Hey guys...I was just wondering what might cause my engine not to rev like it used to. After I rebuilt my engine and got it all balanced it'd go 7600 rpm no problem. About 2 years ago a piston cracked and I threw in a replacement set without rebalancing and the redline dropped to ~7200 rpm... Slowly it seems to be getting less and less, although it pulls stronger than it ever used to thanks to twin 40 Dellorto's, aluminum flywheel, and MSD ignition. Anyway it's dropped slowly over the last year...7000, 6900, 6800, 6700, etc.... Right now it's having problems going past 6500 rpm. I think the stock single valve springs may be the culprit so I just bought some NISMO inner(dual) ones to help out...sound like a good idea??? I think maybe I should also replace the outers with some new ones too, but I figured the inner ones would help out enough. Does it sound like a valve float issue? The car pulls sooo good and then it just pretty much stops. Will adding stiffer springs hurt a 100,000 mile engine and cause too much stress/wear? Thinking about just rebuilding the whole thing, but I don't have a lot of time to do it right...basically 3-4 weeks to have it done and ready to be shipped to Japan. I'm thinking I may just buy a cheap A15 short block from a junkyard and start rebuilding it on the side...if I finish before leaving and the current A15 holds up I think this would be the way to go. Still pondering though....low compression/turbo/EFI or moderate compression/NA. Any thoughts/suggestions? Thanks!

-Andy

Possible causes:

- Fuel problem (power valve or other problem) in carburetor
- Fuel pump volume problem?
- Weak valve springs. Just test them with a spring scale
- Spark problem (weak coil or bad wires)

-Carbs have just been rebuilt and are clean as a whistle
-Dellorto's have no power valves and they are guaranteed not to be the problem...I've used 3 different carb setups on this engine, each pulled to over 7000 rpm, but these Delloro's pull the hardest especially at the upper rpms
-Fuel pump is newer...I suppose it's a possibility, but highly doubt it my Air/Fuel ratio guage shows no lean spots
-Coil is Accel Super Coil 50,000 volts, brand new 8.8 mm Accel Race Wires, and MSD 6AL capacitive discharge....NO lack of spark here
-Valve springs are used, and not new they've got over 100K on them if not more. I'm pretty sure they're tired.

I called around a few places to find some new springs...nobody could get them except Nissan for $43/set. I'm gonna just throw in the inner springs along with some more match porting/polishing on the head, probably tomorrow and Friday. Should run a lot better, we'll see.

-Andy

Man what a difference! I took the head off, match ported it to the intake and header, as well as the gasket, and then threw in the inner valve springs. The car runs great! Redline is back above 7000 like it should be and feels like it's got a lot more power through all the rpms. Got to replace the slave cylinder before I can really get to drive it hard, but it still is great. Does anyone know where I can order Dellorto Idle Jets in the US like online or over the phone? Porting out the head didn't help an already lean off idle situation, so I need some bigger idle jets. Let me know!

-Andy

Glad to hear it, and to know that the valve springs can indeed get "tired" and need replacing.

Maybe some motorcycle shops carry Dellorto jets?