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ghornbostel
Greg Hornbostel
Nebraska
(76 posts)

Registered:
09/02/2013 01:41PM

Main British Car:
1957 TR3 Buick 231 evenfire V6

Weber Carb Tuning
Posted by: ghornbostel
Date: September 11, 2014 07:17PM

So the engine (Buick V6) for the TR3 is together and now the job of tuning the carbs for the cam, 10:1 compression and a slight amount of head porting. Engine runs good 3000 rpm and up. Started with a .45 idle jet and had a hesitation and popping in exhaust and intake. Drill the jets out till the hesitation and popping went away and the jets are at .80 mm. Beings how there isn't a 80 idle jet for sale I have this feeling that perhaps something in the idle circuit is amiss although I have had the carbs apart and the passages are clean. The float bowls also siffen out for some reason causing a very rich startup and concern about the gas washing the cylinders down. Distributor is mechanical advance (36 degrees) and timing is set at 9*. Carbs are 3c ida with 30mm chokes. Any ideas...

Greg Hornbostel


mgb260
Jim Nichols
Sequim,WA
(2461 posts)

Registered:
02/29/2008 08:29PM

Main British Car:
1973 MGB roadster 260 Ford V8

Re: Weber Carb Tuning
Posted by: mgb260
Date: September 11, 2014 07:59PM

Greg, I would check the floats(brass for leakage, plastic for fuel absorption) and needle and seat. I would also limit your timing to 32 and set initial to 12. Also, Webers only need about 3psi fuel pressure.


DiDueColpi
Fred Key
West coast - Canada
(1365 posts)

Registered:
05/14/2010 03:06AM

Main British Car:
I really thought that I'd be an action figure by now!

authors avatar
Re: Weber Carb Tuning
Posted by: DiDueColpi
Date: September 11, 2014 10:19PM

Hey Greg,

The richness on start-up is your first concern.
As Jim said, fuel pressure is critical and must not exceed 4.0 psi. 2.5 to 3.0 psi is recommended.
Almost any fuel pump will need a regulator to meet this requirement. So check it. You will be surprised.
Once the pressure is correct then move on to the float settings.
These are never correct and need to be adjusted, even on a new set of carbs. (they are not set at the factory)
First you need to confirm that all of the needle and seat assy's are tight clean and not leaking.
Then they all need to be adjusted so that the distance from the tip of the ball to the face of the upper housing is 18mm exactly.(for 3c only)
Various thickness's of washers are available to do this. Stacks of two or three are not uncommon as well as sanding one down if needed.
On to the floats. Make sure that they are clean and leak free. Just give them a shake. If you hear fuel inside then they are done for.
If you happen to have plastic floats do yourself a huge favour and replace them with brass.
Install them into the carb base and you're ready to adjust them.
Here's the tricky part. And you might want to make some guages out of some tin for this.
With the float (the flat portion not the seam) raised 12.5 mm above the carb base top. The needle and seat tab should be exactly 18mm from the carb base top.
The float setting on a Weber is one of it's most critical settings so take some time and make it perfect.
Now that that's done
Set your idle speed screws to 1 1/4 turns in from closed.
Consider this a maximum setting as anything more will expose the progression holes and make you life miserable.
If more idle speed is needed then open up the idle bleed screws ( the small ones with a lock nut on them at the base of each throttle bore) as needed.
Set the idle mixture screws at 1 1/2 turns out from seated and start the old girl up.
Once warm then grab your sync meter and settle the idle down to where you want it. Make sure each barrel is drawing the same amount of air and use the idle air bleeds to make it perfect.
Now one at a time, screw the idle mixture screws in until that cylinder just starts to drop off. Then back the screw back out until the cylinder just starts to pick up again. Ignore the internet hyperbole about where the screw should be. Your engine wants what it wants.
You will be adjusting the idle speed again as it will have now changed, which will affect the mixture, and around and around you go until it's perfect.It's not hard it just takes time.
Now we can play with the idle jet. They come in stock sizes from 45 all the way to 80. This is related in 0.mm
Almost always, somewhere in the 50 to 65 range works well.
If you run well just off idle, say to 1300-1500 rpm and then fall down up to 2500 or so. Then you need to change the idle air bleed.
This is incorporated into the idle jet holder. These come in sizes 60 to 140 again in 0.mm
Smaller air bleeds will pull more fuel sooner and larger will pull less fuel later.
So a careful balance of the idle jet and the idle air bleed will be able to accommodate any engine.
This is also where your cruise fuel economy comes from so smaller idle jets are just good stuff everywhere.
Once you get the low speed worked out (below 3000rpm) let me know and we'll make some beautiful power together.
(was that weird, or was it just the scotchy scotch talking?)

Cheers
Fred


ghornbostel
Greg Hornbostel
Nebraska
(76 posts)

Registered:
09/02/2013 01:41PM

Main British Car:
1957 TR3 Buick 231 evenfire V6

Re: Weber Carb Tuning
Posted by: ghornbostel
Date: September 11, 2014 11:50PM

Thanks guys. The fuel pressure is regulated and set by gage at 2 1/2 psi. I suppose I could check the gage (Inglese that came with the carb setup). I haven't changed the needle-seat assemblies and have a new set of them. Floats are brass and good although I had them set to 5.5 - 6mm. I'm a little confused with the idle air bleed. Carbs are 40mm ida and I don't think they are removable. All that is attached with the idle jet holder is the idle jet unless I'm overlooking something. There is a brass plug with a 1.1mm hole at the gasket surface with the top of the carb and I was under the impression that it was the idle air jet. Tomorrow I shall go through these carbs using the dimensions and proceedures outlined. I'll try the initial 12* timing but I believe its kicking back at anything over 9*. I'll hunt down a fresh set of weights for the 32*. As far as making beautiful power together I get the drift and it really gets with it now. I haven't taken the engine over 4500 rpm yet and have been wondering what would happen if the carbs had 36mm chokes in them instead of the 30mm ones. All in due time as I agree that the important part is the fuel richness on startup.

once again, thanks for a fresh start to the problem.
Greg


mgb260
Jim Nichols
Sequim,WA
(2461 posts)

Registered:
02/29/2008 08:29PM

Main British Car:
1973 MGB roadster 260 Ford V8

Re: Weber Carb Tuning
Posted by: mgb260
Date: September 12, 2014 01:07AM

Greg, You probably have too much vacuum advance, limit it to 8-10. Advance should be all in at 2500.


ghornbostel
Greg Hornbostel
Nebraska
(76 posts)

Registered:
09/02/2013 01:41PM

Main British Car:
1957 TR3 Buick 231 evenfire V6

Re: Weber Carb Tuning
Posted by: ghornbostel
Date: September 12, 2014 01:38AM

Jim, I don't have the vacuum hooked up. Its all centrifical. Fred, I'm a little confused about the float setting. 18mm from gasket surface to needle-seat tab and 18mm from gasket surface to tip of ball of needle-seat. What about the thickness of the gasket. I think I know what it needs to be but just making sure that the gasket doesn't play some preload factor here.
Greg


DiDueColpi
Fred Key
West coast - Canada
(1365 posts)

Registered:
05/14/2010 03:06AM

Main British Car:
I really thought that I'd be an action figure by now!

authors avatar
Re: Weber Carb Tuning
Posted by: DiDueColpi
Date: September 12, 2014 01:28PM

The float setting allows for the 0.5 mm gasket thickness.
This setting is unique to the triples. The two barrels use the 5.5mm setting.
You are correct. The idle air bleed on the IDA 40 3C is the brass plug that you saw. My bad! Mixed up the 3's and 2's.
The only real option here is to pull them, solder them closed and redrill them.
If you have the nerve you can drill them for the screw in main air correction jets.
One last note. Pull your plugs and check them frequently while you are rejetting. Just one instance of rich running will foul them enough to cause a problem. If they are black at all, it's going to miss fire. If you don't have a plug cleaner, you can use a propane torch to burn off the contaminants. Reducing the plug gap to 25 to 30 thou. while tuning will help out as well.

Cheers
Fred



ghornbostel
Greg Hornbostel
Nebraska
(76 posts)

Registered:
09/02/2013 01:41PM

Main British Car:
1957 TR3 Buick 231 evenfire V6

Re: Weber Carb Tuning
Posted by: ghornbostel
Date: September 12, 2014 06:44PM

Well now, a cool Nebraska day of tuning weber carbs. I'll have to take them apart again Fred because I just read your post. I now have a feeling that the fuel pressure is too high. After getting the engine running I found that it was only running on 3. Checked everything and then checked the float levels through the standoff tubes. No fuel in the lead (closest to the pump) carb. Pulled the plug over the needle-seat and pushed down. It was stuck closed?? Lowered pressure one psi and no problem. I closed my idle jets down to .5mm and balanced everything out and as it stands now no hesitation on a snap throttle but there is a back fire through the carbs and exhaust every once in a while. My idle jets are out to 3 turns. Tomorrow is supposed to be sunny and in the 60s. I'll go for a road test then and then setup the floats again. I don't have a lot of room between the carbs and the hood. A K&N filter won"t fit although it is close. How short a velo stack can I get away with. I have made a 3" foam filter and there is about 1 1/2" between the tubes and top of air cleaner.
Greg


ghornbostel
Greg Hornbostel
Nebraska
(76 posts)

Registered:
09/02/2013 01:41PM

Main British Car:
1957 TR3 Buick 231 evenfire V6

Re: Weber Carb Tuning
Posted by: ghornbostel
Date: September 14, 2014 07:51AM

Its back together and running. Everything is balanced idle at 900 rpm. Right bank of cylinders has a solid exhaust sound. Left bank has a slight popping sound (p.....pp..p.p.....p)
Greg


ghornbostel
Greg Hornbostel
Nebraska
(76 posts)

Registered:
09/02/2013 01:41PM

Main British Car:
1957 TR3 Buick 231 evenfire V6

Re: Weber Carb Tuning
Posted by: ghornbostel
Date: September 15, 2014 09:38PM

and around and around we go. The exhaust sound was because the two carbs weren't drawing the same air. After adjusting with the idle speed screw (it wasn't touching the lever) things progressed. I still have some adjusting to do. One of the needle-seat units is still in the carb as the cap will probably have to be machined out. I'll have to order fuel block gaskets and will get one of them at that time. Engine is running very well at .6 idle jets. It has been returning to idle (1000 rpm) consistantly. There is still some flooding after the engine is shut off but I believe it is the old needle-seat. Fred, I have the nerve to drill and tap the idle air out. What should I use for jets or should they just be make special to say a 6mm or 5mm thread.
Greg


DiDueColpi
Fred Key
West coast - Canada
(1365 posts)

Registered:
05/14/2010 03:06AM

Main British Car:
I really thought that I'd be an action figure by now!

authors avatar
Re: Weber Carb Tuning
Posted by: DiDueColpi
Date: September 16, 2014 12:10PM

My go-to jet for that sort of thing, is the main jet for the old Carter/Edelbrock AFB.
It's cheap, relatively small, available in every size imaginable (and I have tons of them from carb tuning).
The thread is 5/16 x 24 and a hole drilled at 0.250" (1/4") to a depth of 0.200" (just over 3/16") and then threaded with a bottoming tap, works perfectly.

Cheers
Fred


ghornbostel
Greg Hornbostel
Nebraska
(76 posts)

Registered:
09/02/2013 01:41PM

Main British Car:
1957 TR3 Buick 231 evenfire V6

Re: Weber Carb Tuning
Posted by: ghornbostel
Date: September 18, 2014 12:29AM

Thanks Fred.

Greg


ghornbostel
Greg Hornbostel
Nebraska
(76 posts)

Registered:
09/02/2013 01:41PM

Main British Car:
1957 TR3 Buick 231 evenfire V6

Re: Weber Carb Tuning
Posted by: ghornbostel
Date: March 15, 2015 10:20AM

So winter has turned to spring. The flooding problem hasn't gone away but I believe I'm getting my head around it. I had a "ah ha" moment standing in front of the beast admiring the fine looking carburator setup and it occured to me that when I fabed and installed the air cleaners that I shut off the ability of the louvers to vent the hot engine compartment air. Not while the engine is running but when the engine is shut off. The air cleaners in effect keep the hot air around the float bowls. To prove this I removed the air cleaners and problem goes away to some extent. I made a heat shield and installed it between the manifold and carbs and this really helped but when the air cleaners went back on it worstened again. Guess I'll be putting another row of louvers in the hood to allow the air to go around the air cleaners. The first two rows were done to allow cold air into the carbs before air cleaners. With the air cleaners on the carbs the tops of them are only about 1/2 inch from the hood. The engine is really starting to run well. Time to send this off and go for a drive!!!!!!
Greg


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