QuestionI just put an Alba Performance Pipe and Jet Kit on my 2001 Warrior. It ran fine before but wanted to get more out of the bike. Anyways, not 2 minutes into the test ride the bike started spitting and sputtering and backfiring. I put a new NGK DR8ea plug but it fouled out almost immediately. I pulled the carb to double check my installed. Here is what I have K&N filter, prefilter,147.5 main jet, 50 pilot and 2 turns on the air/fuel screw 6 inch breathing hole in lid of airbox. Any reply would be greatly appreciated. I am stumped. The plug comes out severely carbon covered.
AnswerHi Jeff,
You'll have to tune the air-fuel mixtures (jetting).
I'll need more information if you want my assistance. Answer the following questions and we'll go from there:
1. What is the average temperature where you ride?
2. What is the altitude/elevation where you ride?
3. Do you have the service manual?
4. What size jets were removed (stock main jet 145, pilot jet 42) and how many turns out were the pilot screws prior to the jet kit?
Include your email addres as requested. I return tech files by email. See sample tech files below.
Respectfully,
Mark Shively
Drop-In Jet Kits
By Mark Shively
With respect to the engineers who designed these products, my experience with jet kits are they usually require additional tuning to get the correct air-fuel mixtures. Jet kits are engineered to make power improvements for the intended model application.
Many of my customers buy these kits, drop them in per instructions, and expect a well running machine. Why doesn't every engine with these kits installed perform as expected or proclaimed? The reasons may be many and include: environmental variables, interpretation of instructions, skill level of installer, available tools, condition of the engine, and more. If it were that easy, you would not likely be reading this.
It should be known that factory motorcycle engineers do an outstanding job designing engines to operate under a variety of elements and variables. Think about it, a stock motorcycle must and does runs very well in a variety of climates and other elemental conditions. If not, their products wouldn't sell well. Dealership service departments would be overwhelmed with unsatisfied new motorcycle owners.
When we make changes to the stock air intake, carburetion, and exhaust, we unknowingly de-tune the engine in most cases. Who cares when the result is that desirable new exhaust sound? Most riders would not notice that their engine was de-tuned unless the problem was an obvious change from what they were used to hearing, feeling, or seeing.
What I'm trying to explain is that making changes to the OEM design may require on-going tuning. For example, at the Daytona International Speedway, I would have to tune the Yamaha TZ250's carbs (Lectron carbs) for the morning practice air temperatures. By noon the temps have changed and the engine requires new air-fuel mixture tuning to produce optimum performance. Tuning changes are required constantly as the environmental elements change and as engine components are changed or modified.
The same can be said for a street motorcycle engine, though not as important to tune as often as a roadrace engine. In any case, the air-fuel mixtures must be very close or performance problems will likely be noticed.
If you're about install a jet kit:
Review the instructions in advance of the installation. When ready, follow installation instructions carefully. Work patiently and be prepared for the task. Expect to perform additional tuning to dial-in the carburetors.
If you've already installed a jet kit and are experiencing problems with performance or installation:
Review the instructions and review your work step-by-step. Verify each step is properly installed. Having a second person verify your work can be helpful. Review the illustration below and learn about tuning each range of carburetion. Make necessary tuning adjustments one at a time to know what effect each change makes. Doing otherwise is fruitless causing you to waste time un-doing and changing things. If all fails, have a local tech perform the work for you.
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Adding Aftermarket Exhaust
By Mark Shively
Changes made to the stock air intake, carburetion, or exhaust require some tuning to correct air-fuel mixtures. If one of the three components is altered or changed, the other components need tuned, altered, or changed, too.
Backfiring indicates the A/F mix is leaning out on deceleration. This is normal with such modifications and is reflected on the appearance of the plugs. The appearance of the plugs may or may not vary much. Learn more about reading plugs at www.ngk.com and click the "Plug 4-1-1" link. Navigate the menus that follow. Tuning should improve the backfiring, though may not eliminate it totally.
Tuning carbs is time consuming and usually requires removal of the carbs numerous times correcting the mixtures. Most shops avoid such work due to the time required to perform such work. Its test and tune work.
You can get the mix close scientifically (math) or by jet-kits, but additional tuning will still be necessary to dial the mix in. Per the Clean Air Act, tuning carbs is illegal other than minute pilot screw adjustments. Some shops will not perform such work.
Engineers designed the stock engine and components to work well under a variety of elements and conditions. They do a wonderful job.
We change the components with aftermarket parts and expect the same reliability and performance engineers have provided us. Often the case, we detune performance in trade of a cool sounding exhaust.
