Suzuki DT 55 (1986?) Oil injected 55 hp

[31900]

Suzuki DT55 (1986?) Oil injected 55 hp. Motor not used 4 years, 3 carbs cleaned, new fuel, head gasket replaced. This motor will start and run but not idle. At revs removing the centre (#2 cyl)plug lead motor speeds up!! 1 and 3 cylinders run fine. Throtteling down to idle, begins to miss then backfires and stops. Past owner reports no problem.

 

[fridays]

Re: Suzuki DT 55 (1986?) Oil injected 55 hp

Check your fuel pump diaphram.

 

[31900]

Re: Suzuki DT 55 (1986?) Oil injected 55 hp

Thank you FridaysMarine. Fuel pump diaphragm checks out OK. It is located on the bottom cylinder, not the centre one causing the problem. Any more ideas please?

 

[jim dozier]

Re: Suzuki DT 55 (1986?) Oil injected 55 hp

Remove the airbox and stick 2 fingers in the throat of the #2 cylinder and see if it picks up any. It sounds like that cylinder is running lean and the primary suspect is the carb even though you say it was cleaned. Who cleaned it and exactly what was done to it. Was it completely dismantled and cleaned and rebuilt? Were the idle circuits cleaned and then properly reset? Was the float valve replaced and properly reset?

 

[31900]

Re: Suzuki DT 55 (1986?) Oil injected 55 hp

Thanks jimd. Will try it and let you know.

 

[fridays]

Re: Suzuki DT 55 (1986?) Oil injected 55 hp

Were the carbs syncronized after cleaning. #1 & #3 could be leading #2...also if you have the carb off check for broken reeds, not uncommon in 1986 and 1987 55hp & 65hp models.

 

[31900]

Re: Suzuki DT 55 (1986?) Oil injected 55 hp

Thank You FridaysMarine. I appreciate all the help being given. I will have some time this week to check things out. By the way, the carbs were professionally cleaned by 2 diferent tradesmen. The first thought the crank seals are the problem. The second disagreed and went back to the carbs and fuel pump but could not find the problem and gave up on the motor for the time being. Suzuki discontinued and uncommon down under.

 

[31900]

Re: Suzuki DT 55 (1986?) Oil injected 55 hp

All suggestions followed up. Fuel pump diaphragm OK, fingers down throat of all carbs makes no difference, confident that carbs twice removed are clean and synchronised and all necesarary work done by outboard tradesman. Reed valves appeared OK from superficial inspection. On running have noticed charging circuit OK but tacho fluctuating and unreliable. Excellent spark, new plugs. Still mystified. Could it be electrical/timing?

 

[31900]

Re: Suzuki DT 55 (1986?) Oil injected 55 hp

Compression test normal and even. Took cover off flywheel cover found TDC marks and marks for all 3 cylinders along flywheel 120 degrees apart. Removed spark plugs and with srew driver onto pistons checked for TDC for each cylinder. These do not seem to correspond to a 120 degree separation and they do not all line up. Is it possible that this motor does not have a solid crankshaft and that the sections have moved? Is that normal or do I have I got a broken crankshaft? Could this indicate the lack of synchronised timing and back firing? Sorry my background is electronics. Signed Desperate Aussie.

 

[jim dozier]

Re: Suzuki DT 55 (1986?) Oil injected 55 hp

Man this is weird. I don't know if those cranks come apart on that model or not, somebody here might know, but I don't think it would even run if it was busted. I don't think it would run if it could be installed out of sync. I think you may be on to something with the timing. From your description it sounds like #2 is not firing at the right time. I am not too familiar with the Suzuki ignition even though I have a 1987 DT85 because mine has yet to act up. When you took the flywheel off did you notice anything that was loose or not bolted in its place. Its pretty evident on my DT85 which coils go to which cylinder, how about yours, are you sure the firing order is set up right? I would also look for any cross arcing, maybe one of the other cylinders is arcing over to #2 or vice versa and screwing up the firing order. Try running it in the dark with the cowling off and look for arcs. Keep us posted, I like a good mystery.

 

[fridays]

Re: Suzuki DT 55 (1986?) Oil injected 55 hp

Bingo..maybe. First check the flywheel key to make sure it is not sheared. Your post revived my memory ( I've been selling Suzuki since 1982) and the first year for the 55-65 triple, i.e. 1985 here in the U.S., they DID have some with loose cranks that twisted. They tend to run poorly that way as you can imagine. The few I heard about ( I sold one of them) usually twisted within the first 50hrs.. Double check your piston timing vs. flywheel..you may have found your problem.

 

[31900]

Re: Suzuki DT 55 (1986?) Oil injected 55 hp

Thank you jimd and FridaysMarine for your help. We will be pulling the motor down in a couple of weeks and I will fill you in on the results.

 

[echozulu]

Re: Suzuki DT 55 (1986?) Oil injected 55 hp

some suzukis have crankshaft seals not only at the ends of the crank but also between cylinders, yes rubber seals... i havent read all youve done maybe cooling water is entering cyl thru inner exhaust cover

 

[31900]

Re: Suzuki DT 55 (1986?) Oil injected 55 hp

Thanks echozulu. There has not been any indication of water ingress. All spark plugs nice and black. It really seems to be a timing problem with #2 cylinder the odd one out. On checking piston movement in relation to flywheel, there was some rotation of the flywheel when the piston at top of its stroke does not move, indicating some slack. This slack could be moved around + or - TDC depending on the direction of rotation. I am sure the answer will be found when we pull the motor down. I'll be in touch with the results.

 

[31900]

Re: Suzuki DT 55 (1986?) Oil injected 55 hp

Still have not had the time to pull the motor down. Will let you know the results. Keep tuned...