Jeep Wrangler Forum

Jeep Wrangler Forum (
-   YJ Tech Forum (
-   -   Open throttle quickly....Bogs then ... big acceleration! (

5double0 07-27-2011 06:28 PM

Open throttle quickly....Bogs then ... big acceleration!
Open throttle quickly....Bogs then ... big acceleration!

Motorcraft 2100 108 with 47 jets.
4.2L with 126k miles
Accel Super stock coil (yellow)
Spark plug gap at .035 (whatever stock setting is)
timing at 11 BTDC (better throttle response than at 9, but probably why idle is at 1100rpm)
occasionally diesels for a second or two after key turned off.
Idles after start with manual choke open at 1100rpm
w throttle plate full closed

I get a little bit of what might be valve clatter when first shifting into
next higher gear if I don't wind it up higher before shifting.
(Perhaps the rockers need to be re-torqued?)

if I'm slow or gentle to open the throttle, then it's smoother past the initial acceleration, and once past that...good to go.

Motor can be hard to start. Takes quite a few turns and then starts, but not snappy...also takes a good 7-10 mins to warm up other wise very hesitant when opening the throttle.

Stays idling no problem

Carb completely torn apart and cleaned and reassembled.

Do I have the wrong jets? or what????
Not enough gap?
Vacuum issue?
It seems like I have this as good as I can get it without other brains on this one.

Thanks in advance!

Jeeps do not get stuck...The mud just doesn't want to let them go! :punk:

scott howard 07-27-2011 06:47 PM

i would install a hei i will send you a link to a good one.
how many miles on timing chain ?

AMC JEEP 232 258 4.0 4.2 6 CYL HEI DISTRIBUTOR 6511-R | eBay

CapnRich22 07-27-2011 06:51 PM

first thought would be vacuum

5double0 07-27-2011 06:58 PM

Scott, assuming the neglect the previous owner gave it...or just lack of wrenching knowledge, I will take a leap and say it's does however appear that the water pump was done and the loctite is still fairly clean and orange (gasket making material I would suppose). Honestly not sure if it was done at that time or not. I wondered if the timing was not always right. But when I had my timing light going and watched it idle, it never seems to waiver much at all. not much left as far as vacuum lines...tried the carb cleaner trick and no dip in idle at all.

5double0 07-27-2011 07:04 PM

I thought of this too. It does seem like it misses occasionally when idling. can't say for sure, that might be normal idle... It doesn't act like it misses when revving, but maybe I just do not have a smooth 4.2L to compare it to. I can have it in first, let the clutch out slowly, and it will pull itself up a grade or up to higher speed without bogging. the bogging is from a quick rap on the throttle. if slow, it's better.

goatman 07-27-2011 07:10 PM

I've been lurking this forum for awhile and signed up to put some input into this thread.

I really believe you have an accelerator pump issue. I have a couple cars with carbs and your problems are pretty text book signs of a bad pump. I don't know the motorcraft carbs, only qjets, but you should be able to look down the carb with the intake off and pump the throttle and see a stream of gas shoot into the intake.

5double0 07-27-2011 07:18 PM

I've checked that, and saw gas flow into the venturi rings (i guess that's a word for them).....I just don't know how much of a stream or dribble they should have. When I cleaned this carb really well, (3 times) it originally had what appeared to be sand in the bowl and then after cleaning it was a jelly consitency but now all of that is clean and clear. I pulled the tank and cleaned it, lines are clean and all rubber lines are new as well as filter. Do you think the pump's little rubber valve and spring are weakened possibly? The one thing I did not do, was put a rebuild kit in it. I just cleaned the existng and re-installed everything. Major difference, though from before.

5double0 07-27-2011 07:28 PM

And Scott, thanks for that link. There seems to be two camps...The Team Rush and HEI camp....I like the price on that Dizzy. I will need to change plug wires as well, but still about the same cost as the Team Rush method with new plug wires....I just truly hope this is discussed and really hashed out, because I have done a ton of digging on the web for people with similar issue, and the debates start going in different directions...never seeming to resolve it. Good thing is the rebuild kit is cheap and available and the Motorcraft 2100 is so simple. Any thoughts on the spark plug gap and jet size with this configuration? I would be willing to put the timing to 9 btdc and re-gap if the throttle response improves. I have heard of people going to .045 after the dizzy upgrades.

scott howard 07-27-2011 07:29 PM

The pump linkage has a couple different adjustment holes.
try a different setting and see if it helps.

scott howard 07-27-2011 07:31 PM

yep i have the mc 2100 with the 1.08 bore and a 48 jet , hei, and plug gap set at 45

5double0 07-27-2011 07:40 PM

Ok. You think perhaps it's just opening way too fast? When I would open it very quickly by hand, the carb would make a sucking sound like a major change in vacuum occured. It was as if fuel could not keep up with how much air was quickly sucked into the carb. Does that description make sense? I've just never had a hesitation like that from carbeurated engines i've owned in the past.

5double0 07-27-2011 08:04 PM

Thanks everyone for the thoughts! I am going to make sure my rockers are torqued properly after hearing Squarepushers motor rev in the motor does not rev near as easily and smoothly. I might have more going on....But I will check the threads later to see what new info is there! Jeep people rock!

goatman 07-27-2011 09:07 PM

I think putting a rebuild kit in it would be a wise move and a cheap thing to know that the pump seals in it are good. It should be a strong stream, not dribbles.

Tyewilly 07-28-2011 12:20 AM

X3 on accelerator pump, should have a strong spray.

5double0 07-28-2011 06:33 PM

Will do (the rebuild kit) tomorrow evening or first thing Saturday! I will post results. On another note, after thinking hard on this....I left form work to go home and decided to leave the manual choke closed more than half way vs. how I normally open it completely and drive that way. It was quicker on the throttle and less of the dead spot, but still dieseled upon turning the key off once home (about a 15 minute drive after 5 min warm up). I did notice that I could drive away much quicker by leaving the choke closed more than halfway vs. open. (Took less warm up time before driving better). Perhaps that is a "DUH" thing, but this is my first carb with a manual choke.

5double0 07-31-2011 12:59 PM

I will postpone the rebuild kit untill 2 weeks and will update when complete! Thanks for all the replies!

All times are GMT -5. The time now is 05:10 AM.

User Alert System provided by Advanced User Tagging v3.1.0 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.