I had a similar problem, verified on the dyno as fuel related. Raised the float levels slightly higher than stock (one was way low) and was able to rev higher but there was still bogging on acceleration from cruise at freeway speed.

Switching from 20wt 3-in-one oil to 30 wt. helped noticeably, now it was put-putt- putting where it was totally bogging before. Then I installed some modified (by someone who knows what they're doing, not me) needles and it made a big difference. Almost there but I think the needles need a little more polishing to be perfect. The head's not stock, guess it needs more gas at mid-range. Got some good advice from members along the way, thank you.

Maybe try thicker oil first, it's easy.

I'm not sure where I read it but I think ATF is like 20 weight?

I'm not sure thicker oil will help, because it feels like it's constantly bogging on the highway. not sure how to explain it. it;s like the engine just isn't smooth and happy when its in that range. A bit more throttle and the engine perks up and moves along just fine.

the slides are stationary during cruise unless i change throttle position, so I'm not sure if adding thicker oil will make any difference. the throttle response is great, it never stumbles or sputters when i put it to the mad hard, i believe this would indicate that the oil is fine?

If it's the cam you could get smaller tires. So you'd have slightly higher rpm cruising around town at 35mph or so. I had the maybe the same problem and going to 65 series instead of 70 seems to have fixed it. Less top speed I guess, but when would I go 125 anyway.

Edited August 22, 201410 yr by Stanley

I'm not sure thicker oil will help

the throttle response is great, i believe this would indicate that the oil is fine?

I would agree with your assessment. The oil is there only for transients. If you're keeping a steady foot, the oil doesn't do much of anything. Might apply some "anti-oscillation" damping for the loop, but other than that, it's a non-factor.

Also, if you can punch it and it doesn't sputter or bog, then that's another data point indicating that your oil is of a suitable weight.

As for the problem you're having... Are you sure it's not an ignition issue? Timing slipping around from sloppy gears or bushings or something?

How do the plugs look? Can you tell if you've got a mixture issue one way or the other?

Edited August 22, 201410 yr by Captain Obvious

So what needles do you have? Stock needles might be too small.

You could experiment with slightly raising the needles in the piston. If the shoulder is not flush with the groove, you could push it in further or closer to being flush. This might put a smaller part of the needle in the transition zone for more fuel.

How do the spark plugs look?

When you synched the carbs did you do that at 2500rpm and idle?

Possibly slack in the linkage?

As for the problem you're having... Are you sure it's not an ignition issue? Timing slipping around from sloppy gears or bushings or something?

How do the plugs look? Can you tell if you've got a mixture issue one way or the other?

My timing used to jump all over + or - 5 degrees with the points, but now that i have electronic the timing marks are rock solid when i use the timing light. the stock distributor is solid, bushings are good.

every time i have had the plugs out they looked to be a nice golden brown. but to get a real condition under that situation i would have to quickly shut the car down after a minute or so of that rpm/load range to get an accurate indication, once it settles back down to in town speeds the car runs and drives great, so the plugs would indicate proper mixture after a minute or so in those conditions.

So what needles do you have? Stock needles might be too small.

You could experiment with slightly raising the needles in the piston. If the shoulder is not flush with the groove, you could push it in further or closer to being flush. This might put a smaller part of the needle in the transition zone for more fuel.

How do the spark plugs look?

When you synched the carbs did you do that at 2500rpm and idle?

I have no idea what needles i have, I guess i should go have a look at one. the needles are properly seated as in the z therapy SU DVD.

I first synched the carbs at idle, then at 3000rpm since that is where the car sits on the highway. they are dead on. I am convinced this is a needle/fuel problem.

Possibly slack in the linkage?

linkage is all brand new, there is some slack, but you sync the carbs with the slack taken up anyway, so it shouldn't be an issue.

OK, so i pulled a needle out, it says SM on it, no numbers that I can see.

What am i after for a 2.9 stroker?

I would think SM's would be pretty close for a stroker.

How does the engine do in a heavy load low rpm scenerio- let's say pulling a hill with some moderate throttle in a higher gear?

seems fine, maybe a little bit jerky on the throttle.

there's no cam in the car from what i can tell, maybe it needs one.

Well, I checked the black wire with white stripe on my coil (which i can only assume is my coil voltage feed/tachometer wire) an it is feeding 12v to the coil with the key on.

My coil reads 1.4 ohms across the positive and negative terminals. So I have to assume this is a factory 1.5 ohm coil without the ballast resistor in place. I'm pretty sure I should have a 3 ohm coil if i'm running it at 12v shouldn't i?

I don't think this will cause poor running though, if anything the coil will generate a hotter spark with the extra voltage. Will the coil deliver crappy ignition if it is getting more voltage than it's supposed to have? It doesn't seem to get hot, I can place my hand on it after a long drive and it won't burn me, but it is warm.

I bought a Crane PS20, 1.5 OHMS., when I put the ZX dizzy on my 240. Zed Head had a FSM for a ZX that showed that to be the right OHMS. Arne, a 240 guru suggested the Crane. Mine runs way better after doing what they suggested.