1987 Suzuki DT 75 power loss

[mac 89]

Had the boat out running about 3800 RPM when I hit three four to five foot swells the engine fell off to about 2000 RPM no alarms. Limped back the dock real rough idle. I've been troubleshooting it ever since and will try to keep this short. Gas is fresh with marine Stabil and marine Heet in it. New filters checked for water in the separator none. Spark is strong and blue, new plugs. Top and middle plugs are firing bottom is not. Compression is 148 top and middle bottom is 141. This is a rebuild with only about 12 hrs on it. Cleaned the carbs all passages are clear re-did the bottom one three times to make sure good fuel to all three. With the engine running I plugged off the top and middle carbs with my hand, the engine tried to die both times. The bottom carb was barely sucking a spewed fuel on my hand. Is this bad reeds? I've been running it on 50:1 premix while testing and confirmed the oil injection is working. Sorry for the long post. I'm really frustrated thanks for any help.

 

[99yam40]

Re: 1987 Suzuki DT 75 power loss

If you have good spark on #3 but no suction, then my thought is it is sucking air in some where besides through the carb.
Have you checked the fuel pump? I think it runs off of the pulse on #3 crank case

 

[mac 89]

Re: 1987 Suzuki DT 75 power loss

I have not checked the fuel pump since it is keeping the primer bulb hard and the line goes from the bottom carb to the middle and top carbs and is keeping them full. Where else could air be getting in? The plug is wet and the hole smells of gas like it"s getting fuel. Maybe just not enough? Idle screw is set 1 1/2 turns out. Fires right up on two cylinders.

 

[mac 89]

Re: 1987 Suzuki DT 75 power loss

Sorry Captain. Took me a little time to understand what you were saying. I saw another post where another person was having pretty much the same problem I'm having. The fuel pump is driven by the crankcase pressure on the bottom cylinder so a small hole in the diaphragm could "flood", too rich, the cylinder. Or the O ring my be leaking air into the crankcase reducing the suction through the carb. Hope my thinking is right, so going to check the pump out. Any input is appreciated.

 

[mac 89]

Re: 1987 Suzuki DT 75 power loss

Took the pump apart, looks worn but no holes. Waiting on new parts, figured I rebuild it since it's apart. Pulled the reed assembly out. No cracks in the reeds and they seem to be laying closed but they seem sticky. How should they be?

 

[CalebWindham]

Re: 1987 Suzuki DT 75 power loss

Did you resolve this issue?

 

[mac 89]

Re: 1987 Suzuki DT 75 power loss

No. I rebuilt the fuel pump and replaced the reeds. I have checked the electrical checks, pulser coils, cdi out put, counting coil,etc., all fine. Waiting for the mechanic to call me.

 

[bigman348]

Re: 1987 Suzuki DT 75 power loss

Did the mechanic have a fix for your problem? Having similar issues on a dt65.

 

[mac 89]

Re: 1987 Suzuki DT 75 power loss

Not yet. Still waiting to get it in.

 

[suzukidt75mayer]

Re: 1987 Suzuki DT 75 power loss

I am having a simiar problem with my 1987 Suzuki dt75. When running on the lake the boat will jump forward, then lose power and then jump again. It has good compression on all 3 cylinders, great spark, all 3 are getting fuel, but at idle speed if you pull the top spark plug wire off it has a different tone, same with the middle. When I pull the bottom plug wire there is no change in the tone or anything. So the third/bottom cylinder isnt firing all the time, because like I said it jumps, and when it does that you can feel that all the cylinders are firing. So any ideas what could cause the bottom cylinder to not fire? It has me stumped! I think it might be the CDI Module, but not positive. Any help is greatly appreciated.

 

[deejaycee_2000]

Re: 1987 Suzuki DT 75 power loss

The DT65/75 have a general problem with their fuel pump diaphrams, if you at any time replaced this then you don't have to worry about that again ... the CDi unit will hardly ever fail, they are pretty decent .... reeds also hardly ever go bad .... coils fail all the time, change your coils around and see if the problem shifts to the other cylinder then you know it's the coil ....

 

[mac 89]

Re: 1987 Suzuki DT 75 power loss

Sorry for the delayed response. Thanks for the input D. The mechanic went through the electrical connections to make sure they all had good contact and that seems to have fixed it. He told me he wasn't sure what they did to fix the problem because they don't really get in to the old two stroke and mostly deal with the fours. I think they might have replaced the gear counting coil, that's the one that was giving me high readings. The number three coil has a longer plug wire than one and two so I'm not sure if I could switch it around but I agree with your suggestion. Thanks for the replies. Fresh plugs help it to.

 

[deejaycee_2000]

Re: 1987 Suzuki DT 75 power loss

The coil wires must all be the same length ....