# Briggs & Stratton 6.75HP Won't Run Without Continuously Pumping Primer



## cordy74

I have a Briggs 6.75HP engine on a Cub Cadet push mower that starts great with just a couple of pumps of the primer bulb. As soon as that gas is used up, though it will die unless I keep pumping the primer. It will stay running until I stop pumping the primer.

I have pulled the carb off, cleaned it up and hit it with some compressed air to get all the grit out. I then replaced the needle & seat, float pin, engine-side o-ring and intake-side gasket but the engine still behaves the same.

I even took a carb off another engine I had sitting around and I get the exact same thing. 

I'm kind of at a loss at this point. I can't imagine both carbs would have the exact same problem so I'm left wondering if there is something outside the carb that I'm missing.

The engine is a 125K02-0243-E1.

Any help is greatly appreciated.


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## mikeinri

Is there a fuel screen or filter, maybe in the gas tank or somewhere in line (upstream of the carb? You may have a blockage. Also, can't hurt to check the condition (or just replace) the fuel line(s).

Mike


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## cordy74

Mike - Thanks for the response. I can check the fuel line but I'm pretty sure the carb isn't starving. If I pull the bowl off the bottom while it is connected to the line the gas will just pour right out of it. This thing is really starting to tick me off.

As I said, it runs great when I pump the primer. It's almost as if the main jet is still blocked but and it isn't drawing any fuel up from the bowl. But as I was blowing air through all the ports I could feel it coming out elsewhere in the carb. I know this should be a simple fix but it is escaping me.

I also pulled and checked the primer bulb. The bulb is in great condition; still very flexible with no signs of dry rot. The screen behind the bulb is also clear of debris. Since the engine will run while I pump the primer or spray starter fluid into the intake but dies when I stop it just seems like there is an air leak on the bowl which is preventing it from getting the vacuum it needs to draw fuel up through the main jet. I replaced the bowl gasket when I rebuilt the carb and as I said before, the other carb I tried is acting the exact same way. 

When I get home tonight I'm going to try running it without the gas cap on to see if the vent holes are plugged (I don't have much hope in that solution though) and I'm going to try a different spark plug.

Any other thoughts on this thing?


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## cordy74

PROBLEM SOLVED! After I don't know how many hours I finally figured this pesky thing out.

I knew the carb had to be clean after everything I did to it but it would only run as I was pumping the primer and injecting a LOT more gas into the intake. That started me thinking that it was sucking in extra air somewhere between the carb and the intake valve. I started by taking the carb off again as well as the carb mounting plate. this left a plastic tube sticking out the side of the engine. I took the coil off so I could access the tube (which is labeled Intake Manifold in the IPL). The Intake Manifold is a one-piece molded plastic contraption that bolts to the block at the intake valve. Once I loosened the two screws holding the manifold on I removed it and saw a torn gasket beneath it. I also noticed that the gasket was not even remotely the same shape as either the manifold or the block mating surfaces. when the manifold was installed it left a rather sizable opening into the block. This was the source of my extra air. Just to make sure I made myself a quick gasket out of some thin carboard I had sitting around, put the whole mess back together and PRESTO!! It starts on the first pull and runs like a champ.


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## Basementgeek

Glad you got it figured out. I am not sure how long cardboard is going to last.

BG


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## cordy74

I'm going to try to pick up the actual gasket this week. My main reason for making one out of cardboard was that I thought I finally found the problem but didn't want to take the time to run to the parts store to pick up a gasket until I was sure it would run. I was on the verge of just pitching the whole thing in a pond at that point.


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## mikeinri

Way to persvere through that! Not sure that I would have had so much patience, although I have been known to get my Irish up and not let the machines win (this is not always cost-effective...).
Mike


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## BPezdek

A million thanks for your post Cordy! It would have been a really long time (never) before I would have looked to an intake manifold air leak as being the cause of my problem! I too, was ready to chuck the rascal of a mower in the nearest pond but it now starts and continues running on first pull! Thanks again!


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