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06-13-2010, 11:10 AM | #1 |
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Tuning Dual 94's
I'm building a 59AB and am putting on dual 94 carbs. This is my first attempt at 2 carbs. Do I tune the carbs one at a time to get them close and the engine running good, then install both and fine tune with a unisyn or just start off at once with both installed? Seems like the one at a time method would isolate problems easier, but as a novice, I just don't know.
Advice??? Thanks in advance |
06-13-2010, 11:14 AM | #2 |
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Re: Tuning Dual 94's
You'll want to split the vacuum of the power valves between the two carbs (i.e. instead of having 7hg from the single carb, you'll want to get two 3.5's or thereabouts. Also jet accordingly. I haven't actually done this yet on my own flathead, but I read a lot of info about it over at the HAMB. When you use a uni-syn, you have to bear in mind there's going to be a difference in tuning between the carbs with the air cleaners on/off. Someone else will chime in with more/better info I'm sure.
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06-13-2010, 07:04 PM | #3 |
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Re: Tuning Dual 94's
I just finished a pair for a customer on a flatie.
Read the hamb board holley 94 page and seen all the suggestions. After a couple trys , i blocked off one carb and synced the throttle plate to a number ( i think it was a 8 on my sync tool) removed and then ran the other carb and adjusted as a single to the same number. Wasnt exactly right even still. Removed both carbs and installed power valve block offs and it was perfect. Talked to the guy last night and the car has been great ever since. Another problem i noticed while doing this car was the manifold vac dropped 2 inches with the two carbs versus one carb, just something else to consider..... |
06-13-2010, 07:34 PM | #4 |
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Re: Tuning Dual 94's
The 94's tune quite easy if their in good working order. Running these one at a time is the right answer. You must make sure the throttle bore are closing or it wont idle well. Jetting will be stock 49-50 and depending on cam 6.5 PV's. Usinf the 42 crab is a very good ignition system, again providing it in good working order. Before you start run a compression check, if all cyls. aren't close you'll have trouble balancing. Running with out PV's is old school and creat a lean condition at WOT. If your running a LONG cam dro the PV"s to 4.5. I don't use a Uni-Sync. Good luck.
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06-13-2010, 07:39 PM | #5 |
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Re: Tuning Dual 94's
FF,
Bubbas got it. I build a lot of muticarb setups and when using 94's I always block the power valves unless my customer insists that he wants them. If the engine is close to stock try #50 jets, plug the PV's AND the vacuum hole in the iron base. Try one carb at a time...turn the mixture screws in individually until the engine lags a bit then turn out about 1/2 turn. Now ,running on one carb ,take her for a drive. around 50 or 60 you should feel the engine buck slightly this is to be expected. Set the second carb up the same and test drive it to be sure. Once the carbs both behave the same ie slight buck at 50-60 you are ready to install your linkage and drive it for real. You will have to carefully reduce the idle speed but refrain from touching your mixture adjustment. The buck will have disappeared running 2 carbs. Charlie ny |
06-14-2010, 05:04 AM | #6 |
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Re: Tuning Dual 94's
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06-14-2010, 08:00 AM | #7 |
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Re: Tuning Dual 94's
I have tried many different setup combinations over the years, including blocking the PV's. I have now settled on a simple setup of, 3.5 PV's, stock jets and the air/fuel screws out 3/4 turn. I do not use a uni-syn. Both idle screws are used to set the idle, and you want to "hear" equal air draw on each carb. If you find a miss on your test drive, turn the air/fuel screws out a little more. Pete's Rod Shop
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06-14-2010, 09:06 AM | #8 |
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Re: Tuning Dual 94's
I'm in the PV camp, having used 4.5 PV's with dual 94's in an 8CM. The cam is an L-100. Ol' Ron recommended the 4.5's, jetting is 50's. The perforance has been excellent. Initially, I tuned each carb on a single manifold by ear, then installed them on the dual manifold.
richard, Louisville, ky |
06-14-2010, 12:16 PM | #9 |
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Re: Tuning Dual 94's
In response to an off site email I just received regarding FF's 2x2 question about power valves.....
I rendered my opinion and JWL and others rendered theirs. Because they had a different opinion than mine does not mean that I took offense in any way ,shape or form. JWL especially has done us Flathead guys absolutely the greatest service thru years in providing advise and compiling a wealth of knowledge in his great book. We may take different roads but our goals are the same. Charlie ny |
06-14-2010, 12:20 PM | #10 |
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Re: Tuning Dual 94's
Air cleaners were mentioned up there...many stock and I think most of the tiny chrome aircleaners are restrictive junk. Do your tuning with the air cleaners off, then install them. If anything changes, they are acting as chokes and will cause problems much more serious than the tuning effects.
What you really need is a large paper filter with OEM quality element...let the world know if you find something that goes on there and looks good! |
06-14-2010, 12:27 PM | #11 |
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Re: Tuning Dual 94's
On fuel supply...only text I have at hand is a 1935 Ford engineering book, which gives 16 to 1 as an approximate ratio for part throttle cruising, 12 to 1 for full power load. Big difference there, too much to kludge. Lean end typically can't even run at full power, rich end is excessive enough to wash oil off of the walls and rapidly kill engine at normal driving range. Gotta experiment til you find a suitable opening point PV.
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06-14-2010, 12:42 PM | #12 | |
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Re: Tuning Dual 94's
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06-14-2010, 03:54 PM | #13 |
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Re: Tuning Dual 94's
I've been working with several fellows regarding fuel mileage. One engine is a 296, L-100 cam and C4. 3200lb car gets 20 plus MPG on the open road and about 12 in town. Another is a 276, l-100, std/OD, 37 4Dr. 18/14 mpg and I still have some under test. Trying to get accurate results is up to the owner/driver and trust. I no longer make these conversions and must rely on others to manufacture the conversions. Unfortunately not all engines are the same and there is no one dist fits all. Most carbs are junk, even after professional rebuilt. Case in point two pro. built 97's were replaced with the new English 97's. Performance and mileage was up in both cases. I do this because I like to help and the findings are free, do what you want with them.
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06-14-2010, 10:23 PM | #14 |
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Re: Tuning Dual 94's
I run dual 94's on my '50 8BA. Isky 400JR, Johnson valves, bored 30 over, Ross pistons, Offy heads and intake. I have the 3 hg power valves in both carbs and stock jets. Upgraded to the new ball seats and ethanol resistant gaskets. Need it here in the Fort Worth, TX area as we have a 10% blend in our fuel. Reamed out the shafts and installed a new set. Specifically one for the primary and one for the secondary. There is a difference. I have the stock fuel pump regulated down to 3.5 psi which has resolved any blown out seat issues. I have had no issues in the 6 years I have been running this set up. Had '97's before but always had stumbling and had to constantly adjust the setup. The '94's have proved more reliable. I used a good quality MAC vacuum guage to set the vacuum and moved back and forth until I had maintained a steady reading. Holds a good 16-18 hg. vacuum. I have had good luck with Vintage Speed out of Florida on my parts and they have been helpful on information. But as a HUGE supporter of the HAMB the Holley '94 social group has been a big help.
Pics of my setup below. Needs a good cleaning. But hey, I love driving her! |
06-14-2010, 10:26 PM | #15 |
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Re: Tuning Dual 94's
Good to see your post Richard. Are you taking the '40 to Charlotte?
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06-15-2010, 12:09 AM | #16 | |
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Re: Tuning Dual 94's
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06-15-2010, 08:51 AM | #17 |
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Re: Tuning Dual 94's
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