Possible timing problem after my cam swap: my engine doesn't like for the initial timing to be set below 25*. If I set it below that it labors and wants to die. If I set it between 25* and 30*, it acts ok but revving it up results in total timing reaching ~42*. I'm afraid that when I get it on the road it'll ping with timing that high. I'm wondering why it labors so bad when I try to set it below 25*. This just doesn't sound right to me.

Current ign system is msd 6a, pro-billet dist. 85551, blaster 2 coil. Cam is Comp XS274 solid and I have a fully degreed ATI balancer.

Also, engine runs very rich. It is smoking at idle but hard to tell the true color of it at nite. I strongly believe the smoke is because the mixture is so rich, the O2 sensor indicates +1V reading which is dead rich. I even jetted down 2 jet sizes, to 76 from 78, which did not help. I think the timing situation is helping or causing the mixture problem.

Anybody have a thought on the timing?

Brett

 

Is it possible that you're one tooth off on your timing gears?

Steve

 

I installed the chain with the cam gear with the dot at 6:00 and the crank gear with the dot at 12:00.

Would it even run with the gears one tooth off?

Brett

 

Would the valve lash being off cause this? I re-adjusted the valves after breakin Tues nite.

This is how I did it: Balancer at TDC, #1 rockers loose, #6 rockers tight, adjusted #1 lash. Moved bal 90* cw and adjusted #8, moved cw 90* more and adjusted #4, and so on.

Brett

 

It's possible to get the gears one tooth off and still run. Ask me how I know. I doubt that the valve lash would cause a problem. If it was too loose, you would hear the noise. If it was too tight, you would have no compression and possibly some bent valves and pushrods.

I used to run my big blocks (and will do so again shortly) at 18 to 20 degrees of initial timing and 14 to 16 degrees of mechanical advance for a total of about 34 to 36 degrees by 2500 rpm. Vacuum advance would add about 12 to 15 degrees more on top of that, so I don't think you'll hurt anything running a total of 42.

You might also check into that severely rich condition, as a flooding carburetor (needle stuck open, for example) could cause a poorly running condition as well. I'm still leaning to cam timing. Despite all of the posts so far about timing Chevys the way that you have, I always put the dots on the gears together since it was easier to ensure that they were aligned. Of course, then I had to rotate the engine to bring it around to TDC on #1 cylinder before installing the distributor. Which wasn't a problem since I always spin the engine around many times while adjusting the valves. I adjust each cylinder at TDC for that cylinder by watching the movement of the valves and verifying TDC for the cylinder. That way I don't have to bounce around. A remote starter switch helps for that, by the way.

Steve

 

What were the symptoms?

Brett

 

I just put in a double roller timing chain last weekend and I'm sure I'm off a tooth. To get it run smooth the vacuum can is all the way forward. I'm going to reset the distributer this weekend...

 

Very low power, refusing to idle or run properly without the timing being over advanced. The engine will start and run. While I have only done this once (believe me, that's all it takes), back when I was in the business of auto repair, I had many vehicles brought to me after someone else had replaced the timing chain/belt for whatever reason and managed to get it off. In some cases by more than one tooth. It can happen.

Like I posted earlier, check out the carburetor before pulling the front of the engine off. But I can't think of much else that could cause these symptons. Possibly a large vacuum leak, but you should be able to hear that. Oh, I do recall one other time. A guy with a Ford F150 and a 400 had rebuilt his engine and replace the crank with one out of a 351 (yep, it fit), and the resulting smaller displacement and lower compression (can you say 6.5 to 1?) made the engine act very similiar.

Brett, I just went back and reread your post. If you had the dots pointing at each other you should not have had a problem, but it could still happen. I wish that I was there, it makes diagnosis much easier. I'll try to do a little more thinking about this.

Steve

 

One tooth off on the chain or the dist?

Brett

 

I know on Cloyes chains, if you use the 6 & 12 approach, which I did, you are firing on #6 Not #1...#1 is 12 & 12...1 tooth on the distr. end

 

Hmmmm. Sounds ominous. I'm sure that I put that chain on right. I distinctly remember getting the cam dowel at 3 o'clock and putting the cam gear and chain on at that point. The 2 dots lined up at 6:00 and 12:00.

I'm going to try a road test after work. I'm going to take apart the carb once more and check the timing again. I'll be sure it's at 27* and see what happens.

Brett

 

This only comes into play when you install the dist. When I stabbed it, I used the method I have used forever, which is to plug the ol finger into the #1 plug hole and crank her over till your finger gets blown outta the hole.

The Comp instructions said to use the 6 and 12 method, which I did.

Brett

 

Sounds like you did it right. This is gonna be interesting when you find out what's wrong....

Steve

 

I guess I'll take her for a test drive after work today...after I make sure the timing is at 27* and after I take the carb apart one more time...

Brett

 

From what you discribe this is exactly what mine did with a hot cam (performer RPM). I checked the timing chain position and the distributer and everything was set correctly, I couldn't figure out why it needed 30 degrees advanced timing to run.
Edelbrock's tech support told me that I needed at least 9.5:1 compression which I don't have with my L48 and 64cc heads. I think my compression is about 9:1, maybe 9.2.... first i thought that's bs, but then I installed a milder cam and now it's running great. My other option was better pistons but I'm too worried abot the crank and the main bearings...
Hope this helps.

 

Two things to look at. You may have a couple problems at once.

High Initial: Your mechanical advance may be kicking in at intial. 12°+16°=28°. Heavier springs to retard the advance(easy, inexpensive test).

Runs rich: Check the float and idle mixture settings. Are they equal?

Just some more ideas.

 

After monkeyin around with the carb last nite, I got the timing set to 18* and it idles pretty good there. However I jetted down my Holley 850 DP from 78s to 71s and it still shows dead rich on the O2 sensor. I think I might be getting some intake contamination because one of the times I pulled the carb off last nite, I noticed there was black gas puddled in the ribs on the floor of the intake. I wonder if this is from reversion or oil contamination. I'll prolly yank the intake after work today...won't take but just a minute.

Brett