# briggs and stratton 18 hp twin II fuel starving?



## snroc

Hi, new to this site, need help. 18 hp opposed twin, flat head. Model 422707. Only runs with about half choke. Done a LOT of reading. New fuel lines, filter, completely disassemble carb, cleaned thoroughly, including main jet and all passages. Tank is clean, cap is good. New gaskets and main jet, float is good. No slack in govenor spring. No change at all. Plz help. Thanks.


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## jhngardner367

Welcome to the forum,snroc!
Have you got a fuel pump on it? Is it working properly?
If it has a fuel pump(most twins do ),is it attached to the carb,or separately mounted? If it mounted separately,disconnect the hose from the carb,and hold it in a container. Roll the engine over,and see if fuel is pumping.
Next,check the gasket(s) at the carb base,and manifold-to engine gaskets,for leakage,by starting the engine,and spraying carb cleaner at the base of the carb,and manifold mounts. If it runs differently,you have a leak,and should replace the gaskets.
You should also check the float level.
If all seems good,check to make sure that both cylinders are firing. Start the engine,and remove the right spark-plug wire.It should drop rpms,but not die.Then repeat on the left side. if either one causes the engine to die,the OPPOSITE side is not firing,and you should check the sparkplug,and the coil.


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## snroc

Yes it does have a fuel pump, I put complete kit & gasket set in carb & pump, as well as new filter (see thru), & all new fuel & vacuum lines. It maintains a constant level of fuel in filter, and runs pretty decent as long as choke is half way out. Both cylinders fire consistently. Needle valve & clip were replaced with kit. When you push choke in it will begin to "hunt" or surge' as if starving for fuel. I have mowed with it once by adjusting the choke cable to compensate, but it gulps fuel! Also, carb is ice cold and condensates when engine is warm.


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## snroc

I will definetly check gaskets as you suggest. I read on another forum where a guy had to use gasket sealer even though he had new gasket. I will also check float level, could be too low. Replaced all lines, & fuel filter last night, & thats when the condensation from the carb started. Thanks so much for the suggestions so far & by all means, keep them coming. I will follow up as I progress. Hopefully we can solve this & maybe help someone else with the same issues.


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## snroc

Well I got home this evening & checked intake gaskets with carb cleaner, no leaks. Re checked fuel pump just to be sure, moving plenty of fuel. Checked all hose connections, all good. Ran out of daylight before I got to float adjustment. I did find that it will run at full throttle with no choke, without surging, but is lean & will not adjust. I will try raising the float on Friday evening, sure hope that's it. Any thoughts that anyone might want to share in the mean time would be much appreciated. Thanks so much for the help so far.


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## jhngardner367

A low float level,OR a governor out of adjustment will make them "hunt". Set the float level so that it is equal height in front,and back. Next, check the governor setting,as follows:
with the engine off,set the throttle at full(wide open throttle). Then loosen the bolt/nut on the governor arm,and while holding the throttle wide open,turn the governor shaft counter-clockwise,until you feel it stop.Tighten the pinch bolt,and adjust the high and low speed needles(if equipped).


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## snroc

I will check the float level per your instructions. Also, thanks for the info on the governer setting, very helpful. Also, just noticed you are a veteran. From me & my family to you & yours, thanks for all you have done & the many sacrifices made. America's many freedoms are enjoyed because of those who serve.


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## jhngardner367

You are very welcome !


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## dangeroustoys56

I had a similar issue with a 17HP opposed briggs twin - no matter how many times i cleaned the carb, it refused to run right. 

I bot a gasket kit which comes with a pump rebuild kit for $20 from my local Cub cadet dealer - thing fires right up and runs perfect.

When gaskets get old, they leak- the original gaskets didnt look too great. For a gasket kit, you need the motor numbers and how many screws hold the pump cover on ( if its mounted to the carb) .


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## snroc

Hey, thanks for the help. I got the kit, cleaned the carb, main jet, float bowl, all passages, replaced the fuel and vacuum lines and filter, and replaced all parts in pump. Used carb cleaner to check for intake leaks. Cleaned the tank & fuel outlet from tank, checked the fuel cap vent, and ran without cap. No change from when I started. It still will run decent with the choke about half way out, but gulps gas. It will run with no choke at full throttle only without surging, but is very lean, and surges till it dies at half throttle & below. Needle valve & clip also replaced. Carb looks good inside. Float level is good. Really got me stumped. Motor seems strong otherwise, no smoke, no knock.


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## jhngardner367

How did the sparkplugs look ? Were they both tan/grey,black&dry ,black & wet ?
Also,check the timing key.Even a slight mark will change the timing.
Run a compression test on both cylinders,and compare the pressures.A difference of 25% indicates a problem.
The governor link has 5 slots--make sure the spring is in the CENTER one.
Governed idle speed =1000-1300 rpm.
Check the vacuum(use a " T ",at the pump vacuum port).


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## snroc

I had a conversation with a co worker about this engine & he commented that this carb was used on several engines. I purchased the engine used. Could the carb have possibly come from a smaller engine, & the main jet be sized for the smaller engine? Any thoughts on how to check jet size? Thanks.


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## jhngardner367

That carb was used on both V-twin,and horizontally-opposed twins,but were virtually the same on all of them.
I just had one that did the same thing,and I found that the throttle shaft was worn pretty badly. I replaced the carb,and it runs great,now.
You say the carb runs cold,and condensates ? Is there a plastic spacer under the carb ? If not,there should be!With out the spacer,the air/fuel mix goes through to fast,causing it to run "COLD".Another reason that it won't run at low speed,without the choke,could be a head gasket/valve leak.


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## snroc

Thanks for the reply. This is a 3 screw fuel pump, not sure if that matters. There is no spacer under the carb, only the intake gasket. Could you possibly post a pic or maybe a part number for the spacer? This is my first experience with a twin engine, learning as I go. I' ll need to get a compression tester before I can check on that. How did you diagnose the worn throttle shaft? The mower was given to me with a blown 18 hp single. I got the opposed twin at a bargain, but if I keep spending on this thing, I'll have more in my "bargain" than it's worth. Just need to get it dependable so I can mow with it. Thanks for all the great help so far.


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## snroc

I pulled up a parts diagram and found the plastic spacer, #29 I think, & it is missing on mine. I'll have to get one ordered. If you could, I would still appreciate some help on diagnosing the throttle shaft. Thank you so much for all the help so far.


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## jhngardner367

Just wiggle the throttle shaft from side to side/up & down. If it moves more than .005"(it will be noticeable),then it's worn. There are bushing kits frt this,but they require taking the shaft/butterfly out.


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## wjjones

Got any pictures of this engine?


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## snroc

Thanks, I will look into the throttle shaft, & check on the bushings if needed. I do have a pic.


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## jhngardner367

Hey,snroc,...have you checked to see if there's water in the fuel?( by the way, it loaded ok,so I deleted the second post,for you )


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## snroc

Thanks, posting from my phone, so I,wasn'nt sure on the pic. I have completely cleaned the tank. The throttle shaft and compression check are the next items to check. Still got to order the spacer for the carb also. Been a little under the weather so hav'nt gotten to it yet.


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## wjjones

The last time I worked on one of these it ended up being the fuel pump diaphragm one of the little springs in there was missing.


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## snroc

Thanks for the reply, already replaced springs, gaskets, & diaphram in pump.


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## jhngardner367

I think you'll find that the carb spacer will help. just make sure there's a gasket between it and the carb,and the spacer and the manifold.


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## snroc

Well i have felt a little better today, & was able to muster up the energy to tinker for a while. Stumbled accross a briggs and stratton troubleshooting guide online & it kept refering me to the fuel pump mostly, since I had already been thru the other items on the list. So, I took it apart again, went thru all parts, & with the help of another link I found, determined that the cup that fits over the diaphram spring (assuming my 3 screw uses this part), was missing, and again cleaned the interior components of the fuel pump. I reassembled the pump anyway, realizing I would need to order another fuel pump kit & cup for the diaphram spring. I also found that I actually DO have the plastic spacer under the carb. I started it up, & it of course still ran lean and required a bit of choke to run without surging. I went thru the left over parts from the carb kit, & decided to use the shorter idle mixture screw, hoping I could get a bit more adjustment from it as opposed to the one in the carb. It seems I got lucky on that part, and with the help of a little choke, & some tuning, got it to idle, and run almost perfectly. I put my son on it & sent him mowing so I could observe & listen to the engine. All was well for 30 minutes or so. Then, it seemed to run rich all of a sudden. My first thought was, GREAT! Maybe some trash in the carb I might have missed came loose, & I would just push in the choke, adjust the carb, & be OK once I went thru the pump again, but not so. I now have it running too rich with no adjustment, even after replacing the stock idle mixture screw! I'm pretty well spent for a few days, & will need to get the pump kit anyway. After that, I'll take the carb back apart to check, & redo the pump again. Sorry for the long post, & appreciate all the great help & suggestions! Gonna rest for a few days & try again. Thanks All!


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## tractorpullman

I have a 18hp twin flat head engine that doesnt run rite if i let it set and idle to long the lets to much fuel in and dies out and if i run it above 3000 rpms it will run itself out of fuel the governor linkage is not attacked i do not think that would be a huge issue but i could b wrong i rebuilt the carb and the fuel pump. plz help thx


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## jhngardner367

These engines have a maximum rpm of 3600,so you should make sure the governor is connected,and adjusted properly!
It sounds,tractorpullman,as if the float is sticking open/mis- adjusted,or has a hole in it,allowing it to sink.

Snroc,you might want to check your float, too. I just got through ordering one for a twin that was doing the same thing. Found a hairline crack in the float.

Tractorpullman,hows it looking in Clare county? Pretty cold/wet here in Ingham County ! By the way,there's a real good parts supplier just south of you,in Mt.Pleasant ! It's called " Motorcycle & snowmobile Salvage"' but they also have lawn tractors,and even boat motors,and thier prices are very reasonable !

Motorcycle & snowmobile Salvage
4101 E. River Rd.
Mt. Pleasant,Mi.
48858
(989)-772-3442


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## thalamander

If you put the screws on the carberater all the way on and then adjust them there are screws for ideal seed and the float. You should look up the manufacture way to adjust it


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## indypower

Last year I chased the same problem on Kohler. Cleaned carb. No change. Adjusted valves. just a little better. drained gas tank- found some water- better, but not as good as it should be. replaced gas filter- saw crap in it. Better. after 10 mins running right back to same as before. Gas filter again had black stuff in it. Removed gas hose and could not see thru it end to end. Was plugged up. Pushed a long phiilips screw driver thru it to see what it was that clogged it. It was the inside of the gas hose that had deteriorated due to the ethonal in the gas today. I was told that sometimes this E-10 gas is more E-12. These older engines do not like ethonal at all. Check your gas lines. If they need replacing, make sure you get gas hose that is ethonal resistant.


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## shizcol

i just picked a older agway mower and am having this same issue.. thought maybe if i cleaned the carb it might help.. havent had a chance to do any of the above yet tho.. i have the same engine.. seems these engines are known for this..


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## AdkBill

Our 16 bhp Vangard-powered generator was running erratically. Checked fuel filter, gas tank, lines, etc.; no luck; you could see the fuel filter not filling up as the engine ran lean.

After lots of trial & error, found out that the vacuum for the diaphragm pump was being weakened by a slight leak in the valve cover oil filler screw cap. When the hole was covered (by the palm of a hand), the engine ran smoothly again.


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## rogerh9405

I have an engine like this that had the same problem that I fixed by accident and I think you may have the same condition. My engine would perform the same as yours (lurching or hunting at low rpm vroom, vroom, vroom) and ran fine at high rpm or full throttle. My problem was the choke cable itself. Over time it had came loose and got hard and harder to start in fact it finally got to where I had to start it with starting fluid and I broke down and took the covers off to adjust the chock cable. The choke should close completely when engaged and open with about a 3/8 to a half inch gap if you were measuring the butterfly to the carb wall. When you are pulling the cable in a little you are mimicking the correct adjustment. Check to see if the choke closes completely and opens about 3/8 an inch when disengaged. Oh and if the choke cable is out of adjustment your throttle probably is too so while you are there make sure the throttle isn't leaving anything on the table when you have it in full throttle position. Good Luck!


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## string_wizard

Hey, you wouldn't happen to have any more views of this engine would you ?. I would like to see how/where your cables are positioned ?.


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## Hustler

snroc said:


> Hi, new to this site, need help. 18 hp opposed twin, flat head. Model 422707. Only runs with about half choke. Done a LOT of reading. New fuel lines, filter, completely disassemble carb, cleaned thoroughly, including main jet and all passages. Tank is clean, cap is good. New gaskets and main jet, float is good. No slack in govenor spring. No change at all. Plz help. Thanks.


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## Hustler

Id suggest leaks under the carb, or intake manifold leak, or try combo vacuum inline with the one on the carb..doesnt sound like fuel issue..having to choke to compensate for air coming n elsewhere..


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## unsquidly

Hustler said:


> Id suggest leaks under the carb, or intake manifold leak, or try combo vacuum inline with the one on the carb..doesnt sound like fuel issue..having to choke to compensate for air coming n elsewhere..



Since this thread is over 9 years old, I would hope that they either solved the problem or gave up on it by now......Just saying......


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