Suzuki DT65 -79, driving me nuts...

Nick L

Recruit
Joined
Jul 13, 2000
Messages
3
Hi all,<br />Got a problem I've been trying to solve for some time now. The engine starts just fine (every time) and runs perfect at idle, low and mid RPM's. "Pedal to the metal" for anything in between 3-20 minutes and suddenly there is a drop in RPM and the engine "chokes". Sometimes it's hardly noticeable, sometimes I have to ease the throttle back and hit it again. After this it runs OK for a while, until the same thing happens again. I'm getting alot of grey hair over this.<br /><br />I've done the following in my attempts to fix it. I've rebuilt, cleaned, adjusted and synchronized the carbs. Installed an external fuel filter. New fuel line, primer bulb and connectors (both motor and tank). New sparkplugs. Removed the flywheel, cleaned, inspected and tested the charge and trigger coil to be within specification. Adjusted the timing advance linkage to specifikation (static timing). Checked and adjusted the dynamic timing. Checked the thermostat and it's working. Water is coming out of the "tell tale (?)" and the egine temp seems to be OK.<br /><br />I mean, what more can I do? Anybody who has an idea and I would be very grateful.<br /><br />Regards,<br />Niklas Lejestrand, SWEDEN<br />(appologies for any grammatical incorrections...)
 

corm

Lieutenant Junior Grade
Joined
May 12, 2000
Messages
1,241
Re: Suzuki DT65 -79, driving me nuts...

Hi Nick,<br />It sounds like your fuel pump is getting weak.Try squeezing the primer bulb by hand next time to see if it makes a difference.<br />Or the motor is running just warm enough for<br />the gas to start to vapor-lock,poor gas will do this.Or gas with a lot of alcohol in it<br />will act this way.I don't know what quality of gas you have there. One last thing,check the vent on the tank and if it's built in the<br />anti-siphon valve also. post back.<br />...have fun...corm
 

Nick L

Recruit
Joined
Jul 13, 2000
Messages
3
Re: Suzuki DT65 -79, driving me nuts...

Hi corm,<br /><br />Tried this with the primer bulb, no difference. I have even meassured the fuel pressure and it's 2 psi at idle and between 3 and 3.5 at full throttle. My shop manual says it should be atleast 2.5 psi going full ahead.<br /><br />I don't think I've ever heard of anyone getting bad fuel here in Sweden. Everything is so regulated here. "Big Brother sees you...". The "cheapest" fuel yuo can get here is 95 octane, unleaded. If there is any alcohol in it I don't know.<br /><br />The tank vent is OK, it's just a small hole drilled in the "neck" where the cap is mounted.<br /><br />I'm thinking it might be the CDI unit (powerpack) but would you get a symptom like this if it were? Would it not rather be like "dead" then? Well I don't know.<br /><br />Thanks for your help, corm.<br /><br />Regards,<br />Nick
 

corm

Lieutenant Junior Grade
Joined
May 12, 2000
Messages
1,241
Re: Suzuki DT65 -79, driving me nuts...

Hi Nick,<br />Wow 95 octane,lucky you. The highest I can buy is 92. Sounds like you have covered the fuel sys completely. That leave the Ing sys.<br />It can act like that before it dies totally.<br />Which part is a question I can't help with today. They are hard to test when they are not totaly dead.<br />...good luck...corm
 

Capt DHD

Seaman
Joined
Jun 17, 2000
Messages
62
Re: Suzuki DT65 -79, driving me nuts...

Hello Nick:<br />Ditto on the 95 octane.<br />Any chance you have a slight exhaust leak? Base gasket or side cover, under the motor cover. The engine could become starved for oxygen at top end and react this way, but by your description it would have to be a slight leak, hard to identify. If this is the case, it will become worse as you put more time 0n the engine.<br />Just a thought.<br />Good Luck, Rob
 

Nick L

Recruit
Joined
Jul 13, 2000
Messages
3
Re: Suzuki DT65 -79, driving me nuts...

Hi corm and Rob,<br />Yes this is not an easy one. Thought I knew my way around engines (been fixing car engines for years...) but this one beats me. I will have to wait and see what happens. Hopefully I can use it this season and tear it apart during winter to see if I can find the cause of this problem.<br /><br />Thanks anyway for your support.<br /><br />Regards,<br />Nick
 

nicko

Cadet
Joined
Aug 2, 2000
Messages
13
Re: Suzuki DT65 -79, driving me nuts...

Bad gas is everywhere. Drain the tank and then test.
 

keepa

Cadet
Joined
Apr 12, 2001
Messages
6
Re: Suzuki DT65 -79, driving me nuts...

Hello Nick, Have you checked your rpm's at wot? I have a suzuki (40hp) and had an experience with my over rev limiter when I changed props. As the manual explains that the high end is 5200 to 5600 rpm's, I was just over 5600 and the engine would act as if I had a fuel problem. After I had performed many of the same things you had I discoverded it and wished I had checked it first. <br />I hope this helps you tame those grey hairs.<br />good luck, Keepa
 
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DJ

Guest
Re: Suzuki DT65 -79, driving me nuts...

Nick,<br /><br />See if you can borrow an inductive type timing light. Clamp it on the spark plug wires one at a time until you see the spark go away from one or more cylinders when it starts acting up. If you do lose spark on one or more I would suspect the power pack.<br /><br />If they all remain firing even when it's running poorly-it's fuel related.
 

Yepblaze

Lieutenant Commander
Joined
Jun 1, 2001
Messages
1,686
Re: Suzuki DT65 -79, driving me nuts...

I have 80 suzuki and I could clean the carbs and fix it many times till I removed the rotting foam hood liner. That removed the fragments going in the bowl vents, and being sucked up into the main jets. <br /><br />The crap would settle out if the motor was messed with at all. Then run like crazy till it sucked up bits again.
 
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DJ

Guest
Re: Suzuki DT65 -79, driving me nuts...

Nick L,<br /><br />Yepblaze may have a very good point. My DT-140 had VERY sensitive carbs. It would lose power in the mid range and vibrate when even one of them (carbs) was malfunctioning ever so slightly.<br /><br />Test the spark too. Hope all is well there. It's a lot cheaper to play with carburetion.
 

sirlespat

Petty Officer 3rd Class
Joined
Jan 27, 2001
Messages
87
Re: Suzuki DT65 -79, driving me nuts...

Had similar trouble with a mates boat that ran well on the shore and had intermittant loss of power on the water. It looked like ignition failed intermittantly (based on loss of timing light during power loss). After much fluffing around we went through what changes he had made over winter. Turned out that the sparkplugs were replaced with new ones. we replaced the sparkplugs again no further problems.<br />I have no idea how a new sparkplug can have an intermittant problem they seem such a simple device! (But easy and cheap to change one more time) This problem only came to light with a timimg light but be careful..automotive timing lights can behave in wierd ways at high rpm on 2 strokes (timing looks unstable)<br />My two cents worth!
 

Bear

Lieutenant Commander
Joined
Mar 1, 2001
Messages
1,627
Re: Suzuki DT65 -79, driving me nuts...

This an old one from july 14 2000!<br />His problem is solved. It was a too small fuel connector (for a smaller engine).<br /><br />/Bear
 
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