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Hard start

H

hacmjim

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Hi, I have a 69 roadrunner, 383, 4speed. Motor has a 480 lift comp cam, 600cfm edlebrock carb and intake as well as headers. All is new. Problem: getting it up to temp and shutting it off and restarting maybe 5 minutes later, starts very hard and if I give it gas, it has a huge backfire, then starts. Runs well otherwise. Never overheats. Any thoughts would br appreciated.
 
mMine did the exact same thing for years until i switched to a high quality electric fuel pump. When it's hot, I turn the key on for a few seconds to pressurize the fuel system then start it.
 
Well....I've had fuel boiling (aka vapor lock) & my problem was solved with carburetor heat spacers (thick, cardboard looking carb base gaskets) & you might take a look at how you fuel line runs (close to exhaust?) and insulate it. ALSO, if your engine is cranking slowly (you didn't say exactly what a "hard start" was), then look at the headers being too close to the starter. If this is the case, then insulate the headers with header wrap & do something similar on the starter. High heat = high electrical resistance = slow turning starter.
 
If it backfires on start..one thing is there is alot of gas vapor in the exhaust from cranking it over. I would check the fuel line route and also the issue with the headers/starter as stated above...you may also check the timming
 
Thanks for the replies. Added info: i installed a carb spacer, moved the fuel line, insulated the fuel line. Timing is good. WhaT I meant by the hard starting comment is that it turns over fine, but just won't fire. Guess I should consider an electric fuel pump?
 
Your other option is adding a return line.
Personally, I would do that before the electric pump.
 
Next time this happens, put the accelerator to the floor and start it. When it fires, let off so you don't rev the motor with low oil pressure. I have given up determining why this happens on my car. As my parents would say "it is what it is". In the end, I just want to get on the road and enjoy the ride. Has been doing this for many years now off and on in the heat of summer, no discernible patterns, and it drives daily, no issues.

If you have backfire often then that will need to be addressed. But hard start I wouldnt stress too much.
 
had the same thing happen on a 68 charger i had.spaced carb,insulated fuel line,put on a holley electric fuel pump.nothing solved it.best i could figure was fuel was turning to vapor and staying in the air cleaner assembly.crank and caused a super rich condition,hence slinktrr's answer.ended up selling the car before i ever really solved it.
 
Electric pump did not help me. Went back to mechanical for reliabilty and less noise. Some of it is characteristic and the rest technique. Under 5 minutes, it may light right up. Otherwise, needs 40 minutes between starts. With a hot restart you may get lucky with a light tap pf the throttle while cranking. I've got the spacer too. As long as ethanol boils at 173f, this problem will persist. When our cars are running perfectly cool at 180-195, it is above the boiling point for that unwanted crap.
 
Timing to advanced ?
 
Sorry was eating when I read this post missed your post about timing being good..
 
Dennis H said:
Electric pump did not help me. Went back to mechanical for reliabilty and less noise. Some of it is characteristic and the rest technique. Under 5 minutes, it may light right up. Otherwise, needs 40 minutes between starts. With a hot restart you may get lucky with a light tap pf the throttle while cranking. I've got the spacer too. As long as ethanol boils at 173f, this problem will persist. When our cars are running perfectly cool at 180-195, it is above the boiling point for that unwanted crap.
Click to expand...
Do you US guys have no non-ethanol options where fuel is concerned? We here in BC have Chevron 94 which at least claims to be ethanol free. It's pricey but all I run in the Super Bee. I do plan, however, to run a return line...if only for piece of mind.
 
Once again, have you verified choke adjustment? You never responded. An improperly adjusted choke can wreak havoc with starting a warm engine.
 
Lionized said:
Do you US guys have no non-ethanol options where fuel is concerned? We here in BC have Chevron 94 which at least claims to be ethanol free. It's pricey but all I run in the Super Bee. I do plan, however, to run a return line...if only for piece of mind.
Click to expand...
91 Summer/Winter blend is the best we can get. No ethanol-free in these parts. Car ran better back East (US) back in the day on Sunoco 94 Ultra.
 
SlinktRR said:
Next time this happens, put the accelerator to the floor and start it. When it fires, let off so you don't rev the motor with low oil pressure. .
Click to expand...

This is what works on my GTX. Seems to be a common issue with Mopars.
 
With today's fuel, I've had the following cars and starting charateristics are all the same:
69 - 350 w/ original Quadrajet
79 - 360 w/ original Thermoquad
68 - 440 w/ original AVS

All carbs rebuilt, tuned properly, and chokes completely functional.

All start with choke and 5 seconds of cranking when they sit for more than 2 days, cold. Full press of the pedal when cold. When hot and within ~2 hours they all start with nothing but a twist of the key. If I hit the pedal it floods instantly, then I have to hold it WOT. After more than 2-3 hours I hold the pedal open just barely, about 10-15%. I make sure there is no accelerator pump shot either, push slow and only a little. They all start right up. Today's fuel needs to have a lot of technique.
 
i'm guessing a very slightly leaking fuel line,
just went thru this issue myself and that is what it turned out to be.
the leak was barely noticeable and it took me a long time messing with the car
before i spied it.
 
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