[John Strenk]

Originally Posted by mcmud

.. don't tell anyone I said this .......

Don't tell anyone you said what???

OK, it's a deal, I won't tell, but you don't tell them a little trick about drilling a wee little hole in the throttle plate that allows you to bump your idle up and still get normal progression....

All this fun you guys are having is making me want to put a Weber on mine.

[TheGhost]

Originally Posted by IdahoJeeper

I've done the check for vacuum leaks with a can of starter fluid but the adapters and spacers that interface the carb and manifold seem to have some "play" in them like something is loose.

The adapters certainly shouldn't have any play in them. I'd take the carb off and work my way back down. I did check mine to make sure they were flat before installing them.

I put a sheet of 1000 grit wet / dry paper on a piece of glass on my bench (this is what I use to sharpen my chisels & planes - it keeps things really flat), sprayed a little liquid wrench on it and using little, if no pressure start making figure 8s on the paper (this helps to knock any burs off as well). There were a few high spots on the plates but this evened everything right up. Make sure you clean the plates up good before moving on.

Next make sure you really clean the manifold and get all of the old stuff off. I then ran a tap into each hole and cleaned it out (if I recall correctly - it is a 5/16 - 18).

Then I installed the studs in the upper plate with some Loctite and made sure they didn't come through the bottom of the plate - then set it aside to let it cure. They could come through and push the plates apart it appears.

When I installed the plates, I coated them with a thin layer of Lucas Red and Sticky grease. I torqued the base plate down @ 25 ft. lbs. - I think - I couldn't really find a good spec but this seemed to work fine. Make sure you start them straight and that the heads don't stand proud of the plate. Same with the next and finally the carb.

Nothing rocking or loose.

This worked for me.

[mcmud]

Originally Posted by John Strenk

Don't tell anyone you said what???

OK, it's a deal, I won't tell, but you don't tell them a little trick about drilling a wee little hole in the throttle plate that allows you to bump your idle up and still get normal progression....

All this fun you guys are having is making me want to put a Weber on mine.

Oh, thats good....

You must be speaking of the tiny little hole that should not exceed 1mm and be placed on the side of the throttle plate that is opposite the enrichment holes... the one that should be between 2-3mm inward from that edge. No Sir....not me.



You know... these guys may be having a weak ignition issue and this may be a great time to mention such as the 'ol aux. grounds issue thing. But I best leave that for you guys to discuss, I'll read along about stuff like that.

As long as it doesn't get tooooo loud.

Speaking of such as that that brings me to the thought of mtbtweety's mention of he and I working at the issues he has been facing. Over rich idle mix while running weak idle jets and an open throttle plate. Although he has had improvement with being able to stick to the "rules" with the settings he has still reported a weak burn. I think that late valve timing or possibly a valve overlap may be a possibility in his case.

Seems like the time is right and the coast is clear for him to join in to open discussion as this forum has many members that are able and willing to contribute in helping him and others resolve their engine woes..

Point is all issues of weak performance can not be attributed to just the carburetor.

I do want to make a point here to anyone who reads this and is expecting to set a Weber.

Do not rush to the mount. Do not rush through the mounting. Ask questions that pertain to that most important process prior to setting it... especially if you are not one who will follow the directions that come in the box and most especially if you purchased a second hand Weber.

IdahoJeeper... Thanks for being such a good sport and allowing us to have an oportunity to have a constructive discussion with a bit of fun added in that those guys are having in your thread. Oh yeah how about those mid bracket speed test?

Curious minds want to know.

[TheGhost]

Originally Posted by mtbtweety

If I unplug the PCV port to check manifold vac, the vac pulls about 18" Hg, and flutters a bit, and decreases RPM.

A little bit of flutter is OK but it could indicate some other problems. I'm not sure what you are considering a flutter or how that flutter is happening - but here's a few things to consider:

1. STICKING VALVES: When the needle remains steady at a normal vacuum but occasionally flicks (sharp, fast movement) down and back about 4", one or more valves may be sticking.

2. BURNED OR WARPED VALVES - POOR VALVE SEATING: A regular, evenly-spaced, downscale flicking of the needle indicates one or more burned or warped valves. Insufficient hydraulic valve clearance will also cause this reaction.

3. WORN VALVE GUIDES: When the needle oscillates (swings back and forth), over about a 4" range at idle speed, the valve guides could be worn. As engine speed increases, needle will become steady if guides are responsible.

4. WEAK VALVE SPRINGS: When the needle oscillation becomes more violent as engine rpm is increased, weak valve springs are indicated. The reading at idle could be relatively steady.

There are a few more - but these are general rule of thumb indicators that I've used and found on other applications. I haven't really done too much with the 258 - so I'm not completely sure what is "normal" - I can tell you mine is pretty steady - I'd say less than 1/2" change at idle if that much. As long as you haven't put a big over-lap cam in it these are a few things to consider if it's more than just a little flutter.

And wrapping all this back to the carb - if one of these things is a problem, you'll likely have a hard time getting the carb to tune properly until whatever is causing it is fixed.

Good Luck!

[mtbtweety]

Here's the video of the flutter. thoughts?

YouTube - Scrambler manifold vac

[TheGhost]

Again not having that much experience with 258s - but I'd say that's probably OK. It's more than mine, but that could be a difference in the gauge itself. You're not getting any big fluctuations - staying within an inch - no intermittent or consistent drops - my opinion is OK.

Cool to add a video - that takes all the guessing / interpretation out of it!

[mtbtweety]

Thanks TG. That's what I was thinking, also. It seems OK.

The problem I have is similar to others in some respects. I can get it to idle smoothly (75/60 jets, ~2 turns on mix, and 0" Hg), but it's idling just a smidge less than 500 RPM. The exhaust also smells incredibly rich. It's this smell that I'm concerned about now. I've also been experiencing a lot of knock at highway speeds - of course, mine runs 3000 rpm at 70mph. Any more gas, and it knocks like crazy. I may be asking too much of the engine, but I don't think so....

...man, I can't wait to get the 5spd installed.....

edit:
here's video of several successive WOT runs. Seems OK to me. Thoughts?
http://www.youtube.com/watch?v=d-Y8AqFJboc

[swatson454]

Originally Posted by mtbtweety

Here's the video of the flutter. thoughts?

YouTube - Scrambler manifold vac

I see it pulsing pretty rapidly and I can hear the rockers tapping. I'd definitely get the valve adjustment taken care of first. You'd be amazed at what a difference that can make.

Shawn

[CSP]

The valves aren't adjustable on the AMC engines.

[TheGhost]

Good - I'm glad someone else saw it and had an opinion. I wasn't sure if that was just gauge or if it was an adjustment issue. My speakers are shot on my computer at work - so I can't hear what's going on!

[mtbtweety]

Originally Posted by swatson454

I see it pulsing pretty rapidly and I can hear the rockers tapping. I'd definitely get the valve adjustment taken care of first. You'd be amazed at what a difference that can make.

Shawn

Thanks Shawn,
How exactly does one adjust the valves on this engine? I'm familiar with OHC engine valve adjustments, but I'm not seeing any adjustment locations on the rockers with the 258. Does it require shims somewhere?

[CSP]

Originally Posted by mtbtweety

Thanks Shawn,
How exactly does one adjust the valves on this engine? I'm familiar with OHC engine valve adjustments, but I'm not seeing any adjustment locations on the rockers with the 258. Does it require shims somewhere?

Originally Posted by CSP

The valves aren't adjustable on the AMC engines.

The rockers are non-adjustable.

[swatson454]

Originally Posted by John Strenk

Don't tell anyone you said what???

OK, it's a deal, I won't tell, but you don't tell them a little trick about drilling a wee little hole in the throttle plate that allows you to bump your idle up and still get normal progression....

All this fun you guys are having is making me want to put a Weber on mine.

Originally Posted by mcmud

Oh, thats good....

You must be speaking of the tiny little hole that should not exceed 1mm and be placed on the side of the throttle plate that is opposite the enrichment holes... the one that should be between 2-3mm inward from that edge. No Sir....not me.

Curious minds want to know.

Not that I would ever consider such a thing (insert Dr. Evil pinky finger here) but if I had a situation in which I had a carb with a single idle circuit, my idle air bleeds were known to be clean and clear, my idle jet size was known to be of adequate size, my initial advance was at a setting known to work and I was still not able to get enough volume of air to idle the engine without opening the throttle plates into the beginning of progression, I might reference these two pages. Hypothetically speaking, of course! Purely for entertainment purposes only...


Sorry for the poor quality. At least the cat didn't puke on this one, jeeze.



Shawn

[mtbtweety]

Thanks CSP. So, no adjustment on hydraulic valves. I'm not taking the head off this thing to correct a bit of stink. Any other thougts?

[John Strenk]

Originally Posted by mtbtweety

..... I'm idling ~500 RPM now. If I unplug the PCV port to check manifold vac, the vac pulls about 18" Hg, and flutters a bit, and decreases RPM. It smooths up once the PCV is reconnected (or if I free the vacuum port on the vacuum pump). It seems to be running well, but the exhaust still smells rich. I've been avoiding a rebuild of the carb, but suspect that's next. I'm running 8* of timing. It's been great seeing what others are doing, and learning from it!

I'm not sue what vacuum pump you are talking about.

Do you till have the the computer attached or did you nutter the engine already? Do you have any other emission equipment hooked up?

I see you have nuttered and Team rush upgrade. I hope you are not running those silly platinum plugs by any chance.

Ignition is important, I had a 258 that would not idle below 900 RPM and turned out to be the prestolight ignition. I improved the ignition and it would idle all the way down to 500 RPM.