Carbs to be rebuilt in the Spring

USA car? On my 78 308 GTS, with fresh major service, K&N air filter, and test pipes in place of cats; I had a dyno shop change the main jets from 125 (stock) to 130, then 135 and finally 140, to optimize the air/fuel ratio. It was still very slightly lean, but he was afraid the next bump would put us over. Gained about 16 hp or so....final correct hp at the crank was 214hp. Stock (usa) 78-79 308 is 205 hp. Obviously my car was not making even stock 205 hp because the K&N was causing an excessively lean situation. Changing jets is a 10 minute procedure.

BTW, with the richer jetting, you may need to go to a hotter plug. I was using NGK 6's, but 5's might have been better.

Oh, and $250 per carb for rebuild is a rather excessive charge. I think my independant Ferrari tech charged me about $500 for all four, including all the final set up and adjustments needed.

 

jpl,
there was a thread a few days back where a couple of FChatters were discussing sending their carbs to Pierce Manifolds for service. You would have to take the carbs off yourself though (not exactly simple, but definitely do-able - you'll spend 80% of the time looking for the right wrench to get at the nut under the accel pump).

davehanda,
Did you change your air correction jets any, or was the K&N the 'air correction'? Now that my '79 308 is finally old enough to be exempt from emission tests here, I am going to start trying to regain a few 'lost' HP myself.

thanks

 

My carbs are at Pierce Manifolds now, currently "in process." Very pleased with their service.

Note that they seem to be on an "appointment" basis, and I was lucky to have my carbs squeezed in due to a "cancellation!" My impression was that they had a fair amount of demand and that otherwise their first opening was April...

Taking off the carbs was the coolest thing I had done to date with the car. Was a lot of fun, actually. You'll make it less painful by just GOING TO SEARS and buying a Craftsman Professional ("polished") stubby 13mm wrench. A little penetrant sprayed on each stub helped out a fair amount.

 

rejetting the carbs for mo power should only be done on the dyno so they can monitor A/F ratio and HP.

 

The air correction jets are part of the carb, they control the amount of air allowed into the emulsion tubes to mix with the fuel amount, which is controlled by the main jets.

 

Also note the air correction jets impact the mixture most significantly in the higher RPM range, roughly 6000rpm in my experience.

On a side note, air correction jets--UNLIKE the other jets in our Webers--meter AIR as opposed to fuel. Correspondingly, going UP in size--allowing more AIR--will make for a LEANER mixture in the range affected by the air correctors. This contrasts with going up in size in the main jets or idle jets, which meter FUEL, which as a rule makes for richer mixtures.

--Mike

 

On my 78 308, we left the air correction jets alone, and only richened the main jets....richening the air correction my have been helpful though, to finalize the tweeks.

I am highly suspect of any 78-79 (USA spec) 308 making 220hp at the wheels without significant modifications. Did the dealer actually provide the dyno sheets, or is this just "salesman talk"? Only a very well running Euro 308 might make those kind of numbers.

If your car IS a Euro 308, then I would be hesitant to do any changes, except on a chassis dyno with an exhaust analyzer to verify the base line performance, and note the changes. Which is really how you should do it with a USA car too...even though you can use my info. each car can take to the changes a little differently.