Using my old Qjet carb while my rebuilt gets rebuilt AGAIN LOL! Problem is the fumes with the old set up are so potent when sitting at idle that the exhaust brings tears to my eyes even though the car seems to be running fine. My rebuilt motor does have a new cam etc., but I don't recall the carb being so rich when I pulled her off prior to the rebuild. Went in with each adjustment screw until engine ran ruff and then backed off until she smoothed out. Was worried that if I backed out too far she would backfire or miss under load. Any ideas? o No:
any leaks under the car? Have you checked you return lines to your gas tank? If these are cracked and old this could be the source of the fumes? Also is it wet underneath your hood? as if gas is leaking somewhere? Scott
No leaks, lines are fine. Fumes were reduced somewhat when I let more air in. Carb has been a bit fickle which is why I was replacing her. Just looking to buy some time.
Rich idle is a common sign of a stuck power piston. With the engine off, Place a small flat-head screwdriver down the bowl vent (angled forward), and see if you can push the power piston down about 1/4". Letting the pressure off, the spring should push the piston back up. If it's stuck in the up position, the metering rods are letting waaaaay too much fuel past the main jets. Sometimes, engine backfires can cause carbon deposits to get onto the power piston and freeze it in place. Shooting some carb cleaner down the bowl vent, and working the piston up & down can free it. Sometimes, the metering rods, themselves, get bent. Last Q-Jet I rebuilt, one of the rods had a tip that was bent 90 degrees: useless. Summit racing sells replacement rods, and they even have NOS jets by RPD.
Went in and found no resistance. It was like I was pushing/poking thru a membrane. Soaked t with some gum-out started her up and then, and only then, did I backfire thru the carb. Took her out for a run where she missed and hesitated a bit off the light, then leveled out. Took her home, shut her down and had some mild after run. Seems like I might have made things worse so I soaked her with some more cleaner and I'll see where we're at tomorrow.
Sounds like you missed the piston altogether and were pushing thru the top gasket over the float and around the rods... Not gunna help any... The power piston sits forward the front of the carb thru that vent hole... If you pushed the gasket too much out of place, the rods can bind as well as the float... Hopefully you were gentle with your probing... I was trying to find an illustration online to help, this is the best I can do at the moment, http://www.cliffshighperformance.com/tech_qjet_history_2.html The piston slides up and down in the hole by the pencil tip on the right... You may need to replace that top gasket and possibly the float if you probed to hard... The float needs full upward movement to close the fuel inlet needle.. It also just could be that you needed to adjust the idle screws some more. Use a vacuum gauge and dial it in for the highest steady vacuum.. http://www.secondchancegarage.com/public/186.cfm Another thing that may or may not be happening is that one or more of the bottom carb plugs is leaking fuel internally... What is the carb number your working with?
I think thats exactly what I did. My Bad! Just went and re checked the piston and it is working fine! Not gonna go too crazy as the carb is being replaced buy an updated rebuild. Its a 72 Qjet carb# 7042244KC 1432 that I had rebuilt some time ago. At the time I was told that the bowl area had some minor pitting but it didn't seem to effect performance. However, as I was trying to get the most out of my motor I decided to get a different Qjet carb with larger primaries and updated hardware to hopefully improve on overall engine performance.
Both the 750 and 800 cfm carbs dialed in at the track - not much difference. Towing and marine applications will benefit more from the extra 50 cfms on the primary side... Yet, it can't hurt either.. 200 primary cfms for cruising around, and 600 more for the floor.... Make sure your new carb has the adjustable apt screw for even more fine tuning.. The apt screw raises and lowers the primary piston stop to really dial in the rods.. Get yourself a copy of Cliff Ruggels book. Alot of great tips to help you get the most from your carb... And no more Nasty fumes....
Thanks for all the information and recommendations! One thing on the positive side is that although I'm sucking gas and running rich with the current carb the car has awesome top end power as a result of the engine mods. Now I just need to get the other end in line. Hopefully I'll get my new set up soon which had 73 primaries vs. stock! :beer
