Won't idle anymore.....and seems to flood?

[fussfeld]

My setup, as of last Tuesday, won't idle anymore and seems to flood---because after it stalls it takes about 30-60 mins to be able to restart.

Granted, it had been sitting for a few months, BUT after i re-activated it this past Sunday and Monday, it  ran well (by my standards at least---no stalling or flooding...)

The ONLY things i did Monday night, was 1) to get the secondary plates (not air flaps) to open more.   This is a jeg's reman (i know, i know---didn't have time to do it right yet....) off of a truck casting.  #17084349-ish.  i can get the exact number if necessary.
When it was shipped, the secondaries really didn't open at all.  i have now gotten them to open about 30-40 degrees.

2) And then did some "spirited testing" let's just say.

i did this secondary throttle adjustment Monday night.   The problem didn't really start until Tuesday morning AFTER i did a full throttle test.   Almost immediately after this first acceleration test, i could sense that the low speed and idling wasn't normal/not as smooth as normal.

The truck seems to run just fine (by my standards at least) above say 1200 rpms.  It seems like it could do this all day.   However, if i go to a stop sign etc.  it will just stall out.   Or if i stop and put it in neutral it will also stall out.

Since the problem happened just after a day of the carb functioning normally, i don't think the idle tubes could have gotten plugged so soon?

i am happy with the increased performance, but i'm not concerned about that anymore, because if i can't get the thing the idle, what's the point?

i will say that i got the engine to 3900 rpms, which i never did before getting the secondaries to open.  i don't know if that has anything to do with the new problem?  (Note: i have 2.56 rear diff)

-----choke does work fine.

----- fuel pressure last time i measured was about 5.5 lbs at idle and low speeds.  Once i open the throttle, it would goes down to about 2.5-3.5 lbs.   Electric pump.

----- Normal (for me) idle is 1000rpm neutral, 600 in gear.   Won't do any of that anymore.   If i put it in neutral and keep my foot on the pedal, it will stay running at 800+rpm all day.  Once i let off, it putters out.


So, to sum:  Engine will no longer idle and getting flooding.  Ran good until immediately after adjusting the secondary throttle plates to open more and after doing acceleration tests.

[fussfeld]

Cancel it:

The choke wasn't opening;  The plastic plug that normally slides over the blade on the choke housing broke off and i was just using the metal clip portion----NOT the right way to do it.

i may have jarred it while adjusting the secondaries, OR it may have just moved under vibration.  Whatever the case, it lost contact.

This little plug is something that is not really discussed much, but really shouldn't be overlooked.

i'll be ordering a proper plug tomorrow and doing it the right way.

[fussfeld]

UNCANCEL IT:

Choke had nothing to do with it.  It's still doing it.

[Cliff Ruggles]

First thing to check is the secondary throttle plates to make sure they are full closed and sealing up the bores.  Often when problems occur after going to WOT the huge plates are open some pulling in fuel off the rear nozzles flooding the engine.

Since it's a Jegs "remanufactured" carb difficult to help out.

I avoid anything commercially remanufactured like the plague.  Have one on the bench right now sent here from a customer who bought one and it's JUNK.  Main casting is leaking between the DCR passage and main fuel bowl so it drains the bowl into the engine after shut-down.  He bought it for his big block Chevy pulling truck and just wanted me to check it out and tune it because it wouldn't work on the dyno.  It's not going to work on anything and the best sound it will make this week is when I "tink" it off the dumpster outside the shop!.........Cliff

[fussfeld]

The secondaries do close all the way and seal.

Just ordered an SR kit.      i'd like to try that as a last effort.  If that doesn't work, time for a new/different carb.

[77cruiser]

I had a super rich idle at one time after some idle tuning mods, kept going leaner & leaner on the idle circuit, still rich.  Only thing I could find was one of the sec. idle bleeds was plugged.
I don't know if it was siphoning or what.

[Cliff Ruggles]

They don't use good parts in those builds so for sure it should work better with one of my kits installed.  Keep us updated....tks...

[fussfeld]

Main body to base plate screws:

Any particular/general torque settings?   Or just get 'em snug?

[Cliff Ruggles]

Pretty much as tight as you can get them with a flat blade screwdriver and use lock washers on the screws as those thick gaskets will compress some with time.......

[tayto]

Maybe others will say other wise,but after heat cycling the carb a dozen or more times over the course of a week or 2 i will come back when the engine is stone cold and go over all the screws again. I think aside from over tightening the 4 mounting bolts a lot of people will tighten the screws down with engine hot and cause warping.

[Cliff Ruggles]

Over tightening the long front bolts will "pull" the front corners of the airhorn down and warp the entire front of the airhorn and main casting. 

It's really NOT a big deal as some other "experts" have eluded to.   As long as both parts are warped at pretty much the same rate and they gasket gets compressed there will not be any problems. 

I do see a few that are "humped" up enough between the long bolts and front center airhorn screw to seep, wick or leak some.  This usually happens on the accl  pump side.  The fix for that 99 times out of 100 is to gently run the front of the airhorn across a belt sander to flatten it slightly more than the main casting.

At this point installing one of my kits with a .015" thicker (and better material) top gasket and gently pulling down the outer bolts to re-conform the top the middle section is a perfect fix.

To date I'm over 15,000 work orders since going full time and keeping records and in all those carbs I've effectively sealed all of them up in that fashion except about half a dozen where they were pulled down so hard the casting and airhorn were warped over 1/4" and the head of the bolts had just about chewed their way clear thru the top!!

Warping really isn't a big problem 99 times out of 100, and I've gotten so good at flattening airhorns it's about a 3 to 5 second operation then assembly begins.

Our SR rebuild kits for the early carbs automatically come with the .015" thicker main body to airhorn gaskets.  I also put one in the HP kits in addition to the standard thickness.

IF you want a thicker gaskets I'll substitute it with any kit order at no additional cost, just ask when placing an order.

I will also substitute the HP accl pump assembly and larger fuel inlet seat as well if you need those items in your rebuild kit........Cliff

[fussfeld]

Nope----still doing it.  Baffled.


i am only getting 3lbs fuel pressure according to the new gauge.   So i don't think that is the problem.


So, to recap:

1) All i did was bend this tab to get the secondary throttle plates to open;  The secondary plates really did not open at all when i first got the carb.   i got them to open to at least 70%.



(This is not the actual carb in question though.)

2) Did an "acceleration test."   

3) Immediately after the "acceleration test,"  did the symptoms start:    i can't keep it running below 900-800ish rpm if i take my foot off the pedal.   After it stalls,  very difficult, if not impossible to start, unless you wait 30mins. to an hour.  Then, it starts.    Starts cold ok.

Could moving that tab cause other problems?    It must be something simple, but i'm baffled.

[fussfeld]

P.S.

4) i DID NOT take the carb off the manifold when i bent that tab.   You....are/aren't supposed to take the carb off when you do this....?

[Cliff Ruggles]

Yes.  ALL linkage adjustments should be made on the bench with the baseplate removed.  Then you can tell for sure that the throttle plates are opening all the way up, and that they are fully seated when closed.

If they are hanging open any at all you will get a "flooding" condition as the high vacuum at idle will suck fuel directly from the secondary nozzles instead of the idle mixture screw holes.....

[fussfeld]

i was hoping it WAS the secondaries hanging up----then it would be an easy diagnosis.   But they appear to me to be sealing up normal:   Here's a pic.  i had a light underneath as well:



They looked to be sealing up normal when on the manifold as well.

IF the secondaries are closing normal, is there anything else that might cause fuel to discharge from the secondary nozzles?