help with 17082224

[bruno]

mods feel free to move this post if it should be in another topic.

[Cliff Ruggles]

I've been away for a few days, BURIED in orders and trying to finish up a few things.

Do you have control with both mixture screws after the clean-up?

I'd also make sure you don't have any leaks at the exhaust "channel"  under the carb.  That looks like one of those older intakes with the "hot-slot".  There can be issues using a later carb on those intakes not sealing at the "U" shaped channel in the baseplate.....

[bruno]

it is a “hot slot” manifold, but i did follow your directions a few years ago and plugged the holes at the ends of the slots with pipe plugs. i do have a metal spacer with a thin gasket under it, then the 1/4” gasket above.

i currently do not have control with the idle screws, or atleast very little. it will run decent with both seated. checked for coil bind, and that’s not an issue. will double check for vacuum leaks with some propane shortly.

[bruno]

just confirmed there is not any vacuum leaks i can find. sprayed carb cleaner all around base of carb, throttle shafts, and intake. no reaction. i do get an immediate reaction with a tiny shot over the primaries though, so i assume i’d get same reaction if there was a leak somewhere.

vacuum at idle now is 16.5”. timing is set at 5 degrees btdc, and VA is adding 19 more for total of 24 at idle. seems to idle very smooth, but still only get about a 30 rpm drop with both mixture screws seated. when i cover the air horn, it does sound better. if i pull off a vacuum line, it immediately revs up 100 rpm. so maybe i’m closer than i thought?

still have no idea where timing “should” be.

[bruno]

sorry for all the questions, but wondering about my throttle angle. i can turn down the idle to 450 ish, then any lower and it won’t stay running. is it possible too much of the transfer slot is exposed, not giving me control with the idle screws? i have the idle set at 750 in park right now. i don’t see any nozzle drip, but also have never seen it before, so maybe i’m missing it?

[bruno]

well i’m almost certain there is no nozzle drip, i used my inspection camera to watch, and the nozzles are dry.
i also tried leaving a manifold vacuum open and lower the idle speed back to 750, i still had no control with idle screws, and it ran much worse. put it back to where it was. so i’m thinking it wants more idle fuel, and by covering the air horn, i’m acting like a choke, and causing the fuel to come from the main at that point?? as in “shifting the vacuum signal above the throttle plates”?

[Cliff Ruggles]

Double check the gasket being used under the carb to make sure it seals off the "U" channel on top of the steel shim gasket.  I've seen problems there with using those carbs on the early intakes.

I'm not fond of that much timing at idle and very seldom use MVA on engines like you are tuning.  High compression engines don't need nearly as much timing at idle unless the cam has a LOT of overlap. 

My last 455 in the Ventura was a perfect example of not wanting, needing or responding well to a lot of timing at idle speed.  The idle was simply more stable with improved control using the mixture screws with 10 degrees initial timing.  If I tried to hook  up the VA using manifold vacuum engine RPM's increases slightly but the idle just wasn't a stable in and out of gear and I lost some sensitivity with the mixture screws.  It also developed a very light "skip" in the idle note that you could hear in the exhaust.  Ran OK like that but not nearly as solid as it did with less timing in it.

Your idle fuel set-up is a tad lean for what you are doing and that shows up if it likes a lot of timing at idle and any engine speed increase tipping in the choke flap or cutting off some air to it with your hand at idle speed......

[bruno]

i installled threaded pipe plugs in the ends of the exhaust slot in the manilfold, so “shouldn’t” be any exhaust gases there to leak into carb. it doesn’t leak to the exterior, as i sprayed all around the base of the carb. unless i’m missing something else there?

should i open up the idle tubes, or DCR? or both?

[Cliff Ruggles]

Installing plugs at each end of the exhaust channel was a good move.

However, you still need to use a later model gasket UNDER the carb to seal off the "U" channel.  If you remove the carb and flip it over you will see that the factory steel shim gasket BARELY covers the channel and if positioned incorrectly there can be a small vacuum leak there.  Same thing IF you use an early style (pre-1972) carb to intake gasket under the carb. 

Many of those gaskets are NOT long enough in the front to seal off the channel in the baseplate.  That channel often supplies "weak" ported vacuum to a tube in the front of the baseplate to route vacuum to the EGR.  It's still a leak either way but may not show up at idle speed.....FWIW

I would reduce the lower IAB's to .067-.070" and do nothing else and see how it responds......

[bruno]

sounds good. i don’t believe this ever had an egr, but i’ll take some pics when i take the carb off. pretty sure i made a metal plate to go between the gaskets. either way i’ll take pics, and i’ll try your recommendation, and post the results.
there is a possibility you sent me the metal spacer to go there when i ordered the original kit.

[bruno]

cliff, i took the carb part to close up the LIAB, and decided to remeasure everything as best as i could. i used my drill bit set, but it is a cheap one, and after verifying the sizes with calipers, it seems i have a bit of a gap in sizes that i need. so here are the sizes:
UIAB- .066-.071
LIAB- .066-071
MAB- .085
DCR- .051-.058
idle tubes- .034-.037(think you sent .036”)
idle discharge holes- .085
idle bypass air- .093-.095

i have not put anything back together yet, waiting to hear your suggestion if i should still close up the LIAB or not. also i’m thinking it needs more idle fuel, so was thinking of taking idle tubes to .038”. again, will wait to hear what you have to say. more questions in next post!

[bruno]

are baseplate numbers supposed to match main body numbers? my base plate number is 17060558. everything seems to line up correctly, but thought i’d check, as i have no idea the history of this carb before i rebuilt it. there are no “rebuilder tags” or anything on it though.

i also have a question about throttl blade angle. i will add some pics showing where the blades sit at my current idle setting(750 in park), and fully closed. I assume because i do not have any nozzle drip(i think!) this is fine. but i assume lower would be better?( in which case i would need more bypass air? thoughts?

[bruno]

throttle angles

[bruno]

base gasket stack. Metal spacer is homemade from sheet metal.

[Cliff Ruggles]

I like to see exact precision with these things, it does make a difference. 

The hot slot is still open on one end with your gasket arrangement.  It still should seal off since you are using the 1/4" thick open gasket in there but for sure I'd put the stock gasket down correctly first, then a metal one over it to completely seal things off, then the others on top of that deal.  Currently you are relying on a very small amount of sealing surface just in front of the primary bores to seal things off.....