4.2L acts like it's governed

[cdlongjr]

Finally got to drive the YJ yesterday. Acceleration seems to be slower that the CJ5 was. She wouldn't go faster than 55 mph. Several times she coughed, (mini backfire), but picked rite up again. Timing is on the money & I have a Ford iginition. Carb is an MC2100, (new rebuilt from auto parts store). Plugs are 12s, not 14s like the manual says.Vacuum gauge is steady @ 16". B&M TH350 auto Transmission . Serious shimmy in the front end around 40 mph, but not all the time. Seems to be worse accelerating than decelerating.4" lift w/ 32" Armstrong tire on American aluminum wheels.

 

[IOPort51]

Finally got to drive the YJ yesterday. Acceleration seems to be slower that the CJ5 was. She wouldn't go faster than 55 mph. Several times she coughed, (mini backfire), but picked rite up again. Timing is on the money & I have a Ford iginition. Carb is an MC2100, (new rebuilt from auto parts store). Plugs are 12s, not 14s like the manual says.Vacuum gauge is steady @ 16". B&M TH350 auto Transmission . Serious shimmy in the front end around 40 mph, but not all the time. Seems to be worse accelerating than decelerating.4" lift w/ 32" Armstrong tire on American aluminum wheels.

don't guess it could be because it is a YJ.
how about the exhaust?? Catalytic converter maybe??
I would think the vacuum gage would indicate some thing.
is it higher than 16inches at idle?? IMHO sounds like a breathing problem to me.

 

[cdlongjr]

I'm pretty sure it's something w/ the MC2100. When the Weber was on, she'd do 65 easy. Problem w/ the Weber was it ran sooo rick it looked like I had a diesel when she was @ idle. Couldn't get the Weber to lean out.

 

[IOPort51]

I'm pretty sure it's something w/ the MC2100. When the Weber was on, she'd do 65 easy. Problem w/ the Weber was it ran sooo rick it looked like I had a diesel when she was @ idle. Couldn't get the Weber to lean out.

I have to admit I am hoping that Elwood will jump in here, he knows a lot more about that carb than I do. I would like to ask what the size of your 2100 is. I have a 1.8 and a 2.1 and I am thinking about putting one of them on the J-10 when I have the CJ up for a driver.
One last question, did the Webber require a fuel pressure regulator??

 

[dalefan88]

weber does recommend a regulator. i have a 1.08 motorcraft on mine and it likes both screws 2 turns out. anything alittle more or less the engine runs like

 

[cdlongjr]

Yesterday I played some more. Changed the fuel filter. 18" of vacuum @ idle. Pinched off hose to brake booster to make sure booster wasn't leaking. Timing @ 14 degrees. 40 mph was about tops. Engine seemed to die. If I pumped the accelerator, power comes back. Carb has 121 stamped on the driver's side of the fuel bowl. Power valve has no numbers stamped on it.
Weber didn't have a regulator. PO had replaced the fuel pump. The guy I sold the Weber to bolted it on a AMC 258 i6 / 4.2l & says it runs great. Go figure?

 

[dalefan88]

Yesterday I played some more. Changed the fuel filter. 18" of vacuum @ idle. Pinched off hose to brake booster to make sure booster wasn't leaking. Timing @ 14 degrees. 40 mph was about tops. Engine seemed to die. If I pumped the accelerator, power comes back. Carb has 121 stamped on the driver's side of the fuel bowl. Power valve has no numbers stamped on it.
Weber didn't have a regulator. PO had replaced the fuel pump. The guy I sold the Weber to bolted it on a AMC 258 i6 / 4.2l & says it runs great. Go figure?

the 1.21 might be to much. go to a parts store and get a regulator maybe. thats the only thing i can think of. i rebuilt my carb, turned the screws out 2 turns, pumped the gas to fill up the bowl and she fired right up and been drivin her every since.

 

[Petescj]

Timing for a AMC 258 i6 / 4.2l is around 8 before top dead center for the Cj version. Shouldnt be different for the Yj ??

 

[IOPort51]

If the carb was too big, would it starve the engine??
I like the timing idea, being 6 degrees off could make a difference. is this an automatic Transmission ?? that may put it a bit higher but I don't believe it will be above 10 degrees BTDC.
I can't wait to see how this comes out.

 

[mtruckstuff]

Did you release the emergency brake? Kidding, of course you did. Where did you pick up vacuum for the distributor? You need to go to manifold (below carb butterfly) or they run poorly.

 

[cdlongjr]

Vac for dist is off the carb base on passengr's side. No vac leaks that I can find w/ carb cleaner. Slight fuel leak where fuel line comes out of the pump. Pump is fairly new. She ran good w/ Weber, but Weber was too rich & too much trouble. Timing is 12 degrees.

 

[cdlongjr]

Engine just seems to shut off @ 40 mph. If I pump the gas, the engine comes back sluggish, but still only does 40 mh. Acceleration is very slow. Choke & throttle plates are opening fully.

 

[IOPort51]

If you are one of the millions of good people in the world that believe that if you buy it new at the parts house it has to be good, can I show you some property I have down on the gulf?? I can show it to you any time, the tide is out. Do you like mangrove trees??
I would have that carb back on the counter so fast they would think you had never left the store. IMHO you have problems with the fuel pick up, without digging out the break down on that carb I can't be more specific.
good luck

 

[rushpowersystems]

Timing is affected by altitude and chain stretch, if the engine is older you should add 2 to 4 degrees and if you are at high altitude you should add 2 to 4 degrees. So I look at the repair manual as more of a suggestion, here at 4000 foot level we run carb engines at + 4 to 6 as long as the engine does not ping under load.

You really need to isolate this from a MPH to RPM situation. Wind it up in first gear and see if it does the same thing, if so note the RPM, if not have the 3rd gear checked in the tranny. If so you know it is in fuel or timming. Make sure the vac advance is working, and make sure you have at least 5 psi fuel pressure under load. Make sure the mechanical advance is working. Check to make sure your butterfly on the carb is opening all the way (lower and choke), if you have an ECU your could have a problem with it retarding the timing. Exhaust could be blocked, compression low, or burnt valves. Your float could be set too low and you are actually running out of fuel.

There is a lot that could be wrong here, start with the tranny and run open exhaust and see if it improves. Check compression and fuel pressure, dist advance, and post what you find.

 

[IOPort51]

My question at this point is what else did you change when you changed the carburetor??
If that is the only thing that changed it kind of narrows things down a bit.

 

[cdlongjr]

The only thing I changed was the carb. It's an MC2100, stamped 121, with a heat activated choke. After installing, I sprayed the carb & base w/ carb cleaner. No leaks. I did hook the fuel line to the vent on the top of the fuel bowl & started the engine. It ran, but not correctly, (I have no vacuum @ the front & rear top ports). I checked the MC2100 on the J-10 & saw I had it hooked up wrong. After hooking the fuel up correctly, I warmed the engine up & checked vacuum w/ a gauge on the PCV valve hose. It was 15" & the gauge wasn't steady. I reread the article on the "2100 on a AMC 258 i6 / 4.2l ". I changed the plumbing on the canister to match his diagram & the gauge held steady @ 15". The manual w/ the Mighty Vac said low vac was caused by leaks or timing. I checked for leaks again, none. I moved the dist counterclock wise until the vac was 20", about a quarter of a turn. Engine didn't sound rite under load. Checked timing w/ gun, was way advanced, couldn't see the mark. I set timing to 10 degrees. Vac is 18" & steady. Throttle & choke plates are opening fully. I have installed a new down pipe on exhaust. Float is set @ 1/2" down from top of fuel bowl to the front rite corner of the float. I have the idle mix screws out 1 & 1/2 turns. If I continue to turn them out, the engine speed increases & doesn't go back down.

 

[cdlongjr]

Advanced the timing to 14 degrees. vacuum is17". Vacuum advance moves when I apply vacuum w/ Mighty Vac. Couldn't find fuel pressure gauge. Cracked the out line of the fuel pump. Stream seems weak. Will replace the fuel pump this afternoon. Removed the dist cap & put a 3/8" breaker bar on the bolt that goes to the crank. I turned the crank until the rotor moved. I put a reference mark across the AC compressor pulley assy. I went the opposite direction until the rotor moved. Measurement was 1".

 

[rushpowersystems]

Was the down pipe to replace the EGR butterfly? If you have not replaced this have you wired it open? How about some history, has it always done this? When did it stat? What color is the exhaust - black? With your vac gauge connected to constant, rev the engine to 2K and hold it there for about 5 seconds, when you release the throttle you should see the needle on the vac gauge jump by at least 5 numbers. If not you have low compression. Is the needle steady or does it shake.

 

[rushpowersystems]

note the stats on the last post show i am short an "r", better staRt using spell check.

 

[IOPort51]

stat is a word.
spell check just corrects spelling , not supply the right word.
I guess that would be a job for "word check"??