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Post by wheeliehappy on Jul 18, 2017 6:31:30 GMT -5
good morning Gents, I have a 73 RD350 I'm putting together, it was a basket case and is coming together slowly, however it has carbs from a 76 400, the setup on the original 350 and the 400 carbs ie main jet size and so on. I'm wondering do I set the carbs up as they were suppose to be for a 400 or do I set them up as if they were the original carbs for the 350. Does anyone know. if you put 750 carbs on a 500, would you set it up as the 750 or as the 500.
just a bit more info the Main jets on the RD350 with a standard setup are much bigger then the jets on the 400
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Post by mraxl on Jul 18, 2017 9:26:59 GMT -5
good morning Gents, I have a 73 RD350 I'm putting together, it was a basket case and is coming together slowly, however it has carbs from a 76 400, the setup on the original 350 and the 400 carbs ie main jet size and so on. I'm wondering do I set the carbs up as they were suppose to be for a 400 or do I set them up as if they were the original carbs for the 350. Does anyone know. if you put 750 carbs on a 500, would you set it up as the 750 or as the 500. just a bit more info the Main jets on the RD350 with a standard setup are much bigger then the jets on the 400 Putting a carb designed for a larger displacement cylinder on a smaller cylinder means there will be a larger dia air intake and thus reduced air draw than with larger cyl (350 vs 400). When the larger carb was designed for a larger vacuum draw from the larger cyl that means the jetting will be lean if used on a smaller cyl. All jetting will need to be richer than initial large carb jetting. So, the answer is neither OE jetting will be correct. |
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Post by wheeliehappy on Jul 18, 2017 9:48:50 GMT -5
Ok just to clarify, go with the original jetting of the carb?
example a 73 RD350 would have Mains of 180 stock, a 76 RD400 (different carbs) would have a mains of 125
so to make sure I understand, because I'm using 76 RD400 carbs on a 73 RD350 I should use the 400 carb specs, is that what your saying, Do I get it?
The jetting examples I use were just samples I"m not saying that they are correct, just examples.
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Post by Curtis on Jul 18, 2017 10:58:37 GMT -5
It's easier to replace plugs opposed to cylinders
Go rich, do some plug chops,
As Dale said, the larger bore is going to pull less air, but other factors come into play - chambers, pods, porting, squish change, they all have to be accounted for.
I would be more inclined to try and split it down the middle of it was a huge variance and work from there
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Post by wheeliehappy on Jul 18, 2017 11:18:49 GMT -5
mostly I"m trying to find a reference point, because I'm using RD400 carb on a RD350 is my reference point based on the carbs or is based on the engine.
I know there will be fine tuning after that
Thanks I think I have a better understanding now
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Post by autofobe on Jul 18, 2017 13:52:36 GMT -5
They both use 28mm carbs.the 400 uses a 120 main 25 pilot.The 350 uses a 130 main 25 pilot.
I would throw them on to start & do some plug chops.Those are stock numbers so if you have chambers & porting you would have to go up a couple on the main any way.The 350 makes power higher than the 400
hence the bigger stock main.
Brad
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Post by mraxl on Jul 18, 2017 13:58:32 GMT -5
mostly I"m trying to find a reference point, because I'm using RD400 carb on a RD350 is my reference point based on the carbs or is based on the engine. I know there will be fine tuning after that Thanks I think I have a better understanding now As stated, there are numerous factors involved.... In general, use the STOCK jetting of the 400 carbs PLUS two sizes on the main, one size on pilot, lower the needle clip one step. If the 400 carbs were just laying around there is no telling what jets might be in them. EDIT: I just read that both engines use the same size carbs... if that is so, disregard everything I've posted! |
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Post by wheeliehappy on Jul 18, 2017 16:58:46 GMT -5
Ok Thanks guys, for some reason I thought the 350s were quite a bit different for jetting, I thought both stock the 350 was much larger, sorry about that. I have all stock brass for the 400 carbs as per a 400, as I was going start out that way. They are not the same carb they are different model but I guess they are the same size.
didn't meant to waste anyones time.
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