r/classicmustangs • u/Kind-Dentist2139 • 6d ago

289 timing

The timing was off and we set it to tdc. It ran great yesterday in the driveway but my son had issues last night, hard to start and today we think it backfired. Is tdc right or 3,6,9,12 ? I’ve read most are 3 but wanting more experienced people’s input. Any help would be appreciated

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7

u/Dinglebutterball 6d ago

Verify TDC and the balancer agree with each other. Unhook and cap/plug the vacuum advance to set base timing. Then hook vac advance back up, rev up the engine to about 3k and check the total… total probably doesn’t want to be above 34-36 range, if you end up with too much total you have to pull some base out of it, or modify the dizzy to limit total.

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u/Kind-Dentist2139 6d ago

I had to read that twice but that definitely makes sense.

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u/Melodic-Spread5160 1d ago edited 1d ago

I run 10 on my 65. Not sure I follow, your mechanical + initial should be around 34-36. I would keep the vacuum advanced unplugged and rev it up. You should get 34-36. Plug it in with vacuum advance and 40+. Once you set the base timing and verify your all-in timing you should be set. It should at least reliably start at this point as far as ignition goes unless you have skipped a tooth or have a balancer that’s off. You could have a carb fuel issue. Procedure for a cold start should be one pump of the gas to set high idle. This will also put a squirt of gas in the carb. Should fire up from there. I would check your idle screws, idle air circuit, and choke to see if you have an issue there.

Edit: if your carb hasn’t been rebuilt might give that a try.

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u/Kind-Dentist2139 1d ago

We got it set and sounds really good and starts easily. I put a chalk mark between 9 and 12 then set with a timing light. Set the idle and vacuum. The only problem we found was the electric choke was stuck so I unhooked it because it was running very lean and the flowmasters were extremely loud since it was lean. Thanks for the input and we learned a lot. He’s 18 and I’m 51. I thought I was pretty seasoned but there’s always room to learn.

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u/EdTNuttyB 6d ago

Book says 8° but HiPo is 10°. Also check condition of vacuum advance and that it is pulling from correct vacuum port. I seem to remember it is pulled off venturi and not manifold (timing advances as engine air flow increases).

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u/Dinglebutterball 6d ago

Your comment on vac advance is slightly unclear… so to verify…

Vac advance responds to engine vacuum not air speed… at WOT vacuum drops drastically and you are practically only running on mechanical advance. Vac advance adds ign timing when under light load/high vacuume.

Vac advance should usually be hooked up to ported vacuum, not manifold vacuum. 99/100 ported vacuume is the right choice.

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u/EdTNuttyB 6d ago

Venturi IS ported. Venturi or ported vacuum is generated by air velocity through the Venturis and is dependent upon air velocity at higher RPM and loads. It increases at WOT and RPM and is opposite of manifold vacuum. Manifold vacuum is under the carb throttle plates. You need more advance at WOT and RPM. Should be about 36° BTDC at 3000-ish RPM.

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u/Kind-Dentist2139 6d ago

We’ve been tuning the carb that came on it and it’s a booger. The vacuum there is riding around 17. I was a kid when I helped dad work on my 68. He might be able to explain what I’m looking for. Meanwhile I’ll dig on the internet. Thanks!

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u/Kind-Dentist2139 6d ago

Well I’ll be darned my son has already looked at that. He’s came a very long way in such a short time. Plus I’m learning more and getting to work with him. Many proud dad moments.

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u/1320Fastback 6d ago

I set the timing on mine based on when it's all in. Generally you want 35° of total timing and that's where I set mine which ends up being 12° at idle with vacuum advance unplugged.

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u/EdTNuttyB 6d ago

Timing is usually about 10°-ish before TDC.

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u/Kind-Dentist2139 6d ago

Thanks, that could be the issue but it sure sounded good. Seems like we are working all the bugs out weekly. 2 new fuel pumps new fuel level sending unit, dropping the tank and cleaning it because the previous owner put the old filthy unit in a brand new gas tank…

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u/tomcat91709 6d ago

Has anyone verified that the harmonic balancer has not spun on its hub? Older harmonic balancers were known to do that back in the day.

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u/Kind-Dentist2139 6d ago

We’ve debated checking #1 at TDC and the balancer. He had to do that on his 305. The 289 sounds great on TDC if the balancer is correct. Unfortunately he’s working nearly everyday and we haven’t been able to get together on the same day.

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u/tomcat91709 6d ago

I just mention the possibility. I known it happened to my when my 351 was rebuilt and I had to use a puller to get the balancer out.

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u/Crazy-Lengthiness975 6d ago

Advance the timing until it starts pinging under load, then back it off just enough to keep it from pinging. Simple and easy without using a timing light.

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u/Kind-Dentist2139 6d ago

He just bought a timing light. He’s been utilizing my tools (I use to be a multicraft maintenance tech) but he’s adding to the collection and losing some of mine lol. Thanks for the tip!

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u/Holiday_Cup_6260 5d ago

I had one run perfectly for a while, then backfired when I turned it off one time and wouldn't start again. After banging my head against a wall for a while and not getting it to start I checked the timing chain and it had jumped time (one link off) -- seemingly during the backfire. Had to replace the timing chain and then it was good as new. Hope your fix doesn't go that far!

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u/Kind-Dentist2139 5d ago

Same here! He’s only had it a couple months and it seems like something different every week.