Gun-shot backfire and Holley carburetor

I have the same issue with my EF running a Holley center hung 2BBL. The backfire always startles me. And as mentioned, it runs like butt when in the rocks. If I'm nose up for too long, it will start to blubber and spew heavy black smoke through the exhaust right before it dies. The only way to get it to restart at that point is to crank it with the carb wide open. This condition has put me in tenuous situations more than once. I have tried running with the float adjusted low, added the float bowl vent extension and even added a regulator lowering the pressure to 2 psi while in the rocks, nothing helps. My my bottom line is this: I need to bite the bullet and inject it. I hope the OP can get his to run satisfactorly.

 

You need a dash pot!!!http://www.earlycj5.net/forums/showthread.php?49482-V6-dashpot
I put a new one on mine it stopped the back firing..any auto parts store will have one..its less than $10.00...

 

Quick 'n easy fix...find a side hung float bowl. Put in a spring loaded needle & seat while you're at it....

 

Double check your exhaust system. Even an air leak by your muffler can cause a backfire.

 

You have lots of good advice here. FWIW, you mentioned #61 jets. Sounds pretty big to me. I run a Holley 4bbl 4160 and changed the stock #51 jets to #49.

 

You're probably running the 0-8007 390 cfm 4bbl, which comes with a #51 jet stock.
The OP has (I think) a 350 cfm 2bbl, 0-7448, which comes with a #61 jet.
Apples & oranges....

 

I think I have (had) multiple problems. I took your advice and searched the forum for information about the distributor. The "odd fire-even fire" thing is confusing. But for sure the distributor was installed incorrectly. It was that way when I bought the jeep. I think I have it installed correctly now and the backfire is substantially less frequent, but still a problem. I installed a new pertronix ignitor and coil, so I don't think the dwell is an issue. I'm still confused about whether or not I have the right distributor and/or cap though. Apparently a "even fire" cap will fit on an "odd fire" distributor? Is that right? How can I tell if I have the right one? It starts and runs great. Since I re-installed the distributor to the "correct" position, it seems like the vacuum advance can and vacuum hose are awfully close to the fan when the timing is set to 5º BTC. Is that the way it is supposed to be? Here are a couple of pictures about that:



The less frequent, but still annoying, backfire is only coming from the passenger side. I hooked the shop-vac blower up to the tail pipe again to re-check for exhaust leaks with soapy water. I found a significant leak right where the exit elbow is welded onto the end of the muffler. The air from the shop vac blows out of there too fast to make bubbles, you can feel it on your hand. Could this be the cause of the backfire? It seems too far "downstream" and too close to the "exit" for it to be a contributor. What do you think? I will seal it up with some aluminum tape just to see if it makes a difference. Here's a picture of where the leak is:


I'm still unsure about the carburetor re-jet idea. I tried adjusting the idle adjustment screws as recommended by Holley, starting at 1.5 turns out. But there is no change in vacuum at all if I turn them out (richer) any more than that. Should I turn them back "in" (leaner) until the vacuum starts to drop? I know it has been said here that those adjustments only effect the idle, but it is when I completely let off the accelerator that I get the backfire, so isn't that the same as being in the "idle" position? I bought some smaller jets, but I haven't installed them yet because the other issues seem like more likely causes.

Many thanks to everyone contributing to this thread.

 

I could be wrong, but the cap looks like an even fire model to me. I'm sure someone better versed will chime in shortly.

Your current distributor position is about where mine ends up. There really isn't any room for the vacuum can anywhere else in the rotation since I have power steering. Strange thing about my distributor I recently realized that it is a cobbled together deal. The mechanical advance is marked CCW(it retards the timing with RPM)the points are mounted for CCW rotation but the vacuum is CW. I locked the mechanical advance down until I can replace it. Maybe make sure yours is correct.

 

Sounds like yours may have parts from a reverse rotation marine application. Yes, there were some marine 225's that ran backwards used in dual engine boats to counter the torque twist of the other engine that ran standard rotation.

 

YES!!! NO MO BACKFIRE! Searching the threads to find out about oddfire distributors and caps I was led to this post:

http://www.earlycj5.net/forums/showthread.php?97416-Pertronix-dwell

It turns out that the magnetic ring on the new Pertronix Ignitor that I installed had one of the magnetic rings that had been marked wrong. They put a little cutout on the outside of the ring and the instructions tell you to line it up one way. It is 180º off. I don't know if they printed the instructions wrong or put the cutout on the wrong side. Anyway, after reading the post linked above I went out and rotated the magnetic ring 180º and re-set the timing. Runs smooth, sounds good on both sides, plugs look real good on both sides, the distributor cap is now in a position where the vacuum advance can is not so close to the fan, and NO BACKFIRE at all.

Thanks to everyone who posted suggestions!

 

I'm glad you got your backfire figured out. Now it's time to enjoy your victory. Drive it!

Interesting. In all my years of working on boats, I've yet to see a 225, reverse or standard rotation, in a boat. I've seen plenty of big three stuff, but never any 225s. I would love to see one!

 

John,
Take a look at these pics of Evinrude Sportsman 155 boats.
http://www.omc-boats.org/gallery/sport2.html

When I was a teenager, my Dad had one of these for a couple years. It was a really nice boat, and the V6 was rated at 155 horsepower which was plenty for even the heavy glass hull.

Don

 

Thanks for the link Don. I cannot believe that I've never seen one of those propulsion systems before. I learn something new everyday...

 

Yes, looking at that link gives me the itch to see if I can find one to restore. Just what I need, another expensive hobby.

Don

 

Don, I know all too well how expensive the boat hobby can be...mehh