Sanity check me, por favor

I've been experiencing some fuel issues with the Triumph this week, and I want to pick the collective GRM brain.

'64 Triumph TR4, dual Zenith-Stromberg carbs, fuel cell, inline fuel filter.

I started off with a low-pressure electric pump at the tank (behind the filter) with a pressure regulator holding pressure to 3psi at the carbs.

Started kind of hard. Idled smooth for a minute or two, but then started varying from 800 to 700 to 800 to 600 to 800 to 400 to 800 to stall, with an rpm change cycle time of about 2 or 3 seconds. Would idle passably if the choke was partway closed. Same idle symptoms when warm. Ran and drove, but was down on power under load unless the choke was at least partly closed. Black plugs.

Analysis: starving for gas -> insufficient fuel delivery -> ran okay a month ago without the cell and extra inline filter -> fuel cell outlet/fuel lines aren't blocked -> extra filter must be constricting the flow. Pulled the filter (there's one built into the pump).

Still ran like crap. Fuel delivery was better. Same symptoms, just took it longer to start showing them.

Pulled the carbs, checked float level (was okay), diaphram condition (was okay), damper oil (was okay). Reinstalled, same symptoms.

Rebuilt the mechanical fuel pump, reinstalled, replumbed the fuel line with the inline filter but without the electric fuel pump. Didn't get a chance to get it out of the garage, so I don't know if the loaded symptoms are the same, but the other symptoms are the same.

At this point, I'm thinking I need to check for good strong spark. Assuming the spark is good (should be, brand new coil/distributor with electronic ignition/plug wires/plugs), I'm thinking the carbs are set too lean.

What say ye?

Sounds right, although to be absolutely sure the fuel tank isn't at fault, try running it with the mechanical pump feeding from some gas in a container. If it still doesn't work you can be pretty sure it's either a spark problem or a blockage in the carbs - you didn't change the carb settings so if they're suddenly running lean, something is wrong.

Thanks, Gameboy. I haven't changed the mixture on the carbs in the past 6 months (sat for several years before that), so it isn't a recent incorrect mixture adjustment that's throwing me off.

Maybe its still not getting gas fast enough to keep up with demand, and is starving out (which would explain why it idles okay for a while, then gets progressively worse until it dies, and why it feels down on power even with the choke fully closed under load). I'm not sure if the symptoms I'm getting correspond to lean or rich, and hate to go charging into something without knowing more or less where I'm starting from. The plugs are carbon-ed up, but that may have more to do with running it with the choke closed than mixture.

I've always heard "90% of carb problems are ignition/ timing related", so I like to double and triple check before I go adjusting carb settings.

If it was too rich closing the choke should make it worse.

You are right that 90% of carb problems are ignition and it's good you've gone to that side. At my shop (Eclectic Motorworks), we start all driveability/tuning work with a check of the dwell (if there are still points), timing at idle (vac disconnected), timing with advance fully in (about 3500 RPM and again, vac disconnected). Dwell should be close to 60 for a TR4, idle timing should be around 15-20BTDC and fully in should be near 32-34 BTDC. Plug wires, etc. should be good too. Spark should be strong enough to jump 1/2" or more.

Once you've eliminated the ignition, go to the carbs. People often jump very quickly to fuel pressure or feed, but if your problem is primarily at idle, lack of fuel is rarely the issue. These cars will often idle for 1-2 minutes with the fuel in the float bowl. Sometimes the car can drive a block or two if an electric pump has shut off--the float bowls hold that much. Generally fuel delivery issues play out at high rpm--the engine just runs out of steam above 3500 RPM for example.

We have seen several cars that had liners in the tanks that pealed off due to our friends at the ethanol/corn lobby and I guess there is a chance your fuel cell is damaged and blocking the pickup, but that would play out more on driving than at idle.

Since your idle is varying so much, I'd first look for vacuum leaks by spraying carb cleaner around the mounting bases and throttle shafts. If idle quality improves, you've got vacuum leaks to address.

Next, I'd do a partial disassembly of the carbs to look for physical problems, dirt, etc. Looks like you've already done that, but it may be worth doing again--sometimes I've missed things the first time.

If I were betting, I'd bet you've got two or three small problems aggregated to make a large problem. We see this all the time--maybe you've got slightly weak spark with a couple of small vacuum leaks. None of these by themselves would be a big deal, but when combined they are frustrating. So if you find one problem, keep going as you may find another before you get it completely licked.

--Carl

Having to use the choke indicates a lean mixture. On thing often overlooked, Fuel pressure may be fine but violume is not.

Agreed.

I may be overthinking it, but (for the sake of arguement) if it was too rich, could it be asking for gas faster than the fuel pump is delivering? This (overthinking again) would run the fuel level in the bowl down to the point that it would actually starve/lean out unless the choke was pulled (thereby reducing the increasing the fuel:air ratio back toward the correct mixture). If this were the case, the carbs would be delivering a mixture that was usable, but in lower-than-ideal volume, so it would be down on power...

Its probably just real lean, and excessive choke use is jacking with the plug condition.

My money is on vacuum. Air is getting in somewhere.

The fuel pump can deliver something like 1 quart of fuel per minute. I've never seen a choke drain the float bowls. (I have seen cars with over a gallon of fuel in the oil when the choke got left on for extended periods!)

You can check fuel delivery as Gameboy suggests by cranking the engine and running the fuel into a container. If it dribbles out, you've got a fuel delivery issue, but if it starts filling fairly well, you're in great shape.

If you've got vacuum leaks, you're running lean, and pulling the choke will compensate. That's much more likely than a delivery problem.

--Carl

Thanks, Carl.

I'm using a Pertronix Ignitor distributor with a Flamethrower coil.

The fuel cell shouldn't be an issue (in terms of liner, anyway) as it is brand spanking new. Haven't burned through the first fill-up yet.

Idle is mostly okay, no issues to speak of if you use 20-30% choke. I can't use enough choke at speed though; wants to stall out anywhere above 2k rpm.

Carbs are clean.

I suspect that this IS multiple small issues working together to screw me around. I'd bet even money the throttle shafts are a little leaky, and I wouldn't be surprised if the mixture is a little off. I'd be really impressed if I've got spark enough to jump 1/2" , but I'll have a look.

Okay, vacuum. I'll play this game. Where could I be getting a high pitch whistle/whine at idle? Passenger side, in the general vicinity of the rear carb.

I'm second-guessing myself now; with dual carbs, is there supposed to be a vacuum connection to BOTH carbs or just one?

spray carb cleaner in that direction. If there is a leak, it will pull it in and idle faster. It should help pinpoint it.

Be sure to wear safety glasses. I've heard that if you get carb cleaner in your eye you'll wish it was brake cleaner instead. I know that even a few airborne droplets of brake cleaner can hurt like hell.

I'm on my lunch break, ran home to tinker with the car.

Spark will jump 1/4" fairly consistently. Don't have any carb cleaner, but ether on the throttle shaft bushings didn't change the idle. That said, the throttle shafts have about 1/32" play side-to-side.

This is driving me bonkers.

Order of business.

1. Check/clean plugs, plug wire connection points.

2. Check/rectify ignition timing.

3. Test drive to warm up car/see if ignition fixed the problem.

4. If problem persists, synchronize carbs and adjust fuel mixture per owners manual.

5. Test drive to warm up/see if carbs fixed the problem.

6. If problem persists, check plugs for mixture problems, adjust as required.

7. If problem persists, re-check vacuum with carb cleaner.

8. Adjust valve lash (unrelated, noticed over lunch that they're making more noise than I'd like).

9. Once its right, change the oil.

What am I missing?

JohnInKansas wrote: What am I missing?

LSX swap?

Sorry, you knew one of us fools was bound to say it.

Carl Heideman wrote: If I were betting, I'd bet you've got two or three small problems aggregated to make a large problem. We see this all the time--maybe you've got slightly weak spark with a couple of small vacuum leaks. None of these by themselves would be a big deal, but when combined they are frustrating. So if you find one problem, keep going as you may find another before you get it completely licked. --Carl

NAIL on the HEAD. Its amazing how many times 2 or 3 unrealted failures will surface at once. It 's hard to let your mind think that it's even possible sometimes.

EDIT!! make sure the fuel cell is vented!

jhaas wrote: EDIT!! make sure the fuel cell is vented!

Thought of that already, thanks.

I'd say either ignition timing, or more likely a leak of some sort. Could be the carb base gasket, intake gasket, or an unplugged/pinhole leak vacuum line.

My money is on vacuum leak. Spray carb cleaner at the joint between the head and intake while the engine's running (have a fire extinguisher handy!). Many times I have seen old gaskets that sealed cold but not hot and vice versa. If a nut or bolt is missing from the manifold that is a HUGE possibility.

Don't forget to shoot it at the underside of the manifold/head junction. Sometimes you can grab the intake and wiggle it, look for changes in idle etc.

Well, I lost a bunch of work time to errands, but I had time to get through 1 through 6 on my list. Too late to get carb cleaner by the time I got back in town, so I'll do that tomorrow.

Timing was dead on. Plugs were a tad wide, narrowed them up a few thousandths. Tinkered with the carbs, decided I didn't like the slide action (it felt like it needed some lubing), so I cleaned the slide bores, slides, caps, and reassembled (MUCH nicer). Set the mixture according to the Haynes manual (tighten until metering nozzle just touches the bottom of the slide, then back the other direction 3 turns). No dice, same symptoms. Just got back to the house, went and did 6 or 7 two-mile loops, adjusting the carbs a little richer each time. I'm now 2.25 turns richer than the manual suggests, same symptoms (though the butt dyno liked it better the richer I went). Idles much smoother and slower now than it did before the 15 mile test-and-tune session. Seems much more willing to take off in 1st without stalling or bogging down as well. Doesn't want choke until 3.5k in 1st, 2k in all others (though there is a sweet spot in 4th where, if you hold the throttle just right, you don't need choke and it will gradually accellerate). Plugs 1 and 2 look pretty damn close (clean, with just a touch of tan), while 3 and 4 look like they're a bit rich (3's dry and sooty, 4's dry and sooty with some carbon deposits).

I suspect I've got a vacuum leak (as, it appears, does everyone else). I'll get some carb cleaner tomorrow and see if I can track it down.

In the meantime, I've broken my tach cable, blown the relay on the temp-sensing fan switch, and (I think) toasted my alternator. Hooray for crappy old cars.

Yeah, I've learned over the years that with SU's or 'Bergs a vacuum leak at one on a multi carb setup will make the cylinders fed by that carb run rich. No, I have no idea of why; I kept trying to figure it out and finally said the hell with it, I just accept that it's some weird British trick.

That whistle you're hearing is very likely a leak. The carb clean will help you find it. We never mess with anything else in a tune up until we've verified perfect ignition and no vacuum leaks. You can't do any carb tuning if the timing is off, same thing with vacuum leaks.

The higher RPM/non idle troubles probably are not vacuum leaks. I'd consider ignition again (did you check it at high RPM?), or something weird like an overheating coil (do you have a ballasted coil with no ballast resister?). If these ignition tests still show no trouble, then fuel issues come back into question. Partially plugged jets will show trouble at higher RPMs, sticking needle/seats, float height issues (did you accidentally put the floats in upside down?--I've done that when I've been in a hurry). And of course fuel delivery could be a problem even though it's unlikely--did you check with a can?

Finally, you said your fuel cell is brand new. Did it run fine before you installed that? Then I'd look at the venting or something weird with the internal pickup.

But I think you have vacuum leaks too. I still think you're chasing multiple problems.

--Carl

Here's a rough representation of where the fuel cell is relative to the pump, and relative to where the tank used to be.

I'll see how fast the pump is moving gas this afternoon.

Well, it does look like this may be something after all. If the tank is now below the pump, the pump could be losing its prime or just plain having trouble sucking the fuel uphill. The stock tank will gravity feed fuel to the pump, this one may not. A lot of pumps aren't very good at sucking fuel above the tank.

--Carl