I have an nci 94 tri power on 324 olds motor. The issue is leaking power valve on idle. I reduced fuel pressure to 2 lbs. checked float level and set it to 1 13/32” ( off of the edelbrock spec) and checked and replaced fuel seat, needle and gasket. Checked and realigned the throttle body butterflies as they were a little off and causing them to stick. And finally changed the power valve and gasket. I did this in an orderly manner not just change stuff out. Idle mixture screws are set to 1 1/2 turns out. BTW this the primary. After doing all this and still showing gas from dripping from the Venturi cluster. While idling I placed my hand over the secondary carbs and can feel vacuum from them, is that normal? ( I’m thinking no). So I’ll probably pull the secondaries off and check the throttle bodies. Any thoughts?
There some much better then me,but my 2 cents; Power valve used in 94s,can and often dose go bad with just one little backfire{ so leaks ,goes super rich/bad} Plus just a little too high with float set,and over flow/leaks< even more if your big cam rolls engine a lot.. I got so feed up with blown out 94 blown out PVs,I just put plugs in PVs. Run sq. pump on highest setting on all four of my 94s { have 4x2 set up }with all 4 all the time. =Still has a flat spot/stall out,if I don't hit it hard enough< so all pumps working,or get into it to slow at low speeds n RPM. Hight of floats is very close to maxed out { too low an,it stalls from not enough gas} Not what I'd call tuned great,but works,with out power valves;< 97 power valves are a better design { even though they are older design,an don't blow } Would love to hear from anyone with better ideas too ! All 4 of mine are Ford
Where did you get the replacement power valves? New Holley PVs will not work in 94s. The seal area is machined different and the new valve will feel tight before the gasket makes contact. They will leak. Lots of places that work on 94s have the correct valves. Lots of info on this issue on here.
Good info, my carbs are repops of unknown origin NCI is printed on the side. The replacement was more of a Hail Mary than a diagnosis and repair. I replaced it from a buddys stash. I’m going to reach out to vintage for advice, but the replacement appears to look identical to the original
You know, I don’t know. I will find out as I’m contemplating swapping out the secondary to the primary (via switching them on the throttle body) just to see if a got a wonky primary
As mentioned, original GM Tri-powers used end carbs with no idle circuits, and extra thick throttle blades that close 100%. Yours are still idling unless you figured out how to seal off that circuit. .
On a Rochester set up a friend has he plugged the idle circuits and worked the butterfly’s with valve grinding compound . Polished em up with tooth paste. his bases would hold gas when testing them. On my set up I bought bases. No idle circuit, thicker butterflys and a strong spring that completely closed the secondary carb bases. The set up came with power valve plugs to eliminate them on the secondary carbs. Never messed with multi 3 bolt carbs. Wondering if they get treated similar.
I would think not. Power valves are intended to provide slight enrichening by responding to minor variations in vacuum during cruise. I think that if the secondaries are coming in, you're probably not in "cruise".
Yes, I see NCI does have a website. Their carbs look like those being sold on a number of outlets. Perhaps contact NCI to see if they sell replacement parts if needed. It would be convenient if the old 94 parts were compatible. But that's not always the case with reproductions. I have never seen any of the new repops in the flesh. My only exposure has been the newmerious threads on here lately and they range from good, bad, and ugly. I would take the troublesome primary carb apart and check for basic thread fit, castings being flat, etc. I would also confirm the configuration of the secondaries. If no idle circuits then you need to fix the throttle blade fit. Should be no reason with some work to get the setup working. I love multi carb setups, but they are absolutely not set it and forget it propositions.
No. The idea is that there is no vacuum pulling from the secondary’s. Normally no power valves in secondary’s. put block off plates under the secondary’s until you have the primary sorted ? your chokes should be left in place on secondary’s, just not hooked up, according to @Bruce Lancaster and others on here.
@Dreddybear did a 94 post about those carbs and has run multiples before if what’s already been posted doesn’t get you there, only quickly glanced at it all. I think @Joe H is probably on it with the secondary carbs idling though
I have been at the home of NoChop (OP) a couple of days this week helping with this issue so I would like to add my perspective. The issue is fuel dripping from the main discharge nozzles during idle resulting in a rich condition. We cannot reliably adjust the idle mixture and expect to get results until we clear this condition. We set the float level and drop. Replaced the needle and seat. No change. So we are looking at the power valve since it operates by allowing fuel into the main nozzles. The NCI carbs use standard Holley 6.5 power valves like you would see in a 4 barrel so we replaced it with another one (a new one from my stash). Not that we thought the diaphragm was leaking, but that the valve might be leaking fuel when it is not supposed to. No change. We did re-center the throttle valve in the bores because they did not seat correctly. My thinking was that maybe they are leaking enough vacuum to signal fuel from the mains, they close much tighter now but no change. The vacuum at idle is about 12". Thanks to Anthony for helping us understand that the secondary carbs are not supposed to leak vacuum at idle. The secondary carb issue is likely not related to the center carb idle problem, but it does explain why it idles at 850 with the center carb shut tighter than ever.
Think you need to tackle one issue at a time. Make a solid gasket to go under the secondary carbs to block them off and get their leaks out of the equation. I would also disconnect the linkage to the secondary carbs. Then see if you can get it running correctly on just the center carb. Usually I would expect a vac leak on the secondary carbs with no idle circuits to cause a lean condition, but you have the opposite, so getting them out of the system should reduce the variables you are chasing.
The NCI website lists both primary and secondary 94's. No idle circuit or power valves on the secondary's... https://nationalcarburetors.com/NEW-Ford-1939-1948-239-272-LONGSHAFT-SECONDARY_p_2517.html
I wonder if the floats are set too high ? I have the same problem, (fuel dripping from nozzles) as you have seen on my recent thread. .
Just to be sure, is the fuel that is dripping from discharge nozzles on the primary carb? or secondary carbs? I have had this problem with my 3x2 set up on my Y block. My carbs are old Ford 94's. To combat this I have lowered the float level a little lower than what is called for. My main problem is that it runs rich when driving up a steep driveway. While this has helped, I still have to lower the float a little more and make sure they are all the same. IF your problem is on just one carb, you could take just the top off of each carb just to see if the fuel level is the same on each. I have made a tool that screws into the holes that the brass plugs go on the bottom of the float bowl. this is like a banjo fitting screw that attaches a fitting with a hose barb. on the hose barb put a clear hose and install. Make sure the hose is pointed up and when running yo can see just how much fuel is in the float bowl.
so why would it do this ? I am curious, as my twin carb 1&1/16 Holleys started to really foul driving up a long hill, to the point of cutting out. I thought that maybe the floats were too high, but would like to know the exact cause.
so is that now 1&11/32 ? which is possibly the original recommended setting ? Some recommend even lower, seems they are finicky carbs when it comes to float levels.
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