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Cannot cure surge

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colriverrat

Contributing Member
"HELP!!
I have a Suzuki DT65

"HELP!!
I have a Suzuki DT65 2 cyl outboard that just seems to NOT LIKE to run at 1300-1500RPM. I've put new pistons and rings in, completely overhauled the fuel system including the reeds. Carbs are synced. Timing is set to factory specs.It has CDI ignition with good spark.

The motor starts right up and idles great both in and out of gear.

The motor runs great at all rpms except between 1300-1500. If I give a very slow but steady acceleration it "Skips" over this flat spot and runs awesome. If I decelerate quickly back to idle it is fine as well.

If I try to just run at a fast troll at 1300-1500 RPM the motor surges, coughs, and sputters. It wont die but it is not happy at that rpm. It sounds like a plug misfiring, but only at that one rpm. It does the same thing on decel. It runs fantastic until I get down to 1300-1500rpm then starts that coughing and surging.

Is it common for 2 strokes to have an rpm where they just are not happy? I'm perplexed I just cant figure this one out."
 
"Hey there my polish buddy. <[

"Hey there my polish buddy.
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Did you use a carb balancer stick to synch? I hate to second guess you but it sounds like you don't have it synched correctly. That RPM is right at the transfer spot from idle into midrange through the carburation. Have you tried riching it up a little so it will transfer through smoother. Coughing and sputtering is lean not enough fuel. They all have a unhappy RPM range but that engine ran pretty good all through the RPM range."
 
"THX Robert,
I have a homema

"THX Robert,
I have a homemade manometer to balance/sync the carbs. It is 20' of clear flexible tube. It is folded in two and taped to a yard stick. The bottom of the tube is then smoothed back out to a free flowing radius. I then filled it with about 4oz of red dyed water.

One tag end goes to the top cyl intake port, the other to the bottom. I set the RPM to 1000 like the manual says. I then adjusted the carb linkage nut till the water is perfectly centered.

This is a VERY sensitive tool. Just a minute fraction of a turn on the linkage nut will change the water level from one cyl to the other. I even went so far as to smoothly throttle the motor up to 3000 rpm to be sure the balance remained perfect.

I will richen the pilot and see if that helps. Someone else suggested a clogged oil recirculation tube.

My motor at 1300-1500rpm, acts like an idling big block V8 with a massive cam, it just lopes."
 
"Still having the problem. WTF

"Still having the problem. WTF!!! I cannot figure this one out. It coughs, surges, sneezes at 1300-1500 rpm. I pulled the carbs again. SOAKED EACH OVER NIGHT. Blew them out put back together re-synched and the problem remains WTF?????
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"
 
"I forgot to update, it has a

"I forgot to update, it has a brand new Suzuki fuel pump. Got the pump a couple months ago from Browns Point.

How do I do a crankcase leak test?? If the crank case or reed plate or carb base gaskets are leaking, why am I only having problems at that narrow RPM range
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I also replaced the reeds when I put the new pistons and rings in. The new piston sets are .050mm oversize Suzuki parts.

I used the HIGH DOLLAR Suzuki sealant for the crank case halves and the reed cage/intake adapter. ALL NEW GASKETS AND SEALS have been installed and YES I lubed the crank seals before installing.

Could the problem be in the ignition system???? I set the base timing at 3* ATDC as per the Suzuki manual. The timing stays at 3* ATDC up to 1400 RPM then the lingage starts advancing the timing. At 1500 and up THE MOTOR RUNS AWESOME!!!!}"
 
"UPDATE

The motor only run

"UPDATE

The motor only runs like sh*t in the 1300-1500RPM range. It idles GREAT, it runs AWESOME above 1500RPM."
 
"What kind of "tweakin&#34

"What kind of "tweakin" Should I toss the sync tool and tune by ear??? Set the throttle to where it is running poorly and tweak carbs till smooths out?? Or tweak the piolet screw till it smooths out?? BTW IS TURNING THE AIR SCREW IN LEANING OR RICHENING??? Right now its dead nuts on sync according to my tool, but runs like crap in the transfer circuit"
 
"sounds like you did not clean

"sounds like you did not clean right

also you sync to lowest carb, then start with the highest one"
 
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