Bonneville America Forums Forums Technical Forums Performance Mods jets

Alright guys, now that the snow flies it's time to start thinking about winter mods. Among the many is rejetting the carbs. I plan to go to K&N filters with TOR's and have no AI. I've seen in the performance guide that some have had good results with mains ranging from 136 to 160. Any suggestions on how to decide? I'd like to get it right on the first couple of tries.

I'd go for the highest reasonable one. That way it'll either run great or be too rich and you can go down a size or 2 from there depending on how it runs. If it runs pretty good but start cutting out when you really goose it and get the rpm's way up, go down a size and you should be good. if it cuts out a lot even when riding less than WOT then back off a 2 or 3 sizes. thats how i've done my jetting and it's worked well, plus it's best to be on the rich side than lean.

Blackdog,

Here's my guess.

Because you're going with K&N's, AI removed, & the TOR's, - I'd put in something like 145 to 150 mains, 1 shim on each carb needle, and leave the pilot jets stock.

Also, do the 7/64th vacuum-hole enlargement.

-BT

I also have a question. How do you know when the jets are too large. My TA had stock 42 jets and I'm now running either 128/45 or 132/45 as I'm not sure which mains the service dealer put in when my Specialty Spares were put on. I think it was 132 as that is what came with the pipes, but the dealer said 128 and that it was better not to go up on the mains any more than necessary. After riding a bit with VERY loud popping on deceleration, they put in the 45s that came with the pipes which totally eliminated the proplem. I don't notice any cutting out in normal range or at max. rpm. Fuel ecomony is down though (35-39) but the plugs seem ok, just a little black around the base and fairly clean electrodes. I might be a little rich - there's no bluing problem with the headers.

what do the plugs look like? i put home made striat pipes on my speedy .i also drilled out the airbox .snorkle gone ai gone.i went with 42/130 and got nice dark color on the plugs.it's cold here too.45s seem a little rich.with a k&n you should be good with 42s/135 .depending on were you live.no mater what the plugs will tell you all you need to know

The plugs are black aound the threads at the base but the electrodes look pretty clean. If it's too rich what would the plugs look like?

Do not go by the threads or the tip of the electrodes, go by about 1/4 way down the ceramic for a color guide. You want a nice tan color to them. Blacker is richer, whiter is leaner.

If you get a tan color but only on half the ceramic, (around the ceramic, not up and down it) try indexing your plugs. This is seating them, using a small washer sometimes for correction, so that the actual gap is pointed directly at the combustion chambers. Old moto-x trick, gives a more even burn from the plugs.

wow"tan color whould look good on race day!if you racing a two stroke dirt bike.dark brown is were it's at.4 strokes give you good color on plugs and you want to be looking at the ceramic.get a flashlight look at the base all the way inside it should be at least brown.as long as it's not blowing smoke out the pipes and running like crap richer is better for a longer life.

I just rode about a 100 miles today. I'll pull the plugs and look at the ceramic part carefully. I may report back later, based on what they look like.
Thanks,

Ok, pulled and looked at the plugs. They were evenly tan top to bottom looking carefully with a flashlight. They were not "brown" and definietly not "white". They are black sooty only around the threads. So, I guess I'm not running too rich. The bike runs great, no missing or hesitation at any rpm. I was puzzled as to why my gas mileage is so much lower than most everyone on this forum. I filled up today and it came to 36.2 mpg. This was based on the odometer that I re-set at each fill up. I probably run 60% city 40% highway and 50% of the time 2-up (together - 280 lbs.). The worst I've gotten is 32 (all city mostly 2-up) and the best is 41 (all hwy. solo). I've averaged 36.8 over the last 600 miles. The total mileage on the bike is only 1600. I did get about 5 mpg better before changing exhaust, removing AI, and re-jetting cabs (done by service dealer). No doubt, it runs and sounds a lot better now. I appreciate all the help and input.