Loud Whistle From 94 Carburetor

[WQ59B]

REVIVAL ::
Have a rebuilt 91-99 Ford carb on a stock 59AB flathead/intake. Truck starts, idles & runs well, but have whistling vacuum leak.

3 times now have started the truck cold & timed it. Parked, it takes about 7 minutes for the truck to warm to the point the carb starts whistling, and it's quite noticeable. Wiper port is plugged.

Once the upside-down bolt was loose, turned out the threads there were partially stripped. Epoxied in a stud and used a nut. Checked all surfaces, all gaskets, replaced bottom one twice with new, sprayed exterior with carb cleaner along all seams (no effect), rocked carb by hand (tight- no effect), checked all screws... cannot find the source. If I rev the engine after the whistle starts, it's still there.

Seems logical the whistling is triggered by the heat once it warms up. Why/ where/ how? Prior to that the cab base was sweating & very cool while running. Would a phenolic spacer be prudent?

[51 MERC-CT]

Someone told me once that he used a propane torch to track down a carb. whistle/air leak.
With the engine idling crack open the torch without lighting it.
Pass the torch around the suspected areas of the carb.
If the idle goes up then further pinpointing should lead to the source of the leak.

[Phil Gillespie]

Its possible to get a small vacuum/ pressure gauge as used for checking fuel pressure and air leaks. The vacuum gauge will be a safe method for checking and with a small nozzle on end of flexi hose finding sound not be too hard.
Phil NZ

[WQ59B]

Tried the hose/listening method, and it is difficult. With engine/fan running and the carb so relatively small, there was nothing conclusive heard anywhere around the outside. IMO, a torch gas test would be the same thing- difficult with the fan blowing and even less targeting than carb cleaner shot via a straw. Fuel is running thru a regulator @ 2psi. There is no change in RPM pre- versus post-whistle.

I realize this sort of thing is basically impossible to diagnose remotely, but it's certainly not easy on-scene, either. I'd like to find someone local whose been around flatheads for a few decades...

[Crankster]

Originally Posted by Ralph Moore

I climbed over the engine while he drove, the sound was loudest going down the road about 35 mph.

Say, as long as you're up, why not put a timing light on the damper and make sure the vacuum advance is working OK at highway cruise?

[WQ59B]

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SO this HAS to be related to something heating up if it consistantly takes about 7 mins of run time to happen. The aluminum sections of the carb never get this warm, and I believe the cast base of the carb never got 'hot'- it was sweating & cool for most of that time.

Unless it's the intake that somehow is sucking air, but I've not disturbed that and by looks, no one else has since FoMoCo bolted it down.

If I install a phenolic spacer- that still needs a gasket on both sides, correct? I'm not driving this in really cold weather (no heat anyway)- icing shouldn't be any issue.

Oh- the mechanical fuel pump is still there- I covered all 3 ports while running- no change. Should I plug those ports for any reason?

[revkev6]

since you say you had a stripped out stud, that would be my first place to start. I'm guessing your carb is leaking between the carb flange and the intake. epoxy is nowhere near as strong as metal....

[RalphM]

Originally Posted by Crankster

Say, as long as you're up, why not put a timing light on the damper and make sure the vacuum advance is working OK at highway cruise?

I was going to try that, but I couldn't find a timing light small enough to hold in my teeth!

Reminds me of the guys that drove non stop across the country back in the fifttys I think. They had running boards all around the car and could walk around and fill gas, check the engine. I think they even had a set up where they could change a tire while going down the road.

[WQ59B]

(Partially) stripped threads were at the upside down screw, between the bottom & center sections. I JB Welded a stud into the upper section so the sections tightened down with a nut instead of turning threads in the aluminum.

I've read mention of 'thicker copper' gaskets- where are these available?

[oldredford]

I bet the vacuum was loudest at idle. Goes away when you speed up. Figure that....

[RalphM]

Only ever heard of copper head gaskets, not carb gaskets.

[WQ59B]

Whistle remains when revving motor. Only variable it the truck has to warm up first (7 mins of idling), that's when it starts. One of these clues has to be tell-tale (7 mins, still there when revving)....

[slowforty]

Had anyone mentioned a leak around the Throttle shaft? Did you try spraying WD 40 or carb cleaner around the carb?

[WQ59B]

Sprayed the outside all over- no difference in RPM.

UPDATE :: Took carb off (Ford script 91-99). Tilting it in mid-air and fuel was running out the throttle shaft. This is a 'truck' carb with the manual throttle on the other end of the throttle shaft- that's where it was dripping. I have an 8BA carb, so swapped bases.

Put everything back together, truck ran a good 12 mins with no whistle. Problem now is I lost a really smooth idle- it would not idle without throttle and even then ran rough.

Adjusted mixture screws for some time with not much in the way of results. Can't drive it this way. Any issue in swapping the bases as far as idle quality?

I'm not above sending both out in a box to a reputable rebuilder....

[JSeery]

Looks like time for the rebuild.

[WQ59B]

I did rebuild the carb that was on the truck- cleaned the swapper base but of course there's not much to that. Idled so nicely before, feels like a bit of a sucker punch.

I read someone recommending a carb rebuilder on this board somewhere - anyone recommend anyone?

[JSeery]

There is a big difference between cleaning up a carb and installing new part and having it completely rebuilt. All the surfaces will be squared up and all the rod holes resized, etc. There is NY Charley and Uncle Max. One specializes in 94s, but don't remember which one. A quick search of the Barn should tell you all you need to know.

[flatjack9]

Charlie NY is the man you want to talk to.