DT40 tops out at barely 1000 rpm

[James R]

Re: DT40 tops out at barely 1000 rpm

If incompetence is suspected then anything could be wrong. If you, like me, have a persistence in these matters a manual would be of great help.
These motors are a good sound motors and usually worth the effort.

 

[btruong]

Re: DT40 tops out at barely 1000 rpm

i do have a manual, its a shop manual for 1990s 2-stroke Suzukis.

about checking the timing, how does my motor "sense" throttle position? how does it know the position of the throttle to advance the timing?

 

[James R]

Re: DT40 tops out at barely 1000 rpm

There is a TPS attached to the lower carb. You can disconnect at the plug and if that is causing the problem the motor will run correctly by default. The motor will run quite happily with this disconnected. The smooth acceleration will be the only thing affected.

 

[btruong]

Re: DT40 tops out at barely 1000 rpm

the manual also talks about a throttle position sensor, supposedly mounted on the carb. i have 1 carb by the way. there is no sensor attached to the carb. it has the throttle lever, the oil pump linkage, choke, and some kind of sensor connected to the choke only.

 

[James R]

Re: DT40 tops out at barely 1000 rpm

Sorry. I am sure that my input has led you astray.
You are correct there is no TPS.
Your system employs a combination of stator movement and mathematical calculator built into the CDI to advance the ignition timing.
My Seloc manual has an excellent set up procedure in the maintenance section.
If you have this then follow the procedure carefully step by step.
It sounds like sync and advance retard is your problem.

 

[btruong]

Re: DT40 tops out at barely 1000 rpm

i was a little confused. haha. thanks though, for clearing things up.

i have a clymer manual and it has a section about timing adjustment. i cant seem to get it right though. i will try again though, removing the flywheel to get a better look at things.

do you think you could scan the section from the seloc manual as to help me better understand this? itd be greatly appreciated.

thanks james! im still quite reluctant to take my motor in for a $100 diagnostic and am persistent in fixing this up myself.

 

[James R]

Re: DT40 tops out at barely 1000 rpm

With apologies I dont have a scan capability.
The Clymer should be similar. The info is in my Maintenance chapter.

 

[btruong]

Re: DT40 tops out at barely 1000 rpm

i decided to remove the flywheel today. it all went good so im going to carry out the adjustments and synch tomorrow. the inside of the flywheel has like a magnetic strip, right? what if this has slight rust on it? can i just sand it off with fine sand paper?

 

[James R]

Re: DT40 tops out at barely 1000 rpm

The rust wont affect the magnets capability. Iron dust from sanding can get in everywhere. Best leave it alone.

 

[btruong]

Re: DT40 tops out at barely 1000 rpm

oh. alright then. dont want to make anything worse. thanks.

the manual calls for putting the throttle at full, rotating the stator till the "A" mark aligns with a projection on the crankcase, and adjusting the throttle cam until it holds the throttle lever (on carb) fully open. i got this part nailed down. then it says return it to idle and adjust it so the alignment mark "B" lines up with the projection. the problem is, after doing this, the stator doesnt rotate enough to bring it back to fully open.

i noticed the throttle cable (from remote to engine) is badly frayed and rusted. the replacement is on its way. is this why the adjustments were messing up?

 

[btruong]

Re: DT40 tops out at barely 1000 rpm

sorry if im pounding everyone with questions, but i need this boat running ASAP. i need some assistance trying to knock out some possibilities.

1) gearcase (driveshaft, gears. etc)
2) prop pitch
3) weight of boat

my supportive reasons are

1)i dont see how lack of lubrication or anything can lower wot rpm; they would just seize. correct?
2)the motor wouldnt reach high rpm after the rebuild with the same prop before rebuild.
3)even if the boat was water-logged, shouldnt i hear the motor revving trying to push the boat?

im trying to narrow it down to a single area to inspect/repair/replace.

 

[99yam40]

Re: DT40 tops out at barely 1000 rpm

Your compression is not good if one cylinder is 20# lower that the other. you list a 15 p prop and 13 p factory.

With low compression and too high of a pitched prop the motor maybe just not able to handle the load.

 

[James R]

Re: DT40 tops out at barely 1000 rpm

Motor set up should be done with the throttle cable disconnected at the motor. Meke the set up by moving the throttle mechanism by hand. Once you have the motor set up you can re- attach the cable adjusting it to match the motor set up.

 

[bartelso1]

Re: DT40 tops out at barely 1000 rpm

The best way is to disassemble completely and soak in carb cleaner, blow out all passages and jets with compressed air, and then reassemble. Make sure to adjust all linkage, sync, and adjust the carbs as the manual states. Not sure what all comes in the kit for DT40 and if you need those parts replaced.

i have a dt55 and had same problem-cleaned bottom carb and has run great since

 

[btruong]

Re: DT40 tops out at barely 1000 rpm

the 55 had multiple carbs, right? how thoroughly did you clean them? how similar was your problem?

 

[btruong]

Re: DT40 tops out at barely 1000 rpm

okay guys, i finally got around to checking the timing. i checked it statically following Joe Reeve's and this: http://www.themarinedoctor.com/cgi-bin/YaBB.pl?num=1209250610 guide.

my shop manual says 2degrees ATDC at 1000rpm and
25degrees BTDC at 5000 rpm

i grounded the spark plug wires and disconnected the remote throttle control.

my friend cranked the engine over while i held the timing light.

i got 3degrees ATDC at idle and when i advanced the stator to WOT, i got 14degrees BTDC.

im 9 degrees off. could this be causing my lack of power? if so, what do you think needs replacing?

i already did the adjustments for static timing. both alignment marks line up at idle and WOT.

when installing the new steering cable and tightening the motor mounts, the transom was compressed and water dripped off the bolts. i know the transom is rotten now. is it okay to keep it like this until we get the motor in full running condition and then replace it? or is it a major safety concern?

 

[99yam40]

Re: DT40 tops out at barely 1000 rpm

why worry about the transom on a boat that has low compression on one cylinder and timing out of whack and only runs at 1000RPM.
Sorry,I do not know enough about the Suzuki's so I will have to bow out , but will keep reading

 

[James R]

Re: DT40 tops out at barely 1000 rpm

Hi Back Again.
Looks like the max advance is way out.
Do you have a fax. If you have then give me the number and I will fax you a copy of the set up from my manual.

 

[btruong]

Re: DT40 tops out at barely 1000 rpm

yes, i do have a fax machine at home. ill PM you the number. when is it convenient for you to fax? ill PM it then.

thank you for your help, honestly. im just staying on the safe side since my fax is in-line with my house phone.

 

[James R]

Re: DT40 tops out at barely 1000 rpm

Mine is also my home. Put your number on my PM and when I get it I will fax you.