Aug 16th I'll be turning 41; I think that would be a good place to go :-)

1.beerjet
2.mdunn
3.marcsrollin
4. brad
5. Flytime
6.sebastian (lurker)
7.crewchief22
8.bkplesh and klesh
9. forkedup
10. Luckie Stiff (if the boat is alive)
11. COORS HEAVY
12. stc315 (local support)
13. Speedymopars

Lots 'o torque with a diesel. You would just need to have an A3/A4+ impellor, prob run great.

I soooooo want to go. I just flew over it on my way back to Phoenix, and it looked very nice.....

Quick update.
A fast blend of the bowls,radiusing guide,no port match yet.
Disapointing !  only picked up 12 cfm at .500. stock valve, and seat.
I'll give clear steps of a,b,c and results. this is step 1 of 3.

You were only shooting for 15cfm from what I remember - 12 is most of the way there....

yes - but that is .015 from the open throttle position - that is so you don't bottom the pump diaphram.

Any backfiring or dying when you whack the throttle is 99% of the time acc pump related. The other thing to check is if the carb is leaking fuel via the PV port (blown PV). With the carb full of fuel, without the vaccum of the engine running, there should be no fuel dripping from the bottom of the carb.

The ignition load is greatest around torque peek.

The spark voltage and resulting current will take the easiest path.

Let's go with a bad wire that is burned through as a simplistic thoretical example (I don't think you want me to get into a physics course here):

These are theoretical numbers for an example, ignoring impedance, transmission line charatoristics, and a host of other things we don't need for this. Your numbers will vary.

At idle, with no load, your spark plug gap is the equivalent of 50 ohms.
You have a burn in your wire, and that gap is the equvalent to 500 ohms.

The spark will ignore the burn in the wire, and the voltage will jump the plug gap - this causes a spark inside of the cylinder and the fuel will ignite.

Now, as your RPM and load increases, that resistance from the plug gap goes up. At torque peek, that 50 ohms may be 1000 Ohms now.
The voltage will now take the 500 ohm jump to the header rather than the plug, so no spark inside the cylinder.

At the higher RPM beyond peek, the the load may drop to 400 ohms, so the plug once again fires.

The main thing to understand is there is a variance in what the plug load is based on RPM and load, it isn't constant, and it isn't straight up.

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If the resitance of the plug is too great, and there is no other path (like you gapped them at .300) it is possible there will not be a spark at all. A specific voltage will jump a specific gap. Beyond the gap it can jump, there will be no spark.

Compression, gap, RPM, and timing all change this plug loading. 

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It is also possible that your gap is too small, in that case there is plenty of current, but there isn't enough open air spark to keep the mixture lit. Again, this goes up around torque peek and back down again in higher RPM.

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All this can be trumped by an MSD box that is bad, possible something like the rev limiter is sorta kicking in - did you remove the pill?

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Also a distributor / rotor / cap that is misaligned can cause the same issue. You are looking for something that is marginal, not something that is completely dead or disconnected.

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First thing - check the cap and rotor, make sure no moisture and everything is installed correctly and there isn't any burning.

Next, check the wires. Unseat and reseat. look for burns. Measure the resistance with an ohm meter. With MSD 8.5's, it should be 50-70 ohms a foot. With the other MSD's, 500-600 Ohms a foot. In my opinion, any plug wire over 600 ohms a foot is not on my vehicle. A quick check is to bring your old plug wires with you and swap them out. Many times old plug wires work better than the wires that replaced them.


Then double check the plug gap. Set to .045 as a starting point. Too big, possible the spark is not happening, too small, the mixture isn't staying lit. .045 is a safe gap range with a N/A engine. if you are running boost (though I don't remember you saying you have a blower), then gap them to .030.

Once that is finished, set the timing. Too much timing (as will more compression, boost, nos) will cause the plug loading to go up much like you increased the gap.

If all that checks out, Disco the vac advance, swap the coil, then swap the MSD (in that order). 

Torque peek is where the greatest igntion load is - where is your cam's torque peek?

Try backing off your ignition a few degrees to see if it helps at 3500 RPM. Personally I'm leaning towards an ignition issue in this order -

Burned plug wire(s)
Significantly wrong gap setting
insuficient voltage
confused limiter
cap rotor phasing or clearance issues (too big of gap)





 

I was out there today doing some tuning....

OK, when I hear that, I think that the plugs have a bad gap on them, causing them to foul on the acc pump. In addition to the plug gap, This can also be caused by a marginal coil or wires, a confused rev limiter (if it's a 6 al pull the pill), or incorrect rotor phasing in the cap. Don't discount something stupid like moisture in the cap or the cap not seated 100%. When you get on it at low RPM, the load the ignition sees is the greatest - so any easier path the current will take. Light load won't always show ignition issues.


OR

The floats are too low

OR

the secondaries have debris in them.


OR

The secondary acc pump is too big (too much fuel) or the secondary spring is too light ( I missed if it's a DP or a vac).

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You also could be having lifter issues if you have a hyd flat tappet, see if changing the weight of the oil changes where it happens at.


What is your gap set at (set to .045) ?
What plug wires are you using?
Have you separated the adjacent firing cylinders (example: mopar / Chev 5/7 ; Ford 3/4)
Have you verified the cap is dry and on 100%
All plug wires are seated?
The plugs are tight?
The wires can't and aren't arcing somewhere?
You have a reasonable acc pump cam(s) installed (white / pink) , and not some mondo squirter size (.028-.035)?
Jetting is near stock for the carb?
Fuel pressure is OK, floats set to sight glass?


My dual carbs want a .035-.037 squirter and pink cam. Not much pump shot cc wise, but all of it immediately. 
Jets seem to get too much fuel for too long on the acc pump if the carbs are left stock - no convertor or gear to contend with in a jet, so they don't need as long of duration - if this happens to be when your secondary acc pump starts (and you have a dp) - you may just have too much  fuel for too long of duration at that point.

I'd have to hear it to be sure though, these are just some things that come into my head.

Makes me happy I have a mopar. Autolite 75's for all the big blocks with factory iron heads, and Autolite 65's for everything else (including 4's, 6's, etc) including most aftermarket BB heads. 

Sheet - put an A4 on the SOB, and fly....

BTW a teenager driving a 16 footer with a outboard merc 125 is way more dangerous.... It's the operator that ratches up the danger factor, not the HP .....

Cam was custom ground by clay smith cams for my application, so clearance should not be a problem (with correct length pushrods)  He told me my stock length should be correct, but I am not sure he remembered that I was changing to roller rockers.  I changed from non adjustable rockers to 7/16 studs and 3/8 guide plates.  Scorpion roller rockers will be here tomorrow.  I am 99% sure there has been no block or head decking done and the stock pushrods seemed to work for the old cam.  New cam is solid lifter so I hope all the reading I did to determine correct push rod length helps.  I borrowed a pushrod length checker from Marcsrollin and will order the hardened pushrods tomorrow.  Crane cams told me that a wall thickness of .060 would be sufficient for my application.  Any more advise is greatly appreciated.  I need to get this right to get to Parker with a running boat

www.pushrods.net

Smith Brothers makes the best.

The old cam may or may not have the same base circle as the new one, if that changes the pushrods will either be too short or too long. Typically solid and hyd cams do NOT take the same length,  as the solid lifters are shorter from the pushrod perspective.

I am running .125 wall 3/8ths pushrods in mine - any flex causes the valve to not lift as high and can cause breakage and instability in the valvetrain if it gets severe enough. On an engine that is constantly seeing high(er) RPM's, pushrods is probably not the area to skimp.

Need to know the before numbers too - every bench is different!

Thanks for the post.

Yep, simpler is better. I'm happy now I have nothing in the way anymore - now I just have to worry about getting clogged with debris.