Erratic idle and stumble all of a sudden

8

86sebring

New Member

May 15, 2005

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Aug 18, 2005

#1

• Aug 18, 2005

• #1

This is on a edelbrock carburated 302. It has been running fine and very smooth until last week, when it started hesitating. I havent touched it and all of a sudden the idle is either very high or it just dies. When driving it stumbles at low RPM's, there is no smooth acceleration until about 3500RPM, thats when it pulls very good. I checked the timing, which is good. Could it be dirt in the carb or a vaccum leak what else? Whats the best way to find a vaccum leak?
thanks

 

1

10secgoal

Active Member

Dec 1, 2003

2,801

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49

San Diego

Aug 18, 2005

#2

• Aug 18, 2005

• #2

Sounds like a vacuum leak. Get a guage for like 15 bucks. an awesome tool, that you WILL need again at some point. The needle will be irratic, and jumpy.

 

R

Ramrod48

New Member

Aug 18, 2005

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Aug 19, 2005

#3

• Aug 19, 2005

• #3

Yep , sounds like a Vacuum leak, Like { 86 } says get you a vacuum guge , You would be surprized the diff things you can do with one , As far as looking/ finding a leak Sometimes it can be pretty tough to track one down. Check every thing on the intake mainfold from the block to the carb., Get a can of Carb cleaner , An with the engine running start spraying around the intake runner , the base of the carb. ( Any where theres a gaskit ), If your gauge jumps up temp. then you found your leak. You gotta do this on a engine before it gets to operating temp ., Check all your Vacuum hoses, any nipple that may have been plugged off , the PCV Valve.The brake power booster if you got one ? I dont know how old your Carb. is but I've seen high milage units sucking air around the throttle shaft's . ,, Do you have an EGR Valve ? I'v seen them get some carbon build up an not seal off . causing a rough Idle . Let Us know What You Find , Good Luck

 

oz

Founding Member

Jun 29, 2000

1,079

10

58

Plymouth, MI

Aug 19, 2005

#4

• Aug 19, 2005

• #4

If it's not a vacuum leak it may be some crud is stuck in the carb's idle circuit. Since it goes away at higher RPM (as the carb transitions from idle circuit to power circuit) it may be junked up.
Spray some carb cleaner in the little holes, etc in the main bores of the carb while you're spraying it around looking for leaks.

 

R

Ramrod48

New Member

Aug 18, 2005

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Aug 19, 2005

#5

• Aug 19, 2005

• #5

Another thing that has helped me in the past on funky carbs, Pull the coil wire . Cover the top of the carb. with a thick large rag. (ie a towel, dont let wifey see you )Why holding it there get a bud to crank the motor over for you. Not allways but most times if you got some KAKA in the carb passage ways, It will suck it rite out. You may have to try it a couple of times. An if it works what a diff. Good Luck

 

8

86sebring

New Member

May 15, 2005

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Aug 19, 2005

#6

• Aug 19, 2005

• #6

thanks guys for all the replies. I was kind of leaning toward a issue with the idle circuit myself, since it pulls very strong above 3000- 3500 RPM.
Ramrod- You are being serious, right? Cover the carb with a rag (lintfree, I guess) and turn the motor over... I'll give it a try

 

8

86sebring

New Member

May 15, 2005

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Aug 20, 2005

#7

• Aug 20, 2005

• #7

Update

So today I used carb-cleaner, sprayed it around the carb area while it was running, but did not find a leak. I took the carb totally apart, cleaned it, put it back on, same result, no consistent idle, erratic low end power, good top end power.
So I bolted on a Holley that I had waiting on a shelf, more top end power , but still erratic idle and low end stuttering.
WTF, now I'm confused, could it be something electrical? Electric choke, points, condenser, plugs
HELP Please

 

1

10secgoal

Active Member

Dec 1, 2003

2,801

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49

San Diego

Aug 20, 2005

#8

• Aug 20, 2005

• #8

Could be possible the springs in the distributor. I found myself with the same problem at one time. Would do it more when hot, than cold. The springs inside were to the verge of begining to advance. They seemed to advance a little, which raised the idle, then it would come back down. I took a timing light and saw the slightest movement at the dampner. was kinda hard to say at the time if it was the springs, because a change in rpm would cause the timing to change, naturally. I bumped the timing 2 deg, and lowered the idle. All better.

 

68 Coop

New Member

Aug 13, 2005

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Mesquite, NV

Aug 20, 2005

#9

• Aug 20, 2005

• #9

If your floats are good, then I would guess timing too. It sounds like it a little too advanced, if memory serves. Find a hill, normal little stretch, get up to 35/40, then kick it in the ass. If it stumbles, try backing it off about an 1/8" at a time. It took me almost 2 solid hours to get my car right. Still haven't hooked it up to a light to see what it reads yet. SBF's like about 12* inital, and total timing in by 3000, which is about 35* to 40*.

 

8

86sebring

New Member

May 15, 2005

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Aug 21, 2005

#10

• Aug 21, 2005

• #10

thanks for replies.
10secgoal: So if it is the springs in the distributor, all you had to do was advance the timing 2° or did you replace the springs also?
68COOP: what gear are you using for this timing test?
I checked the timing, it is at 10° at about 1000RPM and close to 38° at 3000RPM.
BTW: the car does not have power brakes, so the only places for a vacuum leak would be around the intake, carb, PCV valve and hose and the small hose going from the carb to the distributor, correct?
thanks again

 

68 Coop

New Member

Aug 13, 2005

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Mesquite, NV

Aug 23, 2005

#11

• Aug 23, 2005

• #11

I just ran it in Drive to figure it out. My car runs better than it ever has, but I think the carb and intake was a big help also. Hope I answered your question, I'm kinda confused on waht you mean really.