idle but no rev

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  #1  
Old 09-10-06, 06:18 PM
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idle but no rev

hi all. ok, here's the deal. I have a briggs 252412 / 0154 01 / 78120411 running a 5000 watt gen. when i first got it(it had set for 2 years) put gas in and it started once and no more. Found out mice had ate the coil wire. replaced old points type with solid state. then started fine but rough idle. decided to rebuild carb. taking it apart i discovered threads on high speed valve stripped and glued, carb nozzle broke in two(top half missing) and other things, so i bought a new carb (392587) and installed it. it started right up but ran slow. thought the screws might need adjusting so turned the nozzle screw in. it started revving,or surging, then all of a sudden it just started over revving.thats a scary sound when you are sitting right next to it! oil and smoke everywhere. got it shut off and it sat for 2 days. went out today and turned out the screw and it started ok, but still low rpm. when i try to speed it up using the screws, at a certain point it starts surging (governor moves up). if i let this continue, eventually it will take off full over rev again. It did this once, and i manually held the governor back which slowed it down some, but adjusting either the nozzle screw or the idle adjust did nothing. It will not rev manually, if i try, it dies. it seems to run at the slow idle forever, but very rough. turning the idle screw in makes it go faster, or turning the nozzle screw in makes it go faster. to get the idle i have now, i have the idle screw in all the way, and the nozzle screw about halfway out. the only diff i can see between the 2 carbs is the old one opened the butterfly by being pulled down, and the new one has to push it up, so i guess the throttle shaft? is reversed. I have clear fuel line so i can see gas in it. took new carb apart and blew it out but it looked clean (as it should). Any ideas? i would like this to run right and for days if necessary. It also does seem to hog the gas pretty fast. Thanks for any help. Oh, i do have a new head gasket on the way.
 
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  #2  
Old 09-10-06, 06:50 PM
Azis
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Sounds like you have it too lean. The main jet or high speed nozzle is usually set 1 1/2 to 2 turns from lightly seated.
When the engine leans out it runs hotter and will over rev. Also if when you try to advance the throttle it dies, usually a lean setting can also cause this as to advance rpm the engine needs more fuel. Surging is generally a sign of too lean a setting also.
The idle setting should be set as follows befor adjusting the high speed.
With the butterfly closed (throttle at idle) the idle speed screw should just begin to touch the idle stop on the carb. Once the high speed is set the idle can be set.
 
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Old 09-11-06, 03:02 AM
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Lets see if I have this right. New coil, new carburetor and still won't run right. You say the throw on the carburetor is different between the old and new throttle. I'd say you have the wrong new carb! You are speaking of "idle" but this engine should never idle. Being a generator, I'll bet this is a fixed RPM throttle and should only run at operating RPM's. The Briggs part number for the replacement carburetor should be 392587 and, if so, should have the exact same throttle/governor linkage setup. Anything different and you'll never get it to throttle up or operate at all for that matter. Are you sure you aren't referring to the choke, perhaps, rather than the throttle shaft? If you, in fact, have the correct replacement carburetor and you still have a throttle/governor problem then I'd check the static adjustment of the governor arm first and then, if still troublesome, get into the engine to inspect/repair the governor assembly.
 
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Old 09-11-06, 06:31 PM
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puey...yes new coil,yes new carb,yes, wont run right.yes throw is backwards. no,it's the right carb. yes,fixed idle. yep, thats the right number. exact same linkage but backwards. i took both apart and they are identical down to the jet size,except the throw/throttle/piece that hooks to the governor. It did operate, just not well. not thinking of the choke. It's an L shaped updraft carb.2 screws and 1 choke lever, 1 butterfly(to governor). top screw=idle.bottom screw=nozzle. big lever on the lower/side = choke.
default governor position=down, and when wanting to rev,or surge, or run full tilt=up.
i readjusted the screws as stated above, pulled, and it started, then wanted to start surging, then started to over rev. i held the throttle lever down,tweaked the nozzle screw, and it smoothed right out, best it's ever ran. ran that way for about 20 minutes (with the old coil/points hanging from it to hold it down)twice. pretty smooth(maybe 5 misses per minute) and at correct idle/running rpm's. so i guess the butterfly needs to be closed when running right, which would be how the older carb would of worked. So, i should be able to either reverse the new one, or put the old one on. should all be good then, right?
 
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Old 09-11-06, 07:41 PM
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If the throttle is reversed, then something is definitely not right. Either the old carb was wrong, or the new one is wrong. Sounds like the governor may be trying to throttle it down by it's motion when it is actually revving it up. The throttle should be wide open with the engine off, and nearly closed when the engine is running. Does it open with the engine off?
 
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Old 09-11-06, 08:40 PM
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ok, first, i don't know if this engine was original to the generator or not. The only connection it has ever had is where the governor link rod connects to the throttle shaft. on the old carb, it was on the left, and apparently did as you say, open when off, then the governor would close it when running. On the new one, the connection on the shaft to the governor link rod is on the right, so it opens it when running. If i keep it closed manually, it runs fine. I would think if i put it so the shaft is on the left (like the old one) it should work like it's supposed to.
 
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Old 09-12-06, 06:59 AM
Azis
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According to the numbers you posted and the parts listing from briggs, this carb does not have a fixed idle.
It may be possible to reverse the shaft however the butterfly is meant to go only one way. Since there is a idle mixture valve, there should be a seperate idle circuit within the carb. Even if the idle circuit is not used in your application I would sumise that the butterfly valve is still cut to fit the throat only one way. If the butterfly valve is closed to its stop when you are able to make it run fine, then I would think you may be running off of the idle circuit. When running on the main circuit the butterfly should be noticably open some.
I vaguely remember something similar about trying to reverse a shaft but cannot recall for sure, being so, I don't think it was able to be done.
 
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Old 09-12-06, 04:11 PM
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well, i spun the piece on the valve that attaches to the governor linkage, and hooked it up. started on first pull, and operates like the old one did. the butterfly valve stayed the same and had same orientation as the old one. the governor seems to be controlling the rpm's, and i can rev it by hand if i want (until the governor try's to take back over). It seems to be running a little fast, but i am no expert on what it should sound like at 3600 rpm's. i'm used to a much slower idle, not having it hold at a certain rpm. The governor has available motion either way, up or down, which is why i say it's controlling the rpm's.If i start messing with the nozzle screw, the governor trys to take over one way or the other. It does seem to be running hot (like with old carb) compared to when i had it linked the other way, but thats probably ok too. Any idea on what the fuel consumption should be at this rpm? I could probably make an mp3 sound file of it running from about 15-20 feet away if you wanted to hear it. Anyway, unless there is something else I should do or know or check, I really do appreciate the help!!
 
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Old 09-12-06, 09:12 PM
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The rpm needs to be set so that the generator is producing 60 hertz. A "shadetree" way of setting this is to get an old clock. A non-digital, motor driven clock. Crank the generator and plug in the clock. Time it with an accurate watch or clock. Adjust the rpm of the generator until the analog clock is in time to the second with your watch. From what I'm told, this is a fairly accurate way of setting up the generator without using more specialized equipment.
 
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Old 09-13-06, 05:54 PM
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thats a pretty cool idea. of course my multimeter doesnt have a hz setting. Now if i can only find an old analog clock!
 
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