[Tom Vaught]

19 inches of vacuum is a very high cruise number, in my opinion, but basically all of your data as far as rich/lean is out the window unless the fuel level in the bowl is set properly.

I would confirm you actual float settings, before doing any other tuning.

The float level sets the fuel level and the fuel level determines the signal of the booster vs the fuel in the main wells.

Tom V.

[Teej]

Well, at least it's consistent. I took it apart, re-adjusted the float. (Probably back to where it was originally.) And drove in. Definitely drives better than after I had the float level way out, but it's back to the original problem of running rich (well I guess I should say "still" as it never changed). Idle is great at about 14.4 but cruise is still around 10.9-11.3

Double checked the vac level on the drive in also. And it's about as I posted above. The gauge reads 23 at idle, and about 19 cruise. But again, I'd still take that as a relative measurement. My Sears Vac gauge/compression tester said it's about 4 points lower. So call it 19 at idle and 15 at cruise. Still a good vac.

[Willshire]

I find it odd your idle vac is higher than your cruise vac. My tripower is the oposite where i am 14-15 at idle and 18 at cruise. Unless your idle is set a little higher than mine. My tripower is running like crap but perhaps a new set of 62 heads, power piston and jets may fix!

[Tom Vaught]

Originally Posted by Teej

I'm working on the tripower on my '58 and maybe I'm just getting too much information. It started out with a few stumbles and just not quite 'right' and I recently hooked up an LM1 AFR meter to the exhaust and have been chasing things ever since.

It's the stock 1958 370, manual transmission. Originally a 2bbl. I'm using a '57 intake and the carbs are all the small diameter carbs. I could adjust the idle set screws for a decent idle, at about 14.5 AFR but driving at 2500 rpm was getting me about 9.8. WOT was about what I'd say was target with 12.5. I tried smaller jets and that helped a little, but not much. I had #66 in there, tried 64, then all the way down to 57. Still was at 10.3 or so.

Just recently I swapped out the venturi cluster with another center carb I had, and that helped some, now running at about 11.3 during cruise. WOT is still about 12.5.

I don't have the specs on the venturi cluster, but will try to measure everything tomorrow. I'm just wondering where to look next. The 57 jets seem quite small from what I've been reading but its still running rich.

Pulled the plugs, and they look pretty good. Vacuum is great, 20+ at cruise. Timing is what I'd consider normal. 12 Initial. Think it's about 38 total. Vac advance connected to manifold vac. Using the original distributor that is triggering an MSD 6AL and a new coil. Cap and rotor are good. Plug wires are a year or two old. Plugs are R45S.

I'd appreciate any ideas/suggestions or things to look at or try.

Thanks

Thad

I looked up the venturi size on the 1958 Center Carb.
The info I have says the carb has:
"Model 2G: 1-1/4-in. flange, 1-7/16-in. throttle bore, 1-3/32-in. venturi, 278 CFM.

Because the carb is so small, the common method of dialing in the center carb by itself may not work. It could be that the outer carbs, having some air leakage around the throttle shafts/ throttle blades might lean out the cruise if you bolt them back on the engine. As long as you do not open up the secondary carbs you should be able to install one of them at a time and check your cruise air/fuel numbers individually and with all three carbs installed. I would disconnect the linkage on one carb at a time and install a sheet of gasket paper under the outer carb you do not want to test.

It could be the sealing of the carbs was no so good in 1958 and the carb guys intentionally set the air/fuel ratio of the engine at cruise with all three carbs leaking a bit of air.

Tom Vaught

[Teej]

I posted this latest info in the electrical section for some feedback but wanted to add the info here too.

In an effort to make sure the ignition system isn't contributing to my issue, I went to replace the last part that hadn't been updated. The coil. The current coil was a stock style coil that was probably 3 years old. I replaced it with an MSD Blaster SS #8207 and the car started backfiring through the carb as I increased RPM. (Nothing else changed.) Swapped back to the old coil. No backfire.

MSD Tech says the more intense spark is likely jumping inside the cap and an adjustable phasing rotor will help the backfire issue.

Could a weak spark or poorly phased rotor be contributing to my lean running issues?

[dadsformula]

Check your Distributor Cap. Are the contacts Aluminum or Brass? I have had
two separate times that I was left on the side of the road because of the Aluminum
deteriorating in the Caps, and causing the Spark to jump all over the inside of the cap.
Both times changed to a Brass contact and the problem never came back. Something
to consider, as changing a coil should not cause this issue. If you open that
Cap and see Aluminum, also check to see if very small droplets of Aluminum are
scattered inside the Cap. This would be a sure sign of the Aluminum giving up the
fight. First time this happed to me was on a pretty new 1990 Formula. Changed
the Cap and it ran perfect until I sold it 4 years later. If you do have this issue,
it would make tuning that Carb much more difficult, due to the amount of spark scatter
you could be seeing. If the Cap is already brass, this is redundant info but I would
still check that Cap for a crack or some other issue.

[Teej]

Well, I haven't gotten any opinions on the rotor phasing, so I haven't done that yet. (I do have brass contacts in the cap, btw)

But I figured I'd try Tom's thought of all three carbs needing to work together. So I put them back on and something isn't right. I didn't change anything with the center carb and now the car has a serious stumble off idle. Idle is still good at 14.5, but right at tip-in it seems to go way lean(19-20) and stumble. It does this before the linkage to the other carbs actually comes into play. I didn't change anything else. I'm wondering if this is my power valve. I can get a cruise that is decent (13) but it's a lot of work to be past that lean stumble and not into more throttle than I want. It's right at that poit I would typically cruise at...

[Willshire]

Sounds like your outer carbs are leaking air. Mine stumbles too but I have it stripped out so I can't offer any other help.

[Sun Tuned]

Anything been done to the vac advance? Has it been modified any way??
Slotted screw holes? anything wierd?

[Sun Tuned]

How bout the rotor firing tip?

[Teej]

The whole distributor is a brand new MSD 8528 ready to run. So it's a new vac advance, a new rotor, no modifications. Brass rotor firing tip.

If the outer carbs are leaking, wouldn't I get a lean condition at idle as well? It only goes really lean after tip in. I did notice that my vac drops considerably as I start to press past idle. Idle is around 18, at that stumble it's like 6. Sounds like my power valve spring or something but it's weird that it only happened after I put the end carbs on...

[Willshire]

At idle there is enough vac to pull fuel too i think. once the vac drops i would think only air or at least less fuel than at idle through the end carbs.

[Willshire]

Easy way to tell is to plug the the airhorns of the ends to see if the idle changes at all. Do front, then back, then both

[Tom Vaught]

Originally Posted by Teej

Well, I haven't gotten any opinions on the rotor phasing, so I haven't done that yet. (I do have brass contacts in the cap, btw)

But I figured I'd try Tom's thought of all three carbs needing to work together. So I put them back on and something isn't right. I didn't change anything with the center carb and now the car has a serious stumble off idle. Idle is still good at 14.5, but right at tip-in it seems to go way lean(19-20) and stumble. It does this before the linkage to the other carbs actually comes into play. I didn't change anything else. I'm wondering if this is my power valve. I can get a cruise that is decent (13) but it's a lot of work to be past that lean stumble and not into more throttle than I want. It's right at that poit I would typically cruise at...

Like I said in other posts, the accelerator pump covers up the lean hole right off idle.
Bolting on the outer carbs with the springs keeping the linkage/blades closed gets you a 14.5 idle which is close to perfect for a clean idle.

If you remove the linkage between the end carb (rear) and the center carb, you will now have the carbs mounted but only the center carb should be affecting drivability and non wide open throttle conditions. If you have a hesitation right off idle it is usually the pump or the center cluster holes are possibly plugged up. You should see a fuel squirt out of both discharge holes (in the cluster) when you move the center carb throttle lever even slightly.

Tom V.

[Sun Tuned]

Yep, what he said.

I didn't know or at least see where the dist was new. Are the pickup leads polarity correct? If so I still think you need look at carb or vac leak issue.

[Teej]

Played with it again some tonight and tried the shot-gun approach. Tried a whole bunch of stuff at once because I've got to get it running to get to work tomorrow. I'll probably make it to work, but I'm still struggling.

Sun Tuned.. Don't feel bad if you missed that new distributor, this has been a really long thread and I'm not sure I'd even want to read it all. I started out with a stock distributor triggering a 6AL but have been willing to try anything. I had the RTR in my garage so I threw it in there just in case. I'll double check the polarity though, just to be sure.

Pulled the filters and watched the throats with the engine off. I get a good spray from the accelerator pumps on all three. My thinking is that those provide the initial spray of gas before the air has time to pull in anything through the venturi. But if I decide to hold my foot at that spot, the air flow should take over, right?

I then pulled the top off the center carb (again) and checked to make sure everything looked good. Acc pump skirt, spring, ball at the bottom, etc. I tried to get a suction on the port to pull in the power valve plunger, but couldn't make that work so I just decided to swap to the other top I have. Buttoned everything up and went for a drive. End carbs disconnected. Seemed to run OK, but really rich. Basically back to the initial problem that started this thread.

So then I hooked up the end carbs and got that really lean condition and stumble off idle. Took off the linkage from center to rear and rear to front. In the driveway I was at idle, about 14 on the AFR. When I started to push either the front OR the rear idle blades, it went way lean (20+). Granted, I wasn't getting any contribution (air or fuel) from the center carb, but I would have thought I should be still staying within a decent AFR range. They both did the same exact thing though so now I'm not sure how it's supposed to act by doing that. So I opted not to pull the lids off those. Plus they were really hot, I'm not sure what I'd be looking for, and I need at least some sleep tonight.

I can still dial in a solid idle. I still have great vac at idle so if it were a vac leak around a seal or base or something I'd think it would show there. I don't have a can of ether to spray around, but I might try some carb cleaner and see if I find anything.

[carbking]

Tuning on the tripower with the small ends is basically the same as tuning on the tripower with large ends, except easier, as the small ends throttle plates are easier to get to seal.

Suggestion:

REMOVE the end carbs completely, and put on block-off plates.
REMOVE the electronic marvel and put stock points and condensor in the distributor

Now tune the engine. Eliminate so many extra unknowns. I still believe you are going to find the power valve in the center carb open all the time. Being able to run on 57 jets in the center and still rich tells me fuel is coming from the power valve. Why is it open??? Don't know. Perhaps wrong venturi cluster gasket not allowing vacuum to actuating valve? Perhaps incompatible cluster? Swapping parts is risky. Didn't find this spec in your thread, but idle mixture control screws should be out maybe 1 to 1 1/4 turns.

Also would suggest taking Dick's offer of the loan of a known GOOD center carb. If you put it on, and your troubles disappear?????

Once you get the engine purring on the center, then reintroduce the ends, and the electronic marvel one item at a time. If the engine is running well on the center, there should be NO degregation by adding either end carb if the end carb is right.

Jon.

[Teej]

This kind of brings things full circle. I actually started out this thread with a stock distributor (feeding a 6AL) but had a lot of end play in it and was concerned about the advance springs etc. Tried a bunch of things before swapping to the MSD distributor.
I had also already removed the end carbs and only put them back on to test Tom V’s theory that possibly the setup was designed to operate as a whole system and not just with the center carb, given it’s small size.
I know that swapping parts is not optimal, but for trouble shooting, it can sometimes be useful. I swapped in different power valves and still had the same rich condition. I swapped lids (therefor power valve plungers) and still had the rich condition. I tied the power plunger up so it couldn’t contact the valve at all and still had the same rich condition. I tested each valve out of the carb (blowing through it) and both worked as expected. No air at all through until you pressed the button.
(I’m definitely going to take Dick up on his offer to swap it out, I just haven’t been able to catch up with him. )
I also initially tried the idle mix screws 1.5 turns out, but then would adjust them based on the AFR. And I’ve also hooked the AFR to a new car and it reads just like you’d expect at the 14.5-14.7 so I think it’s accurate.

[Teej]

I pulled the end carbs back off last night and we are pretty much right back where I started. Runs pretty decently. No real stumble, good idle etc. But my mixture is WAY rich on cruise, in the range of low 10's. WOT will give me about 11.5, but I don't have a lot of area for that.

Makes me think that my ignition system is running OK. I'll still eventually check the rotor phasing, just because it's weird that it backfired when I swapped coils and nothing else, then went away when it went back. And I did double check the polarity.

[Willshire]

it does sound like your power valve is open when it shouldn't be (at cruise).