DR350 with carb issue


I got a '91 DR-350S which has spark and can idle at 2k when the choke is out. As soon as choke goes back in, or throttle is opened even the slightest, the engine cuts out. It has a Mikuni carb.

A history on the bike, it sat around for a year or two and collected the yellow varnish on the carburettor parts. Cleaning of the carb was then done. The pilot and main jets have been removed cleaned and reseated, the air mixture screw removed and cleaned and the float valve cleaned till spotless. The float valve is a llittle bit worn. Initially the bike would not even idle or make one stroke before the carb was cleaned. Now the carb is cleaned to the best of my experience and it idles at 2k.

Current settings in the carb, The air mixture screw is in about 9 turns in. It has about 1 1/2 - 2 turns till it goes fully in. The needle jet is set to the middle (3) of the 5 settings.

Some experiments.

- Covering the air intake jet holes on the air intake causes side causes the engine to rev up to 4k.

- The slide moves ok when subjected to a vacuum cleaner on the engine side.

- Idling works when the choke is out and sits about 2k.

- Can run the engine on motor start spray and the revs get right up.

Thanks in advance,


I think that you should remove the carb and on the under side of the front of the carb there should be a brass plug (possibly removed) under this plug is a screw head. with the bike running turn this screw until the bike reaches max revs. if you go too far it will cut out. then adjust the idle with the "indexing screw?" on the side of the carb turn it back down to manufacters specs go for a test ride. ? hope this may help?

should mention the name of the small screw under the plug is the idle air control and I think you should start their. sounds like it might be a lean condition. (only enough gas to run while choked) I could be totally mistaken however.

Did you shoot carb cleaner through all the little passages in the body? There's a lot of them and they all need to be clear.

If you did then sorry. Not a lot of folks really know how to clean carbs properly.

Sounds like you have a vacuum carb with an aftermarket adjustable needle.

As others said, re check pilot jet and passages. Make sure you have the correct jets installed, pilot should be a 37.5, main jet can be anywhere from 127.5 (stock) to a 140 (with other mods done). Idle mix screw should be between 1.5 to 2.5 turns out. Also make sure you have all the correct spacers and washers above and below the needle, check the online parts fiche at Ron Ayers to see the exploded diagram. Vacuum carb has a vacuum line that connects the right side of the carb to the back of the fuel tank petcock. Check the line and intake boots for vacuum leaks.

Petcock is another problem area. They can stop flowing fuel, never shut "off", or leak raw fuel down the vacuum line and flood the carb. The petcock has a rubber diaphragm that hardens and causes these problems. Make sure you have good fuel flow to the carb with the petcock in the "prime" position, if so try running the engine that way, it may be starving for fuel.

Another online source for service manual: http://www.suzukidr350.com/suzukidr350/majorrepairs/majorrepairs.htm

Go buy a can of starting fluid and spray it around the carb at idle. If the engine revs, you have a vacuum leak. I JUST had the exact same problem and diagnosed it this way to find the torn intake boot between the carb and the engine.

Good luck, sound like it could be an easy fix for you.

Go buy a can of starting fluid and spray it around the carb at idle. If the engine revs, you have a vacuum leak. I JUST had the exact same problem and diagnosed it this way to find the torn intake boot between the carb and the engine.

Good luck, sound like it could be an easy fix for you.

Thanks for your replies. Im surprised how fast!

The type of carb used on my bike is this one.


Kami i adjusted the air mixture screw to be 1 1/2 turns. BC yes the spring, metal washer and rubber washer are behind the air screw. Jcalis, this carb is just a gravity fed one without the vacuum. I checked behind the fuel cutoff knob its just one output.

Neepuk, yes the engine revs up marvelously with engine starter. I was considering strapping a few cans to my frame and using it like NOS :thumbsup: Here in australia, its sold in cans and is called "Start you bastard". Great stuff!

Your idea has prompted me to take off the manifold boot. The seal doesn't look too good on it! When the bike was idle and then about to take it up in throttle a distinct hissing sound can be heared from the intake manifold. I guess this is the vacuum leak! I will visit my suzuki dealer and look for a replacement seal.

Will let you know how it goes.


You have the BST33 vacuum carb. It has a nipple on the right side that is a vacuum source. This needs to be capped off if you are not using it to operate the stock petcock. The engine will suck in a lot of air through this port and cause the exact symptoms you describe.

See the black rubber cap just to the right of the external brass tube? That is the vacuum port that needs to be capped off.


Post a picture of that starting fluid can. That is a great name for the product, but would never make it here in the states, too non-P.C.

Thanks Jcalis, you identified BST33 is my carb. I had a look at that vacuum port, it appears to have some sort of filler glue in there. I guess the previous owner put it in. I pulled off that manifold rubber and inspected it. The o-ring and the engine hole has some black gunk hardened onto the surface so I cleaned it off with a toothbrush. The o-ring looked a bit cooked, so i pulled it out and put it on the other side which looks a bit fresher. Should i get a new one? When put back together, the engine is still doing the same thing, revving at 2k and cutting out after. Any other ideas.

Btw jaclis, what is the other port on the side of the carb with the black t junction? Does it need to be clogged too?

Here is a picture of "Start ya bastard", a can of engine start spray marketed in Australia.


Yes, the name's not really PC. You know we also have Dickhead matches here...a local company called "Dick Smith" made a competing product for "Redhead" matches and called them "Dickhead" matches. Cool huh :thumbsup:

That pic is great! Too bad we can't have quality products like that here. We get multiple languages and a dozen warnings (do not eat or breathe, you will die, etc.) instead. Lawyers rule!!

The carb pic with the "Tee" is showing the modification for the carb vent line. You put a "Tee" on it, run the orig. hose up into the frame, add a lower hose and route it down and back so excess fuel can drain out to the ground. It helps stop these carbs from loading up with fuel in a tip over.

See: http://www.maximum-suzuki.com/forums/index.php/topic,21395.25.html

You will have to join up at Maximum Suzuki to view the topics. Good place for info on the DR350's.

Can you get the bike to idle correctly with the choke "off"? Is your idle mix screw set for 1.5 to 2.5 turns out? Do you only have trouble when you open the throttle?

Hi Jcalis,

Hopefully the following statements will convey the bike condition:

- The bike will start first time when choke is out, and throttle is off.

- The bike will idle at 2k when choke is out, and throttle off.

- The bike will shutoff when choke is put back in.

- The bike will shutoff when throttle is applied whilst the choke is out.

- The choke must be out for it to turn over in any way.

The air mixture screw is set at 2 turns out. The slide needle is set to no.5 maximum (rich).

The carb has been completely cleaned out, including the pilot and main jets, the air mixture screw, the small holes, the air intake brass jets the float valve, the slider needle and all the little ducts and tunnels inside. The manifold gasket has been turned around to the fresh side.

I have just noticed that all the gaskets in the engine build are silicon glue gaskets. (They type where you can see the blobs of excess silicon on the outer of the case). According to a guy at my work this might be a potential for a vacuum leak or even worse a piston-valve collision. Apparently WD40 will seal and leaks for a split second to see if the engine changes revs. Anyone think this will work?

In summary, the bike has trouble when the throttle is opened and when the choke is let back in.

Hope this helps.


It's been a while since I had the vacuum carb but I believe there is a small (pinhole) passage just inside the carb throat on the engine side. It is just in front of the throttle plate at the bottom. Remove the idle mix screw and spray carb cleaner into it. You should see a spray of liquid coming out that small hole. This is the outlet of the pilot jet circuit and is very easy to clog being so small.

You removed and cleaned all the parts inside, is it possible you have the float assy mis-adjusted? I believe the float setting was 14mm (take bowl off, flip carb upside down and measure the height of the top of the float to the base of the carb). The only other thing could be vacuum leaks. We used to use WD40 to test but they do not have flamable propellant anymore. Carb cleaner would probably work instead. Spray around the intake boots, carb, etc. watching for a change in RPM's. Be careful doing this (fire hazard) and have an extinguisher ready.

EDIT float height adjust pic:


Hi Jcalis,

Thanks for providing those diagrams. By the looks of things perhaps the float level is out. I have a question - is the measurement taken from the base of the float or the rib about half way up. Which end of the float is the measurement taken at? It seems like the float level is too high by the way the valve closes - would this cause the issue?


You measure the highest part of the plastic float assy to the gasket surface on the carb (where the lower bowl and carb body meet). Lift the float and slowly lower it.Watch the metal tab just as it touches the top of the needle valve. That is when you take the measurement.

If the adjustment is off, the fuel level in the bowl will be too high or too low. If too low, the jets will not pickup enough fuel to run correctly. This may be what is happening to your bike.

Hello guys,

Thanks greatly for your input. jcalis, i adjusted the float level on the fuel bowl to 14.6 mm +/- 1.0 mm by bending the tab. Put it back together and retried the bike. Unfortunately no improvement, but I have something to show you. Linked here is a movie taken of the bike while it's idling and shows what happens when the throttle is opened.


I hope this helps...



The carb still seems lean on both idle circuit and main.

Just a guess but does the vacuum operated slide return (by spring) completely down to the bottom of its channel? It will not close off the carb bore completely, there will still be a small opening at the bottom when in the full "down" position. Make sure the rubber diaphragm at the top of the vacuum slide is seated correctly and has no holes or tears in it.

You may want to verify the fuel level in the carb bowl by using a clear piece of tubing attatched to the bowl drain. You will need to shut the fuel off, drain the carb bowl, and attatch the clear line. Hold the tubing "up" and against the side of the carb. (tubing must be long enough to extend higher than the carb / carb bowl mating surface). Hold the bike level and turn on the fuel. Open the carb bowl drain. The bowl and tube should fill up (nearly) to the bottom of the carb / carb bowl mating surface. Be careful, fuel may leak out. Picture will give you an idea of what to look for:


As I can't add to the answer, I can add to the problem. I have the EXACT same prob.

'91 dr350s. Will start almost first kick. But I have to stay off the throttle and full choke the thing. As soon as I push in the choke it will die. As soon as I give a little throttle, it will cut out, then die. The bike ran great last season. But when I got it out this season, I've had this persistant issue. I've cleaned the carb thoroughly. There are some things in this post that'll I'll try as far as checking for air leaks. Mohhingman, I feel your pain. Let me know what you come up with if you get your bike corrected, and I'll do the same.

cswetnam, make sure all passages are clean, remove the pilot jet, main jet, and idle mixture screw and spray w/ carb cleaner. You probably still have some junk in there. Idle circuit passages are tiny and clog with old fuel and varnish easily.

People claim this stuff works well: http://www.seafoamsales.com/motorTuneUpTechGas.htm

Designed to clean 4 stroke gasoline marine engines.

Hello cswetnam,

Sorry to hear you got the same problem. It would seem the issue with the carb is caused by leaving the bike with fuel in the carburettor for a length of time. I know when i opened up my carb it had that "stale fuel" smell, and the parts had been varnished yellow for me. Despite the thorough cleaning the problem still persisted. I think there has to be something deep inside which is blocked, one of the air or fuel passages. It's not the jets, needle, valve or anything like that. I still haven't fixed my BST33 with that problem despite hours of cleaning.

Call me soft, but i went and bought a brand new TM33 Flatside 33mm carby jetted to DR350...put it on and it went first time. The bike's running great now. Apparently the BST33 carbs were put on the Suzukis to pass emission laws. The TM33's are a simpler design and claim better performance. I have no reference though...I just put a TM33 on and BANG off it went. ren ren ren!

But jcalis is right though, it is something inside the carb which is blocked. A carb working last year won't suddendly become incapacitated to work AT ALL just by having stale fuel in it. There must be something blocked. My BST33 carb also has a worn slide with deep grooves cut into it so it was time to get a new one. I phoned the wreckers around my area, their response "Good luck finding that carb". So only option left to get a new performance TM33 pump carby.

For those in Australia with the same problem, try out these guys, they sold me one on Friday over the phone, got it Monday morning. $440


Hope you can find the blockage cswetnam. If you do please share it :confused:

TM33SS is the "dirt" model carb here in the US. You can still buy them new and install on the DR350"s" dual sport models for a nice performance boost. You will need the dirt model intake and airbox boots because the inlet and outlet O.D. are different (smaller) than the stock vacuum carb. You also need to modify the stock throttle tube to allow a bit more "throw" or you will never reach full throttle with the street model throttle assy.

E-start models will also need a spacer on the engine side to push the carb back far enough to clear the starter motor (dirt model carb is a bit larger than original)

You can get them cheap from one source on ebay $220 US: http://cgi.ebay.com/ebaymotors/New-Mikuni-Flat-Slide-33mm-4-Stroke-Carburetor-Pump_W0QQcmdZViewItemQQ_trksidZp1638Q2em118Q2el1247QQcategoryZ35597QQihZ015QQitemZ250215117057QQrdZ1QQsspagenameZWD1V

This carb is also known as Mikuni TM33-8012. He still has some left in stock. Most others sell them for $270 or more.

Hi Jcalis, thanks for your reply.

Yes i noticed with my throttle cable the carb only opens half way. I was planning on getting the hacksaw out this arvo to give it some more displacement. It looks like the US source is much cheaper...with the dollar how it is it would have been cheaper to go US. Oh well! The snorkel diameter is yes smaller, i will be modifying that shortly. For now im satisfied with hooning round the block looking like a kid who got a enduro bike for Christmas. Road registration and tuning will follow. Will post when it is going!

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now