Spitting Fuel Out Of Cylinder During Compression Test

So I recently started working on a 62' CJ5. I disabled the ignition, took out all of the spark plugs to do a compression test, and when I cranked the engine over white mist and fuel droplets sprayed out of the number 3 cylinder. In addition the spark plug was "wet" with fuel when pulled. The compression test was good on all cylinders.

I originally wanted to do a compression test because I am getting very low power. What do you guys think is causing this fuel spitting out of the plug hole?

 

Are you sure it was 100% fuel? A bad head gasket may have let pressurized coolant into that cylinder overnight, and might explain the low power.

 

Welcome.

 

If you got a leaky carb or fuel is getting past (or overflowing) the float bowl, you can bet it’s gonna fill one or more cylinders. I guess in this case the route to number 3 cylinder was the path of least resistance.

He doesn’t waste any time with introductions—-just hits the ground runnin’

 

Good thing a plug wasn’t grounded near by. Ask me how I know

 

I would pressurize the radiator to about 7 lbs for a few minutes and run the test again and see if you still have moisture. Block the throttle wide open and with the plugs out you wont have any vacuum in the cylinders so cover the carb. Welcome

 

Thank you all for your kind and helpful replies. I wanted to give everyone an update as there is nothing worse than finding a thread asking your exact question with no follow up solution.

I did some more investigating and it turns out the previous owner installed an electronic fuel pump. This pump is unregulated and apparently much too strong because fuel is overcoming the float and shooting out of the top of the carburetor (where the arrow is pointing in the attached pic). I'm not entirely sure what this outlet is for yet but I know fuel shouldn't be shooting out of it when the key is at half turn and the engine isn't running.



I have purchased a fuel pressure regulator and pressure gauge and when they come in I'll set the pressure to what the service manual I have recommends (2.5-3.75 psi at 1800rpm 16" above the outlet of the pump).

I've also purchased a fuel pump block off plate because the previous owner left the old mechanical fuel pump on and it's leaking oil everywhere. I was thinking of installing a replacement mechanical pump but I'm not sure why it was switched to electric and I don't want to find out that there is some reason a mechanical pump won't work after going through the trouble to install a new one.

I'll post another update when I get all this installed to let you know if it's solved the problem.

 

That’s the bowl vent the float and ou needle may need looking at.

 

If this engine was running open to the elements, you're going to need to change the oil and filter. I would have just bought a stock fuel pump and avoided the regulator and the block of plate. That much raw unburnt fuel running into your engine can cause damage.

This is one of those times where a picture would have probably shown us what you need to fix. Good luck with your project.

 

Me too. Although a regulator can be beneficial on jeeps used in rough country. The carb float valve in a Carter YF is sensitive to over-pressure, especially on steep slopes, and has a special smaller orifice when used on Jeeps. But many carb rebuilders neglect to install the right one.

 

I may have experienced this problem many years ago. My YF on my Fhead was not in great shape and really just worn out.. It also didnt help that when I bought the heap someone had tried to smash spark plugs, dirt and other garbage into it...

 

This. If the float is bad or the needle worn, the float bowl will overfill and pour out of the tube in your picture. This can also happen as you mentioned where the float and needle are fine, but the fuel pump is pushing more pressure than they can hold. I think you are on the right track, regulate it to proper psi and see if that resolves the issue.

One concern with the mechanical pump is that if the eccentric that drives the pump is worn, a new mechanical pump will still perform poorly. I'm not an F-head guy though, but that is common on the Dauntless V6 models. When you pull the mechanical pump, you should be able to peek in there and see the condition of the eccentric.

 

my thought as well...installing an electric pump is way less expensive than a camshaft...if theres no other reason to tear into the engine why not...

 

This is also a reasonably priced option for a low pressure electric fuel pump (2-3.5 psi) you can run without a regulator...

https://www.summitracing.com/parts/mrg-42s/overview/model/mr

 

Thanks for all of the suggestions. I installed a fuel pressure regulator however fuel still came out the top of the bowl. So I ordered a new float and a carb rebuild kit from rock auto. However upon inspection of the kit it doesn't appear that there is a spring for the needle. In the manual and various instructions I keep reading about this mysterious spring that is supposed to be involved in the float needle assembly but there is not one in the carb now and it doesn't seem that there is one in the rebuild kit.

Does anyone have any insight into whether the spring was phased out in the modern rebuild kits or if perhaps I bought the wrong kit?

Thanks everyone.

 

Get a correct Jeep carb kit from "Mikes." You need the smaller orifice inlet seat with the spring-loaded needle. And set the correct float height for that needle.

Recently discussed at length on another thread here.

 

Just wanted to give an update on this because there is nothing worse than finding a thread with your exact problem and no resolution. I rebuilt the carb and the problem was still there. Turns out I didn't clean where the fuel inlet jet/seat screws into the top part of the bowl. Once I cleaned that up nice the flooding issue went away.

One thing that is interesting is that I don't think the carburetor is the original. The stamped number is 3200S. Mikes kit (this one) came with the needle and seat I needed to get the correct float height. The needle that came with a spring would not work with this carburetor.

All said and done it runs very well now but its pouring blue smoke out on acceleration. I'll make another thread for that here.