What are the key elements to getting a new motor to start easy and idle strong?

[mesquito_creek]

New rebuilt GM 350, 4 bolt, steel crank, .030 over. Edlebrook Estreet aluminum heads, Edlebrook performer intake, Edlebrock 600cfm carb, flat tappet hydrolic lifters and the max cam the head/springs will take ~.5 lift.

I have about 9-10 degree of advance in the idle/startup. (Petronix distrbutor).

It starts super cold blooded. Take alot of pumping the throttle to get it to start cold. Once it warms up it starts pretty easy. But still after sitting a bit it might take a hit or two to get it idling again. Secondly the idle isn't real "strong", I can bump it into gear and it may stall out, not always but the motor will hesitate and recover most times.

Its only got about 30 gallon of fuel ran through it, maybe 3-04 hours total, but I ran it hard in the break in.

Do I have too much initial timing in it?, will retarding the startup timing to 6-8 help? Will dialing in the idle air fuel mix have any effect? Maybe more rich?

Bonus, is once it hit about the 3000 rpm it runs like a raped ape, and you can really feel it start to breathe and hum like a champion....

 

[Shlbyntro]

what fuel delivery are you running?

 

[mesquito_creek]

what fuel delivery are you running?

Manual pump… and I have an in-line guage that shows good fuel pressure at 6-8 psi. But if I let it sit it does take a few times to get the fuel pressure to come back up. It cold starts with 0 psi and has to turn over for a while before I see the needle come up.

 

[Shlbyntro]

antisyphon valve in the fuel line? size/type fuel line, what type and size carburetor? list it all

its sounds to me like you may have a couple issues. engine is starving for gas at initial startup after sitting and possibly an idle/fuel mixture issue either from being out of tune, or possibly too much carburetor for your engine

 

[mesquito_creek]

antisyphon valve in the fuel line? size/type fuel line, what type and size carburetor? list it all

its sounds to me like you may have a couple issues. engine is starving for gas at initial startup after sitting and possibly an idle/fuel mixture issue either from being out of tune, or possibly too much carburetor for your engine

Edlebrock 600 cfm carb… I will add and anti siphon valve, I agree it’s seems to be starved for fuel at startup. Where is best to put the valve? Before or after the fuel pump?

 

[DaveH]

New rebuilt GM 350, 4 bolt, steel crank, .030 over. Edlebrook Estreet aluminum heads, Edlebrook performer intake, Edlebrock 600cfm carb, flat tappet hydrolic lifters and the max cam the head/springs will take ~.5 lift.

I have about 9-10 degree of advance in the idle/startup. (Petronix distrbutor).

It starts super cold blooded. Take alot of pumping the throttle to get it to start cold. Once it warms up it starts pretty easy. But still after sitting a bit it might take a hit or two to get it idling again. Secondly the idle isn't real "strong", I can bump it into gear and it may stall out, not always but the motor will hesitate and recover most times.

Its only got about 30 gallon of fuel ran through it, maybe 3-04 hours total, but I ran it hard in the break in.

Do I have too much initial timing in it?, will retarding the startup timing to 6-8 help? Will dialing in the idle air fuel mix have any effect? Maybe more rich?

Bonus, is once it hit about the 3000 rpm it runs like a raped ape, and you can really feel it start to breathe and hum like a champion....

initial timing helps a bunch. only when the starter struggles or it sneezes through the intake is the tell tell signs of when you have too much, and if the compression is mild you can get away with a bunch.

next thing is make sure the butterfly is open enough. nothing wrong with cracking the throttle during crank.

an electric choke helps a ton.

make sure your mixture is correct down low, can be tricky with a crab to get just right.

since these setting are very temperature dependant, what may be just right when stone cold may not work when the motor has temp in it.

welcome to the old school days of carbs.

 

[RVR_RCN]

I can bump it into gear and it may stall out, not always but the motor will hesitate and recover most times.


Are we talking car engine here? Auto trans? Could be the stall on the converter is too low, need at least 2,500 based on your performance mods.

 

[Shlbyntro]

Edlebrock 600 cfm carb… I will add and anti siphon valve, I agree it’s seems to be starved for fuel at startup. Where is best to put the valve? Before or after the fuel pump?

you want the antisyphon valve to be as close to the tank as possible. maybe try richening up the choke a little and adding a tiny bit of idle speed to the screw

 

[mesquito_creek]

 

[Shlbyntro]

hey, also anything down stream of a pump in a fuel system on a boat should be made up of compression style fittings. hose clamps on standard barb fittings after a fuel pump are a big no no and is dangerous

 

[mesquito_creek]

hey, also anything down stream of a pump in a fuel system on a boat should be made up of compression style fittings. hose clamps on standard barb fittings after a fuel pump are a big no no and is dangerous

If I don’t have hose clamps how do I swallow 1/2 a gallon of gas in the middle of the lake when I forget and run one of the tanks dry and have to switch over bobbing around refilling the fuel lines with the other tank?

 

[mattyc]

The fuel bowls will hold enough fuel for a restart for some time regardless of siphoning, in my opinion.

Is this an engine and carburetor you've ran before, prior to rebuild? Or is one or both of these new? If these have been ran before, did the poor starts occur before the rebuild? Or is it a new concern?

Someone else asked, marine engine? Car?

Tell us about the ignition...
Base timing? Total timing?
Mechanical advance?
Vacuum advance?

How much vacuum does it make at idle?

I've dealt with a couple of startup, idle and off idle problems on a couple different applications lately. Both had cams that produced low vacuum at idle and it seems some idle circuits dont work well in these cases.

Also had two holleys (I realize this isnt a holley but same point) which came with incomplete ports. One with idle air bleeds on the secondary side in the main body that were not completed, and another one where the emulsion holes and idle feed restrictions were not completed in the metering block. I am a believer these driveability issues can all be corrected, I dont believe that you have to put up with lousy idle, poor starts etc just because its carbureted.

food for thought, keep us updated

 

[rivermobster]

initial timing helps a bunch. only when the starter struggles or it sneezes through the intake is the tell tell signs of when you have too much, and if the compression is mild you can get away with a bunch.

next thing is make sure the butterfly is open enough. nothing wrong with cracking the throttle during crank.

an electric choke helps a ton.

make sure your mixture is correct down low, can be tricky with a crab to get just right.

since these setting are very temperature dependant, what may be just right when stone cold may not work when the motor has temp in it.

welcome to the old school days of carbs.

What he said...

Watch your total timing when you bump it up.

Welcome to the days of Knowing how to curve a distributor.

 

[mesquito_creek]

The fuel bowls will hold enough fuel for a restart for some time regardless of siphoning, in my opinion.

Is this an engine and carburetor you've ran before, prior to rebuild? Or is one or both of these new? If these have been ran before, did the poor starts occur before the rebuild? Or is it a new concern?

Someone else asked, marine engine? Car?

Tell us about the ignition...
Base timing? Total timing?
Mechanical advance?
Vacuum advance?

How much vacuum does it make at idle?

I've dealt with a couple of startup, idle and off idle problems on a couple different applications lately. Both had cams that produced low vacuum at idle and it seems some idle circuits dont work well in these cases.

Also had two holleys (I realize this isnt a holley but same point) which came with incomplete ports. One with idle air bleeds on the secondary side in the main body that were not completed, and another one where the emulsion holes and idle feed restrictions were not completed in the metering block. I am a believer these driveability issues can all be corrected, I dont believe that you have to put up with lousy idle, poor starts etc just because its carbureted.

food for thought, keep us updated

Let’s call it a marine hybrid. Started as a 4 bolt marine engine. Still has marine exhaust and peripherals. But it has aluminum car heads/intake manifold/lifters and cam.

Petronix marine distributor, which makes it electronic/mechanical advance I think?

I set the initial timing at 10 per a suggestion here Rdp. But I am going to set it back to 8 and reset idle air fuel. That’s my next step once I start it I the hose again in a few weeks.

It has the steel ball anti siphons on the gas tank but I need to make sure it not getting air somewhere else after.

 

[obnoxious001]

New rebuilt GM 350, 4 bolt, steel crank, .030 over. Edlebrook Estreet aluminum heads, Edlebrook performer intake, Edlebrock 600cfm carb, flat tappet hydrolic lifters and the max cam the head/springs will take ~.5 lift.

I have about 9-10 degree of advance in the idle/startup. (Petronix distrbutor).

It starts super cold blooded. Take alot of pumping the throttle to get it to start cold. Once it warms up it starts pretty easy. But still after sitting a bit it might take a hit or two to get it idling again. Secondly the idle isn't real "strong", I can bump it into gear and it may stall out, not always but the motor will hesitate and recover most times.

Its only got about 30 gallon of fuel ran through it, maybe 3-04 hours total, but I ran it hard in the break in.

Do I have too much initial timing in it?, will retarding the startup timing to 6-8 help? Will dialing in the idle air fuel mix have any effect? Maybe more rich?

Bonus, is once it hit about the 3000 rpm it runs like a raped ape, and you can really feel it start to breathe and hum like a champion....

I would encourage you to work on the total timing, instead of base timing. It's more important for a performance engine. Do you have instructions that came with the Pertronix showing the factory set curve, and also how to change it. I have found more initial timing works better with a performance cam, and recurve the distributor accordingly. That would also help with low end response.

2nd thing I will mention is the Edelbrock carbs are known to drain back when they sit, my friend was running one for years on his 32 Roadster, finally switched to Holley mainly because of that. For boat engines in AZ I remove the choke from the carburetor straight away, if the tune is correct, with the weather we have here it will start fine without it.

 

[rivermobster]

I would encourage you to work on the total timing, instead of base timing. It's more important for a performance engine. Do you have instructions that came with the Pertronix showing the factory set curve, and also how to change it. I have found more initial timing works better with a performance cam, and recurve the distributor accordingly. That would also help with low end response.

2nd thing I will mention is the Edelbrock carbs are known to drain back when they sit, my friend was running one for years on his 32 Roadster, finally switched to Holley mainly because of that. For boat engines in AZ I remove the choke from the carburetor straight away, if the tune is correct, with the weather we have here it will start fine without it.

The Petronix distributors come with a kit to adjust the curve.

I'd want a total of 34 with 20 degrees of advance (to start).

Instructions are here...

PERTRONIX Flame Thrower Billet Distribution Installation Guide

These installation instructions for the Flame-Thrower Billet distributor cover important details such as gear compatibility, spark plug wire compatibility, and ignition timing basics. Keep your engine running smoothly with this guide.

manuals.plus

I think we all agree he needs more initial advance, and not less?

 

[obnoxious001]

The Petronix distributors come with a kit to adjust the curve.

I'd want a total of 34 with 20 degrees of advance (to start).

Instructions are here...

PERTRONIX Flame Thrower Billet Distribution Installation Guide

These installation instructions for the Flame-Thrower Billet distributor cover important details such as gear compatibility, spark plug wire compatibility, and ignition timing basics. Keep your engine running smoothly with this guide.

manuals.plus

I think we all agree he needs more initial advance, and not less?

Engines like to start at 20 degrees. All of my new engines that I build get set at 20 degrees before TDC when I drop the distributor. Of all the dyno tests done on BBC engines I have built, only one of them was a little better at 34 than it was at 36, which seems to be where they like to run.

Funny story about Pertronix. I had heard about how good they were since the late 70's when I worked for Gale Banks. One of the Ford guys there swore by them, but I guess his brother worked for them also. Some years ago I thought I might start using their product, and I made a phone call since they were right there in San Dimas. I don't recall the exact conversation, but they didn't want to offer me any support, assistance or anything else that would make me feel good about buying their stuff, so I never did. End of story on that one.

 

[mesquito_creek]

I am set up on the pertronix with the silver spring and no mechanical advance limiter…

So if I set the initial timing at 20 that would put me at 32 total.

I will try that. I was probably way retarded at 8-10 degrees. Because I thought I was being aggressive at 10 because the OEM motor manual calls for 6.

I will reset it at 20….

 

[RaceTec]

Much easier and more available tuning on a Holley... Also watch voltage, I had a buddy chasing a tuning issue for months to find out it was low running voltage...

 

[Racey]

Use a vacuum gauge and try to get the most possible vacuum while keeping the engine speed desired between adjusting your timing (within reason depending on your advance mechanism) and your idle circuit adjustment and throttle blade closed angle.

If you only have 15 degrees of timing advance swing (17 base, 32 full for example) you may find it struggles on the starter when warm as that could be too much timing at crank/idle.

This is one of the commonly overlooked benefits of EFI, complete timing control under all different conditions, you can only do so much with a distributor and weights/spacers, or electronic with adjustable pots.

 

[rivermobster]

I am set up on the pertronix with the silver spring and no mechanical advance limiter…

So if I set the initial timing at 20 that would put me at 32 total.

I will try that. I was probably way retarded at 8-10 degrees. Because I thought I was being aggressive at 10 because the OEM motor manual calls for 6.

I will reset it at 20….

View attachment 1124228

Looking back, I didn't explain that just right...

34 to 35 total degrees of timing should be your goal.

Set 20 degrees of advance in the distributor.

That Should give you an initial timing spec of 14 to 15 degrees.

Initial timing is hard to nail down due to high idle speeds and bumpy cams, that's why you set the distributor (internal) timing first, the total timing second, and don't even bother with the initial timing, except to verify its Close to what you think it should be.

Hopefully That makes more sense.

 

[mesquito_creek]

Looking back, I didn't explain that just right...

34 to 35 total degrees of timing should be your goal.

Set 20 degrees of advance in the distributor.

That Should give you an initial timing spec of 14 to 15 degrees.

Initial timing is hard to nail down due to high idle speeds and bumpy cams, that's why you set the distributor (internal) timing first, the total timing second, and don't even bother with the initial timing, except to verify its Close to what you think it should be.

Hopefully That makes more sense.

The carb instruction manual says to set idle timing at 10 degrees. So I assume that means I simply use my timing light and twist the distributor until the light shows the crank balancer mark at the 10 degree slot on the timing chain cover guage.

I degreed the cam and validated the guage was dead on tdc 0 degrees

 

[rivermobster]

The carb instruction manual says to set idle timing at 10 degrees. So I assume that means I simply use my timing light and twist the distributor until the light shows the crank balancer mark at the 10 degree slot on the timing chain cover guage.

I degreed the cam and validated the guage was dead on tdc 0 degrees

Like I said, same as many others in this thread have said...

You set the timing by adjusting the Total timing. Initial timing is a non issue.

Carb tuning is a whole Different issue, as DaveH has pointed out.

Tuning is an art. Getting an engine to run Perfectly (great drivability and pleaty of power) is like the conductor of a symphony, getting all the different instruments playing together.

But like with anything, you Have to start with the basics, and spark timing is your base adjustment here, since we didn't build your engine.

The BASIC adjustments I gave you are only a starting point.

We can advise you from there, once you get that done. Hope that makes sense.

 

[obnoxious001]

I am set up on the pertronix with the silver spring and no mechanical advance limiter…

So if I set the initial timing at 20 that would put me at 32 total.

I will try that. I was probably way retarded at 8-10 degrees. Because I thought I was being aggressive at 10 because the OEM motor manual calls for 6.

I will reset it at 20….

Yes, I think you will find it will be a night and day difference, but like I said above, more like 34-36 total. After the engine has been warmed up, put the light on the damper and increase RPM as you watch until the mark stops advancing, that will be your total timing.

 

[FreeBird236]

I love reading this stuff from all you guys with talent. Thanks.

 

[mesquito_creek]

I installed the 16 degree limiters on the pertronix

1) inital timing is set at 18-20, it bounces around with the loopy idle
2) idle set at 850 ish, moves around at idle
3) total timing at 3000+ rpm is 36 degrees
4) yellow 4 Hg meter rod spring, spring is holding the metering rod down and tight.
5) jet is the .010
6) metering rod is the .070/.047

Starts good and idles nice on the hose. Will need a lake test to fully test.

 

[mesquito_creek]

It took me over a year to get this correct, mostly because in a year or more I have only use the boat twice. Ultimately, I believe the issue was timing and lean jetting. I had to order individual larger main jet to get enough fuel to the idle and primaries. The plugs just were showing lean even with the largest jet in the kit. The jets in the traditional kit were just to small. 0.107 in. seems to be were its most happy, solid idle in an out of gear without issue.

I tried increasing the size of the jets on the secondary and went to large. It would fall flat and stop accelerating when I tried to go WOT and the secondaries opened. Jetting that circuit back down cleaned that problem back up.

BUT I am not getting the upper RPM I think I should be able to (max 4200-4400). I think the way I built this motor should have no issue running low 5K. Before we go to prop size, it doesn't seem to matter between 21P and 19P. 19P runs better with the extra low end, but it doesn't really run any more RPM up top.

How do I know if I am running out of carb CFM? this is a 600cfm carb that according to charts and stuff should be enough? Am I potentially needing something more like 750 cfm to get more top?

1) inital timing is set at 18-20, it bounces around with the loopy idle.
2) idle set at 850 ish, moves around at idle
3) total timing at 3000+ rpm is 36 degrees
4) yellow 4 Hg meter rod spring, spring is holding the metering rod down and tight.
5) jet is the .107
6) metering rod is the .070/.047

 

[OCMerrill]

5000*350/3456 = 506 CFM. You could put a manifold vac gage on and run WOT and see what the number is if your really wanting a larger carb. I think you will find it drops pretty near zero however I don't know what kind of exhaust is being used.

I run an Edelbrock 600 Marine carb on my Laveycraft. I think the Hot restart is great but let it sit an hour and it cranks for 3-4 seconds before it will fire up. Thats with no pumps of the throttle. One pump and crack the throttle and instant fire up. I think its the nature of the AFB type carb.

I was wondering did you verify the advance with an adjustable timing light?

I had a 65 El Camino some 25 years ago and rebuilt the Power Pack 283 with a 268H cam. That car ran great even with a carter AFB Carb.

 

[mesquito_creek]

I was wondering did you verify the advance with an adjustable timing light?

Yes….. I might just be at the top of what the motor will do under the weight and load of the boat.

 

[mash on it]

Yes….. I might just be at the top of what the motor will do under the weight and load of the boat.

I'd agree, but the 19" prop has the same rpm as the 21".

Something isn't happy.

Dan'l

 

[Trash]

There is a lot of talk about timing here, which is fine and valid, but that is not the main problem. If you have 8-12 deg of initial that should be fine. Thousands of SBC work fine with this. You have a fuel issue. The motor is going lean when put into gear. If you had wideband installed you would likely see the AFR going to 14.5+ and then stalling under load. I've seen this time and time again on my EFI motor when I would dial down the BPW at idle and go too far. Idle neutral AFR was fine but as soon as I bumped into gear AFR swung to 14.5-15.0 and the motor was not happy. It usually quit.

On the other hand I have never seen a motor quit from being too rich....and I'm talking 9.8 to 10.5 AFR.