Itinerant Air-Cooled

Well I finally started my cross country trip and we didn't even make it out of CT when the engine temps started creeping up to 450 while going up through the western "hills" of CT. I drove a little slower and got them to around 430. Now we are in Ohio and the temps are climbing again, now they are pushing 460.

These are CHT being read with a VDO gauge. I know these are not reliable but I have come to expect that my bus runs at 425-430 on the highway using this gauge and I was ok with that because other clues (and Colin) tell me that the engine is running at acceptable temps. Now I see the temps shoot up like this and I am paralyzed with anxiety.

This morning, before leaving the camp sight, I adjusted the valves and found only the #1 exhaust a little tight (.006 would not go but .005 would). Checked the timing again, and it was right on. My dipstick and fan shroud are cool.

What could be forcing this increase in temp? Could there be something wrong with my distributor?

Please send any suggestions you might have... we are sitting in a McDonald's right now and there is only so much of their music I can take!

Are you timed at 28º BTDC when all of the centrifical advance is in?

just checked it again and it was off from this morning. It is at 28 with the hose off. I have a weber carb. What would make the timing change from this morning?

Well of course I know nothing about a weber progressive (other than I thank god every day that I don't own one) and know nothing about how it deals with vacuum signature that is destined for the vacuum cansiter.

If it were me, I would cap the vacuum at the carb (leaving the distributor so that it is all in at 28º BTDCwith no hoses) and see if driving it that way does anything different.....like runs cooler.

Randy in Maine wrote:Well of course I know nothing about a weber progressive (other than I thank god every day that I don't own one) and know nothing about how it deals with vacuum signature that is destined for the vacuum cansiter.

If it were me, I would cap the vacuum at the carb (leaving the distributor so that it is all in at 28º BTDCwith no hoses) and see if driving it that way does anything different.....like runs cooler.

Thanks for your help Randy. With the hose on the timing goes off the scale. So maybe you are right. Will give it a shot.

As you give the engine throttle to maintain hiway speed the vacuum goes down and so does the amount of advance. While checking the timing there is no load so vacuum is very high with full advance coming in. i.e. you get a false reading with the hose connected and no load.

RSorak 71Westy wrote:As you give the engine throttle to maintain hiway speed the vacuum goes down and so does the amount of advance. While checking the timing there is no load so vacuum is very high with full advance coming in. i.e. you get a false reading with the hose connected and no load.

Could it be that this is NOT happening as you described? Is there any way to check?

I am not sure just what vacuum lines a progressive has on it to run the distributor. We are mostly looking for ported vacuum for most of our distributors and it could be supplying more like a total vacuum or something.

Usually the most total advance we like to see is in the 42-44º area (centrifical + vacuum).

I think that is one of the reasons that most progressive owners like the 009 as it does't care what vacuum you are seeing or not seeing.

Whatever, if you don't hook up that vacuum line you will be running just about like a 009 would be anyway.

I agree w/Randy. Give that a shot (plug the vacuum line as a test) to see what it does to your temps. If you're away from home it could allow you to run cooler temporarily until you can get home to dig deeper.

This worked a little bit. The temps did not hit 450 but they were still high and I was only doing 50 - 55mph.

iwantmybustorun wrote:This worked a little bit. The temps did not hit 450 but they were still high and I was only doing 50 - 55mph.

Sorry I am late to the party.

Your vacuum advance is not likely to materially affect the CHT readings. As noted, vacuum drops out when load increases.
I just did a Nebraska I-80 westbound-with-headwind at 98* between 65-70 mph playing with the LM-1 and Dakota Digital CHT gauge yesterday.
In the name of science, I successively leaned then richened the mixture.
I am horrified to report that the engine loves "pig rich" and I am damn serious here:
70mph at 14.5:1 ratio, the alarm (440*) went off in no time.
70 at 13.5:1, I was 433*
70 at 12.5:1, I was 420* fuel mileage over 150 miles was 16.6mpg
70 at 11.0:1, I was 406* fuel mileage over 150 miles was 16mpg
70 at 10.8:1, I was 399* fuel mileage over a tank was 16mpg.
these all averaged over ten to twenty miles on level sections. Trucks are your friends, consider them geisha parasols fanning your exhaust valves' dewy brows with the ability to cool your CHTs a good 20* if you draft.

There are many many assumptions getting torpedoed out here, like:
I Don't Know Crap About Air-Cooled Thermodynamics - the engine has its own ideas and is much more internally motivated as far as temperatures.

Please adjust your carburetors a little more rich to see if CHTs settle down. As importantly, pull a couple of plugs from each side of the engine after a good highway run and see if there is any whitishness on the outside perimeter. TOO LEAN, you may need to re-jet, because idle screws do not reach that high up in the performance curve.
ColinMoreExperimentsToday

Thank you Colin. I will finish my coffee and go give that a shot.

Amskeptic wrote:As noted, vacuum drops out when load increases.

Unless it's malfunctioning or hooked up wrong. I don't know squat about those progressives. Obviously the manifold vacuum will drop under load but does that particular carb provide the correct "pull" to the can on the distributor?

sped372 wrote:

Amskeptic wrote:As noted, vacuum drops out when load increases.

Unless it's malfunctioning or hooked up wrong. I don't know squat about those progressives. Obviously the manifold vacuum will drop under load but does that particular carb provide the correct "pull" to the can on the distributor?

Most every carburetor on Earth loses vacuum when you open the throttle plate.
That said, there is a vacuum signal that occurs from air velocity through the venturi. That is used to suck gas in to the main discharge port and power circuits like the old PDSITS. The Webers use the typical vacuum advance drillings that are ported.
When you have a stock carburetor set-up and mix up your hoses and put the advance hose on the full-vacuum nipple used for the retard, it drops the advance right out when you open the throttle plate. If you plumbed the advance to the intake manifold itself, you would have full vacuum advance at idle that nonetheless drops out under full acceleration, here the problem would be those who time the engine at idle to 7.5* BTDC, let's say, then they would have an amazingly retarded upper timing range . . . I've seen it!
Colin

Amskeptic wrote:

iwantmybustorun wrote:This worked a little bit. The temps did not hit 450 but they were still high and I was only doing 50 - 55mph.

Sorry I am late to the party.

Your vacuum advance is not likely to materially affect the CHT readings. As noted, vacuum drops out when load increases.
I just did a Nebraska I-80 westbound-with-headwind at 98* between 65-70 mph playing with the LM-1 and Dakota Digital CHT gauge yesterday.
In the name of science, I successively leaned then richened the mixture.
I am horrified to report that the engine loves "pig rich" and I am damn serious here:
70mph at 14.5:1 ratio, the alarm (440*) went off in no time.
70 at 13.5:1, I was 433*
70 at 12.5:1, I was 420* fuel mileage over 150 miles was 16.6mpg
70 at 11.0:1, I was 406* fuel mileage over 150 miles was 16mpg
70 at 10.8:1, I was 399* fuel mileage over a tank was 16mpg.
these all averaged over ten to twenty miles on level sections. Trucks are your friends, consider them geisha parasols fanning your exhaust valves' dewy brows with the ability to cool your CHTs a good 20* if you draft.

Are you not concerned about cylinder walls being washed of oil with the mixture that rich? Did you notice a difference in power from your setting of 13.5-10.8?