Thread: progressive dual quads.

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Hi all sorry i have not gotten back sooner small computer problem then i could not log back on,, anyways, i got the 2 4's working pretty good. very slight stumble at idel just needs a fine tune after motor breaks in. almost done i attached pics of car let me know what ya think.

Nice looking car!
I always like more than one carb!

Pat

Thanks, It is a 1936 plymouth 5 window
i have one question i just bouht a carb tuning dvd because they siad they showed how to tune 2 4's but it did not. so i e mailed the company on the dvd and asked them this is what they said.

I REALLY don't recommend running any kind of progressive linkage between the front and rear carbs on any twin carb set-up. Progressive linkage is great for six pack set ups where one CENTER carb runs the engine evenly up until half throttle, then the outer two carbs come-in later on (progressivly) for full throttle pulling.

Setting a front or a rear carb up as progressive can make the front or rear of the engine run lean, depending on which one comes in later. I would highly recommend running both carbs in perfect sync with each other.

Adjusting the idle mixture screws a bit more on the rich side for one of the carbs will only cause it to run slightly richer during, and right off an idle, but not at part throttle or while under normal acceleration. Under normal driving conditions, you are pulling from the main jets, NOT the idle mixture circuits that the screws adjust. They call them IDLE mixture screws for a reason :-)

Does progressive linkage work? Yes, but as I said.... IF there is a center carb to run the engine EVENLY, and 2 outer carbs that come-in progressivly as you get into the throttle. It is not good for your engine to have one carb running at part throttle while the other is closed. Make them both the same or you're asking for engine damage.

Have a good one,
Arron

Now i am nervuse i don't want to cause any damage to the motor, any suggestions?

Thanks Denny
this is the best pic i can get of the linkage, i'm just worries that i should be set up 1:1 insted of progressive.

yes that is the linkage i have. there instructions say it can be either way progressive or 1:1. depending on how you set it up. i have called there tech line numerus times and can never get a straight or the same answer on how to tune or set up, first it was 2 turns out on bolth, the next time it's 1/2 on front 1 1/2 on rear. then it was 3/4 turn on all. so i set it up 1/2 on front and 11/2 on rear progressive.
my problem now is i talked to a performance engine builder and he said never run progressive unless there is a center carb to even out the fuel or you will damage the motor due to a lean condition in the front (if the front is secondary) so now i dont know what to do.

ok, so for ideling i sould set all the idel mixture screws the same, and have the primary carb open a little before the secondary carb. If i do it that way witch carb should control the idel speed or should i use idel speed on bolth set at the same.

P.S. if i did not mention it before thanks for all your help..

Alot of things are needed to tune it, what type of build is the motor, stock, mild cam, street, race. I ran my cars 2x4's on a tunnel with progressive (not much), on the street, and on the boat with 1:1 with 2x4's on a blower.
I use a synchronizer ($15.-$25.00) and set them the same, 1st you need to set the carb Idle stop screws to what the book say's, you should not have to move them at all, if you do, don't go past the idle ports, or it won't idle right, and or hesitate. Then you start the motor and sync the carbs to the same vacuum, then turn your mixture screws evenly to set the idle, keeping the vacuums the same. once your there, you should be able to use either set up, you may have to back down your accelerator pump shots depending on you motor & or your jets. I don't know what jets you have, or need for your motor, but odds are you need smaller ones.
I adjust everything with the linkage off 1st, the I put it back on and make sure it still idles the same. After you get it tuned you can use the linkage both ways and see which you like best. You'll probably end up with 1:1

Pat