Jump to content

Unofficial Home of Old Simplicity & Allis-Chalmers Garden Tractors

superbman101

Carburetor internal Polishing / custom carb build

Recommended Posts

superbman101

I've been told way back when I first started rebuilding these old Briggs engines that cleaning and polishing the inside of the carb body can help it run smoother. I usually just clean the inside up with some carb cleaner and 400 grit sandpaper where it has some build up.On the last 2 engines that I have redone I’ve taken the polishing to the next level to see how it runs. I wet sanded the internal walls with 600 then 1500 grit and paint thinner. It’s got that smooth chrome look now. It sure seams to Start up a lot easier and ramp up quicker when you step on the throttle :pHas anyone else done this to their engine? All you pullers out there do you have a custom carb build you’d like to share? I’ve considered making a custom carb for my pulling tractor. (Remove the choke flap that slows down the air, fill in the holes where that rod runs through, and polish the inside to glass) Maybe make a custom filter? Any Ideas out there?

Polished Carb1.jpg

Polished Carb2.jpg

57e0576e86778_PolishedCarb1.jpg.6633efbc56968df0e75128c8aa3287a6.jpg

57e0576e98de3_PolishedCarb2.jpg.d81c64ef6a4ba59d4e39c0435a50beaa.jpg

Share this post


Link to post
Share on other sites
Talntedmrgreen

Nope...mine run good and start easy enough, with that crusty, 45 year old carb-patina. I'm a minimalizt when it comes to maintanance. What aint broke don't get fixed around here.

I got to hand it to ya for goin the extra mile though! dOd

Share this post


Link to post
Share on other sites
superbman101

Thanks Josh! The 16hp I bought off you is the one I'm planning on building into a pulling engine :D I figured on this 12hp carb in the picture I already had the thing apart because the needles and gasket were junk :P I agree my Big Ten is the best starting I own so far and I didn't polish it. I have on the 1991 16hp and its a beast. Once I get this 12hp back together I'll upload a video of it starting and ramping up to WOT :P

quote:Originally posted by Talntedmrgreen

Nope...mine run good and start easy enough, with that crusty, 45 year old carb-patina. I'm a minimalizt when it comes to maintanance. What aint broke don't get fixed around here.I got to hand it to ya for goin the extra mile though! dOd


id="quote">
id="quote">

Share this post


Link to post
Share on other sites
rokon2813

I would think if you're going for performance, it would be more important to polish from the bowl in, to get the fuel to the cylinder faster, then from the cylinder out, to get rid of burnt gasses easier.

JMO

I'm guessing thats why you can get a kohler to perform better, a short straight intake, rather than the long 90 degree of a briggs.

It's probably been done before, but what about retro fitting a kohler carb to a briggs ???:o:O

Share this post


Link to post
Share on other sites
superbman101

I've always questioned trying a Kohler carb on a Briggs but that would be sinful :P

People I pull with have drilled their needles out for more fuel too... frankly if you want more fuel just turn the main-jet valve lol ;) that's what it's there for

Polishing the intake tube some people say it messes with the "atomization" (mixing or fuel and air) to allow for an even burn. Any thoughts?

Share this post


Link to post
Share on other sites
Kent

Are you going to port and polish the intake to match the carb body, and then the intake to the head, also. Any little ridge at those junction points, even if it is the gasket sticking slightly inside the opening, can really disrupt air flow...

Wonder what the velocity of the air/fuel mix is as it enters the head when running full throttle? CFM?

Share this post


Link to post
Share on other sites
timflury

I have ported and polished the intake on my 2110. I ground enough material away to match the shape of the gasket both on the intake, and on the block.

Without a dyno, I notice no difference in horsepower.

I wonder if drilling out the outlets on the emulsion tube a little would increase horsepower?

Share this post


Link to post
Share on other sites
HubbardRA

The one thing that I would do to the carb that is pictured is to grind off that sharp edge between the downward bore and the horizontal bore of the carb. Air does not like to flow around corners, especially with sharp edges. The larger the radius on a corner, the smoother the flow, and the more flow.

When Dan was talking about the intake manifold, that is important also. Smooth flow, port matching, etc. all help the flow. Between the carb and valves, you do not want the surface to be mirror smooth. I have seen people go back and glass bead the surface on an intake after porting and polishing to give it a rougher finish. If the surface of the manifold is polished, then droplets of fuel will form on the surface. This messes with the mixture since the mixture leans out while the droplet is forming then gets suddenly rich when the droplet lets go and is sucked into the engine. A little roughness creates just enough surface turbulence to prevent droplet formation and will keep the mixture much more uniform between the carb and the cylinder.

Share this post


Link to post
Share on other sites
Kenh

The drag racers back in the day always said you polish a methanol engine and leave a gas engine "rough. I think by rough, they mean the stone used to do port work and that is as fine a finish as you go.

Ken

Share this post


Link to post
Share on other sites
MikeES

It is all about getting more air into the engine. It is easy to get more fuel in. The polishing helps get more air in per revolution.

So even though there is less energy per gallon in alcohol than gasoline, you only need 6 parts of air for every 1 part of fuel with alcohol, vs 13 parts of air for every 1 part of fuel for gas.

The natural aspirated engine air intake is restricted by carb size, intake size, valve size, and cam duration, and is constant. So with alcohol you put twice the fuel in, to generate more hp per displacement.

Share this post


Link to post
Share on other sites
superbman101

Got a chance to Clean up the inside rounding the corners internally like Rodney mentioned. Going to clean up the part right under the bowl more this weekend when I get a chance between all the other projects :pi used buffing compound after the 1500 grit (just like I did on y last hood) :D ITS SO SMOOTH dOd Planning on making the exhaust port like a mirror too and intake port just remove the casting lines.Does anyone know if the Long Intake manifold is better? I'd assume they are because all the later model I/C engines switch to these.

Carb Polished1.jpg

Carb Polished2.jpg

Carb Polished3.jpg

57e05d96c5e4d_CarbPolished1.jpg.a4087a817ce8e2bc199d6c63d1fb6588.jpg

57e05d96d915c_CarbPolished2.jpg.362e3afcd3ce2fc2100b5b128b5f7844.jpg

57e05d976dbf4_CarbPolished3.jpg.c334d20aee9f6a3342776a63d8f895d9.jpg

Share this post


Link to post
Share on other sites
HubbardRA

There is one more place that I worked on that I haven't heard anyone else talk about. Be careful because this can ruin the engine if you don't do it right. I radius the edge of the cylinder on the side toward the intake valves. If the engine has been run a while, then you can see the point where the top of the upper compression stops moving. I radius from just above that point to put about a 1/4 inch radius on the edge of the cylinder. This really helps the air to flow into and out of the cylinder. I noticed a big difference in the engine when I did this. Lay a straight edge from the outer edge of a valve to the outer edge of the cylinder bore. Do this on both sides. Then do the radius between the two lines. The rest of the cylinder does not need the radius.

I also milled approximately .062 inch off the head. I measured depth of head over the valves, then measured cam lift. Add .050 for stock head gasket to depth over valves. Also add whatever clearance you want between valve and head at maximum lift. I ran with only .010 clearance myself.

Share this post


Link to post
Share on other sites
superbman101

I really like that rounding the edge facing the valves! Good idea dOd The flow from the valve to down in the chamber will be much smoother and less distance to travel. This makes the air flow even faster into the dropping piston causing it to pull in a little bit more overall in from the carb. By rounding that edge you do loose compression but like you said milling the head down just a little will more than compensate for radius.

Have you polished the combustion chamber? I have before and the carbon build up is next to nothing on the last one I opened up to check.

Also has anyone here ran a thin head gasket like copper?

Share this post


Link to post
Share on other sites
HubbardRA

Just remember one thing. When you shave the head, or use a thin head gasket, you are cutting down on the flow area from the valves to the cylinder. Shaving too much off, even though it increases compression, it can restrict flow and hurt the power. Just something that needs to be considered when doing these type of modifications. I have seen people cut down the metal between the valves and piston the same amount that they shaved from the head, in order to maintain the same flow area. Most people who build high performance flathead engines say that flow is much more important than compression.

Share this post


Link to post
Share on other sites
superbman101

Yeah milling the head or using a copper gasket it does make the path of travel smaller. Only thing you and do is choose between the two. Personally I like the idea of cutting the radius and polishing the combustion chamber (and mask off the gasket location so you make sure the gasket material has a rough enough surface to mate and make a tight seal).

Does anyone have pictures of their intake manifold "rough" ideal surface finish to create turbulence? I'm thinking porting a little (removing cast lines), polish smooth, then blast it to an even rough surface.

Share this post


Link to post
Share on other sites
ac-b12

We run a Kohler carb on our Briggs stock altered tractor, it's on alcohol. The kohler carb is nice when you really want high rpm like 6,500 or so but most clubs won't allow it in the stock or hot stock classes. You can normally get 5,500 or so with a cleaned out Briggs carb. On the exhaust side, bore the 1" pipe that threads into the block as big as you can and chamfer the ends so it flows nice before you clamp the stack on. Also clean out the intake tube, it necks down where the carb mounting bolt goes, cut that out and sand it smooth. Little by little, it all helps. Ron

quote:Originally posted by rokon2813

I would think if you're going for performance, it would be more important to polish from the bowl in, to get the fuel to the cylinder faster, then from the cylinder out, to get rid of burnt gasses easier.JMOI'm guessing thats why you can get a kohler to perform better, a short straight intake, rather than the long 90 degree of a briggs.It's probably been done before, but what about retro fitting a kohler carb to a briggs ???:o:O


id="quote">
id="quote">

Share this post


Link to post
Share on other sites
ac-b12

My sources say the same thing, flow is more important than compression. The Flathead design can't provide both. Our Stock Altered tractor only has about 9.5 to 1 compression on Alcohol. Check our videos on Show & Tell under Briggs powered pulling tractors. Ron

quote:Originally posted by HubbardRA

Just remember one thing. When you shave the head, or use a thin head gasket, you are cutting down on the flow area from the valves to the cylinder. Shaving too much off, even though it increases compression, it can restrict flow and hurt the power. Just something that needs to be considered when doing these type of modifications. I have seen people cut down the metal between the valves and piston the same amount that they shaved from the head, in order to maintain the same flow area. Most people who build high performance flathead engines say that flow is much more important than compression.


id="quote">
id="quote">

Share this post


Link to post
Share on other sites
HubbardRA

I went the opposite way once and put a B/S carb on a Kohler engine. It ran good, but I never could get the governor to work right. Since it was going to be run in a class that required 4000 rpm governor, I got a Kohler carb for it so I wouldn't have to spend a lot of time getting the governor working. It could be done, but at the time it wasn't worth the effort.

A Kohler carb on a B/S should work great, especially if you don't need governors. If you do need governors, then it will take some linkage design and trial and error.

Share this post


Link to post
Share on other sites
superbman101

Also had a few other Ideas that I'm trying out on my 16HP puller. :D1. Cut down the tube part that extrudes up level with the silicon base of the Filter2. Round and taper intake (Acts like a Mini Velocity Stack)3. Remove the excess material around the outside of the base flush with the element (wouldn't do this so a mower unless you clean the pre-filter often)4. Obviously remove all rust and polish like I have done in the other pictures

Carb intake Mods.jpg

57e05d9e3ead3_CarbintakeMods.jpg.24e51bb9ff6baccb250cafe6c748bb46.jpg

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


  • Who's Online (See full list)

    • MrSteele
    • IHITDPOST
    • PGL
    • jrmorrill
  • Today's Birthdays

    No users celebrating today
  • Recent Status Updates

    • F.U.N.

      F.U.N.  »  sandyhillbill

      Dear Sandhillbill
      Can you please copy me on this data, for Sun Star parts list.
      :
      September 12, 2004 Mike I sent you a PM and have all the mfgs. available for the tiller/hitch/pto/liftgroup if you need me to send them to you. Let me know. Thanks, F.U.N.    
      · 0 replies
    • gwiseman

      gwiseman

      Club banners are available  for members use during show season https://simpletractors.com/forums/topic/57849-simpletractors-club-banners-available/
       
      · 0 replies
  • Adverts

×