Driveline Assassin LP 4 mil w/ 28mm PWK

[Steven66]

I checked a couple different combinations in the forum search bar and couldn't find an up-to-date 4 mil w/ small carb threads, much less anything driveline related.

To start, I'm planning an engine build pretty soon using the driveline 4 mil LP kit with SLP pipes. Current riding style is mostly open dirt pits, large trails, with some MX. My current setup is a heavily ported 392 with stock carbs and T5's. It's tuned fairly well but the heavy porting really kills the low end (not ideal for my riding style but it's the only running engine I have atm).

At first I was planning a driveline 4 mil LP w/ SLP's and 35mm PWK's but I'm worried about the larger carb setup reducing the off idle responsiveness and being a handful in trails and Mx having 80+ hp (yea I know, too much HP, booooo). I figured with 28mm PWK's I could reach the 70's with and greatly improve the low-end over a 35mm carb setup but I wanted to get some feedback from guys who have actually tested similar setups. Besides that, any suggestions / changes I should make to my build given my riding style? I'm open to anything.

Edited April 5, 2019 by Steven66

[gusto]

Couple of guys running 421s with 28s on this forum. I am one of them. Only thing I would add to your set up is a pingle. The shop that built my engine (low port) there is no noticeable difference in max hp. Fuel economy and snap on bottom end is much better. go for it

[Steven66]

Just now, gusto said:

Couple of guys running 421s with 28s on this forum. I am one of them. Only thing I would add to your set up is a pingle. The shop that built my engine (low port) there is no noticeable difference in max hp. Fuel economy and snap on bottom end is much better. go for it

I had a spare pingle which I threw on the tank. Those 4 mil's drink heavy.

[martin059]

Tony ran a 4 mil from driveline he’s the one probly knows some good facts


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[Ayesully810]

The 35s with slps will still give good bottom end, especially if you are running higher compression with race fuel numbers.  But I ran 35s with race fuel and the mpg was not ideal, I ran a pingel and ran outta gas in the trails a handful of times.  I switched to stock carbs and pump gas and I tell ya, it was way more practical for the type of riding you are going to be doing.  Id stick the the smaller carbs because the bottom end was much more responsive with the smaller carbs, you will be happy with the 28s and still be able to smoke most average joes play dragging.   As far as jetting, with my 35s and race fuel (170+ psi)  I was at 52 pilot, 138 main (small  i know) dont start this low if you go this route, and cel needle in the 3rd or 4th position dont remember.   Stock carbs was 37.5 pilot, 350-370 main, vitos needle in the middle or 4th. 

edit: I now run their 7 mil setup with 35mm carbs.  not much more to $build$ minus the more expensive supporting mods.  gas mileage same story

Edited April 5, 2019 by Ayesully810

[SKEETER]

Unless your open duning, drag racing,  28s will be better option IMO.  You dont NEED those 35s for your type of riding. Why waste more fuel and lose bottom end crisp.  Just my thoughts, but I'm not a CAPTAIN 

[97Screamer]

+1 for 35mm being too much carb. I run 28mm on a 4mil stock cylinder and plan on using them when I install my 421 serval. I own 33s and 35s also, they'll go on the 10 mil. 

[m671054]

18 hours ago, Ayesully810 said:

The 35s with slps will still give good bottom end, especially if you are running higher compression with race fuel numbers.  But I ran 35s with race fuel and the mpg was not ideal, I ran a pingel and ran outta gas in the trails a handful of times.  I switched to stock carbs and pump gas and I tell ya, it was way more practical for the type of riding you are going to be doing.  Id stick the the smaller carbs because the bottom end was much more responsive with the smaller carbs, you will be happy with the 28s and still be able to smoke most average joes play dragging.   As far as jetting, with my 35s and race fuel (170+ psi)  I was at 52 pilot, 138 main (small  i know) dont start this low if you go this route, and cel needle in the 3rd or 4th position dont remember.   Stock carbs was 37.5 pilot, 350-370 main, vitos needle in the middle or 4th. 

edit: I now run their 7 mil setup with 35mm carbs.  not much more to $build$ minus the more expensive supporting mods.  gas mileage same story

37.5 pilot on stock carbs? Just checking. Also is your vito needle way longer?

[Ayesully810]

On 4/6/2019 at 2:30 PM, m671054 said:

37.5 pilot on stock carbs? Just checking. Also is your vito needle way longer?

idk they were red, ran it in the middle now that i think of it. and yes 37.5, when i had it dynod we had a 35 and it was a tad on the lean side, so i upped it but in the summer it would have been fine.  

and yes skeet you are a captain, captain crunch. 

[Big Blue]

I'm running 33's on my LP driveline. 28's would have been my choice but already had everything else for the larger carbs.