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Or Seth, either one
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Discussion Starter #1 (Edited)
I have a .060 over 396 with 049 heads and a small dome (maybe 1/4"ish) on the pistons, I'm guestimating about 10.5:1 Compression ratio. Edelbrock performer 2.0 manifold, with a 750 Edelbrock carb on a 2' open spacer. Unknown (has a mildly lopey idle) solid flat tappit cam, stock looking fuel pump, and stock style HEI distributor w/ vacuum advance hooked to the non-ported nipple on the carb. It's in an 18' flat (well, almost flat) bottom, I think the gears are 18% OD. When I'm not heavy on the gas, engine temp stays right around 120, and if I hot foot it, it'll climb up to about 160 or so.

I have 3 issues at the moment.
  • On the top end it feels like she's running out of fuel, back off the throttle a bit and she comes back to life. I'm thinking it could be a fuel issue. After reading some other posts, I also thought the sparkplug gap might be a bit wide (0.040).
  • I haven't put a timing light on her yet, but there seems to be a very fine line between detonation and backfiring out the exhaust. Advance it a cnut hair and it detonates under load, like 3/4 throttle acceleratin out of a turn. Retard it a smidge and at full throttle it pops and bangs out the exhaust, only at full throttle on the top end. I have found a happy medium, but starting is a pain in the butt. Turns over nicely with the ignition off, but struggles to turn over with it on.
  • RPM... I was hoping to be in the 5500 to 6000 range. The original testing prop was a 12x16 3 blade OJ, and the most I could get out of it was 4200. So, I put on a 12x14 3 blade OJ and the RPM sounds a bit higher but the tach is still saying 4200ish. The boat feels quicker, but slower on the top??? I'm thinking the issues listed above are the limiting factors to RPM. Any input?
So, my questions are:
  1. What should I gap the plugs at?
  2. Should I put lighter mechanical advance springs in the distributor?
  3. Is the Compression Ratio possibly too high for premium pump gas?
  4. Am I asking the right questions?
Thanks guys,
-Seth-
 

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200 Posts
I Would First Go To A Fuel Return Setup To Elimate Fuel Problems.

Call Eric At Oj Maybe Go To 11 1/2 Blade, Your Rpm Sound Perhaps Like A Engine Problem. The Change Of Props Should Change 200 To 300 Rpm Changes With Pitches.
 

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Sounds like your timing isn't advancing or getting too advanced.
Sounds like the carb is running low in the bowls when on top end. Adjust the floats.
 

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Sit N' Spin
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Also if the distributor advance mechanism is locked out, unlock it and set up the proper advance curve, then retime it.
 

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1. Put a small fuel pressure guage at the carb to see what your getting. (very cheap at summit)
2. Put a timing light on it to see what's really happening with the dizzy.
3. What advance at idle?
4. What's total advance?


I'd start here first.




Darrell.
 

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Data

You've got to have data. 1st, check the timing at idle, write it down, check it as the Rs go up, how much advance, and when?......Popping in the exhaust is usually a sign of too much fuel. Unburned fuel goes off in the headers. Fuel pressure is also critical, put a gauge on it YOU can SEE from the driver's seat. Plug gap is the least of your problems. A compression test, or a leak down certainly wouldn't hurt in your "data" collection. 3rd, a "split Second" type 02 sensor and kit will tell you most everything you need to know about air/fuel ratios, (about $200. bucks from Split Second).......It is absolutely necessary that you find the timing curve you have NOW, and then make small changes to the initial and "all in" settings. Tuning blindly, as you're trying to do will be a trying day to say the least, and a dismal failure when all is said and done. DATA, there is no substitute for DATA...........Also try a 2 blade prop, the 3 blade may be too much for your power curve when the engine is trying to get in to it's "happy place"..................Data, lots and lots of DATA, and did I mention, to WRITE IT DOWN............MP
 
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