87 yj 4.2 starts/idles great. Won't hold acceleration. - JeepForum.com

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post #1 of 26 Old 01-10-2017, 10:29 PM Thread Starter
Rlttu66
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87 yj 4.2 starts/idles great. Won't hold acceleration.

New rig, haven't even driven yet (because of this issue). Starts great, idles nicely. Will accelerate momentarily, the acts like is starved for fuel, shudders, and rpms decrease. Only thing I've done so far is replace filter and O2 sensor (cheap and was cracked anyway). This jeep has sat and was not even started in about a year until this week. Please help me think this through. I am very mechanically minded, but new to jeeps (and carbs for that matter). I guess my first thought was fuel pump (but would it start and idle so easily?). Dirty tank, clogged line, pinched return, etc etc? TIA!

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post #2 of 26 Old 01-10-2017, 10:44 PM
timatoe
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This is usually for idle issues... http://www.jeeptech.com/engine/carter.html

Everything stock?

Get a free account at photobucket or imgur or flicker or the such and take some pics and post them here. If it's new to you, you may not even know what is and isn't supposed to be there.

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post #3 of 26 Old 01-10-2017, 11:20 PM Thread Starter
Rlttu66
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Idles smoothly at around 1200rpms. No sputtering, etc. Revs up nicely as well, but won't hold. Again, I'm new to carbs, so a little unsure of what I'm looking for, but I'll describe what I'm seeing.

-pull air cleaner, choke is functional
-watch acceleration jets while manually revving engine. Both jets immediately respond to acceleration with a nice steady stream into the Venturi. If I hold manual acceleration, should fuel continue to stream out of the jets? (It doesn't). After a few seconds running at higher rpms, it bogs down. If I let off, it will return to idle; if I don't let off, it kills it.
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post #4 of 26 Old 01-10-2017, 11:35 PM
timatoe
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Like normal idle is 1,200 rpm? It should be roughly half that. Try getting a free hosting account and snap some pics of the carb and other associated crap around it.

Quote:
Originally Posted by George Orwell
We sleep safe in our beds because rough men stand ready in the night to visit violence on those who would do us harm.
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post #5 of 26 Old 01-11-2017, 11:47 AM Thread Starter
Rlttu66
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Sorry, bad info. Cranked it this morning. More like 700ish
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post #6 of 26 Old 01-11-2017, 09:24 PM Thread Starter
Rlttu66
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Any input is much appreciated. I think it's something simple and hate to admit when I can't figure something out, but I really want to understand what I'm looking for. I got his jeep CHEAP, but I don't want to just throw parts at it until something sticks.

Thanks in advance...have really enjoyed browsing for the last week. Glad to have joined the club.
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post #7 of 26 Old 01-11-2017, 09:48 PM
timatoe
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I'm hoping a carb guru will chime in here. That's not the stock carb, but I don't know what it is either, I tired of mine and went FI.

Quote:
Originally Posted by George Orwell
We sleep safe in our beds because rough men stand ready in the night to visit violence on those who would do us harm.
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post #8 of 26 Old 01-11-2017, 10:28 PM Thread Starter
Rlttu66
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Thanks for the input...and I hope so too. If you don't mind me asking, how big of deal was the FI conversion (labor and expense)?
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post #9 of 26 Old 01-12-2017, 04:16 AM
timatoe
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The Howell kit was about $1,200 because I'm in CA, Affordable Fuel Injection has a kit for under $1K.

It was about a days work, not hard at all just a bit time consuming.

Quote:
Originally Posted by George Orwell
We sleep safe in our beds because rough men stand ready in the night to visit violence on those who would do us harm.
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post #10 of 26 Old 01-12-2017, 10:57 PM
mattsez
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Well, im damn good with carbs.....but not a guru. Sounds to me like the float is to low, and the bowl is running out of gas. Do a test for me. It idles.......how does it run if you hold it to the floor for an extended period? get it in gear, and floor it for at least 10 seconds IN GEAR.If it runs ok floored, but not half throttle, its a failing power valve. Is it a webber carb?....ive seen these with the fuel inlet and return line switched...( if yours has a return line) and it will idle, but the bowls run empty fast as you can imagine. Try that test, let me know how she does. Also spray carb cleaner around base of carb at idle, and at manifold to head......if the spray causes a change, its a vac leak.
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post #11 of 26 Old 01-12-2017, 11:02 PM
mattsez
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does it have a catalitic converter?.....hmmmmm
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post #12 of 26 Old 01-14-2017, 07:14 AM Thread Starter
Rlttu66
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Anybody? Kinda stuck
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post #13 of 26 Old 01-14-2017, 09:32 AM
bgredjeep
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Look up motorcraft 2100. I know there are threads about tuning that carb. You might check that the nutter bypass has been done as well since that carb is not computer controlled.


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post #14 of 26 Old 01-14-2017, 10:11 AM
mattsez
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well i tried to help.....lol...good luck
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post #15 of 26 Old 01-14-2017, 10:25 AM
Mediceagle
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Garage
I had to do the Nutter bypass on mine to fix this issue.
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