220 back firing through carb

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baker10
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220 back firing through carb

Post by baker10 »

I'm lost on this one I need yalls help. Just bought a single mag 220 that's swinging a 70in Q series prop pitched on the #2 mark. The guy I bought it from said he was spinning it at 2900 rpms but the first day I took it out I could only get it to 2500 rpms and it was missing and wanted to back fire through the carb every now and then, also the headers are glowing all the way to the flex pipe so there is a lean issue as well. I've checked everything I know how, sprayed starter fluid around all intake fittings no vacuum leaks, put brand new plugs in it, cleaned the mag points (mag was just rebuilt), pulled one plug off at a time and hit the throttle but it still missing and wants to back fire on every cylinder so I don't think I have a valve issue and there is good fuel flow. The carb is a Holly 500 2 barrel and I just got that rebuilt and gonna put that back on today and see if it makes a difference. Need some help with this one... :banghead: :dontknow:

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trailerdon
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Re: 220 back firing through carb

Post by trailerdon »

Compression test / leak down test . I believe that might get you the answers you seek

baker10
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Re: 220 back firing through carb

Post by baker10 »

If I had a weak cylinder pulling the plug while running would stop the back fire and just make the motor lazy right?

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Bruce
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Re: 220 back firing through carb

Post by Bruce »

could be a broken impulse coupler spring turn the mag off and turn the prop through and see if it has a powerful click and if it does id check the distributer block on the front of the mag pull the cap off (holds plug wires) and inspect all the posts usually youll see carbon tracking from the crack to the housing its more than likely that might try it first
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CypressHunter
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Re: 220 back firing through carb

Post by CypressHunter »

I had a similar issue with backfiring out the carb..... I was running too lean. I backed my idler screws ( i think that's what they are called ) out two full turns from completely in. I was also running too tightening a spark plug gap and when running hard I was pushing oil causing plugs to foul. If i back off the gas it would clear up. Hope this helps. Welcome to the ground power club
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John Fenner
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Re: 220 back firing through carb

Post by John Fenner »

If it is backfiring on multiple cylinders and you have good compression in all, you have a cracked mag distributor block.
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baker10
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Re: 220 back firing through carb

Post by baker10 »

Okay if the problem still occurs when I get the carb back on I'll dig into the mag.

Barry830
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Re: 220 back firing through carb

Post by Barry830 »

Sounds like a mag problem to me. Said you just had it rebuilt.....internal timing may be off.

baker10
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Re: 220 back firing through carb

Post by baker10 »

Ill hit the mag with a timing light and see where its at. What do you set these motors at 25? 28?

Gary S
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Re: 220 back firing through carb

Post by Gary S »

Just because mag was rebuilt don't count it out. I have seen new mag block crack going from work bench and boat.

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