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I give up. I must be stupid. Need help. Can't get this motor tuned to save my life.


Well-known member
Nov 21, 2003
New Jersey
71 Kandy Burple Conv / 02 MY Z06
Today is not my day. I've read all of Lars' papers on tuning, timing, valve lash, etc. You've all given me good advice. I still can't get my new YearOne crate motor tuned to save my life. I've concluded I must not be able to follow simple directions and that I'm a hopeless basket case. :confused: Either that or I'm just missing something and someone here will shed light on my problems or give me a better approach at fixing my problems. I'm writing this post to give you all the details and beg for help; lots and lots of help.
Here are the motor specs...
YearOne Crate - 355 SBC
·Horsepower- 416
·Torque- 426
·Compression ratio- 9.5:1
·Vacuum produced: 12hg @ 800RPM
·Recommended fuel- 92 octane
·Max recommended RPM- 6000
·Block- Seasoned 4-bolt iron
·Crankshaft- Nodular iron
·Pistons- Hypereutectic
·Connecting rods- Powdered metal
·Camshaft- Hydraulic roller
·Valve lift:.520"
·Duration @ .050" (int/exh): 218deg/228deg
·Rocker arms- 1.6:1 ratio - Stamped
·Cylinder heads- Ported Vortec
·Valves- Stainless steel 2.02 int/1.60 exh
·Valve springs: Heavy duty
·Bore x Stroke- 4.030" x 3.48"
·Intake manifold- Dual-plane aluminum (Professional Products - Cyclone)
·Engine fasteners: High tensile strength
Carb - Speed Demon 650 - Mechanical Secondary - No Choke
Distributor - ProComp HEI, Vacuum Advance, Tach Drive
My first problem was in this post. http://forums.corvetteforum.com/showthread.php?t=1522736
I called YearOne and they said must be a catastrophic valve train failure. I'm not there yet. Noisy rockers can be a minor issue. I called Hi-Tech (the engine builder) directly and they said the noise was normal due to the cam profile. Said even the hydraulic roller lifters wouldn't eliminate the noise. Suggested I adjust the lash to make myself comfortable there wasn't a problem. Spec 1/2 turn after 0 lash. I used Lars' 90 degrees at a time instructions and it works fine. None of the rockers seemed out of spec after all this but at least I know now. After the motor started it seemed quieter at first but then the noise came back. I think this is just the way this motor sounds but if you have the same motor and don't hear anything when your head is under the hood please pipe in.

Timing - Steps Taken
I adjusted the timing per Lars' instructions as well. Results are as follows:
  • Static Timing 18 degrees - 600 RPM
  • Total Timing with Mechanical Advance at 2900 RPM- 36 degrees (motor calls for 38 but I backed off for safety right now)
  • Total Timing at idle with Vacuum Advance - 38 degrees (used MityVac to get all the vacuum timing in at idle for tuning). The vacuum can is an adjustable can on a ProComp HEI Tach Drive distributor. They told me it only brings in 18 degrees but the timing light is saying 20. They told me I could adjust the vacuum thresholds by using an allen wrench down the throat of the can to change the specs. I did this but all I noticed was a change in how much advance I could pull in not when. Right now it comes in at 6 in Hg and all the way in at 15-16 in Hg. My motor only makes 12 in Hg at 800 RPM.
If anyone can tell me how to adjust this "adjustable" vacuum can so it comes all in at 10 in Hg please let me know. If it's not possible with these cans then I need to change the can to one of the ones Lars has in his paper.
Right now I think the timing is on the mark. I just need to get the vacuum can right. I'm using full manifold vacuum. Ported Vacuum is the wrong answer from all the papers I've read.

Speed Demon Carb Adjustment
I'm in my own personal living hell getting the carb adjusted. I'm looking for advice on how to get a 650 Speed Demon, with Idle Eze, and Mech Secondaries tuned in on this motor. Specifically I'm looking for advice that does not include comments like "Buy a Holley, QJet, Throw it Out, etc." I think this is a fine carb and the issue is with my tuning not the carb. I could be wrong but I'm willing to be it's a human error at this point.
I've seen responses from a forum member that works for BG in the past. I can't call their tech line during the week because I work. I adjust the carb on the weekend when they're closed. Go figure.
Here is how I adjusted the carb, the problems I'm having, the troubleshooting advice from BG website, and my further adjustments, all of which have not worked.
Carb Baseline Setup - This morning I pulled the carb off the car and started over with these settings.
  • Primary Butterfly open to expose .020 in of transfer slot (used feeler gauge)
  • Secondary Butterfly open .020 (later realized this was wrong after it was on the car)
  • Mixture Screws all turned out 2 1/2 turns at all four corners.
  • Idle-Eze turned out 1 1/2 turns
  • Float levels right at to slightly under 1/2 of the glass (middle mark)
  1. Started car, set timing, car at temp, vacuum all the way in via MityVac.
  2. Set idle via Idle-Eze screw to 800 RPM
  3. Idle very very rich, makes your eyes burn
  4. Progressed around car 1/4 turn in on mixture screws (all four)
  5. Repeat, Repeat, etc until idle was up to 1100 and exhaust no longer burned eyes. Vacuum at 12 in Hg no matter where the setting.
  6. Adjusted idle back down to 800 via turn in on Idle Eze screw.
Took car for ride around the block. Had several problems. The problems, suggested fix from BG troubleshooting guide, and changes I made are as follows:
  • Car surges at idle to light throttle (I'm assuming this is my vacuum can and it needs to be adjusted or replaced)
  • Car stumbles under light acceleration - BG - Open Mixture, Readjust Butterfly (no indication which way) Raise float.
  • Came around corner and stepped on Gas - Thwack thwack - backfire through passenger exhaust. - BG - Lower float level, decrease fuel pressure, decrease jet size, readjust both butterfly valves.
  • Slowed down turned corner slight gas - POP - Small backfire through carb. - BG - Open mixture, increase squirter, increase jet, raise float.
Pulled into driveway and made adjustments. Adjustments that disagreed I figured canceled each other out and were not the problem. For example you can't both raise and lower the float level.
At this point I realized that I set the secondary butterfly at .020 in. In the book it said to cover the transfer slot for motors that idle under 1000 rpm. I backed off on the secondary idle screw enough so that it would cover the rest of the slot but not so much that it was completely closed.
Float level - left alone.
Mixture screws. They were all 1 turn out. I turned them back to 1 1/2 turns out.
Rev'd the engine a few times and POOF! Big fireball out of carb. I'm lucky that I kept my face away from the carb or I'd have been in big trouble. As it was the flash scared the heck out of me and blinded me for a few seconds.

So what's left? Fuel Delivery
Based on the suggestions in BG's trouble shooting guide it could be a fuel delivery problem, or rather too much fuel delivery.
The fuel pump is a Jegs hi flow mechanical pump. I don't have a return line connected. In addition, I don't have a pressure regulator or fuel pressure gauge.
The reason I don't have the regulator is I couldn't figure out how/where to plumb it with the limited space I have. Here's a pic.

I didn't get a fuel pressure gauge because every other post I saw stated that these don't work very well under the hood and that they were a waste. Either way I figured they were more important for high revs and that I would be more likely to suffer from fuel starvation than too much pressure. I'm not convinced the regulator is going to solve anything but I need to put one on now to eliminate it from the mix. I'm also going to find some kind of fuel pressure gauge to take that off the list as well.
After the big backfire through the carb I shut her down and put her back in the garage. I'm pretty :mad ticked off right now. Between bad weather, less daylight, business travel, etc. I've been messing around with this tune for a month. I need to get it stable so I can get the car in for paint before it gets too cold. Any and all help will be appreciated.
Thanks in advance and sorry for the long post. When you reply it would be good if you break it down to.
Adjustable Vacuum Can - How to or get a new one.
Timing - General comments
Carb mixture - Carb settings
Fuel Pressure/Regulator - Parts suggestions and comments on if this is likely the real problem or not.

Jeg's has a regulator that connects to a carb spacer that would work(but i would hate to get rid of that killer fuel line setup you have now)Have you tried putting the stock fuel pump back on with the return line attached and noticed any difference?How does the car run with the vaccuum advance disconnected?
Do you have a fuel filter? It sounds like a clogging issue. Sorry if you covered it and I missed it. . . but that's how they act.

You said the float level was in the middle of the sight glass? If so it way to high.It should be right at the bottom of the glass.A too high float level will defently make it run rich not only at idle but at any rpm.Here is a suggestion If possible find someone with a good working carb and install it on your engine see how it runs. I had the same trouble once had bought a new carb wouldent run for crap no matter what.So I called my buddy over and told him to bring his lemans over since he at the time was running a 750cfm carb vs my 650 that ran like poo.I used his carb and bang! like new!
I hope you’re not using one of those $50.00 distributors found on e-bay! I just went through this last summer on friends 350. The quality of that distributor was so poor the counter weights were actually riding directly on the base plate never allowing counter weights to fully come back to the home position. He ended up replacing the distributor. On the vacuum advance canister I would screw in the adjustment screw just until it bottoms and then back out counter clockwise 4 turns. This is a good starting point. After you get the motor running good find the steepest hill you can and put a load on the motor and adjust the canister until the motor starts to knock and then back it off until it stops.
Although, 12 inches of vacuum is rather low and thus you may have other problems with accessories down the road it should be enough.
It looks like from the picture you provided your running a 3/8” fuel line? If so the high flow pump may be producing to much pressure and a regulator will be needed. Most regulators are ported for the use of a gauge. You will want to run the fuel pressure at around 5 to 6psig.
On the carburetor adjustment air/fuel mixture screws I would attach a vacuum gauge to manifold vacuum port and adjust one side at a time in/out to obtain maximum vacuum at gauge. Then readjust idle speed to what you want and adjust other side to max vacuum adjust idle speed. You may have to do this a couple of times each side to get it dialed in. Count the final turns each side and set the opposing secondary mixture screws the same.
I would start with ignition setup. If your getting backfire through the carburetor this sound directly related to a ignition problem.

Vacuum leak, bad carb and timing would be my suspects. Sounds like the problems I had after installing a crate motor in my 75. Went to a different carb and solved all problems.

Your engine compartment looks great!
Made good progress today. Found some stupid mistakes.

First I want to thank everyone for their feedback especially those of you who went the extra mile to send me PM's. Based on all the feedback, my own frustration/confusion, and the premise that the most likely problem was something I did wrong I started all over again from scratch.

First things first. Despite previously checking the timing several times and presumably following Lars' papers I decided to throw all my timing findings to date and started over.

I pulled the cap and rotor and checked the mechanical advance. What I noticed is that the advance moved fine until the very last bit of travel and then it got much harder to turn. This suggested to me that the advance on mechanical isn't linear and it was possible that all the advance was not coming in even at 3000 plus RPM despite the fact that advance stopped climbing at 2800 RPM.

I also noticed that the amount of rotation around one third (more or less by eye) the distance between the each spark terminal. There was no way my previous reading of 18 crank degrees was accurate nor the technician's assurances that 18 crank degrees was all that was in there. 1/3rd the distance would be 15 dist degrees or almost 30 crank. I put the lightest springs I had on the mech advance and closed her up.

Bad timing was a recurring theme supported by my observation above. Also the fuel level was another theme. I lowered the float level and I retarded the timing and fired her up. She hated it at first, without the vacuum advance she barely idled. I ran around the carb trying to get the car to idle. The motor was cold but I had to do something. What I noticed was that the motor picked up speed when I adjusted the secondary mixture screws a bit more than the primaries. I'm assuming this is because I have a problem with the butterfly settings but regardless this strategy got the motor to idle. The fuel levels are at the bottom of the glass.

Now the most excellent findings. With vacuum advance disconnected and a "running idle" with preliminary carb adjustments I was able to run the RPM up to 4000 RPM. (Didn't want to push my luck) The timing jumped up very quickly at lower RPM stayed for a bit at mid RPM and advanced further with more RPM. The timing stopped advancing at 2800 RPM and stayed there up to 4000 RPM where I stopped. I set the timing at 36 degrees while running at 4000 RPM.

When I let it drop back down to idle it wanted to stay above 1000 rpm but I was able to get it to come back down. I checked the timing and it was at 12 degrees. I turned off the motor and put the mid range springs back in.

Started her up again and check the timing at 600 RPM. Still 12 degrees. Still not happy idling without vacuum advance. 14 in Hg of vacuum on the gauge.
I pulled out the MityVac and pumped up the vacuum can. (Note I ran the allen screw adjustment all the way in then backed out 2 turns as suggested by one of the responses to my post) I pumped the vacuum up to 20 in Hg and checked the timing. Timing was either 33 or 34. It was steady but about in the middle of 33 and 34 using the advanced timing light. I let the vacuum out and let the motor settle down again. I plugged the can into manifold vacuum and checked the timing again. It was at the exact same point 33-34 degrees.

Now I have all the timing information I need to get this stable.
Initial Timing - 12 degrees
Mechanical Timing - 24 degrees
Initial Plus Mechanical Timing - 36 degrees
Vacuum Advance - 21 to 22
Total Timing - 57 to 58 (5-6 degrees more than max desired)

Since the vacuum can is coming all the way in at idle that's a good sign. I think if I back out the allen screw on the can I can reduce the total vacuum timing. Hopefully I can get it down to 16. That would put all the timing at cruise into a max of 52 degrees.

That's it. I ran out of daylight. I can't get to it again until Friday night or Saturday morning. I plan on taking the carb off again and making sure the butterflies are set at .020 primary and .000 secondary. I'll set the mixture screws and Idle-Eze per Lars instructions for the Demon. At the same time I'm going to go around and check the lash one more time. I plan on pulling a few push rods to check to make sure they're straight as well.

I'm also going to suck it up and order a pressure regulator, fuel pressure gauge, and under hood water temp gauge. I don't have any room to plumb the regulator down by the fuel pump. I'd like to put it right in line connected to the fuel lines coming off the carb. I found the following.

Jegs Aeromotive Fuel Pressure Gauge 027-15632 and

Jegs Aeromotive Regulator 027-13201

It's hard to see how large this is but it appears the part will fit in-line with my -06 AN connections. The line off the carb is fairly stiff. I'd put a 90 degree AN fitting on the line going to the fuel pump and the plumbing should fit. I don't have anywhere to "bolt" the regulator to that I can think of. Will this work OK?

Also, I'd like a temp gauge right on the engine because the stock gauge doesn't give me the exact temp I need to see. I wanted to put one in the fitting at the front of the intake just in front of the thermostat but I'm not sure what size fitting this is.

Once I have all this in I'll need to get the carb adjusted. Any input based on what I said above is appreciated as always.

Any advice on how to get the carb preset now that I have the mechanicals in order would be appreciated.

Thank you all. Please keep the feedback coming. Sometimes you need to just start over and throw out what you think you know and begin with a fresh empty brain. Based on my discoveries today the brain must have been empty all along the way.


Big progress was made this weekend. I've got a decent (although not optimal) tune on her today.

- Pulled and replaced all the plugs. They were all black and sooty due to the terrible adjustments I had on the motor. Nice new clean plugs fired up right away.
- Adjusted the lash again. No more clacking noise (could be the adjustment could be the better tune.) You can still hear the rockers the slightest bit but no hard noises just a "schwering". Withe the stethoscope you can tell they're all much better.
- Pulled and adjusted the carb per Lars instructions. I set the butterflies at .020 on both Primary and Secondary. I adjusted them both evenly to obtain the idle speed (600 without vacuum advance while tuning). I ended up leaving the mixture screws at 1 turn out since I couldn't tell any difference in the motor idle or vacuum turning in either direction with the initial 1/4 turn test on driver's primary. I did try to turn them all in 1/8th in and the idle dropped so I pulled them back out to 1 turn. Idle eze turned all the way in.
- Left the timing at 12 degrees static for the carb adjustment since that's what came out ok last week. It might need to be bumped back up to 14 or 16 but I'm not playing with it right yet.

Took the car around the block and the surging was gone under light throttle. Under very mild acceleration from stop she pulled great (recognize it wouldn't do much at all before). Downshift no problem. It wants to spin the wheels with just the slightest amount of foot in the pedal from start (a great sign!). Accelerated through 1-3 up to 55 and ran fine (I didn't get her into the secondaries yet cause I'm still gun shy.)

I think it's down to "fine" tuning. Getting the timing optimized and additional adjustments to carb.

I'm thinking the vacuum can is fine. I'm going to adjust it to see if the allen screw limits the total advance as I expect it to. The Crane Cams adjustable vacuum can instructions don't make sense to me as this can does not have the timing limiting cam as described in the Crane instructions. Also my observation of the linkage inside the distributor shows the screw actually seems to limit total advance on the can and I can't see a reduction in the vacuum required to advance it all the way. I have no idea who makes this can as there are no markings on it or instructions with the distributor from ProComp.

Timing, now that I'm not afraid of backfiring I'll check the total timing one more time and be sure I'm at 36-38. Static might have to come up 2 degrees.

Carb Tuning Questions - Carb Experts, I'd like a little more insight on what the adjustments are doing so I can be sure I know what's happening when I make minor tweaks from here. Specifically.

Secondary butterfly settings and Transfer slot. Since I have both butterflies set the same I'm wondering what the impact is of this slot. What happens when more or less of the slot is exposed below the butterfly? Since more increases Idle does this end up bypassing the idle circuit? What happens with less than .020?

Why does BG recommend the secondaries be set at .000 and primaries .020 for motors that idle at less than 1000 RPM? What is Lars thought process on why they should both be the same? Is there an advantage to closing the secondaries .020 more than the primaries (per BG) or is the way Lars told me to do it right on the money? I'm idling about 800 RPM with the vacuum connected.

The Idle Eze is completely closed with no apparent ill effect. How does this impact how the motor runs? Is this an adjustment I just don't need since my cam (although a little aggressive) doesn't have enough duration to take advantage of this?

Is there a good tuner in the DFW area I can take the car to now so I can put it on a scanner and see what's happening real time to make the final adjustments?

Choke - I have no choke on this car. It' won't be run in freezing cold weather but I'll probably drive her on a few day's in the low 40's. This will be a street driven car not a dragster. Do I need a choke? If I don't put a choke on will I end up fouling my spark plugs when the motor is warming up?

Fuel Regulator and Pressure gauge - No one has replied about how I'd like to set this up in my post above. Thoughts here would be good before I order the part from Jegs.

Thanks to everyone for helping me get this far. I'm pretty sure my biggest problem was misreading the total timing the first time and then getting myself upside down on the carb tuning due to frustration. I appreciate all your kind words of encouragement that kept me down off the ledge and the technical advice and expertise that got me this far. I look forward to your additional comments.


i may be able to shead a little light on a couple questions you have. first off is the carb. i have been playing with my Demon for five years and learned a loads as of lately thanks to an oxygen sensor. the Demons come from the factory set really rich, they are more for max power and not street driving. basically what you want for street racing and not for going to the drive-in. easily calibrated out though. the idle feed restrictors are bigger than they need to be in most cases. the idle feed resrictor jets control the amount of fuel that the idle mixture screws have to play with. since you are at, or less than, 1 turn on your mixture screws, you could stand to drop the idle feed restrictor size. i would drop them 0.004" in orifice size, if they are 0.039" then drop to 0.035". this will give you more adjustment with idle mixture screws. contrary to popular opinion, the idle mixture DO NOT stop working when the butterflies are opened. idle mixture settings will sway heavily on your gas mileage as well. remember that you are not opening the throttle much to obtain 2500 rpm cruise speed. the secondaries are still at idle as well. my carb had 0.039" restrictors that were hogged out to 0.045" for alcohol by the engine shop where i purchased the carb. i ended up with 0.031" to get it working correctly. the car went from 6mpg to 26 mph just cruising. it also suffered from fouled plugs and eye watering exhaust. now she burns super clean. you may also have to drop to 0.031" restrictors with your motor. the good news is you have vacuum. with that much, tuning your power valves is a no brainer. just check the vac at idle and in gear and install a valve that is 2 to 3 under your vac reading. i like tuning without a power valve. just block it off and install eight sizes bigger jets, tune car, re-install power valves and reduce jets by eight sizes, then fine tune agian. it's alot of extra work, but it takes the potential problems of a bad power valve out of your tuning efforts. next is the idle ease and secondary butterflies. the more you shut down the secondary, the more you limit the idle circuit feeding the motor. opening the butterfly much past the 0.020" opening will start letting the carb pull fuel from the main circuit. the idle transfer slot should never be open more than a perfect square on a street engine. ones that make good vac, 12" +, at idle will most likely need the secondaries closed. the idle ease is just a circuit that allows extra air under the butterflies so you can close down the idle transfer slot and lean out the mixture on lumpy cammed motors that need air, you most likely will never need or use it with this motor. it is a new way drilling the butterflies with little holes without actually drilling them. lastly is fuel pressure regulator. i suggest you get a by-pass style regulator. the cheap Holley regulators shut off flow when the set pressure is reached. the by-pass style bleed pressure back to tank. they both limit pressure to the carb, but the by-pass style allows cold fuel to circ to the carb. this keeps your pump from vapor locking and your float bowls from boiling in traffic. i had problems with my car when running the Edelbrock high volume fuel pump and Holley regulator. the damn thing would get sick after two minutes in traffic. by sick i mean, black smoke, raw fuel, stumbling, coughing, hacking, back firing and dying at the light. i almost set it on fire a couple times, yes i mean arson, litteraly. installed the high dollar Aeromotive by-pass and all ills were cured. granted my pump is and internal by-pass and has no provision for return to tank just like the vast majority of electric pumps. i just installed my regulator on the fuel log inlet and paralelled the return down the inlet hose to the factory return line. i used AN fittings for inlet and exhaust and a barb fitting for the return line. not a big fan of hoses for fuel lines, but replace them twice a year with good stuff. also you don't need a choke. it is only for when the motor is cold. you can install a circ pump block heater for about $30 (available at any parts store) and pre-warm your engine with good old electricity. or you can give her a pump and a crank and a little babysitting until she's warm. the engine actually runs lean when cold with no choke, so don;t worry about fouling plugs. hope this helps you out or least gives you ideas for tuning and getting it set-up right. happy tuning, Brian.

Is there a good tuner in the DFW area I can take the car to now so I can put it on a scanner and see what's happening real time to make the final adjustments?

Fuel Regulator and Pressure gauge - No one has replied about how I'd like to set this up in my post above. Thoughts here would be good before I order the part from Jegs.



Good to hear that some progress has been made.

Regarding a tuner..do you mean a dyno that will measure the A/F ratio? If so let me know there are a few good people in the area.

Regarding the regulator I will take a few pics of mine tomorrow and post them here by lunch time for you to review. All -6 an lines and fittings and the same regulator that you have in the pic....very clean look.

I have a Holley tuning book you can borrow, which is almost the same as the BG (basic principles). I have cams and jets and a few Power valves that are the same for the Holley of BG.

Let me know.


Bad news....

The lifter noise is back! I paid a mechanic that works on race motors to look at it today. He checked the lash and set it. Motor continued clacking like heck still. Pulled the covers the preload was gone.
He told me the valvetrain is toast. He's not sure if it's the cam or the lifters without pulling the motor apart. :ugh

I've got to call YearOne on Monday and see how good they are about their warranty. This motor didn't even get 3 miles on it.
Keep your fingers crossed for me.
Bad news....

The lifter noise is back! I paid a mechanic that works on race motors to look at it today. He checked the lash and set it. Motor continued clacking like heck still. Pulled the covers the preload was gone.
He told me the valvetrain is toast. He's not sure if it's the cam or the lifters without pulling the motor apart. :ugh

I've got to call YearOne on Monday and see how good they are about their warranty. This motor didn't even get 3 miles on it.
Keep your fingers crossed for me.


I owe you a call I know. This sucks and is not good news, but depending on what they say it may turn out to be OK (new engine). They better pay for freight both ways!!

I just came back from the dyno and i am not to hapy regarding the net HP that I have, but I will start a different post on that.

keep us all updated so we can follow this companies warranty promises.

Keep the faith for now...my engine that I received from them is now purring like a kitten!!

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