
OK...which ones are they? R7583, R7584, R7585, R7586, R7587?Quote: I used a NAPA kit
Not my favourite, and hasn't been for a long time, but probably not the cause of your problem.Quote: I picked the best, used floats out of my "collection".
Also probably not causing your problem, but these Nitrophyll floats absorb fuel and get heavy, so a new one is a good idea.Quote: The back carb also has a 3-valve, but the long arm is broke off. The plug & ball are gone from the diagonal "well".
Not good.  Quote: Here's something I found: I can cup my hand over the back carb, and it almost dies instantly. If I cup my hand over the front carb, the idle just gets rougher. I think I might be running on the back carb.
I think so too. See here for comments on how sometimes you cannot rebuild a 1920 to work correctly due to corrosion clogging the metering block.Quote: Note: The intake has a small hole to feed vaccum to the back carb, but theres not a hole for the front carb. Problem?
If I interpret your description correctly, you mean there's a small (about ΒΌ") hole adjacent to the throttle hole on the manifold's rear carb mounting flange, but not on the front. If that's what you mean, then a previous owner of this manifold didn't implement the PCV correctly. There's a threaded hole in the middle of the manifold's balance tube. That's where the PCV should connect. The rear carb's PCV nipple can be capped/plugged off and then the small hole you mention will be irrelevant.Quote: I'm kinda stumped over this
I think you've got at least one bad carb.
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