oversized carb, or just badly tuned?
10-18-10, 04:07 PM
#1
oversized carb, or just badly tuned?
I bought this 85 GS yesterday for a GREAT deal. I was told the only thing wrong was a snapped throttle cable. Check it out, and when I get there, I noticed it already had a holley carb, RB manifold, and full true dual RB exhaust. SWEET... And some other choice upgrades I keep finding...The guy didn't have a battery so i never even tried to start it. I figure, at this price, I'm taking it no matter what...
So today I fix the throttle cable and change the plugs, then do a few other precautionary things to make sure I don't ruin it on the first start up. Including spraying a bit of carb cleaner into the carb before start up. I have no idea how long it's been since it's been cranked over... Turn the key, it starts right up runs for a few seconds then dies. Try to restart, no go. Spray some more carb cleaner, boom... cranks up just fine. I continue to spray a bit of carb cleaner before each time I start it or it will not start up. So I turn the idle screw so the carb is a bit more open for start up, it cranks up and holds idle clean at 2500 for a little while then starts to die out as I am turning the idle screw down. I do this a few times and every now and again, I try to throttle it (all of this done standing over the engine, not with the gas pedal) it I throttle it really soft, it will rev up smoothly. But i have to do it very slow. if I just try and throttle it, it just bogs and wants to die.
It never stayed running on it's on more than one minute. And it will only start if I spray some carb clean before hand.
I do not know if it's a 600cfm or another size, The guy didn't even know what the racing beat manifold was called... So any guesses, to large of a carb, or badly tuned and need to be rebuilt? (by rebuilt, i mean the carb, not the motor)
So today I fix the throttle cable and change the plugs, then do a few other precautionary things to make sure I don't ruin it on the first start up. Including spraying a bit of carb cleaner into the carb before start up. I have no idea how long it's been since it's been cranked over... Turn the key, it starts right up runs for a few seconds then dies. Try to restart, no go. Spray some more carb cleaner, boom... cranks up just fine. I continue to spray a bit of carb cleaner before each time I start it or it will not start up. So I turn the idle screw so the carb is a bit more open for start up, it cranks up and holds idle clean at 2500 for a little while then starts to die out as I am turning the idle screw down. I do this a few times and every now and again, I try to throttle it (all of this done standing over the engine, not with the gas pedal) it I throttle it really soft, it will rev up smoothly. But i have to do it very slow. if I just try and throttle it, it just bogs and wants to die.
It never stayed running on it's on more than one minute. And it will only start if I spray some carb clean before hand.
I do not know if it's a 600cfm or another size, The guy didn't even know what the racing beat manifold was called... So any guesses, to large of a carb, or badly tuned and need to be rebuilt? (by rebuilt, i mean the carb, not the motor)
10-18-10, 04:32 PM
#2
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Is it getting fuel to the carb? I would start with the fuel filter.
If it is a 600cfm carb it is to big but it should run. If you can get it to start with carb cleaner than it isn't getting any fuel.
If it is a 600cfm carb it is to big but it should run. If you can get it to start with carb cleaner than it isn't getting any fuel.
10-18-10, 06:31 PM
#4
I know its getting fuel for two reasons. It ran for about a minute. And there's no way that would stay running that long with a little spray of carb cleaner before tart up.
And the first time I tried to start it, it **** fuel out of the top, pretty sure it was a stuck float, because I tapped both sides of the bowl with a dead blo and that didnt happen again.
And the first time I tried to start it, it **** fuel out of the top, pretty sure it was a stuck float, because I tapped both sides of the bowl with a dead blo and that didnt happen again.
10-18-10, 08:26 PM
#5
One thing i noticed is It has a holley fuel pump and regulator also. I think it is flooding it badly...
The fuel pressure was close 7 psi. And I'm pretty sure a stock or street ported 12a with a holley will only need about 3-4 psi of fuel pressure.
The fuel pressure was close 7 psi. And I'm pretty sure a stock or street ported 12a with a holley will only need about 3-4 psi of fuel pressure.
10-18-10, 09:02 PM
#7
Im going to try againg tomorrow after I lower the fuel pressure. That should make a difference either way. After that, i'll probley remove the bowl to see what jets are in it...
Does anyone know how to identify the CFM on the carb without removing the carb? Just to make sure it is a 600 and not something else...
Also, it's still running a return fuel line, first time i seen that on a 1st gen with a holley. Should I remove that and block the line off?
Does anyone know how to identify the CFM on the carb without removing the carb? Just to make sure it is a 600 and not something else...
Also, it's still running a return fuel line, first time i seen that on a 1st gen with a holley. Should I remove that and block the line off?
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10-18-10, 10:17 PM
#8
I know its getting fuel for two reasons. It ran for about a minute. And there's no way that would stay running that long with a little spray of carb cleaner before tart up.
And the first time I tried to start it, it **** fuel out of the top, pretty sure it was a stuck float, because I tapped both sides of the bowl with a dead blo and that didnt happen again.
And the first time I tried to start it, it **** fuel out of the top, pretty sure it was a stuck float, because I tapped both sides of the bowl with a dead blo and that didnt happen again.
10-18-10, 10:49 PM
#9
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10-18-10, 11:39 PM
#11
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Im going to try againg tomorrow after I lower the fuel pressure. That should make a difference either way. After that, i'll probley remove the bowl to see what jets are in it...
Does anyone know how to identify the CFM on the carb without removing the carb? Just to make sure it is a 600 and not something else...
Also, it's still running a return fuel line, first time i seen that on a 1st gen with a holley. Should I remove that and block the line off?
Does anyone know how to identify the CFM on the carb without removing the carb? Just to make sure it is a 600 and not something else...
Also, it's still running a return fuel line, first time i seen that on a 1st gen with a holley. Should I remove that and block the line off?
might as well keep the return line, we're thinking it'll help keep the fuel/premix mixed better in the tank. plus it takes work to remove it, so why bother?
10-19-10, 11:08 AM
#13
My money's on a low-delivering fuel filter or crapped up tank, along with some gumming in the carb.
A -7 will idle for a surprising amount of time just off fuel in the bowls and even longer if a trickle is getting through to fill them, but once the throttle opens, if delivery can't keep up with demand it'll starve out.
Harder to troubleshoot that on a Holley, since there's normally no sight glasses and you can't check the bowl levels just by opening the top.
Is the Holley prepped for oil injection, or are you pre-mixing?
A -7 will idle for a surprising amount of time just off fuel in the bowls and even longer if a trickle is getting through to fill them, but once the throttle opens, if delivery can't keep up with demand it'll starve out.
Harder to troubleshoot that on a Holley, since there's normally no sight glasses and you can't check the bowl levels just by opening the top.
Is the Holley prepped for oil injection, or are you pre-mixing?
10-19-10, 11:29 AM
#15
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only thing wrong with an autozone kit would be you giving money to autozone.... i'm sure the kit is fine though
10-19-10, 03:51 PM
#16
bought the "trick kit" from auto zone.
I rebuilt it and gave it a pretty good cleaning. The jets in it were both 66. the only jets I have that were smaller were 64's, so i put them in. I still believe these are also to big. I lowered the fuel pressure down to 6, as it was closer to 8psi.
Took a few try's to start, but i think that was because the bowls didnt have enough fuel in them when i first tried to start it. But when it started, it stayed running on it's own but was still very touchy to throttle revs while cold. After it ran for a few minutes and warmed up, I could rev it up just fine and i even took it for a drive. It drove good and i would turn the car off every now and a again to see if it had any trouble restarting, and it would start right up...
So the rebuild made a huge difference. But i did not rebuild the bowls or even adjust them. I left them alone to see if the car would run with them the way they are. I'm going to get some 56 jets to see if that cures the cold starting problem, which i believe it still has. I'm letting the car cool down now and going to try starting it again soon when it's completely cooled off.
I'll eventually swap it for a 465 or a set of webbers...
Thanks for the help.
Oh, as a side not. The owner before me tried to modify the RB manifold and screwed it up pretty good. They milled down the face about an inch. not porting anything to a smooth edge at all. just basically milled it down and left everything completely flat. I'm sure that's effecting it also...
I rebuilt it and gave it a pretty good cleaning. The jets in it were both 66. the only jets I have that were smaller were 64's, so i put them in. I still believe these are also to big. I lowered the fuel pressure down to 6, as it was closer to 8psi.
Took a few try's to start, but i think that was because the bowls didnt have enough fuel in them when i first tried to start it. But when it started, it stayed running on it's own but was still very touchy to throttle revs while cold. After it ran for a few minutes and warmed up, I could rev it up just fine and i even took it for a drive. It drove good and i would turn the car off every now and a again to see if it had any trouble restarting, and it would start right up...
So the rebuild made a huge difference. But i did not rebuild the bowls or even adjust them. I left them alone to see if the car would run with them the way they are. I'm going to get some 56 jets to see if that cures the cold starting problem, which i believe it still has. I'm letting the car cool down now and going to try starting it again soon when it's completely cooled off.
I'll eventually swap it for a 465 or a set of webbers...
Thanks for the help.
Oh, as a side not. The owner before me tried to modify the RB manifold and screwed it up pretty good. They milled down the face about an inch. not porting anything to a smooth edge at all. just basically milled it down and left everything completely flat. I'm sure that's effecting it also...
10-19-10, 04:02 PM
#17
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correct me if i'm wrong, but if the carb is too big, wouldn't it have stumble when you rev it beacause it can'tcan't keep up with the hectic air flow of a smaller engine?
10-19-10, 04:23 PM
#18
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Oh, as a side not. The owner before me tried to modify the RB manifold and screwed it up pretty good. They milled down the face about an inch. not porting anything to a smooth edge at all. just basically milled it down and left everything completely flat. I'm sure that's effecting it also...
10-20-10, 12:42 AM
#23
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the RB manifold is individual runner, so it takes a different carb setup than a normal v8 style plenum manifold. or you can just make it plenum style, like yours is
