Carb needle valve hints?

[Rich_G_SC]

Hi, hoping someone may have some advice. I have regular issues with the carb fuel needle valves either sticking open or closed. I change them out, blow compressed air thru them etc but it seems every few weekends the problems crop back up and I lose a session. I recently missed race 2 of the Driverz Cup event at Road Atlanta, no fun.

Anyone have advice? Maybe I just need to pull it out and blow air thru it before every weekend? I run AvGas if that makes a difference.

Thanks in advance!

[FVRacer21]

Rich,

Are you running a filter?

Even a small piece if fuel cell foam will find the needle and seat.

I have been running an EMGO cleanable metal filter in the line going to the pump. It seems to flow enough not to be a restriction and keeps things out of the pump also. When I had a cell going bad I had to clean it every heat but got me through a few races.

There are larger ones with AN fittings but I stay away from the clear plastic ones. They work in an emergency, but I prefer metal - even if you had to buy some generic at the local auto part stores.

ChrisZ

https://www.summitracing.com/parts/emg-14-34472 (use hose clamps not the ones supplied) also comes in 5/16 size, other colors

[DannyPip]

Do you know or can you determine your fuel pressure? It is entirely possible that overpressure is blowing fuel past the float valve.

I'm not 100% sure exactly what is recommended for the 28 PCI Solex. I do know that Solex carbs 30PICT and up recommend no more than 1.5 psi. It is the same float valve, isn't it?

I need to check mine, I think I have the same issue.

I stacked a bunch of gaskets under the pump to drop the pressure on a dual Solex 35 setup for a customer of mine.

[BLS]

Rich, the fuel shouldn't make any difference. I'm assuming from your description that you have replaced the needle valve and still have the same issue.

The response (ChrisZ) regarding a filter is a likely issue. 2nd, what float are you running? The standard float can cause issues, but it will be on the track usually, and IIRC, fuel starvation in right hand turns.

When I was actively racing I used the clear plastic filters and just replaced them often.

[FVRacer21]

I'm not 100% sure exactly what is recommended for the 28 PCI Solex. I do know that Solex carbs 30PICT and up recommend no more than 1.5 psi. It is the same float valve, isn't it?

I had a problem at New Hampshire and traced it down to a bad fuel pump.

I was only running 2 psi deadheading the pump and less than 2 with a Tee.

Dave Car says anything less than 3 and the pump will not keep the carb full.

Now I changed it and ended up with around 5. This is more than people normally run with a street car, but think of the amount of fuel we flow while racing. I think it will drop down - I am am interested in checking it after Thompson.

I have read bad things about pressure regulators, so the gasket fix it the way to go, but err on the high side.

ChrisZ

[Rich_G_SC]

Thanks all for the replies!

I do have an inline cylindric aluminum body fuel filter. I've had it open a few times to check for clogging and will do so again, may be time for a new one.

I have never checked fuel pressure, that would be something new to look at. I will say that, when things are clear, I have no issues with fuel delivery so hopefully I'm OK. Our group doesn't do fuel testing so I took the sampling T out of the setup - its straight fuel line from the pump to the carb (filter is pre-pump).

Float is black plastic with the weight epoxied to the bottom. Again, haven't had any on-track issues with fuel cutout on corners thankfully.

Every time I've had an issue it is in the paddock not being able to start. Either too much fuel flooding the carb or none coming through. Perhaps replacing that filter will help.

Thanks again,
Rich

[BLS]

"Float is black plastic with the weight epoxied to the bottom. "

That should be fine.

I'd guess contamination, but since you have a filter that seems unlikely to cause excess gas (flooding). Unless the filter is damaged and allowing stuff to pass through. Make sure the fuel passage itself isn't corroded. Could be corrosion breaking loose and keeping the needle valve from opening/closing. That would seem to cure itself over time though.

Just so we're clear - sometimes it will not start and no gas is available in the bowl and sometimes it is flooded with gas coming out the bowl vent tube?