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So I got it finally figured out!
I was way off on the jetting.
I searched for vm mikuni set ups on Sportsters to see what jetting they ran.
300 main is what most run. I was told to start with a 180.
The biggest jet I had was a 280, so I gave it a try, no more bogging down.
Checked the plugs and they were still a bit lean.
I'm gonna try drilling a few out to 290 and 300 and see how it feels and looks.
This is my first time feeling this engine with the mods I made.
I have to say, Im really impressed on how good this little engine feels. No problem drifting around the corners now!
Its gonna be perfect for the buggy once its dialed in.
Thanks for your help guys!
Ok, So before all the mods, Top speed I was hitting was 30MPH.
Did some jet changes today and my buddy did a side by side drive down a long street by my shop in his f250 Van, maxed out at about 50MPH! Nice!
This VM Carb didn't come with an Air jet so Im having difficulty finding the mid range on the Pilot screw so I have it set at about 2 turns out and adjusting the idles screw till it sounds good.
Im sure I can get a bit better takeoff once I get an air jet. Plus I could try going down a size on the Pilot also.
Now for the confusing part, so yesterday I tried the 280 and it looked Rich. Biggest jet I could find today was a 290, So I picked it up just in case.
I went to my neighbors machine shop and we measured the the 290 and he gave me to drill bit sizes bigger so I could drill out one of the 155 or 160 that I had.
I drill both out and still got Lean readings on the carbs. No more Bogging out but it sure is guzzling gas thats for sure.
I looked up the VM series carbs used on Sportster 1000's, they use a #30 Pilot and #300 Main.
Im thinking Im close to a #310 now with the drilled out jet and it still looks like its lean.
Granted, the VM Carbs for the sportster are 38mm, mine is bored out to 42mm.
I guess Im gonna have to find some bigger main jets.
Here are some pics of the Plugs from the last drilled out jet, which was .061in./1.57mm.
Mounted up an Equus 8068 Tach yesterday on the 35HP Vanguard. It has the Inductive Spark plug pick up. Didn't work at first but on the trouble shooting section it says to try reversing the direction of the pickup. Works pretty good now. It has like a half second delay but nothing to complain about.
Bought it at Oreillys for about $90 and its fairly easy to wire up, as long as you don't already have a mess of unecessary wires under your dash. I really need to go through the harness and consolidate it to only what is needed.
But all and all it seems to work ok with the inshop test.
I also ran wires to mount a cheapy Horn that i had sitting around. Last time we took the buggy to Dumont I kept thinking, I wish I had a horn to tap and signal my buddies when I was about to pass them on the outside or inside while riding the wall of a Bowl.
Now that I have the Tach, I can get the tuning down better. It sounds like 5000 RPM is right about where it will be Maxing out, can hear a slight ping right about 5000 so I don't think I want to go beyond that. Better then the Original 3600 rpm with governor. https://www.youtube.com/watch?v=SbC1MjkFi2Y
Okay, so I went and get another set of Brand new Plugs.
I went with the Autolite Double Platinums at about $5 each compared to the regular Autolites at $3 a piece. Wanted to see if there would be a performance jump.
I have been driving all over town accumulating jets from various Moto Shops spending about $4-6 bucks per Jet!
But I found out a place about 5 miles from my shop that has pretty much every Jet and sells them for $2.50 each!!!
So I picked up a few more in the bigger Main range to try with the new plugs. Drove the buggy a few blocks over to an Industrial St. that has a good 1/4 Mile straight run. I changed the Plugs to the new ones once I got there. had my buddy in the Pass side and another buddy pacing in his truck.
Started with 20 Pilot and 350 Main.
Ran it up and down the street about 3x making sure I ran it at WOT. Plugs looked brand new still!
So I went back to the shop and changed out the Jets. I didn't have anything bigger then 350 which is about a 1.40mm Drill bit, so I drilled another jet to the next Drill bit size I had which was about 1.70mm. So im calculating that Im at about 420 by now. The VM Hex jets go all the way up to 660.
So now Im using a 30 Pilot and 420 Main.
I did a few more runs and read the plugs again. Top end feels good, just keep on going.
The front Cylinder is on the Left, which is starting to look Richer then the rear.
The 30 Pilot is looking a bit Rich on the plug ring so Im thinking of trying the 22.5 Pilot that I have next. Still a bit lean on the Porcelain for the Main.
Im thinking Im gonna need to go up more on the Main to about 450+.
The new double Platinum Plugs are easier to read then the cheaper ones because the threads are Silver. The cheap ones have black threads.
Well once I get this 42mm figured out, I'll at least have enough Jets to tune the 40mm. This way I can use the 40 for the Dunes and the 42 for the hard pack desert Long distance runs.
Heres a pic of the Plugs. How do they look to you guys?
Well I finally figured out my jetting range on this VM Mikuni!!!
I was too lean on the Pilot which caused it to hesitate on take off. Jumped up to a 60 from the 30 that I was originally playing with and WOW! That was the ticket!
Im gonna pick up a 45, 50, 55, and see which one feels and looks the best.
I have the Idle set at about 1200. I started with a .5 Air jet and then drilled it out a bit. Im still having some trouble getting the Pilot screw to show much of a difference after 2 turns out. It will slightly increase in RPM but after turning it out a few more times it doesn't really drop after the rise in RPM's. It will drop once I get down to about 1.5 turns from fully closed.
Im not really sure if I need the Air jet at all?
Gonna play with the Needle and Main to tweek it as close to perfect as I can, but all and all, I think Im ready to take it out and tune in the dirt soon!
I drilled out the Highest Jet I had which was a 520, the plug was still looking lean with the 520 at WOT.
I'd say Im close to a 600 Main by now. Plugs look a bit rich so Im gonna have to pick up some more mains between 520-600 to see which one feels best.
The Tach is working great and makes it a lot easier to understand whats going on with the tuning.
Next mod is gonna be the timing. I probably should have done that before tuning but I wasn't quite sure how to go about it and there isn't much info online on the process. I'll take Nubs insight and see if I can figure it out once I pull off the flywheel cover and see whats going on underneath.
Question:
Im maxing out the engine at WOT at about 4500 RPM, no pinging or irregular sounds from the engine, just feels like its reached it's.
Should I be getting more RPM's out of it or does that have to do with fine tuning the Main Jet to get a higher RPM out put?
Nubs, you said your 24HP was getting up to the 6500 RPM range, is that because you have an aftermarket CAM thats why its getting up in the higher RPM's?
Clips rolling the buggy around the parking lot. Have to wait till everyone closes their shops in the evening before I can play around with the buggy and jetting, but it does sound pretty beefy! ;-) Buggy1 - YouTube Buggy2 - YouTube
Last edited by Hollywoodc; 04-03-2014 at 05:17 PM.
I just wanted to say thanks for all your guys Insight and help. I hope somebody can take from this thread something that will help them on their builds.
I spent a lot of time trying to figure out the VM Carb and Jet range. There is no standard listings for this particular carb that I could find. But from the point I'm at now, the setup makes a huge difference on this engines performance compared to how it felt stock.
I still have the other 40mm VM that came. I'm thinking I'll keep the tuned bored out 40mm to 42mm for High desert higher speed runs, then I'll tune the 40mm VM and use that one for the Dunes.
Im thinking the 40mm will have a bit better lower end punch for Roosting in the dunes. :-)
My setup has an electric pump, is there a way to check the pumps pressure and how much pressure should it be pumping for a Mikuni setup?
I'm wondering if I was getting such a lean reading with the big jets because the pump wasn't filling the bowl fast enough. But I think I would have felt a hesitation in response once it hit the bottom of the bowl.
I did a compression check on both cylinders and front was showing 100-110 rear was showing 110. I hope that is adequate for these big block engines.
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