Carburetor swap weber 38

What rpm do you want your engine to idle at?

Do you have a digital tachometer like ones built into a timing light? The dash tach is a no-go for accurate synching/adjustments.
 
Yesterday I actually tried a digital multimeter with tachometer for the first time when checking my timing. It’s not an expensive unit I must admit.
Idle when warm was at 950-1000rpm on the multimeter. While the car intrument tacho showed 1100rpm.
 
So if it idles now at 950 and that is where you want it:

1. Check airflow with synchronmeter. If out of balance, lower the higher carb’s linkage screw a little and raise the lower one a little to even the flow out but keep idle at 950. Adjust until both flow evenly at 950 rpm.

2. Turn front carb idle mix screw in until rpm drops. Turn the screw out, listening and watching for rpm peak, keep going until rpm drops or runs poorly, turn it back in to the midpoint of the 2 extremes. Repeat for rear carb.

3. If idle has dropped or increased, repeat steps 1 & 2 until carbs are synched, idle is 950, and mix screws are where the engine likes them. Final adjustment is always the mixture screws.

4. Check the flows of both carbs at 3000 rpm, if they don’t match then you have a linkage issue.
 
  • Like
Reactions: Ezz
I am not a tuning expert, others here have been a helpful resource in my efforts.

As a starting point, the hat that you have will provide a good measure between the carbs, the other hat that you mentioned (picture below) that is available will enable you to make sure that the barrels within the carb are synchronized.
1729001178363.png


For example, the throttle butterflies should be adjusted to ensure that one side is not uncovering the progression holes more than the other at idle. This could be due to linkage tension or the adjustment at the screw that is on the progressive cams (arrow shown in the picture below).

1729013908623.png


@Stevehose mentioned in my thread (link) "Have you checked the flow on the secondary barrels? They should be flowing <.5 or so at idle." In the 38/38 there is really no secondary (as I understand it) as both barrels are opened simultaneously, but I will also admit that I still have a lot to learn.
 
Stevehose said:
So if it idles now at 950 and that is where you want it:

1. Check airflow with synchronmeter. If out of balance, lower the higher carb’s linkage screw a little and raise the lower one a little to even the flow out but keep idle at 950. Adjust until both flow evenly at 950 rpm.

2. Turn front carb idle mix screw in until rpm drops. Turn the screw out, listening and watching for rpm peak, keep going until rpm drops or runs poorly, turn it back in to the midpoint of the 2 extremes. Repeat for rear carb.

3. If idle has dropped or increased, repeat steps 1 & 2 until carbs are synched, idle is 950, and mix screws are where the engine likes them. Final adjustment is always the mixture screws.

4. Check the flows of both carbs at 3000 rpm, if they don’t match then you have a linkage issue.
Click to expand...
But.. there’s 2 mixture screws on each carb. Maybe your instructions is for the 32/36?
My question earlier was about how to adjust the 2 screws if not equally on both sides of the carb.
boonies said:
I am not a tuning expert, others here have been a helpful resource in my efforts.

As a starting point, the hat that you have will provide a good measure between the carbs, the other hat that you mentioned (picture below) that is available will enable you to make sure that the barrels within the carb are synchronized.
View attachment 191389

For example, the throttle butterflies should be adjusted to ensure that one side is not uncovering the progression holes more than the other at idle. This could be due to linkage tension or the adjustment at the screw that is on the progressive cams (arrow shown in the picture below).

View attachment 191419

@Stevehose mentioned in my thread (link) "Have you checked the flow on the secondary barrels? They should be flowing <.5 or so at idle." In the 38/38 there is really no secondary (as I understand it) as both barrels are opened simultaneously, but I will also admit that I still have a lot to learn.
Click to expand...
I did pay special attention to the synchronization of both butterflies on each carb watching carefully that the progression holes were exposed simultaneously before attaching the carbs to the manifold. Some minor adjustments were made.
 
Copy paste from instructions on racetep.com

"By having 2 mixture screws you are delivering fuel from 2 places in the intake manifold. The Mixture screw closest to the engine will no doubt need to be in much farther than the outer mixture screw. This is Okay. I do not recommend Stagger jetting the idle circuit on a 38 DGES (In other words, do not use 2 different size idle jets even though you need to adjust the screws differently. This can cause part throttle dirveability issues.)"
 
You must log in or register to reply here.
Back
Top