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ChadS
06-23-2005 08:52:07
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Re: ChadS! Few carb questions for ya! in reply to superih, 06-23-2005 08:04:25
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Im thinking they are measured in 32s. Id say it is relitive to engine compression as to the amount of vacuum pressure. Venturi size does affect it slightly, smaller venturis will make a higher reading, too big, and it will be too free flow, and be erratic. To the best of my knowledge the numbers of venturi for which model, is like this,,,
#23- SH-350
#25-M
#27- SM-MTA
#28- SMTA-400
#29- 400-450-and some 460's
#30- 6 cyl, 263ci
#33- 6 cyl-291-and some 301's
#35- is the biggest one Ive found, and that's in the 301 6 cyl out of the 715 combine. In most H's that I tune, that has the shebler carb, a 28 works the best for the C-164-175 at 10% over rpm with compression ranging from 150-175 psi. They usually have to be rejetted, but it picks up some hp along the way. They usually sweat, and frost over at the carb flange, till the engine warms up and intake warms up too, and goes away. If it still sweats, or frosts, it is taking to hard of a breath, and pressure is high. Plugs go bad, may seem rich upon acceleration. On the M's warmed over M's like the 29-35, they vary so much from tractor to tractor, its hard telling, just have to know what the engine is doing, as far as compression pressure, manifold, cubic inch, One M can have 155 psi of compression and use a 29 and run and have torque, and another M can have 180 psi, and need the 35. Just depends on what parts are on it. See, the M with 180+psi could have a different cam, or head, manifold that makes that engine unique and create its own patterns to look for when tuning. At 175 psi inthe H-450 engines, better be at least 90 octane. As far as to know what you need to do, go bigger, or smaller on venturi sizes, cant just sit and listen to it run sometimes,,, more information is needed, compression pressure is the main thing, heads, cams, carbs and fuel modifications affect the engine from there on out. Throw in the newly rebuilt engine getting broke in too fast, or not enough, and your gonna chase ghosts till its never ever right, too much is done too fast, and something else that is out of whack creates a whole new problem that did not exist before. Cover the bases, all of them, best tools are a spark plug socket, compression guage, when the plugs even out in color, and so does the compression, then its time to tune, bolt torques on the pullers that have less than 2 -5 hours that have not been rechecked. Few more hours of break in time, keep an eye on plugs and compression, valve lash, and engine temp. ChadS
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