New Rebuild, Will Not Idle

I can't figure out why this thing won't idle. Any ideas will be greatly appreciated.
76 Spectra jet
460 mainly stock rebuild. Edelbrock Performer intake manifold. I rebuilt this about 3 to 4 years ago and ran it on an engine stand to break in the came. Ran great and idled nice.
Now my boat is ready for the water, so I put in the engine and it fires right up, revs up nice, but when the rpms come down it struggles and dies.
I took the Holley 4010 vac secondaries off and took it apart, cleaned the heck out of it, carb cleaner, compressed air all over, same problem.
Found a like new Marine Edelbrock 600 on Craigs. Bought it for 225 slapped her on, same thing, revs up nice then dies as it comes to idle.
I put a vac gauge on it, bounces at 16 and with my hands cupped over the carb I can get it to idle and a steady 20 on the vac gauge.
Sprayed throttle claener all over the carb and intake but no sign of leak.
Did a compression check, all between 95 and 110. It has maybe less than an hour of run time on a hone with file fitted rings.
Pulled the intake and valve covers. Pulled rockers and checked valves for any sign of valve sticking, all smooth. Replaced intake gaskets, siliconed lightly both sides of gaskets torqued in sequence to 20, 25, then 30.
Just got done trying it and same thing. It will Idle when timing is advanced to about 30 but will not idle at 10.
I have a new Mallory YLM 567 EV breakerless with a Mallory coil and a ballast resistor.
I guess I'll pull the top off the carb and check the floats but it seems like a vacuum leak, but where?
I am getting more depressed by the minute.
It wants to run strong but not idle. See through inline filter with good fuel flow.
Any help will be welcomed.
Details of build in Spectramarine section: http://www.riverdavesplace.com/forums/showthread.php?53625-SPECTRALEN-s-20-Rebuild

SPECTRALEN said:

It will Idle when timing is advanced to about 30 but will not idle at 10.

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What's the total timing with the advance all in? Maybe before you monkey with carbs anymore you should put a timing light on it and see what happens as you bring rpm up and back down.

obnoxious001 said:

What's the total timing with the advance all in? Maybe before you monkey with carbs anymore you should put a timing light on it and see what happens as you bring rpm up and back down.

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That's what I was thinking. Could be a distributor issue.

I'll check that next.
Are you thinking something with the distributor?

Is it possible that a defective anti siphon valve could be the cause?

one other thing is to look down the carb when your trying to get it to idle. do you see fuel???? also listen to the carb . what do the plugs look like??

Would I be able to see fuel with the butterflys closed at idle?
Plugs are kinda black.
Listening as it stumbles and dies, it sounds like vacuum type of suction sound.

You need to verify that your timing mark is accurate! Put the #1 cylinder at TDC, using a piece of wire as a feeler through the spark plug hole, and keep rocking it back and forth untill you get absolute TDC of the piston (it will be close enough, within a couple degrees anyways). Then see how far of your timing TDC mark is. You might be surprised! Its not uncommon, especially once the balancer / cover has been off from the factory. Balancer could have spun, timing pointer bent, aftermarket timing pointer not accurate, etc....

Hey first i just took a look at your pics!!! that fuel pump you have is it a high pressure pump???? you do not have a pressure regulator on it???? my guess you are over 7psi and it just pouring in , which is why you cant idle. Now when you look down the carb you should NOT see any fuel at all.

SPECTRALEN said:

Would I be able to see fuel with the butterflys closed at idle?
Plugs are kinda black.
Listening as it stumbles and dies, it sounds like vacuum type of suction sound.

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Black plugs usually means fouled (fuel fouled)

Sucking sound is good from the top

Make sure the choke is open all the way when the engine is hot! then at idle look down there should be NO fuel dripping ( MY guess it is!!!)

obnoxious001 said:

What's the total timing with the advance all in? Maybe before you monkey with carbs anymore you should put a timing light on it and see what happens as you bring rpm up and back down.

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This, and

Is it getting fuel from the idle circuit?

How long did the carb sit with our lovely fuel in it?

Brian

"I put a vac gauge on it, bounces at 16 and with my hands cupped over the carb I can get it to idle and a steady 20 on the vac gauge."


This tells me you may not have enough idle circuit fuel. If you raise the idle to 1000rpm will it run?

Sounds to me the carb may be gunkedup in the smallest of passages that carb spray won't fix without effort.

and I have to ask....are you using new fuel that hasn't been sitting?

Brian

Fuel is new. I ran the engine w/o issues on the stand with my fuel line sitting in a gas can. I am going to try that and see if that helps. If it does, there is an issue with my anti siphon valve, tanks, separator, pick ups, etc.
I'm going to install a small fuel pressure gauge inline. Look for too much or too little, although the inline filter has plenty of fuel there.
Check that full timing advance.
Then, pull the carb and take apart. Spray with cleaner, concentrate on idle circuit, compressed air, then adjust floats and choke and say a prayer.:bowdown:

Bigbore500r said:

You need to verify that your timing mark is accurate! Put the #1 cylinder at TDC, using a piece of wire as a feeler through the spark plug hole, and keep rocking it back and forth untill you get absolute TDC of the piston (it will be close enough, within a couple degrees anyways). Then see how far of your timing TDC mark is. You might be surprised! Its not uncommon, especially once the balancer / cover has been off from the factory. Balancer could have spun, timing pointer bent, aftermarket timing pointer not accurate, etc....

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When you rebuilt it, did you change the timing pointer, balancer, or the front cover the pointer attaches to? If you did, it may not be accurate and you may be trying to make it idle with the timing way off. Is it an adjustable pointer by any chance? If timing is off by 10 degrees the wrong way, it wont wanna idle without a ton of fuel

Well, the best progress yet. Timing at 10 degrees idle is at about 30 degrees full when reved up.
The more i played with the timing and the choke plate it seems to want to idle. I kind of think that when the carb idle circuit and mixture screws and the choke are all out of wack, and then the electric choke goes into a warm engine mode because it's been getting 12 volts the whole time, and then the motor wasn't ran long enough to be warm because of the stalling out and such, it just takes some time to adjust.
I still want to go through and know everything I can about adjusting this carb, but at least for today I can say she was reving up and coming to an idle.:thumbup:

Oh yea, put on the fuel psi gauge and no more than 6.

Took the boat out for the maiden voyage. Started right up, went into choke mode nice. As I started backing away from the dock and slowly moving the accelerator I started getting these gas surges. I can bring it back to idle, no surges at the 750 rpm. We putt with the surges out to where we have some room, slowly go into a throttle down to put it on plane and I get a hesitation and then a series of backfires through the carb. I'm able to play with it and get some pulls just over 4000 rpm with more left and it feels great. Jet drive loads nice, throws you in your seat, but the backfires are there.
Rechecked the timing, Just under 10 at idle and 30 at full advance.
I read somewhere about the jets in the carb being too small?
Could the air butterfly valves be opening too quickly making the secondaries too lean? They seem to be non adjustable?
Could my ignition have a problem that's only under load? Put a new cap on the distributor.
Bad fuel?
I am so close. This thing wants to run but there is something holding me back. I'm almost thinking of going back to a Cobrajet cast iron intake, like something stupid is wrong and I just can't see it. I am just getting frustrated.

Just look at the poor kid.

Valves too tight?

Outdrive1 said:

Valves too tight?

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These heads have the original valve train, I checked the valves for sticking with a pry bar and they all felt smooth. Compression check was good.

Did you do a cylinder balance check to see if it's missing at idle?

Found some spare jets and needle valves. After looking over the paper work I received from the guy I bought the carb from, It appears he installed a kit for this thing to be on a 4.3 v6. The spares brought the jets from .089 to .101 and the needles I took ouit were 68x52 and put in a set of 68x47. I also moved the accel pump rod to the closest hole towards the carb.
WOW:yikes, what a difference.
No more surges, idles nice, I did have a slight bog that was more likely when the secondaries kicked in.
So I know i'm going in the right direction and will try more richer changes like needles or the springs can go a little tighter too or even up the secondary jets.
All in all, it was a good day for the project.:thumbup:
Oh Yea, I'm getting a little oil wanting to come out of the dip stick. Going to look into the spark plug boot rig or something like that.