When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Executive summary. Rebuilt engine, only starts with starter fluid, once warmed up stalls when blipped. Need advice on what to try next. You guys have been a HUGE help through the last few months, and we are nearly there!
Details:
Amateur mechanic, first car of any kind that I have worked on. Learning like crazy!
1981 FB 12A. Everything OEM stock.
Car was running great before rebuild. Was a first time starter, even started when stalled by accident, started fine hot or cold.
Rebuilt engine myself over last four months, prompted by multiple fluid leaks. New seals, gaskets, o rings. Now runs with zero leaks.
Did not rebuild carb because I am scared of it and car was running fine. Simply removed from engine and let it sit untouched for three months. Then scrubbed the grime off in a tub of diluted purple Simple Green and blew out the openings with an air gun.
Car has fresh gas added on an almost empty tank (did not flush).
Battery one year old, very little use, fully charged.
After rebuild will only start with starter fluid.
Once started need to hold revs at 2500rpm until warmed up, then will idle at around 1100rpm. A little choppy, and RPMS at dash fluctuate plus/minus 100rpm.
If I treat the accelerator gently, the car pulls nicely so I think the compression is good? I can do a simple check with a pressure gauge with non return removed it that helps.
Once the engine is running and warmed up, if I blip the gas pedal with a sharp stab of the foot the engine dies immediately. Very consistent and repeatable. A total pain as any aggressive move on the accelerator kills the car and I have to push the car off the road and restart with starter fluid.
Timing checked at 1100rpm with timing light. Bang on the yellow dot. Checked with vacuum lines removed from dizzy, did not check the higher rpm timing.
Idle screw seems odd. I can turn it one way and get the idle speed to increase, but I cannot get it to drop below 1100rpm even after several turns the other direction to that which sped the engine up. Maybe throttle cable too tight, but dont think its connected to the stalling/starting issue?
Have not touched the adjusting screw on the carb to the left of the idle speed. (Fuel mixture?)
Got zapped by a spark plug cable or something around the dizzy cap whilst turning the dizzy to fine tune timing with engine running. That normal or a clue?
What to try next? Thanks!
Last edited by Slow_sevens; 04-12-22 at 07:24 PM.
Reason: More info
If it stalls when you blop the throttle you need to check your accelerator pump circuit. Pull the air cleaner off and look down the carb. You should see fuel squirt down the primaries when you blip the throttle.
With that said. It sounds like you need to rebuild your carburetor. Don’t worry, it’s not very hard, in a nutshell it’s taking it apart, cleaning it, and putting it back together with new gaskets. If you can rebuild your motor you can rebuild your carburetor.
To give you a head start, you’ll want to find a specific rebuild kit with metal crush washers for the fuel inlet/outlet and banjo bolts. I can’t remember the name off the top of my head but some searching around should get you what you need. You’ll also want to keep the factory needle valves and seats. The aftermarket ones tend to get stuck sometimes and can be a headache to get running well. Also leave the floats alone and do not try to adjust them. Last thing is if your needle valves are stuck open after rebuilding the carb, tap on the banjo bolts with a small hammer and that will reseat them. You may have to snug up the banjo bolts again after doing this.
Appreciate the response. May indeed rebuild the carb. Just got to get my head around the idea.
On the test you suggested.... just to clarify...with engine running and warmed up and at idle speed, if I look down the barrels of the carb and I give the throttle cable a yank I should see a spray of fuel in the barrels. Or as we suspect their will be no spray and the engine will die. I know, dumb question, but you are dealing with someone who just had to pull their tranny because he forgot to install the rear main seal during the engine rebuild!
If/when you rebuild the carb this will make a lot more sense, but you can actually do it with the engine off and cold. All you need is fuel in the bowls (the rear one I believe to be specific). You can check the fuel level looking through the sight glasses.
All the accelerator pump circuit does, is a diaphragm gets pushed in and that squirts fuel into the primaries. When you let off the throttle the diaphragm refills with fuel and is ready for the next throttle blip.
1)
Accelerator pump was also my first thought. At any speed (hot or cold) the air flowing through the carb draws the appropriate amount of fuel from the regular fuel jets. But sudden throttle inputs need a little extra shot of gas until the main jets catch up to the air flow. If your A.P. isnt squirting then you get a sudden lean spot. I know this was said already, just wanted to reinforce the idea.
The A.P. is on the driver side of the carb, below/left of the cable bracket. It is mechanically connected to all the linkage on that side of the carb and should move whenever you move the linkage (pull cable, push gas pedal, turn linkage by hand). Looking down into the carb you should see a stream of gas squirt into each of the primary (smaller) barrels.
2)
Throttle. You should be able to get the RPM down below 1000. Check where your cable mounts in the bracket. There are 2 nuts so you can adjust the slack to the carb. The bare wire/cable should be just-slack when you're not on the gas. If this isn't the problem then you need to look for ...
3)
Vacuum Leaks. Often a high or moving idle speed is due to a vaccuum leak. Double check all around the carb and rats nest looking for disconnected or damaged tubes. Be sure any nipples that don't have a hose are capped-off (rubber caps). Make sure the distributor advance lines are connected. Sounds like a small vac leak. When I first started-up after swapping on a Holley intake I had a Big vac leak and the engine wouldn't come down below 2200 rpm. My avatar picture is my header on that night, not long after cold start. Looks like neon.
All-in-all it sounds like you have both a non-functioning Accellerator Pump and a small vac leak.
Well gents, looks like you did it again. Float windows front and rear both show has half way up glass so know I have gas to the carb. When I pull on the throttle cable I can see a lever pushing into the back of the accelerator pump. But when I look down the two smaller openings in the top of the carb as I give the throttle cable a yank... no squirt at all. Not even a dribble.
Carb rebuild kit on the way. Now I know what I have to fix kinda looking forward to this. Sitting at a bench sure beats wrestling with a transmission under the car. And the more I look at the carb the more it looks like bicycle derailleur and brake technology, all springs and levers. And I fixed bikes for a living for 20 years. Bikes are also metric, which jibes nicely with Japanese cars.
When you take apart the accelerator pump circuit there are 2 check ***** and two brass weights. The check ***** are the same, the weights are different so take note of where they went. One should be fat and short, the other skinny and long. The long one goes in the inlet, and the short fat one goes in the outlet side.
04-12-22, 07:01 PM
