Sbc Falling on its face..

[shortbed70]

Well I just did a cam swap, broke it in per lunati' direction, changed the oil and put some street miles on it 70 to be exact... Then took a friend for a ride and when I stood on it it popped and coughed and fell on its face for like a second or two then pulled like normal.. Timing is 12 initial and 30@3000. I'm thinking the float levels might be a tad low but I didn't have that problem with the old cam! Any ideas?

[cableguy0]

More timing first of all. You should be at 36-38 total with vacuum advance unhooked and plugged. What kind of carb are you using? you likely need to increase the accelerator pump volume. If its an Edelbroke you can move the accelerator pump rod. If its a holley you can go about it a few different ways. You can change the change the nozzle, change the accelerator pump cam to slow or speed up the pump shot.

[shortbed70]

Speed demon 650. I'll try and give it more timing but do t want it to start hard. I'll try that tomorrow...

[cableguy0]

With that carb... All I can say is good luck. Most of the best carb guys around don't want anything to do with a demon. I know the previous models were plagued with crazy issues that nobody could figure out without using a magic wand.


If you don't advance the timing more you will be losing so much power its ridiculous. 6 or 8 degrees of timing could be 50 horsepower or more depending on the engine itself. If you have a starting issue you need to address that separately. Make sure your battery cables are of proper thickness and cables clean. Make sure the battery is healthy. Make sure the starter itself is strong enough.

[Marv D]

I'd say 3part issue...
Get the float levels up where they should be, (cableguy and I are of like mond on the Demon carb... not a fan!)
check the accelerator pumps for initiation as soon as the throttle is moved and if you need to up the squirter size,, do it.
and get the timing corrected.

Agreed even the most efficient chambers will like 10-12° advance static and 33-35°+ total,, all in by 3500-4000. Todays ethanol 'enhanced' fuels tend to like more advance than previous true 'gas' (0 ethanol) fuels. About 95% of all pump gas sold in the US is is 10% ethanol now that MTBE has been banned.

[crazy longhorn]

Originally Posted by cableguy0

More timing first of all. You should be at 36-38 total with vacuum advance unhooked and plugged. What kind of carb are you using? you likely need to increase the accelerator pump volume. If its an Edelbroke you can move the accelerator pump rod. If its a holley you can go about it a few different ways. You can change the change the nozzle, change the accelerator pump cam to slow or speed up the pump shot.

I agree....but on a street, pump fuel ride , I like 34-35 0n the total. If you cut the decks, for quench, you will see more on that sb chev Longhorn

[shortbed70]

Gonna mess with it tomorrow afternoon! Float levels, timing and check pump arm... I just don't understand why I didn't have this problem until after I changed the camshaft

[Ironangel]

What Lunati cam? What cam came out of it and what oil are you running? I agree with a little more timing as well. My Lunati cammed (10120701) SB 350 likes 15-16 initial and 35+ all in at 3500. With that said and all cam lobes still intact with a zinc ladened oil, then you can bet it's the carb. Your previous cam may not have revealed a weak shot or even a rich shot where the new cam with a different vacuum signal and grind would.

[cableguy0]

Originally Posted by shortbed70

Gonna mess with it tomorrow afternoon! Float levels, timing and check pump arm... I just don't understand why I didn't have this problem until after I changed the camshaft

The cam dicatates how the engine will perform. Its the heart of the engine. The time the valves stay open and how far they open is dictated by the camshaft. That directly affects the air/fuel requirements and timing requirements of the engine. Its common and stock engines are very forgiving because they are made in a way to work well with almost anything you bolt to them.

[shortbed70]

Originally Posted by Ironangel

What Lunati cam? What cam came out of it and what oil are you running? I agree with a little more timing as well. My Lunati cammed (10120701) SB 350 likes 15-16 initial and 35+ all in at 3500. With that said and all cam lobes still intact with a zinc ladened oil, then you can bet it's the carb. Your previous cam may not have revealed a weak shot or even a rich shot where the new cam with a different vacuum signal and grind would.

Cam is 1012703LK and it was broke in with Lucas 30wt break in oil just like it said to be. 2-2500 for 20 mins ten 500 increase for a min each till a total of 3500 then down 500 each min till 1000 rpm then shut down. Ran the valves, they were good and pushrods were spinning cause I marked them and then filled with Brad Penn 10-30 high zinc oil and a wix 60010 filter (I think that's the number)
I just came in from checking things and found I forgot to tighten the dizzy bolt and it walked so reset at 15 initial and 34-35 total at 3500! I think my weights in the dizzy are loose or sticking so I will address that later. I also found out my fuel regulator was stuck and pushing 7.5# fuel pressure to the carb and the back float bowl was way low and the front was a touch... Big swing so next time it's out of the trailer I will see what she acts like! Next thing I will be changing to another carb built by a friend of mine with a speed shop.

[Ironangel]

Originally Posted by shortbed70

Cam is 1012703LK and it was broke in with Lucas 30wt break in oil just like it said to be. 2-2500 for 20 mins ten 500 increase for a min each till a total of 3500 then down 500 each min till 1000 rpm then shut down. Ran the valves, they were good and pushrods were spinning cause I marked them and then filled with Brad Penn 10-30 high zinc oil and a wix 60010 filter (I think that's the number)
I just came in from checking things and found I forgot to tighten the dizzy bolt and it walked so reset at 15 initial and 34-35 total at 3500! I think my weights in the dizzy are loose or sticking so I will address that later. I also found out my fuel regulator was stuck and pushing 7.5# fuel pressure to the carb and the back float bowl was way low and the front was a touch... Big swing so next time it's out of the trailer I will see what she acts like! Next thing I will be changing to another carb built by a friend of mine with a speed shop.

Cool, keep us updated. The first thing that popped into my mind after reading your initial post was a wiped out cam. I give em a heavy dose of Isky Rev Lube rather than the red Karo syrup they send in the box. You should be ok, that's good oil your using.

[shortbed70]

Maybe this weekend I will get it out of the trailer...

[shortbed70]

Well on to the next attempt to fix... Plugs, wires, cap and rotor and if she still does it I'm going to buy a new carb or just say f it and go FI!!! Damn thing ran better with a flat cam!!!

[Rickysnickers]

Originally Posted by shortbed70

Well on to the next attempt to fix... f it and go FI!!!...

I'm with you on that. I recently did a head/cam swap on my truck and I'm getting to this point too. I cannot get my Edelbrock carb to run right.

[cableguy0]

Originally Posted by Rickysnickers

I'm with you on that. I recently did a head/cam swap on my truck and I'm getting to this point too. I cannot get my Edelbrock carb to run right.

That's because its an edelbrock carb.

[TJ's Chevy]

Still don't get what the problem with eddys are. Never had an issue with mine. Only had an issue when a stinkin fuel filter was plugged solid! Holleys are known to nasal leak like a water fall so be prepared to sit and crank on it for hours when things are hot. After using my eddy for 6 years I am now starting to get a little nasal leakage, but...turn the pump off and let the motor idle for a bit and all seems fine. That carb was way cheaper and worked like a top out of the box. 600 cfm 1405. Back when they were $290 and the same Holley was well over $300.

[shortbed70]

I've ran both and to me it's purely preference.... I'm not blaming the carb yet, wires and new dizzy first then carb but could also be an intake gasket leak or something like that but before I go that far "KISS" first

[cadillac_al]

This is when it is nice to have multiple vehicles that you can swap known good carbs back and forth. If you are running the points ignition I would suspect that area. My truck came with an Eddy carb and I planned to change it but it has been working pretty darn good so it is still there after 5 years.

[shortbed70]

I'm running an old Hei dizzy with mad hidden module...