Isn't a 152 main jet too lean?

[oachs83]

I just got my R up and running after buying it with a hole in the piston. I replaced the CDI as well. Anyways, I went out today to play with jetting. The carb is a Keihin 38mm PWK. When I got it, it had 48 pilot and a 152 main. I noticed most on here run in the 170 range for a main. I thought maybe the 152 is the cause of the burnt hole so I started jetting with a 168 main. It was very flat at WOT and I fouled a plug in about 3 minutes. I stepped down to a 162 and it ran a bit better (still flat) but then fouled another plug about 10 minutes later. The only jet I had leaner was that 152. I put the 152 in and it ran great, lots more snap and the WOT was not flat anymore and sounded crisp. Well about 30 minutes of ride time I checked the plug and it was brownish black. Put it back in and about 5 minutes later plug was fouled. So I looked in the manual and realized I should be running a BR8es not a BR9es. Put the BR8 in and it ran even better the best I have got it to. Pulled harder and in about 20 minutes never fouled. It got dark so my riding was over. I checked the plug and it was a very even chocolate brown maybe a tad lighter. Now IMO I now have the perfect plug color and it runs great but according to most everyone they are running a much richer main then me and I am scared to burn this piston.


Little info on the R:: it has a 2mm overbore, a FMF pipe and silencer, open airbox, new reeds, and the leakdown test @ 10lbs. dropped 1/4 of a pound in 10 minutes and could not find a leak anywhere with soapy water. Thanks for the help.

[1promodfan]

Well the funny thing about jetting is, it has a lot to do with your climate. On this forum we can get you close, but only you can really get it "dialed in". Maybe you should try a few sizes up........does it sound zingy kinda like a 125cc motor??

Let me tell you this, from a 162 to a 152 main is a BIG jump. You need to read this article, maybe it will help you.

http://www.duncanracing.com/TechCenter/Keihincarbjett2004.pdf

[JohnBeton]

I live in Belgium, and I use a 150 main. It scared the hell out of me when I noticed everyone here was running at least 160.
But it was jetted by a honda specialist and runs perfect so nothing to worry about.

[oachs83]

Well I stepped it to a 155 and it seems ok I will try it there for awhile. It did seem to load up real easily after idling. So I stepped down to a 45 pilot and it does not seem to load up as much. Now I did not take it for a ride but in my garage I let it idle as I worked the throttle up and down the rpm for about 3-4 minutes. I checked the plug again and it is a chocolate brown but was shiny. Like there is just a trace of fuel left on the plug. That probably is not a good indicator though? I probably need to drive it. I just don't understand why I seem so much richer than most on here and I know the clutch side seal is not leaking. I am sure I will foul this plug out as well though, that's just my luck.

[Ruf Racing]

Yeah, sitting in the garage won't tell you much. You will need to ride it again. To get a good read on the plug color, you need to run the bike in the RPM range you ride, then kill the engine. Pull the plug, that will be the read for that range. If you go out and ride it hard like you normally would and come back to the garage idling, the plug will look different than it did running hard. Good luck.

[86 Quad R]

yea! later today get out there ad run it thru the motions, get the engine good and warm(with its throat cleared) and afterwards do a WOT plug chop(at least three gears) and see what the plug looks like. also play around with the mid range and then tinker with the pilot jet/screw. afterwards, do another WOT to see where its at then. :cool:

[Aceman]

Jetting will never be right if your float height isn't set correctly. Have you checked it?

[headache]

what clip is the needle on? if thats too rich i will make you think your main is too big when it isn't. Same with the pilot jet

[oachs83]

I have no time to play with it today. The needle clip is 4th down float level is at .61 according to my micrometer.

[mfr422]

oachs,
jetting is an art, not a science. most of the time, jetting is dependant on the machine,not what your buddy runs. it sounds like your'e spot on to me, I run a similar setup and use a 152 and 45 combo with a ddj needle in the third clip (middle). Altitude has more to do with it on R's than anything. none of my friends have as lean jetting as I do and I have four different R's to look at. You really need to listen to what your machine is telling you as jetting recommendations are just educated guesses. Imo there are two good ways to jet 1 is the plug chop (I use this method to check after I'm done for verification). I've found that it takes a little ride time to get a true plug reading.

I use the riding method that you've already used, Jet it WAY fat and back your main down until she runs right, you can even go lean on purpose for a run to double check but don't run her too hard or long! after I have my main set I jet the pilot and or needle, I try to leave the needle alone as it's the easiest to fine tune later. normally most R's i've jetted end up with a 50 or smaller pilot.

The best thing you can do for your piston is RUN A GOOD OIL!!
I always recommend a synthetic premix mixed 40-50:1
I have run redline at 50:1 for the 15 years I've had my R and have never had a failure. synthetic oils are far superior to anything else and can be mixed at higher ratios than petroleums with greater protection, but that's a whole other subject!!

remember, R's are generally very forgiving on thier pistons If you pay attention to what your motor is telling you. I wouldn't let the previous owners mistakes affect you, your plug is a chocolate brown/black and that's what you want to see!! Roost On!!

[oachs83]

mfr422, thanks for the info. I know my plug color is where it is at I just was nervous to see the burned up piston and the engine leak test only dropped a 1/4 lb. Although I did need to change CDI so that to could have burned the piston. I have a full bottle of 100:1 Saber Amsoil that is mixed 40:1. I was thinking after this tank is gone I will mix it 50:1 and see if the plug fouling comes to a stop.