Need help tuning motor!

[prayers1 153]

I can't get rid of the flat spot off idle when I stomp on it.

 

Here is some facts and what I have tried.

289 bored 60 over, stock crank, rods and new flat top pistons.

1965 screw in stud heads, 190/160 valves, decked 1/8th.

Hydraulic Comp Cam #31-226-3, 512 lift 280 Dur. @ 50 230, Center line 106, Roller tip 1.6 rocker arms.

Stealth Warrior Intake, Holley 570 Street Avenger

4-spd wide ratio Top loader, 3:50 gears.

Mallory Unilite Dist. 37 Series Mechanical Advance.

 

The Power Valve was 6.5 and jets were 54/65, I had 12" of Vac.

Holley suggested changing to a 5.5 PV and up the jets to 56/67

Base timing is set at 12.

 

With the above changes, Vacuum is 10.5-10. After 1500 rpms, the engine winds fast, but below it is a DOG.

 

I’m thinking I need a faster advance, I switched the Mallory 37 Series to a 47 Series Vacuum Advance. I tried using vacuum at the manifold and ported sides. I upped the timing to 16-18* I changed back to the 6.5 power valve. Vacuum is now between 10 -11".

 

It’s still flat off idle, but only when I kick it down.

 

 

Mallory states that the Distributor has built in 24° (crankshaft degrees) of mechanical advance (between 3,000 and 3,200 RPM).

The advance on the timing light broke, so I’ll pick up a timing tape.

 

Do you think it maybe the springs to the secondaries?

 

What do you think is the problem?

[LoneWolf2U 136]

Check the adjustment on the squirter pump arm. Not sure about the 570's but most have a spring and shaft with nut which allow you to time/amount of the squirt.

I have mine set so the squirt from the pump starts as the throttle plate moves open.

It takes some trial and adjusting to get them right.

[prayers1 153]

I spoke to Holley this morning and they said the same thing. They also said to put a tighter spring, 1 size up on the Vac Sec. I'll go and check it out.

 

What do you all think my Timing Advanced should be set at?

 

Thanks!

[prayers1 153]

Accelerator pump is tight. I checked the mixture screws, only have the 2 up front. Drivers side was 1/2 turn out and the other side was 2 full turns out????

 

I've done this setting with a Vacuum gauge several times and I always find the Drivers side leaner. I was surprised to see how lean it was today.

 

Any suggestions!

[Chris'69Mach 23]

Both screws should be set turned the same amount. I believe Holley sends carbs out fatory tuned with the screws set at 1 1/2 turns out. Start from there and do 1/4 turns to dial them in .... Whatever you do to one screw, you need to do to the other screw.

 

So, say ... starting at 1 1/2 turns out, you get good pressure at 1 3/4 turns out, both screws would need to set 1 3/4 turns out.

[LoneWolf2U 136]

Accelerator pump is tight. I checked the mixture screws, only have the 2 up front. Drivers side was 1/2 turn out and the other side was 2 full turns out????

 

I've done this setting with a Vacuum gauge several times and I always find the Drivers side leaner. I was surprised to see how lean it was today.

 

Any suggestions!

 

When you say its tight, what are you refering to?

There should be some clearence to the lever to start with.

 

The idle mixture screws sholub be close to each other, maybe not dead on but near. Having one side way out while the other is way in maens there is a vac leak some where, my guess is the carb or spacer gasket.

 

Your timing will be what ever you can run as long as your total is around 36-38*

Find your total timing by running it at 2500rpm and see where its at. Once you know this let it idle and check your base timing. you can increase or decrease your base till you get the total in range. then retest.

Edited November 19, 2013 by Mach1Rider

[prayers1 153]

Just enough to slide a piece of paper between them. As soon as I press down on the acc pump spring, gas squirts in.

 

A friend suggested, somewhere 16-18 initial with a total of 36-38* all in by 2500-2800,

but the guy who built the motor said never to go above 32*@3000.

 

His reasoning is that sometimes motors can run too good and can squash the piston.

I really thought it was a lot of bull, but being on the cautious side, I kept base at 16*

 

I got a hold of some timing tape and I'll try your settings.

Also, since I'm having trouble on the primary side, I think I'll up the squirter .035.

[LoneWolf2U 136]

Try removing the play at the lever first. I have the truck set with a slight preload so it will give it a shot as the throttle plate opens. it needs to have the fuel to get going till the vac pulls it out.

[Rcodenewf 44]

Vacuum sounds low considering the cam selected.

 

While the engine is idling slowly close the choke plate by hand and see if the engine speeds up...if it does, then it is lean.

 

JOhn

[prayers1 153]

Things recently done,

Changed discharge nozzle from. 031 to. 035, set intial at 18*; Advance came in around 36 @ 2400.

 

The Acc pump is good and tight.

 

I reset the mixture screws, the highest is still 11. I did take out the 5.5 power valve and replaced it with a 6.5. I did notice if I turn the screws in or out a lot it still stays around 11, only when I turn it all the way in the motor starts to run rough.

 

I took it for a test drive and it seemed ok going through the gears. I got to a quite road and nailed it at a dead stop, for the first time it had for a 10th of a sec, power but quickly bogged then the rpms built up again and went through the power band. It happened 3xs in a row.

 

When I got home I rechecked timing, it was at 20, I reset it at 16.

I think the Dist was't tight enough.

 

So what do you think?.......a

Edited November 21, 2013 by prayers1

[buening 63]

I had an off-idle bog on a brand new Street Avenger 670cfm. I ended up taking the bowls and metering plates off, and shooting carb cleaner in all passages. I reassembled and it eliminated the bog. I think I had a passage slightly blocked causing a lean condition

[prayers1 153]

I just got the carb back about a months ago, it was sent to holley, they took it apart, cleaned it and bench tested it. Holley is the one who said to rejet it, change the power valve to 5.5 and the nozzel to. 035.

 

I did just that and still it bogged, then a friend said with that size cam, to go back to the 6.5 PV and up the intial and advance timing. I'm still having that dead spot or bog. Im not getting that snap, off of 1st gear.

[buening 63]

Have you checked the vacuum with a guage and observed the needle to determine if you could have a vacuum leak? Typically off-idle bogs are either the carb being lean (either jetting or idle transfer slots covered up by butterflies), or the engine has a vacuum leak. When it is a vacuum leak, the vacuum is at its lowest at idle and will cause an off-idle bog in the carb up until the vacuum increases with RPM. Years ago I had a holley that also had an off idle bog that I just couldn't get rid of. I pulled the carb and checked the idle transfer slots from the underside and they were all completely covered. Adjusting the curb idle speed screw until I had 0.020" of exposed slots did the trick and eliminated the bog.

 

 

I personally wouldn't touch the nozzles yet, its merely a bandaid to the likely cause of the bog. Typically the nozzles are the last things to adjust from my limited experience.

[prayers1 153]

Using the Vacuum gauge is how I adjust the mixture screws. I start at 1 1/2 out and go from there. The left side is always leaner. I'm getting about 11, with that I can turn the screws in or out a lot and it still doesn't really move until I get them close to close.

 

I can't see anything wrong with the fuel system, new tank, lines filter and a clean carb.

 

I ordered a set of Distributor springs, maybe a lighter pair will open it up.

 

In the back of my mind I am concerned about an engine vacuum leak. I once tried to spray around and no results. I'm gonna try the Cigar, blow the smoke in a hose trick.

[buening 63]

Does the vacuum gauge for the most part have a steady reading (some small needle shake of 1 or 2in will happen with your large cam). I don't have a good feel for what vacuum reading you should have, but 10 does sound low. Do what John suggests and cup your hand over the carb (or use choke plate as he suggests) when running to see if the RPMs increase.

 

Also watch this video to make sure you aren't victim to poor manufacturing by Holley:

[prayers1 153]

Yes, it does shake 1-2in. I've been told by Comp Cam that low Vac is a result of the Cam. A 351W 280H Cam gets 12-13.

 

I've noticed when slightly turning the screws, as recommended, the needle sometimes jumps 2" and so does the rpms, but it quickly drops down back to 11. I tried repeatedly to capture that upswing but to no avail.

 

I will try cupping the Carb.

Thank you!

[LoneWolf2U 136]

Try this, Start with engine at operating temp.

Turn the idle speed up to 1200 rpm.

Adjust the mixture screws till you have the smoothest idle.

reset idle down to 800.

Loosen the accel screw 2 full turns(this will remove any gap or slack) and test drive it. Let me know what it does.

[Chris'69Mach 23]

When you have your pressure gauge plugged into the carb .... are you using the port on teh base of the carb or the one high on the carb near the choke?

[prayers1 153]

Mach1Rider-Ok,but that will have to wait for better weather, a wintry mix is moving in.

After I do that and before I test drive, what do you think I should have timing at.

 

Chris’69Mach- I’m using the port under the front bowl, the smallest one of the two.

[prayers1 153]

Mach1Rider- Krudy day outside, so I've been doing some reading and found that if I adjust the mixture screws while the transition slots exposed (at a higher idle more than 1000 rpms), I will get an inaccurate reading on the vac gauge.

[LoneWolf2U 136]

Skip the vac guage, your tuning it by ear to have the best and smoothest idle.

You cam is large enough to have a low vac reading anyway.

Try your base timing at 10-12* with vac advance disconnected.

With your build, the book settings are just a baseline to start with. You need to tune the engine to the componants you have.

[prayers1 153]

Nothing really changed after resting the mixture screws around 1200 rpms.

 

I picked up an Advance Curve kit and changed the springs to where advance will start at 1000 rpm's instead of the factory setting of 1500, my total came in around 37* and I changed the Carb cam to the green one and placed it on #1.

 

I did notice a change but no head snapping events. It did feel like it was getting too much gas higher up so I puuled off the road and changed the Carb Cam back to the Orange but I set it at the #1 spot. It did make an improvement.

 

Something to think about:

At idle, when I manually snap the throttle there is an immediate delay, but when I snap it at 1000 rpms it screams.

 

Even with total at 37*, there is NO pinging when in 4th gear at 1000 rpms going up hill.

 

I'm thinking of putting in the lightest spring. Advance will kick in at 600 rpms?????

[Boogerschnot 12]

Have if you get an immediate delay at idle.. Maybe you need to check the accelerator pump spring adjustment again. I adjust mine so that it squirts at the slightest blip of the throttle but so that it has a slight bit of play in the spring when you are at full throttle, so that it doesnt bind up the linkage.

 

do you use the small hose barb coming off of the main circuit just in front of the choke for your timing? That is the timed port. Anywhere else will give you full vac.

 

The carb should be tuned for idle, at the idle 700-800rpm with the engine in drive.. Or neutral for the manual trans. Check that your timed port hose it not leaking, causing the lean bank.

[prayers1 153]

The accelerator pump spring adjustment, IMO is very tight. It was adjusted by Holley a month ago when it was sent in under warrentee. Factory settings call for .015. IMO I think it's rather tight, no play what so ever.

 

I believe I'm getting my vacuum advance from a timed port, the one mounted high on the passenger side of the metering block.

 

It's hard to tell if I'm having a timing issue or carb. I still have to rule out a vacuum leak. I already tested it with carb cleaner, no signs of leaks. I'm gonna try the smoke test to be for certain.

 

Any suggestions??

[MikeStang 247]

I wouldnt think that you should need more than 10-12 degrees initial timing.

It is a Vac Secondary carb correct:?

I have the Holley Tuning video on CD I can loan ya if you like maybe it will help.

 

Seems you have accelerator pump arm set so that as soon as you tap the gas its squirting.

I think maybe your advance aint coming in soon enough.

Shouldnt have to give it much gas for the advance to start kicking.

You check your float settings.

I usually just run my carbs square on the jetting also.

if carb is Vac secondary you may wanna look at how fast the secondaries are opening

Bring it to Baton Rouge LA and we will fix it.

I have a nice HP 950 and a Holley 795 Street avenger sitting here we can try out.

Mike