Spitting out top carb Suzuki DT115

[Numlaar]

Hey all,

Still working on this darn motor...

1987 Suzuki DT115...

Runs fine for first 20 ish mins (sometimes 30), then starts surging, missing, at idle it will pop and once in a while backfire...

If you pull off the silencer box, you can see it puff smoke out of the top carb every once in a while...

I have had the carbs all rebuilt, and have it at a shop now cause I got tired of trying to find out what was the problem...

they are saying it needs reed valves... I want to verify what you guys think?

I thought if reeds were an issue, the problem would happen all the time, and not wait till it was warmed up?

thoughts?

 

[Numlaar]

Re: Spitting out top carb Suzuki DT115

Well an update on this issue...

I'll try to make it short as possible, but its a lengthy issue...

I went ahead and had the shop replace the reed valves, I also had the carbs rebuilt for the 3rd time in 3 months, as well as having the fuel pump rebuilt, and all new hoses, connectors, primer bulbs, vacuum test etc...

I am absolutely positive this is no longer a fuel issue...

The engine runs perfect for about 20-30 mins then it starts "Surging" at anything half throttle and up... thats the best way I can describe it... its not quite a cylinder cutting in and out, but could be. RPMS jump roughly 500rpm best guess (Tach does not work, thats an entire other issue).

I have had everything, and I mean everything on the fuel system done many times over, the shop where its at now, says they can't figure out what it is, and I need to take it to Suzuki... I called two different Suzuki dealers, and they flat out refused to work on it... (they said its too old, and they dont have the proper testing equipment)... (Its not that old, its an 87)

I am at my wits end with this freaking motor and am looking for advice on how to proceed... any and all suggestions would be welcome.

Here's a condensed list of whats been done, checked, replaced:

Fuel System:
1. New fuel pump,
2. New fuel hoses,
3. New primer bulb,
4. New anti-siphon valve,
5. New water seperator (entire assembly)
6. New in line filter under the cowl
7. Had entire gas tank cleaned, and checked, and replaced with fresh new, non-ethanol gas

Electrical:
1. New spark plugs
2. Spark tested under load (showed good spark all 4 cylinders, even under load in a test tank).
(Unable to test CDI, or TCU)

Mechanical:
1. Full compression test, 125psi all 4 cylinders
2. Fuel pressure checked ok
3. Fuel vacuum checked ok
4. Vaccum leaks (none found)
5. Entire new front intake gaskets, from airbox to crankcase (carb, silencer box, intake, etc.)
6. New reed valves

Motor has amazing pee stream strength, and operates at a nice temp. Starts fine, idles fine, and works great for 20-30 mins, then starts surging.
SO thats it... anyone help on this?

 

[99yam40]

Re: Spitting out top carb Suzuki DT115

pick up the equipment needed to test the CDI inputs and out puts, and test when the problem is happening to see if there is something going on in the electrical part of the system if not the it still has to be the fuel.
It took me close to a year to finally figure out that a previous owner had drilled out the main jets on my C40.
too much fuel will keep a cylinder from firing properly just like not enough

 

[SparkieBoat]

Re: Spitting out top carb Suzuki DT115

when they clean out the fuel tank did they check the vent? sounds like a possible clogged vent to me. it also could be an electrical component breaking down after getting hot.

 

[Numlaar]

Re: Spitting out top carb Suzuki DT115

pick up the equipment needed to test the CDI inputs and out puts, and test when the problem is happening to see if there is something going on in the electrical part of the system if not the it still has to be the fuel.
It took me close to a year to finally figure out that a previous owner had drilled out the main jets on my C40.
too much fuel will keep a cylinder from firing properly just like not enough

What equipment would I need? From my understanding these years do not have any real diagnostic equipment available, and thats why no one wants to work on it...

 

[Numlaar]

Re: Spitting out top carb Suzuki DT115

when they clean out the fuel tank did they check the vent? sounds like a possible clogged vent to me. it also could be an electrical component breaking down after getting hot.

Yes the vent was checked and is completely open, and I can run it with the gas cap completely off ( so getting PLENTY of air) and it still does the same thing...

I am thinking something electrical breaking down as well... but no idea where to begin... I cant afford to just start throwing parts at it... the CDI is 1200 bucks alone, I can get an entire new motor for that!

 

[SparkieBoat]

Re: Spitting out top carb Suzuki DT115

for around $100 you should be able to get a certified Suzuki dealer to do a diagnostic...might be your best option..then decide if you will fix/sell/or keep for parts.

 

[99yam40]

Re: Spitting out top carb Suzuki DT115

What equipment would I need? From my understanding these years do not have any real diagnostic equipment available, and thats why no one wants to work on it...

A manual,
a DVA peak reading meter
or a DVA adapter and regular meter to measure the voltages
maybe test harnesses or some way to tie into the wiring while it is running

Here is something that gives some general info, but you realy need a service manual to give steps for testing,equipment needed, and the specs
http://www.outboardparts.com/troubleshooting/printguide.htm

 

[Numlaar]

Re: Spitting out top carb Suzuki DT115

for around $100 you should be able to get a certified Suzuki dealer to do a diagnostic...might be your best option..then decide if you will fix/sell/or keep for parts.

Yeah thats the problem... I called TWO "certified" Suzuki Dealers (one where suzuki was their only motor line), and they both said they couldnt help... that their testing equipment didnt go back that far, and I have the "bad years" for the motor, where it has electronic controls, but no way to get any "real" data from the motor...
So they basically told me to pound sand in a polite way...

 

[Numlaar]

Re: Spitting out top carb Suzuki DT115

A manual,
a DVA peak reading meter
or a DVA adapter and regular meter to measure the voltages
maybe test harnesses or some way to tie into the wiring while it is running

Here is something that gives some general info, but you realy need a service manual to give steps for testing,equipment needed, and the specs
http://www.outboardparts.com/troubleshooting/printguide.htm

I have a manual, and a digital multimeter, but it doesnt begin to tell me how to test a CDI unit...I think this one is a bit beyond my capabilities... but thanks for the info..

 

[dank91]

Re: Spitting out top carb Suzuki DT115

i am having a same kind of issue except after 2 or 3 minutes it just shuts off mine is a 88 dt140 and there is a stator on the flywheel that sends current to the cdi and im thinking thats what my problem is the higher the rpms the better it runs,

i purchased a online manual for 20 bucks at selocmarine.com and it has the diagnostics to test cdi, you can either use a stevens cd-77 peak voltage tester or a suzuki cdi tester w/ test harness

basically you are checking for input voltage to the cdi from the pulse coils and charge coil, if voltage is good then it isolates it to the cdi unit itself

another thing is the low oil system will only let the engine run for 30 minutes if it detects a problem

 

[stylesabu]

Re: Spitting out top carb Suzuki DT115

i recommend factory manual

 

[SparkieBoat]

Re: Spitting out top carb Suzuki DT115

that is a good reason to stick with one of the big 3..OMC, Merc, or Yammy...but you should be able to test it with the info listed above..if you already have a multi meter you can order a DVA adapter for under $30 here http://www.usatoolwarehouse.com/usatoolwarehouse/ESI-640.html

 

[crb478]

Re: Spitting out top carb Suzuki DT115

Just going out on a limb here, but the the first thing I would do is to run the motor until it starts surging or missing and then use an inductive timing light on all four plug wires to see if it is still getting a good regular spark. Often when coils heat up they can stop working or work intermittenly. I would also verify that the motor is timed correctly and that the timing is not moving, If you haven't messed with it I would suspect that it is fine though.

 

[SparkieBoat]

Re: Spitting out top carb Suzuki DT115

speaking of inductive timing lights does anyone know what the difference is in a cheaper one as opposed to a more expensive one?? I am looking at 2 right now one is $29 the other is $99. one is the Equus 3551 the other is Equus 5568. I understand there is probably a quality difference but I have purchased a lot of cheap tools and they work fine and a few that I wish I had got a more expensive one. So any thoughts on inductive timing lights? I am sure this will help this poster also is why I posted in his thread. He does need to get one also and do the test cbr mentioned above. I have a regular timing light and have gotten by with it so far but it is starting to give me trouble.

 

[99yam40]

Re: Spitting out top carb Suzuki DT115

Spitting,popping, or back firing could be called lean sneeze.
may be your top crank seal is letting air into the top crank case and leaning it out.

A timing light would be a good thing to try, but the DVA would tell you if there is bad input or output voltages of the CDI. If all of that is good then check the ignition coils and wires.
Then it is back to the air/fuel ratio in each cylinder which could be the seal.

Not sure about the differences of those two lights, may need to check there specs to see what they say. My Snap On has been a good one and still works great, I picked it up over 30 years ago and it was second hand

 

[SparkieBoat]

Re: Spitting out top carb Suzuki DT115

I think the spitting problem has been resolved with the new reeds and other work listed at the top..I think that now the problem is surging from the bottom of post #2. But if it is still lean sneezing that could be the issue.

 

[James R]

Re: Spitting out top carb Suzuki DT115

Have you considered that it could be dirt or water in your fuel tank.

 

[Numlaar]

Re: Spitting out top carb Suzuki DT115

Have you considered that it could be dirt or water in your fuel tank.

Yes... see below on the things I had done:
5. New water seperator (entire assembly)
6. New in line filter under the cowl
7. Had entire gas tank cleaned, and checked, and replaced with fresh new, non-ethanol gas

 

[James R]

Re: Spitting out top carb Suzuki DT115

Sorry, did not read thoroughly enough. One last question on fuel. Has PTFE tape been used on any of the fittings.