Technical rochester questions

That`s a cool "inline" hot rod I'll write how it goes with the Styleline. Thanks.

 

I have just one more question. This time about the ignition. what should I light on, with my timing light, i can see a mark (only did a very quick look) ? and what to adjust it to? And im doing it with vacuum off, right? By the way, I have found one that has some jets for Rochester, so hope it is running in the weekend

 

Yep...unhook the vacuum hose (plug it) and if I think a stock 216 likes about 5 degrees advanced. Shine the timing light on the balancer and dial it in with the distributor. If it pings under acceleration (I doubt it will) take the timing down as needed but should be fine at 5 degrees.
Good news on finding some jets and have fun with it.

 

Hi again guys.

Just bought a flowmeter to syncronise the carbs. And a neon ignition light. Adjusted both and now everything should be great. But still when i'm driving the car for 5min. or so, it start to run uneven, especially under acceleration from low revs. It idles just fine. But when i'm coming home to the shop all the spart black. I attached two pictures so you Can see it. Maybe my jets are to big, they are 0,051. I think they are made in 0,020 to 0,090. Should i put smaller jets in when going from one to two carbs? Can any of you help me?

Regards Andreas from Denmark




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Andreas...If those jets are available in smaller sizes, .045 would be a good start. If all that is available is .040" (approx. 1 mm) then start with that size in both carbs. Number & letter drill bits are available in 'between' sizes, so you can tune accurately, a little at a time. My guess is in the .045" size.
These jets are measured in thousandths of inches of diameter, so yours now are .051".

When you think you are at the right size, take a piece of string (kite string or packaging string) and holding the jet firmly, tie the string to your workbench and polish out the new bore (hole) with the string. A magnifying gl*** will show why.

 

Okay. Thank you very much. Don't you think, that smaller jets will help me get it to run properly???


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The fact that your problem occurs after a few minutes of driving makes me wonder if the choke is adjusted and working properly. When the engine warms up a bit the choke blades should be fully open. You may also still have a problem with the float level, needle and seat, power valve or excessive fuel pressure making it run too rich. All this stuff should be working right before making jet changes or you may end up chasing the same problems all over again.

 

The choke is manuel, so it makes no fuss. The fuelpump is the original, so i think the pressure is okay. I bought two overhaulingkits, and changes the acceleration pumps, balls and springs in power valve, all gaskets and cleaned it all. But i have to look at the float level, but what should I adjust it by? In my Chevy bibel, they only shows a original tool to adjust it with. Do you have any measurements to adjust after???

 

Get some drills and solder up your jets and start with a smaller hole and keep at it.

 

Yes it was a good way to find the right jets. What would you use to solder it?

 

Any house hold copper pipe solder.

 

Before you take out the jets, check your power piston (it is inside of the housing that holds the jet)
these will get stuck or not slide freely causing a run rich condition.

 

Oh yes, i remember that from when i cleaned an put in the new parts in the carbs. It´s like a aluminum pisten, with a spring under it, and a tip i the other End which push to the little ball. If it`s not line up perfect, it stucks. I lined it up when doing it, but maybe i should look again. That has not crossed my mind. Thank you very much.

 

Any one know how to adjust the float???

 

1 9/32" from bottom of float to gasket area, upside down
1 3/4" float drop, right side up, bend tab to adjust.

 

Cool Rick.
Now i have two thing to check. If that does not work, I order some jets.
Should the flowmeter stand on a specific number, or must the two carburetors just be same?
Thank you guys. I let you here how things work out.

 

After reading through your thread,I believe I understand your problem. There are a couple ways to zero in on the cause of your drivability issues. The troubles you have probably did not exist when you had only one carburetor. To verify that conclusion, make a block-off plate from any kind of thin material that won't melt to fit between a carb and the manifold. Don't change anything else. Go drive the car with one blocked and one operating. See that it drives well. Next, swap the block-of plate to the other carb and repeat driving. Does it drive basically the same as the other carb did? If so, both carbs are generally OK. In the course of this test, be sure to drive enough to get the engine well up to temperature in order to burn the carbon off the spark plugs. When test is done shut car off with out goosing the throttle or excessive idling. Pull some plugs, the porcelain should look tan to parchment in color. If they still look "sooty" but less so than before, you may need to continue driving on one carb or the other until you get the motor cleaned out of carbon.
Next, open each carb and get me the number off each main jet(should be 45 or 51, some two digit number).Also we need the number off the "power valve" jet ( should be something around 61). If both carbs don't have the same jet sizes, scrounge through other Rochesters until you find matched pairs of jets.
Now to get the engine to run well with both carbs operating we need to understand what changes will occur to the operating conditions of each carburetor.
#1 Each carb is only flowing half as much air through it for any operating condition (engine load, RPM, idle, etc).
#2 The vacuum signal the engine (air pump) sends to the each carb will be divide between them any speed above the idle where vacuum is highest.
#3 At wide open throttle the vacuum the engine now develops will be roughly half it was with one carb no matter the engines load or speed(RPM).
#4 For any given power demand asked of the dual carbs the same amount of air is needed as with a single carb setup. Same amount of air but twice the jetting capacity.
#5 The vacuum signal each carb sees is now altered. Rochester BV/CV carbs use a vacuum operated power valve to supply enrichment under heavy load or wide open throttle condition.
We must conclude that the overly rich condition you engine is experiencing is caused by a low vacuum condition which causes the vacuum valve & spring to prematurely open the power valve.
The solution is to lessen the spring pressure that opens the valve so it takes less vacuum to hold the valve from opening the power valve. This will take some experimentation, start by cutting about 3/16" from the spring's coil length. You may need to do this again and again, cutting another 1/16" at a time. I found 5/16" shorter about right for an air fuel ratio of 12.6:1 at wide open throttle. The next issue will be to smooth out the off-idle and part throttle tractability. The main jets will always flow more than enough fuel for idle as the idle screws will dial that back. But you will likely still be too rich in the midrange. Get a set of jet drills, they size clear down from #60 to #80 (smallest). And you'll need a "pin vise". Start by soldering up fully the existing orifice in the jet and then drilling with a bit a few thousandths smaller. Again it may take several tries to get it sufficiently leaned out. Ideally, you want to get the air/fuel ratio down to the high 14:1 area. Drive the car through varying operational demands and observe response to throttle. When it ceases to falter and stumble on hard acceleration you are close to the right size jets. Don't go too small as a too lean mixture while good for economy is hard on valves.
The ideal method of refining the jetting is to acquire a DEPO air/fuel meter and a Bosch wideband O2 sensor. With that meter and a vacuum gauge, you would to be able actually see what jetting change need to made.
I hope this helps get you on track.
Best Regards and good luck with all your endeavors, KB.

 

Ohh man thats many pifalls. I will try blocking them of each at the first. The jets, was 51 and 52, and now both are 51`s. The only jets, are the main jets (in my case the 51`s), right??? The flowmeter im using is like the one i attached below.

 

I've never seen this type of synchronizer. I ***ume it has some adjustment facility to allow for a mid sweep deflection of the needle. If so, I'm sure it will work fine for balancing carbs. Your carb balance at this stage of your modification is of small consequence as that is only critical at idle and just off idle(part throttle) balance to all 6 cylinders.
The power valve is another jet, they are also found in various sizes. The power valve routes fuel around the main jet through a separate channel in the carb's housing.The check ball is there to block the main jet's byp*** flow when there is higher vacuum. The vacuum piston pushes the check ball aside when vacuum is lower by a spring behind the piston. One experiment that you could try is to outright remove the spring from the vacuum piston temporarily to verify that the power valve is the cause of your overly rich condition. By removing the springs, the check ball should never be opened no matter how low the vacuum drops. The engine will only be fueled by the main jets. You can backtrack by reinstalling the springs, knowing that they exert too much force against the vacuum the engine is generating at that particular operating condition. A weaker or shorter spring will improve this situation.
I hope this explains what is going on with your setup and how to get it corrected.
Best regards and good luck with all your endeavors, KB.