Carb issues

B

bobl

Well-known member
An easy way to check to see if it's a fuel pump or delivery problem is to rig a gravity feed auxiliary fuel tank to your handle bars and go for a ride. If it runs good that way, blocked fuel petcock, lines, or bad pump.

edit: I talking about going around the pump etc. and gravity feed directly to the carb.
 
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ratpick

ratpick

Well-known member
Is the air box modded?
My drz 400 with modded air box will sometimes do that is strong side winds.
 
ST Guy

ST Guy

Well-known member
ratpick said:
Is the air box modded?
My drz 400 with modded air box will sometimes do that is strong side winds.
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This! I had a Suzuki 650g once that inrejetted and had K&N pods on it. I found that at steady state cruising on the freeway, I could induce a stumble at steady throttle by simply changing the location of my legs to the bike. And I tuned the carbs on CC's dyno and had them perfect.
 
haybaler

haybaler

Mechanical
carb fixing

A few ideas:

1. Send carb to customcarbservices.com
Guaranteed!

2. You make it sound like you're running out of gas, is that correct? Can you run a test sitting still, hold throttle at 3500-4000 rpm [keep a fan on motor during test]

If confirmed running out of gas, usually only two places where gas gets stopped, petcock and float needle. Check out the petcock, and suspect the new float needle because some aftermarket kits include junk needles, maybe wrong size or sticks.
 
M

motomania2007

TC/MSF/CMSP/ Instructor
Sounds like to me your carb is not adjusted properly. My suggestion is a little bit more troubleshooting:
While riding along at steady state when you say you get the issue that arises, very slightly roll off the throttle just slightly and then report back what it does.
Also repeat the test and when the bike stumbles very slightly roll on the throttle. And see what it does.
I also suggest test riding without the air filter installed. And repeat the above two tests.
All of this assumes that the following are correct first:
Valve clearances are correct.
Spark plug gap is clean and correct.
There is no air leak around the carburetor. You can check that by with the bike warmed up and idling use carb cleaner with the straw installed and squirt around all the joints of the carburetor and every vacuum line connected to the carburetor.
 
DannoXYZ

DannoXYZ

Well-known member
R3DS!X said:
yup. sprayed carb cleaner and compressed air through all kinds of passages.
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auntiebling said:
that isn't necessarily enough.

find little wires to stick through everything you can
...
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Yeah, spray carb cleaner no longer works with removal of chlorinated compounds (trichloroethylene, carbon-tetrachloride, or chlorobenzene). I used to use carb-cleaner to clean inside of sprocket-covers and sludge drips off like black-tar. Nowadays, carb-cleaner just runs off slightly grey having dissolved nothing. Good luck dissolving dried petrol plastic stuck deep inside carb-circuits with it.

To truly clean all fuel passages, you need to use lots scrub brushes of different sizes, ultrasonic soaking and micro soda-blasting. There's tonnes of areas that hasn't been thoroughly cleaned and restored to factory-fresh clean. Such as poking out all lateral bleed-holes on emulsion-tube of needle-jet holder with appropriately-sized guitar wire (different bike shown below, but similar on yours). You'll find it'll shove out little plastic plugs like little grains of sand:

uc


Rob said:
Guitar strings... get to work.

Chemicals and air won't knock off the glazed old gas that's coating your passages.... I thought what you thought and did what you did... then did what we're telling you and it ran just fine.

Edit: I think what we thought is good for maintenance... but not for raising the dead.
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edzx6 said:
Out of the 14 bikes SVJ and I are working on at any given time only 2 have fuel injection.

I can tell you right now that either one of the small ports in the carb is clogged still or something very tiny got loose after your rebuild and lodged itself somewhere new. The only thing to do is take them off again and clean again. You may do this 2 or 3 more times.
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Yup, even best mechanics have had to remove and disassemble carbs for ever deeper cleaning. I recommend you do full refurb 1st time around. Well 2nd time around now.

uc

uc


I've used Gordon @ customcarbservices.com many times and carbs always comes back factory-fresh clean and bike runs like it just came off showroom-floor. Unless you plan on cleaning carbs for living, costs of ultrasonic cleaners and micro soda-blaster simply doesn't make sense for home DIY.

He also takes care of little things that'll trip you up. Such as splitting carbs and replacing O-rings on fuel-rail. All float-bowl seals and sets float-level height to spec. Bench-sync as well. There's also an o-ring on plunger assembly and pilot-screw, did you replace them? Old non-sealing O-rings will cause intermittent vacuum-leaks and random drop-outs.
 
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B

bobl

Well-known member
Another thought. Try opening the choke when the bike misfires. Also, I had a similar problem that turned out to be a bad connection on one of the coils (it had two). The lead to that coil was green with corrosion. I would wind up to redline, pull with good power, but steady state running would miss. Worth a look.
 
R3DS!X

R3DS!X

Whatever that means
haybaler said:
A few ideas:

1. Send carb to customcarbservices.com
Guaranteed!

2. You make it sound like you're running out of gas, is that correct? Can you run a test sitting still, hold throttle at 3500-4000 rpm [keep a fan on motor during test]

If confirmed running out of gas, usually only two places where gas gets stopped, petcock and float needle. Check out the petcock, and suspect the new float needle because some aftermarket kits include junk needles, maybe wrong size or sticks.
Click to expand...

Custom carb service sounds appealing but I want to sink less money into this bike. I was hoping to sell it for a profit.

I tried running the petcock in reserve and IIRC that will bypass the need for vacuum.
Still wasn't running right. I guess when i take it apart again i can replace the new needle with the old and see if that helps.

So I was running it around town some more and it's not JUST when holding throttle it seems to be intermittent in general but never at idle, never when giving it beans. just sometimes somewhere in-between.
 
CDONA

CDONA

Home of Vortex tuning
Pilot jet, different needle taper, slide cutaway, idle/air screw, affect midrange.
 
haybaler

haybaler

Mechanical
Intermittent problems are the worst!

Is it the petcock?

"Vacuum petcocks contain a thin diaphragm that allows fuel to flow in the ON position when the engine is running. After several years, the diaphragm degrades allowing gas to leak past the diaphragm, flow down the vacuum line, and enter the carburetor. The excess fuel causes an abnormally rich air fuel mixture. An excessively rich mixture will result in poor fuel economy, poor idle, weak performance, bogging, or the engine may not run at all." From: https://dr350.fandom.com/wiki/Vacuum_petcock

Someone suggested running with auxiliary gas tank; that would rule out petcock and vapor lock theories.

Several people suggested overhaul by carb services; that might rule out carb problems theory.

Now, we can just keep guessing: spring weakness at top of diaphragm allowing slide to flutter?

Sending sympathetic vibes...:(:(
 
bcj

bcj

Spagthorpe RA
A friend had a mid 90s DucMonster with the same sort of problem.

After a ton of faffing around, it turned out that the main needle jet hole had become ovalized from vibrations and weren't nice and round anymore.

Nothing for it but new carbs. He sold the Monster.
 
Lucytriple

Lucytriple

Wrrrench
bcj said:
A friend had a mid 90s DucMonster with the same sort of problem.

After a ton of faffing around, it turned out that the main needle jet hole had become ovalized from vibrations and weren't nice and round anymore.

Nothing for it but new carbs. He sold the Monster.
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Yeah, that totally happens! The good news is you can order new emulsion tubes from good ol, local, Factory Pro.

http://www.factorypro.com/jets,needles,emulsion_tubes,pilot_jets.htm

While we're on the subject of Factory Pro, here is a link to Marc's guide that I've studied my entire career.

http://www.factorypro.com/tech_tuning_procedures/tuning_carbtune,CV,high_rpm_engines.html
 
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M

mark665

Member
Stock settings on a stock bike should work great. Make sure things like springs, jets, needle settings, etc. match what's in the manual. Frequently people faced with a non-running carb will fiddle with it vs. cleaning it properly in an attempt to get it to run.

Carb cleaner + compressed air doesn't make a carb rebuild. The carb should be disassembled, sonic cleaned/dipped in solvent, then rinsed, dried, etc. I always replace the jets with new, particularly the pilot, as it's usually cost-effective (under $5 for a single) vs cleaning.
 
J

JimE

Rider
DR350, eh? Carb problems, huh? Yeah been there done that. Had a pile of them.

Best advice? Get a TM33 pumper carb and throw the stock one in the bin. Same with the stock petcock. Yamaha Raptor petcock fits and is pretty cheap.

Not in the budget? Is what it is. Only personal experience advice I can offer on the stock CV carbs is to really take a good look at the CV diaphragm and mechanism. I've caught tiny tears in the boots, had to polish the varnish off real old passages, leaky floats, etc... Keep it simple. It probably is. Carbs are actually pretty simple devices. Patience is hard.

Still stuck? Call Jesse Kientech up in Grants Pass. He's mostly retired now but still does some stuff. That guy has probably forgotten more about the DR series of bikes than the collective BARF will ever know. Not kidding. Super sharp. Really nice guy. Be nice and buy something from him if he has it (he has wound it down may not have 350 stuff anymore).

Could be worse. I'm currently trying to get a laptop to talk, via an OBDII seril mated to a Fiat 3-pin cable, to a salvage '17 Hyper. Driver for the OBD serial is in Chinese, native for the software is French, bike is Italian. I'd rather have a carburetor to fix....
 
M

Motorcycletutor

Member
Carb gaskets?

Done a few carbs. Plus one on valve adjusy. Also Is there a gasket between manifold and cylinder head? Cracks there can muck up mixture. Also what is condition of ignition system? Old wires old coils old plugs loose dirty corroded etc ?

Ken in oakland
 
Lucytriple

Lucytriple

Wrrrench
R3DS!X said:
So I was running it around town some more and it's not JUST when holding throttle it seems to be intermittent in general but never at idle, never when giving it beans. just sometimes somewhere in-between.
Click to expand...

When it gets hot only? Electrical problems sometimes wait to show up until components get hot. A pick-up going bad, for instance, will feel like you're running out of gas and then get better for a bit until one day it just quits.
 
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