3x2 tuning

[Robert D.]

When i run my car (67 435hp) it runs fine but if i shut it off or it stalls once up to proper temp its very hard to start again it turns over fine just wont fire up. Any ideas why doesnt seem like vapor lock and the choke isnt being pulled shut so i cant figure out why this would happen any ideas would be welcome.
the second question is is there a source or manual for adjusting the high idle circuit on these cars some time when i start it the high idle dosnt kick in
and last question is my neutral safty switch doesnt work is there and adjustment? it is part of the reverse light mechanism correct?
thanx bob defalco

[Stuart F.]

Re: 3x2 tuning

Bob;

You deserve some replies on your thread. I wish I could help you, but I'm trying to sort out my son's 69 L-89 which does some of the same things, I.e. Stalls when braking for a stop light, and then restarts hard with long cranking. I just rebuilt the tri-power carbs and will be setting them up on the car. I'm hoping that correct float adjust on the center carb will cure the stalling problem. As for the high idle, the only carb adjustment I can see is to bend the linkage tab that fits into the plastic high idle cam. Perhaps the choke spring that fits into the "divorced" choke stove may be weak, but it's hard to tell under warm ambient conditions of the summer. The connection rod may have an adjustment to it, but you have to check service manual for it. I don't have access to one, and the rebuild kits don't come with any adjustment information. So, as it goes, I'll be watching your thread for information, and studying the archives.

Good luck;

Stu Fox

[Robert D.]

Re: 3x2 tuning

Thanx stu going to start with the float adjustment alittle good luck with yours
bob

[Donald A.]

Re: 3x2 tuning

When i run my car (67 435hp)
and last question is my neutral safty switch doesnt work is there and adjustment? it is part of the reverse light mechanism correct?
thanx bob defalco

Bob - you indicate a 1967 435HP so you have an L71 and those are 4-speed cards, not automatics in 1967. There was no "neutral safety switch" for a manual transmission 1967 Corvette to my understanding. There is such a switch for M35 (auto trans) cars, but not for 4-speed cars.

[Robert D.]

Re: 3x2 tuning

OK great thank you Don

[Stuart F.]

Re: 3x2 tuning

Is there a backup light switch, perhaps?

Stu Fox

[Don W.]

Re: 3x2 tuning

Hi Bob and Stu,

Look here: http://lbfun.com/Corvette/Tech/vettetech.html under the section "fuel and intake" for some carb and 3X2 tuning info.

Don

[Robert D.]

Re: 3x2 tuning

Awesome info
Thank You
Bob

[Stuart F.]

Re: 3x2 tuning

II agree. Thanks Don. I'm printing out the tri-power info right now as reference when I tune my son's set up. I'll use the opportunity to teach him some basics as well. I did the same thing when we were working on his 62fuelie.

Thanks again.

Stu Fox

[Stuart F.]

Re: 3x2 tuning

Today, I finally got a chance to do an initial set up on my son's tri-power. I had set the new float valves to the adjustment of the old valves, but found that I had way too much level in the center carb and a slightly high level in both end carbs. I made a rough readjustment given that the car was not on a level surface (close, but not ideal). That got us to a "no leak" condition. On the next start up, we ran it a little longer, but not fully warmed up. It had cleared the high idle cam, but still wanted to stay at about 1350 rpm and would not kick down. This scared me some as right away I thought "vacuum leak!" Upon shut down, it did diesel a short bit which confirms we have a problem of some sort. The idle speed adjustment screw was ineffective. I'm trying to research this some more, but am certain all gaskets are correct, and we didn't change any thing else. Perhaps someone knows off hand of some peculiar characteristics of this set up like the mechanical linkages or some thing that would hang up an end carb throttle???

Oh well, I'll figure it out sooner or later. I would just hate to pull these carbs off again. Oh, did I mention; I still hate Holleys!

Stu Fox

[Peter M.]

Re: 3x2 tuning

Hi Stuart,Check that the throttle shafts on the end carbs aren't hanging up.Regards,Pete

[Timothy B.]

Re: 3x2 tuning

Hi Stu,

I would remove the end carburetors and block the intake manifold and run the engine to see how the primary carburetor works. If it adjusts and idles the engine cleanly the secondary carburetors are where you can turn you attention to.

Get a small block of wood and make a gasket to block the other attachment holes, I know it's a PITA but it may take you to the problem carburetor.

[Ronald F.]

Re: 3x2 tuning

Stu, have you checked for a spark when this happens?

[Stuart F.]

Re: 3x2 tuning

Thanks Tim. My son mounted the carbs and he has a tendency to over tighten everything. Perhaps he uncovered the characteristic I've read about, that being the distortion of the throttle bases causing the shafts to bind. I will first look at doing a starting fluid spray test to look for any exterior vacuum leaks around the bases, then probably loosen the mounting bolts/nuts and re-torque them using my torque wrench (not used by my son the first time). I tried to find instructions on adjusting the mechanical linkage linking the end carbs to the center carb to ensure closing from WOT.

Stu Fox

[Ken A.]

Re: 3x2 tuning

I've never heard of this method, why would you want to do this when the secondary carbs are not functioning at idle?
Easy to check for leaks internally-just look down the throats at idle.