Can't find vaccum leak. Backfiring, missing on acceleration.

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boeing7873
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Re: Can't find vaccum leak. Backfiring, missing on accelerat

Post by boeing7873 » Wed Mar 18, 2015 12:49 am

edzz wrote:when you rebuilt the carbs did you replace the accelerator pump seals?


http://www.aa1car.com/library/carburetor.htm


http://www.thecarburetorshop.com/Troubleshooting.htm
I have changed them... but your logic is good! I also suspected about them... however I could see the jets of fuel when I pump the throttle after rebuilding the carbs. Maybe I could check them again.
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Re: Can't find vaccum leak. Backfiring, missing on accelerat

Post by pinzinator » Wed Mar 18, 2015 8:41 am


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Re: Can't find vaccum leak. Backfiring, missing on accelerat

Post by boeing7873 » Fri Apr 03, 2015 8:25 am

Engine still a mess.

After finding the hose for vacuum balance between the intake manifolds, I expected all problems to be solved.. but unfortunately i am still dealing with backfiring and low power on acceleration. I need to pump the throttle to get the engine to carry load to start the truck.
Idles ok, actually idles very smoothly.

Running pertronix - nkg bp6es plugs changed yesterday - blue Bosch coil
Carburetor rebuilt to the best of my skills and knowledge. New gaskets. Float level checked with the correct tool/technique with engine pump running.
New fuel pump.
New fuel lines. and transparent clean fuel filter.
Got a timing light gun and set it to my best guess of about 5 to 10 degrees advance (about 10 mm from block mark to pulley mark.)
Tested auto advance with RPM and it looks like it is working fairly well. Back and forth.
Idle screws are to 3 turns out now.
Adjusted all valves and found all exhaust valves to be tight. Now all back to 0.2mm.

I bought starter fluid. Sprayed the base of the carbs and the shaft ends. No noticeable increase in rpm.

UPDATE: took the tunnel out, ran the engine without the tunnel and sprayed ether all over the carbs, manifolds, all gaskets.. no RPM increase, and no explosions ( :roll: ).

SO: I am back to 0.
I am now going to start with ignition again, and check timing again. Next, all the voltages again.
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Re: Can't find vaccum leak. Backfiring, missing on accelerat

Post by edzz » Fri Apr 03, 2015 11:48 am

-running pertronix so condenser is not used, it is now just a filler for the hole it fits in.

I cant spot mention if your running civilian distributor cap, rotor and wires. if civilian cap has the rotor been shortened as required?

popping, spitting, backfiring on deceleration is commonly an exhaust leak, I fought with this until I followed Jim L's advice and used high-temp exhaust silicon gasket sealant on my flange gaskets. this didn't get rid of any real performance issues just quit causing people on sidewalks from having their little accidents.

back to the carbs Im assuming you have been using Jim L's excellent write ups on the carbs.

http://www.goatwerks.com/carb.htm and http://www.goatwerks.com/carbarticle.htm
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Re: Can't find vaccum leak. Backfiring, missing on accelerat

Post by boeing7873 » Sun Apr 05, 2015 11:35 pm

edzz wrote:-
back to the carbs Im assuming you have been using Jim L's excellent write ups on the carbs.

http://www.goatwerks.com/carb.htm and http://www.goatwerks.com/carbarticle.htm
Yes I have... and found that the front carb is probably the culprit... the acceleration pump puts about half of the flow the back pump does...
I started another thread since I am back to carbs.
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Re: Can't find vaccum leak. Backfiring, missing on accelerat

Post by audiocontr » Mon Apr 06, 2015 6:48 am

Did you check the fuel level in the bowls?
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Re: Can't find vaccum leak. Backfiring, missing on accelerat

Post by Maxf » Sun Apr 12, 2015 7:24 pm

Also helpful in this kind of whacky timing backfiring situation,. Disassemble the distributor so you can see down into the housing where the centrifugal weights for spark advance are. [The dist does not use vacuum for spark advance] Mine was so rusted in there the weights were intermittent and caused symptoms as described above. ...Just a thought.
Thanks,
MaxF

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Re: Can't find vaccum leak. Backfiring, missing on accelerat

Post by boeing7873 » Sat Nov 25, 2017 12:07 am

I think it was all a lean mixture. Significant change with new idle jets. Changed the 55s for 60s.

JC
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Re: Can't find vaccum leak. Backfiring, missing on accelerat

Post by boeing7873 » Wed Dec 20, 2017 9:46 am

Still dealing with the problem. Changed the idle fuel jets, now will change the idle air jets and see if this works. It is definitely lack of fuel from the idle circuit.
My air idle jets are 130s, I will go to 110 and probably back to 55s on the idle fuel.
Will report!
JC
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Re: Can't find vaccum leak. Backfiring, missing on accelerat

Post by audiocontr » Wed Dec 20, 2017 7:19 pm

It appears more of a carb issue than anything else. Worn throttle shafts... Butterflies that won't seat, lots of possibilities.

Might consider sending to Jim for a rebuild and tune. I eventually bit the bullet and sent mine after countless hours of fiddling. You can find my video on YouTube

Who knows how a previous owner messed them up?
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Re: Can't find vaccum leak. Backfiring, missing on accelerat

Post by Jimm391730 » Thu Dec 21, 2017 3:03 pm

Be sure to check the "balance hose" that is hidden under the air tin and connects the two intake manifolds together; the hose there gets significant heat at engine shutdown and is never seen unless you remove both the front and rear air tins from around the carbs.
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Re: Can't find vaccum leak. Backfiring, missing on accelerat

Post by boeing7873 » Thu Dec 21, 2017 6:22 pm

Changed that hose... twice, just to make sure. But I agree with Mr Audiocontr... ol? I am dealing with something in the carbs. What is really bothering me is that some days are better than others.. temp? Humidity? Don't know.

The number of things are finite, and you just mentioned the last things I have not played with: shafts, shaft seals and butterflies.
I just don't want to go there.. :( $$ :(
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Re: Can't find vaccum leak. Backfiring, missing on accelerat

Post by Jimm391730 » Fri Dec 22, 2017 12:00 am

things I have not played with: shafts, shaft seals and butterflies. I just don't want to go there..
Testing is easy: at idle, spray around the butterfly shafts with starting fluid; any leaks and the idle will increase noticeably. No change, they are not your problem.
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Re: Can't find vaccum leak. Backfiring, missing on accelerat

Post by pinzi » Fri Dec 22, 2017 2:30 am

So you changed the sparkplugs.....did you get the ignition order right....the pinz engine dous not have the normaal 1.3.4.2 ignition sequence but 1.2.4.3..... just my thoughts :wink:
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Re: Can't find vaccum leak. Backfiring, missing on accelerat

Post by boeing7873 » Fri Dec 22, 2017 5:28 pm

Ignition order ok, engine runs great at all regimes except for that little stumble at lo RPM.
Jerome
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