Blower surge, can it be eliminated?

[jimsplace]

Why do blower motors with carburetors on gas surge when idling. Are there things that can be done to reduce or eliminate this.
Yes, this is my first blower and I am learning. 2x dominators - 14-71 - 540 bbc.

[sanger rat]

Turn in your idle mixture screws.

[atxwrangler]

Why Would You Want To?:d I'm Trying To Get Mine To Do That!:d

[sanger rat]

Because it's nice to idle right onto the trailer at 1100rpm's.:)

[DMOORE]

Because it's nice to idle right onto the trailer at 1100rpm's.:)
Not if ya have an outdrive.
Darrell.

[Heatseeker]

I tamed my idle with advice from Timinator here on the board. He wrote an article for the mag on this very subject.
You'll need to remove and take apart your carbs to drill some small holes(I can't remember the diameter) in the butterfly plates. You could contact Timinator for the particulars. He was very helpful when I did it.
I got my idle down to 900-1000 rpms with very little noticable surge.

[IMPATIENT 1]

Why Would You Want To?:d I'm Trying To Get Mine To Do That!:d
turn out your mixture screws:D

[Slacker]

You'll need to remove and take apart your carbs to drill some small holes(I can't remember the diameter) in the butterfly plates.
I got my idle down to 900-1000 rpms with very little noticable surge.[/QUOTE]
Same here

[TIMINATOR]

Usually start with .092(3/32) in the PRIMARY throttle plates, one in each plate next to the shaft on the idle hole side, centered side to side. You may need to go to .110, but come up to that size in steps, try it in the water loaded first before going bigger. You WILL have to reset the idle speed and mixture after doing this mod. I do it on the trailer, backed into the water, warm the motor thoroughly first, and get it close, then you can touch it up later. We also typically boost reference the power valves too, but that is more for motor(bearing) longetivity. I prefer to not have the surge because it wastes fuel, and is harder on the drive when idling through the channel. The rpm flucuation is directly sent to the drive, whether in gear or not the U-joints and input shaft bearings are turning, as are the coupler splines. I would rather have my boat sound wussie than replace parts and buy more fuel. I don't think my motor sounds very radical for what it is, thats the way I like it. I can idle in the backwaters for an hour and never have it die or foul a plug. Thats my preference, yours may vary. TIMINATOR

[Jerrys59]

Because it's nice to idle right onto the trailer at 1100rpm's.:)
Not real nice shifting in and out of gear at 1100 rpm. not a good thing!

[Schiada76]

Switch to a v-drive, 800 to 2000 rpm surge is noooo problem.:D

[TIMINATOR]

Mine idles in gear at 750/800 rpm, so no drive/shift issues. TIMINATOR

[flattie]

The only way I can get mine to surge is put a enderle hat on it. Or start it up when its cool outside it will surge a little until it warms up

[sanger rat]

Not real nice shifting in and out of gear at 1100 rpm. not a good thing!
I'm running a Jet. Carbs and cam design were done by Timinator.

[TIMINATOR]

Sanger, ya get everything adjusted ok? Hows it all working? Havent heard from ya. Ya gonna come to the cookout in September? The drive won't be toooooo bad! LOL Timinator

[sanger rat]

Everything is good so far. Just a tad rich but I'll leave it that way with the cooler weather that's starting to show up.

[TIMINATOR]

Cool, keep in touch. TIMINATOR

[jimsplace]

OK - I don't like the idea of drilling holes in the butterfly, but i am running out of other options.
After the holes are drilled, does that require different main jets, and does it usually require backing out the idle mixture screw initially to get it started and adjust from there?

[Havasu Hangin']

Holes on the butterflies do not always work. In fact, mine actually surges less now that I put butterflies back in with no holes.

[Blown 472]

OK - I don't like the idea of drilling holes in the butterfly, but i am running out of other options.
After the holes are drilled, does that require different main jets, and does it usually require backing out the idle mixture screw initially to get it started and adjust from there?
What holes in the butterflys do is give the engine more air when it is at curb idle, if you are having to crank the screw for the throttle in more to get it to idle you get into the transition slots and they will start pulling fuel, the holes allow you to close the throttle angle and still get enough air in to let it idle. Main jet has nothing to do with the idle, and once you are into the main circut those holes are not doing a damn thing.
Keep in mind too, that the "idle mixture" screws do control the mixture, they control the amount of premixed air fuel that gets discharged below the throttle blades. What controls the mixture is the air bleed and the orifice in the metering block.

[jimsplace]

I can get it to idle with smaller air bleeds and backing the idle mixture screws out about 2 1/4 turns. The motor then wants to run rich (black smoke). It does not seem to have a happy medium, it either wants to surge (rump-rump 1000 to 1600 rpm) or it can idle at 900 with black smoke.
The carbs. do not have power valves and do not have provisions for them.

[@theRVR]

I can get it to idle with smaller air bleeds and backing the idle mixture screws out about 2 1/4 turns. The motor then wants to run rich (black smoke). It does not seem to have a happy medium, it either wants to surge (rump-rump 1000 to 1600 rpm) or it can idle at 900 with black smoke.
The carbs. do not have power valves and do not have provisions for them.
I have been reading your post, and what basically happening is by drilling a hole in the butterflies (the side of the hole needs to be by the edge of the butterfly .100" away, but the hole location on the butterfly needs to be next to the idle mixture opening on the side of the chokes) by doing this you move the air signal from the side where it doesn’t mix with the fuel to where it can mix better with the fuel. Bottom line, there is only one way to make a carb work and that’s a good air signal. This works for all carb application not just blown motors. Now for the surge, it’s from having the mixture to rich, if that’s what you like, then let it surge…. But another bottom line, there’s only one way to make horse power and that’s to burn the fuel. You want a BIGGER bomb, you need more dynamite.

[ghittner]

"There’s only one way to make horse power and that’s to burn the fuel. You want a BIGGER bomb, you need more dynamite.
I'm gonna use the he** out of that quote........ LOL!:D

[@theRVR]

"There’s only one way to make horse power and that’s to burn the fuel. You want a BIGGER bomb, you need more dynamite.
I'm gonna use the he** out of that quote........ LOL!:D
there's royalties…… :D

[Placecraft Dragstar]

Because it's nice to idle right onto the trailer at 1100rpm's.:)
That is where it will be is on the trailer:D

[jimsplace]

I thought the idle surge was from the motor going into a lean condition. Basically, it pulls fuel and air, fires and because it is now starting to go lean, the motor speeds up, draws more air and fuel, fires the mixture and goes lean again. It then just repeats this process.
Is this not correct?
The motor will idle smoothly when it is rich and producing black smoke. The excess richness gives me the idle I want, but that is covering up what I am looking for, which is a smooth idle that burns cleanly.

[@theRVR]

I thought the idle surge was from the motor going into a lean condition. Basically, it pulls fuel and air, fires and because it is now starting to go lean, the motor speeds up, draws more air and fuel, fires the mixture and goes lean again. It then just repeats this process.
Is this not correct?
The motor will idle smoothly when it is rich and producing black smoke. The excess richness gives me the idle I want, but that is covering up what I am looking for, which is a smooth idle that burns cleanly.
No that's pretty much a blower motor’s caricature when it’s too rich, be it gas, alcohol, nitro, carbureted, or injected. You must have it really rich that’s bringing the idle back smooth but black smoke like you said.
Try adjusting the idle mixture jet with the butterflies, you need to have a little opening with all the butterfly that has an idle screw associated with them so there is a vacuum signal to the idle passages. A blower is always trying to get in more air that what the carburetor will give it at an idle so it acts like a choke is on, and if there is 2 carburetors it’s important that the linkage is adjusted right so that both carbs open exactly at the same time test this with your foot on the throttle so you use the linkage in a real world.

[jimsplace]

I think you are accurate in your explanation.
I went back and adjusted the idle screw along with the idle mixture screw. Guess what - it idles very evenly at about 1200 rpm on trailer and about 1000 in gear. (V-Drive) I am very pleased with it.
My next question concerns idle mixture screw location. They are only out about 1/4 turn or slightly less. I would prefer to have them out a little more, maybe 1 - 1 1/2 turns. If I enlarge the idle air bleed, I think that could be accomplished, but does it hurt anything, increasing the air bleed just to get the idle screw where I some wiggle room. It is very sensitive to adjusting the idle mixture screw when they are in that far.
It is running really good right now. There is no hesitation anyplace and it pulls really strong.

[@theRVR]

You are correct, if you open up the air bleeds you will have to open up the mixture screws accordingly. NO it will not change anything at cruse or wide open, you will end up with the same air / fuel mixture as you have now, it’s just that your mixture screws will be in a different position.
I know what you’re talking about, I have mine at about ½ turn open and they are more sensitive that way.

[@theRVR]

I think you are accurate in your explanation.
I went back and adjusted the idle screw along with the idle mixture screw. Guess what - it idles very evenly at about 1200 rpm on trailer and about 1000 in gear. (V-Drive) I am very pleased with it.
My next question concerns idle mixture screw location. They are only out about 1/4 turn or slightly less. I would prefer to have them out a little more, maybe 1 - 1 1/2 turns. If I enlarge the idle air bleed, I think that could be accomplished, but does it hurt anything, increasing the air bleed just to get the idle screw where I some wiggle room. It is very sensitive to adjusting the idle mixture screw when they are in that far.
It is running really good right now. There is no hesitation anyplace and it pulls really strong.
where do you play with your boat? I'm 20 mile north of blythe, ca. on the colorado

[jimsplace]

I am in Texas. The Brazos river is where we play. This summer has been mostly lost due to rains in the late spring and early summer. Just got the boat out for the first time with the blower about two weeks ago.
I had been told I would like the blower once it was on. There was a time I was really starting to question if that was true. A motor that is not running like you want can be frustrating.
I had been told my carburetors would not work on a blower, or using a 14-71 with a .740 lift cam, it is going to surge and you can't get away from it (my friends at Holley), drill the idle feed, again Holley (they did not know where the idle feed is located on three circuit carburetors).
I have not tuned the boat yet, and the only thing done to the carburetors has been to increase the main jets 4 sizes to 90's. I probably will end up taking them back down some, but that remains to be seen.
I almost afraid to change the air bleed because it runs so good. At least it seems like it to me. I know it is faster than the tunnel ram that was on it. The boat took a good set and I ran it maybe 800-900 feet and still pulling very solidly. The gps was 113.
Thank you for the direction. I know every motor is different, but on this one you got it right. Thanks

[@theRVR]

I'm glad to hear that it worked out, yes there all different just like women but if you want to be happy they must be happy. I thought about opening up my air bleeds but if I need to fine tune it because of hot weather or something I'll just turn one idle screw to find that happy idle. In my case I’m running a blower with a pie shaped opening on the bottom, so all the air/fuel mixture going through the blower it get’s remix so to speak. I’m not wanting to work on my stuff as much as I use to, I was always busy running fuel funny cars around the country,(NHRA) but now that that’s over (for now) I’m thinking of freshen up the boat and motor, but it just runs and runs for now and I’m not sure I want to mess with a good thing.

[Gearhead]

Jim,
Just measure the size of the idle air bleeds before you drill them if they are pressed in bleeds or if they are screw in bleeds just change the size and retain the original. This way if you don't like the change... you can go back to where you started from. I think you will like the change getting the scres in a more tuneable relationship.
Gear

[jimsplace]

Gearhead
Thanks - I do have removable airbleeds. Changing them is not a big deal other than figuring out what size to go to. I am sort of cheap and prefer not to buy any more airbleed than I have too. A set or two of "spares" is OK, but showing off how many extra airbleeds I have is not my thing - if you know what I mean.

[1968Droptop]

Jim Guthrie Racing set up my carbs. I had a similar question about the air bleed jets. He told me to find out what I had and go up 10% larger. There is numbers on each one like a fuel jet. You should be able to go online and detiremine the size with that number. What ever it is now, go 10% larger. A 1/4 turn is definetely on the tight side, but I hear you on the it's running perfect right now thought. In the long run your probably better off with larger air bleeds for more precise adjustablity. Bonus that you too have the screw in units. Drilling out pressed in ones can get scary....only get one shot to get 'em right.

[jimsplace]

I appreciate the suggestion on the 10%. That sounds reasonable. The ones in now are 53's. Some where around here, I have some 63's and when I find them, I will put them in and use some .018 wire that I have, and stick them in the air bleed, for a trial size. The area of each wire inserted is subtracted from the 63's diameter.
I have found everything else but my missing 63's, they must be here someplace.
If they don't show up soon the, 10% sounds like a good start and will give me more wiggle room. If that isn't where I need to be, it will give me a good idea how much that helps and go from there.
Thanks