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Thread: Engine idles rough, sputters bad when throttle opened up

  1. #1
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    Engine idles rough, sputters bad when throttle opened up

    I have a freshly rebuilt 289. The timing is set, dwell at 30 to start and the valves adjusted to .026 cold. It starts right up, but has some miss and when I open up the throttle, it bogs down big time and mis-fires. Although I have been out of practice for 20 years, I think I rebuilt the carburetor correctly! But I may have missed something. I can't seem to find any vacuum leaks as well. Any thoughts why I can't get this thing to smooth out rev up like a new motor should? BTW, the carb is a 2bll Stromberg WW.


    Thanks.

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    Golden Hawk Member StudeRich's Avatar
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    Was it running strong BEFORE the Carb. Rebuild? Knowing that, would rule out many other issues including Electrical ones.
    StudeRich
    Second Generation Stude Driver,
    Proud '54 Starliner Owner




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    President Member christophe's Avatar
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    You should hook a vacuum tester to it. The readings will tell you the whole story.
    Nice day to all.

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    More info please, did this start right after the re-build or later.cross wired? bad fuel pump, dying coil or condenser? more clue's please.Luck Doofus

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    verify you have the firing order correct , its easy to get a couple of plug wires mixed up will cause miss/bog and will still start idle well enough
    1957 goldenhawk

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    The engine had blown head gaskets when I purchased it and ran bad. So I can't compare with that after the rebuild. It has a new coil and condenser, points cap and rotor. I suspect I must have done something wrong in rebuilding the carb. I'm just trying to pinpoint what I may have missed. What should I look for in a vacuum reading?

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    18436572 All checked.

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    President Member RadioRoy's Avatar
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    Have you done a compression check with the new head gaskets?
    You haven't mentioned the year of the car. Does it have a PCV valve?
    RadioRoy, specializing in AM/FM conversions with auxiliary inputs for iPod/satellite/CD player. In the old car radio business since 1985.

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    It's a 64 Hawk with full flow and PCV valve. Not done a compression check yet. It was bored out and a valve job done. At this point, I just assumed it should have just ran fine off the bat. Pretty much everything is new. Reground cam, new lifters, pistons and the crank polished. And all new bearings.

  10. #10
    President Member RadioRoy's Avatar
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    If the PCV valve is stuck or corroded, that will affect the fuel to air ration significantly.
    RadioRoy, specializing in AM/FM conversions with auxiliary inputs for iPod/satellite/CD player. In the old car radio business since 1985.

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    My PCV valve was bad and leaking. I plugged the inlet at the throttle plate and it made no difference. Still wont rev up.

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    President Member Dwain G.'s Avatar
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    What's in the tank for fuel?

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    President Member christophe's Avatar
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    Quote Originally Posted by jostanton1 View Post
    What should I look for in a vacuum reading?
    Here is a link to an example:https://www.classiccarrestorationclu...oubleshooting/
    There are many others. You just have to google vacuum tester readings.
    For what it's worth, I've seen such troubles caused only by defective spark plugs.
    Nice day to all.
    Last edited by christophe; 09-20-2018 at 02:57 AM.

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    Starting to sound like a really lean mixture. when you cleaned the carb did you remove the main jets, takes a special tool most of the time. a lot of Sif,Fonk, and Gradeu collect above the jets. Luck Doofus

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    I am taking the carb in for a professional rebuild. I think I blew it on my rebuild as I could not remove the jets. Thanks everyone for the tips!

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    President Member Son O Lark's Avatar
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    Is the spring on the points you replaced?

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    President Member Kurt's Avatar
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    Before you remove the carb,try introducing a little more fuel. Another trick is to close the choke part way and see if that makes it smooth out any. If it does continue to look at the carb. If it doesn’t, try a new set of points. I have have brand new points that were bad.
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    President Member RadioRoy's Avatar
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    Make sure that plug wires 3 and 5 are not swapped. They are routed in different channels to prevent cross firing with the old copper wires. It's easy to swap the two.
    RadioRoy, specializing in AM/FM conversions with auxiliary inputs for iPod/satellite/CD player. In the old car radio business since 1985.

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    Hi it's me again! OK I got the carb professionally rebuilt. The engine runs quite a bit better and idles. However, still misfires at high speeds and lacks power. We did a compression check. Cylinder #7 was only 90 psi and all the rest were 122. We pulled the head to look for evidence of a broken ring and the cylinder looked OK. All we saw were a few light scratches, but the other 3 cylinders had the same appearance. The heads were done with with the new style teflon valve seals and surfaced. We are stumped at this point and do not know where to go next. Also, no signs of a gasket breach. Any input? Thanks.

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    President Member 345 DeSoto's Avatar
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    Valve settings?...

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    All clearances checked out good.

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    President Member Dwain G.'s Avatar
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    This car probably has the pink resistor wire from the ignition switch to coil + terminal. As a test, disconnect it at the coil, tape the end off, then run a temporary wire from battery + to coil + and go for a short drive.

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    Right now, the left bank head is off. If and (hopefully when!) we get it back together, I'll try that.

    Quote Originally Posted by Dwain G. View Post
    This car probably has the pink resistor wire from the ignition switch to coil + terminal. As a test, disconnect it at the coil, tape the end off, then run a temporary wire from battery + to coil + and go for a short drive.

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    OK, I my head passed the pressure test at the machine shop. A OK. I pulled #7 piston to check for a broken ring. No broken rings, it looks perfect. I'm stumped as to why that cylinder cranks at 90 lbs and the other seven crank 120. Could I have put a ring on upside down? The top ring has the bevel up, and the center ring has the notch down. I don't have the ring packages anymore so I don't have the instructions to reference. Thanks.

  25. #25
    President Member christophe's Avatar
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    As it is a fresh rebuilt, did you have the cylinder walls deglazed? If not, the rings might take some time to be fully seated. 120 looks not like a perfect value either. On a rebuilt engine, I usually get around 140/150.
    You should run it a little while and check again the pressures. If after pouring a teaspoon of oil in the concerned cylinder, the pressure gets better, the problem is located in the ring area.
    Berst of luck.

  26. #26
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    The engine was bored out .020 and new pistons and rings were installed. When I pulled the piston in question, the rings were installed correctly, and it looked perfect. I don't know where to go from here other than put a new head gasket on and put it all back together and pray. BTW I used the thick head gaskets. Would that be why the numbers are low on the good cylinders?

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    Golden Hawk Member jclary's Avatar
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    Timing, vacuum advance diaphragm pinhole, and valve adjustment...just a few easy to overlook items that could cause poor performance. Even though you said in an earlier post that the valve clearances checked out, lots of mechanics will continue to tweak the adjusters to try and match "hydraulic lifter" quietness. Solid lifter engines will have some clatter (music) when adjusted properly.
    John Clary
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  28. #28
    President Member christophe's Avatar
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    If your cylinder walls show a crosshatch pattern, they have been deglazed. Unless you did the job yourself, you should ask to your mechanic if this step has really been performed. Yes, thicker gaskets mean less compression. If you used chromium piston rings, these take a little longer to be fully sit in. Check what John said and go for a hundred miles run while checking water temperature and oil pressure. Then , check compression again. If the piston is still out of the engine, remove one of the rings and place it into the cylinder to check the end gap with a feeler gauge.
    Best of luck.

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    Thank-you very much! I'm on it.

    Quote Originally Posted by christophe View Post
    If your cylinder walls show a crosshatch pattern, they have been deglazed. Unless you did the job yourself, you should ask to your mechanic if this step has really been performed. Yes, thicker gaskets mean less compression. If you used chromium piston rings, these take a little longer to be fully sit in. Check what John said and go for a hundred miles run while checking water temperature and oil pressure. Then , check compression again. If the piston is still out of the engine, remove one of the rings and place it into the cylinder to check the end gap with a feeler gauge.
    Best of luck.

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    Quick question. Thin shim or thick head gaskets. Pros and cons. Before my rebuild, my average compression tests showed 125- 140 psi. The right bank ran 130-140 and the left was mostly 125. After the rebuild with thick gaskets, I'm only getting 122 psi on seven cylinders and 90 on #7. Number 7 also was low only having 110 before the rebuild. Thanks crew!

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    Take Christophe's advice and check ring end gap. if you break one ask your FLAPS for a single piston ring set for a 194 chev "6".that will save the bewildered look on the counter guy's face when you say Studebaker. Luck Doofus

  32. #32
    President Member christophe's Avatar
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    Just to be on the safe side, removing (or installing) piston rings calls for a special tool if you don't want to harm anything. Sometimes, this can be done by hand but difficult to do without harming the piston. Also, the end gaps positions must be respected.

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