Strange timing issue

[MikeyM]

Hi all,

Happy holidays. In chasing down an off idle stumble in our '69 Bee 383 (Holley 600 80457-2), before I was able to get an adjustable timing light, my initial timing looked to be about 12*. I got the stumble about 99% cured with carb adjustments and the car was responding to throttle input very nicely. THEN I got my hands on the digital timing light in order to set up the full advance with no vacuum and all that fun. I was shooting for 34* due to ethanol, safety, etc. and after landing at 32ish, the initial landed on 14*(Seems to be a MP perf adjustable vac adv dizzy). The odd thing is now the stumble is back... a bit; and I did readjust the carb afterwards. When I aim the timing light at the balancer and then increase throttle, the timing mark seems to retard a few degrees then increase. And at speed, say around 200-2500 RPMs, the timing mark is stable. I've adjusted the accel pump to where the pump arm moves right when the throttle is touched and I have #35 squirters. I was about to change jets to the next size up but wanted to post up here first to see if you guys had any ideas on the timing thing. I was thinking timing chain but the balancer mark doesn't seem to jump around at speed. The Holley was on the car when we got it so I'm trying to work with it so we can enjoy it for a while. The original jetting, according to the Holley site, is 66 and it has 65s in it so I was going to go back to 66s to see if that makes it happier. Anyway, any input you all have is most welcome.

Thanks for the read,
Mikey

 

[Doorkicker]

I've read this several times to make sure I'm understanding you... and i think I'm there. I will say that the marker jumping back before moving forward is likely just the inductive pickup. Each timing light has different levels of accuracy. If it's SUPER consistent, then I would check for a lose timing chain by hand. It "could" explain continued idle choppiness... but the odds are not a stretched chain. How old is the chain/engine?

As for the overall stumble... are you certain the markers (the marker on the cover and the mark on the damper) are in the correct spot?

 

[MikeyM]

Ahh.. good to know on the timing lights. Didn't realize the that about inductive pickup, thanks.

As for the mark on the balancer, etc. it's the original engine with under 70k on it. To my knowledge, it's never been out of the car. The timing cover is stock, so is the balancer and I tried grabbing the balancer by both hands to see if it would spin at all, but it does not. So that leads me to believe that both are seemingly in their correct spots. And I don't, and never have, heard any engine pinging.

Regarding the stumble, the carb has a the stock 6.5 PV in it. I have a 10.5 PV but not sure if that would help as the stumble seems to be in the transition ckt.

Thanks,
Mikey

 

[ruffcut]

I was thinking loose timing chain also.

 

[steve340]

Try a 30 or 31 squirter - can't hurt.

 

[lewtot184]

80457's are lean on the main jets. Big squirters don't work for what your doing. Try a .025 squirter with tubes and a white 218 pump cam in the #1 position.

 

[MikeyM]

Thanks, everyone,

I will give the suggestions a shot. What about going from a 65 to a 66 main jet? Also, I currently have the orange pump cam in there now. Is the white a little more aggressive?

Thanks,
Mikey.

 

[Canadian1968]

The timing mark retarding is the adjustable timing light . I went threw the EXACT same thing with mine. Felt kinda dumb once I figured it out ! Set your new digital light to 0 and check it again, bet it doesn't retard.

As for the stumble . I would try disconnecting your VA and see if it still does it

 

[MikeyM]

Ahh.. good call on the vacuum advance. I'll give it a shot. Will do on the timing light. I think you're right now that I'm starting to remember

Thanks,
Mikey

 

[steve340]

The orange cam is most likely the one you need.

 

[lewtot184]

Here's a pump cam chart. You can pick your poison.

 

[Some Car Guy]

How are your wires? My car had an old set of the repop wires. I found they were both brittle at the ends and also when you ohmed the ones that had good ends, they jumped all over the place when the wire was moved around. I forget exactly what the coil wire was like, I remember it was wild as I’d never seen it before. I found tracking in the distributor cap and I think it was jumping a gap from the wire to the cap terminal.

 

[MikeyM]

Thanks Lew. I had the blue cam installed before I really understood how to adjust the carb. Now I do (but am certainly no pro), so I rebuilt it, removed the blue cam, installed the orange cam.... then lost the damn blue cam somewhere in the garage (DOH!!). It did run much better, idled better, etc. I adjusted the idle (in gear) and am pulling about 14" + or so of vacuum and about 16" in neutral @ about 800+ rpm. The accel pump is adjusted per Holley specs and the pump arm moves as soon as I touch the throttle. Secondary throttle plates are barely cracked. I did notice what seemed to be a barely noticeable, very light surging on the highway under certain throttle conditions that, likely, a passenger would not feel so, hearing that these carbs are jetted lean OOTB I upjetted from 65s to 66s and that issue is now gone. It does respond MUCH better when fully warmed since the carb work and jet change. The engine is a stock '69 383 HP engine - under 70k miles. In reading from others with similar engines / configurations, it seems the smallest jetting I'm seeing used is 70-72 so I might increase to 70s, try it out and read the plugs.

Other info that might be of interest: At cruise, about 2500-2800, vacuum is about 15" and my power valve is a 6.5 (I do have a 10.5 that I have not installed). Also, when using a vacuum gun, the vac advance plate starts to move at 5".

Canadian - I haven't disco'd the VA yet but will as soon as I get a chance to test.

Car Guy, the wires are new Moroso 7mm and the cap and rotor are new. However the cap is a Wells unit and does not have the internal ridges to prevent the tracking you mentioned. Also, the wires don't seem to grab as positively as the previous black cap I had (brass terminals and ridging) Good call on that, thanks. I don't care for that design so I think I'll swap it with a Standard Blue Streak cap just for my own satisfaction.

Anyway, hope all that helps.

Thanks,
Mikey

 

[Canadian1968]

Those idle numbers sound pretty good. Did you adjust the timing then? If so what is it at. ?

 

[MikeyM]

I did. idle is at 14* initial, 31-32* full mech. advance with vac hose disco'd. I do have the MP adjustable vacuum can and the VA starts at 5".

 

[MikeyM]

So just for kick, I went from 66s to 67s and the stumble is pretty much gone once warmed up. However the “response” feel seems to be a tad less although smoother. I’m thinking this might be because of it being a bit too lean and then the mains come in? Don’t know. I was thinking of bumping up the timing so I get about 35° full mechanical advance. But that would put me at about 16° initial, which I’m not sure if that is bad or not. Any thoughts? Also… For those of you who are running stock 383 HP engines with manifolds, is your jetting roughly the same?

Thanks,
Mikey

 

[Bird 426]

Before you throw more jetting at it, you say that your vac is in the 14-15 area. Rule of thumb is half, so try a 7.5 power valve.

 

[MikeyM]

Thanks Bord, copy and will do. I know it’s pretty subjective but what are your thoughts on a stock 383HP with 67/68 jets? I think the smallest I’ve seen mentioned for the same engine is a 70 to start with. Any idea what the stock Carter’s came with?

Thanks,
Mikey.

 

[Bird 426]

You are in the ballpark with 66's or 67's. I do not have a 383, but 418 stroker with 6-pack. I'm at 66/67's and 7.5 PV, manifold pressure is about 15, but my end carbs contribute a little. Sounds like you are pretty close. Your hesitation is about gone, see what your plugs look like after a little driving.

 

[Geoff 2]

One of the 'problems'.....with this sort of problem......is that folks do not make a big enough change. If you suspect leanness, go up 2-4 jet sizes, not one. Making a big change will point you in the right direction & THEN you fine tune from there.....

Try this simple 5 min test: engine idling [ in gear if auto ] slowly adv the dist to see if idle rpm increases/gets smoother. Keep going until you have the highest rpm. Lock the dist & test drive. I am betting the stumble will be gone. Keep rpm below 3000 because you are only testing for tip in response. Report back.