Suzuki DT25 Carb Adjustment

[al40]

Hi, I have a '92 Suzuki DT25 and am trying to find out the best way to adjust the pilot screws to the best posn. My service manual tells me they should be 1 to 1.5 turns out (from seated posn) but how do I optimise them. <br /><br />On single carb engine I just turned screw at idle and set it at mid point between where the engine started to bog down (well actually slightly richer than mid-point). What is recommended procedure to do this with 3 carbs. <br /><br />Engine does not idle atall well (although it runs fine at higher RPM). <br /><br />(I've still to check reverse switch / resistor and throttle sensor which can both also apparently affect idle but want to adjust carbs anyway)<br /><br />Thanks.

 

[al40]

Re: Suzuki DT25 Carb Adjustment

should I just adjust them all a little at a time or do them individually? If I do it individually, how can I tell when it's correct? will the effect of adjusting 1 carb be noticeable? <br /><br />Thanks.

 

[FHARVELL]

Re: Suzuki DT25 Carb Adjustment

When this model came out, the EPA was coming into it own, requiring tight manufactoring specifications. Many carbs had a screw for adjustment, but they also had a cap to make adjusting them nearly impossible. With the stringent EPA standards in place, few -once- set ever required any additional adjustment. Carb (linkage)adjustment (which is normally the only thing that might need an adjustment if work was done on the carbs) on a multi cyclinder setup is simple if you follow the procedures in the manual (adjust the linkage at WOT setting so all valves are fully opened) but VERY easy to mis-align if your not sure what your doing. In a three cyclinder engine, the middle cyclinder is usually controlled by the computer as opposed to being fired by a pulser coil, a faulty shifter switch can cause the 2nd cyclinder to mis-fire. Check the spark plugs for fouling. Sparks plugs are tell-tale indicators of the condition of each cyclinder from the carb to the spark. Black sootie plugs mean the fuel mixture is too rich or timing is off. Also you could try pulling a plug wire one at a time to determine which cycliner is mis-firing. Usually setting the low speed idle to specifications is sufficient and rarely requires an adjustment out of the norm - I'd suspect something else as a cause for rough idle.

 

[jim dozier]

Re: Suzuki DT25 Carb Adjustment

It may be that you need to pull the carbs and clean the idle orifices. It's hard to tune a dirty carb and you can't clean the orifices from the outside of the carb. If the DT25 is similar to the DT75 & DT85 the idle mixture screw is adjusting air, so opening (unscrewing) it allows more air in and leans the mixture. Screwing it in will enrichen it. Someone else may have a different way of setting them, but I would unscrew all of them the book spec number of turns out from lightly seated. Then I would try various adjustments such as enrichen all 3, 1/8 turn and check, enrichen all 3, 1/4 turn and check, etc.) The goal is not to have 1 cylinder rich and 1 cylinder lean which makes for a crappy idle. You may be able to tell if the idle is too lean if the engine is "sneezing". Partially choking the carbs manually would improve a lean idle.