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chart to cross mm carb jets to std jet sizes?


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7 replies to this topic

#1 heep70

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Posted 30 January 2007 - 06:27 AM

Anyone know where, have a chart or know how to cross MM carb jet sizes to std jet sizes? Thanks, Greg

#2 Reveeen

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Posted 30 January 2007 - 07:16 AM

Most jets are stamped with the orifice diameter in metric or English units. On a metric carburetor, a number such as 120 means 1.2 mm.; on most U.S. units, 50 indicates .050 inch. There are exceptions; check with a carburetor shop to be sure. Convert millimeters to inches by dividing by 25.4.
(from: http://running_on_al...d.com/id26.html )
If I was increasing, or drilling to increase the jet size, I would fit a numbered drill into an existing jet to get the numbered size, then increase as I saw fit. If you are working with a metric carb any jets you are going to get that fit correctly are metric too, so I'm not really understanding the need to convert, but the above formula will work for you. In improper idle conditions the "usual" is to adjust the air bleed rather than jetting.



Anyone know where, have a chart or know how to cross MM carb jet sizes to std jet sizes? Thanks, Greg



#3 heep70

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Posted 30 January 2007 - 08:06 AM

Holley jets fit webers and Motorcraft/Holley carbs.

That is what I was thinking about the jet sizes. Just wasn't sure.

I am putting a Motorcraft/Holley 5200 carb (weber look alike) on my Toyota and the Subaru. I have a whole mess of Holley jets I wanna use if needed.

#4 heep70

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Posted 30 January 2007 - 08:19 AM

Thats an interesting tech article.

#5 Reveeen

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Posted 30 January 2007 - 10:23 AM

The Motorcraft/Holly carbs were built under licence from Weber and almost identical to the carbs found on Vegas (the 2bbl Vegas). Out of the box the jetting for a 2000/2300 should be close (these were smog engines), though the carb from a 2000 should be a closer copy to a Weber (completely Metric, if memory serves). An English built Capri will have an OEM Weber on it.
I know you guys like these, but really I can't think of a worse carb to put on anything, and if I found myself wanting a carb for a 1600/1800 engine I would *think* SU, or a pair of SUs, but to each his/her own.
The 2.6L Mitsubishi/Dodge engine uses a Hitachi progressive 2 bbl much like the original (only bigger, again if memory serves).
When increasing the size of a carb on any engine you have to be careful, as the bigger you go (more availaible air flow), the quicker it will lean out if you don't use that air flow at WOT (wide open throttle), so you may find yourself having to richen the mixture.

#6 bgd73

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Posted 30 January 2007 - 11:03 AM

The Motorcraft/Holly carbs were built under licence from Weber and almost identical to the carbs found on Vegas (the 2bbl Vegas). Out of the box the jetting for a 2000/2300 should be close (these were smog engines), though the carb from a 2000 should be a closer copy to a Weber (completely Metric, if memory serves). An English built Capri will have an OEM Weber on it.
I know you guys like these, but really I can't think of a worse carb to put on anything, and if I found myself wanting a carb for a 1600/1800 engine I would *think* SU, or a pair of SUs, but to each his/her own.
The 2.6L Mitsubishi/Dodge engine uses a Hitachi progressive 2 bbl much like the original (only bigger, again if memory serves).
When increasing the size of a carb on any engine you have to be careful, as the bigger you go (more availaible air flow), the quicker it will lean out if you don't use that air flow at WOT (wide open throttle), so you may find yourself having to richen the mixture.


I like your point of view! The original hitachi is a favorite for matching an engine (ea series). Problems are just that simple and do not require this matching game that never seems to be correct from other crabs. Below zero F in temps always reveal the most minute errors, the oem carbs seem to have none. Other than OEM emissions, they even open up quite well for heavier throttling. A higher pressure fuel pump and a regulator with guage does amazing things for oem....
For these bigger 280cfm swaps,It is safe to assume it is for WOT and more cfm? Never worth it to me..
Heck my favorite carb on a 350 cubiuc inch is a "small" 600 cfm (smaller than oem). Warm weather places get away with alot, bad carbs and too much cfm is one of them.:)

#7 Reveeen

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Posted 30 January 2007 - 11:53 AM

The "beauty" of these things is that they are simple and reasonably "bulletproof", they were designed that way, and more you "improve" them, the more unreliable they get.
Look, if Subaru had wanted, they could have made 15,000 RPM engines with overhead camshafts, Honda was doing just that in motorcycles in the '60's, the technology was there, but instead they built what they did for a reason, the same reason we love these obsolete lumps.

Just my .02

#8 GeneralDisorder

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Posted 30 January 2007 - 12:12 PM

I know you guys like these, but really I can't think of a worse carb to put on anything.


Have you ever ran a DGV Weber? Ever ran a Hitachi???

Compared to the orginal Hitachi, it has a LOT of benefits. Not the least of which is the availibility of inexpensive adaptor plates. While an SU (or pair) might be nice, not everyone has the ability to make up any old adaptor plate or sync up multiple carbs.

Please - run Hitachi's if you like them/think they are better. But don't go around telling folks there's nothing worse than a DGV/DFV/5200..... because there is.

GD




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