.67 spraybar hole .

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Tom Foley

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Putting a boat together and going through engines and noticed a wide variation in spraybar hole sizes . . My Mac carbs have a much smaller hole than CMB and honestly I can't remember if I drilled the CMB or it came that way . Findings ? Thanks in advance for all replies .
 
Stick the carb on a flow meter without the needle, if it flows 2+ times more than what you run at I'd leave it.

Huge spray bars don't atomize our relatively thick fuel very well IMHO.  :unsure:
 
So I put the stock HR  cast carb  on the flowmeter with the hole size around .082"and the flowmeter wont even register it flows so much without the needle .  Any more thoughts on this subject . I looked back on some older OPS and Picco carbs and the holes were tiny yet these engines had no problem getting fuel . I get that the larger stinger reduces fuel pressure to the needle and that this could be the sole reason for a larger spraybar hole . Thoughts ??
 
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Tom

I run 9B carbs on the .67 but remembered I had a brand new CMB carb that came on my .67 and the spray bar measures .078 according to the pin guage.

Hope this helps

Bill Hoch
 
So I put the stock HR  cast carb  on the flowmeter with the hole size around .082"and the flowmeter wont even register it flows so much without the needle .  Any more thoughts on this subject . I looked back on some older OPS and Picco carbs and the holes were tiny yet these engines had no problem getting fuel . I get that the larger stinger reduces fuel pressure to the needle and that this could be the sole reason for a larger spraybar hole . Thoughts ??
I've always had good results going 1 or 2 sizes over stock with a wire gauge drill and sometimes more jet

with pipe pressure. Seems the OEM's don't consider we use ~60% nitro here.

My NR46 runs a lot better with stock bore carb, stinger drilled to .413" ID and one wire gauge size larger

jet...might even go up another one...we'll see.
 
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Hell running .100 in a .45 so you take it or leave it at that.

Problem is the aluminum stock one will brake if drilled that thin.

Need to put a K&S  brass tube in it.  Have it protrude about .120 into the boar.

Should be a .470 carb?
 
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Hell running .100 in a .45 so you take it or leave it at that.

Problem is the aluminum stock one will brake if drilled that thin.

Need to put a K&S  brass tube in it.  Have it protrude about .120 into the boar.

Should be a .470 carb?
Well I have had a lot of fast boats in the past and none of them have ever had a spraybar that large . I'm not saying it doesn't work for you but I've never had a situation that needed that big an orifice  If you can make it blubbering rich with the needle it would seem the orifices are large enough . the new CMBs have large holes in the spraybar from the get go . I did not take the barrel out to measure the bore of the barrel .
 
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Well I have had a lot of fast boats in the past and none of them have ever had a spraybar that large . I'm not saying it doesn't work for you but I've never had a situation that needed that big an orifice  If you can make it blubbering rich with the needle it would seem the orifices are large enough . the new CMBs have large holes in the spraybar from the get go . I did not take the barrel out to measure the bore of the barrel .
It is the size of the carb and % of nitro used that determines the spray bar size. 

It is the surface area of the spray bar hole size and amount of air flow across it that produces the vacuum. this produces a pressure drop at the needle. 

It is not the point of being able to make it bubbling rich. it is the point of keeping a good needle at ALL RPM ranges with High nitro.

.100 is a good size for a .470 carb on 60%.
 
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It is the size of the carb and % of nitro used that determines the spray bar size. 

It is the surface area of the spray bar hole size and amount of air flow across it that produces the vacuum. this produces a pressure drop at the needle. 

It is not the point of being able to make it bubbling rich. it is the point of keeping a good needle at ALL RPM ranges with High nitro.

.100 is a good size for a .470 carb on 60%.
I've run this engine before with the AB pipe and .470 stinger ,.083 spraybar , always 60 % and it will idle down and roll right back up just fine . I guess my question really is how did the small spraybars that were around work well enough in the past for many boaters to run so fast in the past ? Smaller carbs were the norm .
 
Just a little antidote.

I am seating up a set of  RS.45 EVO's right now with a VAC .45 carb. It is the same as a .67 carb in barrel size and the body is bored to .470 but the barrel is only .430.

SO stick a .67 barrel that is .470 in it and add a .100 spray bar and off to the races you go......LOL

Just a little tid bit for you all...............................I don't like not sharing just make you feel to good all over when you do ..................

IT IS JUST A TOY BOAT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 
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At this point I'm not really looking to put a bigger carb on it . I want it to be heat race reliable and go four rounds and win the event as well as being reasonably fast .
 
What size cab you got on it?

You have to get this big cab is bad thing out of your mind. If it is set up right with the proper size spray bar it will be good to go.

Carb size has nothing to do with reliability or race ability unless it is not set up right.

Live a little Tom blow a few engs up its good for the soul knowing you went to far some times............LOL

O ****.jpg
 
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At this point I'm not really looking to put a bigger carb on it . I want it to be heat race reliable and go four rounds and win the event as well as being reasonably fast .
Tom Foley. I have a MAC 67 Carb  that I can sell you. The motor is junk and I think the only part worth money is the carb. 
 
What size cab you got on it?

You have to get this big cab is bad thing out of your mind. If it is set up right with the proper size spray bar it will be good to go.

Carb size has nothing to do with reliability or race ability unless it is not set up right.

Live a little Tom blow a few engs up its good for the soul knowing you went to far some times............LOL

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I think you where trying to quote me butt I'm not sure at all. It's what came with it at the time. Nothing has been done to the carb. I'll get you photo and try to get you some measurements
 
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