78 invader with JD heads Settings?

[Truder78]

I finished the rebuild of my 78 invader engine ...seals new nos cylinders, pistons and new JD heads. Rebuilt carbs... new o rings also and fuel pump I have the extra hole needed in the pump. I have the standard jetting, timing, and plugs used in the invader. Can I keep the standard setting or do I need to rejet change timing ect. Any help would be great before I run it on the lake starts ok seems boggy but has only run a few times after rebuild and only at idle to get it up to temp.

[Truder78]

Found old post
 The Liquifire's heads reduce the effective compression ratio from the Invaders 7.3 to 1 down to 6.9 to 1...not a huge deal.....but sacrificing 3-4 ?? HP.
 The Liquifire's stock jetting (at sea level to 4000 feet) is 150 Main jets, 110 (PTO) and 105 (MAG) power jets.....awfully close to the Invaders  stock 150 Mains, and 120 power jets.
 That small difference in jetting may, or may not, be due to the slightly different compression.
 It could also be due to the slightly different air box design and exhaust system that John Deere engineered to fit in their Liquifire chassis., and the way all of those components work together.
 I could find only find one reference for timing in my John Deere manual, and that was to "Align Stator Marks".
 One would think you could advance the timing a couple degrees when you reduce the compression ratio, but I wouldn't even attempt it.. unless....maybe.... I could do all of this with the engine on a dynamometer.
 I second gixxer6..... leave the timing as is, and run the stock Invader jetting.

[gixxer6]

Why are you using the JD heads? 

I shaved the heads on my 81' Invader and never changed the stock jetting.  It runs GREAT on premium fuel, plugs are always a nice chocolate brown and NO bog.   

[rminier]

 Very good research on your part.
 I must echo gixxer6.....the Invader heads are worth another 3-4-5...HP???
Good ones are available from eBay, or many members on this site fairly cheap.
 The Liquifire heads "MAY" allow you to get by with 87 octane gas....but I would slap the higher compression Invader heads on that beast and use at least 89 octane. 
 ......and blow away the deadbeats on their SRX's, Liquifires.....
....OK...a good running SRX is a "tough nut to crack".

[Lloyd (ljm)]

The 80-81 Liquifire's had the timing retarded compared to the Invader's. This made them harder to start. A trick on the early Liquifire's is to advance the timing slightly to make them easier to start. The 82-84 Liquifire's used a high speed retarded (HSR) ignition. On the later ones the base timing was advanced and the timing curve built into the CDI coil combination unit retarded the timing at higher rpms. This produced a timing curve similar to the 4/6 and later mono block LTD's. These later ones are much easier to start.

 This being said. If I was building an Invader engine with JD heads I would use the stock Invader timing.

 There are lots of Liquifire's that have been switched to Invader heads with little difference in performance.