indifferent
Member
My bike is backfiring through exhaust and carb...there is a slight smell of petrol....took air filter off...one carb...front LHS is louder....seems like its drawing more air in than the other three...?
backfiring
- Thread starter indifferent
- Start date
Help Support VMAX Forum:
Missing spark or plugged carb on #2?
You can make a diagnostic plan. For example, perhaps remove the spark from #2 and lay it against the engine. Turn the engine and check for spark. If spark is OK, drain the fuel bowls and look for crud......etc
You can make a diagnostic plan. For example, perhaps remove the spark from #2 and lay it against the engine. Turn the engine and check for spark. If spark is OK, drain the fuel bowls and look for crud......etc
Remember the stock bike needs the resistance of an air filter & box to run properly.
One of the things I found out of place was the #34 Main Nozzle, on a new to me used bike. The screw (#28) holding it in place was loose and was lying in the float bowl.
Another time it was a #42 pilot jet not torqued down, it was loose in the #32 Jet Block behind the #43 rubber cork.
As Radioguylogs said, try the things to check before you remove the carbs and start to disassemble them for cleaning. If that's something you haven't done before, either have one of the guys on here who does it do them for you, or read up on the forum threads and see if it's something you would want to tackle yourself.
One of the things I found out of place was the #34 Main Nozzle, on a new to me used bike. The screw (#28) holding it in place was loose and was lying in the float bowl.
Another time it was a #42 pilot jet not torqued down, it was loose in the #32 Jet Block behind the #43 rubber cork.
As Radioguylogs said, try the things to check before you remove the carbs and start to disassemble them for cleaning. If that's something you haven't done before, either have one of the guys on here who does it do them for you, or read up on the forum threads and see if it's something you would want to tackle yourself.
F 18 Driver
Active Member
Hi, indifferent,
You are describing the classic symptoms of improper synchronization of the carburetors.
Thus, they are pulling in air and fuel at different levels between the 4 carburetors at 1000 RPMs at idle… And up to 3500 RPMs under throttle…
Most of the inexpensive Chinese dial synchronization tools are very inaccurate. My recommendation is to use carburetor synchronization tool such as the manometer offered by motion Pro ( I use the CARBTUNE PRO)… Which is hydraulic in nature and thus the most accurate … Even more accurate than the digital sinking tools which have a 3% to 5% error rate, built-in
Further, when doing your synchronization. Make sure that you have a old-school Tach and dwell to have an accurate reading of the RPMs… Prior to performing synchronization
Make sure the machine is hot and be advised not to push too hard on the adjustment screws whether turning clockwise or counterclockwise because the pressure you place on the adjusting screws will affect proper synchronization
… As a side note, if the machines been sitting for any length of time, check your slow jets.
F-18 driver
You are describing the classic symptoms of improper synchronization of the carburetors.
Thus, they are pulling in air and fuel at different levels between the 4 carburetors at 1000 RPMs at idle… And up to 3500 RPMs under throttle…
Most of the inexpensive Chinese dial synchronization tools are very inaccurate. My recommendation is to use carburetor synchronization tool such as the manometer offered by motion Pro ( I use the CARBTUNE PRO)… Which is hydraulic in nature and thus the most accurate … Even more accurate than the digital sinking tools which have a 3% to 5% error rate, built-in
Further, when doing your synchronization. Make sure that you have a old-school Tach and dwell to have an accurate reading of the RPMs… Prior to performing synchronization
Make sure the machine is hot and be advised not to push too hard on the adjustment screws whether turning clockwise or counterclockwise because the pressure you place on the adjusting screws will affect proper synchronization
… As a side note, if the machines been sitting for any length of time, check your slow jets.
F-18 driver
Last edited:
Vincent Tarling
New Member
- Joined
- Jul 5, 2023
- Messages
- 1
- Reaction score
- 0
Hi, I had the same problem, I found out it was the diaphragms in the carbs. stripped down and replaced them sorted the problem
