Quadrajet Blues. Who can help?

[LX Kid]

Another day of grinding out the bad karma. The motor runs great until I get back to the dock and let it idle or should I say try to get it to idle. Sooooo off came the carb for a third operation and couldn't find any trash, scum or clogged passages. I put it back on this afternoon and still the same thing. Think I'm going to advance the timing and see if the vacuum gage will come up higher than the 15 hgm that I presently have. I had set the timing with a light the other day and could be something with timing. I don't know what plugs are in it now but tomorrow I'm putting in MR43T plugs. Anyone have any idea what my problem could be?

Here's my restoration link: http://forums.iboats.com/showthread.php?t=275835&page=12

 

[Bondo]

Re: Quadrajet Blues. Who can help?

Ayuh,... Is there Any play in the throttle shafts,..??

 

[LX Kid]

Re: Quadrajet Blues. Who can help?

This was a remanufactured carb I bought 1-1/2 years ago and has been sitting on the engine and not been run more than a couple of hours during that time. No play in the throttle boday.

 

[blazer7671]

Re: Quadrajet Blues. Who can help?

Q-jets run either really good or really bad. The thing I do is shoot EVERY hole with carb cleaner using the staw. I asume you bought a carb kit. Next make sure none of the metering rods and vent tubes are bent. The big thing with Q's is the float level, that shuts off the fuel to the bowl when it's full. If it's to high your engine will load and flood out. Another thing Q's have are. WAY to many vacume ports. Plug evey one that isn't being used. That's my experience with Quadrajets and hot rods. Great carbs when they're set up right.

 

[LX Kid]

Re: Quadrajet Blues. Who can help?

I've done this three times in the last three days. Lots of carb cleaner thru every orifice, hole etc and then use compressed air thru them. Ran SS leader wire thru everything to make sure they were clean. No bent tubes. Started mix screws an 2-1/2 turns. Think I'll recheck the float level tomorrow cause now that I think about it I set the float at 12/32" instead of 11/16" as directions call for. The guage was graduated in 32nds instead of 16ths. I should have set it at 22/32". Hmmmm I wonder!

 

[John_S]

Re: Quadrajet Blues. Who can help?

Do you know if it is too lean or too rich at idle? (plugs black or very clean?) When you adjust the mixture scews in and out, are you getting a bog in both directions. Any fuel dribling down the barrel at idle? Are the well plugs epoxied? A vacuum of 15 (steady) is a little low, and too lean or timing may cause that.

Since you have it apart record the values of the primary jets, rods, and 2ndary rods. Make sure they are paired. A number of people have reported carbs from a certain builder having mis-matched parts.

 

[LX Kid]

Re: Quadrajet Blues. Who can help?

It got late this afternoon when I put it back on and tomorrow I'll stick my snout over the carb and see if it's dribbling over. Pretty sure the float is too high. The jets are 69's and can't read the super small letters on the metering rods. Have to get a magnifying glass on it. The original carb had 70's in it.

 

[blazer7671]

Re: Quadrajet Blues. Who can help?

Forgot to ask how it does when you bring it to idle. Does it go CHUG, CHug, chug, cough or just "cough"? Is the power valve sticky or sloppy in its slot? How far open are the primary butterflys? Secondary? Then, the last thing I can remember (its been some 15 years) how far open are the air bleed screws? They are the 2 screws in the front lower plate.

 

[joenapier]

Re: Quadrajet Blues. Who can help?

My original intake manifold / mounting gasket was 1/4" thick and had a metal layer sandwiched in it for heat. My rebuild kit came only with a thin paper intake gasket. When I first installed the carb, I had a vacuum leak under the base and I could not get it to idle under 1400 rpm of so, no matter how much fuel/air mixture screw adjustment I did. I confirmed the leak with a spritz of starter fluid around the base causing the engine to rev a bit.

When I went to a hotrod store and got a new thicker gasket, the problem was corrected.

 

[LX Kid]

Re: Quadrajet Blues. Who can help?

Chug, chug, cough and dies. Installed new Fel-Pro intake gaskets with new carb to intake gasket. "No vacuum leaks!" Used 0000 steel wool on power valve and not sticking nor is it sloppy. Primary butterflies should be closed at idel and the idle circuit takes over. I'm really suspecting bad float adjustment due to me incorrectly reading the guage that came with the kit. I'll let ya'll know later if that was it or not.

 

[John_S]

Re: Quadrajet Blues. Who can help?

My original intake manifold / mounting gasket was 1/4" thick and had a metal layer sandwiched in it for heat. My rebuild kit came only with a thin paper intake gasket. When I first installed the carb, I had a vacuum leak under the base and I could not get it to idle under 1400 rpm of so, no matter how much fuel/air mixture screw adjustment I did. I confirmed the leak with a spritz of starter fluid around the base causing the engine to rev a bit.

When I went to a hotrod store and got a new thicker gasket, the problem was corrected.

Sounds like the base maybe warped. Next time you have it off, check it on a piece of glass.

 

[LX Kid]

Re: Quadrajet Blues. Who can help?

Took the carb cover back off and indeed I had mal-adjusted the float. I also noticed that the two center air bleed tubes were not the same length. Upon further investigation one of the tubes was flared out where it had been bottoming out on the carb's bottom. Pounded it back up level with the other and had to take the smallest drill bit I had (.040) and drilled it out. Put it all back together and same old problem. The primary metering rods are "398" and secondary rods are "DA" Gonna put new Autolite AP25 plugs in and see if the "top dead center" matches the distributor #1 position. This little problem has been kicking my "A**" for several days now.

 

[Silvertip]

Re: Quadrajet Blues. Who can help?

The air valve housing (upper left in your picture) has a tiny spring that sets the pre-load on the secondary air valves (the secondary butterflies). Since you have the housing off, operation of this spring is easy to check. Simply hold the housing and with a finger push the air valve open and let the spring close it. Although this operation proves the air valves are operation properly, the amount of tension may not be correct. This is adjustable. If the spring is too loose, the engine will bog and go rich at quite low throttle settings. If too tight, the secondaries will not open until way late. If adjusting the mixture screws has little effect then there is a vacuum leak either at the manifold, carb base gasket, base to float bowl gasket, or some other vacuum fitting. If this carb had been professionally or unprofessionally rebuilt at one time, the primary and secondary butterflies may be out of sync -- meaning one is partially open while the other is fully closed. If this is the case, carefully loosen the plate mounting screws on BOTH butterflies on the same shaft. Snap the shaft so both plates are fully closed. Tighten the screws. Then there is the idle dashpot that used to be used on cars to help with sudden throttle closure. Don't have one on a boat but bringing the throttle closed slowly when docking may help.

 

[LX Kid]

Re: Quadrajet Blues. Who can help?

Just replaced all the plugs with Autolite AP25's and was really surprised to see Chumpions that I removed. The gaps ranged from 28-45 degrees. They did look like they were fireing good though. Checked distributor and is also installed correctly. New points, condenser, rotor, cap and timed to 8 degrees BTD. No vacuum leaks anywhere and has new Fel-Pro intake gaskets, carb kit, and carb base gasket. No bleed over in the primary. Someone please just shoot me and relieve me of my frustration!

 

[LX Kid]

Re: Quadrajet Blues. Who can help?

Got out the old carb and rebuilt it to see if I could do any better with it. "WRONG!" It started running just fine then discovered that it was leaking gas between the main body and the throttle plate. Even with new acceleration pump it wouldn't squirt very well. I'm ready to admit "defeat!" Who makes a new carb, not re-manufactured, that is guaranteed to bolt on and work? I've been busting my "b**t" for a week trying to make it reliable and go "FISHING!" Summer will be gone before you know it. My two year restoration project is being held hostage by a Rock Q-Jet!

 

[Silvertip]

Re: Quadrajet Blues. Who can help?

Some Q-jets had porous castings which is why the kits came with a rubber deal that was slid into the carb to seal the leaky well. If the porosity was really bad it could dribble enough fuel to kill the engine. This situation also caused hard starting since there was a tendency to flood the engine after shut down. That's all I can offer!

 

[LX Kid]

Re: Quadrajet Blues. Who can help?

Just stick a fork in me cause I'm done. I wanna have some bigger "fish" to fry! If a new carb will make it safe and reiable I'm gonna throw some more money at it. It's time to have a little fun and relaxation. My marine mechanic couldn't fix it and I'm tired of trying.

 

[John_S]

Re: Quadrajet Blues. Who can help?

New carb options:

- Edelbrock 1409 w/ squarebore to spreadbore manifold adapter.

- Holley 650 cfm spreadbore.


With both, expect some fuel line change.

 

[aktrucker]

Re: Quadrajet Blues. Who can help?

Did you, by chance, get that carb from I-5? If so, I know what you are going thru......many on here have cursed themselves for buying from them.

 

[aktrucker]

Re: Quadrajet Blues. Who can help?

Took the carb cover back off and indeed I had mal-adjusted the float. I also noticed that the two center air bleed tubes were not the same length. Upon further investigation one of the tubes was flared out where it had been bottoming out on the carb's bottom. Pounded it back up level with the other and had to take the smallest drill bit I had (.040) and drilled it out. Put it all back together and same old problem. The primary metering rods are "398" and secondary rods are "DA" Gonna put new Autolite AP25 plugs in and see if the "top dead center" matches the distributor #1 position. This little problem has been kicking my "A**" for several days now.

What do the "air bleed tubes" do, anyway?? My "rebuilt" carb that I bought had 2 that were cracked...........