620connor Posted June 19, 2015 Report Share Posted June 19, 2015 How's it going guys. I have a carb question. Will a stock L18 carb from a 74 620 work on a L20B from a 75 620? I pulled a comeplete engine from my local scrap yard, and the L20B didn't have the carb on it. I like the oem hitachi carb and would like to run the one on my L18 if possible. I figure the carb will need to be properly jetted to work but is that all it will need? Or are there more differences that i don't know about. My buddy has a L20B in his truck that has the stock hitachi carb on it, and they look pretty identical except for the bowl glass on the front of the carb. I also plan to have the L20B bored .30 over before i swap it in. Any info would be appreciated. Thanks. Quote Link to comment
DanielC Posted June 19, 2015 Report Share Posted June 19, 2015 The carb should work fine. If anything, the vacuum secondary will open at a slightly lower RPM. Unless you are tuning and tweaking for every last fraction of available horsepower, you probably do not need to rejet it. 1 Quote Link to comment
LenRobertson Posted June 19, 2015 Report Share Posted June 19, 2015 You might look at the "Dime Quarterly" articles on Hitachi and Weber carbs http://dimequarterly...s-ordering.html Go to Volume 1, Issue 3 and Volume 2, Issue 1. I think that tells how to id the different Hitachis and maybe has jetting info. If you feel the need to rebuild your carb, there are articles in the How-To section on Ratsun that may be of help. But as DanielC said, you may be able to just bolt it on and go. Len Quote Link to comment
620connor Posted June 21, 2015 Author Report Share Posted June 21, 2015 Cool, thanks guys. Does anyone know exactly how the secondary butterfly works on the hitachi carbs? I know it uses vacuum to function, but thats all. I'm pretty sure the secondary doesn't work on my stock hitachi, going 3/4 throttle felt no different from going full throttle. Is there a way to check to see if the secondary works? Quote Link to comment
DanielC Posted June 21, 2015 Report Share Posted June 21, 2015 When the air flows fast enough through the primary side ot the carb, it creates a slight vacuum, that pulls the secondary open. The primary also has to be open past a certain point. you can take the secondary vacuum actuator off the carb, two or three screws. There is another holes in the actuator casting. sucking on this hole should cause the diaphragm to pull in. When the diaphragm is pulled in, putting your finger on the hole, and plugging it, the diaphragm should move slightly out, but then hold in that position. If it comes back out, the secondary actuator has a leak. You cannot load the engine enough without driving the truck to get the secondary to open. Quote Link to comment
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