Twin 2 Surging

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  #1  
Old 06-03-13, 04:26 PM
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Twin 2 Surging

Hi guys, I've got a 1999 Murray with a 17hp BS Twin 2 engine, mod 42E707, Type 2631E1, Code 9903155A that has a surging problem. I'm running some Seafoam in the tank trying to clean out the carburetor, but today it started something new. Its been surging at idle mostly and when you shut it down it will frequently backfire one time. Today its shutting off after its been run a while. When I let it cool off a while, it'll crank ok and run again for about 10 mins before shutting off again. I put new plugs in it at beginning of year, and recently cleaned the air filter and changed the fuel filter last week. Ideas? Thanks in advance.
 
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  #2  
Old 06-03-13, 04:49 PM
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Time to remove and completely clean and rebuild the carb.
Also dump out all the old fuel.
 
  #3  
Old 06-03-13, 07:16 PM
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Yep, the carb needs cleaning. The shutting down could be the carb as well, or could be the coil breaking down since these coils are susceptible to heat breakdown and running the engine lean (which causes surging) also increases engine temps, contributing to the heat buildup.
 
  #4  
Old 06-03-13, 08:02 PM
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Thanks guys! I pretty much figured it was time to clean the carb AGAIN! What is ya'll's opinion of running 90 octane ethanol free gas in small engines? I have a station near the house that sells it and it works great in my motorcycle. Haven't used it in the lawn mower engines cause I heard the higher octane gas was actually bad on these engines?
 
  #5  
Old 06-03-13, 09:09 PM
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Hmm, I'm reading about the Flo Jet carb used on my engine(diaphragm type). The Briggs Twin Cylinder "L" Head manual calls for quite a bit of measuring clearances and replacing bushings and needle seat. I know I've read on another post that the seat rarely needs replacing anyway. My plan is to disassemble, clean, blow out all passages and pieces, replace gaskets and reassemble. How likely is it my carburetor would need the additional work which may be above my level of competence, nor do I have the special tools called for?
 
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Old 06-03-13, 10:46 PM
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Nah, most likely not. Just clean it up and remove the main jet and clean the area behind it. That should get you going again. The best thing you can do gas wise is to use non ethanol gas.
 
  #7  
Old 06-04-13, 04:55 AM
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So 90 octane won't hurt small Briggs engines? The "main jet" is labelled as "fixed jet" in the Briggs manual? I'll clean the pilot jet also and see how she does.
 
  #8  
Old 06-04-13, 06:41 AM
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90 octane will neither help nor hurt your engine. All it will do is cost you more money. If you were souping the engine up and running a higher compression ratio the higher octane would become necessary but pretty much all stock engines are set up to operate on regular 87 octane fuel.
 
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Old 06-04-13, 09:28 AM
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The jet is called a fixed jet because it remains one size at all speeds, not because it can't be removed.
 
  #10  
Old 06-14-13, 01:38 PM
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Hi again........I got the appropriate kit to clean up my carb, took it all apart, removed the fixed and idle jets, cleaned everything with carb cleaner and blew out all the passages I could find. Replaced the needle valve with the new one in the kit and reassembled. Float was not cracked or full of gas so looked ok to go back in.

After starting it back up, it ran great for about 20 seconds then died. I finally got it cranked again with a little black smoke from the exhaust but it is back to surging again and fuel is leaking from the carb. What have I possibly done wrong?
 
  #11  
Old 06-14-13, 07:28 PM
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Sounds like something got stuck in the inlet needle area or the float isn't floating (stuck or has a hole in it).
 
  #12  
Old 06-15-13, 09:53 AM
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OK, checked out the float, dunked it in some gas and it does not seem to have any leaks. I discovered what looks like a jet recessed way in a hole just under the fuel pump, flat silver head with a slot(pilot jet?). I did not take that one out during cleaning, is it the pilot(idle) jet and how do I get it out? None of my small screwdrivers seem to fit and don't want to force anything of course? Is the flat silver with a slot a cap covering the jet itself possibly?
 

Last edited by gastorms1; 06-15-13 at 10:09 AM.
  #13  
Old 06-15-13, 10:06 AM
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The idle jet is below the fuel pump. On older models it's a adjustable needle, on newer ones it's a fixed jet. It's down near the base of the carb.
 
  #14  
Old 06-15-13, 10:15 AM
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Is that a cap I see in the hole? How do you suggest getting it off? There is another smaller diameter hole just under this hole, what is that?
 
  #15  
Old 06-15-13, 07:32 PM
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You may have one with the welch plug over the hole. I've never taken one out of one like that, so I don't know. I usually get them clean by blowing compressed air through the passages and using carb cleaner. The other hole is probably a drilled hole made during carb manufacture and is likely filled with a steel ball pressed in it.
 
  #16  
Old 06-16-13, 12:34 PM
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OK, took carburetor apart again today, re cleaned it, paid particular attention to float at reassembly everything looks good. Still leaking gas at start up, seems to be at fuel pump area. Took fuel pump apart and verified it was assembled correct to diagram.

What is the posibility that the fuel pump body is cracked?
 
  #17  
Old 06-16-13, 01:20 PM
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I rechecked how I have the fuel pump assembled and it matches the small diagram slip of paper included with the overhaul kit and the diagram in the factory manual. However, looking at the parts diagram on Jack's Small Engine site, it would lead you to believe the spring and cup go on the FP body side of the diaphragm instead of the carb side?

Diagrams
 
  #18  
Old 06-16-13, 10:10 PM
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The spring goes between the pump body and the diaphragm with the metal cup on the diaphragm side.
 
  #19  
Old 06-17-13, 01:40 AM
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I forgot to mention, mine is a 4 screw FP, its the one showing in the Briggs 271172 manual page 3-2 Fig. 1 with the spring/cup on the carb side of the diaphragm. The 3 screw FP shows it on the FP body side in the manual. Is the manual diagram and the repair kit drawing incorrect?
 

Last edited by gastorms1; 06-17-13 at 02:11 AM.
  #20  
Old 06-18-13, 06:16 PM
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I have tried to assemble the FP with the spring and cup on the body side of diaphragm but it is impossible to get the pieces to all compress together as they should to mount on the carburetor.
 
  #21  
Old 06-18-13, 09:38 PM
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Well, I don't know why my replies aren't showing up. I'll try again:

You are right, the spring goes on the carb side, not the pump side as the diagram shows. I looked at an actual carb to verify since it's been way too long since I opened one to remember. I don't recall ever seeing an incorrect briggs diagram until now.
 
  #22  
Old 06-19-13, 02:06 AM
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I tried a new pump body today and the fuel pump is still leaking and the engine is still surging the little bit I've let it run with the leak. I'm going to ask a mechanic buddy to take a look at it I guess. I've cleaned and blown out the carb 3 times now, the only part I haven't removed and cleaned is the pilot jet under the welch plug at the base of the carb. I picked at the plug a little bit and can see the brass jet under the plug, should I try to remove the rest of the plug and get the jet out to clean? With a plug over it, I suppose this jet is adjustable? Anyone know the best way to remove the welch plug?

To be clear and fair to Briggs, the incorrect diagram is one that appears on dealer's sites and says ARI PartStream and not a Briggs diagram so it looks to be an error on a third party vendor I believe for this model. The Briggs diagram in the repair kit as well as the manual are apparently correct.

Could the suspected bad coil have anything to do with these problems?

Thanks cheese for staying with me on trying to fix this engine and for going to the trouble of checking an actual FP.
 

Last edited by gastorms1; 06-19-13 at 02:51 AM.
  #23  
Old 06-19-13, 09:32 AM
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If you have the plug partway open, go ahead and remove it and see. Use a pick tool or a slide hammer with a screw in it to pull the plug. That is the area of the idle circuit where the surge problem appears to be coming from. I don't know how the coil could cause the engine to surge. If the surge evens out when you apply partial choke, it tells you it's surging because it's not getting enough gas.
 
  #24  
Old 06-19-13, 11:04 AM
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Yep, I remember....before the FP started leaking......that partial choke did tend to smooth it out. I'm going to get another gasket kit for the FP so I don't set the Murray on fire :NO NO NO: and clean up the pilot jet and area. I'll report back later. Thanks.
 
  #25  
Old 06-19-13, 02:46 PM
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Once the welch plug is removed, is it necessary to install a new one? My understanding was these were just used to deter people from making adjustments to the jet?
 
  #26  
Old 06-19-13, 10:33 PM
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Generally they need to be replaced when removed on most carbs, but on this one, I'm not sure. It depends on if the jet orifice is open to the area covered by the plug or not.
 
  #27  
Old 06-30-13, 02:10 PM
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Well, after a new fuel pump body and a new gasket kit, the fuel pump is no longer leaking. The engine is still surging however. While I had the carburetor off and apart rekitting the fuel pump again, I went ahead and cleaned all the passages again and installed new jets that came in a prior rebuild kit that I apparently dd not use. I installed new spark plugs, a new fuel filter and blew out the lines which are clear. There is absolutely no dirt to be seen inside the fuel tank.

The engine starts easily but surges, most noticeable at idle speeds. Loosening the fuel cap seems to make no difference. The pilot jet I was attempting to get to turned out to be a dead end, I made a hole in the side of the carb throttle body I had to seal up with JB Weld.

What have I overlooked?
 
  #28  
Old 06-30-13, 05:45 PM
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Go to a welder's supply shop, pick up a set of torch tip cleaners ($3). Take the jet out of the carb (the one behind the drain plug on the side of the carb). Find the tip cleaner that fits the hole tightly, then pass it through several times, slightly "filing" the hole open with the steel ribs on the sides of the cleaner rod. Somewhere in this carb is a slight restriction. Most likely in that jet or the fixed one you haven't been able to access.
 
  #29  
Old 06-30-13, 06:18 PM
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Thanks for the advice Cheese. Do I need to take carb off engine for this "cleaning" or can I do it installed? Maybe I should get a gallon of parts cleaner with the basket and dip the entire carb body in it for an extended time? Then blow it out real good again?
 

Last edited by gastorms1; 06-30-13 at 06:43 PM.
  #30  
Old 06-30-13, 09:01 PM
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Try the torch tip cleaner first, if that doesn't do it, then go for the carb dip. You don't have to take the carb off for the tip cleaner fix, just take the jet out. Take the drain plug out and look in the hole. You'll see it down there. Some come out with an allen wrench, some with a flat head screwdriver.
 
  #31  
Old 07-03-13, 03:06 PM
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I got a set of the torch tip cleaners and have been poking them in the side of carb with the access bolt and the jet removed. None of them really feel like they're dragging when thy bottom out in the hole so not sure if I'm doing it incorrectly or possibly the cleaners aren't big enough?

I put it all back together and fired it up, the engine runs well enough if I pull the choke out to the "sweet spot." Still surging at idle with choke off and sputters around of course with choke on too much. Ran it a good while and it shut off again I suppose because the coil shut down when it got hot?
 
  #32  
Old 07-03-13, 04:12 PM
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You run the tip cleaner through the jet itself, not the hole it came out of.
 
  #33  
Old 07-05-13, 06:49 AM
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OK, I've tried the torch tip through the jet orifice and its still surging. Would Seafoaming the carburetor do any good possibly? And how would I go about it?
 
  #34  
Old 07-05-13, 06:31 PM
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The seafoam goes in the gas, you run it a while, and maybe it straightens out, maybe not. Sometimes it doesn't straighten out until the next time you use it after it has been in the carb awhile. Sometimes not.
 
  #35  
Old 07-05-13, 07:16 PM
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At this point after all the work I've done on this carb up to this point, what would be the best thing to try next?
 
  #36  
Old 07-21-13, 06:43 PM
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Update: The coil started failing while I was trying to fix the surging problem so I replaced it last week. The engine would shut off after running about 10-15 mins and not start again until cooling off. Got a new Briggs OE armature/magneto from the mower shop. I specifically went with the expensive Briggs piece to avoid a Chinese knockoff which is what was on it and only lasted 3 yrs. The part arrived and upon examining the box.......right next to the Briggs logo.....is "Made in China." I was not a happy camper when I saw that! We'll see how long this one lasts.

Anyway, the engine is still surging at idle but runs pretty good with the throttle up and mower blades engaged. I'm running some Seafoam in the gas, maybe that'll eventually clear it up?
 
  #37  
Old 07-21-13, 07:31 PM
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Maybe it will. For some reason it is still running too lean.
 
  #38  
Old 07-26-13, 08:43 AM
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Here's where I stand with the surging issue with my engine which still persists.

1) Carb disassembled and cleaned 3 times, new idle jet and new main jets installed. Float is not leaking(no bubbles when submerged in clean fuel) and is level. New needle installed, the seat appears very smooth with no signs of wear even under magnification. New gaskets used to reassemble. The hole I inadvertently made in the side of the carb when looking for another jet to clean sealed up nicely with JB Weld. I was careful not to block the vent hole in this recess.

2) Fuel pump body replaced when I suspected it was leaking, new FP gaskets, diaphragm.

3) New spark plugs properly gapped. Old plugs looked normal to me with no signs of gas or oil fouling.

4) Air filter cleaned and oiled.

5) New intake to engine gaskets, mounting bolts torqued to specs.

6) Fuel filter and fuel lines replaced. Fresh ethanol free 90 octane fuel in tank.

In the midst of this issue in the past month the ignition started to fail and the engine was shutting off when fully warmed up and ran only for a few minutes. I replaced the armature/magneto unit with a genuine Briggs part(Made in China!!!! like the failed internet sourced piece that only lasted 2 1/2 yrs! :NO NO NO and it now runs reliably in that department.

The fuel system actually was very clean looking inside when I took everything apart. So no obvious problems noted there.

Let me make sure I'm describing the issue correctly. I call it "surging", I think other term might be "hunting"? The engine RPM goes up and down at idle setting but never stalls. Pulling the choke out slightly smooths out the idle somewhat. When its surging the idle speed screw and linkage of course is opening and closing. The engine actually runs very smooth(like an opposed twin should! Twin II's rule!) under load at about 3/4 throttle with the cutter unit engaged. The exhaust pipe at muffler outlet looks to be a fairly "normal" looking grey color.

What do I need to check next? Is it possibly vacuum related somewhere? I have the vacuum hose hooked up to the port on bottom of carb and the breather hose connected to bottom of air cleaner assembly. I don't hear any vacuum leaks anywhere?

Thanks for your help, Mike
 
  #39  
Old 07-26-13, 08:59 AM
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You've done everything everything you can to the carb.Only thing left is a new carburetor.
 
  #40  
Old 07-26-13, 09:31 AM
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I understand your thinking that you've eliminated the carb as a suspect and are now moving on to the next step, but there isn't one. There are no vacuum ports at all. The only place for a vacuum leak is at the gaskets where the intake and carb mount. It's still a carb problem.
 
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