Well, I've been working with this for a while.

Basically, the car (de-smogged 4-port 13B) suddenly started running horribly at part-throttle. Backfires, surging, .... I relocated my coolant temp sender in the water pump thermostat neck (it broke off in the block) and, since reassembling, this has happened. I'm running a Holley with vacuum secondaries. I've taken the carb down and nothing out of the ordinary. The idle set screws were at 2.5 and 4.5 turns following the waterpump reassembly and are now at 2.0. The vacuum accessories are capped off for now. The choke adjustment doesn't have a heat riser attached and is set at full open. My floats are good and right at the weep holes. The brass fitting RB added on the primary side is capped off (not the OMP fitting - that one's hooked up). I've removed the intake manifold looking for vacuum leaks and put a tiny bit of silicone sealant to each side of a new Mazdatrix 4-port gasket and reassembled. Cap and rotor were replaced yesterday too, since there was a chance the old one was wet, but no improvement was evident.

I originally thought this was a vacuum leak problem, but it doesn't appear to be.

I'm supposed to be selling the car tomorrow (new owner left a deposit last weekend) but don't want to let her go like this. Under full throttle, she does just fine, it's strictly light-throttle that runs so poorly. If you have worked with this stuff, please give me a call at 678-467-0463 or IM me (Critteroso). I'm really under the gun and just don't know what else to do.

Here's my current progress
https://www.rx7club.com/1st-generation-specific-1979-1985-18/help-holley-vacuum-leak-330106/

And here's what I've been using for reference
https://www.rx7club.com/1st-generation-specific-1979-1985-18/alllllrighty-then-holley-thread-novel-285484/


Thanks.

Crit

 

Well, I've broken the carb down again, and still nothing seems out of the ordinary. I ran pipe cleaners through the whole metering block and main body, put in another set of new gaskets, reassembled, set floats, set idle screws at 2.0 turns out, and everything's the same as before. Any ideas on what to try next?

 

Alright, I'm in the garage again for day 3 and still nothing's improved. The car won't hold revs at all. You have to either keep it alive with the AP, or drive at full throttle. To me, that means vacuum leak, but I've been through everything and a vacuum leak just isn't there. Any ideas? I've rebuilt the carb again, making sure to clean out the passage from the primary jet to the venturi, so I know it should be able to breathe, but it only seems to run when the secondaries are open (WOT) so I'm thinking that my primary mixture is off somehow. Ideas?

 

I know you have new parts in there, but did you check the ignition system operation thoroughly?

 

I've checked plugs for spark, and have replaced the plugs with a clean set of spares I had handy. The cap and rotor are new as of yesterday, and i have static timing. What should I check? Would ignition or timing have anything to do with part-throttle but not full-throttle operation?

 

what about the wires? when i saw them they looked kind of old. have you tried swapping those out?

 

Here's a pic of what I'm talking about. The front and rear primary passages have been cleaned exhaustively, yet the rear seems to flow a lot more fuel, or atomize it a lot better. What do y'all think?

 

And yeah, I'll pull the wires from the RX-2 and try them on the 7, but I doubt that's the problem. I'm trying to limit the amount of unnecessary parts I put on now that I've rebuilt the carb with absolutely no change. I'm installing the Dellorto on Sunday, just to limit my work to either the Holley and manifold or the ignition, depending on how things go. If nothing else, I'll at least know more tomorrow.

 

Okay, the Dellorto carb is on there now and the car runs great - just like it did when it was breathing through the Dellorto. So.... what are the likely culprits in tracking down a Holley that won't idle? Tim Benton had mentioned that Holley gaskets, if not the right part or if turned around could block the idle circuit. Any idea how that works or why the Holley won't meter fuel right at idle or progression?

 

have you checked you float level and made necessary adjustments, measuring?

 

Yeah, this is mind-boggling. Both floats are set so that, when they're dry after a rebuild, you can see the fuel creep across the sight plugs, one thread at a time, which looks to be dead on. From talking with Tim, he said that he's seen Holley's with vacuum fittings for vacuum advance and other things at the base and under the bowls, but I don't have any of these. As I understand it, I can only have a leak from the base gasket, flange gasket, vacuum port, or manifold-block gasket. Assuming I don't have a leak, why would my fuel be metered so crazily? The aluminum that splits the primary runners on this manifold are particularly thin, but I take care in making sure that the gasket stays on that little bridge. If that little ribbon of gasket material slipped to the side and no longer divided the two primary runners, would it cause this big a problem?

 

Crit, we can throw your carb on my motor and see if it does anything different. I know I have a 12a, not a 13b, but it might reveal something is wrong with your car beyond the carburator. You sure fuel pump is up to spec on fuel pressure? Tried switching your ignitors over and using the trailing coil to fire the leading plugs? My car seems to run better with alittle bit more fuel coming out of the weep hole then you describe. Have you pulled the bowls and looked for junk in the primary jets?
Does the car run as well with the dellorto as it did with the holley when it was "right"? I know you mentioned the power to be higher with the holley. I wouldn't mind coming over and trouble shooting alittle today, just give me a call. Maybe another mind might help something.
Aaron

 

Yeah, I've tried all those things and am currently reattaching the Holley and resetting the floats. I know they're good, but I have to try something. The car doesn't run at all on the Holley now, but yes, it used to kick the Dellorto's ***. I'll give you a call soon and we can try.

 

Well, it's finally all up and running. I think it was a vacuum leak between the base plate and carb body. Thanks for the help, guys.

 

HA. A whole thread of you answering your own questions and finding your own problems........ Then everybody gets a thank you. HAHA... I would pat my own back if I were you.

 

didnt i tell you to try that???

 

Crappy Holley quality casting. Dont feel too bad, thats actually a very common problem. Race Holley builders (NASCAR) mill them to be flat cause they suck from the factory. What caused it? I thought you said you just rebuilt it?

 

Yes, you told me that, FB II. However, tightening the living hell out of the lower 6 screws didn't help. It took 2 gaskets and RTV in-between to finally get a seal. It's not that I wasn't listening or thinking, I just failed to realize how much that casting sucks.

 

No, the same info was posted in the general section and on vintagerotaries and corvetteforum.com (lots of Holley guys there - if you ever have a question, ask a C3 guy), all of which referenced this thread. So yeah, thanks were in order, you just never saw it here.

 

glad to hear that
ill definalty get my roomate (machinist) to mill the mounting surfaces flat before my holley goes in (on my 302)

 

gas eats silicone atv sealant, you should have used hylomar sealant

 

Whoops!

 

I have hylomar, but needed something that could take a bigger gap, since it was warped. Permatex has a black silicone that's good, but they also have intake mani stuff that's red and holds up against gas.