350 timing problems

[C101971]

Now I know this is a commonly asked question and I had an answer but now I can't find the thread. Anyhow, I've timed my truck, a 71 c15 4 speed stick, however, it idols great and all is well till about 4 grand on the tac then she seems to redline. A month ago she would blow past 4 grand. I noticed the sticker in the bay says 4° for manual trans at 550 RPM, but everyone is telling me to do it at 8°. Kind confused here if someone could clear the air

[jocko]

That is your initial timing setting only (i.e. set with timing light). 4 or 8 will not affect your ability to rev past 4000 rpm, either will work, so must be a different issue (assuming you've actually set it at 4 or 8 recently?). Vac and centrifugal advance are more in play at 4K rpm. Are your centrifugal advance weights still in place/intact (remove distrib cap and make sure the little short springs are attached to the counterweights)? If you haven't changed anything else, then something needs to be fixed (rather than just re-adjusted). Fuel line clog? Fuel pump headed south? Did you monkey with the mixture screws when setting initial timing? Still have a points ignition? Have you set them recently? (should be 30 deg dwell, best to set with a dwell meter rather than a feeler gauge). If they haven't been changed, that would be a start. Kinda need more info on your setup and what you've done, tried, changed.

[Steeveedee]

Stock ignition? HEI? how old are the plugs and wires? How old are the cap and rotor? This isn't a base timing issue.

[C101971]

Originally Posted by jocko

That is your initial timing setting only (i.e. set with timing light). 4 or 8 will not affect your ability to rev past 4000 rpm, either will work, so must be a different issue (assuming you've actually set it at 4 or 8 recently?). Vac and centrifugal advance are more in play at 4K rpm. Are your centrifugal advance weights still in place/intact (remove distrib cap and make sure the little short springs are attached to the counterweights)? If you haven't changed anything else, then something needs to be fixed (rather than just re-adjusted). Fuel line clog? Fuel pump headed south? Did you monkey with the mixture screws when setting initial timing? Still have a points ignition? Have you set them recently? (should be 30 deg dwell, best to set with a dwell meter rather than a feeler gauge). If they haven't been changed, that would be a start. Kinda need more info on your setup and what you've done, tried, changed.

Have not tinkered with much since I rebuilt the top end and it was fine till the timing chain went out. It ran super healthy, smooth power band. Then I did the timing chain and gears and triple checked to make sure everything lined up, set initial timing and now she's being fussy, as far as setup, brand new in the last few months,Holley mechanical fuel pump, Holley street demon carb, Edelbrock preformer dual plane, inline fuel filter, timing chain and gears, breather valve, new driveshaft, all new vaccum lines. All I can think of right now

[C101971]

Originally Posted by Steeveedee

Stock ignition? HEI? how old are the plugs and wires? How old are the cap and rotor? This isn't a base timing issue.

HEI, plugs are decently new, few years, plug wires are a year old, cap and rotor are a few years old but has no signs of excessive wear

[AussieinNC]

At around 4k, all your advance should be in..you should see around 30 all up around 4K...

This could be as simple as a clogged muffler....does the exhaust sound different than normal?

HEI...could be the module maxing out...do you have another module to swap in and try?

Finally, the timing set you put on...did it have a 3 way bottom gear ? Sometimes the gear is put on 4 degrees retarded, which limits the cam overlap,,,improves low end torque but sometimes peaks out up top...

Are you sure you got the cam gear index marks perfectly in line ?

...cam gear index at 6...crank gear index at 12...just one tooth off late on the cam and it will be running like a slug...

[jocko]

Originally Posted by C101971

Have not tinkered with much since I rebuilt the top end and it was fine till the timing chain went out. It ran super healthy, smooth power band. Then I did the timing chain and gears and triple checked to make sure everything lined up, set initial timing and now she's being fussy, as far as setup, brand new in the last few months,Holley mechanical fuel pump, Holley street demon carb, Edelbrock preformer dual plane, inline fuel filter, timing chain and gears, breather valve, new driveshaft, all new vaccum lines. All I can think of right now

So, just to be clear on what you're saying: it was running fine with ALL the things you did EXCEPT the timing chain r&r - is that correct? i.e. after that, it was all gummed up? That's an important clue - would eliminate all the other changes made as causes.

Concur w/Aussie's question - was the timing set crank gear a 3 keyway type? Most perf aftermarket ones are these days. If it was, do you know if you did your valve timing with the the cam gear dot at 6 o'clock, the crank gear dot at 12 o'clock AND the crank key in the zero retard/advance keyway of the timing set's crank gear?
Did you set initial timing with a light after you got the timing chain in? Did you ever remove the distributor? When all complete, where were the dots and what cylinder's distrib tower was the rotor pointing at?

[C101971]

Originally Posted by jocko

So, just to be clear on what you're saying: it was running fine with ALL the things you did EXCEPT the timing chain r&r - is that correct? i.e. after that, it was all gummed up? That's an important clue - would eliminate all the other changes made as causes.

Concur w/Aussie's question - was the timing set crank gear a 3 keyway type? Most perf aftermarket ones are these days. If it was, do you know if you did your valve timing with the the cam gear dot at 6 o'clock, the crank gear dot at 12 o'clock AND the crank key in the zero retard/advance keyway of the timing set's crank gear?
Did you set initial timing with a light after you got the timing chain in? Did you ever remove the distributor? When all complete, where were the dots and what cylinder's distrib tower was the rotor pointing at?

Yes it was all fine till I did the timing chain and gears, they are lined up as perfect as it gets

[C101971]

Originally Posted by AussieinNC

At around 4k, all your advance should be in..you should see around 30 all up around 4K...

This could be as simple as a clogged muffler....does the exhaust sound different than normal?

HEI...could be the module maxing out...do you have another module to swap in and try?

Finally, the timing set you put on...did it have a 3 way bottom gear ? Sometimes the gear is put on 4 degrees retarded, which limits the cam overlap,,,improves low end torque but sometimes peaks out up top...

Are you sure you got the cam gear index marks perfectly in line ?

...cam gear index at 6...crank gear index at 12...just one tooth off late on the cam and it will be running like a slug...

Yeah they are perfectly lined up, I'll try a new distributor later. No it did not have a 3 way bottom gear

[toolboxchev]

What else is possibly cooked after loosing the timing chain and gear?

[Grumpy old man]

You rebuilt the heads then the timing chain went and you replaced that now it doesn't want to rev over 4,000 rpm ... Sounds like your ready for a new cam ... What are you doing revving past 4K ? Post up some pictures of the truck and the engine ...

[demian5]

Originally Posted by C101971

A month ago she would blow past 4 grand. I noticed the sticker in the bay says 4° for manual trans at 550 RPM, but everyone is telling me to do it at 8°.

I run mine at 10-12 with no issues (stock motor, MSD billet dist, no vac advance, mid-length headers, performer manifold, demon 650 street carb).

What did you change?

Does it NOT blow past 4k in neutral (parked) or when under load only when driving?

Are you starving for fuel? (clogged filter, bad pump, crap in tank/carb)

Timing wouldn't keep it from going past 4k, it would just take longer to get there. Something else is up.

[weq92f]

Please explain exactly what happened when your "timing chain went out."

Was the engine running when this happened?

-klb

[C101971]

Originally Posted by demian5

I run mine at 10-12 with no issues (stock motor, MSD billet dist, no vac advance, mid-length headers, performer manifold, demon 650 street carb).

What did you change?

Does it NOT blow past 4k in neutral (parked) or when under load only when driving?

Are you starving for fuel? (clogged filter, bad pump, crap in tank/carb)

Timing wouldn't keep it from going past 4k, it would just take longer to get there. Something else is up.

Neutral is fine, only under load does it not received past 4k

[C101971]

Originally Posted by weq92f

Please explain exactly what happened when your "timing chain went out."

Was the engine running when this happened?

-klb

I was driving in slow traffic and noticed the room drop a bit, thought it was vapour lock. But when I pulled over the fuel was not bubbling and it ran super rough, checked for play and it was very stretched

[AussieinNC]

Could you so a compression test on all cylinders and post the results...

With the engine idling, what is the level of vacuum in the engine?

Make sure your distributor is bringing up the advance when the rpm increases....you want to see 34 - 36 degrees at or above 3000 rpm...

Set timing with vacuum line to distributor off and plugged...set to 6 BTDC with engine rpm around 650....

The vacuum source for the distributor MUST be ported vacuum...meaning at idle there should be no vacuum applied to distributor.

This sounds like the cam is retarded one tooth on the cam gear...but the compression readings and vacuum readings will tell us more...

[jocko]

stale fuel?

[68 P.O.S.]

Clogged fuel filter, kinked fuel hose, bad fuel pump, old gas?