Vortex VLR 100 - FAQ

[elmt1]

Hi Dan,

Thanks for the suggestions. I haven't checked the reeds but should since there is a lot of grit here that could have caused problems before I got an air filter. I think the grit mixed with rain is why I have worn out two chains/sprockets since getting here. I feel like the other items have been pretty well checked but not completely eliminated. I'll check the reeds this week.

When I got here, I was using a 10-78 and was seeing top RPM each session average between 15,500 - 15,600. I dropped 1 tooth to 10-77 and was seeing about 15,300 - 15,400 and it felt pretty good unless I screwed up in the hairpin turns section. Over time, my top RPM dropped to the 14,800 range with the 10-77 so I rebuilt the carb, cleaned the head, checked the alignment/caster replaced the chain, rebuilt the clutch, etc. That helped some and I was back over 15,000 but not where I started. So I went up a tooth to 10-78. Not a lot of difference and still below my starting top RPM with the 10-77. I then went to 10-80, which got the RPM back up and it pulls better again on the hairpins section but the top end/speed is off.

Thanks!

[Fred]

There can be many other reasons why you are not hitting higher revs other than the motor. Tires , chain, axle rotation, temperature, carb settings , squish measurement etc etc so I wouldn't go diving into the motor just yet. If you have not replaced a ring yet do so .. make sure it's gapped properly. You can also do a bleed down test of the main bearing lip seals with air to see if you are loosing any power out of them which would necessitate replacing them.
Bottom end should be good still. The VLR is very easy to strip and rebuild I did one at Challenge of the America's in 25 mins the other day... don't be affraid to get into it yourself ..

[[email protected]]

Hey David,
I chased some rpm issues with my first engine last year, after starting to use the second engine which had no issues I swapped a couple of parts in order to diagnose
what was causing the lack of top end rpm ( could no longer get over 14100 with engine 1) engine 2 topped out at 15500.
Due to running it without an air filter in the airbox on engine 1 I had damaged one of the reeds, but the issue was resolved when I swapped carbs. Upon rebuilding carb 1 I found debris inside it also from the lack of air filter. you will require a vacuum pump that will also do pressure to test and rebuild your carb.

Watch this video: https://www.youtube.com/watch?v=gdWR9sTq6Tw&t=327s

after the rebuild carb one was back to life and back to 15500.
when buying the carb kit make sure to get the one that comes with the needle/popoff valve.

Glenn

[elmt1]

Thank you both for the suggestions. I have gone through some trouble shooting to try to eliminate alignment, tires, carburetor, brakes, chain, gearing, clutch, etc. I feel like I have those pretty well covered but there is always the possibility that I am missing something that isn't engine related. I did just recently do the full carburetor rebuild and a few weeks ago the mini rebuild (driving in heavy rain and also knats seem to trigger carburetor problems). The reeds seem like a strong possibility and even though I have broken down just about every piece on the kart many times, I haven't looked at the reeds, checked compression or bleed-down. I was surprised at what I found in the airbox recently, and feel pretty dumb for not putting in an air filter. My only excuse is that my kart didn't come with one and that seemed to be the norm at the time. Also, I feel like I really should have checked the compression after a couple of hours so that I would have a baseline.

I will definitely check the reeds tomorrow night when I go to the track but may just run it a couple hours and pull the engine so I can check it when I get home. OTK is little over an hour drive from where I live now so getting a ring would be easy and it sounds like replacing it is something I should do. I haven't actually rebuilt a 2-stroke motor for a really long time (40 years or so) so even just replacing the ring seems challenging at this point, but I grew up working in a machine shop and have always had a reasonably complete machine shop, so I am fairly comfortable with that type of thing. At some point you just have to give it a go and chalk it up to a learning experience if you make a mistake. I have had a few learning experiences in my short karting career

Thank you!

[elmt1]

I think I found the majority of issues today with my motor. It turns out one of the reeds had a corner broken off that left a hole about 5mm square. I replaced that and it helped but it still wasn't great. I took apart the carburetor, which I had rebuilt about 3 days before and couldn't get the popoff to work like it used to. I did get it to seal but it seemed like it would go up to about 11 lbs and go off down to about 7 and keep leaking down from there. I took it apart and cleaned the needle and it then held at 7 lbs but it wouldn't really pop like it had in the past. I took it out and it had no throttle response. I ended up putting my old carburetor, which has at least 20 hours on it without a rebuild and it was a lot better. Now I am getting much better throttle response and the kart getting much higher RPMs. I still need to get the needle jets adjusted a little better but it is a lot better.

I was told that it is a good idea to rebuild those carburetors with a full kit every few days of driving. The guy who told me this runs their local team here and said that the needles will break down and get soft and that the plastic gasket will also wear fairly quickly so they do it as insurance. He showed me how to check the reeds and I found that one of the reeds in my old motor was cracked also so I will buy another set to keep on hand since they are pretty cheap and apparently, they are not bullet proof. Now that I know how easy it is to check them, I will probably at least look at the reeds every 3-4 days on the track. I am also just going to rebuild both carburetors and keep them ready so that I have so that I have a quick way to see if the carburetor has fallen off.

[Fred]

Make sure you put the reeds in the right way .. they have a slight curve to them. Your carb seems OK , it should pop off around 10 - 11 depending on how you have it set .. you will never get it to hold pressure all the time it will eventually bleed down. I would say your crank lip seals need replacing by the sounds of it.

[elmt1]

Hi Fred,

They had a bigger race here this week and I was able to enter. I ran my motor with about 25 hours on it on Thursday but it didn't have the pull that most of the others had so I went ahead and rented a motor for the weekend. It seems to be significantly stronger than my motor. With the rental I went with two less teeth in the rear because and it will easily go 500 rpm faster with the same gear. My motor when I arrived would hit 65 and fell to about 63 recently and with the rebuilt rental, I was hitting 66 alone and 68 if I was behind someone. In the past, being behind someone meant nothing and they just pulled away, now I can actually close on them. It was a night and day difference. My times improved by about 3/4 of a second based on motor alone. Unfortunately, I had to give them back their motor, but I did give them my older ROK VLR to rebuild. They also mentioned that I had the old style header in both of my motors, which they say makes a difference.

Thanks!

[elmt1]

I got my motor back from the engine rebuilder and it was really worn out. With all the parts it needed, it came to $1,200, which included piston, connecting rod, piston pin, main bearings, seals, reeds, new style exhaust header, new style timing plate, ring gear and dyno testing. The connecting rod assembly was the most expensive part at $348. I will use the new motor at the next race they have here and give them my alternate motor, which I am hoping will be a lot less to rebuild because it shouldn't need as many parts.

--David

[Fred]

I am guessing the Dyno testing was a good chunk of cash too ! You have put a lot of hours on that .. the best way is to do a little and often and rebuild it yourself.

[elmt1]

Hi Fred,

Yes, the basic rebuild service with the guy I went to always includes dyno tuning and break in and is $500. I would really like to get to a point where I could hone and drop in a new piston myself so that I could learn more about the process. Unfortunately, the motor that I had rebuilt lasted all of 3 days before it locked up. It locked up on lap 5 of the main of the Rok Cup winter series race they were holding here. I learned a lot but it was still disappointing because I had guessed rain and had rain tires/setup along with 1 other person. The other guy that guessed rain won the race and the series. Part of the problem was probably that I had geared down for the rain 2 teeth and the first few laps were dry. On the lap it seized it was still pretty dry and I hit 16,200 rpm at the end of the straight when it knocked a few times and locked up sending me straight off the end of the track.

I had gone about 5 minutes richer and the exhaust temperatures were about 1,100. The guy who rebuilt the motor said it didn't look too lean and asked if I had mixed my gas that morning. I told him I had only topped off the tank and he said the oil probably separated due to the cold conditions. I read that Motul oil mixes easily and the warmup went fine. Another reason I question it is that my kart stand requires me to stand my kart on its bumper to load it up and I had done that 3 times just before the race as I vacillated between rain tires and slicks so it should have been somewhat mixed. One of the guys in the race, who has been racing a long time said it could have been related to the rain, which seems plausible to me that water interfered with the flow of fuel somehow. Another long time racer said I probably should have gone with 6 oz per gallon rather than 5oz but I have always used 5. The high RPM probably contributed also but I have seen that my motor got up to 16,400 more than a few times with drafting and haven't had problems.

Thanks!

--David