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Vintage Why are my SU's doing this?

Thanks for all your suggestions! I'll keep futzing with the carbs, do a comp test and lower my base timing from 16 degrees to 10-12.
My rebuilt head has stock everything so I'm more concerned about valve float at redline than a flat cam lobe, and it's the iPd Isky cam so not a huge amount of lift.
I may also just have to keep running it until the gas is at 100%
The jets slide smoothly and are spring loaded properly in place
 
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Timing helped a teeny bit. Spark is strong. Comp test between 130-160 all cylinders - the gauge spiked but didn't hold, so my rings are toast or all my valves are stuck open a little. Or the gauge is crap, again. Gas flushing continues. So much rusty oily crap that the liquid in the fuel bowls has separated into layers, I keep soaking that up and crank to refill. I refuse to get a new gas tank ☺
 
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^^^This.

The layers you're seeing in the float bowls is water in the fuel. Clean the bowls thoroughly making sure to blow out the jet tubes while lifting the pistons. Then connect an external tank with fresh fuel until you have the tank professionally cleaned. Pump fresh fuel through the lines and pump before connecting them back to the carbs.
 
Thanks guys, I'm learning. I'll have the tank cleaned and blast out the bowls. The gunk stuck both #2 cylinder valves open, they're shut again but it either wrecked 2 cam lobes or both pushrods, though I spin them and they don't seem bent. ��
 
That doesn't seem very likely? But I'm not looking at it first hand, obviously.

Cam lobes can be somewhat fragile on the engines, but not really from just a small amount of running while you're messing with the carbs.
 
It's been run maybe 10-12 hours since I got it running, but yeah I really shouldn't have reused the old lifters. I did break in the cam by running it at part throttle for 20 minutes, and I installed it with the Isky moly lube.
The #2 cylinder intake and exhaust valves were stuck, same as last time, they came back up but they must have jammed on the way down. Those two pushrods are new/thicker. At least one valve on each cylinder isn't sealing 100%, the engine develops acceptable compression #'s but they don't hold. All the rocker/valve clearances were set to .016", now the stuck valves' pushrods are flappin' in the breeze with like a 6 mm gap. I suppose it's possible the pushrods are bent but in my (limited) experience they tend to bend evenly across their length, rather than at one end, it should be easy to tell by spinning them. I'll pull the rocker shaft and investigate, if the cam is ****ed I'll just get the iPd kit with cam lifters pushrods and stainless cam gear.

I learned my lesson with bad gas! Draining that **** out ASAP, I'll dump in some acetone to help decrustify. Bowls cleaned, another couple filters etc. Maybe I'll chem-dip the entire fuel pump. I know some radiator shops.
 
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smncutler said:
I'll dump in some acetone to help decrustify
Click to expand...

Why not just pull the tank out and clean it in the driveway?
I think 122 gas tanks are pretty easy to remove.

I've heard of people pulling the tank, throwing small sharp stones inside and shaking the hell out of it to loosen the scale.
 
Check that the needles are seated correctly in the slides/pistons. They need to be flush. if they are out or to far in the mixture will be wrong the entire rev range. while they are out there should be a numbers/letters, writer them down. In the haynes Su carb book it should state which needles you should have and a richer leaner list. I believe there were the actual measurements of the needle thickness in the back.
Also if you smash the spring they are painted ( some have no color) make sure that they are correct.

While running if you push one piston all the way up with a screwdriver the car should run,not well but run. Then do the other side. If they are different you can help narrow down if it is one carb or not and also tell you that its not an ignition problem. I have also you a temp gun and see if the exhaust manifold at each post is roughly similiar temps .
Tim
 
OP six MM of valve clearance says you get to pull the head and figure out what went wrong.

Start there. Carburators will not ever 'behave' with an engine that has big issues.
 
Hehey, I was only half serious. I pulled the tank and sloshed it around, dumped out a massive pile of rusty chunks. More gas-n-slosh 5-6 times to get it past the baffle. I hate myself. Half the valvetrain on order.
I think 32 gallons worth of Seafoam in 10 gallons of premium is good enough ish, tank no longer looks chunky thru the fuel sender hole. Or is this a case of my protracted hubristic rationalizing of total bull****?
 
OP you've managed to shake loose the big chunks from the tank. The fine bits are what get past every filter known to man and will do so forever and ever amen if you don't fix it right. Irony.... Having one repaired with a liner has been a $200 thing here. You have how much time with how much mess + proper disposal of gasoline that is now fit only to light the white man's fire to save what? Oh... I get it... You enjoy getting to be in the carburators every three months. To each his own!

I'm also only half serious. We all know that you'd not burn that fouled fuel adding ghastly hydrocarbons smoke to our precious atmosphere.
 
I like the struggle, it's more interesting. I did get a huge amount of rusty silt out, it left a brown skid mark on my driveway, but there's probably more. I'll see what happens!
 
Well the fuel is minty fresh now, runs pretty okay even on 3 and a half cylinders. Has more power, not nearly at 100% but it's driveable. Took up some slack on the two floppy rocker arms so pushrods wouldn't fall out entirely. I'll just drive it how it is until new cam and lifters arrive.
 
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smncutler said:
Well the fuel is minty fresh now, runs pretty okay even on 3 and a half cylinders. Has more power, not nearly at 100% but it's driveable. Took up some slack on the two floppy rocker arms so pushrods wouldn't fall out entirely. I'll just drive it how it is until new cam and lifters arrive.
Click to expand...

And a head gasket kit hopefully ;-)

regards, Kay
 
while its down, pull the tank, toss a chain in it and seal it up with some gas in it, strap it to the bed of a friends truck and tell your buddy to run a Dukes of Hazard rally on the bumpiest road possible, flip it and repeat.
 
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