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I have a 1974 Triumph TR6 that we bought from a guy that had to move. It has a solid lifter cam, 3 two barrel weber carbs, headers, all the goods. The carbs are setup on an Individual Runner Manifold with a single vacuum tap at the center of the manifold. Each carb barrel feeds one cylinder. They are adjustable with idle speed, and idle air bypass. It seemed to have gone out of tune and no matter what I do, the car will not idle. I have entirely disassembled all the carbs and let them soak in carb clean for 3 days each to clean out any fouling but the problem stayed. The problem is: the car wont idle at anything under 1500rpm and even then it sounds like it will die. A weird thing happens when I cover one of the throttle barrels of a carb, the engine smooths out and accelerates rapidly. They seem to work fine after about 3500 rpm but that's way too high to expect to drive anything and the power output of the car is way down. Any and all help would be appreciated. I have experience with all sorts of 4-barrels but this multi-carb setup has me baffled. Thanks for your help!


A.J.

[ April 16, 2002: Message edited by: NeedBoost ]</p>
 

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first try seting all your idle jets the same amount.turn them in till they bottom out.then turn tem back out say 1 1/2 turns each.then hook a vacum gage to each carb.mercury gage would be better.and adjust each one a little at a time till you get equal vacum on each carb.you might have to adjust the linkage between carbs at the same time.I have done this on motorcycles.you got to have pataince doing this to get it right.take your time.hope this helps.I'm assuming all 3 carbs have to run at the same time like a motorcycle?

[ April 16, 2002: Message edited by: Oldbuz ]</p>
 

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The carbs don't have individual vacuum taps on them. I tried reading from the manifold tap but couldn't get much more than about 12in of vacuum. Oh yes, when I was reading the vacuum, the needle would jump rapidly and as I adjusted the carbs, the oscillation dropped to only a few inches in each direction. When I opened the throttle blades, the vacuum fluctuated wildly in rapid oscillations from around 9in to 15in. I hope this extra information helps describe my situation a bit more. Perhaps there's a sticky lifter somewhere but last time I lashed the valves, they all seemed to move. Please advise.
 

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sorry I am not to framiliar with mutiple carbs myself.I thought I could get you to a base line wiyh thge info I posted.If I remember right from what you say the vacum gage is doing fluttering all over sound like a burnt or bad valve.if it is at all possible try to get the motor to run on just 1 carb and add the other 2 in 1 at a time.don't know how yours is set up to work.I know the 3 duece set up on a V8 is set to run on 1 carb for normal driving the the other 2 kick in as you give it full throttle.
 

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HP BOOKS has a book out thats written by PAT BRADEN there book # is 774.
the name is weber carburetors.
it's pretty easy to deal with, and if your are going to keep those carb's your going to need it more than once, as they are a pain to deal with on street driven cars.
JOE
 

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Here's a link to a supplier that has a comprehensive PDF file about tuning these carbs, click on the "Technical info" link.

<a href="http://www.webercarburetors.com/" target="_blank">http://www.webercarburetors.com/</a>

[ April 17, 2002: Message edited by: 4 Jaw Chuck ]</p>
 

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I know what you mean. I noticed the same thing (engine smoothing-out when air is restricted) during my tuning of my Webers. But I'm getting close to getting my system properly tuned. It takes some time. Perhaps we can share notes. What type of Webers do you have DCOE? IDA? IDF? I'm using 4 48IDFs on my 406. (See Backfire Issues in this forum).

Timing could be the issue. Webers like to hit peak TOTAL advance early - like around 2000 RPM. But most likely it is a jetting problem. What happens when you get below 1500 RPM? Does it seem like it is getting too much fuel or not enough? Check this out after the carbs have been synchronized.

Get a synchrometer (Not The UNISYN piece of junk). Inglese sells one for about $60. The Synchrometer is a meter with flow values and not a ball the bobs up and down.
 
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