Where Did My Power Go?

[colby45]

Not sure where to go from here, I'm sort of at a loss. So we started the fully rebuilt 170 in my Bronco last weekend. It started right up without much hesitation. Got the timing set to 8 degrees BTDC (with vac line unplugged) and set the mixture on the (also) completely re-conditioned Autolite 1100. Everything seemed great. Idles great, starts right up and hardly even needs choke.

We took it out on for a cruise and it's dogging bad. Floored in 3rd gear it can't get over 35. I'm not sure where my power went. Here's what else I've tried:

Checked all the vacuum lines for leaks. There are none. Plugged the wiper vacuum port at the fuel pump just in case they were leaky.
Checked vacuum advance. Seems fine. Were getting about 3 degrees advance at idle and total timing at at (2200?) RPM is 23 degrees.
Put in new points, set gap, checked dwell (dwell is 38 degrees, spec is 37-42)
Checked throttle cable adjustment. Seems fine. Throttle plate opens fully when the throttle is on the floor.
Dist cap, rotor coil and plugs are less than a year old. The cap did seem to have a small amount of play in it if I try and wiggle it around.
Plugs are brand new - Motorcraft

The only thing I can think of is either we aren't getting spark in multiple cylinders, or something is going on with the carb? Holley completely rebuilt it and set everything back to stock and flow tested it. It doesn't stumble or break up or start hard or anything. Just has not much power. I'm gonna check spark at the plugs tomorrow.

Anybody have any suggestions that I missed? Thanks guys.

[Digger]

I'm not an expert on the I6s , but 3° at idle and 23° at 2200 rpm / light load seems low.

Open / large combustion chambers, like old engines tend to have, need more advanced timing in order to give more time for the flame front to propagate.

My 9:1 comp, 351W is running 15° at idle and 28.5° at 2200 rpm / light load.

Timing Table.jpg

I would check the plugs for color. Also, are you hearing any light "popping" from the engine at cruise loads?

[colby45]

Thanks Digger. I'll check the plugs tomorrow. Yeah I wasn't sure how far I should advance. The Ford manual from '66 says advance a max of 9 degrees BTDC for altitude and you won't see any performance gain beyond that so that's why I settled on 8, but sounds like it could benefit from a little more advance. From your table, how did you settle on 15?

No popping under cruise load as far as I can tell, but it bogs so bad in 3rd, I honestly am not sure.

It also hesitates just slightly going from idle into power like when you take off from a stop.

[Digger]

I built the table by sampling specific sections and bumping the timing up and down until I got the best response from throttle input. Then interpolated between those points to fill in the blank areas. Idle timing was a specific area I played with. I could get slightly better throttle response using timing greater than 15°, but I dialed timing back at 750rpm to created a dip in the table at idle. Timing below idle rpm has a slight bump so if the engine rpm sags, the timing rises and naturally adds torque.

On your vacuum retard, is there a spring you can change? Either the distributor is pulling too much advance when you tip in the throttle or you need more accelerator pump to correct your bogging. It's much harder to over fuel these engines on acceleration than it is to under-fuel them.

When you go from idle to power, are you easing the throttle in or mashing it to the floor?

No popping is good. I would always hear a light popping if was lean or didn't have enough advance. The results seemed the same, the flame front was late and still burning when the exhaust opened, which made a distinctive noise.

[colby45]

I mean I can change the springs on my breaker plates to adjust the timing curve if that's what you mean. I'm not entirely sure that's the issue though because it seemed like the curve was good before the engine rebuild and it's stock as far as I know. However, if they are 50 year old springs, maybe they need a refresh.

When I go from idle to power I'm easing into it and it still stumbles a bit. I haven't just mashed it yet since it hasn't been running well.

I'll have to figure out how to adjust the accelerator pump on the 1100 as I could see that being an issue. When you open the throttle with the engine off I see a strong spray of fuel into the throat of the carb so I know the accelerator pump is at least working.

I'm going to add some timing using the vacuum gauge method and see how that goes. I do think we need more advance.

I might put in a Pertronix too since I'm pretty sick of dealing with the variability of points.

[Digger]

I mean I can change the springs on my breaker plates to adjust the timing curve if that's what you mean. I'm not entirely sure that's the issue though because it seemed like the curve was good before the engine rebuild and it's stock as far as I know. However, if they are 50 year old springs, maybe they need a refresh.

When I go from idle to power I'm easing into it and it still stumbles a bit. I haven't just mashed it yet since it hasn't been running well.

I'll have to figure out how to adjust the accelerator pump on the 1100 as I could see that being an issue. When you open the throttle with the engine off I see a strong spray of fuel into the throat of the carb so I know the accelerator pump is at least working.

I'm going to add some timing using the vacuum gauge method and see how that goes. I do think we need more advance.

I might put in a Pertronix too since I'm pretty sick of dealing with the variability of points.

The Pertronix we installed in the Fairlane really woke it up. (points were sad). I would focus on the accelerator pump after you reset your base timing. It would be strange if it were off. I don't see too many people needing to adjust it.

[colby45]

Okay sorry it has taken me so long to get an update on this, work has been really eating into my Bronco wrenching time, but here's what's going on:

Adjusted the base timing to 14 BTDC, which made a huge difference. No ping and no overheating and the Bronco is running great. When we first adjusted it, things felt better but still not perfect.

Here's where the embarrassment begins...got back from driving it with the new timing and realized I had a g rear drum. One drum was almost completely locked up, the other side was rubbing pretty bad too and one front drum feels like it's sticking a bit. I feel really really stupid for not checking that. Did a rear brake job and she's running great now. Cruises without hesitation. No problem hitting 60, I haven't driven anywhere I could go any faster because I want to do the front brakes too before we venture too far from home. That all needed to be done so not a huge loss. Rear brake hardware all looked original and unmolested. I honestly can't believe it was moving as well as it was with that much brake resistance.

Lesson learned, check the simple things first.

BOBS 2 68S was also kind enough to give me a Pertonix he had from a 6 cylinder he wasn't using, so I'm getting ready to throw that in too. Thanks Robert! Certainly can't hurt to squeeze a little more life out of the little 170.

[BOBS 2 68S]

Way cool. Glad you are making progress.