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06-26-2016, 02:30 PM | #1 |
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Location: Denmark, Aarhus
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221 cui stumble and backfire
Hi
I finally got my 1935 back on the street but only to run into at new issue :-) The engine has had a complete rebuild at a machine shop and I therefore took time to rebuild both the carb and the dist. to make sure everything is in perfect condition. I’m running a Holley 94 carb with 0.050 jets and a 7.5 power valve. Idle screws are 1, 5 turn out from bottom. Float is set 1 11/32 and float drop 1 7/16. Link is set at standard (middle hole) The dist. got new points, set to 0.014 and the vacuum brake has one turn in. Timing is set by TDC on piston 1 and advanced with 2 lines on the dist. from TDC clockwise. It starts immediately and runs perfect at idle. But when I drive the car it will not take rpm above 40 kmt in second gear and 60 kmt in third without stumble and some backfire trough the exhaust. Hard to say how many rpm as I don’t have an rpm gauge. When I depress the pedal, at standstill, it’s the same rpm issue, just a bit more backfire. I need advice - thanks
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1935, Ford V8 "UTE", 221 rebuild flathead. Less is More Last edited by TDS; 06-26-2016 at 04:42 PM. |
06-26-2016, 04:51 PM | #2 |
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Re: 221 cui stumble and backfire
Even though the engine was rebuilt, your symptoms indicate sticky valves could be an issue. Have you tried dribbling some Marvel Mystery Oil down the carb at about 1000 RPM until it begins to smoke and stall? Might do the trick. You may also want to pour about 1/4 pint of the MMO into the tank with each fill up (petrol).
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06-26-2016, 05:02 PM | #3 |
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Re: 221 cui stumble and backfire
Make sure the spark plug wires are hooked-up correctly from the distributor to the plugs. What's the story on that 94 carb?....Rebuilt?
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The only thing nice about being imperfect is the joy it brings to others.... "Silver rings, your butt! Them's washers!" "We shot our way out of that town for a dollar's worth of steel holes!" - from 'The Wild Bunch' - 1969 https://www.youtube.com/watch?v=7NReUd2_0u0 Last edited by petehoovie; 06-26-2016 at 06:14 PM. |
06-26-2016, 05:29 PM | #4 |
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Re: 221 cui stumble and backfire
The first backfire likely blew your powervalve.
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06-26-2016, 06:33 PM | #5 |
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Re: 221 cui stumble and backfire
Run the revs up with one wire 1/4 -3/8 from the head ,if it turns from blue to a weak yellow spark then its a ignition problem .If it runs better with your foot flat to the floor or the choke out a little its a fuel problem ,possible dirt in jets ,Pump ,or blocked line ,vacume leak .Pull the carb top to see were the level is .Ted
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06-26-2016, 08:26 PM | #6 |
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Re: 221 cui stumble and backfire
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The only thing nice about being imperfect is the joy it brings to others.... "Silver rings, your butt! Them's washers!" "We shot our way out of that town for a dollar's worth of steel holes!" - from 'The Wild Bunch' - 1969 https://www.youtube.com/watch?v=7NReUd2_0u0 |
06-26-2016, 08:33 PM | #7 |
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Location: Virginia
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Re: 221 cui stumble and backfire
I had similar problem a year ago with flathead missing under load in second and third. Turned out to be condenser. Bought a car years ago that owner had given up on fixing because of a bas miss-and it ended up being a crossed up plug wire.
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06-26-2016, 08:52 PM | #8 |
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Location: maryland
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Re: 221 cui stumble and backfire
same here ran great at idle and just above then try to pull out into traffic and would start to misfire bad on all cylinders condenser was the problem
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06-26-2016, 09:01 PM | #9 |
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Re: 221 cui stumble and backfire
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06-26-2016, 09:55 PM | #10 |
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Re: 221 cui stumble and backfire
did you run-in the cam and lifters??....Mike
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06-27-2016, 12:10 AM | #11 |
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Location: Denmark, Aarhus
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Re: 221 cui stumble and backfire
Im sure the sparkplug wires are connected correct but I will check again :-)
The shop told me it was ready to go. They adjusted the lifters. Sticky valves could be the problem - will try som MMO. The condenser is new but I will try exchange it with my spare. Will post update..
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1935, Ford V8 "UTE", 221 rebuild flathead. Less is More |
06-27-2016, 03:24 AM | #12 |
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Re: 221 cui stumble and backfire
Check for a vacuum leak
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06-27-2016, 09:06 AM | #13 |
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Re: 221 cui stumble and backfire
The 35 helmet doesnt like rpm with the large strap points and large point cam. ( later ones used individual points with small distributor cam.
I run a ton of these on a tester and they commonly just dont want to rev up much above 3000 or so without point bounce. New points with some added (bending) tension usually will fix the problem..... |
06-27-2016, 09:57 AM | #14 |
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Re: 221 cui stumble and backfire
One more item that can have similar symptom is a weak fuel pump.
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06-27-2016, 11:08 AM | #15 |
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Location: Detroit suburb, MI
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Re: 221 cui stumble and backfire
I agree, except the original post said it was an exhaust backfire. Sounds like a weak ignition problem. Possibly unburned fuel in the exhaust popping when the ignition does fire. A carburetor related issue (bad accel pump or lean condition) would pop out of the carburetor. Sal |
06-27-2016, 11:18 AM | #16 |
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Re: 221 cui stumble and backfire
Fuelpump!
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06-27-2016, 02:08 PM | #17 |
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Re: 221 cui stumble and backfire
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06-27-2016, 03:01 PM | #18 |
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Re: 221 cui stumble and backfire
Been through same symptoms: Small bacfires and hesitation/misfiring at speed.
TDS: All parts are new or rebuildt. But what about the fuel pump? |
06-27-2016, 03:27 PM | #19 |
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Re: 221 cui stumble and backfire
A Holly 94 will not work with a 35 manifold ,due to the heat riser hole feeding exhausted into the base of the carb ,Ted
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06-27-2016, 03:42 PM | #20 |
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Re: 221 cui stumble and backfire
Terminology has always been a bit off when it comes to the term "backfire". It doesn't explain whether it was a carburetor fire or an exhaust fire. The dictionary refers to both for the term but the technical definition is a fire back through the induction system. A fire in the exhaust is an "after fire". It is sometimes difficult to tell which is which unless the exhaust sound like a cannon going off.
Last edited by rotorwrench; 06-27-2016 at 03:49 PM. |
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