Backfire through carbs.

[396375]

Well I got my 2004 Vmax a few days ago.I haven't riden in 25 years and was surprized on how nervous I was.I've only been around the block a couple of times.Last time out I heard a noice that seemed to coming from the front end.For lack of a better word it sounds like a chirp.I checked out the front end while it was on the stand and everything seems ok.This bike has less then 5000 original miles and it looks to me that it was well taken care of.I'm a part time mechanic and I have done a lot of work on old Muscle cars but not much work on bikes.

I heard a fairly loud back fire the other day when trying to start the bike.This morning I decided to check the air filter and while the air filter was off I thought I would start it up.It started back fireing through the carbs.Not real bad like a big bang.When it backfires a smal cloud of spray comes out the carb.It is worse with the choke on but still noticable with the choke off.I don't remember how a Vmax should idle but it sure seems choppy to me.Almost like a mis or a radical cam.There also seems to be a bog around 3000-4000 RPM just reving in neutral.

I've seached back fires and just wanted to get opinions before I start pulling the carbs apart.

Thanks.

PS.Just incase does anyone know a good Vmax mechanic in the Toronto area?

 

[Jan Bee]

Try this before removing them---
http://vmax.lvlhead.com/tips/shotgun.htm

 

[396375]

I almost forgot.I did wash the bike yesterday with a hose.The back fire was there before I washed it but maybe worse after.Not sure on that one.

 

[Fire-medic]

Likely plugged carb passages, due to the low miles and sitting for a long time. A teardown and thorough cleaning will probably eliminate your issues and restore an even idle. The 'on the bike' method may help, but I suspect removal, disassembly and cleaning will be required.

 

[396375]

I changed the plugs & fuel.No difference.I blew out the jets and added half a can of Sea Foam.No difference.I backed out the idle screws and squirted Sea Foam through the jets with a syringe and poked a thin welding rod through the jets and that helped a lot with the back fires,but it still does it.The motor revs a lot better too.The bog is still a problem when driving.

How do you drain the tank completely?

Thanks to all who posted and PMd me.

 

[adambweird]

I use a kerosene hand pump and empty as much as possible then add a small amount of fresh and cycle the ignition with the fuel supply line to the carbs off and draining into a container. Ill do that a few times then pump out the tank again and repeat the sequence 2 or 3 more times. Does a decent enough job.

 

[dannymax]

I changed the plugs & fuel.No difference.I blew out the jets and added half a can of Sea Foam.No difference.I backed out the idle screws and squirted Sea Foam through the jets with a syringe and poked a thin welding rod through the jets and that helped a lot with the back fires,but it still does it.The motor revs a lot better too.The bog is still a problem when driving.

How do you drain the tank completely?

Thanks to all who posted and PMd me.

There's a drain bolt on the bottom of the tank.

 

[Eugene Brad]

Just a thought and a guess but check the tank vent line. Make sure that isn't clogged and causing a vacuum in your tank. That could maybe cause some intermittent backfire?

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[one2dmax]

When riding are you putting the bike back together? The faux tank cover must be installed as well.

396/375 (L78 Camaro, Corvette, Chevelle, Nova, Impala or?)

 

[396375]

When riding are you putting the bike back together? The faux tank cover must be installed as well.

396/375 (L78 Camaro, Corvette, Chevelle, Nova, Impala or?)

I don't know how to multi quote so thanks to every one.

:doh::redface: Oh ya.I knew that

3 L78 Novas and 1 L78 SS Post 4 speed.Thanks Sean.

Curious.How do you get the air box base off?

 

[Eugene Brad]

I don't know how to multi quote so thanks to every one.

:doh::redface: Oh ya.I knew that

3 L78 Novas and 1 L78 SS Post 4 speed.Thanks Sean.

Curious.How do you get the air box base off?

Mine pulled rite off with a little wiggle. If that don't work there are clamps at the top of each carb, long Phillips ought to do it

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[396375]

I put everything back together and the bike seems to be running fine.I don't know if anyone else has noticed,holy sh*t these bikes are fast
I still hear the odd backfire under the cover so I'm still searching but the bike is now fun to ride again.
Thanks to all.

 

[one2dmax]

They do tend to have a cold sneeze when set right. Should go away when warm. You can also try to add some choke (which add's fuel and not restrict air like the name might imply). If that helps it then you may need to do some minor tuning or find the air leak causing it to go lean.

Nice Nova collection! All 375hp cars is a collection for sure. I've got a wider variety of numbers that some are easy to figure out and some not so much. A partial list of some of the older stuff:

454450
440390
428360
427390
427385
400366
396325
330310

 

[396375]

They do tend to have a cold sneeze when set right. Should go away when warm. You can also try to add some choke (which add's fuel and not restrict air like the name might imply). If that helps it then you may need to do some minor tuning or find the air leak causing it to go lean.

Nice Nova collection! All 375hp cars is a collection for sure. I've got a wider variety of numbers that some are easy to figure out and some not so much. A partial list of some of the older stuff:

454450
440390
428360
427390
427385
400366
396325
330310

Ya.I figured it's a tuning deal.I'd be on it right now if it was an 850 Holley.
I don't think anyone has done any work on this bike considering the low mileage and all stock parts.I did notice that the small brass plugs on the carb were gone if they did come stock on all these bikes.I got a couple of leads on local bike mechanics that know their stuff.All my buddies are lunatic car drag racers,me included.

OK.I'll take a shot at your list and I won't Google them.
LS6 Chevelle
440 Mopar Six Pack
Cobra Jet
BBC Oval Port
427 Impala
Ummmm Pontiac Ram Air III ?
BBC Oval Port Chevelle
This is an old one.64-67 Cutlass.Maybe multiple carbs?

The cars I listed were all from my past.The L78 was my favorite motor.Headers,slicks and a big gear made these cars Street Rulers.Hemis,Six Packs and Cobras were NP.I'm 67 now and started my list 50 years ago.Right now I have a 72 442 parked beside the Vmax.I pulled the numbers matching drivetrain and dropped in a 502 crate motor with a 200 shot of NOS.Yes.It's a handfull on the street even with DRs.:biglaugh:It really flips put some people when a 67 year old fart pulls up beside them at a light.

Thanks

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[one2dmax]

OK.I'll take a shot at your list and I won't Google them.
LS6 Chevelle
440 Mopar Six Pack
Cobra Jet
BBC Oval Port
427 Impala
Ummmm Pontiac Ram Air III ?
BBC Oval Port Chevelle
This is an old one.64-67 Cutlass.Maybe multiple carbs?

Very nice!
Very good on your guesses! Got most of em right! There are a few muscle car guys on here but not that many (and fewer who I think could have got as many correct).

70 LS6 Chevelle
69 Road Runner 440 6 Pack
69 Bonneville Convertible 428
66 Corvette Convertible 427
67 Impala SS 427
69 RAIII GTO
68 RS/SS 396 Camaro
67 Cutlass (x2) 330