Hot Start with new Carb
June 19th, 2014, 08:19 PM
#1
70 Cutlass SX
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Hot Start with new Carb
I have finally come up to Newport to drive my car for the first time this year. This winter I put a newly rebuilt carb on the car, and it worked fine, though I was not able to take it out on the road.
The carb rebuild involved enlarging the idle tubes.
Now that I have driven it I am pleased with the performance: no pinging and the idle circuit works well. No vacuum on the carb port at idle, so definitely on the idle circuit.
I made no changes to the timing.
However, I now have a hard time starting the car, especially when the engine is hot.
When cold I have to crank the car for about 15 seconds before she fires up, either with me not touching the pedal, or with me depressing it a few times. She acts as if there is no fuel in the carb at all.
When hot, I have to crank a few times at about 10 seconds each, and after the third of forth time she fires up, only to stall out after a second or two. Today it took about three or four of these sequences to get her going properly. Once running all is good: idles fine, good response.
Tomorrow morning I am going to work the accelerator pump before I start up, to see if it is squirting fuel, and so indicating that there is at least fuel in the bowl.
The choke is working properly, with the flap wide open when hot.
I am either too rich or too lean, but unlike goldilocks I cannot find the spot that is just right.
Any ideas?
The carb rebuild involved enlarging the idle tubes.
Now that I have driven it I am pleased with the performance: no pinging and the idle circuit works well. No vacuum on the carb port at idle, so definitely on the idle circuit.
I made no changes to the timing.
However, I now have a hard time starting the car, especially when the engine is hot.
When cold I have to crank the car for about 15 seconds before she fires up, either with me not touching the pedal, or with me depressing it a few times. She acts as if there is no fuel in the carb at all.
When hot, I have to crank a few times at about 10 seconds each, and after the third of forth time she fires up, only to stall out after a second or two. Today it took about three or four of these sequences to get her going properly. Once running all is good: idles fine, good response.
Tomorrow morning I am going to work the accelerator pump before I start up, to see if it is squirting fuel, and so indicating that there is at least fuel in the bowl.
The choke is working properly, with the flap wide open when hot.
I am either too rich or too lean, but unlike goldilocks I cannot find the spot that is just right.
Any ideas?
Last edited by pcard; June 19th, 2014 at 08:34 PM.
June 20th, 2014, 07:47 AM
#5
70 Cutlass SX
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Eric - I will do that today. I am also getting my timing light back tomorrow and will double check the advance.
Joe - I thought the same, but the choke is wide open when the engine is hot.
This morning I checked the accelerator pump and there was lots of fuel squirting out, so the bowl is full.
I have narrowed it down a bit too; the issue only rears its head if the engine is hot and has been sitting for 20-30 minutes. I have no problem if I stop the engine and then immediately restart.
Joe - I thought the same, but the choke is wide open when the engine is hot.
This morning I checked the accelerator pump and there was lots of fuel squirting out, so the bowl is full.
I have narrowed it down a bit too; the issue only rears its head if the engine is hot and has been sitting for 20-30 minutes. I have no problem if I stop the engine and then immediately restart.
June 20th, 2014, 08:30 AM
#6
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Location: Austin, TX
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Is this a stock carb and intake or aftermarket? Insulating base gasket or spacer under the carb may help with hot starts if it's a heat soak issue boiling off fuel in the carb.
On cold start, is the choke fully closing when the gas pedal is depressed? Proper procedure is to do this once to set the choke. Sounds like you are either not touching the pedal or pumping it multiple times, both of which could make for harder cold starts.
On cold start, is the choke fully closing when the gas pedal is depressed? Proper procedure is to do this once to set the choke. Sounds like you are either not touching the pedal or pumping it multiple times, both of which could make for harder cold starts.
June 20th, 2014, 09:06 AM
#7
CH3NO2 LEARN IT BURN IT
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June 20th, 2014, 09:31 AM
#9
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my 85 442 403 has done this lately.
I believe it to be flooded either from dripping in or boiling in during heat soak.
My cure has been to use WOT to allow in max air while cranking, then in a second or three of running somewhat above idle, all is well. Cleared out.
I believe it to be flooded either from dripping in or boiling in during heat soak.
My cure has been to use WOT to allow in max air while cranking, then in a second or three of running somewhat above idle, all is well. Cleared out.
June 20th, 2014, 12:02 PM
#10
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I do the same thing after driving in our 110+ summer temps then trying to restart the engine. I came to the same conclusion about fuel percolating during heat soak.
June 21st, 2014, 05:11 AM
#12
70 Cutlass SX
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Hookem - this is a fairly stock setup, with the only modification being that the idle tubes have been enlarged somewhat. That was done because the carb was not on the idle circuit, and has worked wonders for my idle quality and vacuum readings. I wonder if this makes the carb more prone to percolation.
Dr. - good references, and since I never run in the cold I will be considering blocking off the heat crossover.
Octania - I will try this method. I had been hesitant to do that for fear of flooding, but will just keep the throttle open without pumping.
Today I will be checking the timing, and also seeking evidence of fuel percolation.
Thanks!
Dr. - good references, and since I never run in the cold I will be considering blocking off the heat crossover.
Octania - I will try this method. I had been hesitant to do that for fear of flooding, but will just keep the throttle open without pumping.
Today I will be checking the timing, and also seeking evidence of fuel percolation.
Thanks!
June 21st, 2014, 06:27 AM
#13
70 Cutlass SX
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If you google "ethanol fuel percolation" there are some interesting links to read on this.
The fuel I have in the car at the moment was put in during the winter, so I will fill up with summer fuel and see if it makes any difference.
The fuel I have in the car at the moment was put in during the winter, so I will fill up with summer fuel and see if it makes any difference.
June 24th, 2014, 07:59 AM
#15
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After a busy weekend here is an update on this.
I checked the timing and all is fine there.
I opened up the idle a bit, but that made no difference to the start.
I verified the choke and all is good there too.
I filled up will some summer fuel.
While the weather has not been as hot as it was last week, the same problems remain: hesitant start when cold, hard start after sitting for 20-30 minutes when hot.
I have tried a few starting procedures, and have the following observations:
- when cold, if I pump the accelerator three times, wait 5 seconds, then crack the engine starts immediately,
- when hot, if I crack immediately after shutting off, then the engine starts immediately,
- when hot, 20 minutes after shutting off, if I pump accelerator three times, wait 5 seconds, then crank with throttle wide open then the engine will start after a few seconds cranking, hesitates a few seconds, then idles well (very rich smell from exhaust).
I believe that the fuel is percolating out of the bowl on shut down, but is not emptying the bowl. The fuel level is low, but still enough for the accelerator pump to draw. The level of fuel in the bowl is low enough to cause the delay in starting.
I checked the timing and all is fine there.
I opened up the idle a bit, but that made no difference to the start.
I verified the choke and all is good there too.
I filled up will some summer fuel.
While the weather has not been as hot as it was last week, the same problems remain: hesitant start when cold, hard start after sitting for 20-30 minutes when hot.
I have tried a few starting procedures, and have the following observations:
- when cold, if I pump the accelerator three times, wait 5 seconds, then crack the engine starts immediately,
- when hot, if I crack immediately after shutting off, then the engine starts immediately,
- when hot, 20 minutes after shutting off, if I pump accelerator three times, wait 5 seconds, then crank with throttle wide open then the engine will start after a few seconds cranking, hesitates a few seconds, then idles well (very rich smell from exhaust).
I believe that the fuel is percolating out of the bowl on shut down, but is not emptying the bowl. The fuel level is low, but still enough for the accelerator pump to draw. The level of fuel in the bowl is low enough to cause the delay in starting.
June 24th, 2014, 10:06 AM
#17
CH3NO2 LEARN IT BURN IT
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Depending on many variables (ambient temps, altitude, available fuel blends local to you etc...) You may want to back off on the float level adjustment. The factory spec was for yester-years gas not this current corn water crap. So along with the heat mitigation methods I mentioned try lowering the float 1/32" or 1/16th.
With the engine good and heat soaked turn it off pull the air cleaner and see if you see or hear the fuel burpin down the primaries. Let it sit for a half hour heat soaked. Then actuate the throttle while looking down the primaries. No fuel shots from the first and consecutive pump actuation's would indicate fuel boil off or a severe bowl leak or a combo of both.
Sometimes you can see the fuel percolating into the primaries while its idling. Does the engine idle ok when cold and then gets rough and pops through the exhaust when heat soaked? If so the fuels likely burpin over into the primaries due to boil. Riser block offs, a phenolic base gasket and eliminating the riser thermo valve in the exhaust manifold will be your friends here.
I think you will like the results gained from the heat mitigation methods I explained. These methods have completely fixed fuel related hot starts on several cars(now for fuelie vettes!). I also mitigate heat on the starter by wrapping the head pipe by the starter with a thermo exhaust blanket and a heat shield on the solenoid.
Hope this helps.
With the engine good and heat soaked turn it off pull the air cleaner and see if you see or hear the fuel burpin down the primaries. Let it sit for a half hour heat soaked. Then actuate the throttle while looking down the primaries. No fuel shots from the first and consecutive pump actuation's would indicate fuel boil off or a severe bowl leak or a combo of both.
Sometimes you can see the fuel percolating into the primaries while its idling. Does the engine idle ok when cold and then gets rough and pops through the exhaust when heat soaked? If so the fuels likely burpin over into the primaries due to boil. Riser block offs, a phenolic base gasket and eliminating the riser thermo valve in the exhaust manifold will be your friends here.
I think you will like the results gained from the heat mitigation methods I explained. These methods have completely fixed fuel related hot starts on several cars(now for fuelie vettes!). I also mitigate heat on the starter by wrapping the head pipe by the starter with a thermo exhaust blanket and a heat shield on the solenoid.
Hope this helps.
Last edited by droldsmorland; June 24th, 2014 at 10:09 AM.
June 24th, 2014, 11:19 AM
#18
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Join Date: Jun 2011
Location: Austin, TX
Posts: 878
Agree with the above post and try something like this:
http://www.summitracing.com/parts/fe...FaJaMgod31gA8g
On cold start, one pump of the pedal should put a shot of gas down the carb throat and completely shut the choke plate. Should not need 3 pumps unless the choke did not close (extra priming) or your boil-off issue did not provide the needed shot of gas on the first 2 pumps. Your pull-off valve will crack the choke plate open a little once it starts.
Manual says you should give it a half pump on hot start. Are you watching to see if you get a shot of gas each time you pump the pedal? Holding the throttle open while cranking would be like starting a flooded engine, allowing the boil-over fuel to move on downstream as you start and could cause the rich odor.
http://www.summitracing.com/parts/fe...FaJaMgod31gA8g
On cold start, one pump of the pedal should put a shot of gas down the carb throat and completely shut the choke plate. Should not need 3 pumps unless the choke did not close (extra priming) or your boil-off issue did not provide the needed shot of gas on the first 2 pumps. Your pull-off valve will crack the choke plate open a little once it starts.
Manual says you should give it a half pump on hot start. Are you watching to see if you get a shot of gas each time you pump the pedal? Holding the throttle open while cranking would be like starting a flooded engine, allowing the boil-over fuel to move on downstream as you start and could cause the rich odor.
June 24th, 2014, 02:38 PM
#19
70 Cutlass SX
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Join Date: Apr 2011
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Thanks guys: the engine idles perfectly once started. I get the shots from the accelerator pump (checked visually). I will visually check for percolation when hot tomorrow.
I removed the heat riser last year, and am investigating a thicker gasket. Blocking off the heat cross over is a larger task than I want to do this year.
I will refine my starting procedures and advise.
Unfortunately I only have another three days in the US until September, but the weather has been so beautiful this past 10 days in Newport I feel very lucky.
I removed the heat riser last year, and am investigating a thicker gasket. Blocking off the heat cross over is a larger task than I want to do this year.
I will refine my starting procedures and advise.
Unfortunately I only have another three days in the US until September, but the weather has been so beautiful this past 10 days in Newport I feel very lucky.
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