WTB 140 PG Distributor OR #84 Points Cam

['68_Corvair]

After reading what you posted do you know what main jet you have in the carb?

The primaries are 51 jets, and the secondaries are 48 jets. New jets are cheap so I wouldn't mind trying swapping them out as an experiment. Do you think a set of 52's or 53's might work better in the primaries?

As for gas, I have been putting 91 octane 100% gas in it.

[Lane66Monza]

If you are using a lower grade ethanol octane, move up a grade or 2. Do that before you start changing parts. Back off your timing 2 degrees, if you have it set to book value.

I didn't run my the More Door 110 I sold at book value. I set it at 12 degrees and had no pinging issues at sea level or up to Maggie Valley atltitude (3k). But I used premium at Maggie Valley, NC, but mid-grade is fine at sea level.

[jimbrandberg]

'68_Corvair wrote:
" I was hoping that a 339 distributor with the full centrifugal advance coming in a little later might fix the problem."

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Yes you are correct the 330 centrifugal advance is "all in" at a relatively low RPM, like under 3000.

The 319 distributor for 110 Manual and PG is "all in" at a much higher RPM, like over 4000.

I don't have Specs in front of me but I would expect 339 is somewhere in the middle.

Since a 140 Manual and a 110 share the same 891 cam, the theory must be that the extra breathing afforded with the 140 can support more advance sooner. Blocking total advance or retarding advance completely will hurt performance. The most advance the engine will bear without pinging is where the power is.

I believe you're on the right track.

I have a Sun distributor test machine as well but I've only found the time to test that distributors are performing as designed. The one time I started goofing around with weights and springs it did not go as expected.

If the distributor bushing is worn you can see on the Sun machine that the timing gets wonky between the cylinders, a difference of several degrees, especially with points.

I can't give up a 339 distributor at this time.

Just my opinions and I could be wrong.

There was a guy in the Ultra Van group who knew a lot about distributors and tailoring advance for RPMs. His name may be Jim Davis. An Ultra Van pulling a long hill on a Summer vacation needs all the help it can get, they can be overtaxed quite easily and the engine pinging may be difficult to hear. It sounds like Ken has a pretty good grip on it as well.

[Lane66Monza]

I went through the distributors in my cargo trailer last night and this morning. Thereis no 339 no in my bins. Last seen was on a table at Helen. I leave it there. So I can't help him with a 339, but I have a complete 319 minuspoints and condensor.

I sent him a PM early this morning about the XR-too he has. I missed the reading the posting on the jet sizes before I sent my PM to him. Here is the contents of that PM.
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Put the XR-700 electronic ignition in your distributor. Hook a Fast Coil to the distributor. Back your timing off 2 degrees from where you currently have it set. Add premium gas to your tank. Hopefully, it is almost empty. If not, back off timing 3 degrees and fill tank with premium. Drive the car to see if pinging occurs, where it had previously occurred.

When tank is close to empty, fill with premium. If no pinging ocurred, set timing up 1 degree. Drive it again to check for pinging. Keep doing this until you get to pinging condition, then back off 1-2 degrees and be happy with your engine's best running condition. This is assuming the carbs are set up correctly and balanced

But I have to know, did you rebuild the carbs? What size jet is in each one? I took out 49s from my carbs and installed 51s, due to ethanol fuel. Post the carb jet size so the gurus on the forum know that info.

Al

[Frank DuVal]

I set it at 12 degrees and had no pinging issues at sea level or up to Maggie Valley atltitude (3k). But I used premium at Maggie Valley, NC, but mid-grade is fine at sea level.

While at first this seems backwards, since less octane is required at higher altitudes (Denver runs 2 points lower octane on the three common grades, i.e. regular is 85 octane). Did you run premium because the engine was always climbing a mountain so it was under more stress at Maggie Valley? Here difference in price on ethanol fuel is big jump to mid grade, small jump to premium. Some stations are 80 cents from regular to premium, 60 cents to mid grade. Be mindful.

Here in Virginia we always run premium in 110 HP Corvairs. Not worth the risk of holing a piston. Well...... until non-ethanol came along and we can't get that in premium. So turn the timing back... Lower performance, but less parts replacement on seldom used cars (fuel related parts that is). I rarely use a timing light anyway, just advance until ping and then retard until it does not ping under various loads.

[66vairguy]

The primaries are 51 jets, and the secondaries are 48 jets. New jets are cheap so I wouldn't mind trying swapping them out as an experiment. Do you think a set of 52's or 53's might work better in the primaries?

As for gas, I have been putting 91 octane 100% gas in it.

Bob Helt, who I have great respect for, started the "new ethanol fuel requires bigger jets" talk. This was a bit of a mis-statement as it was for the older carburetors before the "power enrichment valve" was added in 1965. But now a lot of folks insist you have to up the jet sizes 1 or 2 sizes on all carburetors. What I find with engines with #53 jets is excess carbon deposits in the heads chambers and ring gaps of the pistons.

On the 65-66 carburetors I use a #51 jet for primaries and a #48 for the secondary just like originally done at the factory. I run 91 octane 10% ethanol and the car runs fine. No ping, plugs look good.

The 68 emissions control carburetors used #52 primary, #49 secondary. This was done to enhance the air injection reaction system that works optimally with a "slightly" richer exhaust gasses.

Just my