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Won't rev over 3500 RPM
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Author:  armyofchuckness [ Thu Jul 06, 2017 7:31 am ]
Post subject:  Won't rev over 3500 RPM
Well, the Flying Valiant is flying again, sort of. I've got it running and driving, and I've clocked a little over 600 miles on it sorting out bugs. We're trying to drive it from Gainesville, FL to Carlisle in five days, and while they engine has been running great, I can't for the life of me get it to rev above 3500 RPM. It acts like there's a stop in the engine and just sits at 3500 in first. Sometimes it will sputter and after a while it will buck and I'll back it down. Here's the specs:

1964 Valiant, 1974 225 bored .060 over.
Ported, polished head with the enginebldr valves, hardened seats, and .100" planed off the head.
Offy 4bbl intake with Eddy 1403 500CFM set one stage lean on power and cruise modes, but it's been giving me trouble at just about any rod jet and spring combo I throw at it.
Recurved electronic distributor from DusterIdiot
Dual Dutra Duals
Erson 280/270 cam
HEI system with Mallory Promaster 29440 coil
Stock fuel pump and filter on 5/16" line routed the SSD way.

We've tried just about every lean combo on the tuning chart. We couldn't get it above 3200 RPM initially, but we set the plunger to the lean setting and put the weakest springs in the carb and we were able to get it to creep up to 3500.

I've adjusted the timing from everything form 10° advance to 30° advance, and that seems to make no difference. Vacuum advance on the car seems to have suction.

I have an o2 sensor and gauge, but it's the Westach needle gauge and a one wire o2 sensor and it's all over the place. I think the sensor might be fouled because the car was running super rich at stock settings which is why we've stuck to lean testing. It still puts out a puff of black smoke on initial startup, but that goes away at idle and friends watching the car haven't seen any black smoke while I was driving it.

Any ideas?
Author:  Dart270 [ Thu Jul 06, 2017 8:33 am ]
Post subject: 
I doubt it is a mixture issue - more likely ignition related.

Did you try swapping coils or plug wires? Try a known good stock coil and see how that works. Is the ballast resistor tailored to the coil you are using? I know nothing about that coil but it looks like crazy overkill to me. A stocker should do just fine in your application.

Could be a distributor reluctor/rotor phasing problem? I had this once and it would work until about 2000 RPM then spit and sputter. I would think it would change some with timing advance, though. Can you put your previous dist in there, or your whole old ign system (points or whatever)?

If you can't figure it out with "new" parts, then go back to the old ones that worked well on your engine before.

Also, did you absolutely verify that the tach is set to 6 cyl instead of 8 cyl? You could be at higher RPM than you think... This sounds crazy, but I know a guy who blew up 2-3 Slants before he figured out the tach was set wrong...

Any chance the cam timing is wrong? If it's really advanced, then it won't rev very high.

For carb changes, try completely disconnecting the secondaries and run on primaries only. Tune mixture from there, then hook up secondaries again. It should rev just fine and make power on the primaries. Or, can you plop an adapter plate and a BBD (or whatever is your old carb) on there to test? I have seen carbs be gummed/plugged from the factory and not work right ever.

A few initial thoughts...

Lou
Author:  sandy in BC [ Thu Jul 06, 2017 9:46 am ]
Post subject: 
a crappy hei module can limit your rpm.
Author:  armyofchuckness [ Thu Jul 06, 2017 10:18 am ]
Post subject: 
Quote:
I doubt it is a mixture issue - more likely ignition related.
I'm leaning towards that too, but there's still some concern it may be a flow issue with the carb. I know we've been able to squeeze another 300 RPM out of the carb, but that could be just from leaning it out a little.
Quote:
Did you try swapping coils or plug wires? Try a known good stock coil and see how that works. Is the ballast resistor tailored to the coil you are using? I know nothing about that coil but it looks like crazy overkill to me. A stocker should do just fine in your application.
Coil and wires are brand new. Wires are Magnecor 7.5s. I don't have a trustworthy old coil. No ballast resistor in the system. I'd be shocked if either were the issue, but it's something to consider.
Quote:
Could be a distributor reluctor/rotor phasing problem? I had this once and it would work until about 2000 RPM then spit and sputter. I would think it would change some with timing advance, though. Can you put your previous dist in there, or your whole old ign system (points or whatever)?
Old distributor was sacrificed as a core for the rebuilt one. I have a new one still in the box on the shelf we can try though. That's the plan for tonight.

Quote:
Also, did you absolutely verify that the tach is set to 6 cyl instead of 8 cyl? You could be at higher RPM than you think... This sounds crazy, but I know a guy who blew up 2-3 Slants before he figured out the tach was set wrong...
Tach was rebuilt by Redline specifically for this engine. The engine will rev up into the 4,500 range when it's in neutral, but not when under load. I did not test to see how high it would go and backed off around 4500.
Quote:
Any chance the cam timing is wrong? If it's really advanced, then it won't rev very high.
I've thought of that too. Charlie put the cam in and we double checked it twice before getting the car running. I really doubt it's that.
Quote:
For carb changes, try completely disconnecting the secondaries and run on primaries only. Tune mixture from there, then hook up secondaries again. It should rev just fine and make power on the primaries. Or, can you plop an adapter plate and a BBD (or whatever is your old carb) on there to test? I have seen carbs be gummed/plugged from the factory and not work right ever.
I traded the old BBD for a discount on the paint job, but I do have a brand new Eddy 1406 600CFM sitting on the shelf. (This 500 is the one you gave me, remember? :wink: ) I may just do a swap out with that and see if the problem goes away, but if it's an ignition problem, that would really save me getting gasoline everywhere.



The module idea is intriguing. It's just an aftermarket module from RockAuto. I have a spare one I could swap out if nothing else works.

Thanks for the advice!
Author:  Dart270 [ Thu Jul 06, 2017 11:06 am ]
Post subject: 
I like the Eddy 1406 carb swap idea, and the distributor and HEI swap idea. If it revs to 4500 in neutral and does not spit/break up/backfire, then reluctor phasing is less likely.

Lou
Author:  afastcuda1970 [ Thu Jul 06, 2017 12:02 pm ]
Post subject: 
Are there any restrictions in the exhaust? Clogged muffler?
Author:  armyofchuckness [ Thu Jul 06, 2017 1:14 pm ]
Post subject: 
Exhaust is a 2" Y off the Dutra Duals that joins to a 2.5" pipe that runs through a brand new Flowmaster style muffler. Exhaust and pipe are all brand new. 2.5" should be more than enough flow.
Author:  SlantSixDan [ Thu Jul 06, 2017 2:54 pm ]
Post subject: 
I'm with Sandy: the module should be suspect № 1
Author:  DusterIdiot [ Thu Jul 06, 2017 4:41 pm ]
Post subject:  Yep...
I would check the tach setting as that is fairly critical... I know the curve on the distributor is good, I just wound Spencer's car up to 6000 in park with the same recipe yesterday... and I'm using less coil and only the primaries on the Holley 390... the module might be highly suspect..

I also notice that the literature for that coil specifically recommends 8mm wires... but I don't think magnacore's products would cause a spark breakdown or wire crosstalk that way (watching under the hood at dusk with no lights on will reveal any "light show" in your ignition system....I have had stocker style 7mm wires have issues above 5000 rpm)...


Quote:
I have seen carbs be gummed/plugged from the factory and not work right ever.
Yes, especially if it's a factory 'reconditioned' carb....

I also see you said "Flowmaster Style"... is it a Flowmaster or a 'knockoff'... if it's a knock off and the muffler wasn't oriented correctly the baffles can work against exhaust flow can get pretty restricted at high rpms....
Author:  armyofchuckness [ Thu Jul 06, 2017 5:53 pm ]
Post subject: 
Ok. I futzed with the timing a bit and we're now sputtering at 4K RPM consistently. Again, I really doubt it's the tach since it was done a conversion done by Redline, and their quality is pretty top shelf, but I'll see if I can verify it with a diagnostic tool that does RPMs.

I'm going to try the module next. I'm also going to check the spark plugs to make sure they aren't fouled.

For giggles, we threw my buddy's Edelbrock 1406 600 CFM on the car. It's brand new out of the box. We just set the idle mix and off we went. It still sputters at 4K RPM but the power is markedly improved.

I would like to up the spark plug wires to 8mm. I got a good deal on these ones so I gave them a go, but that was before I got this monster coil.

Great advice, guys! I really appreciate it. I'll keep you posted.
Author:  69val6 [ Thu Jul 06, 2017 7:43 pm ]
Post subject: 
Please try a different ignition module before you change anything else. I've seen brand new aftermarket ones do that. They're not made as good as the used to be. See if a Chrysler dealer in your area has an OEM one in stock. If not, then try a Napa Echlin or Standard ignition one. I don't trust any of the value line ones from the parts stores.

Joel
Author:  69val6 [ Thu Jul 06, 2017 7:52 pm ]
Post subject: 
Whoa, I should have read your specs a little closer. I see where you have an HEI ignition instead of the Mopar electronic ignition. The same rule applies though. Watch out for value line parts.

Also, test your pickup coil to see if it's putting out enough volts for the module. If you unplug it from the module, put a DVOM on the two wires and crank the engine. If it's an OE chrysler style, you should get a little over 1 volt AC while cranking. I've had good ones put out 1.5VAC while cranking. Weak ones usually put out around .75VAC or less. At around .4VAC the module won't make spark at all.

Joel
Author:  armyofchuckness [ Thu Jul 06, 2017 8:00 pm ]
Post subject: 
It was the ignition module. Congrats to Sandy, Dan, and Joel for winning Slant Six Web MD. Got a nice name brand module and made night and day difference. Just ordered a second one so I'll have a spare in case things get dicey on the way to Carlisle next week. The car only has 750 Mike's on it since a total frame off restoration. Now I've got basically four days to chase gremlins until we make the two day drive.

Thank you all for the advice!
Author:  Dart270 [ Fri Jul 07, 2017 4:54 am ]
Post subject: 
Congrats, and enjoy the tuning and the ride!

Lou
Author:  wjajr [ Fri Jul 07, 2017 11:12 am ]
Post subject: 
Frame off????
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