Ok, first time fumbling around rejetting a carb, so please excuse what quite possibly in a really stupid question...and yes, I am googling/searching a lot..

TM36-68 with BB 351...bike is running hotter than I'd like (header glows after a few minutes idling), so want to get it a little richer...

My head scratcher is what jet(s) I have to change, or all of them, to achieve a richer condition...

Running this now:

Pilot: 17.5, Main: 130, Needle jet: P4, Jet needle: 9EBY01-50 –3rd from the top, Air Jet 0.9, 2 turns out.


I'm thinking the pilot jet, as this one, as far as I can understand, controls fuel between 0 and 1/4.. And maybe main to 132.5?

But before I go tearing into it again, I want to make sure I'm on the right track.

Pic of plug after about 50 miles attached..

Thanks

 

The pilot jet and pilot screw (idle mixture) control fuel flow at idle. Be more concerned about how the engine starts and runs at small throttle openings.

Ride on
Brewster

 

Full choke normally won't start it. Half choke starts pretty good. Idles well with small fluctuations in rpm (+/-200rpm). Pulls hard thru the gears, maybe slight surges at speed around 4-5k. Backfires on deceleration, sharp cracks but that could be the two bros exhaust making it sound nastier.

As I said, just wondering if making it richer will get rid of the glowing header...also don't really want to be running lean, if I am, for too long...

Thanks!

 

best bet will be to up the needle a notch or two. It'll richen up the mid range and top end. It's also free and easy to do. Just pop the tank off and open the top of the TM, adjust the needle and put it all back - 10 minutes.

Not many people run anything more than a 130 main jet even with a 351 from what I've seen. That being said, untill KLXster did the dyno charts everyone was perfectly fine using 120 and 124 main jets on their bikes at sea level... so.. who really knows without an AFR gauge.

try the needle on the 4'th notch or even 5'th and see what happens. Test it out, get it hot. TM's are temperature finiky. Seriously ride for at least 15 minutes and work it. Then check your header. If it's better and the mid range feels a lot stronger than the top end, you can go with a 132.5 main jet and dial the needle back to where it was.

Also if you don't want to try changing main jets, you can try the P6 Needle jet. I had the AFR gauge on my stock bore when I tuned the carb and the P6, P4 noticeably leaned the bike out in all rpm ranged. I had issues with consistent fueling with the P6 but I think that's due to the lack of a perforated needle jet that 4 strokes generally have. The Solide needle jets are typically used on 2 stroke applications from what I've read.

 

Are you still running the Air Injection System ? Don't go near that carb until the Air Injection System is removed and capped off.. "Cherry Red Header" is caused by this system..

Also, are you forcing your 351 to suck through an airbox lid ? If so, you might want to consider not doing that..

 

Air system removed and blocked off wits bills plate.

But wouldn't removing the lid introduce more air, making it even leaner?

 

Dash, I've been curious about one element in your setup since you initially posted it. That issue of the bike not starting on full choke but starting on half choke is a little unusual from other bikes I've seen or heard of with this carb. Now, there can be quite a bit of difference concerning how long the choke can remain at fully engaged depending on ambient temperature and bike/carb setup. However, IMO the bike should start with full choke under most any circumstances when the engine is cold. Now, many bikes can start up with this carb without the choke sometimes, often, or all the time...once again...depending on outside temps, engine build, and carb setup. Seems like you'd have to have an extremely rich pilot/idle circuit...or some other issue...in your carb to not allow it to at least fire up on full choke. A given carb setup might require the full choke to be immediately disengaged after if fires up, but IMO it should at least start. Your carb jetting/adjustment numbers look about identical to mine, so that surprises even more that your bike won't fire up with a cold engine on full choke.

 

I've been wondering the same thing, and right after I read this, I went out and, too make sure I wasn't crazy, tried it with full choke.

To my surprise she fired right up. So I retract that, she will start with full choke, actually quite easily too. Not sure why I didn't notice that before. But that takes one element out of the equation.

 

Almost all single wall exhausts will glow red even orange if left sitting and idling for several minutes. Exhaust gasses are around 1300-1500 degrees, more than enough to get a good glow going. It only takes about 900° for steel to start to glow red. The cool air when riding will cool it below a glow.

I had a well jetted SR500 single glowing bright red in sub-freezing weather when I let it idle for about 8 minutes or so to warm up. Within less than a quarter block it was no longer glowing.

It isn't unusual and it is not a sign that the bike is running too hot. That is found with spark plug readings in absence of any sort of instrumentation for more accurate readings. Temperatures at the exhaust valve can be between 1200-1800°F. Plenty warm enough to create a glow on a steel pipe without any air circulation around it.

 

Good to know. At least one possible mystery solved...LOL! I was beginning to think some other issue was at play. Glad the choke circuit seems to be working as it should.