# 750 Edelbrock Too Big for 65 389?



## SLSTEVE (Dec 8, 2020)

I’m running a new 750 Edelbrock on my newly rebuilt .030 overtired 389 engine. I ran engine to break in the cam and the fumes almost ran me out of the garage. Seems like it’s running way too rich. I haven’t timed the engine with a timing light, nor have I adjusted the air/fuel screws on the carb yet. Is this carburetor too much for the engine? I did install a tri power cam in the engine when it was built. Not sure what heads are on it, they were on the 65 389 engine when I bought it. It was originally a 2 barrel and I put an Edelbrock aluminum Performer intake on it after it was all rebuilt.


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## SLSTEVE (Dec 8, 2020)

SLSTEVE said:


> I’m running a new 750 Edelbrock on my newly rebuilt .030 overtired 389 engine. I ran engine to break in the cam and the fumes almost ran me out of the garage. Seems like it’s running way too rich. I haven’t timed the engine with a timing light, nor have I adjusted the air/fuel screws on the carb yet. Is this carburetor too much for the engine? I did install a tri power cam in the engine when it was built. Not sure what heads are on it, they were on the 65 389 engine when I bought it. It was originally a 2 barrel and I put an Edelbrock aluminum Performer intake on it after it was all rebuilt.


That’s rebuilt, not overtired.


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## Mine'sa66 (Oct 30, 2019)

Running rich or lean isn't governed by your carb's maximum flow rate.
750cfm is in the range for 400ish cubes.


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## SLSTEVE (Dec 8, 2020)

SLSTEVE said:


> That’s rebuilt, not overtired.


Sorry, it’s overbored not overtired


Mine'sa66 said:


> Running rich or lean isn't governed by your carb's maximum flow rate.
> 750cfm is in the range for 400ish cubes.


So I will set timing and then adjust air/fuel on carb and see what happens.


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## PontiacJim (Dec 29, 2012)

SLSTEVE said:


> Sorry, it’s overbored not overtired
> 
> So I will set timing and then adjust air/fuel on carb and see what happens.


A cam with a lot of overlap or tight LSA will push unburned fuel out the exhaust and give you that watering eyes experience.

However, make all your adjustments as you pointed out - timing & carb. The 750AFB also has the power valve and springs to keep then closed at high idle vacuum conditions. They are under those small covers with the screws on the top of the carb body. If you don't have enough vacuum to hold the power valve down because your engine has a lower vacuum due to the cam selection, the power valve is in the unseated position and allowing extra gas to flow through the carb that you do not need at idle. You can purchase weaker springs which work with less engine vacuum and will keep the power valve down at idle and not dump extra gas through the carb - kinda like running rich.

So if you can, check engine vacuum after you get your timing set and idle mixture screws adjusted.

There is an online Edelbrock 750AFB owners manual on line and you can see the adjustments that can be made.


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## Baaad65 (Aug 29, 2019)

That's why I run my timing different than most, 20° on the balancer, 14° bushing with a vacuum advance limiter of 10° burns the fuel off at idle.


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## SLSTEVE (Dec 8, 2020)

PontiacJim said:


> A cam with a lot of overlap or tight LSA will push unburned fuel out the exhaust and give you that watering eyes experience.
> 
> However, make all your adjustments as you pointed out - timing & carb. The 750AFB also has the power valve and springs to keep then closed at high idle vacuum conditions. They are under those small covers with the screws on the top of the carb body. If you don't have enough vacuum to hold the power valve down because your engine has a lower vacuum due to the cam selection, the power valve is in the unseated position and allowing extra gas to flow through the carb that you do not need at idle. You can purchase weaker springs which work with less engine vacuum and will keep the power valve down at idle and not dump extra gas through the carb - kinda like running rich.
> 
> ...


Thanks Jim for your information. My harmonic balancer has two timing marks on it. Which one do I use?


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## armyadarkness (Dec 7, 2020)

750 is perfect for that engine. Just need to dial everything in. Give me a buzz later if you want.


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## PontiacJim (Dec 29, 2012)

SLSTEVE said:


> Thanks Jim for your information. My harmonic balancer has two timing marks on it. Which one do I use?


Check this out - 1965 balancer. It shows the 2 timing marks on the balancer and what they represent.









Pontiac Tune-Up Specs 1955-70


Purchased a 1970 Tune-up Guide for both cars and trucks. Neat little handy booklet. Here are the specs related to Pontiac which spans the 1955-1970 models. Just click on each of the 5 documents to see any of them, then you can expand those for easier viewing.




www.gtoforum.com


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## SLSTEVE (Dec 8, 2020)

PontiacJim said:


> Check this out - 1965 balancer. It shows the 2 timing marks on the balancer and what they represent.
> 
> https://www.gtoforum.com/threads/pontiac-tune-up-specs-1955-70.137739/[/URL or I’m





PontiacJim said:


> Check this out - 1965 balancer. It shows the 2 timing marks on the balancer and what they represent.
> 
> 
> 
> ...


Thanks again Jim. Exactly what I was looking for!


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## geeteeohguy (Feb 2, 2008)

What Pontiac Jim said you can take to the bank. The 750 is perfect for a 389. Just need to get the timing curve and mixture fine-tuned. 👍


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