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Starts a bit rough, but runs sweet once started....?

J

jakeslim

1/2 ton status
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Sep 18, 2002
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Location
Napa, CA
Finishing touches on my 69 k5's newer engine. When I start it, it stumbles a bit then if I pump gas, it will "pass" the difficult stumbling stage and idle perfectly and does not stumble if i press the pedal fast or slow. What is the cause of this? Choke(electric)? Coil? The vacuum is perfect according to the gauge. Hmmm...any ideas? /forums/images/graemlins/thinking.gif
Oh yeah, its got an electric fuel pump also.
 
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are your floats set properly? /forums/images/graemlins/thinking.gif

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/forums/images/graemlins/blush.gif hmmm..not sure, but remember it runs great once I get it to pass this stumbling for a few seconds at start up....
would floats cause this?
 
I was thinking that th gas inside your carb was low dueto the floats being set too low at startup. then the fuel pump will fill and maintain the carb while the motor is running? What happens when you immediatly shut off the motor after it runs good and then restart? I would say that it runs good it also may be the choke, stumbleing until the motor warms up, like a chain saw with the choke set wrong.
 
its an electric fuel pump so its getting plenty of fuel. When I shut if off it shuts off perfectly(no stumbling). When I restart it, same thing stumbling until I push the pedal all the way down, then it fires right up. I can then take my foot off the pedal.... /forums/images/graemlins/thinking.gif /forums/images/graemlins/doah.gif would problems with valves cause this at startup. I know timing is right on.
 
Try retarding the timing 5 degrees and see if it makes a differance...If it's too advanced it starts really hard, The extra gas could just be the "extra kick" it needs to fire up..I speak from experience...Good luck,
Zak
 
i am positive its not the timing. While trying to find optimal timing, I easily had it retarded and advanced with the same condition. Is it possible for air/fuel mixture to cause this, or would that cause it to be a constant problem instead of just at start up...?
 
Personally if that is the only problem I wouldn't worry about it.

I'm assuming that it is not a "stock" motor, and that you've done cam and other upgrades.

If so I don't think you could expect it to operate perfectly, especially if it is carbureted. With a bigger cam you don't have the optimal vacuum at idle like when it was stock.

That's my opinion anyways. As long as my truck runs good on the trail and road, I just don't worry so much about all the gliches.

Oh yeah, I did have one thought. Is the fast idle set properly?
 
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Oh yeah, I did have one thought. Is the fast idle set properly?

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/forums/images/graemlins/thinking.gif...not sure.... /forums/images/graemlins/thinking.gif..would that cause a starting problem? Is that the screw that the throttle lever rest on? If so yes. If not I better hit the books /forums/images/graemlins/doah.gif
 
It's on the same side as the choke, as a matter of fact it is part of the choke linkage. If you search the net you can find some pics. It may be that you need to kick it up some. I don't know what RPM it should be set to off the top of my head.
 
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It's on the same side as the choke, as a matter of fact it is part of the choke linkage. If you search the net you can find some pics. It may be that you need to kick it up some. I don't know what RPM it should be set to off the top of my head.

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electric choke linkage? Ok, I'll check it tomorrow. If anyone else has anythoughts throw them my way. I want to put this to rest tomorrow since the rain is letting up. /forums/images/graemlins/waytogo.gif
 
Well if it's carburated then setting the choke AND the fast idle are definately key fators to a smooth start, atleast when cold, the fast idle screw is almost exactly opposite of the regular idle screw. Facing the carb from the front of the truck it's on the left side, down low by the base of the carb and between the choke coil and the carb itself. Usually a philips head screw...good luck...
Zak
 
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