Going For The Brown

[scooterspal]

I was always told you adjust your single cylinder bike (scooter or motorcycle) to obtain a nice coffee brown color on the porcelain insulator of the spark plug. That was the ideal. Not too rich and not too lean. Some have said this is not always the case... with trials bikes anyway. That you cannot tell that much about the jetting from the spark plug.

What I can tell you for sure is that when I got my TLR200 last month it seemed to be running way lean and very erratic. Hard to keep running. Sputtering and coughing. I have read where the 200's made for sale in the US were factory set that way to appease the EPA (Environmental Protection Agency).

Pulling the plug told me the story. It looked almost brand new. No carbon on it at all. To me, at least, this meant it was not getting sufficient gas. So began my journey in search of the brown plug.

Here's what I've done so far.

1) Completely disassembled and ultrasonically cleaned the OEM TLR200 carburetor.

2) Removed any and all traces of the California emissions system. That meant removing the combined air and fuel venting system Honda had installed on the carburetor. I now have only a single tube running from the bottom fuel overflow port to under the engine. My plans are to install the new T-Vent system on the two side vent ports of the carb. Basically, the system ensures consistent carburetion by sending the carburetor vent hoses upward to eliminate vapor lock and bogging. It consists of some clear tubing (I plan to use 3/32" vinyl tubing made for window washers) and a couple of T-fittings available at any auto supply store. After leaving each vent port the T-fitting splits the path with one hose going down towards the ground and another going up and into the air box. Should the lower hose become clogged with water or dirt the higher hose will remain clear. There is an existing piece of right angle hose on top of the air box already from the emissions system. Both hoses will feed through there and into the air box.

They also sell complete kits for around $20 that include a small foam filter you fit inside the air box. This one is made by Helix Racing and sells for $18 US.

3) Removed the old Honda OEM paper-style fuel filter and installed this newer type that uses a fine bronze metal mesh cylinder. This one, the one I'm now using, is a K&N #81-0221. $5 to $9 US.

4) Purchased the infamous Carb Improver Kit (Honda #16012-KJ2-305) for around $18 US from Honda. This consisted of a new needle and clip, a new air mixture screw and a new cap. Comparing the old and new needle I found the length to be identical but the new needle has a narrower taper. Therefore, it would be providing more gas (richer mixture) at any given position. BTW: There were no additional height adjustment grooves in the new needle. Just the single one like on the OEM version. It can be shimmed, of course. I left mine alone.

The new air mixture screw was identical to the OEM version. It measured the same. The only thing I could see that might be different was the new screw had a sharper edge where the "space capsule" top met the base. This may have simply been a manufacturing thing. Perhaps the new screw was just in case you damaged the original trying to remove the cap. That would seem to make sense. BTW: The easy way to get that cap off is to heat it with a small butane torch or cigar lighter. It will slip right off with no effort at all.

5) I removed the OEM #92 main jet and installed a #105 main jet (about $6 US). These are the same style main jets used on many Honda dirt bike carbs, like the CRF100F for instance, and are easy to get.

6) The #38 slow jet on the OEM carb is not common. AFAIK no other carb uses that same style and I cannot find it listed on the Keihin web site. Some suggest boring this jet out with a very small drill (something like a No. 78 or No. 77) bit to make it a #40 or higher. For now I have left mine original.

7) With the bike at a smooth idle I then began to turn in the air mixture screw until I could hear the speed stop increasing and begin to drop back off. I then backed off (turned back out) on the screw until the revs came back up. That's where I left it sans the cap for now.

For around $32 and my efforts I found the bike now runs way better than when I got it. Stronger and richer sound when idling and very strong and steady when twisting the throttle. Dumping the throttle from high revving did not cause the bike to sputter at all much less stall, as some owners seem to experience.

Interested in hearing from others on the brown spark plug issue and what they think is correct.

For the record: I wish to thank all those who have been helping me with this bike. I'm able to share back now because of the help I have received.

Edited July 15, 2010 by scooterspal

[stevec]

Check this thread for slow jets:

http://www.trialscentral.com/forums/index....mp;#entry192710

[scooterspal]

Thanks for the links. I also found this on a web site for Harley folks...

Keihin and Mikuni jet sizes are based on a #100 jet being 1.00 mm. So that would make

#35 0.0138"

#38 0.0150"

#40 0.0157"

Numbered drills available near those sizes, along with their inch and jet number equivalent:

No. 78 .0160 #40.6

No. 79 .0145 #36.8

No. 80 .0135 #34.2

According to this poster, the rate of flow is based on the square of the diameter of the jet. This would mean going from the OEM #38 pilot jet (at .0150") to a No. 78 drill size (at .0160") to give you a #40.6 jet size would give you an increase of 14% in the flow of fuel.

The next larger drill size is a No. 77 (at .018"). Using that to enlarge the #38 stock pilot jet would increase the fuel flow by a wopping 44%.

Edited July 14, 2010 by scooterspal

[esteve]

4) Purchased the infamous Carb Improver Kit (Honda #16012-KJ2-305) for around $18 US from Honda. This consisted of a new needle and clip, a new air mixture screw and a new cap. Comparing the old and new needle I found the length to be identical but the new needle has a narrower taper. Therefore, it would be providing more gas (richer mixture) at any given position. BTW: There were no additional height adjustment grooves in the new needle. Just the single one like on the OEM version. It can be shimmed, of course. I left mine alone.

There's a lot of useful information here; thankyou.

On the subject of the new needle, do you know what code is stamped on it, at the top, below the circlip groove and above the working area. I'm trying to make sense out of a variety of needles I have to choose from for my carburetor rebuild here: http://www.trialscentral.com/forums/topic/47707-tlr200-carburettor-rebuild/

[scooterspal]

Hello esteve:

Sorry, but I just saw this posting. I do not know the exact # on that needle as it is sitting inside the carb at the moment. However, I will be opening the carb in a few days and can try and get you that information.

I'm waiting on a #40 pilot jet to arrive and want to give that a try. My main complaint is the 200 is hard to start and that might be due to using too small a pilot jet. I'm currently running with the OEM #38 that came on the bike.

Honda does not have one specifically for the TLR200 carb... at least not sold here in the USA. However, information I have found in another forum seems to suggest the #40 pilot jet for the older Honda CB bikes will fit the TLR200 carb and from the pics it appears to be the same series... but we will see.

Honda #99124-076-0400

For what it's worth, I have always been a great believer in looking at the spark plug for hints on how to do your jetting. It has served me well with all my other street and dirt bikes.

See my notes above in this thread.

George

Edited July 1, 2014 by scooterspal

[axulsuv]

George ;Glance thru my "new bike in the shop thread " I'm pretty sure I listed all the carb mods I did to my son's reflex in there , It fires first or second kick cold and always one when warm . No hesitation , cough or sputter at all now . Get the K&N filter and take the rubber silencer off the top of the airbox too , helps alot with response .

Have fun with the old girl , and make sure your valves are adjusted correctly

Glenn

[scooterspal]

I installed the TRL200 carb kit and I have the #105 main jet, same as you have.

Your pilot jet is not mentioned unless I missed something. Which one are you running with?

Find no specific K&N filter for the TLR200 on the K&N web site.

Why do you feel that is needed? The OEM filter seems to work fine if installed properly.

Edited July 1, 2014 by scooterspal