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Need orifice size of main jet for 5hp pulsa-jet carb

#1

T

Telesis

Engine is a 5HP Briggs horizontal shaft I/C engine. 132212-0362-01 Carb part number: 492611
It utilizes a fixed jet in the pickup and mine is plugged. The engineer in me would like to know what the actual jet size is and then I can run a micro-drill in to clean it out. Based on my experience, I'm guessing I could use a .020 to start and the engine would likely be OK but that's a guess. I'm thinking it's bigger than that.

I've looked all over the net but can't find that piece of data. Maybe one of you know or have this common carb or equivalent on the shelf and could give me an idea how big it is.

Thanks in advance for your consideration. Any help appreciated. Thanks!


#2

R

Rivets

I’ve been doing this for over 50 years and this would be the first time I’ve heard that the pickup oriface being plugged. Never seen spec on this. Are you sure that is the problem? Most common problem with those carbs is that the pump diaphragm is old and not pumping properly to draw fuel from the tank to the auxiliary tank. Have you checked that the auxiliary tank is full of fuel? Have you replaced the diaphragm? I would start here before drilling.


#3

StarTech

StarTech

First it appears someone has changed the carb as the IPLs has it using a regular adjustment needle but that was the original carb too. But those fix idle mixture jets are somewhere between a #80 and a #75 drill bit; closer to the #75. Possible #76 but I don't have that one here yet.

1720117483279.png


#4

T

Telesis

Thanks guys. Yes Rivets I'm positive it's plugged. I have it in my hand and it's real easy to blow on the pickup and no joy. (I agree 90% of the time it's a bad diaphragm and/or a dirty/plugged tank pickup screen. Otherwise they are pretty bulletproof. The diaphragm in this carb was toast and clearly it's been sitting a long time)

Based on your data StarTech, I think I'll use an .020 and give it a whirl.

Thanks again for your prompt responses. Happy 4th!


#5

T

Telesis

I thought I'd make one more observation since Star mentioned this may not be the original carb. When I look at a Briggs 498298 carb, it does indicate for example, that it is a sub for the part (492611) that is listed in each of two IPL's (new from current B&S site and original/old) I have for this engine. When I look at all the photos of the 498298, it is exactly the same as what I have including the fixed main jet.

So I'm guessing I misunderstood what you were trying to tell me. If you don't mind Star, can you clarify what you meant please?

Again, thanks!


#6

R

Rivets

Now I’m confused. There is a main pickup tube (long one) through which the pump draws fuel from the main tank to fill the auxiliary tank. Then there is the nozzle through which the fuel is draw from the auxiliary tank into the carb body. Neither one of these has a jet. Where is the jet you are talking about located. Second, if you plan on drilling out a clogged jet I recommend you start with a number 78 drill, (.016”) first. If it doesn’t do the job for you, you can always go larger. Finally, do you have the original carb 492611 with an adjustable idle screw or superseded carb 498298 with fixed idle jet?


#7

T

Telesis

I thought I'd make one more observation since Star mentioned this may not be the original carb. When I look at a Briggs 498298 carb, it does indicate for example, that it is a sub for the part (492611) that is listed in each of two IPL's (new from current B&S site and original/old) I have for this engine. When I look at all the photos of the 498298, it is exactly the same as what I have including the fixed main jet.

So I'm guessing I misunderstood what you were trying to tell me. If you don't mind Star, can you clarify what you meant please?

Again, thanks!


#8

T

Telesis

Sorry for the confusion Rivets. I'm referring to the nozzle that is drawing fuel from the aux tank into the carb body. That has a brass insert with a small orifice which I assumed, perhaps wrongly, was the "fixed main jet". If you look up a Briggs 49828 on their store and look at the bottom view of the carb, you can see what I'm referring to. If that is not the fixed main jet, I apologize for the wrong terminology. In any event, that is what is plugged on mine, and that is what I was originally trying to find the size of.

I hope this demystifies it a bit.


#9

T

Telesis

Telesis said:
Sorry for the confusion Rivets. I'm referring to the nozzle that is drawing fuel from the aux tank into the carb body. That has a brass insert with a small orifice which I assumed, perhaps wrongly, was the "fixed main jet". If you look up a Briggs 49828 on their store and look at the bottom view of the carb, you can see what I'm referring to. If that is not the fixed main jet, I apologize for the wrong terminology. In any event, that is what is plugged on mine, and that is what I was originally trying to find the size of.

I hope this demystifies it a bit.
Click to expand...
498298 (missed a digit)


#10

T

Telesis

I have the adjustable idle screw.


#11

T

Telesis

Telesis said:
I have the adjustable idle screw.
Click to expand...

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#12

StarTech

StarTech

Okay I see with clarification that you are referring the main nozzle jet. That one I don't know the size. Never had to check it. Now on extremely dirty carbs I have had to drill the steel next to it in the tower to clean out that area. When dealing with rusty tanks anything is possible.

In this case I would start with the smallest bit to clean out and work up to one that don't fit. Just these small bits are rather short so you might to follow up with some fine wire that fit thru the hole. BTW ultrasonics does fairly good of cleaning these areas but not a cure all.
1720127174465.png
ANd don't to install the filter screen on that tower. It will catch a lot of the large bits.

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#13

T

Telesis

StarTech said:
Okay I see with clarification that you are referring the main nozzle jet. That one I don't know the size. Never had to check it. Now on extremely dirty carbs I have had to drill the steel next to it in the tower to clean out that area. When dealing with rusty tanks anything is possible.

In this case I would start with the smallest bit to clean out and work up to one that don't fit. Just these small bits are rather short so you might to follow up with some fine wire that fit thru the hole. BTW ultrasonics does fairly good of cleaning these areas but not a cure all.
View attachment 69120
ANd don't to install the filter screen on that tower. It will catch a lot of the large bits.
Click to expand...
Thanks for the reply. I have a couple sets of micro-drills and I use a hand-held pin vise with them. As you indicated, I too have had kinda 50/50 luck with ultrasonics.

One last question. I've taken a closer look at the pics of the 498298 replacement carb and, like your pic above, I see the needle screw on the side but no spring. Is this a non-adjustable idle screw that is intended to be left fully seated? (I believe Rivets may have alluded to that as well) If so, it's the first time I've seen that. I guess you can teach a really old retired dog new tricks!

I appreciate your guy's input!


#14

R

Rivets

Things are getting clearer. I agree with Star, if you are going to try drilling it open start small and work your way up. I’ve been punching jets for many years, started with Zenith and Rochester carb, and can tell you there is no going back I you go to big. A trick I’ve learned, never try to hold jet in one hand and your pin vice in the other. Because of the drill size they break easily. I broke many before learning to clamp the jet in a hand vice and that vice in a bench vice. That way I have more control and can always drill down. Second, there should be a spring on the doe mixture screw. The purpose of the spring is to put tension on the screw to keep it from moving.


#15

StarTech

StarTech

But if it is fixed version then it is just fully seated. They have a tiny hole in them with a cross drilled hole.


#16

T

Telesis

Thanks guys. First, the idle screw on mine is definitely adjustable as you can see in the pic. I think the new Briggs replacement is not adjustable (as well as the cheap Chinese knockoffs that cross to this). I think they are as Star describes.

Second, I don't know how the main jet we've been discussing is installed in the first place(or removed for that matter). There is no slot in it. Perhaps it's pressed in. No matter, as I'll drill/clean it in place by hand. The carb lays flat on a table so it's a pretty easy task. (I've broken a couple micro drills on other jobs as you describe Rivets so I can relate!)

Thanks again for all your insight!


#17

C

ChuckT

Telesis said:
Engine is a 5HP Briggs horizontal shaft I/C engine. 132212-0362-01 Carb part number: 492611
It utilizes a fixed jet in the pickup and mine is plugged. The engineer in me would like to know what the actual jet size is and then I can run a micro-drill in to clean it out. Based on my experience, I'm guessing I could use a .020 to start and the engine would likely be OK but that's a guess. I'm thinking it's bigger than that.

I've looked all over the net but can't find that piece of data. Maybe one of you know or have this common carb or equivalent on the shelf and could give me an idea how big it is.

Thanks in advance for your consideration. Any help appreciated. Thanks!
Click to expand...
I recall a discussion (in the '70s?) to the effect that a carb orifice needs to be reamed not drilled. Drilling supposedly leaves a pattern behind.


#18

J

Johner

Use the old jet if it comes out into the new carb. If a new carb sometimes the main jet needs drilling. I'll bet if you really clean the old carb it will work fine. Find the size of the old jet by inserting micro drills until you find a "go, no go". size.


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