Any carb guys, jetting?

[jerrys84]

Almost time to get the mustang out of storage... I was thinking about the problem i was having last fall before i put it away. when the secondaries open, there was no additional power, it just fell on it's face.. which leads me to believe the secondary jets are way lean... I did replace the power valve and it did the same thing...


running a holley 600 cfm.. just curious what jets or maybe just a jet size to start with?? I could buy a bunch of jets and play trial and error, butt i really don't want to end up with 10 pairs of jets..


Motor is reman 302 bored .60, only mods on the engine (at this moment) are intake, cam, 89 heads and headers with open exhaust...


I remember our dirt bikes doing the same thing when they were jetted wrong..

[jim_howard_pdx]

Hey,

Most problems fall into three categories.

First, if the vacumn diaphram is shot, then the secondaries are not opening. You cannot test this on the motor since the secondaries only open under load, not from reving the engine. To test, you should hear a suck and click sound when going from full throttle acceleration to normal driving. If you hear no sound, the diaphram is gone or someone has removed the bleed ball bearing from the vacumn canister. A replacement diapram is $8.00 or so, and I would recommend going with a quick change top so you can exchange springs without major disassembly. Make sure that the ball bearing is in the vacumn canister, otherwise the secondaries will remain open after your full throttle activity instead of closing properly. THIS IS NOT GOOD.

Second, my Mustang makes 414 hp and I use the latest opening BLACK secondary spring. WHY? Because I am using 2.5 gears right now, and if the secondaries open too fast the car just lies flat and does not come on until the engine labors up to 5,000 rpm. If the engine is running flat, there is a chance that you have the secondaries opening too soon. Go to a heavier spring. They are colored and run light to heavy in this order: white, light yellow, dark yellow, purple, silver, brown and black.

Third, you may have an internal or external vacumn leak or more commonly the PVC tube or valve might be SHOT. Replace both the PVC and the tube and test the engine with a vacumn guage. If you are pulling air in from under the intake, you will spend months trying to get the car to pull under throttle and nothing ever happens. Make sure you check the torque on your intake manifold, and then very carefully spray starting fluid on everything that transports vacumn. If the engine picks up rpm, you found the leak. I alway check at the base of the carb and the throttle shafts. Remember that a bad pvc valve or pvc hose can wreak havoc with accelleration, so always check this FIRST.

Try these and email me at jim_howard_pdx@hotmail.com if you have additional questions. Make sure to leave me a return email address. I do not check this website more than once every other week.

Jim

[juiceman]

well unless you have a d.p or did the block conversion there are no jets in the secondaries to change. you may have to change the plate to a block and buy jets but i would say check everything else out first. are you sure the secondaries are opening? and with open exhaust you will not make power on a stock 302. it will fall on its face.

[Dark Knight]

check the float level... make sure there is even fuel in the secondary side... if it's a DP, make sure the acc. pump on the secondaries is working too ;-)

[jim_howard_pdx]

Jerry 84

What type of carb are you running? Vacumn Secondaries or Double Pumper? Primary jets should be about 65-70 and secondary jets should be 72 to 76. Run these and check the plugs.

Have you checked the ignition timing and proper function of the distributor's advance?

Are you running fresh, properly gapped spark plugs, spiral core wires, and a fresh cap and rotor? Have you checked the coil for proper operation under load?

You need to ELIMINATE IGNITION problems before playing with carb settings.

Put a vacumn guage on the engine and check it at every 500 rpm writing down the readings. With no loading, the vacumn should be fairly high. If vacume pumps or stumbles then we have a leak somewhere. No amount of carb tuning can correct a vacumn leak. Holleys most often leak around the base gasket and the throttle shafts. You may need a new carb if the throttle shafts are shot.

You need to check the PVC valve and the line. If they are wrong, the car will never pull under acceleration.

You need to verify fuel delivery. First check the float level. Then consider using a 3/8 fuel line and a 110 gph pump with a regulator. This will provide bowl fill at WOT.

With a stock cam and 1.7 lifters I would try a 65 to a 68 primary and a 72 or 74 on the secondary. A bad power valve makes the car run like dog poop at idle, but it will run great under acceleration, so I do not think this is your problem.

You may be having fuel delivery problems. You should probably be using a 3/8 inch fuel line, a high performance fuel pump at the tank, and verify that your float levels are properly set. A 300+ horsepower engine will need at least a 75 gallon per hour pump. I prefer to use a 110 gph pump and a pressure regulator to maintain about 6-7 pounds of pressure. A stock fuel pump usually delivers between 40-50 gph. This is hurting your top end.

Hope this helps. Email me at jim_howard_pdx@hotmail.com and I will be happy to help you through the checks. PVC check first, then check your vacumn levels and look for leaks. Distributor check comes next looking at initial advance and full advance. Freshen up the plugs-wires-cap-rotor. Then check your carb. I think your secondaries are opening too soon. If you have a double pumper you may need to go to a vacumn secondary. If using vacumn secondaries you should be using a purple, silver, or brown spring on the secondary diaphram. When all this is done, then we can fine tune with the jets.