Ask the Editors Week of May 16 2011
Hello ATV Connection readers, welcome to our latest feature! Due to the rising popularity of the Ask the Editor forum, we have decided to expand the idea and post responses to the homepage.
For those of you who are new to this, basically, if you have an ATV related question, you can ask our editors for help/advice. Create a forum account if you don’t already have one, then create a new thread in our Ask the Editor section. It’s easy and fun!
So, without further ado, here are this week’s questions…
Dear ATVC:
I just picked up a 2003 Yamaha Raptor 660. As far as I know, all it has done to it is a Curtis Sparks exhaust, stage 1 cam, and aluminum airbox (with dual Uni foam filters).
At first I thought the jetting was off because it kept cutting out so took the carb apart and discovered it still had the (stock) 22.5 pilot and the others jets were 144 and 146. We put 25’s in the pilots and left the others alone, now it seems to run better but backfires a lot. Any idea on what to jet it at or why it’s backfiring so much?
Tjb_450
Without elevation specifics, it’s difficult to say for sure what size jets will tune your Raptor into smooth running condition. Typically backfiring on the Raptor is a result of a slightly lean condition- do you find that the backfiring is prevalent when you run the engine with the choke on? Does it backfire more often upon warm up or does it make no difference whether the motor is cold or hot?
It could be an issue as simple old fuel in the tank.
Try running fresh fuel and conducting a little research as to potential causes of your condition. The best place to start is to remember that 140/145 jets are the OEM stock sizes… It sounds to us like 144 & 146 are a bit on the small side for the exhaust system/your riding conditions.
Give Curtis Sparks a holler for the exact jetting specs required for your area (give them your city & state if you don’t have specific elevation numbers). Our estimates lead us to suspect you’ll end up somewhere in the 150/155 range with a stock intake, on up to 160/165 range on account of the aftermarket airbox/ Uni filters.
Curtis Sparks can be reached at: (661) 872-4343
Dear ATVC:
My son and I are restoring a 1985 Suzuki LT230. We rebuilt the entire carburetor (new everything). The timing is set dead nuts after re-boring cylinder and replacing the piston and rings.
Engine is hard starting and when does start engine will only run with choke on idle revs up pops through carb and goes down. When you crack the throttle, the engine backfires through exhaust and carb. Any ideas would be great, thanks.
1985LT230
It sounds to us like one of two issues: Electrical or carburetor jetting. We’ll begin with the more likely of the two, the jetting. It sounds to us that the machine is running lean. Since you said this was an ATV restoration project, have you made certain when rebuilding the carb to jet for your area’s elevation and to accommodate for any modifications you performed in the process? You did note having performed a cylinder bore, which can often demand jetting changes. Other mods that would certainly demand larger jets are the move to an aftermarket exhaust system or freer-flowing air box.
There is a remote chance that your ATV’s electrical system is putting out weak or intermittent spark, which can be determined easily enough: Remove the spark plug but leave it connected to the wire, place the diode near a metal surface and kick the engine over. If you don’t see strong consistent sparking during each kick, the culprit could be the stator, wire, or even the spark plug itself. The absolute worse case scenario could be the CDI box or a short in the machine’s wiring but in the KISS (keep it simple, stupid) tradition of wisdom, we recommend ruling out the more likely culprits first.
That leads us back to the carburetor jetting. We’re quite certain this is where your problem lies.
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