Okay - Lucy's poly 301 now has an operating Carter WCFB model 2126 vacuum secondary 4 bbl. It came off a 331 hemi and has been bolted to a 392 hemi intake manifold. The carb was kinda rough, but all passegways were cleared out (even pulled the welch plugs) and a rebuild kit was added. I've gotten her to run, but am stuck with a low idle lope/roll - as if the motor has a cam (which it doesn't). I've pulled it apart twice and have done the following: 1) reset float levels 2) reset secondary throttle plates in their bores - they're tight. 3) set the vacuum diapragm to the second adjustment hole to aid in secondary closure. 4) adjusted linkages to get to the factory 10 degree opening of the secondaries at WOT. 5) staked the throttle shafts in thir bores to eliminate freeplay due to wear. None of this has had a significant effect on the roll/lope. Oddly - and this is what has me stumped - if I place two fingers over the secondary venturis and *partially* block the air flow, the motor smooths out. If I block the secondaries entirely - the motor will die. This makes no sense; I've never experienced this and I've rebuilt plenty of carbies. Anybody have insight?
Your lope could be caused by a few degrees too much advance. Partally plugging the venturis causes a variation in the vacuum advance, as well as fuel mixture.
Just reread your post.By "secondary venturis" do you mean the small venturis in the primary bores, or the actual secondary bores? If the last, there's something holding the rear throttle plates open, there should be no airflow through them at idle.
I had a similar problem with a Carter, turned out to be the wrong gasket in the kit for the intake causing a vacuum leak. Apparently several gaskets were used over the years. Spray some soapy water all around the carb fittings and base, a vacuum leak will cause a stumble; any air pressure will cause bubbles.
Guys - I thought about the ignition lead; rolled that back to where she backfired - still loped. thought I had the prob nailed when the secondary throttle plates were re-adjusted - it made no difference. I did check, BTW - there was no daylight thru the plates B4 I put the car back on. Also thought about the vac leak; sprayed the base of the carb, the intake gaskets - pretty much everything. Normally, a leak would cause a change in operating condition - it did not. There WAS two sets of float bowl/throttle body gaskets; I used the one most similar to the gasket on the carb - but it wasn't identical. The one that was a better fit (IMO) didn't have the same porting. I guess I'll pull it apart tomorrow and check that... *sigh* part of the fun - sometimes you gotta build it 4-5 times to get it right!
Manifold sealed to heads? Was it swapped at this time, or was it on before problem occurred? just .02... -bill
Just to throw another curve at you; in my experience a lope at idle has usually been caused by too rich a mixture, while a vacuum leak is usually manifested by a fast idle. My best guess is that an incorrect gasket was installed, maybe... Good luck!
I did that - no change. As for the gasket comment earlier - I swapped out everything at once on account of the 2bbl manifold had three large cracks in the heat riser passageway. There's a whole story about getting the manifold/gaskets to fit the motor - I've checked all this quite thoroughly after installing it twice - and it fits. On A/F ratios (rich vs. lean): A motor that stumbles at curb idle AND has a characteristic exhaust smell (partially burnt gas) is rich. A motor that lopes (changes idle speed up and down on a semi regular interval) is runnin' lean. The finger check is whatcha do for a shadtree A/F measurement - partially blocking the airflow changes the A/F enough to change the idle characteristic. If it dies - then the motor was rich to start with; if the motor smooths out - then the baseline was lean. Ooo...I just remembered! I had a '63 Rambler with the 327/4bbl (small Holley) that had a similar problem - turned out the metering block was not mating up to the carb body correctly. I did not check the WCFB carb body for flatness; I just *assumed* the casting was flat. I think I'll check that tonite. I appreciate talking thru the prob here guys - thanks!
385 cfm rated fwiw. Any chance the power piston is hanging up on a rough spot? Or one of the metering rods is slightly bent which would hold it up allowing excess fuel in at idle? Were one or both of the low speed jets - found on the primary side of the main body when viewed from the top - left out? (Low speed jets were not installed on all models.)
C9 - Thanks for the interest - do appreciate it! I thought WCFB's were rated at 400 CFM (1-1/16" primary and secondary venturis), but 15 CFM is literally a fart in the wind when it comes to a stocker motor like this. All I know is it was std equipment on 331's making the same amount of HP - so both the jetting and calibrations should be fine for the 301. I thought about the power piston issue - I ran into that once on a 'vette motor with a pretty wild cam. The low vacuum signal caused the PP to be really sensitive; cleaned it up with some emery cloth and cut a couple coils off to get it to 'synch' with the motor. Anyway, yesterday I popped the vent cap off the metering rods/accel pump, and watched the whole shebang in action. The rods backed outta the mains just like they were supposed to under load - then sucked right down at idle. They'd pull out when it began to stall - but you'd expect that. Low speed jets - This carb had high speed jets and emulsion tubes (air bleeds) of the same size on both the primary and secondary sides. I pulled all the jets and tubes, opened all the bitty orifices on the tubes, and bolted it back together. I didn't see anything that looked like a typical lo-speed jet, and it's been 15 years since the last WCFB rebuild, so there are things that have slipped from memory. There was a jet in the accel pump circuit on the floor of the body - but that was clearly in the accel pump circuit, and nowhere else.
It's freakin' me out too, man! It maketh no sense. I've taken pride over the years in my ability to 'tune' carbs, and I'm beginning to think that this is God's way steppin' on it. Guess I need that now and then. Oh well...it's just the engineering equivalent of a crossword puzzle. It WILL get solved - eventually!
I tossed the 385 cfm bit in there cuz it's all that I have listed. A 400 cfm - or other size - version doesn't surprise me. I don't think you'd miss the low speed jets. They're on a direct line with the longitudinal webbing between primary and secondary venturi's, right in front. Although if I saw threads down in there I'd be suspicious. I'm with Tommy, the partial blocking of the secondaries with your fingers and the way the engine reacts is a little confusing. I too would like to know what you find. Got another known to be good carb you could try? I don't think it's an ignition problem although like dad used to say, if you think it's the carb it's probably the ignition. Changing airflow and having the engine react is not caused by ignition. What I'm thinking in swapping in a temporary carb is that would perhaps point to an airflow/vacuum leak problem in the manifold if the other carb does the same thing. Live close to Woodward Ave do you? You probably had to learn jetting and advance curves at an early age....
Sounds like 'lean roll' to me. When you blocked the airflow a little, it smoothed out,because it needed to be richend up on the idle mixture. It could be a blockage in the idle air or fuel passages. Maybe someone drilled out the air emulsion tubes,in the past. Do you have a spare ,carb known to be good? Try that if you have one. Good luck.. Sparky
<Hijacks own thread> If you only knew... Last weekend (warmish and dry) was a four lane lineup - hotted up BMW M3, some guy inna WS6 Firebird with ghost flames, a white sn95 Mustang and Max, my daily driver. Lite went green; we all hit it... I've got the winter tires on Max; he's pretty useless in 1st and 2nd. I blew trans #2 (third gear) recently; so Max was pretty crippled. Even so - They still all saw tailights. And that's just a regular ol' day at the Center of the Known Motoring Universe - honest.
When I had my 64 GTO (built to the limit of my checkbook) a bunch of us used to tow it out to Woodward a few times a year to get some fast cash. Royal Pontiac did the prep and did they ever know how to set that baby up! Im fresh out of ideas not already mentioned on the WCFB but I keep suspecting the intake base gasket. Do you have any gasket material to cut out a new one AND note any discrepancies between the original, the carb base and the intake surface. Can you cobble a known good carb of any style onto that intake? The 4GC small base and Holley 4000 have the same pattern or get a wide base to small base adapter.
Had a similar problem with the WCFB on my 287, not 3 months ago. Crud in the fuel idle passages. Boiled it overnight with chemtool, and it cleaned up. No prob since.
Royal bobcats were the whip! Didja know Royal Pontiac set up the GTO's for GM's magazine tests? They're the reason mags now do a 'blind' pic of cars for performance testing... The killer was a 389 Grand Prix that clicked off a 4.9 0-60 time; that's what raised the red flag. NO WAY was a full-sized Grand Prix capable of a sub 5 second 0-60 in stock form! Intake gasket - it's a good call, but the bugger is tight as a rat's ass. I'm thinking it's the gasket between the throttle body and the carb main body. I was gonna tear into it tonite, but it will have to wait until tomorrow.
Had another thought; have to brag whenever that happens... propane boost test: run propane to each venturi (well, at least the primaries) and see if it changes side-to-side. May help narrow down choices, if it's a leaking runner or blockage or whatever that's only affecting one side. -bill
I really want to thank everyone who's taken the time and energy (and brainpower) to think this one thru - Thanks! I was gonna tear into the carb last nite, but had to go to a damned PTO meeting - Parent/Teacher, not Power Takeoff! There is a type of individual who is drawn to those sort of things - it's the same wherever we've lived. Anyway, I'm divin' back in tonight, and the plan of action is: 1) gonna run it one more time - I like the propane idea; will try that and see what happens. 2) Afterwards, the carb will be torn apart (again) and will receive a thorough soaking (again) in an attempt to free up any residual crap that migh be lurking in passages. 3) the carb body will be checked for flatness, and machined flat if need be. 4) while apart - the carb body to throttle body threads will be re-tapped to accept 12-24 screws which will be bottomed out in their bores for good thread purchase. The 10-32 screws holding the whole shebang together were at that *point* where another quarter-turn would strip them out - youse guys know what that feels like - it's icky. I'm hoping to have the dealie back together and on the car Thursday for a report out.
EUREKA! (the exclamation, not the town in norcal) Did pretty much what was mentioned earlier, and discovered the following: 1) The throttle body, while sealing well on the secondaries, was slightly warped. when tightenedagainst the manifrold, it would cause the car body to pull away at the front mounting screw, which was why the front screw was partially stripped. Of course, this played havoc with the curb idle mix, as the ports between the throttle body and the car body for the idle mix are at the absolute front of the WCFB - they're part of the index pins between the throttle body and the carb body. The carb body was re tapped using a modified 12-24 tap, and the retaining screw were indexed to run within 0.020" of the bottom of the bores for max purchase. The sealing of the two parts is truly tight as a rat's ass now. 2) The driver's side mounting holes are open to the runners - which means the carb mount bolts/studs MUST be sealed for good idle. that was done. and... The damned thing IDLED! the prob with the fingers over the secondaries was a separate issue... 3) The secondaries would not close all the way. whe coupled with the other air leaks, the whole shebang ran rough. After fixing the other leaks, the transfer ports worked properly - and when they didn't close, the car ran on high idle. tore the diaphragm apart, and the damned thing is dry as the friggin' Sahara - hard, brittle and cracked. there are holes in it to the point where it ain't gonna open at WOT - defeating the reason for a 4 bbl. that's the final leak, BTW - the diaphragm secondaries are leakin' into the manifold, adding a slight miss to the passenger side. Soo... Anybody got a line on diaphragm material? ideally, I need a 1-1/2" rollling diaphragm - if you got it...
I laid in bed and racked my brain as to what would be the best substitute diapragm - and arrived at the rubber gasket that's used for modern master cylinders. It's a low resistance, rolling diaphragm designed to minimize the amount of air in a hydraulic brake system. All I need is one that's a minimum of 2.825" wide - if such an animal exists (and I'm pretty sure it does) I should have the replacement fabbed up and ready for a test drive by Thursday. It still runs rougher than I'd like, but it runs well enough to drive. Sometimes driving an old carbie will cause it to smooth out - we will see.
The Jalopy Journal
