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09-10-2021, 03:51 AM | #1 |
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Join Date: May 2010
Location: Murfreesboro, TN
Posts: 258
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Tuning issue- seeking thoughts
Hey y’all.
I’ve got a situation with Ms Mayberry (rebuilt 272, stock everything) that I would like to hear your best guesses as to what the heck the deal is. My wife and I decided to make a run down to Jiffy Burger in Manchester, TN, last Saturday. So we jump into the ’55 and head down Highway 41. She cranked fine, idled good, and accelerated as normal, but at cruising speed, say 50mph, the car seemed to be starving, as if it was wanting more fuel. Not actually missing, but like “gimme more gas”. Oh, it still had passing power and pulled off from stop lights just fine. We made it to Jiffy Burger and had a yummy meal. So, on the way back, it seemed to be doing the same thing…like horses wanting to run, but can’t get turned loose… So, and this is the interesting part…I decided to play ‘what would this do’ from the driver’s seat and I pulled the choke out about one-quarter of the way…. And wow, what a difference. The engine ‘woke up’ is the best description. It started feeling like the way it is supposed to run. Now, my logical thought is ‘maybe some trash in a carb passage’ even though it’s a new tank and I run 2 fuel filters…or is this how an engine reacts when the carb jets are too small? A few months ago, I had changed my carb jets from a #50 to a #49. I have sooty pipes and the plugs showed a little bit of ‘excessive fuel’ coloring, so I dropped the jet size…and I cannot honestly say that we have had it out on the open road since I did. What do y’all think? Did I lower them and create my own problem? Go back to the #50’s and it will be fine again?? What else could pulling the choke out a little and it start running fine, point to? Thanks y’all. |
09-10-2021, 06:27 AM | #2 |
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Re: Tuning issue- seeking thoughts
You didn't say how you ran the car before changing the jets, sooty pipes before could mean just poking around the block speeds. Put the 50's back in and take it for a road trip at highway speeds, put your foot in it, in other words, blow the cobs out it.
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09-10-2021, 09:34 AM | #3 |
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Join Date: Oct 2017
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Re: Tuning issue- seeking thoughts
It does sound like a cruise circuit problem, but a single # jet size is unlikely to cause this, unless the carb jetting was already cut really close to begin with. It is possible though. You'd notice this particularly in cold weather. I'd probably look first at a restricted air cleaner or possibly a fuel pump issue.
Look carefully at the spark plugs - the "base ring" is the key for the clues to jetting. |
09-10-2021, 11:15 AM | #4 |
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Location: 215 E. 6th Street Northport, Michigan 49670
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Re: Tuning issue- seeking thoughts
Check the fuel pressure past the two filters. It may be restricting the fuel flow
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Bob from Northport Northport, Michigan |
09-10-2021, 12:06 PM | #5 |
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Location: Murfreesboro, TN
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Re: Tuning issue- seeking thoughts
Thanks guys..all good ideas...I'll keep you posted...
ps . we ran it all over the area...not just puttering around the block... |
09-10-2021, 04:58 PM | #6 |
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Re: Tuning issue- seeking thoughts
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09-10-2021, 06:45 PM | #7 |
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Re: Tuning issue- seeking thoughts
Let's see a good clear sharp close up picture of a spark plug or two?
"Lean surge" or misfire at cruise is most definitely a signal of not enough jet but still find it tough to believe that a single step down would make a dramatic change generally speaking. Typically most carburetors are setup so far on the rich side of things a single step change wouldn't even be detectable. Adding choke as a remedy definitely points to a lean condition though. I wonder if there is a piece of crud in one of the jets, something like that. |
09-10-2021, 06:53 PM | #8 |
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Re: Tuning issue- seeking thoughts
Running better with the choke part way on can also indicate a vacuum leak.
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09-10-2021, 08:05 PM | #9 |
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Re: Tuning issue- seeking thoughts
I also suspect a vacuum leak.
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Alan 1929 Special Coupe 1941 Pick-Up 1955 Victoria |
09-10-2021, 08:49 PM | #10 |
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Re: Tuning issue- seeking thoughts
I also would suggest a vacuum leak. Check all your vacuum hoses for cracking, especially at the ends
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09-11-2021, 03:09 AM | #11 |
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Location: IN A 'GALAXIE' FAR FAR AWAY
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Re: Tuning issue- seeking thoughts
You run two separate fuel filters? How are they placed?
First you need a vacuum gauge to help diagnose (vacuum and fuel pressure/volume). If it indicates a lean condition, the following is the safest way to find it, other than a smoke machine - Note using propane, it is best to slowly open the valve and point the pickup hose to the carb/TB opening and try and stabilize the curb idle, You then go though the method shown on the video to hopefully find the leakage source. - https://www.classiccarrestorationclu...-leak-014793/# CAUTION - Using CARB CLEANER or STARTING FLUID to diagnose can lead to facial hair loss and dirty undies ... Is this a car or truck?
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09-12-2021, 04:47 PM | #12 |
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Re: Tuning issue- seeking thoughts
Old gas?
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09-12-2021, 06:22 PM | #13 | |
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Re: Tuning issue- seeking thoughts
Most likely -
Quote:
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09-13-2021, 07:48 AM | #14 |
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Join Date: May 2010
Location: Murfreesboro, TN
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Re: Tuning issue- seeking thoughts
Couple of items,
I do have a vacuum gauge and will be using it. It's a car. I use nothing but ethanol-Free gas in my old cars...gas is fresh, well as of 3 weeks ago. Fuel filters WERE in series - I say were because I have removed one. Pertronix electronics is now installed. Initial start-up, timing check/set will be Wednesday night. New plugs will be going in Friday night. The #50 jets have been reinstalled. Checked the vac hoses and the only one that might have been leaking was the hard line going into the back of the carb (for dist advance) and it doesn't seem to tighten up. The fitting is tight, but the line can just slide in and out. That's where I'm at 9.13.2021. Getting her ready for the Habitat for Humanity poker run on Saturday, 9.18.21 Thankyou for ALL the suggestions- they DO help! |
09-13-2021, 09:48 AM | #15 | ||
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Re: Tuning issue- seeking thoughts
Quote:
Quote:
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***** - WHY IS IT ... - ... that everything you buy in the grocery store is either wrapped in or contained in plastic but the government doesn't want you to carry it out in a plastic bag? WONDERING IN W(BY GOD)V ...
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09-13-2021, 04:41 PM | #16 |
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Join Date: May 2010
Location: Murfreesboro, TN
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Re: Tuning issue- seeking thoughts
2 filters because I had an original "renewed" tank start to fall apart and my system was full of gunk...yes they were between the pump and carb. Got a new tank and was just paranoid...filters are clean, so only need one anyway..
OK - will fix fitting leak not entirely sure how, but lemme look at it. |
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