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Old Jun 23rd, 12, 02:40 PM   #1 (permalink)
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problems running past 3500-4000 rpm

Ok, here is my problem. I have a 1980 with a 350 bored 30 over, gm 272-284 cam, dart 72cc heads 202 exhaust, 180 intake, with accel 140003 vacuum advance distributor, and a borg warner super t-10 trans.

My problem is that when i run past 4000 rpm in first gear the car kinda sputters and wont go any higher rpms. i shift and it does the same thing in every other gear only difference is the other gears do it at about 3500-3600 rpms.

My question is why does this do this? Should it push higher rpms as i am told it should.

I would like to know any possibilities and possibly how i should go about fixing the problem?

if you have anything you need to know to help answer my question let me know and i will get the info for you.
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Old Jun 24th, 12, 09:49 AM   #2 (permalink)
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Re: problems running past 3500-4000 rpm

Start with fuel filter, vapor lock so make sure the gas tank or gas cap is vented.

Carb floats could be set to low, make sure your getting full throttle.

Could be a bad pick up module in the dizzy, check with a timing light to see if the timing retards at 3,000 to 3,500rpms.

Valve adjustment, what set up are you running and what is the valve lash.
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Old Jun 24th, 12, 11:53 AM   #3 (permalink)
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Re: problems running past 3500-4000 rpm

I'll continue with change spark plugs.
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Old Jun 24th, 12, 11:59 AM   #4 (permalink)
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Re: problems running past 3500-4000 rpm

While it is POSSIBLE you have a spark issue, you are most likely starving for fuel.
I would check the following:

1. Fuel filter (or filters)
2. Fuel pump (check pressure first, then do a volume test).
3. Clogged "sock" in the fuel tank
4. Improper venting
5. Kink or other restriction.

Didn't see what carb you are running. Lots of carbs have fuel filters at the inlet, and many guys put another one in line. The in line filter gets changed, because you can seel it. Easy to forget about the ones you can't see.
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Old Jun 24th, 12, 01:51 PM   #5 (permalink)
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Ok ill check those. the carb
is eddlebrock 600 4 barrel I believe.

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Old Jun 24th, 12, 01:54 PM   #6 (permalink)
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Re: problems running past 3500-4000 rpm

Has it always done this?
It does it no matter if WoT or increase rpms slow, under load and free rev?
If so I would be looking at your plugs or the cent curve timing.
With a vaccuum gauge in cab does it happen at a consistant vaccuum ?

or a crook power valve in the carb.
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Old Jun 24th, 12, 01:58 PM   #7 (permalink)
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I do not have a vacuum guage in the car. Could that help find the problem?

Also I have roller rockers, could I possibly just need to do a valve adjustment?

And ill check to see if it does it sitting still when I get home in a few and let everyone know.

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Old Jun 24th, 12, 03:14 PM   #8 (permalink)
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Ok so I hooked up a vacuum guage and sitting still the car only got to 4500. When I would rev it it would get up to 15 psi of vacum then would start to kind of back off and when it would start to sputtered the vacuum was gone and it would drop to 3500 rpms

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Old Jun 24th, 12, 09:08 PM   #9 (permalink)
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Re: problems running past 3500-4000 rpm

Quote:
Ok so I hooked up a vacuum guage and sitting still the car only got to 4500. When I would rev it it would get up to 15 psi of vacum then would start to kind of back off and when it would start to sputtered the vacuum was gone and it would drop to 3500 rpms
ok free rev...goes up to 4500.. then 'starves'.. vaccuum is in inches of mercury NOT psi
Now take up slow...then when the engine staves, about how many inches dose it start to starve (15" ?) then the vaccuum drops, and the engine picks up again about 3500 rpms ??? that right?
Now cruise on the road, take the rpms up reasonbly slow constant vaccuum ...what vac and rpms dose it happen?

While at it what intial timing ?
What idle timing...with VA attached?
What rpms and timing is the cent all in ..no VA
and with VA?
Are u 100% sure that tdc on the balance is correct...check it.

Is the pvc valve working?

Repeat question
Has it always done this?
Has this engine ever been dialed in..or the carb and dizzy simply bolted on and go?

And check the tank cap, filters are clean and installed the right way around, as suggested by others above.
Ifit does it startionary, a free rev, I doubt very much the carb bowls get emtied fast enough to cause the issue.
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Old Jun 24th, 12, 09:17 PM   #10 (permalink)
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Re: problems running past 3500-4000 rpm

Jason,

Check the items the others are suggesting first as they are relatively simple and cheap..easy to fix for the most part.

Out of curiosity...how old is the engine, how much use does it have (run time) and could you tell us about the valve springs? Are they matched to the cam (advised by the grinder/builder) and what machining has been done to the heads? Which roller rockers do you have, and I am guessing you have guide plates installed too?
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Old Jun 25th, 12, 08:18 AM   #11 (permalink)
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Honestly I don't know much about the parts on the engine since the guy that had the car before me did the engine. Everything I know is from fixing a litter problem and from what he told me.

I think im going to take and have it timed and dyno tuned and see if that helps and possibly find out of they see the problem.

But in the time I have before I can get to phoenix to get it tuned ill try to find out more about it

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Old Jul 4th, 12, 07:21 PM   #12 (permalink)
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Ok so I replaced the distributor today

And while messing around wither the timing I noticed my inline fuel pressure guage was reading zero while the car was running.

Could my fuel pump be the problem?

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Old Jul 5th, 12, 04:15 AM   #13 (permalink)
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Re: problems running past 3500-4000 rpm

A good possibility. Fuel could be evaporating due to heat.
You might install, for troubleshooting purposes, a clear filter after the fuel pump and it should always be full.

Is the gas cap venting - vents into the tank but not out?
With a vacuum gauge 'Tee'd' on the inlet line to the fuel pump, it shows a vacuum?
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Old Jul 5th, 12, 05:30 PM   #14 (permalink)
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Another thing I noticed yesterday while messing around with it, is that when I rev the engine to about 4000 rpm and it starts to do its thing, with the air filter off the carb, I noticed that it shoots what I believe to be a mist of fuel up out of the carve almost like a back fire but it doesn't pop like a backfire

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Old Jul 5th, 12, 06:59 PM   #15 (permalink)
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Re: problems running past 3500-4000 rpm

The symptom posted would be consistent with an intake valve open, either sticking open, or a weak valve spring.
You should see a variance in the vacuum gauge reading. The gauge would be steady and read a high number, ie, 15" or above up to 4K rpm, then once the mist appears, the vacuum reading will decrease, maybe bounce in rhythum, with the 'miss/mist'.
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