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Discussion Starter #1
I know this is a dumb question, but I have to ask it. Why is the jets and squirters different sizes from the primary to the secondary. The reason I ask this is because I've seen some carbs have the same sizes for the squirters and jets. Why can't you just have the same sizes for both, is there a right and wrong.
Thanks in advance
 

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I know this is a dumb question, but I have to ask it. Why is the jets and squirters different sizes from the primary to the secondary. The reason I ask this is because I've seen some carbs have the same sizes for the squirters and jets. Why can't you just have the same sizes for both, is there a right and wrong.
Thanks in advance
No such thing as a dumb question----just dumb answers and you came to the right place for that! Primary and secondary differ due to engine requirements thru the rpm range. There are exceptions to the rule. Side slung, butterflies open at same time for drag apps, worked carbs that are built for idle to W.O.T. in a heart-beat. But to generalize the question, if you are cruising along at 2800 rpm do want the same amount of air/feul as if you nailed it for a race. M
 

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Just to add to what Mark posted...

You will also notice that most carbs also run power valves in the front. That is another reason your seeing the 8-10 jet size differences.
Another is air bleed sizes are also usually different from front to rear which gets back to what Mark was saying in his post.

Most "race" carbs are pretty square but the "street/strip" stuff is built this way for fuel/cruise purposes.
 

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"No such thing as a dumb question----just dumb answers and you came to the right place for that! "

LOL,
Another couple semidumb questions about carbs from the noobie gallery.

What is the reasoning behind spread bore carbs?

In a well engineered carb at least with vacuum secondaries doesn't it all sort of equal out anyway?
 

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For a dedicated drag motor, I prefer to plug the power valves, and run the jets and squirters square (all the same).
 

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steelcomp was here
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"No such thing as a dumb question----just dumb answers and you came to the right place for that! "

LOL,
Another couple semidumb questions about carbs from the noobie gallery.

What is the reasoning behind spread bore carbs?

In a well engineered carb at least with vacuum secondaries doesn't it all sort of equal out anyway?
Small primaries provided good throttle response and good economy for around town driving and highway cruise. They also sounded cool when you mashed the gas...buuhhwaaaaaahhhhhhh:D
 

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They do sound cool, I love the sound of a motor sucking through a carb better than the throaty rumble of the exhaust.

So the reason for the question. I'm swapping out my old troublesome 650 holley 4011 spreadbore on my bonestock 8:1 454. Pretty tame motor for this place, but it's in a cabin cruiser and that's the way I roll, LOL

I'm torn between the 650 4175 spreadbore or the more conventional 4160 in either a 600 or 750. I don't run this motor much past 3200 or so. The 4011 is a bit of a bastard child of the holley family and I would like as conventional and easy to tune and fiddle with replacement as I can get instead an oddball.

I'll need an adapter of some sort to fit a square bore. I'm interested in economy more than performance but it is my impression, since I run that boat at a steady state, that tuned correctly it may not make much difference. Interested in the opinions of my betters.
 

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Small primaries provided good throttle response and good economy for around town driving and highway cruise. They also sounded cool when you mashed the gas...buuhhwaaaaaahhhhhhh:D
When I first started driving, my Mom drove a 455 GS Buick. I use to take the air cleaner cover and flip it over for a little Sat. Nite cruizing. I forgot to flip it back one nite. She gets in it to go to church the next morning with a some of her women friends. She punches it getting on the freeway, and she tells me they all about had heart attackes.:mad: Couldn't drive that thing again for about 3 months.



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Discussion Starter #9
Just to add to what Mark posted...

You will also notice that most carbs also run power valves in the front. That is another reason your seeing the 8-10 jet size differences.
Another is air bleed sizes are also usually different from front to rear which gets back to what Mark was saying in his post.

Most "race" carbs are pretty square but the "street/strip" stuff is built this way for fuel/cruise purposes.
Is that the same reason why the squirters are different sizes too because of the power valve is in the front.

Here is my last question, sorry for asking so many. I recently got a blown motor, I bought a pair of AED 750 blower carbs, when we first started it they backfired, so the carb guy I went through upped the jets to around 10 sizes and the sqiurters 2 or 3 sizes, but on the sqiurters he squared them up. What is the advantage of doing this.
Thanks again
 

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Is that the same reason why the squirters are different sizes too because of the power valve is in the front.

Here is my last question, sorry for asking so many. I recently got a blown motor, I bought a pair of AED 750 blower carbs, when we first started it they backfired, so the carb guy I went through upped the jets to around 10 sizes and the sqiurters 2 or 3 sizes, but on the sqiurters he squared them up. What is the advantage of doing this.
Thanks again
Although a lean condition will cause it to backfire (thru the carb), AED's are usually pretty close out of the box. Because you have "blower carbs" they are manifold referenced. Don't know your current jet size or power valve restrictor size, but it sounds as though he just fixed it by dumping fuel. Were these carbs new and un-molested or did you by them from someone who told you they are "blower carbs"



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Is that the same reason why the squirters are different sizes too because of the power valve is in the front.

Here is my last question, sorry for asking so many. I recently got a blown motor, I bought a pair of AED 750 blower carbs, when we first started it they backfired, so the carb guy I went through upped the jets to around 10 sizes and the sqiurters 2 or 3 sizes, but on the sqiurters he squared them up. What is the advantage of doing this.
Thanks again
The more responses the more questions you will have and that is not a problem here. Its winter and alot of good (some bad) guys willing to lend a hand. My question would be, did it pop thru the carbs or thru the exhaust? Motors back fire for alot of reasons and intake and exhaust pops or flames narrow it down alot.
 

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Discussion Starter #12
Although a lean condition will cause it to backfire (thru the carb), AED's are usually pretty close out of the box. Because you have "blower carbs" they are manifold referenced. Don't know your current jet size or power valve restrictor size, but it sounds as though he just fixed it by dumping fuel. Were these carbs new and un-molested or did you by them from someone who told you they are "blower carbs"
Brand new carbs
 

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Discussion Starter #13
The more responses the more questions you will have and that is not a problem here. Its winter and alot of good (some bad) guys willing to lend a hand. My question would be, did it pop thru the carbs or thru the exhaust? Motors back fire for alot of reasons and intake and exhaust pops or flames narrow it down alot.
It popped through the carbs.
 

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Is that the same reason why the squirters are different sizes too because of the power valve is in the front.

Here is my last question, sorry for asking so many. I recently got a blown motor, I bought a pair of AED 750 blower carbs, when we first started it they backfired, so the carb guy I went through upped the jets to around 10 sizes and the sqiurters 2 or 3 sizes, but on the sqiurters he squared them up. What is the advantage of doing this.
Thanks again
10 sizes on the jet? That's a bad move. You need to call AED and find out what they say. Their carbs are usually right on.
If you first started it and they backfired, did you let it warm up to running temp adn try it? Most carbs, if they;re tuned right, will be a little lean when the engine is cold. Blower engines make this a little worse with the blower in the way of that shot of fuel. Once things warm up, they should be OK.
10 jet sizes puts those carbs way out of calibration.
 

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Discussion Starter #16
10 sizes on the jet? That's a bad move. You need to call AED and find out what they say. Their carbs are usually right on.
If you first started it and they backfired, did you let it warm up to running temp adn try it? Most carbs, if they;re tuned right, will be a little lean when the engine is cold. Blower engines make this a little worse with the blower in the way of that shot of fuel. Once things warm up, they should be OK.
10 jet sizes puts those carbs way out of calibration.

I don't know the exact number of jets off the top of my head but it was around 10 sizes up. And we let the motor warm up around 20 minutes. We really went aggressive on the these carbs because this is a pump gas motor, so we wanted to be on the safe side and go fatter. The jets seem to be a little fat because the spark plugs are really black, we're going to back the sizes down a few when we run the boat next time. We also changed the 30 cc accelerator pump to a 50cc. The squirters seem to be right because it doesn't back fire anymore and doesn't hesitate. When I ran it, it ran really good and I was happy with its performance.
 

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Discussion Starter #17
Then more than likely you had a lean condition and sounds like you are on the right track with going fatter. That is of course if the timing is right. Also the tune is correct.
The timing is 30 degrees advance, it's locked out.
 

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I don't know the exact number of jets off the top of my head but it was around 10 sizes up. And we let the motor warm up around 20 minutes. We really went aggressive on the these carbs because this is a pump gas motor, so we wanted to be on the safe side and go fatter. The jets seem to be a little fat because the spark plugs are really black, we're going to back the sizes down a few when we run the boat next time. We also changed the 30 cc accelerator pump to a 50cc. The squirters seem to be right because it doesn't back fire anymore and doesn't hesitate. When I ran it, it ran really good and I was happy with its performance.
Everything they do to these carbs at AED is intentional, and I wouldn't stray too far from their original configuration without checking with them. It's an easy phone call and John is as nice a guy as you'll find. You could be bandaiding another problem.
JMO
 
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