popping through the exhaust at 4500 rpm or so.. HELP!

[Zedyone_kenobi]

I will have to show you a picture of it. :stupid:

OKAY:

UPDATE with the wideband!

Got the car warmed up. Verified pistons drop uniformly before I went out. CHECK.

Checked timing, still at about 16-17 deg BTDC depending on where I position my head...but rock steady.

Car started up and was running VERY smoothly this morning.. and as usual, had Zero issues driving around normally loafing around.

I make some notes to myself mentally, as it is too hard to drive and write:

2nd gear pull - part throttle, tried this at 20% to 80% part throttle, same results as near as I could remember them...

2000 rpm----13.9

3000 rpm----14.5

4000 rpm----15.8

Popping started

5000 rpm----16-18

Popping too strong to continue at part throttle...

I did this repeatedly with the same results

So, next I kept the car in second and slowed down to 2000 rpm and went to WOT:

2nd gear pull - WOT throttle

2000 rpm----13.9

3000 rpm----13.8

4000 rpm----13.9

5000 rpm----14.0

6000 rpm----14.2

Well this seems to confirm what we already knew but now we have data...Just to reinforce this I tried another test.

I put the car in 3rd gear, and did some 40-60 mph runs using various amounts of throttle input

Every time I could get the rpm to rise under part throttle I had an accompanying leaning out trend until it started popping

The same run under WOT, kept the A/F right at 13.8 to 14.2

My A/F at idle is 13.0ish

So the same problems as before but with data now. :disappoin:

Blue, do you still think slop in the timing set would manifest itself in this manner, where it would only be evident at part throttle. I do not see how my throttle position would effect timing, as that should just be rpm related.

I am going to pull off the valve cover today and have a look see.

I am also going to start seriously thinking about doing an SU swap out now as no amount of 'tuning' will fix this. I will also have at try Bonzi's suggestion.

[Zedyone_kenobi]

Took the valve cover off and had a look around.

Set it to TDC and peeked through the cam sprocket hole first. I took some pictures of it, but they did not come out. But the timing mark on the cam plate, is within the notch on the cam sprocket, and even though the number of which hole the cam dowel goes through is covered up, It looks like a number one is on top at TDC. But I can take more pics to verify.

WHat I was wondering about, is I want to verify this is a stock cam. I have no reason to think otherwise, but it is marked E30 and has an orange painted section..

by the way, all lobes are smooth to the touch and show no signs of scratches or wear.

[madkaw]

I'd say that your AFRS are high for WOT. You should be dipping into the mid 12's at wot- so you are running lean- IMHO. Is that your reason for popping, can't say for sure, but you are lean. The only time I see 15 + afr is during initial throttle tip in and than the AFRS steadily drop during wot and bottom out around 12 ish.

You could try to back down your mixture screws- make a BIG adjustment to see if it makes changes to the AFRS . I doubt you will find anything under the valve cover of importance- but hey, it won't hurt

[steve91tt]

I agree these afr readings look very lean for sm needles. I'd crank the adjusters down until you get the idle in the mid 11's and go for a drive. This might be a bit rich for best fuel milage but it should not be so rich it stumbles.

[240260280z]

The data shows that you are lean when applying light pedal and normal with heavy pedal (WOT).

I assume there was no popping with the heavy pedal? If so then that rules out ignition.

The carbs should roughly perform the same for light pedal and heavy pedal. Since there is more manifold vacuum with your light pedal the first thing that comes to mind is that the leanness may be due to a vacuum leak in the manifold which is neutralized at WOT.

But if there is no vacuum leak then the problem is that your carbs are not metering fuel properly.

I would recommend that you set the jets lower so that your light pedal A/F is lower.

With both light pedal and heavy you go leaner A/F at higher RPMS. This can be the SU piston rising too quickly or the needle taper not metering properly . You can experiment by doubling the springs in the domes to slow the piston rise (for more venturi pullon the fuel) (or add weight inside the dome). Or conversly you can remove the springs forlesspressure so that the piston risesquicker and exposes more fuel. You can also try pushing the SM needles deeper into the SU piston to increase the fuel exposure with piston lift to try and get more fuel in the upper rpms (raising needleis similar to dropping the jets but the exit point of the fuel is higher) .

Reference:

Edited January 16, 2012 by Blue

[30 Ounce]

You may have a reground cam, I've never seen orange paint on one and your base circles look small but it is impossible to tell by just looking at pics. Also as others have said you are pretty lean. Very strange for SM needles. If your positive you don't have a vacuum leak then I'd try baking the timing down to 10-12 and check the AFR's again.

[steve91tt]

Blue, I disagree the WOT are leaner than normal. 14.2 AFR is pretty lean. It may not be lean enough to cause a misfire but I'm used to seeing AFRs staying below 13.5 at WOT. Especially with SM needles.

[steve91tt]

I have orange paint on the stock cam in my 1973 e88 head.

[Zedyone_kenobi]

Another piece of the puzzle maybe...

The shiny link on the timing chain is by the number 3 on the cam sprocket. Which may mean the chain was already advanced as far as it can be to make up for slop. The thing is the chain still feels a bit lose. I will post a video of the chain on the car...

http://www.flickr.com/photos/sdamico/6709111751/

[240260280z]

Actually the WOT plot is very flat.

Does the car have a smog pump or cat upstream from the O2 sensor?

[madkaw]

That's just by chance the link is on #3, that means nothing unless you can see the other shiny link.

[Zedyone_kenobi]

It seems I am at a point where I need to drink a beer and just take a breath today.

Steve, I did just what you guys are saying, with cranking down the A/F until I had an idle around 11.0, but it still went lean then started popping.

What would be great to know is manifold vacuum during engine run. I have a vacuum gage and I can hook it up with a long tube to my old Vac Advance port which is currently plugged, and see what happens to my manifold vacuum under part throttle and WOT.

It is one piece of the puzzle we do not have. All I know is my vacuum is about 20 at idle.