Help With Power Valve Filling with fuel

[rhinosoft]

HI All,

over the last few months I have been dialling in my 445 build in my Thunderbird. All going well but having an issue with the carburetor.

The problem is if I leave car for a week or so and start it up, it blows black smoke until it warms up. Then when I start it hot after a few hours it spits fuel out of the exhaust. Other than that the engine is running well, carb setup with air flow meter and pulls around 15 lbs of vacuum at idle.

I noticed at initial startup that the car blew black smoke and I replaced the power valve (6.5) with a new one and all seemed ok. When I pulled the old valve out I noted the well behind the power valve was flooded with fuel.

This week it happened again, smoke at startup so I checked the power valve again. Yes, the well was full of fuel again. If you click on the image below it should zoom in to an image of the metering plate. This is the best image I could get but it seems to have a lot of hairline cracks in the area between the two jets.

Has anyone seen this before and could it be the cause of the fuel flow into the well? Any thoughts will be greatly appreciated.

The carb is a Quickfuel 780 vac secondary.

Thanks
Graeme

[machoneman]

Yep, it seems the bowl area has cracks and what appears to be a small hole too. I'd get a replacement from QF or if it's new, ask for a freebie for a faulty part. Mention you'll ship it back if they want to see it. I'd also not fool with trying to fix it. 

[My427stang]

I have never seen that, but it doesn't look normal, and looks like it could be the cause

Be careful when you get the new metering block to not overtighten the PV.  They need to be tight, but the 1 inch wrench used to tighten them can cause some damage of really pulled on

[fekbmax]

Quick fuels quality has seemed to suffer some since Holley got involved.

[cjshaker]

To me, those look like normal 'chatter' marks that you get when using a sub-par cutting bit or not using lubricant while cutting or drilling. I don't see how those would let fuel in, but I agree that it isn't normal. Do they extend underneath the gasket? If so, I could definitely see fuel getting past them then.

[rhinosoft]

Thanks for the feedback guys.

I have contacted the supplier of the QuickFuel carburettors and they are happy to check it out for me on a flow bench I think.  They reckon the marks/cracks are casting/machining marks and are normal but lets see.

Will give you an update once things are clear, it has to go somewhere here in Australia.


Graeme

[chris401]

Thanks for the feedback guys.

I have contacted the supplier of the QuickFuel carburettors and they are happy to check it out for me on a flow bench I think.  They reckon the marks/cracks are casting/machining marks and are normal but lets see.

Will give you an update once things are clear, it has to go somewhere here in Australia.


Graeme

The tedious part of some diagnosis is recreating the conditions the failures happen in. You may need a heat soak and slow cool down to get the carb to leak.

[Falcon67]

You can do that with a hair dryer or HF heat gun.  Set the carb on a coffee can, use a turkey baster to put fuel in the bowls, then heat the base plate/metering blocks if necessary.  Usually power valve leaks will show up pretty quick as fuel dripping out the vacuum port for the PV in the base plate.

[My427stang]

You can do that with a hair dryer or HF heat gun.  Set the carb on a coffee can, use a turkey baster to put fuel in the bowls, then heat the base plate/metering blocks if necessary.  Usually power valve leaks will show up pretty quick as fuel dripping out the vacuum port for the PV in the base plate.

Gutsy move

[rhinosoft]

Hi Guys,

got my carburetor back from the QF technicians, what they said is below, not sure where to go now except do as they say? 

Graeme

Tested P/valve in the carby was ok
 
Block was ok no cracks casting lines
 
There  is all ways fuel in the p/v restrictor well area   

Put new gaskets & reassembled unit
 
Had carby on test bench for two days no leaks
 
Nothing out the p/v hole in the base plate were this is drilled thru into body   / p/v sits
 
Customer may need to change p/v restrictor size, P/valve size

Work with the squirter shot size 
 
 
regards
QF Support