3x2 carbs installed, check for leanness?

[Dan Baldwin]

Sorry for the cross-post. Just installed my new used 3x2 45mm OER Racing carbs. Car runs fine, but limited to ~70% throttle at the moment.

Anyway, I need to know if I'm running OK (not lean) so I don't hole a piston or something. Don't have time to get to the dyno before track days this weekend, and don't have an A/F or exh. temp meter.

 

All informed opinions/thoughts welcomed!

 

Thanks,

[Tim240z]

Easiest way I can think of is to do a plug cut and remove and inspect the plugs, or just take it to a shop that has an exhaust gas analyzer (best way).

Tim

[Bob_H]

I was going to reply to the list, but you have it here, so this is better. You really need to find time to run a dyno with a exhaust analyzer if you can. You want to run the piss out of the car for the weekend and you have no idea what the jetting is like. Remember how far off my jetting was when I first started, and it was "supposedly" from a tuned 3.0L motor. It was so lean, I would have burned several pistons if I drove it hard for any period of time. It idled and pulled fine. And free reving with an analyzer is not the answer either. If you can't get a dyno, get a shop that has an analyzer and rollers to let the car be loaded up.

You ran it on the dyno before, find the time so you don't kill the motor this weekend...

-Bob

Instilling the fear of motor breakage in a town near you...

[Dan Baldwin]

Thanks, Bobby, for the slap upside the head. Scheduled to be at New England Dyno tomorrow at 8:30. But now I have to solve the rear carb pissing fuel out the air horns with the fuel pump on, motor off. Guess it's the needle jet. I'd cleaned them out as best as I could. Any ideas on how to rehabilitate one?

 

Thanks as always!

[Ruben]

It could just be that you need to adjust the float level on the rear carb. If you have already checked the float level then it must be the needle valve gone bad. I'm not aware of any way to fix a needle valve aside from replacing it.

 

Ruben

'72 240Z

[Bob_H]

So you think you can join me at Summit point Nov 2-3 with NASA? I'll have the Z there, last time on the track before I start the RB swap!

Glad to hear you have some dyno time scheduled.

AS for the rear carb dumping fuel, it is clearly the float valve/seat, -I assume that is what you mean by needle jet,(valve?).

If you have cleaned it well, and it is metal to metal,(vice some are rubber to metal), then think about putting the needle down into the seat, then tapping it lightly with a hammer to form the seat better. It should be a steel,(silver), needle with a brass seat. You might be able to take them both out and see if they are sealing well. Do you have a psi gauge hooked up to see what pressure you are actually running? Something to consider playing with on the dyno as well,(assuming timing is fairly close, you should be looking at about ~36 degrees total). I run 3.5-4 psi. If you run much more than that, you can very easily overpower the float valve. I assume you have some form of pressure regulator? I am running a holley one, and it is almost backed all the way out to get the low psi I need. You have been spoiled with SU's that can have gross jets that seal much better and can deal with more pressure. An option to consider. You can pick up a cheap-o pressure regulator at autozone or similar. Just plumb it in line to the carbs. I put my pressure gauge btw carb #2 and #3. Bought it at Autozone, the holley Fuel pressure regulator I ordered.

But ~3.5, max of 4 psi for those carbs.

BTW, food for thought on this problem. It pisses out of the carb airhorns when the motor is not running. That means it is likely spilling over into the motor when it is running. I'll bet #5 and #6 spark plugs are running rich.... I would also check the float level...And check to see if the floats still "float". If they are like mine, they can't sink. If they are like weber carbs, they can get a hole in the float and sink...easy fix, drain the fuel in the floats, epoxy the hole, race away.

 

-Bob

[Bob_H]

oh, one more thing about the carbs frequent need to urinate. Is this when the motor is cold as well? Or is it only when the motor is hot, or has been idling for a while? If the second case is true, you have the same problem I have, too much heat in the rear carbs. Driving is no problem, b/c their is airflow through the engine compartment. However, that is not true when idling or driving slow. I can hardly touch the last carb, but the front carb is not too hot at all.

FWIW,

bob

[Dan Baldwin]

Just put 'em on last night, I think the pissing problem is sporadic. It's not the floats, I took 'em out and the don't have any fuel in them. Played w/ the needle VALVE and now it's sealed up fine. If it happened once, though...

Oh yeah, went to start the car and "rurr rurr ruNH.....". Hydrolocked either #5 or #6 while I was running the pump w/ the engine off. No prob, removed the plugs and now all is fine. Did a half-assed job of synching the carbs with the Uni-Syn. As long as it idles and all 6 throttle butterflies are fully open at WOT, I'm happy with it. Actually, it idles better than it did with the SUs!

 

Regarding the dyno trip, they'll be doing A/F, but won't have a Weber expert on hand. Have any handy rules of thumb what to fiddle with for different scenarios?

Like: lean on bottom/rich on top, vice versa, in the middle, during acceleration, etc. Since I don't have any jets, if I'm way off I'll either have to drill out what I've got, fill in with solder and drill smaller, or forget it and put the SUs back on.

 

Can't really tell if the car's slower or faster, but I know for sure it's LOUDER. Gotta be good for somethin.

 

Talk to ya tomorrow.

[Dan Baldwin]

Oh yeah, I had set the fuel pressure at just under 3.5 psi, then found the liquid filled Summit gauge was leaking at the pipe threads. Took it out and applied some pipe dope, no more leak but the pressure went up to 5 or so. That's when the rear carb started pissing, I think. Removed air filter and fuel streams were coming out of 5 and 6. I fiddled with the valve on the carb and reset the fuel pressure. Anyway, it guess it's *possible* that the brief 5psi fuel pressure mighta unseated the valve.

 

G'night now, gotta git home.

[Lockjaw]

I am with the suggestion of checking plugs because you have an individual venturi for each cylinder.

 

If you have a weber, I can get you in the ball park jetting wise, and then you can tweek it from there. Esssentially take the choke diameter times 4 and that is your main jet size. Add 60 and that is your air corrector size. Increasing the main jet adds more fuel, increasing the air corrector adds more air. Dropping the air corrector decreases air. I always tried to keep the spread close to 60 on mine.

 

You would have to be way off to put a hole in a piston, and I would think the engine would not run properly to the point you would know. That is my opinion, so if some of you disagree with me, that is ok too.

 

The absolute best way to tune it is to have an egt on each cylinder, but that is pricey, and not likely to be cost effective.

[Bob_H]

I wouldn't worry to much as long as the A/F is below ~13 the entire run. If you are too rich up top, it is an air corrector change,(can't remember which way), but I'd leave it for this weekend. To rich down low, mains,(smaller). That is real general. Accelerator, etc.., self explanatory for throttle tip in, etc.. Start to worry if you are seeing above about 13.5:1 as the rpms go up. You can deal with some leanness downlow, but stay away up top. About 12.5:1 for the run is nearly perfect. If you see 9 or 10:1, drop a main jet size. Of course, soldering up 6 jets and redrilling them is way fun I'm sure. I'd leave it fat as a pig if it is rich and order the smaller ones for later. If it is lean, drilling is much eaiser. Again, lean down low, but getting fat up top or staying close to the same, increase main size one tick. Good down low, getting lean up top, I think it is smaller air corrector. And I think going to a bigger air corrector is called for if it gets rich as the rpm's rise. It makes sense, but I'm cya,(well, cma) on this one, I don't know for sure. Get a good printout and I'll swing it by my guy next week to see what he suggests. Get a printout with the A/F graph for the run at the bottom. If you can't get it scanned in, see if the shop can give you a .jpg of the file on disk.

Word racer dude,

Bob

ps- you work too late! you are always at work when I am at home getting ready for bed!

edit-by up high and down low, I am refering to RPM. Lean at low rpm, increase main jet, fat at low rpm, decrease main. lean up top, smaller air corrector. the more I think about it, the more i recall that is what we were looking at. the mains are the big one to monkey with. the air corrector helps the higher rpms and fine tunes the a/f up there. think about it, smaller hole, less air and more fuel to mix in the emulsion tube, meaning more fuel available for the main to spit into the carb. yea, lean up top, decrease air corrector. by up top, i would say 4000 rpm +.

[Lockjaw]

Now I do not like drilling jets at all. When I bought my car that came with webers along time ago, the previous owner had done that. You completely loose the calibration.

 

Jets are light enough to have someone stick them in a fedex and overnight them. Thats me though.

[Dan Baldwin]

Hey all, just got in to work after a morning at the dyno. The good news is: 235 at the rear wheels! I was hoping for like 215 max! Guess I should try to scan the runs in, but the jist (gist?) of it is: I'm PIG rich from 4000 to 5000, not too bad everywhere else. Here's a rundown of the runs:

1: aborted (mad shuddering from resonance of bogging engine and dyno drum at low rpm/full throttle).

Upped ignition advance upon advice of dyno guy (1 tick from I *think* 18 deg).

2: 212hp@6500. 125 lb-ft at 2500, 170@3500, 165@4200, 180@5000, 175@6250, 155@6900

A/F >11 2500-2800, 12-12.5 3000-3500, below 10 @ 4400, ~12 5000-5500, 13 - 13.4 6200+

 

Retarded ignition timing 1 tick, back to where it was (I *think* the ticks on the distributor base are 2deg)

3: 229hp@6500. similar torque curve, similar A/F curve

 

dyno guy leaned out the idle screws some

4: 226hp@6700, similar torque and idle curves

 

Retarded ignition timing another tick

5: 235hp@6700

 

Retarded timing yet another tick

6: 235hp@6500, broader peak

 

Retarded 1/2 tick

7: 235hp@6500, slightly broader peak, A/F same as before EXCEPT with a less pronounced rich zone, 4300-4900, AND climbing from 12.9@6500 to 13.9@6500+

 

Seems to me the midrange rich spot could be fixed by smaller main fuel and air corrector jets, from 165 and 220 to more like lockjaw's rule of thumb, which'd be 150 and 210 for me.

 

Whaddaya think?

[Dan Baldwin]

That shoulda been LESS than 11 A/F from 2500-2800.

[Lockjaw]

I don't think you want to step down 3 sizes on the main jet. That is a lot. What emulsion tube you running?

 

Well I have differing theories on carbs too. People always want to move them around on cars, and then start changing jets and stuff.

 

My rule is this. A carb should be jetted for what it can flow, and the AF ratio you want. Once you are there, you chould be able to interchange it on any datsun engine.

 

I could do that with mine. Didn't matter if they were on a stock 2.4, or a maxed out 2.8.

 

What are the spec's on your engine. Just kind of curious.

[Mike C]

Wow! 235 at the wheels with an NA motor? I don't remember specs on your engine Dan, would you refresh me? I'm going to drop my L28 and triple Del'Lortos in my 240 in the next few weeks, I hope.

[Bob_H]

something about "near race cam" specs. like .550 or .590 lift and 310+ duration. That and $1000 worth of sunbelt head work. Yea, that will help. My poor cam is tiny in comparison, practically stock.

Remember folks, his is a near race setup, that he occasionally drives on the street,(dan would disagree ). He wants to win his class in the time trials with COMSSC.

Great numbers Dan. Quite a jump from the 175-180 with the SU's and the still quite big .500 lift 300 duration cam. I guess that goes to show Sunbelt must have a rough idea of what they are doing with that new grind!

-Bob

edit-btw, his motor and mine are very similar. 3.1L, 89mm pistons ground to flat tops,(both had dishes). 0 deck height. He runs the N-42 reworked by sunbelt with their new proprietary grind, and near race specs. Just a tick below John C's cam in size. I think,(not sure), that he has the Nissmo header. Electronic ignition, and that's about it. Other than our heads and cams, we have the same motors, he has 45's carbs I have 40's, he has OER, I have SK.

And no, I won't go into the "N-42 is a better head, see!", cause I'd love to see my head with similar work! ). But I put the priority on the RB swap, so that won't happen.

[Lockjaw]

That is a big cam. We always toyed with the idea of trying one that big, but always chickened out. The biggest we ever ran was a custom crower that was 280 duration and .500 lift. The guy experimented with it in a hydraulic head, and you know the rest.

 

Sent it back to crower and they fixed it, and it wound up with more duration and slightly less lift. I think it was about 292 duration and .490 lift.

 

Whatever it ended up, that sucker came up on the cam about 3500 and it pulled cleanly right off the tach in the guys car. The funny thing was, it did not sound like he was turning it that tight.

 

We always got accused of having a v8 when running that cam too. Kind of funny.

 

So what are OER carbs? I am not familiar with that one.

[Bob_H]

SK was obviously a japanese company that combined the "best" of the weber and mukini's. They are no longer in business, and OER is sort of the replacement. When Dan came to see me, we had each carb apart next to each other. They are very similar, still being a combination of weber and mukini. I don't know if they are still in business. Dan bought it from a guy in Japan who had it on a 3.0 or 3.1 motor.

The beauty of sunbelts grinds is they allow that kind of lift with stock or less spring pressures. Quite an accomplishment. So no worrying about running 200lb seat pressures and 400+ lb open pressures. As long as you can fit the cam in,(i.e. not touch the pistons), you are fine. Dan is really close right now to hitting his pistons. He had to retard the cam one hole to ensure they didn't hit.

I'll bet he posts sunday night like a little kit with a new bike. You'll be able to see the glee on his face.

-Bob

-Bob

[Dan Baldwin]

Won my class at NHIS (south oval)! 1:15.2 to a 1:15.2 and a 1:15.3. CLOSE. Oh yeah, the best from the better-populated V8/turbo-6 class was 1:16.5.

 

The car ran great, but a little soft in the midrange. Pulled like mad up to the rev limiter, though!

 

Something WILL have to be done about the jetting. Note that on my last run the A/F was at 13.9 up top, and every run was pig rich below 3000 and from about 4200 to 4800. But it did WORK over the weekend! Getting jets for the carbs will be tricky, there's no US rep. I've emailed the company in Japan, and they basically said to wire transfer money to a given Japanese bank account number and they'd send the parts. I dunno...

 

General engine specs:

L28 block bored .120" over, Maxima diesel crank, KA24 pistons (not shaved at all), N42 head shaved ported and mild cc work done by Sunbelt (40.6cc chambers), Sunbelt 302 deg/.550" cam setup w/light springs, 2mm HKS gasket, 10.8:1 CR, 93-octane pump gas, 45 (44?) mm OER Racing (formerly SK) carbs, unknown manifold (not long-runner cannon or S-bend Mikuni), 2" air horns, ITG single big oval filter (BARELY fits), Nismo 6 X 1 3/4" into 2 X 2 1/2" header, Flowmaster collector into 3", 3" Walker race muffler alongside drive shaft, 3" Walker UltraFlow in back.

 

The Sunbelt headwork and cam setup was $1500, well spent I believe! Thanks to katman for talking me into it. Speed sure do cost, the air filter and backing plate was $280!

 

With the 2" SUs, it put 177 to the rear wheels at 5000, BUT was breaking up above that due to a busted spark plug (discover later, AFTER I'd bought a loud-ass fuel pump and an MSD 6-AL to fix the prob). It was on its way to 185-190hp at 5500 or so, I'd bet. So, the Sunbelt work plus 3x2 carbs bought me ~45-50hp! Don't know how much from each mod, but certainly the two complemented each other well. Sunbelt head/cam with the 2" SUs had me 8(!) mph faster at the end of the straights at Watkins Glen and at Mosport. Can't wait to get there again.

 

BTW, ever since I cammed the 3.1 liter it's been accused of being a v8. Sounds like one at idle, but rev it and it's obvious. Lap times, however, contribute to the V8 impression The sound at full song is definitely inline-6 music, however. I like all kinds of music, BTW, I-6, turbo, rotary, v8, V12, I-4, V-twin, etc. (but there is NO worse sound than a GM 2.8 V6/automatic through a loud muffler).