hello; I bought a car with a newer ZZ4 crate engine and the carb on it is pictured below. The motor runs fantastic, like the legendary sewing machine - starts fine, idles at 500 +/- operates at 165 and accelerates great with lots of power. So, what's the problem ? Turning the motor off and trying to restart it is almost impossible unless it gets the slightest shot of starting fluid, then it starts up fine. Set the choke - nothing, pump the accelerator - nothing, look into the carb body and gas "appears" to be squirting when the lever is moved. let it sit and it starts back up fine, restart later and its a Rock Star ! The carb does not feel hot to the touch to a point where the gas would be boiling within the bowls, but that's just an assumption so far. Great on any metal work but not much good when it comes to the electrical or fuel systems. Any suggestions where I might start looking or testing? Thanks
It is vapor lock due to modern gas boiling off the short chain hydrocarbons. Go out and repeat this, then smell the carb for fumes. Are you running a mechanical fuel pump???? [These are the biggest heat soak] My 57 Chevy has the same problem so I added a primer pump. And just last week my friend has exactly the same issue with his 67 Camaro [327 2 barrel] So we will install a primer pump. It is not a good idea [for safety] to have an electric pump constantly pumping into a mechanical pump. If the mechanical pump has issues it can fill the oilpan with gasoline. But for priming this is OK Just buy one of those cheap "Facet" blow through pumps. A mechanical pump can draw gasoline through them when not operating. [the facet also defaults as a check valve] I connect the wiring of mine via the ignition circuit using a relay. The relay grounds via the oil pressure sender so when the engine is running the primer pump switches off. Turn the ignition on, you hear it clacking away. Start the engine and it switches off.
I bought a 71 vette that did that, in fact it is the reason the PO sold me the car, he never could figure out what was wrong. It took me a while to figure it out, but it came down to the ignition wiring. Chevy used 12 volts to the coil for stating the LT-1 but 8 volts to run it. Someone had pulled it apart, didn't pay attention to the multiple leads on the coil, stuck one on and taped the other ring into the harness. It would start cold on 8 volts but not hot. Probably not your issue but your post reminded me of that one. You can get phenolic spacers as thin as 1/4", I recently added one to my Olds and I have hood clearance issues if I go to thick on the spacer. I also installed my fuel feed backward (double pumper) so the fuel line comes up the firewall from my electric in-tank pump rather than across the front of the hot engine. Hot gas just doesn't burn as well as the cool stuff.
If its got fuel squirting out of the accelerator pump circuit and not firing I doubt its vapor locked as it has fuel going into the intake . As mentioned above id look at the voltage to the coil while the starter is cranking ( what kind of ignition system does it have ? ) If its poping off on starting fluid ( highly advise you stop doing that) It may be firing from weak spark or pre igniting and when the load is reduced on the starter the voltage goes up and it runs. I had a very similar issue on MY model * with a sbc were it had a unilite and some one ad omitted the 12v wire from the starter when it cranked and had every thing ran through the ballast resisitor that the Mallory Unilite needed . It was start occasionally but if the starter had to really work it would not . Double check the fuel stream when pumping the carb . also watch after you shut it off and be sure its not dripping fuel and flooding it out .
Yes it can be. Most accelerator pumps draw fuel off the bottom of the float bowls. yet no gas gets to the jets [Rochester 2G's are like this] Most vapor lock is 2 things .... 1: gas evaporating and lowering the fuel level in the bowls 2: gas boiling near the mechanical pump .there can be vapor expansion pushing gas back into the tank on the inlet side and a vapor bubble between the pump and the carb. An electric primer pump really works [the pump pushes gas to uptake the expansion] @steve hackel If you don't want to spend $$$ or changing your car.... You can temporary rig up a Marine Primer bulb [before the fuel pump] to test the theory.
All are wonderful suggestions, and thanks for the responses - always learning new things. The Phenolic spacer will probably be the 1st physical correction and I will be looking into all of the symptoms in a day or two. I was having this same conversation last week with another person that was helping out a friend with his 1965 / 396 Corvette, and he was explaining the issues with the poor quality of todays fuels and the removal of those compounds from them
"" look into the carb body and gas "appears" to be squirting when the lever is moved. "" And again the OP stated he has fuel shooting out the accelerator pump circuit .Thus fuel that is needed to at least make the engine start momentarily is going down the intake . If there is fuel going in and its not flooded and there is compression correct timing and spark its going to at least fire and run on the that fuel . He made no mention of it firing and dying from lack of fuel after . He is also stating the carb is not hot it appears to have a thin phenolic spacer as well on the that 770 Holley. It takes about 3 seconds to pull the fuel bowl plug and check fuel level and verify float height as well . If there is no fuel in the carb then start looking at vapor locks , fuel supply and such . The bowls are vented so nothing it locked after its past the needle valve . Vapor lock is when the liquid fuel is vaporized into a gas and the pump can not pump it to the carburetor. Fuel that that's in the carb that is boiling over / turning into vapor is not vapor locked that's a different problem and a electric pump will not change what happens after the needle and seat . It would need to have the fuel boiled out of the carb AND be vapor locked at the fuel pump to not get new fuel into the carb . remember that if the fuel boiled out then then needle is open and there is no lock or from the pump to the carb because the bowls are vented . Again the OP is claiming he has fuel squirting ( as in a liquid ) out into the carb when the lever is moving . He needs to reverify this . he can also check the float level at the sight plugs his carb has in seconds before trying to start it . If its a the bottom of the hole then the fuel level is correct . If so it is was not vapor locked and it did not boil the fuel out .
Millions of SBC's and thousands of ZZ4's running Holley's with zero issues on pump gas. unless you have a vacuum leak that spacer is not your issuer amp . the old vetts especially BBC would get heat soak in the starter and cause higher amp draws and slower cranking . Higher amp draws cause lower voltage at the coil / ignition system and now you have slower cranking with lower voltage and that can and will cause hard starting . This is more so with a marginal battery and high compression engines . If the initial timing is to advanced on cranking it will also cause it to not crank easily and again cause higher starter draw / low voltage to the coil . My 69 BBC 427 Vette was hard starting when hot . but it had zero to do with not getting fuel to the carb . If any thing it had to much . I had to put a starter heat shield on it , bigger cables and a better battery and get the initial timing back a bit more. Double check you have fuel squirting . Make sure fuel is not running in after shut off causing rich or flooding , recheck your float level a the inspection windows in the bowl and then check your cranking coil voltage at the coil . steady stream of fuel from the accelerator means its got fuel .
@steve hackel It does start when Cold or after it sets Awhile After a Run cycle ? With out Start Fluid correct ? Battery is fully charged and no voltage drop during cranking ? If so Do a Test , Wire up a Quick to alligator clamps & a button , Or Remote starter button Tool . To starter & solenoid. Key Off , No power to Ignition , In gauge the Starter so it spines Engine over 2 - 5 seconds then @ Same time Flip Key / Power "" On ""to ignition , Does it start ? Try "with out" pumping gas 1 or 2 times. Then try "with" 1 -2 pumps of gas . This will tell You /use a few things Where to Look Starter Timing Ignition Heat Ext.
If it was blown ( should not be on a modern Holley with blow back protections) it would be running horrible super rich at idle and mid range . The engine runs fine he stated once started and not cranking so. Its to rich ( flooded ) to lean ( no fuel going into the intake ) or no or weak spark when cranking. I have seen the low voltage due to no wire form the starter to by pass a ballet resistor a dozen times on a SBC . Its 30 seconds to check voltage at the coil while cranking it should be battery voltage . it a minute or two th check the fuel level in the carb by pulli gte plug on the die of the bowl and its a second to check the accelerator pump flow and to see if fuel is leaking into the intake after shut off
I agree . when I got my A PU with SBC Dad had changed out the starter and it did not have a post for the 12 volt resistor by pass . every time he would drive it it was hard to start hot . In his case he was getting heat soak from the headers and he also had a lot of initial timing and his battery was older and load tested maginal , This particular truck had a Mallory Unitlite that requires a ballast resistor . It would not start unless it got it spinning and then let go of the key and it would fire some times after the starter was not engaged. the light bulb in my head came on and said hmmmmm . I added a jumper wire from batter + to the coil and it started immediately . I was only getting 7 volts to the coil when cranking hot and I had no or very weak spark and many of the electronic units have no spark below a certain point . Dad had fought the starting issue for 5 years ;(
Don't buy anything without at least trying the solution below. This from the troubleshooting section of my website: HARD STARTING, HOT Difficult starting of a hot vehicle from 5 minutes to an hour after the engine has been operated, can be caused by the volatility of modern fuel. If you have this problem; try using the following method to start the engine: DON’T touch the footfeed (VERY important). Crank the engine over from three to 5 seconds (different vehicles will respond to different times); and then GENTLY (so as not to activate the accelerator pump) press the footfeed approximately 1/3 of its travel. The engine should start, and may run rough. Run the engine at a high idle for about 10 seconds. This issue is caused by volatility of modern fuel. Once the engine has been shut off, the gasoline is heated by the latent heat of the engine, and percolates the fuel from the bowl into the throttle area, forming a mixture that is too rich to fire. If you push the footfeed to the floor (as has been the traditional method of “unloading” a flooded engine) the gasoline continues to flow into the engine (again due to the volatility). By not touching the footfeed, you do not open the throttle plates, and the engine will pump the overrich mixture out of the tailpipe. Once the overrich mixture has been alleviated, gently opening the throttle will allow the engine to start. It costs you nothing except a few trials. I have been suggesting this "fix" for decades, and it virtually always works. One just has to find the "sweet spot" time for one's individual engine. A phenolic spacer may, or may not help. Please let us know if this technique solves your issue. Jon
He stated the carb is not very hot . 2 seconds with a laser heat gun would tell how hot its really getting .
The carb doesn't have to be overly hot; as the damage is done by heating the fuel line from the pump to the carb, which forces additional fuel into the carburetor, raising the level above the discharge nozzles. Sometimes, re-routing the fuel line away from the engine is beneficial. Like I posted earlier; it doesn't cost a thing to try it. Jon
My uncle, who was a mechanic for many years used to call it the footfeed instead of throttle. I never hear anyone use that word any more. Thanks for reminding me of Uncle Brad.
It's a great afternoon and have some time to look into several of the easiest tests you all have recommended. I am printing them out and then sorting them in order of their cold - pre start options. I will keep all of you informed, and thanks.
Was the term from in the days when the throttle was moved from the column to the floor and is a tractor term I have read and heard were you have a hand throttle and a foot throttle . OP the list is actully simple you have either No fuel ( pump , vapor or boiling out issue ) To much fuel ( fuel running i after shut off or your flooding it . No or very low spark ( likely from heavy starter draw , incorrect/ missing wire from starter , weak battery , to small of cables or bad connectons causing a voltage drop to the ignition system while cranking . You state fuel runs in when pumping the carb so I assume its got gas , double check that . If it does see what the voltage is at the coil while cranking. Good luck .
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