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Matt, Engineer
Category: Motorcycle
Satisfied Customers: 21614
Experience:  Honors degree in Mechanical Engineering, worked 8 years as a Formula 1 engine engineer.
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Backfires thur throttle bodies and exhaust all new parts

Customer Question

backfires thur throttle bodies and exhaust all new parts all
JA: How many miles are on the car? How has your mileage been lately?
Customer: brand new 06 gzxr 1000 will idle will reav up but backfires
JA: What is the model/year of your motorcycle?
Customer: motor is in mini sprint
JA: What year is your Sprint?
Customer: new wireharness
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: new seneors ecu comp test leak down all is spot on
JA: Anything else you think the mechanic should know?
Customer: did not check cam timming but guy that rebuit it benn doing it for 30 yyears
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the Motorcycle Mechanic about your situation and then connect you two.
Submitted: 1 year ago.
Category: Motorcycle
Expert:  Matt replied 1 year ago.


to get a backfire when running, either the coils are connected on the wrong cylinders ( so wrong firing order) or there's a lack of compression or the engine is running extremely lean

I'd start by double checking your coil wiring and if you're sure this is OK then I'd repeat the compression test with a squirt of oil in all the cylinders to see if the reading flies up - as this will show if the bores are worn

and if thats OK then check for any leaks after the throttles as any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out and can also allow the engine to rev up when not desired causing rough running.

As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running.

Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.

The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane around each joint in turn. If the engine rev's up you've found your leak.

Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.

Work your way through each possible joint one at a time and you should find it. I use a slightly flattenedpiece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.

It’s also worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a poorly pump will all result in insufficient fuel being delivered to the engine

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