2F smooth then rough, smooth then rough, smooth now rough...

Joined
Oct 16, 2006
Messages
777
Location
Houston, TX
 
 
I’m putting my money on a leaky vacuum booster. When it’s running badly, run a rubber hose from your ear to where the brake pedal goes though the cab into the booster and listen for a hissing noise.
 
Joined
May 6, 2016
Messages
28
Location
Lummi Island, WA
Just occurred to me it's possible the debris I noticed in the bottom of my gas can actually came from my FJ40's gas tank. A week or so ago I noticed a slow drip from the gas tank, so I removed the plug to drain the tank so I could apply gasket maker to get a better seal. The gas I drained went into the can that has crud in the bottom. Hmm.
 
Joined
May 6, 2016
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Lummi Island, WA
I did get better vacuum yesterday (18-19, steadier than before), not sure what changed - maybe just a better connection, as I tried to snug up the gauge fittings before checking this time.

For anyone following the play-by-play here, the broken rocker stand bolt (that snapped when I was tightening it, pre valve adjustment) turned out to be less of an ordeal than I feared. It broke above the head surface and had a jagged edge that I was able to tap sideways (counterclockwise) with a small punch, spun out pretty easily.

Think I'll pull the carb and see if I find any blockage in it, may also drain the gas tank and check for debris while I'm waiting for the new rocker assembly bolt to arrive.
 
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Advrider639

SILVER Star
Joined
May 23, 2011
Messages
430
Location
Athens, GA
 
..... just got a vacuum gauge and connected it for the first time this evening - was getting about 15 with variance (up and down) 1-2......
Yeah that’s not good. 15 seems low and that needle should be steady. If it is fluttering like that your valves need adjusting.
 
Joined
Nov 25, 2014
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388
Location
Western victoria Australia
 
Out of curiosity, have you tried retarding the ignition a bit? Or even disconnecting the vac advance and blocking it off. Sticky vac advance plates can give intermittent timing issues that could explain your symptoms of good then bad idle, especially if vac advance is on the wrong carb vac port. The chugging from a too advanced ignition mimics an out of tune carb.. I know it's a long shot.
Also make sure your ignition system, coil and leads etc are in good nick.
I've noticed some threads recently where a lot of time is spent on carb tweaking, and it turned out to be ignition/electric related.
Don't know if this has been asked, but is the pcv valve ok? If it has one?
 
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Joined
May 6, 2016
Messages
28
Location
Lummi Island, WA
Out of curiosity, have you tried retarding the ignition a bit? Or even disconnecting the vac advance and blocking it off...
Also make sure your ignition system, coil and leads etc are in good nick...
Don't know if this has been asked, but is the pcv valve ok? If it has one?
Good ideas, thank you. I’ve advanced and retarded the timing a bit and didn’t notice a difference in idle quality. My distributor has vacuum retard (I think, I get confused by most things vacuum) and its port is open - this was per advice I got here a while back on vacuum routing. I did stick my finger over the dissy port recently to see if it made any difference, it didn’t.

I’m now leaning toward something ignition/electric, yesterday pulled the carb and cleaned It a bit (mostly the bowl, it had a fair amount of cloudy/flaky gunk at the bottom), but that didn’t seem to make much/any difference. Am planning to try dripping fuel into the carb next, noticed this in another thread as a suggestion to determine if it’s fuel-related or not.

Should also have thought to check PCV sooner, will do that today!

Edit: I had an extra (new) PCV valve and tried it, no noticeable change.
 
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Joined
May 6, 2016
Messages
28
Location
Lummi Island, WA
New good clue, I think: a steady dribble of gas from a syringe straight into the carb barrel definitely smooths out the idle. Must be the carb unless there's a crack in the intake manifold, right?

Assuming it's the carb, is it at all likely it's something that will work itself out if I drive more/harder? I've gone about 150 "easy" miles since getting it back together, have probably topped out at 40 mph so far. Or should I just pull the carb and go through it more carefully as the next step?
 
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Joined
May 6, 2016
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28
Location
Lummi Island, WA
Just came across this post, where I think (hope) @JAFO2014 nailed my problem and offered the solution:

With it idling ( I guess you have to choke it, so hard to see I guess), is gas spewing out the venturi on the passenger side? Maybe you can back the choke out enough to see in the top of the carb. You should not see gas there when at idle. The gas should be getting to the intake via the idle circuit, which dumps the gas out below the butterfly at the bottom. If you see gas being dumped out the venturi during idle then the idle circuit is blocked some place.

In troubleshooting mine I traced the path of the idle circuit. Saw where the passages lead to the fuel cut solenoid. I energized the solenoid and then blew carb cleaner through the passage at one end and verified the cleaner spit out the hole that leads to the bottom section of the carb. This will verify that the fuel cut solenoid is opening.

I had an idle problem that sounds like yours and I ended up finding a piece of crud in the bottom section of the carb that was blocking the idle circuit. If you have the carb off, take off the top. Now remove the idle mix screw from the base and blow compressed air into that hole. This should force air out a hole in the bottom section of the carb that leads up to the top section of the carb, leading to the fuel cut solenoid passage. Make sure the idle circuit passage that leads up to the top of the carb is clear. That way you know that the gas coming from the fuel cut solenoid is getting all the way down.

And trace it through the bottom part of the carb where it leaves the bowl in the first place. It leaves the bowl through a passage, then goes through a jet and up into the top of the carb. Make sure that jet is clean. Once mine had the jet clogged and would not idle.

The gas being supplied for idle leaves the bowl through a passage, through a jet in the bottom part of the carb and then up to the top of the carb where it goes through the fuel cut solenoid. Then through another passage and down to the bottom of the carb on the passenger side where it gets metered by the idle mix screw and dumped out and goes to the intake.
I'm able to back the choke off enough to see fuel spewing out of the venturi, time to pull the carb and find blockage in the idle circuit?!
 
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Joined
May 6, 2016
Messages
28
Location
Lummi Island, WA
Cleaning out the idle circuit did the trick! Somewhat validating to know I was on the right track most of the time (near/at least somewhat related to the idle solenoid), also humbling to have the root cause be debris (enough of it to clog things up a few different times!) - apparently either from old gas I didn't flush or new gas from a dirty can. Thanks to everyone for your help, especially those who offered multiple suggestions and JAFO2014 for having/solving the same problem. :)
 
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