Overhauled Engine running rough and hot on one side...

[SeamusNZ]

Hi all, Hello from New Zealand.

I have albut completed the rebuild of my '62 Monza Spyder convertible. At this stage I have not installed the turbo engine but have instead installed an early two carb engine that I have rebuilt.

The engine starts fine, although it runs quite rough and lumpy until it warms up.

Once running at normal operating temperature I have noticed that the right hand bank is running considerably rougher (popping) and louder than the left hand side. The engine is fitted with twin exhausts purchased through California Corvairs. The left hand side is running much smother (and quieter) although it does have an intermittent miss while idling and at higher revs. I have noticed that the rev counter jumps up a few RPM concurrently with the missing.

The other thing that is worrying me is that the left hand side exhaust is much hotter than the right, to a degree that I can comfortably hold the exhaust tip on the left hand side but cannot touch the tip on the right hand side. I can't hold my hand against the exhaust tip on the right hand side - it is way too hot - is this normal????

I have completed a compression test on all the cylinders and they are all running around 100. I have also relashed the rockers on the right hand (hot) side.

The carbs are both refurbished from California Corvairs. I have balanced the carbs using the special tool with the floating ball.

Can someone please give a lead to where and what I need to sort out. What side should I be most concerned about? The hot side or the cold side. Is this a common set of symptoms for these engines?

Any help and leads would be very much appreciated.

Kind regards from NZ

SeamusNZ

[azdave]

Both sides should be in the same temp range. If you are convinced that you have the valves set correctly and the cylinder pressures are all within tolernace then the first test I would do is swap the carbs from one side to the other and see if the problem moves to the other head. That will confirm quite a few things depending on what results you find. Have you tried that?

[acarlson]

If you believe that you have the engine up to operating temperature, then I would say you have the opposite problem. The cold side is not hot enough... Maybe one or more cylinders are not firing correctly (plug wires crossed ??)...

[gnrand]

Maybe pull the spark plugs and inspect them. Have you checked your timing? Also check for vacuum leaks.

[64powerglide]

Could it be a weak or broken exhaust valve spring on the right bank??? Possibly one or more exhaust valves are not adjusted right & are not closing completely. Either one could blow fire right out the exhaust valve causing excess heat. Just a thought.

[SeamusNZ]

Will try swapping the carbs and report back on the results. Thanks for all your help.

Kind regards SeamusNZ

[terribleted]

Indeed often a cold side is nothing more than a plugged up or maladjusted carb. Roughness often comes with this problem.

[SeamusNZ]

Hi all,

Removed the carb from the cold side after finding that putting my hand over the top of the carb only slowed the engine revs down. The other side nearly sucked my hand in. After checking things out, replacing the mans fold plugs and reinstalling the carb - the air leak was fixed. Relashed the rockets just to be sure - seems to be running much better. Will take her for a run tomorrow and report back. Thanks for your help. Kind regards SeamusNZ

[terribleted]

2 thumbs up!!!

[SeamusNZ]

Running much better, but still running a little rough unless under load. Tell me? How do I know that the timing is right. It seems to run best??? Advanced way beyond the timing marks. Is this normal????

[b74eqcm]

If the timing is very advanced to run well, I would check two things:

- what was the rpm when setting the timing? Mechanical advance comes in very early in Vairs. If the idle speed was set too high (900 or 1,000 rpm) the mechanical advance is already advancing the timing. Try to get the idle speed down to correct value (600 or so)

- Did you remember the disconnect and plug the vacuum advance line to the distributor before checking the timing? IS it connected to the correct port on the carb?

Jim

[SeamusNZ]

Hi Jim

What is the correct port that the vacuum advance kind should be attached to??

Kind regards...SeamusNZ

[bbodie52]

For a normally aspirated Corvair engine, this diagram should help you with the vacuum hose connections...



I have attached a copy of the DELCO ROCHESTER - Models H, HV Carburetor Service Manual. About half of the manual describes operational theory of the various subsystems in the Rochester carburetors. The remainder of the manual supplements the material provided in the Corvair shop manuals, and is useful in performing maintenance and adjustments on the Rochester carburetors. The following paragraphs were extracted from the manual and describe the functions of the two external vacuum ports on the Rochester carburetors.

VERTICAL VACUUM PORT TUBE...

The Model H and HV carburetors have a vacuum advance port drilled just above the throttle valves to provide a timed distributor vacuum advance. As the throttle valve is opened the spark port is exposed to manifold vacuum which acts on the distributor vacuum advance unit. This varies the advance unit so that the correct spark timing can be maintained in relation to the engine load. This helps give maximum economy under varying road load conditions. Both carburetors have a spark port. However, the right unit is used to operate the distributor advance unit. The left carburetor spark port is blocked off by a plastic cap.

HORIZONTAL VACUUM PORT TUBE...

When the engine is started, manifold vacuum is applied to the spring-loaded vacuum break diaphragm. This moves the diaphragm plunger into the assembly until it strikes the cover, which in turn opens the choke valve to a point where the engine runs without loading or stalling. The length of the connecting link determines the amount of choke valve opening.

On the turbocharged engine, there is a vacuum connector on the right cylinder head intake manifold pad to connect the pressure retard device.

[SeamusNZ]

Hi there, thanks god the attached.

As I have stated earlier, I have chosen to install a standard (not turbo charged) engine into my Spyder. At the moment, I have the distributor advance hose coming directly from a fitting on the right hand cylinder head. Is this incorrect??. Should the hose come directly from the carburetor??? What is the likely effect on how I have it set up at present. As far as I know, the verticle tube (I assume where the vacuum hose should go) is blocked off on both carby's.Neither doesn't seem to be drawing air?? Your help is very much appreciated. Kind regards....SeamusNZ

[bbodie52]

A direct connection between the vacuum advance and the intake manifold is not desirable, because a full intake manifold vacuum would be applied to the vacuum advance at idle. As described earlier, the "spark tube" (vertical tube) draws a vacuum from an opening that is drilled physically ABOVE the throttle butterfly valve. With that port, vacuum is not applied to the vacuum advance on the distributor until the throttle begins to open. This applies vacuum to the vacuum advance at partial throttle, providing the engine with some timing advance at low speeds. As increased throttle and engine speed occurs, the vacuum advance has less effect while the centrifugal advance begins to take over.

The vacuum advance should be connected to the right carburetor vertical vacuum port. The horizontal vacuum ports should only be connected to the choke diaphragms. The vertical vacuum tube on the left carburetor is not used, and should have a plastic cap on it to prevent a vacuum leak. If you have an intake manifold vacuum port on the carburetor mounting pad, it should be plugged to prevent a vacuum leak. Such a connection point is only needed with a turbocharged engine to connect the pressure retard device on the distributor.