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Old 08-21-2019, 06:47 PM
Sooner89 Sooner89 is offline
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Default Newly question on modified Briggs flathead

I have 5 hp briggs flathead from a generator. I removed the governor, and stock muffler. I replaced the pulse carb with a new one from amazon, and threaded 3/4" pipe with a 45 degree angle making a angled straight pipe. I also installed a cone style air cleaner. I cann't get it to idle under 2500 rpm. It revs great to 5000 rpm but no idle. The idle screw on the side of the pulse carb has to be screwed all the way in to idle at 2500. What am I doing wrong? Is the exhaust too free flowing? Spark plug looks okay.

Help!
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Old 08-21-2019, 06:58 PM
mckutzy mckutzy is offline
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Hello and welcome... lets see some pics of the setup...
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Old 08-21-2019, 10:48 PM
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What he said
Pics are everything on a discussion forum


In general, the screw on the right side of the carburetor (and horizontally oriented) is the mixture screw. Typically it's adjusted 1-1/2 turns from lightly seated.

The screw on the throttle butterfly on the top of the carb is the idle speed. Turn clockwise to increase idle, counterclockwise to lower.


But that's just guesswork. You may have other issues. Aftermarket Briggs carbs aren't very good, that's for sure.

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Old 08-22-2019, 07:17 AM
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Default Update and pictures

The mixing screw is threaded all the way in, as soon as I turn it out any it dies. The idle screw is screwed all the way out to keep it idling at 2500 rpm. Is the exhaust too free flowing? Does this make it run so lean that it won't idle?

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Old 08-22-2019, 07:18 AM
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By the way thanks for the help
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Old 08-22-2019, 07:52 AM
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Ahh yes. You have the type of carb wherein the mixture is fixed and no longer adjustable. I think it’s the last version of a regulated/EPA carburetor (think California).

In other words, the brass screw on the side of the carb is no longer a needle valve, but an emulsion tube.

So your idle screw looks to be turned in all the way (to HIGH IDLE) or all the way up.
If you loosen that screw, are you saying the engine will die or not idle?



Your exhaust should be fine, lots of people add plumbing pipe to replace a ruined muffler.


EDIT: how is your cone filter attached? That looks janky and ghetto rigged at first glance.
EDIT II: why did you weld a restrictive washer to the end of your pipe, man?

---------- Post added at 09:52 AM ---------- Previous post was at 09:42 AM ----------

What happened to the original carburetor?

Something is really wrong with the new carb. It’s like the idle circuit is faulty or clogged up.
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Last edited by Hellion; 08-22-2019 at 07:47 AM. Reason: MORE STUFF
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Old 08-22-2019, 08:07 AM
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spray carb cleaner around it and see if it changes anything. Im betting on a air leak.
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Old 08-22-2019, 08:34 AM
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What is that washer?
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Old 08-22-2019, 08:40 AM
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Yeah Joe, he could be running with a vacuum/air leak around the carburetor.

Typical rule of thumb is to use two gaskets (stacked) where the carb mounts to the gas tank. Tighten every screw down in a cross pattern, like you’re doing wheel lug nuts.
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Old 08-22-2019, 09:14 AM
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Thanks for the comments. I tacked a washer on the end of the pipe to see if the restriction would help. It didn't. I'm taking it off tonight. I still have the old carb. The new carb didn't help so I think I will put the old one back on after soaking it in cleaner. It has a real mixture screw. The engine dies if it open the screw (turn it out, counter clockwise) this was the same on both carbs. Both carbs act the same. The air cleaner is actually sitting on a nice aluminum adapter I bought. I haven't replaced the gasket from the carb to the engine. That might be the whole issue. What do you guys think?
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Old 08-22-2019, 09:55 AM
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Run it and spray a bit of carb clean right where they come together. If the rpm goes up you have a leak.
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Old 08-22-2019, 09:56 AM
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What he said ^
If there’s a vacuum leak, the carb cleaner will get past the gasket, into the carb and into the engine and VROOM, it’ll sound like you gave it some throttle.
DON’T use carb cleaner—it may ruin your newly painted gas tank. Use ether or starting fluid.


Soaking may be not be enough for the old carb; I’d suggest disassembly and poking all the orifices with thin brass or copper wire.

Before you mount a carburetor to the gas tank, it’s a good idea to ensure that the mounting surface is completely flat and clean of old gasket residue. You can reuse new gaskets but old ones usually get ripped to shreds when you disassemble. Like I said, use two of those gaskets regardless—they’re rather thin anyway.

On most of the Pulsa Jet carbs (in my experience), you’re able to adjust the idle really low—if you go too low the engine usually dies because it’s running so slow, just barely ticking over.
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Last edited by Hellion; 08-22-2019 at 10:20 AM. Reason: MORE INFO
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Old 08-22-2019, 10:01 AM
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Wouldn't the gasket to the engine be more important that the gasket to the gas tank? Is there a vacuum or pressure into the gas tank? I did replace the gasket to the tank and cleaned it before I installed it. I will try the carb cleaner on both areas tonight. Again thanks
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Old 08-22-2019, 10:15 AM
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Both gaskets are important, nay crucial to proper operation. It’s just that the carb to fuel tank gasket is more temperamental.

There’s vacuum being created everywhere along the intake side of the engine, the intake port and in and around the carburetor, and some inside the gas tank. Basically every time that piston goes down on the intake stroke. If things aren’t sealed right, you’re going to introduce more air into the fuel mixture than is needed or desired.... in other words, a too-lean condition.

Carb cleaner is harsh on paint. Your choice.
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Old 08-22-2019, 10:22 AM
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I like your throttle setup you have there... Interesting use of the pins and existing bolts...

As additional note.. Is there a full tank of gas....
As I recall these engines like to be full of gas to run properly....
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Old 08-22-2019, 07:41 PM
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Quote:
Originally Posted by Sooner89 View Post
Wouldn't the gasket to the engine be more important that the gasket to the gas tank? Is there a vacuum or pressure into the gas tank? I did replace the gasket to the tank and cleaned it before I installed it. I will try the carb cleaner on both areas tonight. Again thanks
like Hellion said the gasket between carb and tank insures that gas is getting to the carb if not sealed you're running lean and high rpm the gasket between the carb and engine also prevents too much air from getting in preventing a vacuum leak which will cause it to run lean and high rpm.
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Old 08-24-2019, 12:05 PM
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Default Got it!

The combination that worked is the new carb, new gasket between the intake and the engine, then all screws tightened together.

Thanks for all your help

---------- Post added at 01:05 PM ---------- Previous post was at 01:01 PM ----------

It was a leak on the gasket between the engine and the intake. Now it idles at 1500, and revs to 5500.

Thanks
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