I've been fighting two problems 1- running hotter on expressway, doesn't overheat but does run about 15 to 20 degrees hotter and comes right down when off the expressway. I've gone through everything and system is good with a 4 row, clutch fan, etc. Other problem is at cruise anywhere from 30mph to expressway speed , when you squeeze the gas it seems to have a stumble/lag for second, like a lean spot. My MSD is at 18 initial and 30 total, I have about 11.25cr and 30 is about all I can go on pump 93. Will the vacuum advance help with the overheating at highway speeds and the tip in stumble? I will be putting a innovate A/F gauge in soon.

It should IF the engine can tolerate the extra timing at light load. I don't think it will affect the stumble.

What heads do you run?

Is that an Edelbrock carb?

Kevin

at those speeds your into the main metering on the carb. it may be too lean creating extra heat. take a close look at your jetting.

It's a 360 with J heads, mechanical 6 pack

Lean may cause heat, stumble and detonation. May also stumble because it needs more timing. Do u have an a/f?

(1) put in several gallons of race or av gas & bump the timing up to where it should be for your eng (more total/faster curve (lighter springs) cuz your timing is retarded & see how the temp does. (2) What Lewt said confirm your jetting is in the ballpark just bump em up quite a bit for a test just like purchasing the av gas, a one time deal & blocking the rods up (eddy) is one way to do that to put you on the power circuit. (3) if still running hot then I'm thinking there is either a water flow restriction (likely) or grille (airflow) restriction (less likely). lower hose needs a spring/toss the stat for a quick test (wont hert the eng for just one time). belt tight (I'm sure you've checked it already (pump speed). rad IS unobstructed right? more rare is a rusted up block cooling passages or a slight combustion leak into the cooling system (an emissions testing station can stick the probe into the dead air space above the coolant & it'll show a reading if there are hydrocarbons present (combustion leak), in drive/ebrake on/foot on brake power brake it as a minor leak might need it to be pushed hard for it to show up. Holler how it turns out. water temp gauge you have is confirmed accurate right?

I will have a A/F meter installed in a couple weeks, need to have the bung welded in. When it's on the center carb it runs fine except for the tip in. The center carb is what I drive on 95% of the time it does run out of steam near the point where the two outer carbs open but I guess that's expected.

My center is jetted at 64

Vacuum advance can help keep it cooler a highway speeds (more advance can increase efficiency and reduce heat)... but probably need to tune it carefully with high CR for pump gas. Don't think it will help with the stumble though... when you step on the gas, manifold vacuum drops and vacuum advance should be basically inoperative. Also, lean=hot to a point so verifying AF ratios sounds like a good idea.

Still, it sounds like a strong cooling system... 4 core radiator ect. Probably should keep it cool regardless. Are all cooling components in known good shape?

It's lean as heck I bet. And race gas will do nothing for the leanness.

what a (1) tank addition of some race/av gas will do is allow him to restore his timing to a normal setting to see if retarded timing is what is making him run hotter.

those carbs, if i remember correctly, come with .031" squirter and a white 218 pump cam in the center. i always ditch the big squirter and go to a .025" or .028" with tubes on that small carb. a green pump cam may not hurt. they did come with 64 jets in the center carb.

now let me piss you off. if someone told you to take those carbs off and put a 1050cfm dominator on that 360 you'd say they were crazy. have you ever done the math on them? those deuces have nearly the same venturii area and air flow combined as a 1050 dominator, (factory 6-pak cfm rating was 1030cfm). plus they're not velocity controlled. when those things are opened up air velocity comes to a crawl. no velocity/pressure differential equals no fuel drawn from the bowls. i ran those carbs back in the day for awhile. easy to tune, can be made to drive nice, but absolute torque killers in small engines. the 340-440 vacuum 6-pak carbs are too big for a small engine, and they're velocity controlled.

I don't know, these mechanical carbs on my aprox 400hp 360, with a 4,400rpm stall absolutely rock! Actually feel a bit stronger than the holley 750dp chokeless race carb with annular booster I had on it. That 750 BTW had the same tip in problem. I will play with the carb once the A/F gauge is in.

If you think a stock distributor would be better, are you aware that the MSD curve can be changed (stop bushing/springs) to mimic the stocker?

I'd cut the compression by 1-1 1//2 points and throw some timing in it.

Yes but my MSD has no vacuum advance,

Vacuum advance will help. You can trigger the MSD with a stock points or a Mopar Electronic distributor. But if you have detonation issues I'm not sure how easy you will find it to run the vacuum advance.

18 to 30 degrees, that's only 12 degrees. Try to open it up so maybe 13 to 37 with med springs. The higher timing should help at cruise speed. If the engine has a bigger cam you probably need more main jet and idle jet. What is the idle vac, and I mean 550 to 650 rpm, if you can't get that low there's one of the problems.

Cam is 520/540 lift 244/252 @.050. Vacuum is about 7" in gear idling at about 800/850 rpm
It idles at 1,000 in park.

1. Too much compression for iron heads and pump gas. Either use better gas, lower compression, or get aluminum heads. Take your pick, none of them is an inexpensive solution.

2. Are these the 4782/4783 mechanical carbs with accelerator pumps on all 3 and fuel inlets on the driver side or are they stock carbs with mechanical linkage added ditching the vacuum pods?

3. No one has asked so I will. What jets are in the carbs? All of them. What pump nozzles? What power valve in center carb? Has anything else been altered, such as, Idle air bleeds, idle feed restrictions, main air bleeds, power valve channel restrictions?