Vortex with dual tillotson running rich

[blaneys98]

Just installed a vortex intake and 2 new tillotson carbs. Have both gav adjustments all the way in and the car still running rich and backfiring when revved. (Unsure of the head’s compression - may be stock). Any ideas on leaning it out?

[blaneys98]

Car ran fine on a single tillotson.

[hardtimes]

Originally Posted by blaneys98

Car ran fine on a single tillotson.

Might be a simple adjustment problem when...'it ran fine on single'.


Note that with dual carbs, the central location of fuel delivery is different than with a single. That Is, if nothing different then what is gained by switching ?


Determine which cylinder , that is being served by which carb, is allowing the backfire. Then concentrate your tuning efforts on that carb to address your concern. That carb may need to be adjusted slightly different/richer/leaner.
Check plugs for different appearance after running warmed up; while still fairly cool. Condition(s) of plugs can tell a skilled tech a LOT of what is going on in the engine.


Have you used a tach to determine optimum rpm of each carb while adjusting it , running of course ?
How good is your valve adjustment and seats ?
Do you have ANY gasket air leaks ?
Is your timing right/correct ?
Amount of carbon in combustion chamber(S) ?


Backfire can be caused by a number of different circumstances. Knowing about all these , can help you address each one , maybe eliminate it, and move on up the list.


From your statement. It's obvious that you believe that TOOO much fuel is being let in via carb...and causing backfire ..no ?
Well, your car can/will backfire from running out of fuel also !

[Purdy Swoft]

I run my roadster and speedster with dual updraft carbs .Running dual updrafts is simple compared to dual downdrafts . The aluminum Vortex and the old cast iron manifolds that I run are open plenium. If the linkage is disconnected this setup will run off just one carb and it will idle and rev and all cylinders will be fed . You could test you carbs like this. Install your old tillitson on the front and disconnect the linkages from the carbs . Leave the old carb adjusted just like it was when it was running on the engine before . You may need help because you are not use to this . You need to have the engine cranked and started . Stand beside of it so that you can reach in and operate the throttles on the carbs Hold the throttle closed or at idle on the rear carb. The front carb should rev as the car normally did when you move the throttle . If it doesn't do this you will more than likely have a vacume leak. A vacume leak causes lean operation and sometimes backfire . If you lose too much vacume the engine won't have the suction power to draw the fuel up the manifold and to the combustion chambers . When you lose vacume you will need to choke it a lot or it will go dead. Check that the gaskets are sealing where the carbs connect to the manifold and where the manifold bolts to the engine . Also make sure that you don't have a vacume leak at the vacume line or at the windshield wiper motor. If the GAV adjustment is too closed it will cause lean operation and backfire . Rich opperation does not usually cause back fire . The idel air adjust screws are for fine tuning idle . I usually run the air adjust screws at one and a half turns open off the seat . Tillotson carbs usually run leaner than Zenith so I would probably start off with the GAV open about a full turn . After the engine warms a bit , if the GAV is too rich it will begin to lope . If you are runing dual carbs , I know that I'm not that concerned with super slow idel. Some that know nothing about this type set up may tell you that the GAV has no effect on idle .The GAV sure as hell will have an effect on idle when the carbs aren't running on the slow idle circuit and the engine will begin to lope and may emit a puff or two of black rich type smoke . When this happens , lean the GAV as necessary on the primary carb as needed to smoth out the idel and richness . I mostly run the GAV closed on the rear carb .

I feel that the problems that you are having is caused by lean operation . It could be because the GAV is closed or vacume leaks or a combination of the two. The spark plugs may be TOO cold . I run Cgampion W18 with mine . The timing may be off. Check points gap . Once all these things are checked it should run good .

[blaneys98]

I think Purdy is right, it seems to be running lean under load but rich at idle. Doesn't seem to be leaking air at the manifold, carbs and the vacuum port is plugged. Its still a gravity feed system. Gas is getting to the carbs, but it doesn't seem like there is enough under load. Do these systems need a fuel pump to get enough gas?

[Purdy Swoft]

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I don't run a fuel pump with mine, this is one of the big advantages of the dual updraft setup. You could be running too many fuel filters. I only use the stand up filter in the cut off valve . You could have an air block check the air holes - bowl vents in the top of the carbs, just behind where the fuel lines connect to the Tillotson carbs If the bowl vents somehow got blocked , you will get an air block that won't allow the bowl of the carbs to fill with fuel . I would also try removing the plug under the bottom of the carbs to see if the carbs are even getting fuel. if there is an air lock removing the drain plug under the carbshould let the air out of the bowl so that the gas can flow. Put something under the carb untill you can see the gas flow. there could be a stuck needle valve or some other blockage in the fuel system . if the carb that was removed ran before removal it should still run now unless there is some type of blockage ., Try removing the gas cap and see if that makes a difference . Are you sure that ytou are getting spark to the plugs.Sometimes if they sit for a while , especially in humid weather , the points will have to be sanded to remove oxidation. If mine sits for a few weeks I have to check and sand the points . When you find the problem , please let us know what you find . I hope that some of this helps .

[Benson]

Originally Posted by blaneys98

Just installed a vortex intake and 2 new tillotson carbs. Have both gav adjustments all the way in and the car still running rich and backfiring when revved. (Unsure of the head’s compression - may be stock). Any ideas on leaning it out?

I see that you say that you are using "new" tillotsons.

Are these old style or the "forklift"ones?

If so the answers if Forklift might be totally different?

Like I do not know if GAV is run at 1/4 turn like Zenith?

[Benson]

...

[blaneys98]

Running new original style tillotsons from Macs. New exhaust manifold and new vortex intake. I just tried using some permatex ultra copper gasket maker on both sides of the gasket to see if it just isn’t getting a good seal. (I was previously just using a copper gasket. It takes 24 hrs to cure. I’ll post on Sunday if it works.

[blaneys98]

Looked like there were some leaks at intake and exhaust manifolds. Sealed those with a new gasket and some Permatex copper. Also put on a new Aries muffler to achieve a good seal at the exhaust to manifold connection. Still getting what I assume to be a lean mixture with popping carbs and backfires when revved.

I ran TROG Wildwood this weekend and had to switch back to a single Tilloston setup. The car ran fine on the single carb. Because of this, it seems like the issue is lack of fuel. I was plumbing the dual setup with 1/4 steel line split with an upside-down T connection with each side of the T running to a carb (see below picture before the new muffler). I was getting gas at both carbs and the car idled fine. Gas flow appeared strong through the line ends. Problem is only at load. Thinking of trying a fuel pump, but really don't want to. Anyone have any other thoughts before I do?

[Sparky]

I would guess you are right. I have a Vortex with dual Zenith Bs on my speedster; since the fuel tank is in back I have to run a fuel pump and haven't had any fuel starvation issues.

[Purdy Swoft]

If you are running a micro filter anywhere in the system, that would cause the problem that you are having with the dual updraft setup . I had a similar problem when I tried running a micro stand up filter in the cut off valve . I removed the micro filter and replaced it with a screen style stand up filter and the problem was solved . Micro fine particles that will stop up the micro type filters will pass right through the system with no problem after the micro filter is removed . A micro filter in the sediment bowl could also cause a flow problem with a dual updraft setup . I'm running model B carbs with both of my dual updraft setups I run the GAV closed on the back carb at all times .Tillotson carbs do usually run leaner than Zenith carbs, You will probably have to experiment with GAV settings .

[Kahuna]

Follow Purdy's advice

[blaneys98]

I do have a micro filter in the glass bowl. When I reinstall the setup, I try replacing that with the screen before adding a fuel pump. Thanks for the replies.

[Purdy Swoft]

I have found that any time that the glass bowl is removed, it is best to replace the gasket or it will probably leak .

[Purdy Swoft]

Updraft carbs don't flood the engine as easily as down draft carbs if they flood at all . The original exhaust manifold has been said to be good for an engine producing up to 100 horsepower . Works well for me .

[Purdy Swoft]

Just to add , I feel that a simple dual updraft setup is probably best for street use .The dual down draft setup is best for racing and is more expensive and difficult to set up . Downdraft usually require a fuel pump and a fuel pressure regulator .

[Purdy Swoft]

I don't use air filters on my model A's Ford didn't think that model A's needed air filters . Model A's have lasted WAY longer than the other cars of the day that used air filters on the carbs .This says a lot to me. I have found that air filters on an updraft setup restricts power and causes rich operation . Some wonder why their oil smells like gas . Oil that is diluted with gas doesn't lubricate the bearings as well as undiluted oil Some wonder why that some of the expensive rebuilt engines fail before 10.000 miles ...

[Sparky]

Originally Posted by LowdownA

all good information things i had not thought of, i like the looks of those dual updrafts better than the single downdrafts which is what they recommend for a street motor. is there a way to use air filters i notice in the pictures space is at a premium ? thanks for your reply

I don’t see any practical way to add filters. The carbs are spaced tight and the rear carb inlet is close to the exhaust pipe, as can be seen in the pictures.