Looking for Dyno evaluation/SU carbs-

[madkaw]

Well I took advantage of the dyno while at Zcon this year and I am looking for advice based on my chart. The engine is hardly broke in with 800 miles, but it was running great so I thought I would see some numbers. I am very happy with the numbers based on what little time i got to fine tune. As you can see from the chart I ran lean at about 5200 with my SU's with SM needles. I am also suprised at the richness at the lower rpms since I did so well with my MPG on the way here. I did have a richness problem on the front SU before I left and I'm not sure what exhaust pipe they were reading off of.

I thought the HP and torque #'s were good for the 2.4(.40 over) and the stage 2 cam. I believe there was more there based on the chart since the cam should make power up to 6500rpm. I do have the 280 valves in there also.

It was suggested that I raise the fuel pressure-but I am running a mechanical pump. What options do i have? I checked float levels before I left and set them to stock specs. From what I read these SU's should handle more hp than this.

I was also interested that the afr's fell off sharply at 5100 instead of slowly tapering off.

I was happy to see that I my engine put out 20 more HP then the 2.4 before me with triples(he was running way rich)

[conedodger]

The fact that your cam is supposed to make power to 6500 and you drop off sharply at 5100 could mean you ran out of carb with your SU's and that set up.

[steve91tt]

The fact that your cam is supposed to make power to 6500 and you drop off sharply at 5100 could mean you ran out of carb with your SU's and that set up.

Please correct me if I'm wrong but From what I understand a set of SU's should support anything a 2.4l NA L6 can put out. No?

[Bruce Palmer]

I'll ask the owner to read this over and see what he has in the way of ideas. Forty six millimeter Hitachis supply everything Steve's race motor requires to well past 7 grand with no protests.

Sm's should be fine down low while getting a little fatter up top. What you are describing is bassackwards from that. Velly inellesting!! (from Laugh In)

[madkaw]

I would think that the SU's would handle my meager HP even in stock form with SM needles. I have a set of triple Mikunis sitting on a shelf, but I want to get the best tune out of the SU's before I put them on-just so I can compare.

I checked my plugs today and they were still showing a rich condition on the front carb. The rear three plugs had an ideal color-tan. The richness of the front carb might account for the rich afr's at the lower rpm range. I rechecked the needle setting in the piston and it might have been set in just a bit, so maybe that's my richness issue. I also dialed in the mixture a little and will check the plugs after I get back from my 300 mile run.

[Bruce Palmer]

Let us know what happens. Just talked to Steve and we have some ideas but if you have a one carb issue our ideas may not help.

[madkaw]

Initially I thought I had the richness issue solved when i realized that I wasn't getting the mixture knob turned all the way in -on the rich carb- before backing it out(it was hitting the clamp for one of the hoses on the air bonnet and fooling me that it wouldn't turn in anymore). At that point i also pulled the float covers off and saw a layer of soot lying on the bottom of the bowl-which i cleaned out. I then checked the level of the float and it seemed to be adjusted rich. I pulled the needle and seat assembly apart and checked cleanliniess there. After cleaning I noticed that the needle would stick. took some polishing paper to the edges of the assembly and it got better. On initial start the float bowl flooded, but a couple of taps on the side cured that and it idled fine and I drove it like that and it never flooded again.

Since then- as i stated earlier I pulled the piston and checked the needle position-which I believe needed to be pulled out some(but lighting was low so i'm not sure i actually adjusted anything.

Like you said Bruce, i will drive it home and see how the plugs look. I guess I need to get one issue solved at a time.

[John Coffey]

Please correct me if I'm wrong but From what I understand a set of SU's should support anything a 2.4l NA L6 can put out. No?

No. Modified SUs can be made to work with up to about 240hp but you lose a lot of low rpm drivability. After that you need triples or fuel injection.

[John Coffey]

For the mixture issues you can go one size larger on the jet and then run a needle that has a bigger OD at lower rpm and a narrower OD at the upper rpm. That should help the top end without making to bottom too fat.

[Diseazd]

Check post number 30 on this thread (gives my dyno result with SU's and SM needles).The L28 with Stage III Isky and .080 inch shaved head never missed a beat . The A/F was darned near perfect throughout the RPM range. Guy http://www.classiczcars.com/forums/showthread.php?t=31001

Edited August 2, 2010 by Diseazd

[madkaw]

Okay, I believe i have the richness issue resolved on the front carb. pulled the plugs after the 300 mile day and they were clean around the electrode and tan in color. Just a slight darkness at the top of the threads.

Now to move on to the leaness at top end and get the rest of the HP this engine has. You can definitely feel the HP falling off going thru the gears. By the way, the mixture screws are sitting about a turn and a half out.

Also if I haven't stated, timing with a zx dizzy is about 10 at idle and around 35 total.

[Diseazd]

Steve....I noticed that you said you had L28 valves in the L24 head and you bored it out .040 over with a Stage II cam. Did you use the larger intake and exhaust valves or just exhaust valves? Did you notch the block before installing the head, or did you just bore it out and bolt it up. The reason I'm asking is because I'm in the process of building 2 L24's bored .040 over with E31 heads and L28 intake and exhaust valves. Did you have any valve clearance problems with the larger valves? Thanks Guy