Offy tuning question...

[CobraSix]

After Al helped me with my T5 tranny issues, I decided to just get the car running and check things out only running 1 carb. So I took off the outer two carbs and put block plates in their place.

Now I'm going to give it another honest shot and getting the offy working.

I've got them hooked up , but I'm running into two problems:

1) I can not get the RPMs down below 1000 at idle.

2) I'm not sure when the outer carbs should be opening. I originally set them to open at the point that will allow all three carbs to be completely open at WOT. Is that the right setting? If so, is it right that the outer carbs don't open until around 3500 RPM?

I tried setting the outer carbs lower, but it seems to flood the engine and kill the power.



I must say...with the Offy in place, the car sounds like a fire breathing dragon. I can even get a good wheel spin in now.

One other question, do you grease the mechanical linkages?

Slade

 

[Anonymous]

cobra thats all the fun fun in running a tripower is the tuning i ran one for a while.the tripower that was listed on ebay was mine. the first question i have is what kind of 1 barrels are you running?i assume holley maybe.the second question i have are they brand new or have they been completely rebuilt?can you send me a picture of your set up so i can see the linkages?
forgive me if the way this sounds is like im talking to someone that doesnt have a clue but if i dont say it this way then i'll leave something out that might be pertinent to your problem.
ok with that said lol
your middle carb is going to be your idle circut or main runner as some would call it.so the bottom butterfly (and im going off my set of carbs)should be shut very tight.i had to change to a hevier spring because of engine vacuum was pulling past it.hense running the idle up.almost like you were resting your foot on the pedal. check to see if there is anything like dirt or debris stopping the butterfly from closing completly on all three carbs. when you ran just the center carb did you have a problem with idle? if not then the outer carbs need to be adjusted and when you answer those few questions i can get into adjusting the outer carbs so they dont leak by on non open profile.
for your second question how is the setup getting the outer carbs coming in?is it using vacuum canisters like the 67 vette used and the cryslers used or is it mechanical linkage ? if its vacuum then they are coming in at about the right rpm.you dont want them to come in too soon for around town driving plus like you said they flood out.mine came in around the same but i was using a mechanical set up. if its mechanical there is a way to set the linkage so you can push your throttle down and when you get to just the point of the outer carbs coming in you can control when they come in almost like a mechanical 4 barrel. either way its going to be fun to get it right but ounce it is right your not going to regret it.plus it looks good lol.
have fun and good luck i hope this helped.
chris

 

[CobraSix]

Chris,

I did have idle problems with just the single carb. I fixed that by changing my return spring. I am using Autolite 1100s as the Holleys or Webers would be too tall for my 65 mustang hood. Infact, the 1100s barely clear. The outer carbs are new/rebuilt and the center carb is about 2 years old and was rebuilt by pony carbs.

As of now, I have the idle fuel mix screw closed completely on the outer carbs. I'll try going to another spring on the center.

The linkages are mechanical and they are adjustable. I guess my question is when are the outer carbs supposed to open up. The outer carbs are completely closing at idle.

Slade

 

[gtm1086]

Hello Slade.

Ok here are a couple of things to think about. Vision your set up as the center carb being your primary of a three barrel carb. Your linkage is set up correctly the outer two "barrels" will come in at around 3000 to 3500 rpm.

This is how I did mine. With the outer two linkages disconnected. and the mixture screws and throttle plates shut. I adjusted the center carb so that I had good idle speed and mixture. Remember we are treating this as a three barrel carb. Next hook up the outer carb linkages the idle speed should stay the same. If it jumps up then you need to adjust your linkage down tighter. This ended up giving me a pretty good base set up.

Then I started playing around. I found the set up works better if I disconnect the accelerator pump linkage from the rear carb. I have also jetted down the high speed on the outer carbs. I have also found that opening up the mixture on the front carb slightly did help improve idle quality All idle speed is set by using the center carb. I am using an old set of Holley's if I remember right you are using webbers. Which I think you have a better selection of parts to choose from. Currently mine is running pretty good but is still not 100% but if it was then I would have to find something else to work on.

Gary

 

[simon]

howdy Slade,

Though somewhat fuzzy, I remember there were a couple things to consider when running a multi carb setup.
Gary is right, the whole assembly is to be treated like a three barrel carb with progressively opening throttle plates.

One thing I remember slightly different is that at idle and low rpm, actually only the center carb is feeding the engine, so idle circuit of the outboard carbs is (as far as I know) something closer to unimportant. As far as I remember, the center carb does 99% of the work below 3000 rpm.

tuning of the outboards should basically concern transition at a determined rpm number, like the 3500 you´ve mentioned, and of course WOT.

but thats only theory, so Garys recommendations on tuning one or both outboards for better idle qualities seem pretty sound to me.

One more thing: the more carburetors (or openings to the intake runners) an engine sports, the more intake vacuum drops. As I mentioned above, I can´t recall every detail, but I think that vacuum loss and overall velocity are somewhat connected to transition qualities and shouldn´t be neglected. ...could be one reason (or connected to some reason) why you have problems getting your idle rpm below 1000 revs.

Simon

 

[Anonymous]

Cobrasix, i just got my Weber carbs a few days ago. I also have a 65 Mustang. I was told that they would not cause any problems with hood clearance. I am definitely not gonna be a happy camper if they dont fit. I do not want to modify my hood in any way.

Nazs

 

[CobraSix]

Naz,

The webers alone should be fine, but are you running an Offy too?

I have no actual experience with the webers, but I'm pretty sure Autolite 1100s are about the lowest profile carbs you can get. Part of my clearance issue was the air cleaner that I used. If you go with the small individual air cleaners, there should not be an issue with the webers.

Slade

 

[Anonymous]

Slade, you need to grease your linkage and make sure there is no binding, I have return springs on all 3 carbs and have no problems with them all closing. I did the same as you have done and set all three at WOT, I don't depend on the stops to close the secondaries, because of the return springs, and have them set just back of the throttle arms in case I break or loose a spring.

Close everything on the front and rear carbs (idle screw, air/fuel mix screw, etc.) so that they do nothing, set your center carb correctly, use your Unisys (or whatever) and set it on your center carb, adjust it till it floats the ball in the center, now adjust the front and rear carbs with the Unisys until they float the ball in the center (this will throw off your idle speed, it will increase) now all you do is start backing down the idle screws on all three carbs (using the Unisys) till you get back down to the correct idle.

If you don't have return springs on all three carbs (I found) the other two will not close fully, if you have a stumble when you stomp it (flooding or starving) you may have to adjust your accelerator pumps.

Hope this helps.

See Ya,
Mike

 

[Anonymous]

Hey Cobrasix. Yes i am using the offy. And i am using the individual little aircleaners. I hope they fit. If not i guess it is just another project to do. Thanks

Nazs

 

[CobraSix]

Mike,

My problem is that when I give it gas, it stumbles, almost dies, and then back fires through the carb. I know it isn't the timing as it is dead on at 10 BTDC. I set the mark while re-assembling the engine. I've also had no problems running just the center carb.

Last night, when it back fired it all of a sudden developed several bad vacuum leaks as there is a very loud audible whistling that goes away when I spray the outer carb bases.

This set up is getting very frustrating and I'm thinking about scraping it.

Slade

 

[MustangSix]

Slade,
The outer carbs are supposed to do absolutely nothing until the center carb is at least 2/3rds open.

The throttles on the outers should be completely closed, choke and fast idle disabled or removed, and the idle mixture screw turned completely in. The accelerator pumps must work properly to avoid stumbling when they open.

You'll also have stumbling problems if you are relying on a lot of vacuum to bring in your ignition advance. When the outers open, vacuum goes to near zero and all your vacuum advance disappears as well. These setups really work better with centrifugal only distributors, but are not good at all with the old Load-O-Matic.

Triple Autolites or Webers are real mean when set up properly, but vacuum leaks will drive you crazy until you fix them all.

 

[CobraSix]

Jack,

I removed the chokes from all of the carbs actually, and blocked off the vacuum ports for the chokes. I also have the idles closed on the outer carbs.

I'm stumbling on initial acceleration, not when the outer carbs are opening. I know it isn't the carb specifically because the center carb is the same as I was running as a single and was rebuilt by Pony Carbs and never had the stumble.

I'm having no problems with vacuum until I had the really bad back fire last night that seemed to cause a very bad vacuum leak. I was running around 15 inHG until the bad back fire and now only running around 5. I located the vacuum leak (at least the major one) at the front carb intake base. I tried fixing it tonight, I'll know how it takes in the morning.

About the dizzy. What is a good centrifugal only dizzy? DS2 is both, right? Right now my dual advance (cent and vac) dizzy is running from the vacuum port on the center carb. I'm reading vacuum from the port on the manifold.

jack,

definitely right about the mean sound and ability when working. I had it semi working this weekend, and even got a good 2nd gear, 25 MPH chirp from my tires. I also got a nice long peel out from first. And boy does it sound cool. Now just to get it working again.

Slade

 

[MustangSix]

You can curve a 68 up points style or a DSII so that you only need the centrifugal and you just remove the vacuum can and pin the advance plate. Open the dizzy up, engage the slot with the largest number, and add lighter springs. That will give you a starting point.

 

[simon]

bad case: your backfires just mess up your carb throat gaskets, like I assume what happened to you.
caution: a solid backfire can bend your throttle plate, ruining idle qualities forever. I still have an autolite1100 laying around with a bent plate, oval shaped throttle shaft bores, and a nasty groove hacked into the throat where the plate used to be. Calling those backfire damages "vacuum leaks" is quite and understatement -that carb is basically junk.

I thought you were going to keep it a daily driver (or every-other-day driver), in that case I´d remove the choke units from the outboards only, not from all three carbs.

cheer up, it could be worse... you could be fiddling with a hilborn mechanical injection ...

 

[CobraSix]

Simon,

For some reason, my car runs pretty decent without the chokes engaged. I ran into clearance problems when I used the choke on the center carb. I do have to sit in the car for about a minute to keep the car running for that first 60 seconds, but after that, the car runs okay.

I'll check out my carbs for any damage. It wasn't a very loud backfire, probably would not have heard it with the hood shut and air cleaner on. I do think it is from the intake base because when I sprayed carb cleaner at the base of the intake, the RPMs and vacuum went up. I'll know more tomorrow on how the repairs took.

Slade

 

[Anonymous]

NAZS, you should only have hood clearence problems with the front aircleaner with your Webers. I am running the set up and my front air cleaner just barely touches one of the hood supports or rib things, its not enough to bother me though. I have though of trimming down the part of the air cleaner that sits on the carb for a better fit.

Slade, all of the advice here so far is good. I had someone give me an extra hand when I was setting my carbs to open, it was just easier with 2 sets of hands. I adjusted the slides on the linkage so that all 3 were wide open at the same time, the linkage does the rest on when to open them.

When you get it running right, you'll know, my car screams now compared to how it used to run. I had to add a tch becuase it revs so much faster now...

Bill

 

[Anonymous]

I think Jack is on the right track with the distributor issues, I have a Mallory dual point with mech. advance and never had an issue with timing.

Have you tried running either of the outer carbs alone in the center position?

My car runs OK now even with fuel and vacuum leaks galore, don't give up!

One other thing, have you hooked up the timing light with just the single carb and checked the advance on timing and then the same thing with multiple carbs? You should get the same reading at the corresponding RPM either way (or close to it).

See Ya,
Mike

 

[CobraSix]

Bill, originally I set the linkage so that all were WOT at the same time.

Mike, All carbs were tested on center first to make sure they were working right. I set timing on just the center carb running. I haven't gotten around to getting the car running well enough to get to timing. Also, what part number for Mallory do you have? Just curious.

Slade

 

[Anonymous]

I have the Mallory Mechanical Advance oncly distributor as well. Except I think mine is a unilite. I can look at the part number tonight if you would like...

Bill

 

[MustangSix]

If you block off the outers and run only the center, does it run well? It should. If not, you can start from there to isolate the vacuum leaks, set the timing, etc.