2.0S Tuning saga continues..

[RetroSC]

Well, I think I've got the ignition sorted out now and I've eliminated the problem with it not wanting to rev past 4500.

Now it runs very strong up untill 5K and falls flat from 5K-6K, then a sudden burst of high end power comes on at 6k- redline.
When I say flat, I mean really weak. I can only reasonably pull through that weak rpm band in first or second.. third or higher and I'd need some serious open road.

A couple of thoughts I had:

1. float level's (checked with a homemade gauge and they look good) I have ordered a PMO gauge though.
2. Low fuel pressure and floats are running out of fuel? (not likely, I've got 4PSI and the flat spot is the same whether in first, second, and so on) Also, why would the power come back on at 6K and pull strong to 7+??

Here's my specs on the carbs:
40IDA's
32mm venturies
tall aux ventirues
125 mains
f3 tubes
55 idles
180 air correctors

Here's the problem child!

[jstobo]

I think you need bigger mains. Try them in steps 130 then 135. I am using 135 in my slightly supped up 69 E with 30MM venturis. great low end and revs past 6000 with no hesitation. Good Luck.

[araine901]

I agree with the bigger mains. Are the valves in good adjustment. I could never get my carbs to run good when my valves were not spot on.

[Vintage911Racer]

Are you running Points? If so check the gap and dwell.
How about your distributor? Are the bushings worn and do you have any play in the shaft? Just a slight bit ofplay in the shaft and you will get those symptoms.

I had a motor built very similar to yours. I was running the same carb settings (idnetical) with the same carbs and it ran great. All the way up to 7500. Putting in the 130's and 135's just made it want to fall over above 6200.

Have you cleaned all your jets out? Idles and mains???

[RetroSC]

I'm going to try some different mains this weekend, we'll see if there's any difference.

Just rebuilt these carbs and I've been in them several times since to make sure nothing is clogged. I've also checked the point gap as well.. .012, don't have dwell meter though.

As for the shaft, there's no radial play, bushings feel good. There is a bit of vertical play.. maybe .5mm, very little though.

[Soterik]

I had a semi similar issue on a 67S engine, and it turned out to be the coil.....just a thought!

Eric

[araine901]

If your still running points, I am with vintangeracer on double checking that first. As soon as I switched to Pertronix My carbs were way easier to tune.

[ValveFloat]

Just curious, what is your exhaust set-up?

Have you checked your advance curve?

[RetroSC]

Exhaust is currently an old Ansa style 4-out. I've got a modded two out sport exhaust that I'm going to switch too soon.

Tonight I'll play with the points a bit and see if that helps. The advance looks good to me. 5degrees at idle, 23 at 2K, 28 at 3K, 30 at 4K, 30-32 from there on up.

[ValveFloat]

Exhaust is currently an old Ansa style 4-out. I've got a modded two out sport exhaust that I'm going to switch too soon.

Stock heat exchangers?

[RetroSC]

Yep, stock exchangers.

They're actually off a 74.