Briggs 18hp Engine Idle help

[stargate4]

Hello , Lewis here, from Monterey, Tennessee. I just acquired a 98 Bigfoot with 423 hours on it. It had been sitting un-used for a while. This is the first 6x6 aatv that I have ever been in and was hoping you could give me a little information on them. It has an 18hp B&S Vanguard engine. The first thing I did was replaced the fuel lines and cleaned the gas tank, then took the top off the carb and cleaned it out as well as all the jets and needle valve. I also put a new fuel pump on it from Briggs. It works from a vacuum line to the valve cover. It runs pretty good at full throttle but it will not idle worth a darn. I also have to keep the choke almost totally closed when running it. When I adjust the idling down to what sounds reasonable and to help with the transmission shifting, the engine idles up and down and finally dies completely. When I open the throttle quickly it seems like it is starving for gas. I am going to try putting an electric low pressure fuel pump on it to see if that helps with the problem. I am also going to have to put a solenoid switch on it. The starter doesn't work and I am hoping that is the problem as it looks like a major undertaking to change out a starter. Would you have any insight on the idling problem? Also the transmission is very hard to put into gear. I don't know if the fast idling is the cause of that or not. It changes pretty well when the engine is not running. Any information would be greatly appreciated.. thanks.. Lewis

[Roger S]

Idle mixture circuit. Did you have the idle mixture screw out when cleaning..

with it out, and the top off, spray carb cleaner and compressed air through both ends. Screw is on the side of carb toward pull start. Pull the plastic cap off and discard, remove screw and spring.

Lots of us add electric pumps but only for incline starvation.

[Jeff t-boss]

I agree with Roger S. Re-clean the carb and totally break it down. Remove everything you can and soak awhile in carb cleaner. Then blow out with compressed air. Reassemble and go through your initial adjustment and running adjustments again. I would also hold off on the electric fuel pump for now. You said you have a new B&S fuel pump, so why switch? Just hang in there with the carb cleaning and adjusting for now.

[atvrider93]

almost sounds like you have a leak somewhere with the erratic idle

[new2memax4]

i had the same trouble with mine,same 18hp vanguard. I followed advice of others here and found solutions.That "surging" you describe sounds like the goofy tangs for governor and what goes with, I think "liflod" posted on here how to set these things up and cleaned them,I did just that and it has never run better ,about rolled it on my first powerslide donut after back together.I must admit though I had it screwed up and run worse before I got it right,I got kinda frustrated at first but then I got it squared away

[aktim]

This is AK Tim first time post, have been reading for a while. Be sure and check the main jet straight in from the drain plug on the carb. bowl. It picks up any crap floating in the bowl and you can't see it from looking straight down with the lid off. you have to access it thru the bowl drain. Mine did that had to run with the choke on untill it plugged completly and it quit. It wasn't untill I had the carb all the way off disassemblying it I found it

[Mike]

This is AK Tim first time post, have been reading for a while. Be sure and check the main jet straight in from the drain plug on the carb. bowl. It picks up any crap floating in the bowl and you can't see it from looking straight down with the lid off. you have to access it thru the bowl drain. Mine did that had to run with the choke on untill it plugged completly and it quit. It wasn't untill I had the carb all the way off disassemblying it I found it

This is my bet as well. The same thing happened to me and I too thought that I had cleaned every jet in the carb. I replaced the fuel pump, fuel lines, fuel filter, and even the brass fittings on the fuel tank. Finally in the end I realized that it was sediment in the main jet.

I, like Tim, had to take the carb completely off and only then was I able to get that jet out. If you haven't had that one out yet, try that.

[brushcutter]

The horrizontally opposed 18hp Briggs (if this helps or is even remotely similar)has a port for the low speed idle that if clogged will cause exactly the same symptoms you mentioned.It can be seen from the top and runs down at an angle to the bottom of the bowl to pick up fuel.When mine was plugged I could completly close the screw or even completely remove it from the carb with virtually no change in performance.I had to run at high idle and it popped,spit,sputtered and smoked.It backfired every time I killed it and just ran crappy so I tore it down the third time and that's when I found the problem.Now I can idle it so slow that a fast honeybee can fly in one one exhaust and out the other and not even get singed. Gregg

[6X6]

Mogman has a 16 Vanguard, and had the same issue. I 3rd AKTim and Mike on the main jet, on the side facing the drain, where the bowl is real narrow so you can't get to it WITHOUT removing the drain. (Edit: YOU CAN, however leave the carb on if you really want to, carefully remove the drain(Drop it and your taking your engine cover off to retreive it!), and access the jet through the drain hole with Carb Cleaner AND/or compressed air.) The Low speed like Brushcutter said is the first culprit, but since you said you cleaned the carb already, I also bet on the easy to miss high speed jet.

OH, when you changed the fuel pump, did you change the short pressure line that goes to the valve cover? (I NEVER reuse the pressure lines, too easy to cause too many headaches) If not, then I move my bet to that.

[stargate4]

Idling problems....

Many thanks to all who answered and gave info on the idle problems. Looks llike I am going to have to try the cleaning bit again. I thought I got it the second time but probably didn't. I definately believe it is a carb problem. I did change all the lines when I put the new ones on. I didn't mess with the plastic covered screw on the pull start side though. It looks like it is a major job just to pull the carb off the motor. When the weather warms up a bit so my fingers can move I will try the cleaning again, paying more attention to the plastic covered screw. All the other jets were cleaned pretty good so I think it must be somewhere that I couldn't see. I could squirt carb cleaner through all the jets and the holes where they were and all appeared to be open. Thanks again for all the replys.... Lewis

[Roger S]

Personally, I could clean everything with spray carb cleaner and compressed air, without taking the carb off, or the main jet out. I had a good rubber tipped nozzle, good Berryman Chemtool cleaner and a 100+ air pressure.

If you take that black grill off, between the carb and engine cowling, and hang it on the wall, the idle mixture screw will be easy to access. It's a regular needle valve and spring. There's a plastic cap pushed down over the head of the screw, and the little arm hanging out keeps it from being turned more than a 1/4". Pull the cap off with pliers and discard, place in that misc parts tray, or you can reinstall when done.

When it's clean and adjusted, the engine will idle as low as you want(if the idle speed screw/governor doesn't limit it), and not hesitate under acelleration, and won't require prolonged choke operation. When reassembled, turn it in 'till it lightly seats, then turn out 3/4 turn or so, and fine tune from there.

Th plastic limiter cap is there to reduce tampering by shadetree mechanics/us, and supposed to help the EPA keep the air clean. But it is set borderline lean, and with any age or varnish in the carb, becomes too lean for the engine to idle well or make the transition to main jet without a hesitation.

[stargate4]

Carburetor removal

I am still having problems with the carb on the Briggs 18 hp Vanguard in my Argo Bigfoot. I cleaned it out good, installed new gas lines, cleaned the tank, installed a new fuel pump but still can't get it to idle right. I have to have the choke amost completely closed before it will run at all. It emits black smoke so I think the mixture is too rich. The carb had all kinds of gunk in it and I am thinking it may have corroded some of the surface area or jets. I made sure carb cleaner flowed through all the jets. I am thinking about replacing the old carb with a new one. It looks like it will be a major job. I am looking for some idea of how to begin this task without randomly taking stuff off. I don't have a schematic so it will be a learn as I go job. Now that the weather has warmed up a bit I am going to give it a try and hopefully be able to get it running right by really warmer weather... Any advice greatly appreciated... thanks... Lewis

[Roger S]

The sheetmetal cover needs to come off the front of the engine, to get the carb bolts. Get the air duct out of the way and it doesn't look so hard. Remove the bolts you can see on the top of the red engine cover. Also 2 on each side down below with a 10mm wrench. While the cover is off, other things are in plain view.. like the diode wire that connects both coils (the kill switch circuit) that can cause problems like rear cylinder missing, or engine won't shut off. The air gap on flywheel/magnetos can be set. If the engine is dirty or the air cooled stuff plugged up, it's there for the cleaning.

[stargate4]

Thanks for the reply

Thanks Roger for the info.. I will try the cleaning again before removing the carb. Not having taking anything off except the carb I guess I am suffering from fear of the unknown. It looks like a tight place to be working though. Thanks again for the info... Lewis

[bilimrl1]

Low Idle Jet - running lean

I have a 18Hp Vanguard in my '03 Argo that set up as well, had black gu in the carb and tank. Ran carb cleaner in a few tanks of gas, tore it down on the engine 3 times. It would not idle right, surged all the time and I could not adjust the idle to a level that would allow me to shift gears without grinding them. It turned out, the only problem after getting the gu out was the low idle screw on the bottom portion of the carb facing the right side of the bike was turned in to a "lean" setting. I backed it out 1/4 turn, it purrs like a kitten now. I also had a bad back-firing problem, like a 9mm going off. It's gone as well! Try turning the that little screw out a 1/4 turn and run it for a bit. Fixed my problem.