driveability issue!

[Dan86CJ7]

so i dont know if i am posting in the correct section, so heres my issue.
driving down the highway, get to about 60mph/5th gear...the jeep starts to pop/backfire from the carb?? seems it just doesnt want to take any gas? driving around town the thing rips around fine, can put the pedal right to the floor and it pulls strong? Any ideas where i could start checking? Any help/advise would be appreciated

 

[JR74CJ5]

I would normally say check timing, vac leaks, and air / fuel filter(s)...

but

driving around town the thing rips around fine, can put the pedal right to the floor and it pulls strong?

Throws me off a little... Maybe still a vac leak?

 

[Dan86CJ7]

its got me stumpped too! cause it goes fine around town...have not tried torip the highway in 4th? Haven't had time to check it out yet...firgured id ask the cj world for any advise! seems wierd...i did swap my trannys, and it seemed fine for a few days even on the highway and never had this w/ the old Transmission ? All of a sudden on my way home it started, been going side roads for now.

 

[CJ]

What RPM are you running @ 60MPH in 5th?

Duplicate the same RPM at a different MPH in 4th or 3rd, do you get the same problem?

 

[Torxhead]

So the carb and/or ignition would be the usual suspects. Making sure it has enough fuel pressure, float bowl level good, check the ignition timing-initial and total advance. Check and see if the ignition module is hot to the touch as it should not be.

 

[Dan86CJ7]

What RPM are you running @ 60MPH in 5th?

Duplicate the same RPM at a different MPH in 4th or 3rd, do you get the same problem?

i would guess 2000ish maybe 2500? ill double check that....i can mat this thing from a stop staight to the floor and it doesnt do it in lower gears..but will double check...was gonna rip down the highway in 4th and see if it does it.

 

[Dan86CJ7]

So the carb and/or ignition would be the usual suspects. Making sure it has enough fuel pressure, float bowl level good, check the ignition timing-initial and total advance. Check and see if the ignition module is hot to the touch as it should not be.

though of my vac. advance? just weird all of a sudden...carb is a weber dont even think i have 2k on it since i installed it, did install the holly regulator also....if it were fuel or something would this not effect all gears...its just odd it started happening a week after i put the Transmission in and only seem present in 5th? gonna try the suggested on my way home tonight.

 

[Dan86CJ7]

so i used 3rd and went from 20 to 45ish holding different rpms but did not have this happen?? so confused

 

[CJ]

You say you get to 60 MPH and it sputters and back fires. Is that after a hard accell or are you crusing along and then it starts to happenen? How long are you at 60 before it sputters.

You need to mimic the exact RPM's and times but in lower gears to see if it is a fuel starvation problem, don't just acellerate and let off. I suspect you are starving for fuel once you drive hard for a few seconds pointing to a clogged filter or filter sock not allowing the bowl to stay filled.

 

[CJ]

Also, if you can safely, get on a rural road and run it till it sputters and pops, as soon as it does turn off the engine and come to a stop on the side of the road (in neutral so the engine does not turn over) - pull over SAFELY and off the road.
Pull the air cleaner and while looking down the throat of the carb see if any fuel is left in the carb by working the throttle seveal times, you should see the accell pump squirt fuel into the throat of the carb. No squirt = no fuel.

 

[Dan86CJ7]

the exit i use is about a 1 1/2 mile til the next exit. usually get 5th getting on....crusing down the highway and it starts...just doesnt seem to want fuel....put off the exit and it is fine?


matching rpm is hard as i got no gauge, so kinda going on feel.. but think ive been close enough?
was talking to my shop foreman and he seem to think the same...fuel/ lean misfire...so gonna talk a look at somethings he recommended. start there i guess

 

[JR74CJ5]

What did shop guy reccomend?

I'm with CJ's last post. Check possible bowl sock or fuel filter clogs.

is the holly regulator adjustable? How much is it letting through?


~ Jr

 

[Torxhead]

the exit i use is about a 1 1/2 mile til the next exit. usually get 5th getting on....crusing down the highway and it starts...just doesnt seem to want fuel....put off the exit and it is fine?


matching rpm is hard as i got no gauge, so kinda going on feel.. but think ive been close enough?
was talking to my shop foreman and he seem to think the same...fuel/ lean misfire...so gonna talk a look at somethings he recommended. start there i guess

So I hope he recommended checking the deposits on the spark plugs and fuel pump pressure. A low carb float bowl level could indicate a lean mixture also.

 

[Dan86CJ7]

basically to look for fuel starvation, i was gonna do plugs regardless...if the carb is some what new...how would the float drop?

the holly is adjustable.....1-4 psi, but i just put it on...it been on for a while now w/o issues?

 

[tarry99]

basically to look for fuel starvation, i was gonna do plugs regardless...if the carb is some what new...how would the float drop?

the holly is adjustable.....1-4 psi, but i just put it on...it been on for a while now w/o issues?

Just a wild guess, but check your bowl vent's and loosen you gas cap if you can..........fuel system could be creating a Vacuum?

 

[Dan86CJ7]

drove it last night and it seemed ok? odd! what are you guys running for plugs? i usually grab the champions from my parts dept. may try something different, gonna throw a new fuel filter at it also...maybe bad fuel, gonna take the highway tonight too and see what happens.

 

[tarry99]

drove it last night and it seemed ok? odd! what are you guys running for plugs? i usually grab the champions from my parts dept. may try something different, gonna throw a new fuel filter at it also...maybe bad fuel, gonna take the highway tonight too and see what happens.

Well were all waiting to see what solved the problem............Spark Plugs should not make any difference as long as they are the proper heat range, try the fuel filter,

Question: What type of Spark plug wires? Changed them lately? Got them routed away from any metal? Got an Ohm meter? If so check the resistence and see what values you get.........obviously the longer the wire the more the resistence..............
General rule of thumb as the motor speed increase's as well as the vehicle speed increase's the load on the Ignition and wires also increase's.........Could be a breakdown somewhere.............check your connections and if you have a NAPA or another good store near by maybe you can get them to load test your system.....Just a thought!

 

[Dan86CJ7]

Well were all waiting to see what solved the problem............Spark Plugs should not make any difference as long as they are the proper heat range, try the fuel filter,

Question: What type of Spark plug wires? Changed them lately? Got them routed away from any metal? Got an Ohm meter? If so check the resistence and see what values you get.........obviously the longer the wire the more the resistence..............
General rule of thumb as the motor speed increase's as well as the vehicle speed increase's the load on the Ignition and wires also increase's.........Could be a breakdown somewhere.............check your connections and if you have a NAPA or another good store near by maybe you can get them to load test your system.....Just a thought!

i put napa blue 8mm wires on about a 1 1/2 year ago when i did the cap upgrade....trying the fuel filter tonight...doing plugs cause its been probably 6k+ since i did them and i wanna see what they look like. so new ones go in....ive been told if it runs good under accelleration i could rule out most of the ignition stuff because this is the highest demand for the ignition system, working its hardest...seemed very odd it didnt do it last night...we'll see after work!

i also ran down the highway in 4th right up to 65mph w/o any issues.

 

[tarry99]

i put napa blue 8mm wires on about a 1 1/2 year ago when i did the cap upgrade....trying the fuel filter tonight...doing plugs cause its been probably 6k+ since i did them and i wanna see what they look like. so new ones go in....ive been told if it runs good under accelleration i could rule out most of the ignition stuff because this is the highest demand for the ignition system, working its hardest...seemed very odd it didnt do it last night...we'll see after work!

i also ran down the highway in 4th right up to 65mph w/o any issues.

In High gear getting up to speed is the biggest load............When you have issues like this.........it can be a PITA ...........sometimes just going over what you previously checked also works......Electronic Ignitions can work one minute then gone the next.........
Have you tried taking your fuel line loose at the Carb and blowing air through the line back to the tank? Have you checked the tank and carb vents? Have you ever taken the gas cap off and heard a rush of air?

 

[Dan86CJ7]

In High gear getting up to speed is the biggest load............When you have issues like this.........it can be a PITA ...........sometimes just going over what you previously checked also works......Electronic Ignitions can work one minute then gone the next.........
Have you tried taking your fuel line loose at the Carb and blowing air through the line back to the tank? Have you checked the tank and carb vents? Have you ever taken the gas cap off and heard a rush of air?

no rush of air when fueling.....tonight is the first time im gonna be able to poke around w/ it....got a fuel filter to try