Thunderjet install and testing

[Dave63]

Well.....I've built 2 carbs, with identical internal mods, with one having a Thunderjet installed in the venturi (as TJ requires) and another with the Thunderjet installed in the air intake, in front of the carb.

If you read the literature on these things, they're basically a 3rd fuel circuit that's designed to use venturi vacuum to bring more fuel into the carb, on hard pulls, beginning at about the 4000rpm range.

They have self contained jets in them, as well. You can adjust the fuel flow for optimal HPs. The venturi vacuum draws fuel from the carb bowl, where you drill and install a port. A rubber hose leads the fuel to the TJ unit, where there's an internal jet, floowed by an airbleed collar, and the jet that goes into the venturi itself.

My first one I built, I installed the TJ (red thing on the side of the carb) in the ventiri. Went with a 100 TJ jet, and a 180 main. They suggests dropping your main jet size as with the TJ adding fuel as a separate circuit, there's no need for a large main. The filter adapter is an aluminum plate with a K&N filter on it, and no other BS. The vent line is a crossover for the head vents, with a single stainless line that runs to the catch can.







The one on the bike now, is the same, only I'm running a 190 main in my carb, (Andrews recommends a 195 jet with the EV27 cam I'm using) and a 50 pilot jet, and all the other carb mods installed. I'm running an SE module (6000 rev limiter) and an SE coil, wires and platinum plugs.

What you can't see is the TJ jet that goes in, behind that silver screw in plug, on the end of the red part.






Hre you can see the fuel level in the line. When you whack the throttle hard, you can see the fuel level ride, due to venturi vacuum in the intake system. Of course, that vacuum will be increased on the road, under load and we'll see how well it works, or if there's any noticable gains in Hps. I can turn it off and on, to see how it reacts on a Dyno run. Of course.....it's supposed to rain the next 3 days.

I also have a Pingle high-flow petcock coming, which increases the fuel line from 1/4" to 3/8", as well as the replacement of the fuel elbow. More HP means more needed fuel. Screw gas mileage.

[MrMarty51]

Mine 97 FXDWG has more than a stock cam,lopes like a Crane High Roller,I was told it has 9.5 to 1 pistons with Branch heads.
Does a person need to know all the specifics of equipment installed by previous owner before doing this mod???
Just wondering in case Mine back gets good enough to ride more than about 5 miles at a time,I would like to send Mine carb over to You to have all the mods done.
I was told the carb already has the DynoJet upgrade but I am not sure what to look for to tell.

[Dave63]

Originally Posted by MrMarty51

Mine 97 FXDWG has more than a stock cam,lopes like a Crane High Roller,I was told it has 9.5 to 1 pistons with Branch heads.
Does a person need to know all the specifics of equipment installed by previous owner before doing this mod???
Just wondering in case Mine back gets good enough to ride more than about 5 miles at a time,I would like to send Mine carb over to You to have all the mods done.
I was told the carb already has the DynoJet upgrade but I am not sure what to look for to tell.

KNowing all the mods that are in the engine helps with knowing what exact jetting to run in both the carb and the ThunderJet.

The ThunderJet is a 3rd fuel circuit. It adds fuel in that transition of needle jet, to main jet, where most carbs lag.

If it has the Dynojet upgrade done, I'll know that as soon as I take it apart.

Dynojet's emulsion tube is different, as are they're jets. (threading)

The Dynojet diaphram/slide spring is also different, measuring at 5" long and 8oz to compress, where as a stock HD spring is 5.5" long, and takes 13oz to compress.

I can tell if the slide was drilled or bot as well, and all mine get polished and get a rounded, leading endge for smoother air flow.

If you're serious, we'll chat when the winter season hit and I'd me more then happy to give it the once over for ya Marty.

[Badassbrutus]

I reckonize that cover!!HAHA Your out on furlough..Im out on work realese!!...lol
nice one Dave...

[MrMarty51]

Thanks Dave.
You mean winter has`nt hit??? Well i guess we do have 2 or 3 days coming that are suppose to be about 60 or so.
LOL Babs,The Dr. signed a return to work light duty and that I had reached my max med. improvement so the Montana DOT say`s We do`nt have room in the shop for a light duty mech. You need to load up Your tools and personal gear and go home.OOOKKK,31 years on one job is too long anyhows.

[Badassbrutus]

Hehehe!!

[XDixiecratX]

Gifted mofo.

[chardhin1999]

Originally Posted by XDixiecratX

Gifted mofo.

ya no doubt the guy has mad skills, awesome dave. I was talking to my boss about you and the advise you give to us, she says "it's nice to hear there are helpfull and educated people who are willing to lend there knowledge for free, he sounds like nice fella."
I agree.

[MrMarty51]

Originally Posted by chardhin1999

ya no doubt the guy has mad skills, awesome dave. I was talking to my boss about you and the advise you give to us, she says "it's nice to hear there are helpfull and educated people who are willing to lend there knowledge for free, he sounds like nice fella."
I agree.

[Dave63]

Originally Posted by chardhin1999

helpfull and educated..nice fella."

No need fer name callin'............!!