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Need suggestions,About ready to replace Super G with Thunderjet and go to a Mikuni 45 HSR.Have to see for myself which is a better out of the hole carb.Any of you running this carb on a 124" S&S motor? What size mainjet you running? Dog
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I've not run a 45 on a 124 but I'd bet if both are tuned right, itwill be close..They flow about the same on a 1.78 manifold. You will probably get better mileage outof the 45. When done have someone bore the G to 1.86 in and see how that runs. Also use the wider SnS air cleaner.
IMO with a 124 you should go for a 48. Thisassumesthe 124 crate motor and not the smogged one. Smogged motors will need work before seeing any difference. The 45 might work better here.
Thanks Bruce.My only reason trying this is, I here the Mikuni's have a better off idle response,What do you think? I have always run S&S carbs and have everything I need here to tune them.Boring the Super G got the juices flowing.I have a mill is there a trick to boring the venturi's?I bought my 124" in pieces to polish and build myself,saved a ton.Never heard of a smog motor.What is the difference? Dog
I think that you can tune a G to do as well as far as throttle response goes. In fact the G can be a little touchy at slow speed. The 45 a bit less. The reason is that the G changes air flow through the carb so much at small throttle positions. Think about it air flows around both sides of the butterfly when opening. On a slide, there is only one side, the bottom. Still, IMO, either can be tuned for good response and low end performance.A G with T-jet will have a flatter A/F curve at WOT over the RPM range, where the HSR may not. Not to knock the HSR, it's a good carb. With proper tuning the HSR should give better mileage.
I bored a G one on a mill a long tine ago. While it helped I prefer to do it it a lathe. I've got a fixture that holds the carb so that I can spin it. I bore to say 1.84 then using the compound rest I make multiple small cutsinthe flat spot so that the narrowest point is at the same location as before boring. I then use60 grit to round the cuts, then 120, 320. Doing so will get you about A 7% increase in flow.
A smogged motorwillhave a strange shaped chamber with almost no quench.Piston deck height may be low. It will also have a smog cam in it, something like a 546? I'm not sure if SnS made a smogged 124 but I know they made a number of smogged 117s.
BTW,
It's good to cross drill the air holes in the tjet brass tube to say 0.055 ( stock is 0.040) or you get a rich dip at about 3500-4000. Tjet comes on too early. Run the int jet that give you the best cruise. I'd ignore Zippers instructions here.
Mine has the 640 cam with the good heads,and it doesrun very good.The next thing on the plate will be the deeper air cleaner,look at the venturi for boring,see about theT jet.Thinking about it,the True Dualexhaust has never been tuned,I will do thatfirst.Thank you for the advise,the Mikuniis going to the auction block.Are the Bruce from Big Boys Toys in Maine? Dog
Nope, just a hacker/hobbiest, that livesonthe opposite coast in Southern California. I've played a lot with G carbs and some of it with an wide band AF meter, some on a dyno. The 640 is a good cam but it'll run better if you make sure the CR is above 11 to 1 to help the low end. Also exhaust choice makes a big difference. Sounds like you are running it in a bagger and I'm not sure how the motor/cam performs with true duals. They work real well with a set of free slowingstepped staggereds or bigger piped 2 into 1 like the DandD boarzilla. I run that cam in an 11 to 1, 113 evo and also in a 11.5 to 1, 131 ci twincam. Here a pic of the 131... This one has an HSR48 on it. There might be 2 pics in this post...
Great looking Twincam!! Question on boring the G venturi,take it out to 1.86 and blend it in like stock?My T-Jet does come in a little early, a jet change should delay it a little more.My motor is 10.8-1 close enough.Actually this motor is very crispy.My mufflers are from Kromewerks HP 100's.Take a look in the Touring section,go to Search,and type in baddest bagger,the 2 pics that come up are of my 155" Twincam sleeper RK.
"Question on boring the G venturi,take it out to 1.86 and blend it in like stock?"[/align][/align]If you look at the G venturi, you'll see a bit of a lip. The idea is to open up and round that section at the same time. The smallest ID shouild be at the same location the original lip. I'd bore it to 1.84-5 inches then when you use course sand paper to round the cuts the bore will get bigger. You need to be careful about going much larger as I think you'll get into the O ring seat for the accellerator nozzle (IIRC). 10.8 is on the low side but as long as it's been verified you are probably OK. I'll go look for the bagger. Bruce[/align][/align][/align]
Thanks for the info Bruce,My next move will be to get the deeper air cleaner,drill the T Jet holes out, and jet it smaller.May even try and find another G to play with on the milling machine.Either way the 124" is going to get stepped up a notch.The 155" is used most of the time,you understand why.Dog
Mikuni 45 HSR--124" S&S
