4 mil Dune Bike Questions

[amstall]

I've got most of the stuff built up to put together my '05 roller which I am building to be a dune bike. As of right now here's what I have planned for the motor:

 

+4 mil crank

CPI In-Frames

Dune Port Cylinders

V-Force 3 Reeds

Coolhead w/ cut domes

shifter mods, timing plate, tors removal and all that good stuff.

 

A few questions for you guys.

What mods do I need for my bottom end?

What carbs to run?

I don't know much about long rod motors but is it worth getting?

 

Any other input you guys have I'm more than willing to listen.

[WINDYCITYJOHN400]

The 4mill long rod motor is a very nice motor for dune action. I have the 370 long rod in my wife's bike. (Lots of fun with a +6 arm) It is sleeved for the Blaster piston so rebuilds are cheap. I don't know if going with a bigger bore with sleeves and pistons is in your budget, but I think you would be VERY happy with your 4 mill either way. Ask what the specs are from your builder for his "Dune Port". Some builders just raise the exhaust port 1 mill and call it good. You can get custom cut domes for @ $150.00 from Tim at Titan Racing and he'll have your motor set up for whatever type of fuel you want to run. With Tim's domes you'll make more power than using an off the shelf design. All you need to do is a compression check and a squish measurement and he'll get you set right up.

Start with +4 timing. CPI small bores are an excelent choice. I've got a brand new set of Mikuni flat slide 28's with 4 hours on them if your interested. (The wife wanted less throttle effort so now she's running a 2 into 1)

[Sandfrk33]

I run a hjr 4 mil dune port, stock cylinder motor. Fun as hell in the dunes. Not sure about the carb size, I haven't tried anything bigger than 28's. As far as the bottom end, I'm sure more than a few people will tell you to run an override tranny. I'm sure I'll do it in the next season or 2. Don't forget to put a pancake bearing on the clutch.

[amstall]

I only live 45 min away from F.A.S.T. so I'm going to have Jeff do all my portwork and whatnot. I a little worried about getting "too much power" (if there is such a thing). I don't want to run longer than a +2 arm b/c of the trails at little sahara OK where I mostly ride.

 

Correct me if I'm wrong but the long rod motor is 115mm and the stock is 110mm right?

What more can you tell me about override trannys? prices?

[jbooker82]

Jeff's dune ported 4 mill with CPI's is a fun ride. That is what I am running. I would go with PWK 33's for the carbs.

[RagunCajun]

Stock carbs did fine on my bike but i went with 30oko's just for the hell of it. My builder told me saying with a 28 or 30mm carb will help my low end. The person who does your porting should be able to help you best.

 

I went with the longrod crank, 795 series pistons and stroker domes(noss head).

[jbooker82]

Stock carbs did fine on my bike but i went with 30oko's just for the hell of it. My builder told me saying with a 28 or 30mm carb will help my low end.

 

I just figured match the cabs to the pipes.

 

CPI's Mid to Top end. = PWK33's or 35's

[amstall]

ight...so 28 or larger carbs. what do you guys think about getting an override or straight cut gears?

[jbooker82]

Straight cut gears are deffinatly not needed. I would only get an override if your drag racing.

[RagunCajun]

I was also told strait cut gears aren't needed. And if I rode nothing but WOT Ida gotten bigger carbs.

 

And I disagree on the override for drag only. Mines on a play bike and it's sooo darn fun!

[jbooker82]

I just wouldnt want the possibility of a bent shift fork to ruin a riding trip. My banshee shifts fine with a shift pro kit and a modded star.

[amstall]

I just wouldnt want the possibility of a bent shift fork to ruin a riding trip. My banshee shifts fine with a shift pro kit and a modded star.

 

my current setup has the shift pro kit and modded star and it's still pretty awful at shifting. I've all but given up on finding neutral and I often find myself finding extra neutrals between gears.

[RagunCajun]

Which is the exact reason i went with an override. Never missing a gear. I tried lots of things. The added bonus of staying WOT and shifting w/o a clutch was a very fun and addicting bonus. I let my buddy who never even owned a bike and hardly has anytime on mine beat on my shee, still shifts fine. Now, will the forks needa be replaced in the future, probably but it's worth it. It's not like it's gonna all of a sudden wear down.

[dajogejr]

Backloading the override trans at high RPMs kills the transmission.

It doesn't always wear out the fork...sometimes it grooves up a shaft, etc.

 

If you learn to pull in the clutch at high RPMs instead of letting the motor slow the bike down, a dunable override can last.

The failures we've seen have been from excessive back loading...and the owner would admit it.

 

In a bike ridden like a drag bike they'll last a long, long time.

 

But you're only going 2 over because you want to ride trails. Talk to Jeff about shifting remedy...I'm not certain an override is for you either.

[rubberneck]

For a trail bike i would pass on the override. Put a new clutch cable/easy pull lever, Mod the shift shaft, and make sure everything in the clutch/shifiting assembly is like new. That thing will shift fine and you wont have to worry about how you ride it. I have Jeffs 350 duneport in one of my bikes. Hes gonna tell you to go with 33 pwks. My bike is set up to run t5s and that is what he told me to run. I asked him about 28s and he said trust me i know my motor, run 33s. Havent spent the money to put the 33s on it yet because the stockers run excellent. So my advice to you would be do carbs last. You might find you dont even want to upgrade. Jeffs playport 350 T5 pipes with +5 timing 185psi compression on 110octane, stock carbs and stock reeds. The bike honestly amazes me how it runs for what it is. It truly is a night and day transformation, good power everywhere. Try it you'll like it