Hay guys I need some assistance. I have a 55 caddy with a 331, has 390 heads, opened inlet and exhaust ports and changed the cam to hotter set up. I'm guessing hp of 275-300. Stock is advertised at 250. I installed a tri power set up from a 1960 caddy 390 motor. It is running rich. The Rochester 2 gc in the center has number 60 jets, while the dump carbs have #69 jets. I'm running rich, so need to get the centre carb jetted down. Not sure with what to go with? I think the 58 caddy tri power had 57 or 55 jets in the centre, but don't know about the outers? I was told not to go down more than 2 jet sizes, and that all carbs should have the same jet size. I don't think that is correct on all three being the same. I think the end carbs should have smaller jets than the centre, since more is being dumped out(2:1). I am not a master of carbs so I am inquiring some input from those with experience with this type of set up. Cheers, George.
George, to be clear you are running now with all 3 carbs in a progressive mode? At idle then can you feel any air being sucked in on the out board carbs? Would not be unusual to see those end carbs leak by in an idle state causing a rich issue. Just saying. Have you had the engine running with only the center carb to see how the engine reacts to the center carb jetting?
To summarize ( I think), we have non-stock heads, TOO MUCH carburetion, and an unknown camshaft, but larger than stock, so probably low vacuum. We have no information about compression ratio or vacuum readings. LOTS of testing is in order. One area the OP has disregarded is the jetting in the end carbs (if they are genuine tripower end carbs) MUST be greater than the jetting in the center to compensate for the lack of power valves in the end carbs. We also know nothing about ignition. Perfect carburetion will run rich with faulty ignition. We also know nothing about linkage. Is the original Cadillac tripower vacuum linkage being used? Or aftermarket (which may be holding one carb partially open). This article may (or may not) help: https://www.thecarburetorshop.com/Tripowertuning.htm Jon.
Right now just centre carb running, ends are blocked off. Progressive linkage used and ignition is petronix on original dizzy with rebuilt vacuum advance. Vacuum was disconnected to set timing and gage attached to it, getting readings of 15-18". Jetts in the carbs are #60 in centre and #69 on the ends. Running non ethanol fuel. Right now timing is set at 6 degrees advance. The car stalls if reved up and left to idle as rpms drop.
1958 jets are 0.060 in all three carbs (all three were small carbs) 1959~1961 jets are 0.060 center, 0.069 ends (ends are larger than center) pertronix adds another unknown. Did you upgrade to an alternator when installing the pertronix. Have had a ridiculous number of prospective "carburetor" customers that did not upgrade to an alternator when downgrading to the pertronix. Points/condenser upgrade from the pertronix solved many of their problems. I am not sufficiently familiar with Cadillac engines to know the end result of placing 390 heads on a 331. Need a Cadillac engine guru to chime in here as to applicability. ASSUMING (always a bad idea) that the 390 heads will not have a vacuum leak, and not drop the compression completely off the map (compression test results???); then the engine SHOULD run decent with the possible exception of idle/off-idle/main circuit transition hesitation on a genuine un-bolluxed 1960 Cadillac center carb, when solid block-off plates are installed UNDER the end carbs. If the preceding paragraph is true, and the carb is at fault; it may be that the lack of displacement (quick drop in vacuum) is causing the power valve to open way too soon, contributing to an over rich condition (my bet is still on the pertronix). Final check of the center carb would be to remove the air horn, remove the power valve from the bowl, and plug the threaded hole where the power valve was inserted. No need to remove the power valve actuating valve from the air horn. This test will mean ALL of the fuel above off-idle (unless there is a crack somewhere - unlikely) from the center carb is metered by the main metering jets. Just for grins, figure the area of the 2 main metering jets, and compare it to the area of the FOUR orifices on the power valve. (Helpful hint - they are each 0.059). And just for the record, our experience has been that when installing a carb that was designed for a much larger engine, OFTEN, once all the circuits are functioning correctly, that RICHER, not leaner, jets will need to be installed, due to lower venturii air velocity. And if the power valve test does not solve the issue, just upgrade to points/condenser! Or better yet, a set of factory dual quads AND points/condenser! Jon.
Thanks for the update. I do have the larger end carbs. Jets are as per 59/61 carb set up. I have the generator set up. I will see about the original points and condenser set up. Heads were done by machine shop and only less than 1hr run time on them. I will reassemble the centre carb, I opened to check the jet size, and advance the timing to 12 degree for primium fuel and see how it does. If I can't find the points set up I will switch to alternator and report back. Motor does seem to run nice but the wot to idle, shuts off the motor. I will report back once I make changes. Thanks for the input and direction to go in. G
caddyguy - I was not questioning the machine work on the heads, rather the compatibility of 390 heads on a 331 block. Not my area of expertise, I simply do not know. Jon.
390 heads are better flowing, bigger exhaust outlets intake and exhaust valves are bigger, besides, I had a 390 done, but block cracked, so threw the heads on the 331. Direct bolt up, just used the 390 pushrods. 390 and 331 are the same block, 390 has 4" pistons, 331 has 3 5/8" pistons.Compression ratio on 331 is 9:1 , 390 is 10:1. It actually runs strong.
Ok, we got the petronics out and old school points back in. Re timed. Now she goes to wot and down without stalling. Still burning rich. I rechecked float settings, there good. Vacuum is around 40" at the vacuum advance. Spark plugs are carbonated. See photo. I dropped it so gap is shut, I've reset the gap. Running rich. G
With 59 less cubic inches in a engine combination the factory never produced, you will need to work out the best jetting and tuning for your combo. No reason to expect that what works well on a 390 will work as well on a 331.
Agreed. That is why I am asking for some direction. Switching back to the point solved some issues. Now I tried the removal of the power valve. The motor ran rough with much exhaust smoke. Bowl was 1/2 full when opened, both befor and after the test. I have re installed the power valve as it was. There was a vacuum when I opened the fuel inlet to the carb. Next question there is an access port on the bottom of the fuel bowl. Is it to be connected or just plugged.?
Charlie Price has a few videos covering the Rochester 2G tri power on YouTube that are worth watching.
I watched the Charley price vids, now I know that the port from the bottom of the fuel bowl is for the vacuum advance on the dizzy. Also the jets are over sized and will close them down. I have high vacuum as it is. 40" at idle, normally had 18-24.
Logic would seem to indicate feeding 59 LESS cubic inches would require installation of leaner (smaller) jets. Some of the factory 365 Caddy 3x2 sets used as low as .051 jets in the center carb. At 331cubes, it is not unlikely that you will need to go even smaller. Rochester 2 Jet Main Jet Specifications - Mikes Carburetor Parts (carburetor-blog.com) Depending on your carb numbers, you may need to select from jets in the .040-56 range used by other engines in the small 300 cube range. Plug readings will tell when you got it right, -unless you have something else wrong that is not main jet related.
Plate on distributer is grounded properly and advance is at 39 degree. Waiting on jets to come in. Ordered 55 to 58 size, will see what happens. I will try another vac. gauge. There is a 1/4" return line to the tank.
The vacuum gauge is working proper, I was reading the wrong scale. 40 mm of vacuum which is 12". Thats normal range. I installed 57 jets. Seemed to run nice but still rich. See photos. Also changed them to 55 jets. Still seems rich. See photos of spark plugs. Last photo is 55 jet. Compression on motor is 150 to 155 on all cylinders,as per manual. Let me know what ya think. Smaller jets?
Are you running now with the end carbs blocked off? You must rule out the fact that those end carbs could be leaking by the throttle blades.
Running centre carb only, others are blocked off. Ran motor for 20 min on each set of jets. Cleaned plugs before running jets.
What happens when you drive the car under full throttle acceleration? That's where you don't want to be too lean. Does it ping? The plugs are black, but not that bad for just idling. Reading plugs with today's gasoline is pretty difficult. Judging the air/fuel mixture efficiency based on an idling engine is not that helpful. A 50 miles drive by the feel in the seat is more important. Now I'm rambling, sorry.
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