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240 misfire

Moderator: Mod Squad

Andyman54
New Member
Posts: 2
Joined: Mon Mar 11, 2019 6:09 pm

240 misfire

Post #1 by Andyman54 » Mon Mar 11, 2019 7:51 pm

I've been working on a 1972 f100 recently and have been slowly getting her going. I put a new carter you carb on and tarted it up and it had this big back fire through the carb while under load trying to move it around the neighborhood.

I have had similar issues with a inline 4 boat motor and so i decided to check the hydraulic lifters, opened the cover up and took one out i could not push it in turns out all the lifters were frozen so i replaced them all with new. The bottoms had no major pitting or anything so i do not believe any damage was done.

Fixed that issue nothing changed but it did run a bit better.

Next change spark plugs put a set of new plugs in, and new wires! No change

Also I changed my fuel pump out that was dead in the very beginning so fuel pressure is good as well.

Check timing/ Change distributor .

I bought a new HEI Distributor with a coil built in. Set cylinder number 1 at TDC pointed the distributor in the right direction and it fired right up like a champ runs great when not in gear! Checked it with a timing light everything seems to be correct. The engine is running better than it ever has.

THAT still did not fix the issue... I looked further and started spraying around the carb with carb cleaner to see if i had a vacuum leak somewhere. I did have one so I fixed that issue but no dice. I have also riched the carb out and leaned the carb in it doesnt matter which way i set the screw it will continue to poppopopop through the carb when i try to accelerate.

anyone run into this issue?

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bubba22349
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Posts: 8826
Joined: Sun Jan 03, 2010 4:46 pm
Location: Flagstaff, Az. 86005 near the old Route 66

Re: 240 misfire

Post #2 by bubba22349 » Thu Apr 25, 2019 6:21 pm

Did you do a compression test yet? :nod:
A bad day Drag Racing is still better than a good day at work!

I am still hunting for a project car to build but with my current low budget it's not looking so good. My Ex- Fleet of Sixes these are all long gone! :bang: 1954 Customline 223 3 speed with O/D, 1963 Fairlane project drag car with BB6, 1977 Maverick 250 with C4, 1994 F-150 a 300 with 5 speed.

Jesse73
Registered User
Posts: 38
Joined: Thu Feb 28, 2019 7:13 pm

Re: 240 misfire

Post #3 by Jesse73 » Sun Apr 28, 2019 10:05 am

My truck did the exact same thing, accelerator pump was faulty in the carb. This was a Carter YFA.

Mdixon300f100
Registered User
Posts: 93
Joined: Wed May 02, 2018 6:43 am

Re: 240 misfire

Post #4 by Mdixon300f100 » Sun Apr 28, 2019 4:44 pm

Yea I’ve heard that any intake backfire on these carbs can blow the diaphragm on the accel pump. There’s no safety built in to prevent it.

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