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Help a newbie tune his GST 7.7

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Help a newbie tune his GST 7.7

Old 02-27-2008, 09:20 AM
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cablek
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Default Help a newbie tune his GST 7.7

First of all I would to thank the entire forum for being so helpfull. It's nice to know that a newbie like myself has a place to come and ask "stupid questions" with out getting kicked around.

I am having issues with tuning my GST 7.7. If I start at the defaults (3 1/2 turns out for high speed and and 1 turn out from flush for low speed), I am having issues getting a good tune. I have found that it seems to run best with the low speed at 1 turn in from flush. If I try to run it any richer than that it loads up very quickly and likes to stall if I quickly let off the throttle or apply the brake. I am starting to wonder if I am misreading the directions. I took the 1 turn out from flush to mean that the screw should be be flush with the collar. Is this correct, or is it 1 turn out from bottom? The truck runs okay as is, but I feel like it is missing a little get up and go. Any suggestions would be greatly appreciated.
Old 03-12-2008, 04:04 PM
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slawhammer
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Default RE: Help a newbie tune his GST 7.7

I also a GST 7.7 truck.you did not say if you have 1 gal of fuel or more run thru your truck ..any adjustments should be made after it is up to temp of over 200 deg.Low side is 1 out from flush meaning the rubber is flush.High side 3 1/2 out...If you screw the needles in and bring them out this where you should be for factory settings..1mm on slide carb opening.. clockwise is (going in)LEAN make high adjustment
first ..turn maybe 1/8 clockwise..drive truck bring back check temp redo again keep doing this until about 240 to 250 deg.Then adjust low side in clockwise a 1/8 in..you want to take off smooth no bog down
or stalling..watch for good blue smoke also..last adjust idle stop for rpm..screw in to keep engine running at a good rpm by not to stall out the engine...After you get this down about the only adjustment will
have to make is the high side..that has to do with out side temps for the day and humdity...Also did you cut a hole in your whindshield..drivers side need 1 1/2 to 2" hole for air flow to engine..Hope this will help you out...The adjustments change daily so you always have to make small adjustments..This engine runs best at 250 deg..but you use temp as a ref point..tune for power make sure you got blue smoke
you might have to richen it up abit some times ..counter clockwise RICH..Depends on the day outside..Hope this helps..
Old 03-13-2008, 08:51 AM
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cablek
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Default RE: Help a newbie tune his GST 7.7

Thanks for the advice! What did you mean by "Low side is 1 out from flush meaning the rubber is flush"?

Just not sure what rubber you are refering to.

Thanks...
Old 03-13-2008, 02:10 PM
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DarkFire989
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Default RE: Help a newbie tune his GST 7.7

I would highly reconment getting the OFNA check valve from tower hobbies. It will definently help your tune greatly. If you get it though you have to lean it a bit more because it helps with the tank pressure. [link]http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXEYG3&P=7[/link]
Old 03-13-2008, 02:13 PM
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cablek
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Default RE: Help a newbie tune his GST 7.7

Mine just arrived yesterday. I plan on installing it over the weekend. Will I need to lean both the low and high speed mixture?
Old 03-13-2008, 02:24 PM
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DarkFire989
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Default RE: Help a newbie tune his GST 7.7

I think just the High end. But make sure you are getting good temps.
Old 03-13-2008, 03:32 PM
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The Real Dogman
 
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Default RE: Help a newbie tune his GST 7.7

Actually, you will need to lean both the high side and the low side, But start with the high side and once you can get it running again you will need to lean out the low side to help control the fuel pressure. The Checkvalve actually increases the pressure in the tank and holds the pressure more consistently, and before the checkvalve the fuel pressure variation was controlled by exhaust pressure and when you let off the throttle the exhaust pressure would drop so the low end needle needed to allow more fuel in to stay running so the low end needle was "wide open". Now with the Checkvalve in place the fuel on the low end side is controlled by the needle instead of lower Exhaust pressure, so you will need to lean the low side needle.

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