Had my Q-Jet rebuilt (by a guy we all like..) and I've got a couple oddball issues that have come up on my 65 Gran Sport 401. It runs and idles great, normal off idle and moderate acceleration are fine, it makes a solid 20 inches of vacuum and mixtures smell normal, plugs look good. Timing curve is good, new wires, .040 and no arcing. Fuel pressure 4 lbs and new GF-94 and stone. 1. When I blip the throttle from idle, nothing happens.. the car falls on it's face or stalls. If I try to launch from idle it'll stall or stumble for 1-2 seconds, then rev. It's a fresh rebuild, and the accel pump is working fine. No backfiring or breaking up, just nothing at all... 2. When I get into the secondaries, the car just breaks up like the ignition has gone out of time - no backfiring, but it sputters and wont build revs for as long as you stay in secondaries...I checked RPM by holding it in 1st, it'll go to 4000 without breakup on the primaries..The secondaries kick in when you would expect, and there's good tension on the plates, they're not opening too early or flopping back shut. Any clues on where to start? Thanks,
Thanks Obie -thought about that too. I'm leaning toward not related, but I did just open the plug gaps to .040 and replaced the wires. The reaon I dont think it's related is a I can run the car right up to 4000 rpm in 1st (on the primaries) and it pulls as hard as I want with the secondaries locked out...
Sounds like you need to adjust the secondary air flap. It may be a little too loose and opening too soon. these adjustments are impossible to get correct all the time by a Qjet builder, as each engine situation can be a little different. If you tighten the air flap adjustment a 1/4 turn, I bet you will see a big improvement.
I had to tighten mine a half turn from where it was when i put the spy on guess I new to open up the price, sounds like an airflap adjustment
Ha! You dont want to know. Went out the other morning to run the car hard while the secondaries were cold and locked out, and it started DUMPING fuel all over the engine... got disgusted, disconnected the battery and walked away for a few days. Thought about it, and I has stuck a small screwdriver down the vent the night before to check the primary rod hangar for travel / binding and thought I missed the first time...I sure did. When I missed, I had poked through the airhorn gasket, and drove the little flap that goes around the hanger and rods down againt the float, all bent over. I had gas in my air cleaner, all over my freshly painted block and intake, every little nook and cranny! Damn lucky I didnt burn down my garage! So now the carb is fixed, but we've got snow. I'll try again in a week when i can road test after the salt has washed away. Thanks for checking in on me....
Thanks Obie - been collecting opinions and I guess my next steps are; Double check for vacuum leaks - should be good but I'll check again Shorten stroke of accel pump to cover off-idle flat spot - take that little "nub" off the top of the shaft tighten secondary air valves - I dont think they're coming in too early, but I can try it. Pump shot is immediate, choke pulling off as expected, secondary dash pot is working correctly, secondary cam is new and working correctly, full throw on all throttle plates, good float setting, idle passages and bleeds clear....I'm running out of stuff to check
That happened to my Early '67 carb last three numbers 240 + the fuel plug popped out from the needle seat conversion... pretty sure the '66 carb had the plunger style needle seat as well or if yours has been converted... check that plug is in good and tight or the plunger needle seat didn't go... the later carbs have the newer screw in type needle and seat... and my exact reason for using a newer carb... Freshly Painted Manifold Gas Peeled Paint.... Figured I got off Lucky... Could have been much worse in my case as well..... The Late '67 carb from the 430 last three part numbers 248 has the same throttle linkage and base plate manifold fitment as the '66.. The newer style needle seat and an adjustable secondary air flap... You lose the choke tho.. I removed the choke flap anyways for a little more primary air flow... Matching numbers shouldn't matter for safety and a little piece of mind.... Sorry to hear that it happened...
Hey - havent heard from you for a while! Yeah, I'm lucky because this is a 304 service replacement carb - screw in style needle and seat and adjustable secondary, but old style float geometry. I know it's a good carb, I'm just getting a little frustrated
Got it together did ya.... Off the line delay huh,,, You stated a good timing curve... Are you using points, or a pertronix type... I blew a pertronix module once and scratched my head for weeks, until I threw the points back in to test... Maybe another quick check of the vacuum advance or like you said (possible vacuum leak, a little either spray on there shouldn't matter now... lol.. ) check that all that porting is matched up good to the gaskets... and, With all your new manifold volume, the secondary jetting and spring tension as stated earlier... My float bowl would literally run out of gas because my original needle seat inlet opening was to small to keep up with high fuel demands... Guess it's our big floats as well... Using the high flow .135 needle seat assembly cured that problem... You'll get it figured out, usually it's the simplest thing, once you see it...
Using a pertronix III , pretty happy with it. Though about the larger inlet needle and seat, but I havent even gotten to make a full pass on tnhis thing to figure out whether fuel capacity is an issue. If it is, I'll probably cut down the filler block first. Yeah, I'll figure it out...just need better weather.
Better weather is here! Tore it down, put it back together. The secondary issue is cleared up, so thats good news (not that I know how I fixed it...) Still have the off idle issue - blip the throttle and it falls on it's face. Roll the thottle in, and it'll smoke the tires until you let up. Some observations from today: Power piston moves freely, doesnt bob at idle and lifts when vacuum goes away (strong enough to take the screwdriver with it) Shortened accel pump shaft, works instantly, good stream both shooters, cup stops before inlet and doesnt hang up reset mixture screws, now at two turns out (from noticable idle slowdown point) still at 19-20 inches vacuum slowly close choke at idle and again at 2000 rpm - no change until engine chokes The car only does it after it has been at idle for 10 seconds or so - has good throttle response from 1000 rpm on up and while idle is still settling in....like while it's still running rich from prior throttle opening or vacuum just starting to pull down piston. Any ideas?
Bigpig 455 I would check the duration of the accel pump at a slow rate of throttle ... if it comes up short check the accel well check ball for seating ,fill the accel well, it should hold gas with the check ball seated. If not reseat it by striking with a brass drift to form a new seat. You might want to close the choke about 1/4 - 1/2 with a tie strap & take note if the dead spot goes a way... also check your stone filter (take it out) I have seen them cause a problem off idle & still work well on the upper end (glazed) good luck Rett Mark Campbell
Manifold too cold????? o No: What are the temps on it after the engine is fully warmed up????o No: cat pee not ''flashing'' into a vapor.....need the heat under the carb again??????? o No: La da de da..... :laugh::laugh: Probably aint nothing wrong with the carb.... you may be chasing ghosts.......
Thakns to all who responded Doc - Good point, although the problem is a bit more pronounced than when I ran the blocked gaskets under the AFB manifold...this'll give me a chance to use my pretty little chinese infared thermometer. I'll let you know, because you may be right.. all things point to that the carb is set up correctly. I do have heat to the manifold, but blocked at the carb base with brass plugs. Mark - maybe I'll replace that filter anyway - it looks clean, but I did have some crap run throught the line when I was running with it out (which is why I put it back in, and rebuilt the carb again) The pump shot lasts all the way through into the secondaries at moderate throttle opening speed, after sitting all night. slower opening makes the stream erratic and quit about at the secondaries, but that might be due to varying throttle pressure and speed, and fuel escaping past the cup when it moves that slow. It is not a spring reinforced cup. But we know the well is holding fuel and has a strong stream through throttle range when stomped. I did try blipping the throttle with the pump disconnected, at first I thought it might be better but it was pretty much the same (which some would say means a bad pump???) I do know the primaries do the same thing with the choke closed, but that was with the engine cold, and then the manifold heat issue could come into play..I'll try today with the engine up to temp..I can say that by closing the choke slowly at idle and again at 2k rpm there isnt a noticable difference befoire it dies. One thing the builder brought up - I am running a Pertronix III with a Ignitor II through a resistor wire. It has always worked well in the past (up to and past 5k rpm), but I did recently open up the gap to .040 (from .035) There is no misfiring, but could I be "blowing out" the spark when I nail it? I might grab another set of plugs today and try at .035 for the hell of it - I'm running Bosch platinums and I like them alot, but these plugs have 2 seasons and plenty of raw fuel thrown at them... I did have a charging issue I just fixed. The cheap chinese regulator was charging at 12 volts or less, I bought a Wells VR715 replacement, that cured the charging issue and might have had something to do with curing the secondaries breaking up - that always felt electrical and was happening at the same time. Thanks again for all the tips..
Rett , By removing the accel pump & seeing no improvement it would tend to make me think that it is not working to spec, how ever you might want to try shooting a burst of carb cleaner in the pri side to see if this covers the tip in dead spot. Does this carb have a APT stop adjustment? If so you might try to raise the rods a 1/2 turn @ a time. I have a set of Gessler iron heads on my 455 that have the exhaust heat passages have been filled with aluminum... no heat what so ever to the intake . For sure it is very cold blooded & I don't run a choke ..... I have installed a choke blade for testing & it did't make a lot of differance cold... BUT when it got up to temp it is as if someone turned a switch on & all is well idles, no flat spots, etc. When you take pre heat away from the intake ,and the engine is cold the fuel condenses to fast in the intake runners & is not a good combustible mixture. Rett, is this problem only when cold? After warm up does the dead spot go away? If the problem is still with you after it warms up I would (form a new checkball seat & leak test it with soapy water & compressed air @ the pump discharge passages).A pump with the garter spring would be a good idea also. One more thing , how about swaping the dist for a good known unit,I don't know how your ing is set up but on a pionts system the wire going to the coil wears through @ the base of the dist & when vac adv pulls on the plate it grounds out, on the HEI the pick up coil wire can break off when vac adv is applied . Worth a try I guess. Mark Campbell
Thanks Mark - No APT on this carb, it's a 66. I will try the carb cleaner/tip in thing though. I do have manifold heat, but it does it hot or cold. The distributor is set up pretty well with a new Pertronix III / lead wire and good advance -I just checked it all about a week ago. I do like the idea of a new cup with garter seal - I'll get one from Gessler maybe monday. ---------- Post added at 05:07 PM ---------- Previous post was at 05:07 PM ---------- ---------- Post added at 05:08 PM ---------- Previous post was at 05:07 PM ---------- ---------- Post added at 05:11 PM ---------- Previous post was at 05:08 PM ---------- Just changed out plugs for AC R43S gapped at .035 and richened idle by 1/2 turn- seems to respond much better, no off- the- line bog? That would be nice if I fixed it...Still have light-part throttle fluctuation (hesitation?) , but that could be pump shot. Not quite there yet, but getting close. ---------- Post added at 05:12 PM ---------- Previous post was at 05:11 PM ---------- I cant tell why, but the site keeps adding everything I write to my earlier post..... ---------- Post added at 05:12 PM ---------- Previous post was at 05:12 PM ---------- I cant tell why, but the site keeps adding everything I write to my earlier post.....
Just for fun,,,, put the heat back up to the carb and see what that does..... I dare ya.....i double dog dare ya....heck, I tripple dog dare ya..... wanna go for quads????:Brow:
