TheSamba.com :: View topic - I always drill the butterflies to use only one idf?

Thu Jul 21, 2011 6:12 pm

Hi, in the Bob Tomlinson weber tech appear the next configuration for single idf use:
150-160 fuel,
160-170 airs,
70-80 pump jets,
00 pump ex.,
60-65 iddle
use velocity stacks
and drill hole 1,7mm in the butterflies

i have a dune buggy with 2187cc with C25 (8,5cr - non ported heads 40x35,5)) for solid low end and torque (tank type engine).....i think use a 32 mm vents.....need empirical advice please!!

Thu Jul 21, 2011 6:21 pm

Does it idle OK? From what I understand the only time you need to drill holes is if you are having trouble keeping the throttles out of the progression holes when trying to get the engine to idle. It's a last ditch effort, do it only if you absolutely have to.

Thu Jul 21, 2011 6:41 pm

DarthWeber wrote: Does it idle OK? From what I understand the only time you need to drill holes is if you are having trouble keeping the throttles out of the progression holes when trying to get the engine to idle. It's a last ditch effort, do it only if you absolutely have to.
ok, but with the air pass screws closed??

Thu Jul 21, 2011 6:49 pm

Yes, your air bypass screws should be closed at all times.

Thu Jul 21, 2011 8:55 pm

I've run 3 different singles, they all had holes in the butterflys.

brad

Fri Jul 22, 2011 3:14 am

slalombuggy wrote: I've run 3 different singles, they all had holes in the butterflys.

brad

You drilled the holes?, and if so what was the problem you were curing?

Fri Jul 22, 2011 5:40 am

That's the way they all came. 36 Dell, 40 & 44 Weber (Italian)

brad

Fri Jul 22, 2011 8:54 am

DarthWeber wrote: Yes, your air bypass screws should be closed at all times.

but...my question is....what they are for the air bypass screws then??
thanks Darthweber

Fri Jul 22, 2011 8:59 am

slalombuggy wrote: I've run 3 different singles, they all had holes in the butterflys.

brad

remember size holes in your singles???

Fri Jul 22, 2011 9:00 am

I believe the bypass screws are there so you can balance the airflow between the barrels in one carb. I've never had to use them on my Dells.

Again, you shouldn't need holes in your throttle plates, as Berg would say "It's a bandage on your elbow for a sore on your knee." Think about it, if they were necessary Weber would have made those holes at the factory.

Fri Jul 22, 2011 9:03 am

I have never needed to drill holes in the butterflys on any single Weber application I had anything to do with and I have setup many single IDF fueled engines.

Fri Jul 22, 2011 9:04 am

DarthWeber wrote: I believe they are there so you can balance the airflow between the barrels in one carb. I've never had to use them on my Dells.

carb and engine size you used??

Fri Jul 22, 2011 9:06 am

1776/W120 cam/40x35.5 P&P heads/Dell 40DRLA's/1 1/2" header

and a German 009!! \:D/

Fri Jul 22, 2011 9:08 am

lostinbaja wrote: I have never needed to drill holes in the butterflys on any single Weber application I had anything to do with and I have setup many single IDF fueled engines.

then you have too much experience!!...help me with start my single idf 44 confuguration for my 2187cc with C25 and 1,25 rockers, 8,5 cr and non ported heads 40x35,5........my interest is solid low end and torque for only sand use (tank type engine).....

Fri Jul 22, 2011 9:08 am

DarthWeber wrote: 1776/W120 cam/40x35.5 P&P heads/Dell 40DRLA's/1 1/2" header

and a German 009!! \:D/

remember jets and vents used???

Fri Jul 22, 2011 9:15 am

34mm vents/150 mains/60 idles/180 a/c.
Engine is all mid to top end, not much below 3k but that's the way I wanted it when I built it way back when.

Mon Jul 25, 2011 5:07 pm

slalombuggy wrote: I've run 3 different singles, they all had holes in the butterflys.

brad
factory holes???...you remember size??

Mon Jul 25, 2011 5:34 pm

If you do decide to drill the Butter Flys, hint of advice and to Cover your Butt for down the road.

Just go ahead and buy another/extra set of Butter Flys, look into all the variations of were to drill, even Tom's Book for I have seen differences.

Drill small at first and test, you can always go bigger on the holes later.

And swap them out so you have an untouched set that fits the carb,meaing for down the road in your carb kit. Put the new ones in your carb, but test to see about there action.....

Just saying, carbs are delicate, they can make your engine purrrr, or make it go bang at the worst of times meaning just some loud ass noices...

So, who knows how your carb is going to end up, but testing is needed to find out..... Not all singles are drilled.... Sorry to sound sturn, but once you do it, better be prepaired for reprocussions...... Sorry my spelling sucks.......lol RB

Mon Jul 25, 2011 5:52 pm

2mm holes in the throttle plates are common and fine...if you really need them. That is the biggest you should end up with.....again, if you need it. Start with 1mm which is NOT half the size because the size has to do with flow area so 1mm is far smaller than 1/2 of 2mm. Having said that, most of the time you should not need them.

Remember that air flow thru the butterflies at idle has to do with matching the fuel flow at idle. Getting a picture here? If the idle jets are too large then you need more air so you don't have to open the butterflies as far. As you close the butterflies down the fuel flow thru the idles goes up. If the idle jets are really properly sized then you can close the throttle AND adjust for less flow thru the idle mixture screws. It is about having a proper balance of all the variables and few get it right because they are lazy and just resort to the drilled holes. The idle mixture adjustment gets hinky as you get close to being near the seats if the air/fuel setup are not correct at the idle jet and air bleed. This is what separates the tuners from the builders. A true engine guru has it all down.

The bypass screws are for the nth degree of tuning on any IR setup but especially on the single center mounts. You have 2 different length intake runners to deal with and possible throttle twist from one barrel to the other to deal with and the bypass screws are what you use to synch a center mount setup. Start with both closed and open the one with the lower air flow (or higher vacuum) when synching.

Center mounts are a pain but worth the effort when done right. Set the throttle opening and then the idle mixture and THEN synch them and repeat the process from the beginning. I would do this at least twice completely to get zeroed into the center settings for everything. This is all assuming the idle jets are correct from the word go. Airs and mains are a different area of tuning and don't worry about them until the carbs are set and synched at idle. Once the idle is set DO NOT EVER change it to fix another area of tuning in the RPM range......never. Fix the problem and not the symptom. It is also worth the effort to have vacuum ports put in the manifold halves as well and use 2 vacuum gauges to set the carb up rather than a synch tool. Verify the gauges are the same by switching side to side to see that they read the same as each other no matter what that reading may be. A u-tube manometer may also be used for synch by attaching each end to the ports and the side with higher vacuum will pull the water up that side of the tube. Adjust for a neutral reading or use 2 tubes and set the same. Lots of ways to skin this cat.

Center mount tuning is far more critical than a dual setup and the time to do it right is commensurate with the difficulty. If close is good enough for you on your car then it's good enough for me on your car and run right out and drill some holes.....but not on mine.

RC

Mon Jul 25, 2011 6:36 pm

RockCrusher wrote: 2mm holes in the throttle plates are common and fine...if you really need them. That is the biggest you should end up with.....again, if you need it. Start with 1mm which is NOT half the size because the size has to do with flow area so 1mm is far smaller than 1/2 of 2mm. Having said that, most of the time you should not need them.

Remember that air flow thru the butterflies at idle has to do with matching the fuel flow at idle. Getting a picture here? If the idle jets are too large then you need more air so you don't have to open the butterflies as far. As you close the butterflies down the fuel flow thru the idles goes up. If the idle jets are really properly sized then you can close the throttle AND adjust for less flow thru the idle mixture screws. It is about having a proper balance of all the variables and few get it right because they are lazy and just resort to the drilled holes. The idle mixture adjustment gets hinky as you get close to being near the seats if the air/fuel setup are not correct at the idle jet and air bleed. This is what separates the tuners from the builders. A true engine guru has it all down.

The bypass screws are for the nth degree of tuning on any IR setup but especially on the single center mounts. You have 2 different length intake runners to deal with and possible throttle twist from one barrel to the other to deal with and the bypass screws are what you use to synch a center mount setup. Start with both closed and open the one with the lower air flow (or higher vacuum) when synching.

Center mounts are a pain but worth the effort when done right. Set the throttle opening and then the idle mixture and THEN synch them and repeat the process from the beginning. I would do this at least twice completely to get zeroed into the center settings for everything. This is all assuming the idle jets are correct from the word go. Airs and mains are a different area of tuning and don't worry about them until the carbs are set and synched at idle. Once the idle is set DO NOT EVER change it to fix another area of tuning in the RPM range......never. Fix the problem and not the symptom. It is also worth the effort to have vacuum ports put in the manifold halves as well and use 2 vacuum gauges to set the carb up rather than a synch tool. Verify the gauges are the same by switching side to side to see that they read the same as each other no matter what that reading may be. A u-tube manometer may also be used for synch by attaching each end to the ports and the side with higher vacuum will pull the water up that side of the tube. Adjust for a neutral reading or use 2 tubes and set the same. Lots of ways to skin this cat.

Center mount tuning is far more critical than a dual setup and the time to do it right is commensurate with the difficulty. If close is good enough for you on your car then it's good enough for me on your car and run right out and drill some holes.....but not on mine.

RC

Thanks and considering all comments, i will probably follow his advice testing first without hole in butterflies ...... but two comments ..... First, remember that using a single center mount 44 idf and must be used by the largest idle over the large manifolds, then, probably air miss with the butterfly close .....
But I can not understand is that bring some single central idf 2mm hole factory made? or not?.....