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Carb "backwash?"

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19_again

19_again

Jedi Warrior
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Carb "backwash?"

The last two times I went out, I came upon a good straight, safe (as in no radar) stretch and aired the B out. At top speed I would let off the gas for a second or two and when re-applying the gas it seemed as if the car was actually bogging down a little, as if the application of more fuel was creating a drag. Don't know how else to explain it short of thinking that I had suddenly hit resistance. A second later everything seemed fine and no further issues. This happened twice, anyone else have this experience or an idea what it might be? Clutch not slipping, plenty of power overall.
Thanks,
Mike
 
Re: Carb "backwash?"

Standard carbs? Pistons fall with the "clunk" when released? Proper oil level in dampers? Float level?

Really, I've not a clue without bein' there.

Weird li'l problem there, Mike.
 
Re: Carb "backwash?"

HS4's aud 315 , floats and bowls are fine having just gone through them 2 months ago. Pistons fall nicely, but your question about damper level prompts another. I've always been curious about the 1 inch below the top of the damper barrel measurement, as the barrel narrows it's kinda hard to measure it, so my plan is to mark the shaft on the carb dipstick at one inch from the bottom and when the dipstick is inserted into the chamber and hits the resistance of the oil, that should be at the one inch mark on the dipstick, no? Given that the "float" on the end of the dipstick rides up and down a little, I'd err on the side of caution and not account for that.
PS did you get that pm on your b'day?
 
Re: Carb "backwash?"

Possibly the high vacuum created at closed throttle sucked a bunch of gas into the combustion chambers thereby causing an extremely rich mixture that had to be blown out. Dampers low on oil come to mind first... by pass valve inoperative does too.
 
Re: Carb "backwash?"

Sherman said:
Possibly the high vacuum created at closed throttle sucked a bunch of gas into the combustion chambers thereby causing an extremely rich mixture that had to be blown out. Dampers low on oil come to mind first... by pass valve inoperative does too.
Click to expand...

The high vacuum is downstream of the carb pistons, so there'd be no extra-rich mixture.

My guess is the piston return springs are too strong,or the damper oil too heavy, resulting in an overrich mixture when the throttles are opened again.
 
Re: Carb "backwash?"

Well as I was checking the damper oil level, I found that one of the bolts holding the rear air filter on was loose, nut was gone in fact. Further inspectio showed the vacuum hose not even connected, I must have jarred it loose when timing it last weekend. Rescrewed and connected everything, took a half mile test drive and sure feels better with the vacuum attached. Also filled the dampers to 1 inch below top of dash pot, or just to top of lower chamber...below the dipstick threads. We'll have to see what happens on next drive, but i went about 150 miles yesterday with no other problems than the aforementioned bogging down so I think the vacuum issue is brand new.
 
Re: Carb "backwash?"

Sounds like you've solved it! The oil in the chambers should be in the piston slide, not above it. No big deal if it gets a bit more as it'll be hauled down the slide and sucked into the intake. *POOF!* "Self-leveling" :smirk:

You don't really have a bypass valve so don't fret over that.

19_again said:
PS did you get that pm on your b'day?
Click to expand...

Yes I did and I apologise for not thankin' you!
 
Re: Carb "backwash?"

That was a brain fart! I had Zenith brain again! "The Quality goes in before the name goes on!".... Oh... that was TV sets!
 
Re: Carb "backwash?"

If you ever get the chance, watch the HC and CO levels change dramatically for the richer during de-cel mode with these and other carburetors whilst an exhaust analyzer is hooked up. With the CD or VV type, a hanging slide/piston will cause excessive richness/smoke.
 
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