Sputtering...
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Instructor
Joined: Jun 2004
Posts: 110
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From: Bozeman MT
Sputtering...
Why does my '78 L48 (QJet rebuild less than a year ago) sputter or miss when tooling down the road at, say 35 mph, not excellerating, not idling, just cruising down the road? I hope I explained it correctly. Car runs fine, excellerates great. Just that spot where you are just barely touching the pedal, it seems to miss or sputter..
It seems to have recently started doing it. I looked for a vacuum hose fallen off. I recently upped the timing to about 14 deg before (at idle) this past spring, but didn't notice the missing then. Plugs are new.
It seems to have recently started doing it. I looked for a vacuum hose fallen off. I recently upped the timing to about 14 deg before (at idle) this past spring, but didn't notice the missing then. Plugs are new.
Tech Contributor
Joined: Aug 1999
Posts: 14,370
Likes: 6,364
From: At my Bar drinking and wrenching in Lafayette Colorado
If the car "jerks" or "chugs" as you cruise down the road at steady state, it's usually indicative of an over-advanced timing situation caused by either too much centrifugal advance or too much vacuum advance - not a carb problem (90% of all carb problems are ignition problems). To see if this is the case, pull the vacuum hose off the vacuum advance and try the car out. If the sputtering stops, you have an over-advanced situation. Suggested fix: Time the car for 36 degrees total timing and install vacuum advance unit part number VC1838 (NAPA). This will limit the advance and smooth you out.
If this does not solve the problem, a lean condition may be the cause. Check for issues that can induce a lean condition, such as a vacuum leak, stuck power piston, float height, jetting combo, etc.
If this does not solve the problem, a lean condition may be the cause. Check for issues that can induce a lean condition, such as a vacuum leak, stuck power piston, float height, jetting combo, etc.
Tech Contributor
Joined: Aug 1999
Posts: 14,370
Likes: 6,364
From: At my Bar drinking and wrenching in Lafayette Colorado
Originally Posted by redc3
i hope someone answers this cause ive got very simialar problem. lars insists that its a timing issue but its not, so no help there. 
If you're still having problems, let me know - more than glad to help out or send you a loaner carb if you need it.
Lars
Tech Contributor
Joined: Aug 1999
Posts: 14,370
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From: At my Bar drinking and wrenching in Lafayette Colorado
mem-
No, it won't. The vacuum advance control units for the point-style distributors are different from the HEI. You can probably use a VC1765 on your engine configuration with good luck. If you have an automatic with a little bit of a cam, use VC1838.
No, it won't. The vacuum advance control units for the point-style distributors are different from the HEI. You can probably use a VC1765 on your engine configuration with good luck. If you have an automatic with a little bit of a cam, use VC1838.
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2nd Gear
Joined: Jun 2003
Posts: 2
Likes: 0
From: Jamestown RI
I'm shure glad I saw this post.I had this problem all summer I replaced the wires,dist. cap,rotor and plugs then spent a lot of time trying to fine a vac leak. I never thought it would be the vac advance now it runs smooth with no jerking . Thanks Lars I never wood have found the problem.
Steve
Steve