Finally changed my main jets - what to look out for?

J

JimmyR

Street Tracker
Today I finally got around to swapping out my main jets. I have K+N pod filters, Dominator exhaust (similar to Preds), I forget what pilots (!) and just went down to 135 mains from 140. The bike has been running beautifully, but when I stopped the exhaust smelt a little rich. Advice from various people led me to swap to 135 mains and it still runs beautifully, starts perfectly and doesn't smell at all of any unburnt fuel when I stop.

I don't hear any real change in decel popping/burbling whatever. No throttle hang, no backfiring, everything seems good. Are there any other things I should watch out for? It is a dream to ride!
 
B06Tang

B06Tang

Cafe Racer
It sounds like you are pretty dialed in with your settings. I have predators on my bike with pods and setting at 138s/40s and two turn outs. Without an A/F gauge it is hard to say you have it absolutely zeroed in but it sounds like your bike is responding the way it should. I also paid close attention to the gas mileage I was getting after all the changes...sometimes a big increase in your gas mileage is an indicator of running lean.
 
J

JimmyR

Street Tracker
Well strangely enough one of the things which spurred me into action was that recently my milage has gone a bit weird. Normally I get around 200-210km per tank, but the last two times I ran onto reserve at around 180. I guess stop/start traffic may have contributed to that partly, being involved in silly season riding. I also meant to check the fuel tap but forgot.

I do have some 138s but went straight to 135s because the richness thing smelt pretty obvious. The first thing I did after changing jets was fill up, so it will be interesting to see what happens.

Thanks!
 
B06Tang

B06Tang

Cafe Racer
I didn't mean to suggest you needed to go to 138s. I was using that as an example as I am only 33 ft above seal level where I live but 10 minutes down the road and I am 1,000ft above sea level so it's my happy medium. How many turns out do you have right now?
 
J

JimmyR

Street Tracker
Oh no - I didn't think that! I just mentioned it so you know where I'm at. I just went to check the the mix screws but I can't because they are blanked off. Is there an easy way around this? I'm off for a ride shortly so I intend to check the carb balance once I get back with a warm engine.

FWIW I'm pretty close to sea level and will never get to ride much about that! No mountains here.
 
J

JimmyR

Street Tracker
Ok - just got in from a ride to the beach. Beautiful. Set up the carb tune thing and took all of 5 minutes to set. They were close to spot-on anyway. I must have turned the screw all of 1/8th of a turn!
 
V

vecchio lupo

Scooter
Great Report and great feedback. I am also wrestling with a re-jet and your experience is a big help. I purchased an 03 Bonnie with Toga exhaust and AI removed, it ran super but could be better. I put on an airbox kit from TPUSA, and began the process. My setup from PO was 115 mains with 42 pilots and the screws out 3 turns.

First put in 130 mains and 2.5 turns on advice of experienced tuner, seat of pants Dyno felt like top end was starving for fuel and all around could use a little kick.

Traded up t 135 mains and kept the 42 pilots and went 3 turns. Ran better than ever, no drop off at higher RPMs and strong response but a little choppy off of idle.

stepped up to 140 mains and she was drowning in fuel, it felt real wet and soggy in top end, sluggish and unresponsive although mid range felt good. Also lots of gurgling and popping on over run.

Back to 135 mains and backed screws down to 2.5 turns. strong puller all the way to rev limiter, very smooth transition off idle and no popping or gurgle on the over run.

Thanks JimmyR for your info and now all I need is a pair of mercury sticks to dial it in.

again, good job
 
W

whyme

TT Racer
I have to remember what mains I put in...I smell unburnt fuel too. It's been at the dealer since then and I always mention that it smells rich and they suggest nothing. thanks for the info
 
J

JimmyR

Street Tracker
Well I ride at just above sea level (if i can help it!) to not much more than just above sea level. I ride to the beach a lot so I guess I'm often at 3m elevation or so.

I can't remember for certain but I'm pretty sure I have 42 pilots. I definitely have 135 mains and my mix screws are at whatever factory stock is - probably 2.5? This is with the equivalent of predator exhaust and K+N pods.

So far what is remarkable is that now I smell nothing when I get home from a ride. No exhaust smell at all. When I get home I ride straight into a garage as I have a remote control for it, so any exhaust smell is pretty obvious. With 140 mains it rode really well so I rode it like that for a fair while. The only clue it was rich was the smell. I must check the plugs now that I have been riding with the 135s for a week or two.

Recently now that I have the 135s i thought I should check it out at WOT and ended up hitting the rev limiter, which is something I haven't done before. It seems smooth all the way. This bike really is a joy to ride.
 
J

JimmyR

Street Tracker
Ok - just checked the plugs and the tip of the electrode is kinda mid-grey. The ring around the outside is still black, but the tip is not pale grey and not black. It looks kinda right to my untrained eye actually. I doubt I'll get that slightly brown, "biscuity" colour because I don't think modern unleaded fuels work like that anymore, do they? I use premium unleaded.
 
V

vecchio lupo

Scooter
I think you can get the sandy/tan coloring. My Buell X1 was brown plug tips and this Bonnie had tan tips when I pulled initial service.

I seem to remember that a longish steady cruise produced the most accurate data for plug reading. It is a dark art like tea leaves so until one of us gets a dyno session, we just have to tweak.

135 mains, 42 pilots and 2.5 turns seems to be the start point for a 790 motor with all the mods. I too am at sea level, right on the shores of the Potomac River.
 
J

JimmyR

Street Tracker
I wonder if the type of plug makes a difference? I have some new fancy plugs - can't remember the type - which have skinnier tips. Apparently they last longer than regular plugs. I might try some regular plugs if only to see if I can get that brown colour on them! Oh, and mine is an 865CC.
 
N

normandy

Street Tracker
JimmyR said:
I wonder if the type of plug makes a difference? I have some new fancy plugs - can't remember the type - which have skinnier tips. Apparently they last longer than regular plugs. I might try some regular plugs if only to see if I can get that brown colour on them! Oh, and mine is an 865CC.
Click to expand...

The "fancy" plugs are iridium tipped plugs that flash fuller than regular L tipped plugs. I never noticed any difference in performance but have not had a problem with them either.
 
J

JimmyR

Street Tracker
Hey drlapo - here in Australia we have three grades of unleaded which are rated differently from US fuels. We have regular (91), premium (95) and whatever the oil company chooses to call it's fancy fuel (98). So I use the 95, and it's what Triumph here recommend. I am happy to try regular if it might help though.

Hey Normandy - you are correct! Iridium. I couldn't remember the name. Apparently they spark brighter and last longer. They cost more! They seem to work just fine, but I wonder if the whole "brighter spark" thing means they are more difficult to use as a marker of fuel mixture?

Overall I am happy with how the engine is running. It has never been easier to hit redline.
 
J

JimmyR

Street Tracker
Ok found my fancy mix-screw adjuster thing and checked the mix screw settings. They are set at 2 1/2 turns out. I tried adjusting for highest idle but I couldn't hear any difference so I put them both back to 2 1/2 turns. This same thing happened on my last bike. I tried to set the mix screws using the highest idle method but it didn't matter what I did with the screws nothing changed.

Oh well. I'm obviously not destined to be an auto tuner.
 
F

fordtech48

Scooter
I'm going through my carbs soon and have a question.

The Triumph manual says the 790 and 865 Bonnie mills both use 110 main and 40 pilots. Would this be correct? I woulda thunk the bigger engine woulda had bigger jets. Maybe a typo? Any help appreciated.

Also any suggestions would be nice too. I'm running stock airbox with K&N filter and Staintune Mufflers with baffles installed. Thanks.

(didn't mean to hijack the thread)
 
B06Tang

B06Tang

Cafe Racer
With a stock airbox still left in there, then I would say that you most likely will not need to rejet at all. Take the bike out and see what you have but I wouldn't be surprised if you didn't need to do a thing at all to it.
 
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