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Re: Ran great - then instantly horrible
1952Cecil #1318890 Tue Jul 23 2019 12:50 AM
Joined: Jan 2013
Posts: 1,809
Shop Shark
This may sound stupid, but have you ensured your heat rise flap is moving? Also, do you use choke to start it when cold? Could your timing be off just enough that when you bump the throttle the advance is not turning it enough? Just thinking outside the box.

Chris

Last edited by ndkid275; Tue Jul 23 2019 12:50 AM.
Re: Ran great - then instantly horrible
1952Cecil #1318895 Tue Jul 23 2019 01:07 AM
Joined: Feb 2000
Posts: 4,177
J
Shop Shark
Sounds like the accelerator pump is not working quite right. Rebuild kit should take care of that. It should squirt a pretty good amount of fuel when opening the throttle quickly. It could also be lean and stumbling when opening throttle at speeds. Were all three jetted the same?

Re: Ran great - then instantly horrible
ndkid275 #1318952 Tue Jul 23 2019 02:40 PM
Joined: Aug 2018
Posts: 34
1
Wrench Fetcher
I use the choke to start it - It has been starting really hard on cold starts with current jet / setup, great when warm. Not sure on the heat rise flap. Planning on checking that along with timing and vacuum this weekend. The accelerator pump did squirt out some but no idea if enough.

Carb jets -
Original was unmarked.. looks bigger than .5 - similar to .57
.57 was in it for a little bit - started good but didn't run great
.50 is in it now - starts real hard when cold - runs great when warm at low speeds, cruises good, and accelerates Ok

Going to do full rebuild on one of the carbs and then switch. Suggestions on jet size?


Mike

1952 -3100 with '52 235 Iowa farm truck "Cecil"
Re: Ran great - then instantly horrible
1952Cecil #1318961 Tue Jul 23 2019 04:22 PM
Joined: Mar 2014
Posts: 1,665
J
Shop Shark
Mike a size 50 jet is small for a 235 with a Rochester B and ethanol laced gas. Usually 58 or 57 is what I've seen with a couple of 56 sizes in there when the 235 was a younger engine (maybe 1950 year or so). A 50 jet will make your carburetor run very lean. At this point it is very hard to unscramble the egg, but as I recall the smaller jets were common in the 216 engines...size 51, 52 jets, etc. If I was going to use a Rochester B or BC on a 235, I'd start with a 57 size jet and then increase to 58 if needed.

But honestly before I spent one cent or any more time on a rebuild kit for the Rochester I would consider a Carter. The design is much better and they don't have that wacky power circuit which with unleaded/ethanol gas is just about guaranteed to get stuck in the open position.

If the carburetor you have was really intended for use on a 235, then I'd guess your air horn and possibly float bowl are warped (which is so common with Rochester B and BC it should be automatically expected) and if so, I would bet your power circuit is in the failed mode (meaning your power valve is open all the time). If somebody has put a 50 size jet in there, it could have been because they didn't understand what was happening with the power piston/power valve, didn't know what to do with it and they were trying to get the thing to run leaner. Or it could be that parts have been mixed up a lot in there.

Good luck.


Jon

1952 1/2 ton with 1959 235
T5 with 3.07 rear end
Re: Ran great - then instantly horrible
1952Cecil #1318964 Tue Jul 23 2019 04:33 PM
Joined: Mar 2014
Posts: 1,665
J
Shop Shark
Mike, in case the work I did last summer isn't easy to find, here's a link to where (as I recall) it began: https://tinyurl.com/y4a4bktb

Good luck.


Jon

1952 1/2 ton with 1959 235
T5 with 3.07 rear end
Re: Ran great - then instantly horrible
1952Cecil #1319057 Wed Jul 24 2019 10:11 AM
Joined: Jun 2019
Posts: 33
T
Wrench Fetcher
If you're pulling the carb apart again for a rebuild check out this thread:

https://www.stovebolt.com/ubbthread...ster-carb-not-squirting.html#Post1314009

Mine was giving me an absolute fit until i found that the "T" holding down a spring and check ball was installed wrong and blocking a jet.

Mike's Carbs has a great video on YouTube for rebuilding a Rochester. It's like 45 minutes long. He's also where i got all my rebuild parts from.

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