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post #1 of (permalink) Old 03-26-2004, 10:34 PM Thread Starter
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Why does my Sammy run better in warm weather?

It's an '87 Sammy, stock ECM'd carb with the vent tube mod. It has a new oxygen sensor. My power goes way down on cold days. Most carbed motors run better with cold air that is more dense, but not my Sammy. My gas mileage also gets worse during cold weather, and the power goes down. This suggests an over-rich condition. Do I need a new air temperature sensor, the one on the fire wall? Engine temperature does not seem to be the problem here.
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post #2 of (permalink) Old 03-26-2004, 10:47 PM
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Re: Why does my Sammy run better in warm weather?

If you think it's rich , have you checked the plugs to verify this ? More than likely the carb is getting a bit plugged or one of the sensors isn't up to par , it is 17yrs old . The air temp sensor may help and there should be a test procedure for it in the fsm . Another thing to think about is gear oil weight , these things don't like heavy oil in cool weather at all .
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post #3 of (permalink) Old 03-26-2004, 11:23 PM Thread Starter
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Re: Why does my Sammy run better in warm weather?

I'm running 5w-30 oil. The light oil made a noticeable improvement during the cold weather. But my power has shot way up with the warm weather and the same oil.

When the power first dropped last winter, I found black deposits in the tailpipe. I changed the plugs, even though they did not look bad, like maybe a slightly rich condition with a little oil burning too. I put Bosch plus 4s in the thing, and put on a Bosch super coil (stock case style). The new ignition added slightly noticeable power and the motor ran smoother. I discovered the Oxygen sensor in the exhaust manifold was fouled badly with black soot. I installed a new Bosch sensor. My power and gas mileage increased, but the warm weather has made a
large improvement in both power and gas mileage.

One other thing, this is a no brainer. I found that bolt under the gas petal had back way out and was limiting my WOT. I removed the bolt and gained power, but that was during cold weather. Now my Sammy really scoots compared to what it used to, especially when the outside temp is 60 or higher. It seems like from 60 degrees on down, my power drops off, the colder the temp, the less power. Also, like I mentioned, the fuel consumption goes up as the power goes down and it seems like the loss in efficiency is caused by cooler temperatures. Any more ideas? Thanx for helping me!
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post #4 of (permalink) Old 03-26-2004, 11:33 PM
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Re: Why does my Sammy run better in warm weather?

I was referring to the gear oil in the trans, tcase and axles . Heavier oil in them other than 75w90 does make a difference . Unless the engine is running pretty clean I'd ditch those +4 plugs , they are intended for injected engines that are computer managed .
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post #5 of (permalink) Old 03-27-2004, 08:50 AM
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Re: Why does my Sammy run better in warm weather?

Here's something that I always forget and other folks do, too. Ambient temps reduce your tire air pressure around 1 psi for every 10 degrees. Too-low pressure in your tires will greatly increase rolling resistance and therefore reduce your mileage. The apparent performance also goes down a bit.

I know that sounds too obvious, but on my Toyota Echo I get about 42-43 MPG when its warm and about 36-37 when its cold without changing anything.

Just a thought!

~daxe
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post #6 of (permalink) Old 03-27-2004, 03:00 PM
 
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Re: Why does my Sammy run better in warm weather?

I have noticed the temp changes also and one thing that gets ignored is the thermal
expansion/contraction of the fuel. It also gets denser as temps fall, and expands when hot.

Whether this matches the air density changes I rather doubt, and I can't recall ever
seeing any kind of study on the subject.

How about you Sarge?

I would guess that running it through the F pump, engine compartment hoses and carb
would tend to warn it up some, but not consistantly compared to ambiant air temp.
Certainly racers have played with cold box's to cool the fuel befor the engine uses it,
but thats not practical on the street.

As for summer and winter changes, many areas change fuel additives in the winter
and your mileage suffers to keep the air cleaner. Makes no sense to me either [img]images/graemlins/confused.gif[/img]
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post #7 of (permalink) Old 03-28-2004, 12:59 AM
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Re: Why does my Sammy run better in warm weather?

I know my Weber acts completely different in temp and fuel changes due to seasons . It does somewhat have a bit more power in the summer , although I'd blame the temp changes on the truck for that one . Fuel does change a fair amount here , in hot weather I use different idle jets to compensate the increase in atomization from the extra heat . There are some pretty major changes in oil temp in the engine as well , I do go up a bit in weight for the summer since the motor works so hard anyway . It all adds up , even the resistance of the tires in colder weather is noticeable ....
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post #8 of (permalink) Old 03-29-2004, 06:36 AM
 
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Re: Why does my Sammy run better in warm weather?

I know this sounds stupid, but the choke does work off temperature. Could it be the choke setting is off...ya know, the bend it with a screwdriver setting?
And, the heat supply is from the hot water hoses that come from the firewall, I'm guessing from the heater core.(I'm not looking in there until I have to!)...Make sure the hot water is getting to the choke mechanism.

Matt

btw- I've seen these hoses re-routed as a quick fix to get you home.
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