OK Iam stumped
Thread Starter
Race Director
Joined: Apr 2000
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
OK Iam stumped
A few weeks back my Vette developed a miss. It just kept getting worse until it would hardly idle. The carb is a 825 Race Demon and until now was working perfeclty.
I have an AFR meter and fooled around with the idle mixtures screws for hours and it never got any better eventually it would not start.
Things I have Done:
New Spark Plugs - nada
New Power Valve -nada
I checked the Coilwith ohm meter and it was a bit out of spec. so I replaced that.
I did tests on the MSD 6AL but it seems to be getting spark to the plugs.
The really weird thing is that the front bowl does not fill up with gas while the secondary is where it should be. I swapped the needle and seat front to back and still very little gas in the front bowl.
The fuel pump is pumping gas out the way it should it seems like the gas is escaping somehow and drowning out the plugs. I am worried I am washing the cylinder walls.
I am missing something somewhere, and looking for ideas
I have an AFR meter and fooled around with the idle mixtures screws for hours and it never got any better eventually it would not start.
Things I have Done:
New Spark Plugs - nada
New Power Valve -nada
I checked the Coilwith ohm meter and it was a bit out of spec. so I replaced that.
I did tests on the MSD 6AL but it seems to be getting spark to the plugs.
The really weird thing is that the front bowl does not fill up with gas while the secondary is where it should be. I swapped the needle and seat front to back and still very little gas in the front bowl.
The fuel pump is pumping gas out the way it should it seems like the gas is escaping somehow and drowning out the plugs. I am worried I am washing the cylinder walls.
I am missing something somewhere, and looking for ideas
Last edited by MotorHead; Aug 23, 2017 at 11:40 AM.
Thread Starter
Race Director
Joined: Apr 2000
Posts: 17,673
Likes: 199
From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Second I have had the carb apart about 10 times and the primary line is clear, I even blew through the primary inlet and the air came out in the bowl and shut off when I pushed the needle and seat closed
via the float.
I also tested the float and it was not leaking. I even swapped the rear and front needle and seat valve with the same result.
This is one of the most bizarre problems I have ever encountered. The rear bowl fills up the to the sight glass and the front does not. I drain the back bowl and get 1/2 a glass of fuel and I drain the front and hardly anything comes out. Both floats set to the same position.
My A/F gauge says TOO RICH, it is almost like all the gas is simply pouring into the intake from the front bowl. But the engine does not even sputter or backfire.
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,444
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
You and I got some of the very first demon carbs. I was doing something last year and noticed that I had no fuel to the site glass.
My pri bowl float was (water) logged and did not float anymore. I just bought new floats and it fixed the problem. It only needed one, but I just did both
My pri bowl float was (water) logged and did not float anymore. I just bought new floats and it fixed the problem. It only needed one, but I just did both
Melting Slicks
Joined: Jun 2002
Posts: 2,842
Likes: 99
From: Orrtanna Pa.
I toss in a few ideas...
The primary pump squirts a bit of fuel when you work the throttle? If it does, I would expect the engine to fire, but if the float/ primary fuel delivery is off. then it would stall.
I had a van one time that acted up, and I ended up using a plant mister with fresh gas in it to get the engine running. Just squirt the fuel into the carb. As it turned out, I had about five gallons of water in my tank. Engine would not run unless I disconnected the fuel line, and squirted fuel with the plant mister directly into the carb.
Lastly,....pull the valve covers and check your rockers for excessive play. My 406 developed a miss, that turned out to be two broken pushrods. I would have never believed it.
The primary pump squirts a bit of fuel when you work the throttle? If it does, I would expect the engine to fire, but if the float/ primary fuel delivery is off. then it would stall.
I had a van one time that acted up, and I ended up using a plant mister with fresh gas in it to get the engine running. Just squirt the fuel into the carb. As it turned out, I had about five gallons of water in my tank. Engine would not run unless I disconnected the fuel line, and squirted fuel with the plant mister directly into the carb.
Lastly,....pull the valve covers and check your rockers for excessive play. My 406 developed a miss, that turned out to be two broken pushrods. I would have never believed it.
Pro
Joined: Jan 2016
Posts: 502
Likes: 103
From: Reno Nevada
If this is a fairly new carb, or even if it isn't, my understanding is sometimes these specific carbs tend to have metal filings or metal shavings in the passages. May need to take the carb off and blow the passages out with air or something like carb cleaner.
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Thread Starter
Race Director
Joined: Apr 2000
Posts: 17,673
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
I guess it doesn't matter how many engines and carbs you have worked on there is always something new to screw things up.
Thanks, lots of great ideas but I covered most of them. The primary float is ok in water.
There is spark at the plug and normally if you squirt a bit of gas down the carb the engine will cough and sputter, mine does nothing, I crank and crank and nothing.
When I take the front off there is only a little gas in there. I set the float to approximately the same as the secondary.
I have tried so many things that are mentioned here but I am at a loss, I blew out the carb orifices, I have put new gas into the breather tube in the primary.
I am stumped, even if the engine doesn't start the primary bowl should be full.
Thanks, lots of great ideas but I covered most of them. The primary float is ok in water.
There is spark at the plug and normally if you squirt a bit of gas down the carb the engine will cough and sputter, mine does nothing, I crank and crank and nothing.
When I take the front off there is only a little gas in there. I set the float to approximately the same as the secondary.
I have tried so many things that are mentioned here but I am at a loss, I blew out the carb orifices, I have put new gas into the breather tube in the primary.
I am stumped, even if the engine doesn't start the primary bowl should be full.
Melting Slicks
Joined: Mar 2008
Posts: 2,666
Likes: 289
From: Spring Park MN
I guess it doesn't matter how many engines and carbs you have worked on there is always something new to screw things up.
Thanks, lots of great ideas but I covered most of them. The primary float is ok in water.
There is spark at the plug and normally if you squirt a bit of gas down the carb the engine will cough and sputter, mine does nothing, I crank and crank and nothing.
When I take the front off there is only a little gas in there. I set the float to approximately the same as the secondary.
I have tried so many things that are mentioned here but I am at a loss, I blew out the carb orifices, I have put new gas into the breather tube in the primary.
I am stumped, even if the engine doesn't start the primary bowl should be full.
Thanks, lots of great ideas but I covered most of them. The primary float is ok in water.
There is spark at the plug and normally if you squirt a bit of gas down the carb the engine will cough and sputter, mine does nothing, I crank and crank and nothing.
When I take the front off there is only a little gas in there. I set the float to approximately the same as the secondary.
I have tried so many things that are mentioned here but I am at a loss, I blew out the carb orifices, I have put new gas into the breather tube in the primary.
I am stumped, even if the engine doesn't start the primary bowl should be full.
Mike
Le Mans Master
Joined: Dec 2007
Posts: 6,422
Likes: 591
From: McHenry Illinois
A double pumper should squirt enough from the rear to make it fire even if the front wont. Have you looked down the primaries to see if gas is leaking in instead of filling the front bowl? Sounds like it may be flooded, have you pulled the plugs?
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,444
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
I've had a blown power valve on my demon pri side and my motor just started sputtering because it failed open and was just pouring gas through the down leg front boosters. but you could see it dripping even at idle.
the front bowl stays full
I would try holding the needle and seat open and fire up the pump and see the front bowl fill.
Is your oil full of gas? You can spin off the oil filter and smell it
the front bowl stays full
I would try holding the needle and seat open and fire up the pump and see the front bowl fill.
Is your oil full of gas? You can spin off the oil filter and smell it
Thread Starter
Race Director
Joined: Apr 2000
Posts: 17,673
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Yes it does act the same as being flooded. I have a few things to try today. Thanks to eveyone and keep the ideas coming.
Thanks Frank, is that my 550HP 406ci ? If so you need to check the solid lifters, roll them on a hard flat surface, put plenty of pressure on them and see if you can feel any brinelling. IF those are the same lifters from when I sold it then they should be replaced.
Thanks Frank, is that my 550HP 406ci ? If so you need to check the solid lifters, roll them on a hard flat surface, put plenty of pressure on them and see if you can feel any brinelling. IF those are the same lifters from when I sold it then they should be replaced.
Pro
Joined: Jan 2017
Posts: 651
Likes: 51
From: Beaver County PA
Just throwing something out there: Maybe its not the carb. Could it possibly be the timing chain slipped? Did the distributor move and the timing is off? Does the engine backfire at all. Like I said, just some different approaches. Good luck!
Race Director
Joined: Apr 2007
Posts: 11,150
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From: South Western Ontario
If fuel is going into the bowl and the bowl isn't filling then it has to be leaking out as fast as it goes in. Take the carb off and fill the front bowl with fuel to see where it's leaking from.
Thread Starter
Race Director
Joined: Apr 2000
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
And that is dumping fuel right into the intake manifold.
My AF meter says "TOO RICH" which means it is off the measurable scale, something I haven't seen before.
Will report on the results
Safety Car
Joined: Mar 2005
Posts: 4,255
Likes: 82
From: Brampton Ont.
Just so I understand,
You have a strong spark?
You placed fuel down the carb manually (primed the system) or down the cylinders and it didn't even sputter?
Car cranks over well?
If you have a strong spark, fuel and good battery, then I would wonder if the timing is far off. Maybe the chain jumped a tooth or the distributor moved?
You have a strong spark?
You placed fuel down the carb manually (primed the system) or down the cylinders and it didn't even sputter?
Car cranks over well?
If you have a strong spark, fuel and good battery, then I would wonder if the timing is far off. Maybe the chain jumped a tooth or the distributor moved?
Melting Slicks
Joined: Jun 2009
Posts: 2,343
Likes: 4
From: Anderson SC
Nothing here to indicate timing woes.
-W
Last edited by Clams Canino; Aug 24, 2017 at 11:53 PM.
Safety Car
Joined: Mar 2005
Posts: 4,255
Likes: 82
From: Brampton Ont.