Hello,
I am trying to tune dual empi 44 carburetors and am having little success.
The symptoms:
There seems to be no sweet spot. When I rev the engine it bogs down almost like it is being starved of something.
What I have tried:
Fine tuning the linkage
Changing the fuel/air mixture
Changing the timing from 32deg BTDC
Changing the fuel pressure
Checking for vacuum leaks by resealing the manifolds and using B12 around the carburetors
The Car:
1973 Squareback
New 1776 engine (it ran fine before the stock rocker clip chewed up a valve)
Anyway, any help would be greatly appreciated.
Dual Carburetors Tuning Help
-
GjMan
- Posts: 97
- Joined: Mon Nov 22, 2004 6:21 pm
Don't have experience with those particular carbs, but every aftermarket dual carb set-up I've installed has not been right out of the box. My latest was the Brazilian 34 PDSITs from CB Performance. Had to install smaller main jets and larger idle jets to cure an off-idle stumble. Still not running perfect as I believe the pump jets are too big. Have been putting that job off because the cure will be to solder up the jets and re-drill.
Can't be more specific about your problem, but I believe you will need to change jets to get things right. Do those carbs take regular Solex jets?
Can't be more specific about your problem, but I believe you will need to change jets to get things right. Do those carbs take regular Solex jets?
-
Supperman
- Posts: 3
- Joined: Fri Jun 08, 2007 5:06 pm
I believe the jets in these carburetors are cast and machined. I dont believe they can be changed.
Why would you have to change the size of the jets on your carbs? Did you have a much larger engine? My engine is only a 1776 and it did run with the stock fuel injection. So I would imagine the jets on these carbs are selected to run on this engine size. Unless there was a manufacturing error where the jets are not performing as they should. In that case I could justify changing the jets but not changing there sizes. Perhaps I am missing something, but I would hope that changing the jets on new carburetors is not standard procedure.
Thanks
Why would you have to change the size of the jets on your carbs? Did you have a much larger engine? My engine is only a 1776 and it did run with the stock fuel injection. So I would imagine the jets on these carbs are selected to run on this engine size. Unless there was a manufacturing error where the jets are not performing as they should. In that case I could justify changing the jets but not changing there sizes. Perhaps I am missing something, but I would hope that changing the jets on new carburetors is not standard procedure.
Thanks
-
raygreenwood
- Posts: 11895
- Joined: Wed Jan 22, 2003 12:01 am
Just a question...why would you assume that the carbs you have bought are made for your engine or its size?
The manufacturers of the carbs have no idea what cam you have (which alters vacuum and airflow), what compression you have (which alters vacuum and airflow), what exhaust you have (which alters airflow and can affect vaccum) or what gears and tires you run this set-up with...which affect everything. This is not to mention that you see carbs that are advertized that say "can be run on engine from _____cc to _____cc. "
The fuel injection...which I would have kept in favor of carbs any day....also cannot switch from engine to engine without serious adjustment. Also...if you switch that injection system to an engine that is all else the same...but has the wrong cam...it may not run at all.
Thsi gist of this is...that jets in carbs are set up in teh middle of the road by the manufacturer. They have no idea what they are going to be used in. Jet changes are as common as tire changes. Ray
The manufacturers of the carbs have no idea what cam you have (which alters vacuum and airflow), what compression you have (which alters vacuum and airflow), what exhaust you have (which alters airflow and can affect vaccum) or what gears and tires you run this set-up with...which affect everything. This is not to mention that you see carbs that are advertized that say "can be run on engine from _____cc to _____cc. "
The fuel injection...which I would have kept in favor of carbs any day....also cannot switch from engine to engine without serious adjustment. Also...if you switch that injection system to an engine that is all else the same...but has the wrong cam...it may not run at all.
Thsi gist of this is...that jets in carbs are set up in teh middle of the road by the manufacturer. They have no idea what they are going to be used in. Jet changes are as common as tire changes. Ray
-
Supperman
- Posts: 3
- Joined: Fri Jun 08, 2007 5:06 pm
Well, I thought the carbs would work on this engine size/cam/etc. combination considering the engine ran fine with the stock fuel injection before it stopped working. And these carbs claim to work on engines up to 2200cc's
Although this problem might be the ignition system or the centrifugal advance in the distributor.
Thanks for your comments
Although this problem might be the ignition system or the centrifugal advance in the distributor.
Thanks for your comments
-
raygreenwood
- Posts: 11895
- Joined: Wed Jan 22, 2003 12:01 am
Not being snooty here...but you do realize that the engine running fine with EFI previously....means nothing at all toward running and sizing of carbs. The engine should run fine with the injection. It was sized and tuned to the engine.
If the carb manufacturer says that the carbs should run engines to 2.2 liters...and you are putting it on a 1776.....a difference of 424cc's....why would you think that these two engines could use the same carbs without changes? An engine of 2200cc and an engine of 1776cc will have different cams (probably) different vacuum signatures (assuredly) and different strokes (most likely). All of these affect the volume and speed of the air as it is pulled through the carb. That will affect mixing and the operation of the venturies. This will affect jet sizing. This is all we are getting at.
No such thing as a bolt up carb. It needs to be tuned then balanced. Ray
If the carb manufacturer says that the carbs should run engines to 2.2 liters...and you are putting it on a 1776.....a difference of 424cc's....why would you think that these two engines could use the same carbs without changes? An engine of 2200cc and an engine of 1776cc will have different cams (probably) different vacuum signatures (assuredly) and different strokes (most likely). All of these affect the volume and speed of the air as it is pulled through the carb. That will affect mixing and the operation of the venturies. This will affect jet sizing. This is all we are getting at.
No such thing as a bolt up carb. It needs to be tuned then balanced. Ray