engine running funny

[Mmoore031908]

So I have an 85 k10 with a 305 with a 700r4. I know its a 305 but Im trying to get some input on why my engine is running rough.
I put a new summit SUM-226014 Stage 2 intake, a new summit 600CFM carb, a summit-1065 ADV duration 284 .05 duration 218 .458 lift and 110 lobe separation cam, lifters, valve springs, and distributor. Right now I have the timing set at about 22 degrees BTDC at about 650 rpm in drive. It seems to want more and runs better with more timing. I tried 18 because I have 18 mechanical to give 36 total and it ran like a dog could barely make it up my drive way (which has a slight incline) the more I advanced it the better it ran. With the 22 degrees it runs better but wont go over about 2200 RPMs or so at WOT It hits the 2200 and just flattens out. At 22 degrees it starts fine and doesnt ping.

 

[bucket]

It's at 22* BTDC with the vacuum advance disconnected?

How did it run before the cam/carb swap?

 

[firebane]

284 duration is REALLY big for a little 305. Its going to take some really fine tuning to get that thing to run in that truck.

 

[Mmoore031908]

Yes that is with the vacuum advance disconnected. It ran ok before the swap idled pretty rough but other than that pretty good. Still never went over about 3000 rpms. It would do the same it would hit about 3000 and just flatten out.

 

[rich weyand]

Almost sounds like a slipped timing wheel.

 

[Mmoore031908]

Is that possible even if the timing doesn't jump around? I replaced the harmonic balancer as well. With a new timing tab both put tdc in the 2 o' clock position.

 

[Lastwords]

Use a vacuum gage. If it's jumping around a lot you h ave a vacuum leak. When you installed the cam did you degree it? Put the #1 cylinder to tdc and mark where the line on the harmonic is on the tab. The tabs aren't always accurate. How did you set the valves?

 

[Mmoore031908]

To set valves I rotated each cylinder to tdc an spun each pushrod with my fingers until it had some resistance then went an extra 1/2 turn. I don't have any valve train noise. If the valves were too tight would I get backfire out of the exhaust or intake? I feel like that vacuum is low but it stays pretty constant. At the 650 rpm in gear I have about 10 in/hg at about 900 in park it is about 16 in/hg. Now that you mention it I bought a new harmonic balancer after I had degreed it with the old balancer because I noticed the tab and the old balancer were way off. The old balancer was used with a 12 o clock tab while the new tab I got was a 2 o clock tab. I will check tdc again to make sure that the harmonic balancer tabs line up. I didn't even think about that after I bought the new balancer.

 

[rich weyand]

Chevy used THREE different harmonic balancers, with three different timing tab locations, 12:00, 2:00, and 2:30. But you can dial this in with your timing light if you have the adjustable ones.

The crankshaft keyway at #1TDC is at 45 crankshaft degrees clockwise from straight up on all Chevy small blocks: call it 1:30 o'clock looking at the front of the engine. The three timing tab locations are 40* counterclockwise from the keyway (5* total off vertical, called 12:00), 10* counterclockwise (35* total off vertical, called 2:00, though it's more like 1:00 really), and 2* counterclockwise (about 43* off vertical, called 2:30, though it's more like 1:30 really).

Also, have you checked that your mechanical advance is working? With the vacuum disconnected, at idle you will see your base timing. If you rev the engine, you should see the timing move advanced 15 to 20 degrees by 2500-3000 rpm. If the timing stays on base timing as you rev the engine, the mechanical advance mechanism is stuck. That will flatten your engine out around the 2500 rpm range.

 

[Mmoore031908]

right now I get about 40 or 42 total degrees at about 2200-2300 rpms or so. I went up to 2500 and it didnt change. went down to about 2000 and it dropped to about 38 degrees or so. I put one light and one medium spring in for the mechanical advance so that may be why its flattening out?

 

[rich weyand]

(Got my mech and vac switched around in the OP. This is now correct....)

Stock HEI for these trucks was 20* mechanical advance and 15* vacuum advance. This is in crankshaft degrees, which is what you see with the timing light. You may see distributors or advance kits specced as 10* and 7.5*; that would be in camshaft degrees.

So it's always important to know whether some info sheet or kit instructions are talking terms of camshaft degrees or crankshaft degrees.

The normal setup for a (non-pollution) SBC is something like:
Base timing: 16* BTDC
With vacuum advance at idle: 31* BTDC
No vacuum advance @3000 rpm: 36* BTDC
At cruise (vacuum and mechanical both in): 51* BTDC

Are you sure you aren't supposed to be on a 12:00 tab?

You really need to find TDC....

 

[rich weyand]

right now I get about 40 or 42 total degrees at about 2200-2300 rpms or so. I went up to 2500 and it didnt change. went down to about 2000 and it dropped to about 38 degrees or so. I put one light and one medium spring in for the mechanical advance so that may be why its flattening out?

OK, so if you are reading 22* BTDC at idle with no vac, you are getting 20* of mechanical advance. Perfect.

But I think all of your numbers are off by a constant because the timing wheel and the tab don't match. That 22* should give you detonation when you get on it, and the engine shouldn't flatline in the midrange. I think you are maybe 25* off, which would give the results you are seeing.

Have you tried just advancing the timing 2-4 degrees at a time until you get knocking on acceleration, and then backing off 2 degrees from there?

 

[Mmoore031908]

here are the timing tab and balancer I am running. I may not be able to check tdc today its going to pretty much be raining all day today.
http://www.summitracing.com/parts/sum-161350/overview/ (I made sure it was the same diameter as the one I took off.)
http://www.summitracing.com/parts/sum-g3205(The pointer I cut to where I am just using 0 because the harmonic balancer has timing marks.)

 

[Mmoore031908]

25* off? I have not tried increasing until it pings. Mainly it just concerned me to run that much inital timing but it isnt pinging or anything.

 

[rich weyand]

My point is that you don't know how much initial timing you are running. Yes, the timing wheel you have shows 22* initial timing against the timing tab that you have. But are they right? If you are 25* off, for example, you are running 3* AFTER TDC base timing.

You really, really need to determine where TDC is and get a known good timing mark for 0*.

If you are reading 22* BTDC, getting no knocking, and the engine flatlines in the mid-range, something is wrong, and I am betting it's your timing marks/tab.