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Old 01-13-2011, 11:52 AM
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Issues with cold starting 350 sbc in cold weather

Hello guys sorry to post again but been having some weird issues with my engine starting in very cold weather. Engine is a 350 small block chevy with mild gm zz4 roller cam and old style HEI distributor and a holley 600 carb with manual choke.

Timing is 12 initial with vacuum advance hooked up to full manifold and it adds around 12-14 degrees when running. Total timing is 32 mechanical by 3500 rpm.

If I have my truck sitting for a couple of days and then getting in to start it I give it about 5 shots of gas and it will fire up for about a few seconds or two then dies off. I then try pulling my choke and then I try to turn it over again and it seems to just turn . Tried again and did not want to flood the thing so I put my choke back
off.

So I give it one more shot and it will seem to want to start and some times it will backfire through the carb. I then got frustrated and gave it 3 more shots and pulled my choke and then it ran fine. Am I doing something wrong here?

I have my timing and my carburetor tuned very well and did not have some many problems like this last year during winter months. I could give it one shot of gas or some times 3 and I never used my choke and it would fire right up and not quit and stay running with no problems even after sitting for a few days.

Or if I used my choke I gave it a couple of shots and then kept my pedal down then pull my choke and it fired right up no problem.
I never got any backfire while cranking it as well and this was with all of what I have now.

I have checked float levels and everything else and nothing is out of proper stetting. This is in Ohio with mid 20's for temp so is that the reason for all my problems as I have read carburetors are very lean in cold weather.

I just don't want to give it too much gas and flood the thing and wash my cylinders down. Am I not giving it enough shots to begin with and that is the reason for backfire? It seemed to do a lot easier with no problems like last year. It would do better then this.

Thanks for any help.
Eric

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Old 01-13-2011, 12:30 PM
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This is reality. Liquid gasoline does not burn. It is only the gas vapors that burn. When it is very cold, gasoline does not vaporize very easily. That is why you have to pump the carb, and choke it when it is cold. No way around this.
You can either use a lot of choke, or a lot of pumping, or some variation of both to get the engine to run. Either that, or park the car in a warm garage.

Are the numbers on the timing from last year, or have you rechecked them again this year? Are your spark plugs now a year old? How about the whole secondary ignition system.

The choke and throttle are interrelated. Pulling the choke on, also gives the engine some throttle. If the choke is on, sometimes giving the engine a lot of throttle will open the choke a little. On some carbs, you have to open the throttle, then apply the choke to get the choke to "set" fully. Because the choke opens the throttle slightly, pumping the carb with the choke fully on may not allow a full shot of gas from the accelerator pump, because the throttle is held in a fast idle position. On some carbs, there is a vacuum mechanism that slightly opens the choke after the engine starts and is running. Because of all these carburettor idiosyncrasies, you have to learn how your carb works, and how to deal with it in cold weather.

If everything is in good shape, you just need to learn how to start your car, when it is very cold. You may need to pump the carb one, three, or seven times, set the choke, and then crank it. Keep in ming, those numbers are totally random. You need to find the number that works with your engine.

You might have a problem with the float bowl being slightly low on gas, if you have a mechanical pump. Especially if you pump your car a lot to start it.
You are driving your car, and you park it. The float bowl is full, because every thing is normal. The warm engine evaporates some gas in the float bowl. It sits for a few days, and some more gasoline evaporates from the float bowl. it is cold when you want to start it again, so you, knowing it needs extra gas, pump the carb a few (or several) times. This takes even more gas from the float bowl, and dumps it in the intake manifold. Now, you crank the engine. It starts, and runs briefly, on the gas in the manifold, and before the carb bowl can fill again, the engine dies.
This is normal for a carb engine, and you just pretty much have to deal with it. Modern fuel injected engines have spoiled us.
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Old 01-13-2011, 01:15 PM
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Hey Eric long time no see,,,how you been? Most likely not a cure but dam sure a help for any cold temp start situation,,,you got a block heater in that rig?

TJ
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Old 01-13-2011, 03:41 PM
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Ayuh,... When I cold start any carbed motors in Cold weather,...

I start with Full choke, 'n Full throttle....
Once I get a Kick-over, I go to 1/2 choke, 'n some throttle....
It'll usually start, 'n I play the choke abit, til it's warmed enough to run...
Choke totally Off, might take a minute, maybe 2,...
Depends on the motor/ carb....
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Old 01-13-2011, 04:51 PM
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Hello guys thanks for the info nice to know that I am not totally doing things wrong here. I guess its just weird my brothers stock 305 that is old and worn out you can give it one shot and it starts right up and he has the same carb as mine and no working choke. Anyways everything is new with the plugs and everything else is less then a year old. Nice to hear from you custom10 again. I will have to see in getting one for my truck.

I just set my timing two weeks and my carb idle mixture screws. I just got this engine back in my truck about three weeks ago. I know fuel injection has spoiled us but I never had any back fire through my carb last year. Only difference in engine is the zz4 cam.

But I went out just a little while ago and gave it a couple of shots and it fired right up then died down I gave it a little more almost got a backfire then set choke and it ran like a charm. I just keep getting the backfire here and there on cold start up which kind of worries me.

It caught fire the one day! That got me moving fast for a rag to throw on top of it as my air cleaner was off because I was wanting to check things over as to why I could not get it started and I was looking for any flooding issues from floats and they where fine. Well I will guess I will have to trial and error and see how it goes. Sad part of it is I have to take the engine back out cause the stupid one piece gasket is leaking and the rear main seal as well. O well its keeping me busy. Take care guys
Eric
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Old 01-13-2011, 05:26 PM
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Its starting to sound like a bad coil primary circuit,seriously, they are cheap. I have had several cars that started card when cold just like yours, after they start the rest of the day ,no problem. The coil was the trouble. Try checking it with an ohmeter, if you have a known good spare maybe just put it on to see if the trouble clears up. You had me at "even caught fire once".

A primary circuit that is going open circuit can cause the secondary to fire erradically and out of time, causing misfires and backfires and ...well....
fires
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Old 01-13-2011, 06:07 PM
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A manual choke take a little learning. If it were me I would pull the choke closed, pump it twice and turn it, as soon as it fires push the choke in a little so it opens about 1/4 inch. After a minute, start easing it in until it is fully open at about the 3-5 minute mark.

The last car I had with a manual choke, I made a couple marks on the choke rod where it came out of the dash.
The first was full choke and the second was 1/4 inch open.As soon as it fires you need to get it open a little or you will flood it out.
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Old 01-13-2011, 06:54 PM
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Just some info about how I start my 383 stroker, 750 holley vac secondary with NO choke:

I full pedal press down then several quick short pumps as it cranks. Within a few seconds it fires up and I keep my rpm over 2000 by foot and if I hear it start to sputter down I pump it quickly more a few times to bring the rpms back up. Currently in NYC at 20' air temp it takes several minutes of warming before I can leave it alone at idle without a sputter stall.

Just a total guess, but, if it starts and then stalls and is hard to restart: After it stalls, crank it with no pedal and as it cranks slowly press down on the gas so that you're at 1/2 throttle within 3 seconds. Sometimes that can get you enough air sucked in to avoid a flood and you're not dumping in fuel from the accelerator pump by going so slowly. Choke open. Again, this is just something Ive experienced and might NOT be what you need
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Old 01-13-2011, 06:56 PM
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Quote:
Originally Posted by T-bucket23
A manual choke take a little learning. If it were me I would pull the choke closed, pump it twice and turn it, as soon as it fires push the choke in a little so it opens about 1/4 inch. After a minute, start easing it in until it is fully open at about the 3-5 minute mark.

The last car I had with a manual choke, I made a couple marks on the choke rod where it came out of the dash.
The first was full choke and the second was 1/4 inch open.As soon as it fires you need to get it open a little or you will flood it out.
Try adjusting the fast idle screw also. Sounds like you don't have enough RPM to match the amount of choke your pulling.
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Old 01-13-2011, 11:17 PM
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With most of the manual chokes I have had there seems to be a sweet spot. Pull the cable too much past that and you are stumbling, not enough and no choke effect. I use a brass insert from an old style copper wire marrett, they have a set screw, slide the brass insert over the cable and tighten down, this limits the choke cable pull against the choke cable jacket/hold down right at the sweet spot,,,monkey'n around to find it but once set just pull the cable same amount every time.

Check the power valve after those backfires...
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Old 01-14-2011, 04:38 AM
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Originally Posted by sqzbox
Try adjusting the fast idle screw also. Sounds like you don't have enough RPM to match the amount of choke your pulling.
Better yet, try and find an electric choke model 600cfm or maybe a 650-670 cfm. The 600 is sort of minimal for your app.
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Old 01-16-2011, 03:52 PM
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I know this doesn't help much but I have my 350 with qjet starting at 2 degrees outside temp without a choke rod in place. I hit it once to close the choke and crank it until the carb is full and it starts running on fast idle. I let it run on fast idle for just a little while and kick it back down. It runs a little slow until it warms up and then returns to 800 rpm. I have had other carbs on the motor that would not do this. I guess it is a combination of a well tuned motor and a properly adjusted carb.
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Old 01-16-2011, 05:26 PM
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one reason you may not have had this issue last year is gas. more and more gas no has the 10% ethanol in it.
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Old 01-16-2011, 06:24 PM
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Have you checked to make sure that the accelerator pump is working correctly? I've had engines that were hard starting because the pump just wasn't giving a full shot so you weren't getting enough gas.
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Old 01-20-2011, 04:02 PM
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Hello guys sorry I have not gotten back. I have not had internet for the last week almost because of bad lines and I also finally got my engine back in my truck again for the second time. The stupid rear main seal and oil pan gasket leaked but fixed for now.

It seems it might be gas related wise since with higher prices it would not surprise me it might be watered down some heck I don't know. I don't go to stations with the 90 10 blend.

I like to use the 100 blend with no ethanol. I also got a electric choke to put on my holley as it seems I can't never really get my manual choke to always work right and sometimes no matter how much I set it and mark my cable it is either too much to start off with.

Anyways the electric choke will be easier to tune wise and I won't have to mess with so much trial and error. I also think just because of it being so cold out and only being above 5 degrees with the wind chill factor my engine seems to need quite a bit of fuel to get it going as compared to some times last year. And only giving it a few shots of gas is not enough.

Yes I did check my carburetor and everything is up to spec on it. I give it 5 shots turn it over and it fires right up and then I pull the choke and it runs like a charm. I guess with out enough fuel for priming the engine wise its not un common to have a lean back fire cause of the dense cold air.

Will be getting my choke on soon when the weather breaks as a snow storm is going on right now and will really look everything over real well on the carb just to double check.
thanks guys appreciate your help.
Eric
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