[65 pile]

I have read multiple threads about jetting carbs at higher altitude. I have taken the advice (Tom V. from this thread, http://forums.maxperformanceinc.com/...78#post5749478, post #7) from a previous thread and used the air density at a certain altitude to calculate the difference. According to these differences, I am at 14% reduced at 5,000 ft. here in Loveland, CO.

I pulled the jets from the center and rear carbs. They were #64 in the center and #68 in the rear. I guess the car ran well in Lancaster, PA, which must be somewhat near sea level. I really don't remember, it always smelled rich, but didn't stumble like it does here. I do know it could spin the tires there if I tried and it would sometimes get scratch when I hit second. Out here it stalls if I try to light them up.

Anyway, I just wanted to run my choice of jets by everyone before I went and spent the money on them. The car is a 4spd. with a 389 tripower. I think there was some work done to the engine before I got it, but I don't feel it was too radical, and certainly don't remember what the seller told me (who knows if it was accurate). So, based on the jets that were in the vehicle, and the fact that air density is reduced by 14%, I came up with #59s in the center carb and #63s in the ends. I know the ends are supposed to run a little rich compared to the center. Would anyone recommend #64s in place of the #63s?

Thank you to anyone who offers any advice. This forum has always been very, very good to me.

Happy New Year.

Robert

[Tom Vaught]

One jet change rarely makes a difference that you can easily notice. That is why Holley always recommended making a 2 step jump initially.
Two Steps up then try one step back. Two steps up and one step back. That way you cover all of the jet sizes but the change each time forward is noticable. Same deal going lower for Altitude Testing. I personally would really dial in the center carb jetting to be spot on and then choose the 64 Jets for the ends and if you have no drive issues leave it slightly rich vs slightly lean. You do get decent air in Colorado occasionally.

Tom V.

[carbking]

Robert - I really believe you numbers will be lean.

I totally agree with Tom about dialing in the center (with block-off plates under the front and rear).

I would start at 0.062 in the center. If that is still too rich, then drop off 0.001 at a time. I think 0.062 or maybe 0.061 will be your optimum size for the center.

Once the center is happy, I would start with 0.066 in each of the two end carbs. I think that will end up being very close.

All of the above assuming you are running non-ethanol fuel. If you have to run ethanol fuel (E-10), I would try it as is before making any changes. We have found E-10 is about the same as one size lean jets.

The two-step change for jetting up is great, but jetting down is a little different. You don't want to go lean. This is why I would urge caution.

One other thing, Stromberg recommended a jet change of minus 0.002 on their WW series two-barrel, which has the same general characteristics as the Rochester 2-G series, for an elevation of 5000 feet.

Jon.

[Dick Boneske]

I agree with the other comments. Start with .060" jets in the center. The end carbs will be happy with .066".

I run .061" center carb jets in my 434 ci Tripower. End carbs are at .070". That's at 750 feet above sea level, not 5,000.

[65 pile]

Thank you for the responses Tom and Jon.

I must have had a few too many beers last night, as the post that I linked to was not the post I wanted. However, it was in fact Tom V. that I got the idea to calculate using air density at different altitudes. Here is the correct link http://forums.maxperformanceinc.com/...82#post4836182 (see post #4).

I respect the knowledge you both have. And quite frankly, my knowledge is next to none. I just wanted to follow up with both of you about your recommendations. I have read quite a few articles about calculating the proper jet size and most are coming in at sizes smaller than what you have suggested. Here is a link to one article in particular. http://users.frii.com/gbooth/Cars/Jets.htm This was written by a fellow in the town next to me. Using the information in that article I calculate #60s in the center. He said that he got the best performance from #58s, which I feel would be much too lean. I realize this was written in 1987 and the gas I have access to today is quite different. I am running E-10. Ever since I have owned the car that is all I have had access to.

I guess to summarize, has anyone had actual real world experience at elevations close to this for extended periods? I can calculate formulas all day, but really want to know what works best in actual use.

Finally, looking at what was supposed to be in the car from the factory, the jets should have been #63s in the center. Should I use that as the starting point and drop 2 sizes from there? Or, would you stick with what was in the carb and drop 2 sizes from that? Like I said previously, my memory says that the car was running rich when it was in PA, but that was over 5 years ago, so maybe my memory is a little foggy. If it was running rich then, was #63 the correct size and it had too large of a jet in it?

I feel I am rambling at this point, so I will stop right here. Again, I appreciate all feedback.

Robert

[Dick Boneske]

Robert,

'65 389 Tripowers were shipped with .063" jets if manual transmission or .060" if automatic in the center carb. All '65 389 Tripowers were shipped with .068" in the end carbs.

I think you're overthinking your question. All the calulations in the world can't compensate for different gasoline today, possible mods to the engine in 53 years (especially the compression ratio & camshaft), and your high elevation compared to most of the country.

You already have suggestions from three of us of a starting point. You said you've already pulled the jets. If you need some sizes for the center carb around .058"-.062", let me know. And, for the ends, I can send .064" or .066" jets. All I need is shipping reimbursement.

Good luck.

[Tom Vaught]

Concur with Jon and Dick, very tough to be specific (as you are even asking for higher altitude than what I did for testing at Denver 5200 feet. Basically 2000 feet higher.)

DIAL IN THE CENTER CARB FIRST.

I have used the block off plates to remove the end carbs and run only on the center carb on a new build. In your case it is possible to just make some thick block off sheets out of heavy gasket material and install them.
Less messing around with the fuel lines etc. Remove the link to the rear carbs, LOL.

So whatever you come up with, I would appreciate the data so I could help others down the road.

Tom V.

[65 pile]

Thank you Tom and Dick.

I will use the recommended starting point and go from there. Also, thank you for the idea of using gasket material to block off the secondary carbs. I was thinking it would be a major pain dealing with the fuel lines trying to have only the center operational. Would you also recommend just pulling the accel pumps out of the secondaries so that it's not just squirting fuel onto the block off membrane?

Tom - I will let you know what ends up working the best. I am at ~5,000 ft. so that is just a little lower than Denver. I am getting ready to hit the busiest part of my work year, so it might be summer before I can get the final answer to you. But I will at least post in here for future reference.

Dick - I will send you a PM regarding jets.

Thanks all!

[65 pile]

Please ignore this dumb question. With the linkage disconnected, the secondaries will not operate. Duh!

Originally Posted by 65 pile

Would you also recommend just pulling the accel pumps out of the secondaries so that it's not just squirting fuel onto the block off membrane?

[Dick Boneske]

If the engine idles decently, indicating no air leakage through the end carbs, there is no reason to block the end carbs. If however, the idle is rough, there is air leaking past the throttle plates in one or both end carbs. Blocking them off will eliminate this air leakage, but won't fix the problem of leaky throttle plates. I suspect you have little or no air leakage, making this step unnecessary. The size of the end carb jets has absolutely no bearing on the idle & driveability of the car unless you open the throttle far enough to operate them. As you've already figured out, removing the slotted rod takes the end carbs out of play so you can jet the center carb and evaluate performance with that first.

I have the jets ready to ship--four .066", two .064", and two .060" main jets. I also found a pair of .059" jets you may want in case the .060" jets are on the rich side. We can discuss details on PM about addresses, etc.

[65 pile]

Hi everyone. This is just a brief update, which I will update again in a few weeks, if anyone was following this.

Dick B. hooked me up with some jets. I completely took the carbs apart cleaned them better than they have been cleaned in a long time. I installed .060 jets in the center and went with .064s in the outer carbs. I finally got it running this weekend after having to take few of a few other things.

The update, it still smells a little rich. I have not pulled the plugs yet to take a look. I think the timing needs to be adjusted, but that will have to wait until next weekend when my neighbor who has a timing light and is good at that stuff is back in town. Also, there is some pretty old gas in the tank as well, so I’m going to run that all the way out and put some fresh in before making any additional changes. It isn’t as responsive as I would have hoped, and hesitates for a moment when I punch it. With all of that said, I’m sure it is running better than before, it just needs to be dialed in a little more.

If anyone has any tips for making the final adjustments, as always, I’m all ears.

Finally, thank you to everyone that offered suggestions. And a huge THANK YOU to Dick B. He hooked me up with jets, new accelerator pumps, and answered numerous PMs. It has been greatly appreciated.

[Tom Vaught]

Check out the timing, and get the drive-around modes dialed in, then "The Group" can help you get the transition to WOT better.
All of the Tri-Powers have a hesitation on WOT unless you play games with the pump shots on the end carbs.

Tom V.

[aceaceca]

Here you go. Loveland ,Colorado no less.
http://users.frii.com/gbooth/Cars/Jets.htm

[aceaceca]

I am also currently pondering jetting for my 65 tri power. I have confirmed Royal Bobcats got .070 in outbound carbs. I have not found reference for center carb but I believe it was .068. If my memory serves me I feel we used to run .070 outbound and .068 center. I might start with the old set up. What goes around comes around.

[65 pile]

Thanks Tom. I’ll be sure to keep this updated as I know you wanted to see where things ended up.

aceaceca, thank you. That is actually the link from my post #5 above. That was the exact formula I used to arrive at the jets I used. That and then the advice of Dick, Tom and Jon. My calculations form this formula ended up as a mix of some of each of their suggestions.

[aceaceca]

Correction to my post above. Royal put .070 in center and I am pretty sure .073 in outers.

[Dick Boneske]

Remember, the jet size has nothing to do with idle. The idle fuel/air mixture is determined by the idle circuit in the center carb--nothing else. With your high altitude situation, it may be necessary to run smaller idle tubes, smaller idle bypass restrictors. This would be accomplished by swapping the venturi cluster in the center carb. Typically on a setup like yours, the idle tubes would be .033" and the idle bypass restrictors .042". We can try to find a cluster with tubes at .030" and bypass restrictors at .040". This would be a better setup than the stock setup you now have. I have some clusters from SBC Rochester 2 bbls. that may work. If you want, I'll check the idle circuit sizes.

If the WOT hesitation remains after setting the timing, check it out as follows. Disconnect the linkage between the center and rear carb, so you can drive the car on center carb only. Check out WOT on the 2 bbl. only. If the hesitation still exists, you either have too small main jets in the center carb or the accelerator pump is not working. Very likely it's the pump. Make sure the check balls are in place if this is the case and post the results.

Originally Posted by 65 pile

Hi everyone. This is just a brief update, which I will update again in a few weeks, if anyone was following this.

Dick B. hooked me up with some jets. I completely took the carbs apart cleaned them better than they have been cleaned in a long time. I installed .060 jets in the center and went with .064s in the outer carbs. I finally got it running this weekend after having to take few of a few other things.

The update, it still smells a little rich. I have not pulled the plugs yet to take a look. I think the timing needs to be adjusted, but that will have to wait until next weekend when my neighbor who has a timing light and is good at that stuff is back in town. Also, there is some pretty old gas in the tank as well, so I’m going to run that all the way out and put some fresh in before making any additional changes. It isn’t as responsive as I would have hoped, and hesitates for a moment when I punch it. With all of that said, I’m sure it is running better than before, it just needs to be dialed in a little more.

If anyone has any tips for making the final adjustments, as always, I’m all ears.

Finally, thank you to everyone that offered suggestions. And a huge THANK YOU to Dick B. He hooked me up with jets, new accelerator pumps, and answered numerous PMs. It has been greatly appreciated.

[Dick Boneske]

Stock jetting on a manual trans '65 is .063" in the center carb, .068" in end carbs. Anything above .065" for the center carbs would be rich to the point of black smoke from the exhaust--- and unless you're running a very radical cam grind, unnecessary.

Royal used .070" or .073" jets in the end carbs. I usually use .070" jets to replace the .068" jets. If there's an aftermarket cam, sometimes .073". I remember a guy at Union Grove Drag Strip back in the day with a GTO with a radical solid roller cam who removed the end carb jets completely to richen the WOT mixture. Exhaust looked like a Diesel through the quarter mile, but he ran very well. His name was Ralph Tatum.

Originally Posted by aceaceca

I am also currently pondering jetting for my 65 tri power. I have confirmed Royal Bobcats got .070 in outbound carbs. I have not found reference for center carb but I believe it was .068. If my memory serves me I feel we used to run .070 outbound and .068 center. I might start with the old set up. What goes around comes around.