new guy new motor need help

Discussion in 'Performance Mods' started by bossman, Mar 12, 2011.

  1. bossman

    bossman New Member

    My first post above describes what I have and the mods I`ve made to it so far, I have some technical questions so I thought I would transfer the thread here.

    1. As of now the engine runs GREAT this is with no air cleaner on it, I have a small square foam filter from the ryobi that when I install it the engine runs a little worse, the transition from idle to WOT is slower and the max rpm at WOT seem slightly less. The filter is spotlessly clean, should I just take it for granted that the air filter is going to cost me some performance or is there a mini K&N type paper pod filter that may give me the performance I have without the aircleaner but still filters the air, I have no intention of running my engine without an air filter but this foam unit is cramping my style.

    2. My engine is electric start, it works great. I dont know the brand of engine I have so I cant download a schematic of the circuitry. I`m sure theres a charging circuit for the battery but how do I determine which it is? there is a stub of three wires coming out from the coil area and i`m sure one wire is for the kill switch, one wire must be for the charging circuit and I have no idea what the third wire would be for. What voltage should I be looking for for the charging circuit and does it have a voltage regulator that stops charging the battery once it`s fully charged or do I need to install one?

    3. I want to put an expansion chamber on this engine. I have experience tuning yamaha RD 350`s and 400`s (I`ve owned one of each) and I did the whole expansion chamber, less restrictive air filter and up-jetting so I have a general knowledge of two stroke function and tuning theory but I`m new to the tiny engine hobby. I know the dimensions of the chamber depend on the engines internal dimensions so I must use a pipe for a 50cc engine (I`ve checked and my engine is 50cc) but I will have to learn the length from exhaust port to reflecting cone distance thats right for the power band I`m after (mid range to top end). I know I`ll have to up-jet the carb and I know how to read a spark plug to determine the mixture. Who sells an affordable pipe that might fit my application?

    4. boost bottle. These were a must have on a serious yamaha RD hop-up and I see that there are some available for small engines as well, those of you who have the experience tuning small engines, can you give me advice on the benefits of the boost bottle? I have read here that some folks have not felt a difference and some have.

    Any information you could give me is sincerely appreciated.
    I love this hobby and I havent even put the engine in my bike yet!

    Gratuitous pix of my RD350:

    The day I brought her home, so so sad..............

    up and running but still stock.

    DG expansion chambers, K&N pod filter and y-boot intake, jetted accordingly, hadnt painted the solo seat yet...

    Spark? you want spark? dual accel car coils and iridium plugs, say bye bye to fouled plugs!
    This bike is a screamer, 350cc`s and a serious threat to any period 750 in the 8th mile!

  2. jaguar

    jaguar Well-Known Member

    1. The air filter is just causing the jetting to be richer. Just make it leaner to compensate.

    2. Charging voltage for a 12 volt battery can be 15 to 24 volts as a technicians guesstimate. It may or may not have a regulator to minimize charge when battery is fully charged.

    3. Pipes aren't made for the Grubee engine with a tuned rpm range less than 7000. Click onto my signature link and click onto the 4th link and scroll 60% down to "expansion chambers". The drawing will give you an idea what a pipe should look like for an engine that peaks out around 5000 rpm. Use the free software to figure out the dimensions on a pipe for your engine depending on the rpm's of its intended powerband.

    4. boost bottle. I think the tube leading to them is too small to allow much effect at anything over idle. If it was wider then it would work good.

    Love your RD's man! I had a 350 back in the late 70's and it was a blast!
  3. Dave C

    Dave C Member

    They were such monsters because they derived from the TZ250 by way of the RD250. The TZ is a Gran Prix race motor that's water cooled. The RD250 was the air cooled version. The RD250 I think lasted a year then they brought out the 350. They still make an updated version of the TZ250. It runs very well against the Rotax 250 in roadracing.
  4. motorpsycho

    motorpsycho Active Member

    those little rd 350's were screamers. and you're not kidding about them kicking the pants off the 750's of the same era.