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Carb Starting Problem

Ed Martin

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I'm having trouble starting my 68 Roadrunner 383 with stock intake and 600 cfm Holley carb that I installed late last year (previous post Dec 28, 2018). I can pump the pedal three times (it only cranks), 2 more pumps and with lots of cranking it will fire up but runs real rough and then shuts down even with more pumping. Then will finally start again and keep running after a couple more pumps. I can see the accelerator pump is squirting (at least a couple of times, from under the hood) and choke is setting. It sits at least 2 weeks between driving. I'm thinking maybe some fuel is evaporating from the bowl and there may not be enough left to allow the accelerator pump to deliver enough even though I'm pumping several times. If the fuel pump is bad (leaking diaphragm or bad check valve?), then it would take more cranking than usual to get fuel to the carb.

What does anyone think?

The fuel pump is at least 30 years old. What is a good mechanical pump to use?
 
I'm having trouble starting my 68 Roadrunner 383 with stock intake and 600 cfm Holley carb that I installed late last year (previous post Dec 28, 2018). I can pump the pedal three times (it only cranks), 2 more pumps and with lots of cranking it will fire up but runs real rough and then shuts down even with more pumping. Then will finally start again and keep running after a couple more pumps. I can see the accelerator pump is squirting (at least a couple of times, from under the hood) and choke is setting. It sits at least 2 weeks between driving. I'm thinking maybe some fuel is evaporating from the bowl and there may not be enough left to allow the accelerator pump to deliver enough even though I'm pumping several times. If the fuel pump is bad (leaking diaphragm or bad check valve?), then it would take more cranking than usual to get fuel to the carb.

What does anyone think?

The fuel pump is at least 30 years old. What is a good mechanical pump to use?
You could do a pressure check on the pump; if you're seeing nice squirts of gas and smelling gas during starting attempts that is a healthy sign. How is the choke adjustment? Does is set for cold start? Could be flooding it out if choke isn't set getting too much air. Being a new carb I'd tend to rule out internal issues for it...for now anyway. Another check is filter; but reckon you installed a new fuel filter with install.
 
I see you said the choke does set correctly, though check to make sure the choke setting isn't lost with pumping losing the cold start setting (choke stays closed). No need to press pedal aggressively (opening secondary's)..
 
If you suspect the float bowls are evaporating gas, try priming them with a plastic olive oil bottle first. Works for me.
 
Todays gas evaporates faster then the older gas blends and if car sits for awhile bowls could be empty or low. I would check fuel pressure also since you say pump is old. spark plus fuel it should fireup.
 
I see you said the choke does set correctly, though check to make sure the choke setting isn't lost with pumping losing the cold start setting (choke stays closed). No need to press pedal aggressively (opening secondary's)..
Thanks Ron. The filter is a good point, it did cross my mind. I don't know when it was replaced, but it has been a while. I should replace it to make sure.
Also, I need to see (from under the hood) really how many of the accel pump strokes from the pedal I have been having to do (probably at least five) are really delivering fuel.
When you say "No need to press pedal aggressively (opening secondary's)", do you mean there could be a problem if the secondarys are open when cranking and trying to start?
 
If the choke flap is closing correctly one pump to engage the choke is all that is required.
It sounds like you are flooding it to me.
 
If the choke flap is closing correctly one pump to engage the choke is all that is required.
It sounds like you are flooding it to me.
I second that. Try popping the hood and after putting the pedal to the floor the first time make sure the choke flap is fully closed. Sometimes on mine I thought I put the pedal to the floor but it was only 95% to the floor and the choke wouldn’t fully close. Full close and it fires right up. On my old small block 360 with eddy carb I had manual choke and it would fire with full choke but to keep it running I had to tap the choke a hair open immediately after firing. Then of course disengage choke fully after warm.

If pump is 30 yrs old I would replace anyway for peace of mind. Carter mechanical from summit. Don’t lose the spring loaded pin when you remove the old pump. You’ll need it.
 
Thanks Ron. The filter is a good point, it did cross my mind. I don't know when it was replaced, but it has been a while. I should replace it to make sure.
Also, I need to see (from under the hood) really how many of the accel pump strokes from the pedal I have been having to do (probably at least five) are really delivering fuel.
When you say "No need to press pedal aggressively (opening secondary's)", do you mean there could be a problem if the secondarys are open when cranking and trying to start?
No problem; but to set the choke and prime it shouldn't require flooring the pedal. The check I mention...under hood, with car cold, move the throttle linkage an inch or so and choke should shut. Then move linkage again in a pump action to make sure the choke isn't slipping out of closed choke (plate opening). The tip above on changing fuel pump is good given age of your pump.
 
Don’t lose the spring loaded pin when you remove the old pump.
If you are referring to the fuel pump pushrod, the spring is in the pump arm. The push rod just rides on the fuel pump lobe on the cam.
If it's a stock 383 you can get a replacement Carter fuel pump from RockAuto for about $20.
 
If you are referring to the fuel pump pushrod, the spring is in the pump arm. The push rod just rides on the fuel pump lobe on the cam.
If it's a stock 383 you can get a replacement Carter fuel pump from RockAuto for about $20.
Yes I meant the push rod:)
 
No problem; but to set the choke and prime it shouldn't require flooring the pedal. The check I mention...under hood, with car cold, move the throttle linkage an inch or so and choke should shut. Then move linkage again in a pump action to make sure the choke isn't slipping out of closed choke (plate opening). The tip above on changing fuel pump is good given age of your pump.
Okay, I see what you're saying … just a small movement of the throttle linkage without the need for getting to the point of opening the secondary's. I did this before, but need to check again and that the choke stays shut. Thanks
 
If you suspect the float bowls are evaporating gas, try priming them with a plastic olive oil bottle first. Works for me.
Thanks Ranger16. I have tried this on my old carb and on the new one on the first time startup. Say bowls are dry, do you know how much (ml or cc) to add with bottle to handle say one accelerator pump squirt? Say bowls are full, how many times can you pump the accelerator pump to run the primary bowl dry?
 
Say bowls are dry, do you know how much (ml or cc) to add with bottle to handle say one accelerator pump squirt?
Adding enough gas to the float bowl for "one accelerator pump squirt" won't accomplish much. It MIGHT be enough to get the engine to sputter or maybe even start, but will certainly stall out once that small squirt is used up. I usually give it a healthy squirt (about 1/4 to 1/3 of the bottle) in each vent. That's enough to keep the engine running long enough for the fuel pump to catch up and fill the float bowls.


Say bowls are full, how many times can you pump the accelerator pump to run the primary bowl dry?
I don't know, but it would be quite a few pumps to drain the bowls. I think your foot would get tired before you emptied the bowls.
 
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