Steven66 Posted April 5, 2019 Report Share Posted April 5, 2019 (edited) 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 Quote Link to comment Share on other sites More sharing options...
gusto Posted April 5, 2019 Report Share Posted April 5, 2019 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 Quote Link to comment Share on other sites More sharing options...
Steven66 Posted April 5, 2019 Author Report Share Posted April 5, 2019 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. Quote Link to comment Share on other sites More sharing options...
martin059 Posted April 5, 2019 Report Share Posted April 5, 2019 Tony ran a 4 mil from driveline he’s the one probly knows some good facts Sent from my iPhone using Tapatalk Quote Link to comment Share on other sites More sharing options...
Ayesully810 Posted April 5, 2019 Report Share Posted April 5, 2019 (edited) 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 Quote Link to comment Share on other sites More sharing options...
SKEETER Posted April 6, 2019 Report Share Posted April 6, 2019 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 Quote Link to comment Share on other sites More sharing options...
97Screamer Posted April 6, 2019 Report Share Posted April 6, 2019 +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. Quote Link to comment Share on other sites More sharing options...
m671054 Posted April 6, 2019 Report Share Posted April 6, 2019 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? Quote Link to comment Share on other sites More sharing options...
Ayesully810 Posted April 8, 2019 Report Share Posted April 8, 2019 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. Quote Link to comment Share on other sites More sharing options...
Big Blue Posted April 9, 2019 Report Share Posted April 9, 2019 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. Quote Link to comment Share on other sites More sharing options...
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