WHAT'S LIMITING MY POWER?!?!

I have been trying to follow this thread...let's see if I have it right:

1. One carb spits up badly

2. Revs fine to 5-5500 range both out of gear and under load...then just won't go any higher in either case...and doesn't sputter etc. at max RPM

Anything else pertinent that I missed???

 

Also found this...talks about spitting, and other carb/fuel related issues:

http://www.championparts.com/carb_troubleshooting_guide.pdf

 

Dale -

You're following correctly so far. That guide is GREAT, insomuch as it made my head spin with all the possibilities of causes, and things I can check. Haven't decided which parts/systems to examine tonight, but we'll just keep checking them off.

 

Well I'm not an Automotive Technician (far from it)...and I think you've been getting a lot of good advice here, (confirmed I think with some web searches I've done)...I've only posted the diagnostic listing link, because I thought it might help with the carb spitting, since I had no good ideas of my own on what might be causing that.

I would have guessed (with my limited knowledge) that limited fuel supply would have manifested itself in some sputter and/or jerking or something like that...but I found at least one webpage that said just loss of power might result etc...

If you were in a shop...maybe it would be possible to check fuel pressure and delivery at the hose that feeds the carbs, maybe to eliminate that possibility...but again I'm just guessing on whether that type of testing would work...(or even be a good idea to do).

As a EE, I'm suspecting the ignition system, since it just seems to go limp at a certain RPM (range)...(assuming that the carb spitting issue is a separate problem all together)...but since it's electronic, it may be hard to test/verify without special equipment...(maybe they have a diagnostic port that their computer can be plugged into etc.).

In any case I'm learning a lot from the experts in this thread, and I think you've been getting great advice... and I'm hoping that by posting my summary of your issue(s) it might again help the experts refine their thinking etc....

Anyways, I think you're probably getting pretty close to having this figured out, hopefully anyway....

 

On a carb car, there are brass type filters inside the carbs if i remember correctly. There is a filter from the gas tank to the fuel pump underneath teh car by the fuel pump, and there is a filter (s), at the fuel lines before the carbs. Its been a while, since i converted to TWM throttle bodies. ps, my car ran great up to 5k with the clogged filter, and sputtered out after that. Now, with the new filter, its like a new car...

 

If this is true, and it behaves the same with no load and with load, then the mystery is over. It is your rev limiter or a timing issue. In my opinion, the fuel needed for these two conditions varies enough to rule out the fuel pump or filters.

 

Concur.

 

Could also just be a bad carb (either crapping out or idle balance incorrectly set).

 

You could have that, but the 5000 rpm rev limit issue is not going to be from it.

I concur with the above on the fuel issue: A clogged fuel filter will do more to limit your max speed but not really limit your max revs, especially on a carb car where the float bowls act as a reserve supply for a short period.

 

I'm actually beginning to suspect a bad float somewhere. Gonna take apart the carbs as soon as the rebuild kit comes. I don't want to start pulling fuel lines to check all that stuff before I have all my parts ready to go, because then I can't continue to fire her up and check ignition stuff.

 

Timing wise, could valve timing issues also be eliminated as a potential cause...that is let's say e.g. one timing belt was one tooth off...how would it act then?

If valve timing is eliminated, then does that leave just the ignition...(at least with what we know so far)...and if so, after installation could the ignition timing pickup (I think it's optical) have become maybe misaligned (or whatever)...or would it rather seem then like something in the ignition control box (malfunction and/or setting) is not right etc....

 

Basically, the ONLY IGNITION POSSIBILITIES left are:

1) The Unit itself is faulty, and the control dials aren't related to actual performance. If so, it might explain why there's a rev limit dialed in, which no adjusting of the limiter knob can dial out. Alternatively, or even concurrently, a faulty unit could be misfiring the coils. Again, my friend would need to come back over with his timing light (planned this weekend) to double-check the advance at the flywheel, against the dial settings.

2) That alleged jumper (that I cannot locate) between the Direct Fire Units for each bank is reversed, and throwing off timing. It is NOT illustrated in the manual, which shows that each DFU is wired directly to the control unit.

3) Perhaps my installer did not set the 11th tooth on the trigger wheel at TDC, throwing the timing sequence off, although I suspect he got everything right. So far, all his install work has checked out exactly by the Nick's Forza book.

4) I simply haven't nailed the right ignition advance settings that my particular motor desires.

** We KNOW both banks are firing, the wires are on the correct plugs and coil terminals, it's wired from a legit power source, and it - along with the motor and battery - is properly grounded.

POSSIBLE FUEL PROBLEMS:

1) Could be actual mechanical failure of a carb or carbs. That would include a bad float or other internals. Will check during rebuild whenever the kits arrive from Europe, maybe NEXT weekend.

2) Could be starvation from lack of fuel pump pressure OR flow rate. Need to go out and buy a gauge to hook up.

3) Could be a clogged check valve, fuel filter, gas line, or tank/carb filter. Replacing all those is my very next project. *HAVEN'T been able to source the tank filters, or any good process for cleaning the TANKS themselves, if someone wants to chime in.

4) Carbs may not have been properly synch'ed. I don't have a CO2 tester, but my schnozz can tell you that we have a serious problem. I WILL break out my Weber synchrometer to check balance between the throats during the weekend MegaDiagnostic. I DO, however, trust the mechanic who did it.

**We KNOW that the car starts up easily enough but does not like to stay on without keeping the revs above 1500 for a minute or two while it warms up (sputters out otherwise). Once running, there's eye-stinging fuel stench and lots of carb popping/spitting. Runs fine, but only up to 80mph or 5500 revs, and occasionally backfires on shutdown. We do NOT necessarily believe that a simple one-step bump up in jetting would cause this fuel-spitting behavior or observed rich stench.

COULD BE A VACUUM PROBLEM:

1) The exhaust appears to be unobstructed (although I may pull the muffler and run it with open headers to verify this weekend).

2) Could be a bad engine valve, which I will check via Saabguy's test of turning the engine without the ignition on, and seeing if fuel still spits out. That said, car passed a compression test during PPI with flying colors, and my limited understanding of professional mechanics tells me that if a valve isn't working right, the cylinder should lose at least some compression.........

3) .....which leaves: The amateur, undeserving, pseudo-shadetree-mechanic moron putz previous owner, who tried to service this himself out of dormancy before I bought it, mistimed the cams. This is something I am not even remotely comfortable trying to properly diagnose, let alone repair, so it will go to a local master mechanic as a last resort there. I'd prefer not to have to undertake a major this season, but will do what's necessary.

MISCELLANEOUS DATA POINTS:

1) On my second drive, we got caught in a bad flash rainstorm. When I cranked the wipers up to high, along with high beams and cabin fan, got an alternator warning light and had to kill the wipers and fan. Should perhaps check alternator.

2) Only other thing I've done mechanically (besides electromotive and upjetting) since delivery was IMMEDIATELY install a birdman fusebox. I DID have some trouble wiggling a few connectors fully onto the splitter terminal prongs, which I asked him about. I've been monitoring the new blocks, and no heat or smoking, so it seems okay. Definitely hooked everything up correctly, and found the right fuse amperages.

That should bring everyone up to speed. By all means, please chime in with thoughts if you think I missed covering any bases or want to fill in any blanks.

Your support has been EXTREMELY APPRECIATED, more so than I could ever express. Many thanks!!! I owe some of you a nice meal next time you're in the Windy City

 

Good luck....

 

I've only been following this casually but here are a couple ideas. First, any chance you can take it out and record it while it gets up around the 5000rpm issue? It might make a big difference.

Also this may sound like two stupid ideas and I know one has already been discussed but... You do know the cylinder order goes in a horseshoe pattern starting with #1 at rear right looking from behind the car right? The second is to shoot some carb cleaner down each throat just to clean 'em up a bit.

As for filters the one in the tank is just a screen and may be just about gone if it is anything like mine was. It's also not going to do much but catch really big debris. The primary filter is the canister next to the fuel pump.

 

All depends the weather. I'm planning to shoot some video of the carbs during starting, and idling in the garage to show - and convey the AUDIO - of the carbs spitting and popping. As for taking her on the road, I think it's supposed to be frigid and rainy this weekend. It's not the rain that concerns me, but how deep are the potholes that the puddles conceal here. A test drive may need to wait a week or so. I have a huge can of carb cleaner spray. The spitting was SO bad last time I had her on, I actually got nervous to get near the things while the car was on.

 

Vacuum leaks do not cause a lack of power because there is very little manifold vacuum at high load.

Rich carbs won't cause the power to go away at 5k. The repeated statement that the RPM restriction occurs regardless of load (out on the road) or no-load (in neutral) rules out the carbs as the cause of the problem. They may be badly in need of overhaul/adjustment but they are not causing the RPM limitation.

Valve timing could do it but how would the timing have gotten so far off with a simple belt change by anyone who understands the process?

Ignition remains - IMO - the most likely cause.

Incorrect valve or Ign timing can both cause spitting back through the carbs

It will be interesting to hear what the final outcome is.

One of the big issues here is that there is too much being done at one time. I realize that with the condition of the car, it seemed like installing a new ignition/other work was the way to go but this is a good example of what happens when things go awry. It becomes a death march trying to sort out what happened because too much was changed at one time.

I know this is absolutely no help at all now but it would have been better to have gotten the car to run properly in stock condition before changing anything from known to unknown.

 

Yeah, Mike, you are definitely correct. If I had it to do over again, I would have restored stock specs first. One option I want to look at tonight is turning the ignition rev limiter ALL THE WAY UP. According to the manual, setting it above 15,500 revs actually deactivates it. A quick and easy check, ASSUMING THE UNIT ISN'T FAULTY and the knobs actually do what they're supposed to.

For what it's worth, I (somewhat grudgingly) don't mind having to run all these checks and potentially address all these other peripheral systems because it all SHOULD be done anyway on a 36-year-old car. Wasn't expecting to have to do all this before enjoying my first quality drive, but I'll be happier knowing we thoroughly went through everything.

 

UFI, I have one I can get the number...

 

Conversely, how LOW can you set the rev limiter?
I'd try that, too.

 

Interesting. That would verify that the limiter works at all...

 

+100. The amount of fuel required to rev in neutral and power the car to some speed are very different yet your symptoms are the same. You might have a carb issue as well.

I can tell you really want this to be an alternator problem.

 

Honestly, I'm beginning to think we may be dealing with symptoms of two different issues.

 

While you are doing your tests, put in a new set of plugs. Over the years, I've had bad / marginal plugs right out of the box. Just another variable to eliminate.

 

Had a disastrous time getting the cheap timing light I purchased to actually work, so I didn't get the strobe verification I wanted. BUT....

With the benefit of nearly 200 responses worth of insight into my issues, I now believe we are/were dealing with multiple problem sources.

- First, I tried a bunch of new ignition dial combinations. 13* initial, 18*@3,000, and 8 more@8,000 got it purring MUCH more smoothly. With the airbox lid on, couldn't tell if the carbs were still spitting (they still were a little rough-sounding), but the car sounded and felt much healthier.

- During warmup, I observed something I hadn't noticed before regarding the muffler. When I checked last week, it was a cold night and I could clearly see exhaust coming from both sides on startup. TODAY, after a few minutes of warming, I checked the tips again. On the left-hand side, I put up my open palm and could feel pulses of warm air hitting it. On the right-hand side, I could feel heat, but no forceful bursts of air. On that same right-hand side, I also noticed a ton of condensation building around the inner lip of the exhaust tips. I may have overlooked a real exhaust obstruction at the muffler (unless it was gas that hadn't been detonating).

- I deactivated the rev limiter entirely, and was able to get it well into the 6k range, at idle. Flooring it in lower gears, I now can get it around 6k, but still VERY sluggish on the road, more than I think I initially noticed. It will pull to 80mph, but SLOWLY. Acceleration is LINEAR, but very slow, and feels straining. This newfound ability to get higher revs could be due to better ignition timing.

THEREFORE, pending a bunch more tests tomorrow, I'm thinking we had a mis-timed ignition, (possibly) a mis-tuned carb, a muffler obstruction, AND - since I can get higher revs at idle than under load - maybe a fueling issue.

Tomorrow, I pull the muffler, try again to get the timing light to work, use two different spark testers on the wires and plug ends, and Saabguy's test for bad valve.

First pic is the left-hand exhaust tips. The second pic had to be taken with a flash to show the issue, but that's liquid vapor collecting around the right-hand tips...
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I know several people have mentioned before to check the cam timing? It may have jumped a tooth (or perhaps more than one) on the pulley?

Just a thought - could I suggest you take a quick look at this article (from FChat member carl888) on Robert Retzlaff's excellent 308 GTB site:

Carls Tech Tip #1

Whilst you are not using the original ignition system, there seem to be some similarities with your symptoms and those described in the tech article.