Rebuilt 3.0 engine issue, Hi temps on one side Options

[scrz914]

I have a recently rebuilt flat six engine that I’m going to install in my 914. I built a run stand so that I could do the initial break in and then address any other issues. Start up went well with the expected popping through the Weber IDAs and some backfires through the exhaust. Once warm it ran better. One of the first checks I did was to make sure all plugs were firing by using a temperature gun directed at the exhaust coming off each cylinder. This is where I discovered a huge disparity between the two banks. One side, 1,2,3 cylinders had readings over 500 degrees whereas 4,5,6 was a little over 100 degrees.
My first check was fuel pressure. 3 psi on both sides which is good.
Then I sprayed brake cleaner around the manifolds. Good.
When I sprayed points on the throttle shaft on 1,2,3 there was a noticeable change in idle. It became smoother and increased a little.
My question: could a vacuum leak at the throttle shaft account for the high exhaust temperature? If so, what are my options?
I don’t have much carburetor experience so any expert advice would be appreciated.
Thanks all.

[gereed75]

That seems like a huge disparity on an engine that is running even reasonably well

Be sure that you are measuring both sides at exactly the same distance from the cylinder head on both sides. EGT drops quickly in relation to distance from the cylinder head.

Beyond that, the first thing I would check is carb float levels. High float levels on the cold cylinders will prevent any fuel from entering the carbs once the engine is running.

[scrz914]

Beyond that, the first thing I would check is carb float levels. High float levels on the cold cylinders will prevent any fuel from entering the carbs once the engine is running.

Interesting, I didn’t know that. I’ll check the float levels next.
Regarding the temperature readings, i did use a 6 inch distance on all exhaust pipes.

[scrz914]

Here’s a pic of my setup. MSD 6AL ignition.

[emerygt350]

Truthfully it should be titled "low temps on one side"....


It's a complete mess, no hope. I will recycle it for you.

[930cabman]

(IMG:style_emoticons/default/popcorn[1].gif)

yes, it appears to point to the carb, but seems odd all three on one bank

[VaccaRabite]

Have you gone through the whole carb adjustment process?
Set best lean idle for each bore?

I suspect you will find that the hot side is the side running the engine, and the cold side is just along for the ride.

You need to take time to get a solid baseline for the idle speed and mix screws on each carb, let the engine get warm and then got find best lean idle. You will want a snail or some sort of carb balancing device to make sure each carb is drawing the same. This is also why your carbs are popping and backfiring - they are imbalanced.

This is all standard first start stuff and nothing to be overly concerned about.

Also GOOD ON YOU for taking the time to get this set on a run in stand. It makes all the balancing SO MUCH EASIER then reaching into the engine bay.

Zach

[scrz914]

It did seem to me that both sides could be extreme. 100 degrees on exhaust ports seemed low.
As far as the carb settings, I adjusted mixture screws 4 half turns out and idle screws 5 half turns in. Bypass adjustment screws all the way in.
I probably should make sure there is spark on 4,5,6.

[mb911]

Cam timing is always my go too in this situation

[fixer34]

It did seem to me that both sides could be extreme. 100 degrees on exhaust ports seemed low.
As far as the carb settings, I adjusted mixture screws 4 half turns out and idle screws 5 half turns in. Bypass adjustment screws all the way in.
I probably should make sure there is spark on 4,5,6.

Is it possible you don't have the plug wires connected correctly/right order on the 4-5-6 bank? With a standard distributor setup it would be near impossible to have 1-2-3 working fine and 4-5-6 not getting spark. Or the cam timing on that side is way off.

[scrz914]

It did seem to me that both sides could be extreme. 100 degrees on exhaust ports seemed low.
As far as the carb settings, I adjusted mixture screws 4 half turns out and idle screws 5 half turns in. Bypass adjustment screws all the way in.
I probably should make sure there is spark on 4,5,6.

Is it possible you don't have the plug wires connected correctly/right order on the 4-5-6 bank? With a standard distributor setup it would be near impossible to have 1-2-3 working fine and 4-5-6 not getting spark. Or the cam timing on that side is way off.

I don’t want to get ahead of myself but would a bad MSD unit cause one bank to not get spark?

[930cabman]

It did seem to me that both sides could be extreme. 100 degrees on exhaust ports seemed low.
As far as the carb settings, I adjusted mixture screws 4 half turns out and idle screws 5 half turns in. Bypass adjustment screws all the way in.
I probably should make sure there is spark on 4,5,6.

Is it possible you don't have the plug wires connected correctly/right order on the 4-5-6 bank? With a standard distributor setup it would be near impossible to have 1-2-3 working fine and 4-5-6 not getting spark. Or the cam timing on that side is way off.

I don’t want to get ahead of myself but would a bad MSD unit cause one bank to not get spark?

seems unlikely

[scrz914]

Always good to check the basics. I DID have 4 and 5 reversed. (IMG:style_emoticons/default/wacko.gif) BUT, I think I did that after I started troubleshooting the temp disparity. We’ll see tomorrow if I can make some progress. I’ll let you know.

[Luke M]

A far reach but did you install all of the cooling tins for the cylinders and behind the alt?

[sixnotfour]

TDC #1 valves loose, #4 valves tight.. is what you should have..
Cam timing.. right side is prob. loose at the wrong time ..

[Root_Werks]

TDC #1 valves loose, #4 valves tight.. is what you should have..
Cam timing.. right side is prob. loose at the wrong time ..

(IMG:style_emoticons/default/agree.gif)

I'm not an engine builder but recognize the symptoms.

[brant]

Agree with jeff and all

Not working one bank
Spark
Fuel
Timing

[scrz914]

A far reach but did you install all of the cooling tins for the cylinders and behind the alt?

Yes. Those were installed by the builder.

[scrz914]

TDC #1 valves loose, #4 valves tight.. is what you should have..
Cam timing.. right side is prob. loose at the wrong time ..

Man, I hope the engine builder knew how to adjust valves and cam timing. That wouldn’t bode well for the overall build if he didn’t.

[sixnotfour]

turn engine TDC #1 ...hold right carb, wide open, Should blow back at you 100%...Likewise left carb, wide open, Air should bypass some and able to near at tailpipe...
Cams correctly timed in theory..

If both blow back 100%,, the 456 cam is out of time..