General Tech Engine vacuum, tuning question

[70herald]

Opinion wanted regarding the Heralds engine.
The engine is quite warm at this point. Plugs are nice and clean.
Here is a video showing the vacuum gauge hooked up to manifold vac at idle.
Vacuum is reasonably high, with the needed vibrating a bit.
The engine is still fairly noisy, at speed it is very noisy. I have gone over the exhaust and didn't find any leaks.
Adjusting the vacuum has almost no effect on vacuum level until timing is so far out that the engine starts stumbling.

 

[TuffTR250]

Vacuum is quite high. My TR250 with rebuilt 6 cylinder engine only gives about 15 to 17 pounds. I don't know what is normal for a 4 cylinder. My TR3 does not have a vacuum port so I have not measured it. Did you put vacuum ports through the carb "thick" gaskets? I was wondering how that would work.
Regards,
Bob

 

[dklawson]

For stock engines, normal vacuum readings are the same regardless of the cylinder count. Your vacuum readings are very good. Yes, you have flutter in the needle but 20in of Hg is great. You will see lower values for some hot cams, when there are leaks, or if there are ring problems.

The valves sound noisy to me. Some of the needle flutter could be from poorly seating valves and/or bad guides. What to do about this depends on how much it bothers you. I would at least start by re-adjusting the valves if you have not done so already.

In your last sentence did you mean to say that adjusting the timing had no major effect on vacuum until the engine was about to misfire or stall?

 

[70herald]

Hi
I made my own adapter using an old plastic carb spacer which I cut a slot into and then epoxied a small tube into it. Once the epoxy started to harden I went over it with a razor blade to cut the excess epoxy and smooth it out. Finally I sanded it lightly to make sure both sides of the spacer were smooth.

I am not really sure why the valves should be sticky, everything was rebuild about 2 years ago. Of course the quality of the rebuild may or may not be perfect. I will try to adjust the valves again and see what if any difference this makes.

I was able to move the distributor base a fair amount with no significant difference in vacuum. Of course since the needle is a bit bouncy, maybe I just missed it.

 

[TuffTR250]

70herald, could you post a picture of the vacuum port you fabricated in the plastic carb spacer? Did you make one for each carb or are you using just one? Thanks!
Regards,
Bob

 

[70herald]

Sure it will take me a few days since it is installed in the engine but I will get you a picture.

 

[dklawson]

It sounds like he made his own version of the carb spacer sold as part number MFA338.
https://www.minispares.com/product/Classic/Fuel/Carburettors/MFA338.aspx
2nd link
https://www.7ent.com/products/carb-spacer-w-vacuum-port-hs4-mfa338.html

 

[70herald]

That is exactly what I made out of stuff left over in my junk box. I would have just ordered one, but they wanted more for shipping than the adapter cost :blue: They drilled a hole into the side of the adapter, I just cut a slice in, put in a tube and backfilled with epoxy. Total time 15 minutes