Modifying A Briggs Opposed Twin Carb

[@alandumitrescu6597]

Thanks for the video. Good info here. I have 2 model 42 opposed twins that run on gas I dunno down the carb but the fuel pump is shot and neither supplied enough in the first place. This helps a lot.

[@haulngrassracing]

I tried to go over as much as I could remember. Thanks for watching!

[@DonovanBryant92]

Just got two opposed twins for 20 bucks one is seized the other one spins over but has water in it might throw the two together and make a good engine

[@kurayami3857]

Where the f you find two of them for 20 bucks I'm willing to pay 400 bucks to buy one on ebay and someone bought it before I could I needed it for my racing mower

[@tkskagen]

Good video Haul'n Grass! Now I know how to run my Modified DRM500 without only being able to use only 1/2 of the tank! It's got a Briggs and Stratton 12HP Single Cylinder Flathead, that has no pulse tube off the Breather. But, now I know what & how to do it! Thanks!, :-) -Thomas Port Orchard, Washington

[@willyck948]

you can spray a filter element as well as foam pre filter with silicone spray to capture dirt better just like K&N filter use filter oil basically silicone spray.

[@michaelbenoit248]

What I did was I modified the stock on to that I can gorse fuel straight through the housing, although it still leaks, I pulled off the vacuum line, so now it goes through a brigs fuel pump. It leaks a little, but it’s better than the stock one. These things are already gas hogs, I’ll probably buy the gaskets for it so it won’t leak.

[@robertsaucier183]

I got a ton of questions I just got to figure out which of the more important ones I want the answers to first LOL and hell yeah I love the wrench linkage

[@haulngrassracing]

Send your questions to [e-mail] I’ll be more than happy to try to help.

[@briggsmadness2083]

Very awesome set up I've rigged some Briggs but that was sweet man too bad they don't sell a kit like that for that carburetor u should make them I love the opposed twin engine u gotta b careful the conecting rods break I usually put mystery oil in the gas for upper lube

[@haulngrassracing]

Thanks. Im running a pressure lube opposed twin with billet rods

[@inspireonex]

Fuel in the crankcase won't lock it up in seconds. If you check your oil frequently (before you use your engine) you'd notice it.

[@7.3PSDA2]

Ive just recently put one on my troy bilt mower because the original 15.5 single cylinder was a pile of junk. and im starting to have issues with the gas dumping in the engine. and then it seems to run a little lean so im gunna get the stuff and do this swap not gunna get the adjustable screw or the air filter step up. thats awesome and all but im just gunna change the fuel pump 1st

[@marcemarc6516]

Has anyone installed two separate carb? Or adapted an oversized model. This seems like the weak point to all the oppose twin engines

[@haulngrassracing]

I’m sure someone has at some point.

[@goose278]

I keep searching for someone or for a video that shows that, but they're hard to find. I thought two Mikuni's would be nice.

[@RobertPerrigoOkiechopper]

I have 17 of these 42 C.I. Boxer's that I been collecting over the years. The tractor racers around here like using them. I am going to part with them and just do stock repairs only. I now do all repairs while setting in a wheel chair full time. I am leaving racing. Any interest contact me.

[@mrbuddy3297]

Ahh

[@granjerolunabrillo1487]

is that a after market fuel pump or tap? because it's tapped in to the inlet manifold suggests to me it runs off a vacuum so would make sense if it cut the full off when there is no vacuum rather then pumped fuel when there is, Please can I get some more info on that set up, Many Thanks Andrew

[@haulngrassracing]

Andrew Andrew yes it is an aftermarket fuel pump feed by vacuum from the intake

[@LonniesGarage]

Thanks Man This Video Is Great And Detailed Very Well. Nice Info Here

[@haulngrassracing]

Sorry puppet I just saw your comment. Thanks!

[@joeyswepston0143]

@Haul'N Grass can you move the stock vacum line to the intake manifold where yours is to pick up a pulse so it doesnt drain into the block, but still is the original pulse pump?

[@haulngrassracing]

Yes you can. That’s what most people do with them. I’ve even converted tons of regular mowers the same way.

[@savian1973]

Very nice setup. However if I am just setting this carb up to say run on a Pulse or electric fuel pump, do I need the bowl vacuum and port (blue Hose)? Also once you tap and place the set screw in the original fuel pump is there anyway for it to leak fuel or suck air in from that area?

[@haulngrassracing]

savian1973 to run a pulse pump you need a pulse line and it’s best to get the pulse from the intake. If you’re running an electric fuel pump ( not suggested do to pump running while engine stalls and dies and illegal to run in all classes of mower racing) you won’t need the blue pulse line. Once I tapped the hole for the plug i put thread sealer on it to prevent any air or fuel getting in or out.

[@savian1973]

Haul'N Grass thanks for that helpful information. I got and appreciate it.

[@macthompson4586]

So i did this sam set up on my 20hp opposed twin, my question is after i ported my pulse from the intake and ran my fuel line to the port i put in the same place in the carb. i put my set screw in as well but it is now over fueling very badly piuring fuel out of the top of the carb.

[@haulngrassracing]

Are you using an after market pump or the factory pump?

[@andywanzer4351]

Very helpful

[@lilcujo6175]

Could/ would you send schematics or diagram of the mods you did if someone was really interested in doing the same thing?

[@sakuradev2130]

What is the size on that filter?

[@haulngrassracing]

I believe it’s a 3 inch filter with a 2 inch base

[@ronvi4539]

Have you tried K & N filters? I use them on every engine I can. You might like them.

[@haulngrassracing]

Ron Van Iorns yep that's what I run now

[@stinson87]

looking at the fuel pump mod, why not run the factory pump but connect it to the intake for pulse like you have your current setup? I have 3 opposed twins and a flathead, 8hp / 16hp / 18hp / 18.5hp iv noticed the 18.5 is a marketing gimmick by mtd. im tempted to combine the 16 and 18 for a stroker but currently they both run so well i dont have a need to.

[@haulngrassracing]

Atom RC the factory pumps rely on negative pressure from the engine block. It's more of a weaker signal then a positive pulse from the intake and I've had more stock fuel pumps fail connecting them to the intake. Instead of constantly buying fuel pumps it's easier just to convert it over to a go-kart Style fuel pump.

[@stinson87]

cool, thanks for the answer! ill probably get one to be preventative, all 3 of my opposed twins had the original diaphragms with no damage but i still replaced them.

[@haulngrassracing]

Atom RC did you have them getting the pulse from the intake? The biggest reason to run them on the intake is when the diaphragm fails and its still connected to the block/crankcase it will filled the case with fuel and your engine will lock up before you have a chance to get it shut down (lesson learned) even if running the stock pump always from the pulse from the intake that way if it does fail then it will just flood out the engine and die. 👍

[@stinson87]

currently they are all factory on the case. I'll probably swap to the intake once i dig a bit more into the engine. Still need to split the heads and clean them, debur the intake and exhaust, clean the valves... Iv only ran seafoam in them both thru fuel and oil currently. For the oil i replace about 1-2 ounces of oil with seafoam, run it 30-40min and then drain and replace. For the fuel I add it every time. but they really need a good tear down and cleaning, the 18hp is a 1994 with 3000+ hours, and the 16 has unknown hours and was poorly maintained since 1984. The 18.5 was ran for at least 5 years with no air filter as a mower, and probably never got an oil change... only topped off.

[@ericmcclelland7758]

on my 16hp opposed twin there is some sort of anti backfire jet that is plugged into my wiring harness that goes where the drain plug is on the bottom right where you put the adjustable jet at,could i do the same thing you did or do i need to stay with the stock set up? reason i'm asking is i broke that electric jet while cleaning my carb,it is a wraped with a thin copper wire and it looks like its molded in plastic and it threads into the bottom of the carb bowl,the tractor is a 16yt lawn boy,same as a ford yt.any info would be helpfull,thanks.

[@haulngrassracing]

I've never seen an opposed twin with a backfire solenoid. Usually that's on V Twins. For the ones with the solenoids on the bottom usually they just cut the tip off the plunger and drill the jet out a size or two

[@ericmcclelland7758]

Haul'N Grass The engine is a 16 hp i/c briggs twin 2 cast iron bore on a lawn boy tractor.What i did was clipped of the plunger and put a in line fuel shut off so it wont flood the crank when its shut off.Worked great but i think i'm gonna order a new carb kit and delete the fuel pump like you did and tap into the intake and get a in line fuel pump.drill out the jet.I'm looking for a different transaxle,would dana's be a good choice?thanks for the tips Haul'N Grass.cheers

[@haulngrassracing]

eric mcclelland I'm not sure about Danas, I've never ran them.

[@vintagesimplicitytractors9464]

What were u talking about that side adjuster where do u buy one

[@haulngrassracing]

I got it from ec carbs website. Used to be a kit you can buy but now you have to piece each part together separately into your shopping cart. It just adjusted the rich mixture at high rpm’s. Honestly you don’t need it.

[@cryptopyro]

Can you please give the part number or the web link for the adjustable main jet that is screwed into your modified main jet cover plug.

[@haulngrassracing]

Fabian F I bought it from EC carburetors but now they don’t sell it as a kit. You can buy the individual pieces. Last time I called them about it they said if you call and tell them you want the adjustable main jet for am opposed twin carb they can piece it together but you will have to buy the individual pieces but it only comes out to a couple of dollars.

[@NotMeeither]

If you oil that filter properly it won't let all that dust & dirt through !

[@haulngrassracing]

correct.

[@dirtyburd71]

I saw that one right away! LOL

[@pyralux01]

Great video on "how"........my question is "why"....

[@haulngrassracing]

Easy, to get the best performance and better reliability out of a stock carburetor without having to buy a performance carburetor. The stock fuel pumps are notorious for failing and getting the pulse from the crankcase is always a bad idea. The “why” for the video is to make a better carburetor and to set it up to get the best performance out of it. You can stick with a stock carb and just drill the main jet out. But when your at the track and can make small adjustments and quick tunes to the carb then that may make the difference between crossing the checked flag or loading it up without starting a race.

[@pontiachotshot]

I see now days people are adapting the China motorcycle carbs with elbows from Amazon or eBay.

[@michaelbenoit248]

these opposed twins are really easy to find especially w the vertical shaft. got 3-4 of them for free one in a JD116 & the other 3 out of MTD mowers. the issue w these things is that the starters they come with stock are almost always shot, all 4 of them were & spin over easily was new starter & charged battery. the stock carb fuel pumps on the front of them are pretty problematic, am trying to just bypass altogether they're a PITA. Can someone show how to do it? I think I can figure out how to but it would be nice to see what others have done. I've tried to sell just the engine for a while & cant sell them to save my life, too many of them around, & almost always are good being the starters, & the carb fuel pumps are an issue, other than that they're good runners.

[@FlickTricksOffical]

+Haul'N Grass Do you know how to fix a carb that floods out after 10 seconds? My carb (42CI) will flood out and gas will pour out the vents on top and into the intake.

[@haulngrassracing]

one of two things: 1- the fuel tank is above the carb and should be below the carb. that type of carb can't shut fuel off if it's gravity feed. 2: is your float inside of the carb might be stuck or has developed a hole is has filled up the float with fuel. if your tank is above the carb, relocate it where it sits lower than the carb. If it's already below the carb height then check your float

[@FlickTricksOffical]

+Haul'N Grass I had it at carb level for a test start until it flooded out. So I guess I'll have to try that next. By the way I have the intake / carb on a 13HP Flathead that I modified, I cut off the right intake runner and TIG'd in a cast plug. Then ovaled in the flange holes on the left runner. Reused the intake gasket from the original carb and the flange is the right size. Might upload a video here in a bit of it.

[@haulngrassracing]

I would have to see it to understand

[@FlickTricksOffical]

+FlickTricksOffical Oh and I meant by the flange being the "right" size I mean the 13hp intake gasket fits *directly* onto the opposed twin intake after I modified the bolt holes.

[@FlickTricksOffical]

+FlickTricksOffical Yeah it's a bit much lol. But other than that it was pretty simple, and doesn't look half bad. I'll make sure to explain in the video the whole process.

[@trailerparkgarage6574]

my horizontal shaft briggs flatty had this type of mod done to it from the factory

[@haulngrassracing]

legotec49 yes some of them did but the older carbs were not set up like that.

[@trailerparkgarage6574]

It was on a 1990 engine

[@haulngrassracing]

legotec49 my date code was 85 lol

[@BillyRillkratz]

What spark plug (heat) do you use? Running on pump gas?

[@haulngrassracing]

WurstExpress I run NGK B6HS

[@BillyRillkratz]

Haul'N Grass Thank you again

[@RPM_Productions]

What is the main jet adjust do?

[@haulngrassracing]

Myles Pike helps dial in the air/fuel mixture. Once you get it set (going off of the color of spark plug electrode) generally you won’t have to mess with it again. Make it easier than constantly drilling out the main to get the correct mixture

[@seanbirge5081]

Do you have the trans axle flipped 180 and upside down?

[@haulngrassracing]

Sean Birge there is no transaxle. Just a peerless 700 transmission chained to a racing go kart axle in the back

[@seanbirge5081]

@@haulngrassracing how is it mounted though. Sorry just used to calling it a transaxle. Thanks for the fast reply

[@haulngrassracing]

Sean Birge I used a 1/4” plate that is welded to the square tubing that is used to stiffen the chassis. 700 trans is bolted in place and the output in the bottom goes through a hole that I cut into the 1/4” plate. I believe I have a video of it somewhere..

[@jdhunting6617]

What will cause my carb on my 16hp now come up to 3600 rpm I only get 2450 with load and with out

[@haulngrassracing]

JD HUNTING 66 Unfortunately it could be a number of things. Dirty carb or not adjusted properly, could be a governor issue, too much ring blow by and low compression, possibly a coil issue. What all have you done to the engine & what type of engine is it? ie single or twin cylinders

[@hellrazoryt7792]

How did you get your engine to sit like that

[@haulngrassracing]

You mean sideways?

[@hellrazoryt7792]

@@haulngrassracing yes I've been wondering how to do that would I have to Re drill the mounting holes

[@haulngrassracing]

@@hellrazoryt7792 I believe the holes line up no matter which way the engine sits. I mounted it like that so the hood would close.

[@hellrazoryt7792]

@@haulngrassracing Ok I was wondering because I like the way it sits like that I just didn't know

[@paulcrowder7733]

how do you start it up with no choke?

[@haulngrassracing]

Because it runs rich it doesn't need a choke. Starts up every time

[@paulcrowder7733]

oh ok thankyou

[@haulngrassracing]

No problem. Remember Flat head engines love rich conditions. Running lean gets them hot and they don't like heat

[@paulcrowder7733]

yeah i know i got an opposed on my highly modded mud mower and lately ive been messing with the carb so i wanted to know. but which part do you adjust on the carb to make it run rich

[@haulngrassracing]

Where the drain plug is on the bowl I drilled the main jet and made the drain plug into an adjustable main jet. most people just drill the main jet a couple of thousandths but don't go to far. if you find that it's running too rich just solder up the main jet and redrill to a smaller size. I like the thought of making it adjustable because different weather patterns and temps it always runs different when fully modified so it makes it easier to fine tune and get just right

[@gunnarhansen9679]

I know this is like 6 years to late but that filter is meant for oil it’s a oil filter you have to use air filter oil on it

[@haulngrassracing]

Gunnar Hansen It was a K&N air filter meant for a racing kart. It’s supposed to have a prefilter on it. Later I went with a different type of air filter.

[@danharold3087]

Gunnar is right. The pre filter is supposed to be coarser than the filter it protects. You needed to oil it. Enjoyed the video thanks for posting it and replying to comments years later.

[@haulngrassracing]

My apologies, I thought you were referring to it as an “oil filter” lol. Yes the air filter needs to be pre charged with oil

[@haulngrassracing]

My apologies, I thought you were referring to it as an “oil filter” lol. Yes the air filter needs to be pre charged with oil and then the pre filter goes on the outside. In the video the air filter was charged with oil but didn’t have the pre filter on it at the time. The oil I used was pretty much a clear product unlike the red tint you get with K&N. It was cheaper. Thanks for watching guys!

[@gunnarhansen9679]

Haul'N Grass oh yes sorry I meant oiled and I’m just used to kn oils👍

[@fullsendsonly4631]

i have an 18 horse briggs and i want to run a different fuel pump instead of what i have. at the moment i have to replace the fuel pump because its not pumping gas and surges but only runs with the choke on. help would be greatly appreciated. model number 422707

[@haulngrassracing]

BemidjiRednecksDoingShit usually that indicates a dirty carb. fuel pumps rarely go out and its pretty easy to tell because they stop completely. doesn't sound like a pump issue but more a carb issue. might take the carb apart and thoroughly clean all the passage ways and also check to make sure there's no vacuum leak around the carb by spraying carb cleaner down by the gaskets. if it revs up without touching the throttle then you have a air leak. hope this helps!

[@lrayvick]

I had surging on my 16 hp. Replaced the vacuum hose to the carb. Problem solved.

[@stephanieroach6949]

What is that blue hose for?

[@haulngrassracing]

dixiegirl grits one is the bowl vent tube and the other is the fuel line. you can pick it up at Rural King or any farm supply store

[@RockeyDAproductions]

were did you get the fly wheel?

[@haulngrassracing]

RockeyDAproductions bought it from ARC website. You can also get it on www.eccarburetors.com

[@RockeyDAproductions]

thanks, i subbed BTW

[@haulngrassracing]

RockeyDAproductions I'm sorry I'm horrible with acronyms. Whats subbed? Lol

[@haulngrassracing]

RockeyDAproductions oooh lol ok awesome thanks. Getting things lined out for my next project so stay tuned!

[@RockeyDAproductions]

i kinda do this stuff to, but my budget is non existent, i dont have alot of tools, and im building for muddling.

[@darwinwhitt8546]

ANYONE Have an intake Manifold I can buy ?? I can't find one anywhere

[@JeffreyStrader]

Far too much work only to have the carb function as it did in OEM fashion.

[@haulngrassracing]

Not really. The factory fuel pumps are not as good as the aftermarket pumps plus rebuilding an aftermarket is cheaper. You can get by with the OEM but the extra pressure from higher rpm they don’t last long. It all depends on how serious you want to be and what your willing to do.

[@mrbuddy3297]

Could just put a check valve on the fuken line

[@haulngrassracing]

Mr Buddy For?

[@haulngrassracing]

Egg Boi wouldn’t work. The fuel pump works by moving air in and out which is why they call it a pulse line. If you put a check valve in the air can only move in one direction. It would push on the membrane in the fuel pump but won’t pull it back because the check valve is preventing it.

[@mrbuddy3297]

@@AustinRBa yes for shure

[@mrbuddy3297]

@@haulngrassracing or just put a fricken elevated line on it

[@calholli]

I'm so sick of this 3 screw pump. Its trash.. I've changed it more than once, it's constantly intermittent... and then all the sudden it runs.......... I dont' have a clue why.. and then later when I try to start it up again, same issues. I like this motor ,but that pump carb is terrible.

[@haulngrassracing]

Yeah they’ve not had a good reputation for being reliable. Heavily modified they work good. A lot of racers went with a dual carb setup.

[@calholli]

@@haulngrassracing I actually just got it running again, I had to adjust the little throttle by hand to get it going... I think the governor is making it stick wide open or something... Once I rev it nearly full throttle it stays running fine; but if I throttle it down too much, the governor slams it wide open and it bogs out and dies?? Do you have a video on how to adjust the governor on these? Might be a good quick video to make.

[@haulngrassracing]

@@calholli All the engines I’ve built I removed the governor. Some governors hold the throttle wide open till it starts and runs and then it backs it down to your throttle settings. I don’t have any opposed twins in my possession at the moment. You can try a google search or look on the ol KZbin engine to see if anything comes up.

[@andrehills6015]

Ten minutes to late getting to this video I broke the seal on the pump and gas leaked down into engine an now its locked😫

[@haulngrassracing]

Andre Hills oh crap :-( sorry to hear that. Hopefully it wasn’t a pressure lube or the rare 46ci version. You can get 40/42ci pretty cheap now a days.