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I chased down a squealing distributor once. It acted just like what you're experiencing. Thought it was the generator also, but was a nearly frozen dist shaft. Just a thought.
I use starting fluid to locate vacuum leaks. Spray some around the likely places and see if it affects the engine idle.
I have had a screaming vacuum leak on the Holley / Ford 94 type carburetors. I first assumed it was the back bushing in the generator. I leaned over and rested my hand on the front of the air cleaner and the screaming went away. Turns out the bolt that goes up from the base into the center section of the carburetor was loose and a noisy vacuum leak was created between the base and center section. Careful if you tighten that bolt, it threads into pot metal.
Worth it to run the truck til it's warm & spray some carb cleaner to try & ponpoint the leak? Or just pull the carb, replace the base gasket & check everything else on the carb?
I like to diagnose the issue. You can use any hydrocarbon that will change the running of the motor, starting fluid, carb cleaner, etc. If you don't know for sure where a problem is then you can't be sure you fixed it.
I use a stethoscope with no end in it. Much easier to pinpoint and no spraying explosives around
I second this! I don't like squirting flammable stuff around running engines, even if the sparky bits are far away. Though, an unlit plumbing torch is not going to cause a problem if it ignites, as long as it's not pointed at something important (and you're working with good ventilation)....
When I was young(er) and stupid(er) I nearly lit my arm on fire searching for a vacuum leak on my 92 Oldsmobile with carb cleaner. It was a hot, humid, still evening and I think I got too close to the coil packs...
Oh, I'm still not above a little B-12 carb clean used judiciously through the red straw. I have found over the years that the fan will blow the stuff around and may be hard to pinpoint. With the stethoscope there is no problem fining even the smallest air leak.
No need to worry about the new cable if the transmission is reasonably clean inside and running free. The speedo gear is not a solid connection to the tail shaft, rather it is turned by a "lack of resistance". On the 4-speed crash box the speedo gear is an un-splined fit over the tail shaft and the brake drum flange pushes it against bearing #7065 by way of tightening nut 351165 at the back. When the rear of the trans is all assembled I can rotate the speedo gear with my finger. I thought mine must certainly be broken until I looked into it a bit and realized that it is by design. It's wedged just tight enough to overcome the typical resistance of the speedometer assembly, and the accuracy of the speedo can be adjusted using the spring in the dash cluster. If the speedo is jammed up, the gear in the transmission should be stopped without much ill effect (especially at low speed).
I had a lot of trouble wrapping my head around that... but my speedometer works fine.
Ok so I noticed that same thing with my gear when I rebuilt the transmission but the odd thing is that now my speedometer is way off and varies a lot depending upon the speed I am going. I located another speedo head and plant to install that in hopes of fixing the problem but.....
There is a little friction/spring/tab adjustment in the speedometer head to increase or decrease the resistance on the cable. If reading way high and bouncing around, more friction is needed, if reading too low and not spinning up until going 10 MPH or so, less friction needed. It's a PITA to adjust... I finally put my cluster on the seat next to me and drove around until it seemed right and was comparable to the GPS.
^ Good to know. In the short test drive the other weekend, the speedo didn't move, tho it turned via the busted end of the old cable in the back of the speedo. Perhaps adjustment is necessary... I don't think I went over 5-7 MPH.
UPDATE :: Took carb off and that upsidedown bolt was loose- like hanging down 1/8-in. I didn't leave it like that- must've vibrated loose. Looked at it carefullly & some of the threads at the 'top' of the hole were stripped out. Not sure this is the best thing to do, but I eliminated the lockwasher, carefully cleaned the threads and chased the hole, and reinstalled the screw until tight. Checked every other assembly screw- all good. Checked the carb base & intake for cleanliness & level- good. Replaced base gasket with new and tightened everything down. Nothing appears to be amiss visually. Truck idles beautifully and there's no change in idle after the whistling starts.
Tested again: after 7 mins of idling, the carb started whistling again. Pushed the (small aftermarket) air cleanerback & forth and the note changed very slightly. Going to try the 'red straw carb cleaner' approach next. Perhaps the next gasket up from the base gasket?
QUESTION: I assume the carb whistle has to be either at the height of the butterflys or 'south' of that, where the vacuum is negative. 'North' of the butterflys- isn't it a lot closer to atmospheric pressure?
The upside down bolt isn't holding tight enough, that gasket is your whistle. Try replacing the bolt with a stud so you get bite on any threads left. If that doesn't do it then JB Weld the stud in (you have nothing to lose at that point) or you need a different center section casting.
Also check how bowed all your gasket surfaces are. You can lap the pot metal on a flat (like plate glass flat) surface with wet / dry paper on top. Definitely lap the bottom of the center section first if you have to JB Weld the stud in.
07-15-2017, 05:03 PM
