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Unread 04-29-2010, 08:46 PM   #1
CJ8Extreme
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1983 CJ7 
 
Join Date: Aug 2009
Location: North Carolina
Posts: 339
Bad accelerator pump???

Ok, I am looking for some help/opinions here before I go tearing into my jeep this weekend. I have an 83 CJ7 with a motorcraft 2100 that I rebuilt about 6 months ago. It is running #48 jets at 8* btdc timing. The plugs look great and it has been running great until a few days ago. Oh I will add about a month ago the power valve went bad and I had to replace it. Ok a few days ago I began to notice my jeep was being sluggish under loads, i.e. going up steep hils etc. So now fast foward to tonight and my jeep stumbles under acceleration. The idle is great and high rpm running is fine. Could the accelerator pump be going out on me? I am open to any suggestions here I am sorta at a loss with this one.

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Unread 04-30-2010, 06:29 AM   #2
hotrod351
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1955 M-38 
 
Join Date: Oct 2006
Location: arizona
Posts: 437
i check the accelerator by looking down the bore of the carb and giving it gas to see how it squirts.
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Unread 04-30-2010, 06:38 AM   #3
JeepHammer
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1973 CJ5 
 
Join Date: Aug 2007
Location: South West Indiana
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The accelerator pump is there to get you moving off the line,
When you first start out, or at lower speeds.
If it were an accelerator pump issue, you would notice it most at hard acceleration from a standing start.

If you have a 'Hesitation' when trying to accelerate a little at highway speeds,
Then 9 chances out of 10 it's either a power valve mismatched to your vacuum signal at highway speeds,
Or you have too much timing dialed in for the drive train load the engine is seeing.

I see it over and over again, someone put big tires on the vehicle, then complains about 'Hesitation'.

The taller tires increase the load on the engine, while reducing the RPM at any given speed,
And you wind up with too much ignition advance while the fuel mixture is very lean and the crank isn't moving fast enough...

Did you make any other changes recently?
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Unread 04-30-2010, 08:22 AM   #4
CJ8Extreme
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1983 CJ7 
 
Join Date: Aug 2009
Location: North Carolina
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JH the jeep is being starved of gas when I hit the throttle hard, or at least it seems that way. I can read spark plugs very well and my timing is as perfect as it can get. Nothing has changed except the power valve a few weeks ago. It ran perfect after that. Even took a trip to the mountains for the weekend and it ran great, never bogged on the hills etc. This past week is where the stumble came from. If you really punch the gas at times it can almost shut the jeep off making me think accel pump is bad, but with the cap off the carb it does pump gas. Although one thing bothers me, if you let it cool off for a short period of time and then pump the accel pump there is no gas on the first pump. If you hit it again there is gas.

My jeep came factory with 3:31 gears and I have been running 32" tires for almost 10 years with no issues in acceleration so there is something wrong here for sure. With the carb running right, 1st gears sits you in the seat along with 2nd, 3rd has endless power, and 4th will move down the road if you put your foot on the floor, 5th will soomthly accel if you floor it as well, just to give you an idea of what it normally does.

I understand a mismatched power valve but shouldn't it have done that from the start, not just all the sudden start acting up 5 weeks after the install?
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Unread 04-30-2010, 09:04 AM   #5
JeepHammer
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1973 CJ5 
 
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Location: South West Indiana
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Quote:
Originally Posted by CJ8Extreme View Post
...If you really punch the gas at times it can almost shut the jeep off making me think accel pump is bad, but with the cap off the carb it does pump gas. Although one thing bothers me, if you let it cool off for a short period of time and then pump the accel pump there is no gas on the first pump. If you hit it again there is gas.
Bad valves or diaphragm in the accelerator pump.

Probably has something stuck in the inlet valve since it's draining back if the vehicle sits.

If you have something that got into the valve,
Then you can bet money the outlet valve has stuff in it also.

Disconnect the carb from the fuel line,
Replace the fuel filter,
Then crank the engine to blow anything that might be hiding in the line out before you reconnect to the carb.

Clean out the carb, and replace/adjust the accelerator pump.
Don't forget to lube the pivot points on the linkage so they don't wear and get slop in them.
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Unread 04-30-2010, 02:38 PM   #6
CJ8Extreme
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1983 CJ7 
 
Join Date: Aug 2009
Location: North Carolina
Posts: 339
Well before your reply I decided to throw the old carb in the super sonic cleaner at work. One of the percs of being a Mechanical Engineer for a company that does machine work for NASA I guess. After about 5 good cycles I pulled it out and put it back together and bolted her on. Runs like a champ now. I can floor it in 5th gear and it takes right off with nice smooth acceleration. Thanks for the help guys, this is why I love this place. Everyone helps each other out.

On a side note, this issue did help me learn... and thats the main thing, besides fixing the jeep lol. Thanks again!
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