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Old 07-09-2019, 04:35 PM   #1
drolston
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Default Running too Lean?

The engine is 284" with three 97's and a mild cam (Schneider 248f). Runs great except for overheating in traffic and at Interstate speeds. At my wits end on the overheating; a long story that I will not repeat here.

However, my wits keep nagging me that the plugs just do not get to that toasty brown that I am used to seeing on a well tuned flathead. The plug in the picture was pulled after a 250 mile drive, mostly at 60 - 65 mph and about 2700 rpm. White as a ghost. The plugs are new NGK B6HS; longer (7/16") reach for the Offy heads, and a little on the hot side. I have heard on this board that you can not "read" the plugs for rich or lean, because of modern gas, but that plug just does not look right to me.

All three 97s are jetted at .045, which is stock. I am thinking of taking the center/primary carb out to .048 jets. What does the board think? Do I need to re-jet the secondaries as well? Any chance that running too lean is contributing to the overheating, particularly at speed?
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Old 07-09-2019, 05:48 PM   #2
1931 flamingo
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Default Re: Running too Lean?

Newbie here, but timing and a poorly working cooling system equals over heating.
Paul in CT
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Old 07-09-2019, 06:05 PM   #3
flatjack9
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Default Re: Running too Lean?

To answer your question, lean A/F ratio and retarded timing can cause overheating. If you choke the engine slightly, do you notice an increase in power?
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Old 07-09-2019, 06:24 PM   #4
drolston
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Default Re: Running too Lean?

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Originally Posted by flatjack9 View Post
To answer your question, lean A/F ratio and retarded timing can cause overheating. If you choke the engine slightly, do you notice an increase in power?
Timing adjustment on the distributor is set at full advance, and I keep a little pressure on the vacuum brake. I will experiment with the choke at cruise speed to see if changes performance. But I am also really interested in what others are finding regarding spark plug color as an indicator of rich or lean.
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Old 07-09-2019, 07:07 PM   #5
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Default Re: Running too Lean?

I'd say if theres no silver or black spots on the porcelain and the cars not 'hunting' at cruise, your good to go!
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Old 07-10-2019, 06:10 AM   #6
Terry,OH
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Default Re: Running too Lean?

You may want the B5 plug. As mentioned above does the car run better at speed with the choke a little out? If you decide to increase main jet size, I suggest only one size larger, since you are very close. Just change the center carb jets.
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Old 07-10-2019, 09:04 AM   #7
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Default Re: Running too Lean?

You might try this old trick, I asume the carbs are on progressive linkage. If so, bring the engine up to about 1000/1200. then run your hand over the carb, watch the tac. If the RPM's increase your lean.
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Old 07-10-2019, 02:59 PM   #8
drolston
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Default Re: Running too Lean?

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Originally Posted by Terry,OH View Post
You may want the B5 plug. As mentioned above does the car run better at speed with the choke a little out? If you decide to increase main jet size, I suggest only one size larger, since you are very close. Just change the center carb jets.
Why the B5 plug instead of the B6? Is it a little colder range?
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Old 07-10-2019, 03:03 PM   #9
drolston
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Default Re: Running too Lean?

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Originally Posted by Ol' Ron View Post
You might try this old trick, I asume the carbs are on progressive linkage. If so, bring the engine up to about 1000/1200. then run your hand over the carb, watch the tac. If the RPM's increase your lean.
Yep, two fingers over the carb at about 1200 rpm, and I could hear the rpm come up.

I will re-jet the center carb from .045 to .047, and test it again. Hoping running a little richer will mitigate the tendency to overheat at Interstate speeds.

Does anybody have any opinion regarding plug color as a means to judge mixture? What color are the insulators on your great running flathead?
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Old 07-10-2019, 03:17 PM   #10
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Default Re: Running too Lean?

Reading plugs can be a bit tricky. To do it correctly you need to install fresh plugs, run the engine up to a higher rpm under load and then shut off the power and pull the plugs. Just running them and then looking at them will tell you some information such as oily, sooty, tan, etc, but to really use plugs to read A/F ratio data it requires going through the correct check procedure.
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Old 07-10-2019, 03:24 PM   #11
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Default Re: Running too Lean?

I'm running Autolite 216s in my 8ba,Isky Max 1, Offy heads, Loadamatic & stock carb and my plugs are white also. Temp is 180-190 w/180 stats. A Chevy friend says you can't read plugs anymore, but......i ain't convinced.
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Old 07-10-2019, 03:47 PM   #12
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Default Re: Running too Lean?

If you want gas mileage, take the bus.
On a 284 with 3 carbs you will never realize full potential with progressive linkage.
Straight linkage should give you 20 mpg and the most performance you can expect from that cam.
Go to .047 jets in all carbs.
Go one notch colder on the plugs.
If it still overheats, start looking at the cooling system and for rust and scale in the bottom of the water jackets. Remember, only acid stripping will get rust and scale out.
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Old 07-13-2019, 05:03 PM   #13
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Default Re: Running too Lean?

Road test #1: Full advance on the distributor adjustment and reset vacuum brake to contact plus two turns. Outside temp 94. Still overheats beyond the hot mark for only a few minutes in traffic. At 60 - 65 mph the temp crept past the hot mark. Got pretty noticeable spark knock (pinging) on hard acceleration. Conclusion: retarded spark is not the overheat problem.

Road test #2: Removed the 170 degree high flow (Subaru) thermostats. Gave the vacuum brake an additional full turn in. Spark knock much less but still a bit more than I am willing to risk. Slower to overheat in slow moving traffic, but still pegged hot sitting at idle for three minutes. Outside temp 95. Did not get to 60 mph, but at 50 mph the temp went just over the 3/4 mark. Observation: With speed, baffles and shroud, airflow through the radiator is still not enough to cool the flathead under load (60+ mph). With Dennis Carpenter high flow water pumps and no flow restricting thermostats, it still overheats too quickly in traffic. Conclusion: That pretty little Champion aluminum radiator just does not have the heat transfer capacity or efficiency to do the job.

The same engine (pre bore and stroke) did not overheat with the '41 truck radiator that was wedged in there. And the block was thoroughly cleaned during the rebuild. I will have that radiator re-cored (ouch!) and put it back in.

The .047 jets came today. We will see if it runs any cooler at highway speed, and if that helps the problem of stalling at stoplights.
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Old 07-14-2019, 09:30 AM   #14
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Default Re: Running too Lean?

Y/day went to a show about 45 mi away, avg speed 55, 40 coupe, 59ab, hi-comp heads, 2 97's, duals, no stats. Stock temp gauge, stayed in the middle whole trip, coming back on got on divided h/way and it climbed to 3/4. Block and stock rad clean.You're on the right track with the rad.
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Old 07-14-2019, 04:26 PM   #15
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Default Re: Running too Lean?

Road test #3: Put in .047 jets in the center carb and gave it a hard road test. Performance is as good or better than with the stock .45 jets. The engine seems a little smoother at 60 - 65 mph, about 2600 rpm. It was the same temp as yesterday's test, 94 degrees. The engine ran maybe 10 degrees cooler (about 200 degrees) at highway speed. So running too lean is a contributing factor when under load (high speed). A step in the right direction, but the radiator is still coming out.

The Champion aluminum radiator has 351 square inches of core. The brass truck radiator has 451 square inches. If that does not do it, I am changing hobbies back to model airplanes.
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Old 07-14-2019, 05:08 PM   #16
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Default Re: Running too Lean?

Quote:
Originally Posted by drolston View Post
Road test #3: Put in .047 jets in the center carb and gave it a hard road test. Performance is as good or better than with the stock .45 jets. The engine seems a little smoother at 60 - 65 mph, about 2600 rpm. It was the same temp as yesterday's test, 94 degrees. The engine ran maybe 10 degrees cooler (about 200 degrees) at highway speed. So running too lean is a contributing factor when under load (high speed). A step in the right direction, but the radiator is still coming out.

The Champion aluminum radiator has 351 square inches of core. The brass truck radiator has 451 square inches. If that does not do it, I am changing hobbies back to model airplanes.
What do you have against changing ALL of the jets to .047. ????????
They are not very expensive.
At 65 mph, you are running on all 3 carbs even if the 2 outer ones are partial throttle. That means you are still lean.

If you change to straight throttle linkage, BE CAREFUL, you will most likely have enough torque to burn rubber then.
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Old 07-14-2019, 11:54 PM   #17
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Default Re: Running too Lean?

Quote:
Originally Posted by Pete View Post
If you want gas mileage, take the bus.
Straight linkage should give you 20 mpg and the most performance you can expect from that cam.

I'd love to get 20mpg out of my 06f150.
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Old 07-15-2019, 06:35 AM   #18
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Default Re: Running too Lean?

A point to consider. Per JWL's book and personal air fuel meter testing, Stromberg 97's run leaner the faster you go. The power circuit seems to only come in close to wot. So you need to jet for the maximum speed you expect to drive.

This may be why you are overheating at higher speed. I would say Pete has the right suggestions and you are on. the right track.

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Old 07-15-2019, 06:45 AM   #19
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Default Re: Running too Lean?

I would go start with what Pete has suggested and test it again . . . is an easy test and you might just cool it some more. Bigger jets might just do the trick for the highway related issues . . . BUT . . .

With that said, I believe that your radiator does not have enough cooling capacity to handle the job (my opinion). You mentioned that it will overheat in traffic - just idling. When you're just idling, you're not even using the main jets - just the idle mixture screws . . . so if it overheats sitting in traffic, you most likely do not have enough cooling capacity (given that you've already messed with the advance). I realize nobody really wants to have to buy a new radiator and that cheap aluminum ones are just that . . . cheap . . . but you'll probably find that once you re-core a stock style radiator, that it will cool.

I have a 284 cube motor in my 32 - have Skips water pumps and had the 32 radiator re-cored - stock gen/fan setup . . . I can idle in traffic on a hot day and not overheat (was at the GoodGuys show a couple years ago - took an HOUR in 90+ degree weather to leave the darn place!).
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Old 07-15-2019, 06:51 AM   #20
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Default Re: Running too Lean?

Back to the original question on porcelain color on the plugs. With today's fuels, you'll probably not see the good ole' 'chocolate brown' coloring we used to see . . . usually they will be much closer to white (and what we used to call lean). I use dual AFR meters in my exhaust system (along with EGTs) to really see what the mixture is doing at different load conditions.

Now, if you see the plating start to flake, peel away or bubble around the edge of the plug (or starting with the electrode itself) - then you definitely ARE getting lean. I pay attention to the plating a lot more than porcelain color with today's fuels.
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