Briggs 5hp throttle hunting HELP!!!!!!!!!!

[Cotmullion]

OK, I briefly got my 5hp working fine but now the engine has recently began hunting and running irratically. Basically, you start it on full choke and it starts after 2 or 3 pulls which is fine, but it runs too fast (although that might be because the idle screw is wound all the way in). When you leave it to warm up and change the choke it cuts out. If you give it any throttle it conks out, or it speeds up a bit but not to WOT speed, and then bogs, then speeds up, then bogs.

I have got the mixture screwed 1.5 turns out, I have replaced the head gasket, the diaphragm, the tank gasket and the fuel, but still no improvement. I have checked the governer inside and no teeth are missing on the nylon gear either. Oh, and I have cleaned every orrifice I can get to in the carb including the pickup tubes more times than I can count!!

Now, my suspicions are that I might have warped the diaphragm somewhere when taking the carb apart all those times. Or that I have to adjust the governer arm, or something to do with the goverener, since that is about all it can be besides the carb and spark (I/C ignition upgraded :wink.

What else could cause all this? I am thick so I could be missing something really obvious, so fire away. :shrug:

Below are some pictures of my setup and the bike as a whole, just to give you an idea of what I'm dealing with. The throttle is my own design as you can see. It is a bit rough I know, but the engine worked fine with this same setup before it started misbehaving , so it isn't that. One final thing: there is no governer spring, only the spring shown between the cowl and the throttle on the carb.

Please help! I have been racking my brains and psent hours trying to get the SOB to run right, and I'm all out of ideas :freakout:

 

[The Restore Kid]

If the governor is all setup and working and the motor is surging.. The whole situation sounds like your fuel mixture isn't right.. You can't just screw out your screw 1.5 turns and call it good.. That is just a basic rough starting point.. It sounds like it might be rich.. Does it blow black smoke when it chugs way down then farts back to life?

I like to put my fingers right directly on the throttle shaft of the carburetor when adjusting them.. That way I can eliminate any surging at all, and can hold an exact amount of rpms right to the billionth, ya know? :shrug: That takes all of the guess work out of it... :laugh: And I usually don't have an air filter on em to begin with.. Especially on that carb because you can't do anything with an air filter on it.. :laugh:

But it sounds like it's probably too rich, to me.. It probably wants the fuel screw to be screwed in like 1/8 or 1/4 of a turn... Also, that idle screw that ya mentioned screwed ALL THE WAY in... Those things like to be screwed WAY in, :doah: But not QUITE all the way.. :laugh: So I'd back that off so it's like 3/4 of the way screwed in... Because you don't want the engine to run too fast and not be able to shut it down.... hmy: It's better the engine idles too low and dies, than runs too fast until it dies :hang:

But, about the best you can hope for on those carbs, is get the thing running, and keep it running manualy by hand with one hand, then adjust your fuel mixture screw with the other hand, until it smooths out and sounds good.. :thumbsup: Then adjust your (idle speed) to where the fuel mixture is right..

Using the choke will probably be a bitch with only two hands... So I just leave the choke off, put my hand over the opening in the carb, and roll the engine over once, so I know it's sucked full of fuel, (hand choke method ) then just let it breathe normally and try starting it until it pops and starts..

It'll probably take 1/2 dozen attempts to figure out how far the throttle needs to be open to sustain a run... Best thing ya can do is hand choke the motor, pull until it pops, THEN REALLY QUICKLY grab the throttle and crack it wide open, or 3/4 open or so... :laugh:

That way the engine has a big mouth full of fuel from being hand choked, then allowed to suck as much air as it wants, to be able to burn off all of the fuel... and it should be able to spark to life...

When ya here it pop, throttle it up until sounds like it's trying to run too fast, then let the throttle back off to somewhere around an idle speed.... As if YOU are the governor..

And you should be able to get your motor to respond to you fingers, ya know? :shrug: Twist the throttle open, the engine accelerates until it explodes, or twist it back shut and the engine dies from a lack of air....

Those carbs are kinda junk as far as performance, so you will never make the engine idle down super low and keep on running, THEN take off and go wide open crazy high rpms, all in one setting... It just doesn't work that way..

If you have the fuel screw so lean that you can run the engine until it explodes, it won't pull fuel at an idle and won't idle... :doah: OR if it's nice and rich so the engine starts easy as hell and idles real good... When the engine gets to a high rpm is starts chugging and farting because theres too much fuel for it to burn off efficiently.. :glare:

So you want a somewhere in the middle......

Hold your throttle in your fingers, and get a nice continuous sustained run.. where you can keep it running all day long..... Then slowwwwwwwl y starting increasing the engines running speed... If it speeds up and speeds up and speeds up, you are probably good.. If you try to open the throttle and it just falls flat on it's face and dies.. It is too lean and wants more fuel.. If you open the throttle and it's trying to accelerate, but stumbles and chugs, it's too rich..... :hammer:

You want the fuel set, to a point where you can throttle the engine up easily, and it revs right up vroom vrooom, then you are able to let back off and stop at point where the engine is running a nice sustained idle kind of speed....

when you have your fuel set to that, you can screw your idle speed screw back in to hold the very lowest idle point to that speed..

THEN when you put the air filter back on, it's gonna suck a lot more fuel and you will have to adjust your fuel screw again.. :laugh:

But it should be an easy enough slowwwwly screw it in just a little bit, until your idle comes back to a nice sustained idle speed where you had it idling before adding the air filter, and you should be about good to go...

You will cometo find when ya mash the gas pedal down it'll hesitate some, or get up to speed and ya can't get those real high strong running rpms at top speed... So ya end up leaning the fuel back out just a fraction...

Or it doesn't like to just start and run good.. So ya richen it up just a tad....

You'll probably fine tune and tweak it some at first... Then from time to time even..

But thats basically how ya do one of those junk carbs.. :glare: Get from a decent idle speed to a decent high end speed ( a full range) on you fuel mixture screw.. Then adjust your idle speed to keep a sustained speed for infinity if need be.... Add air filter... adjust again, try to drive down the road.. adjust again.. :laugh:

 

[buckeye]

I sure the hell miss that stuff right there!

 

[Cotmullion]

Good grief, that must have taken you ages to write. Thanks alot :thumbsup:

I'll see what I can do, hope it works...

 

[The Restore Kid]

Whats time to a dog? :laugh:

 

[Square_Chopper]

Man, I always feel like I just walked out of a labotomy after reading a TRK post.

ut: ut: ut: :thumbsup:

 

[bandit 40]

Man, I always feel like I just walked out of a labotomy after reading a TRK post.

ut: ut: ut: :thumbsup:

For sure :laugh:

 

[Cotmullion]

One more thing to throw into the mix: Will advanced or retarded laugh timing cause the problem?

 

[The Restore Kid]

Probably not.. Advanced will cause it to race and wanna run fast all the time.. Retarded will make it chug and backfire and not wanna go.. It's pretty hard to get one out of time though.. Unless your flywheel key sheared then wedged itself close to where it belongs..

 

[Cotmullion]

My key did shear, but I replaced it with a filed down woodruff key the same size

 

[Miniwood]

I would keep it simple:
Start with the diaphragm carb spray can warp them and make sure its seated Correctly.
Also my 5.5 will not run well without the filter and air assembly on the engine.
Lastly, to see if its a fuel issue thake the air assembly off and have a cup of fuel. While the engine is running try to poor in some fuel and throttle to rev the engine; it wont be perfect but if the engine revs up then you know it's a fuel issuue.

 

[Tom S.]

One more thing to throw into the mix: Will advanced or retarded laugh timing cause the problem?

My buddy's motorcycle engine blew up during a race. Afterward, he said "I was up all night putting it together. I think the cam timing is about 6 beers retarded". :laugh:

 

[Miniwood]

Re read your post. Sounds like your govenor arm, govenor spring assembly.

 

[Cotmullion]

I have no governer spring as such, just the top spring you see pictured from the cowl to the throttle arm

 

[The Restore Kid]

OH wow did you never get this figured out?

Yeah you need a governor spring... On that motor it's a real small one. Like a centimeter long, centimeter squared or so.. It's goes between your governor arm, and the throttle piece on your gas tank, where the cable attaches..

If you don't have all of that stuff, you can attach the cable right to the carburetor, and rig it to directly to the throttle plate at the carb... But that will eliminate your governor, and you will have to manage the engines rpms manually..

 

[Cotmullion]

That, Mr Restore Kid, turns out to have been my problem all along!!!! :facepalm:

I wanted to run a governer, but it was being overrode by the throttle return spring (the same as the governer one you mentioned, but over stretched, so I have ordered a new one for undertank use). I am going to now run the throttle under the tank as stock, just waiting on parts.

Well, at least the carb is clean now and the gaskets have been replaced :001_rolleyes:

 

[bandit 40]

That, Mr Restore Kid, turns out to have been my problem all along!!!! :facepalm:

I wanted to run a governer, but it was being overrode by the throttle return spring (the same as the governer one you mentioned, but over stretched, so I have ordered a new one for undertank use). I am going to now run the throttle under the tank as stock, just waiting on parts.

Well, at least the carb is clean now and the gaskets have been replaced :001_rolleyes:

Glad you got her going:thumbsup:

 

[Miniwood]

Is there a little crome tab with a notck in it for your throttle return spring(with a screw holding it to the carb) .
On mine it very sensitive and must be perfect. Along with the govenor spring.

I actually set my motor up with a new return spring. Then i played with several windvain govenor springs.
I ended up with a nice govenor spring that was stiffer/ stronger than the factory spring. You have to get the govenor spring just the perfect length or it will over- ride the throttle return spring;;; and end up with the mess you had.

Now ( with the stiffer gov. Spring) i am hitting the perfect top end RPMs and speed that i wanted.
I made sure i was not overrevung the engine and i have the supporting engine mods.