DT75 - can't get it to stay running

[Gas Giant]

First off, this boat is VERY close to being sold for scrap.

I have an '88 Suzuki DT75 on a Cobia 177. I bought it from someone who had let it sit for a year, and it didn't run anymore. I have had the carbs rebuilt (TWICE), the fuel pump replaced, and replaced the entire fuel system. New tank, new lines, new everything. Also brand new spark plugs, and a fully charged marine battery. The compression is 120 on all 3 cylinders and it cranks over nice and fast.

The latest carb rebuild was finished last Sunday. Today I decided to try and take the boat out for the first time, seeing as how the boat ramps would be empty today. I wanted to warm it up on the muffs at home, but it was extremely hard to start.

But when it did start, it would only run for a few seconds at best. I tried revving it up to keep it running, but although it was pulling higher RPM it still would run strong for a few seconds and then die.

Holding the choke closed (by pushing in on the key - a very annoying way to choke an carb, if you ask me) seemed to keep it running longer, but it would still die after a few seconds.

Seeing as how the carbs were literally cleaned and rebuilt days ago, and the entire fuel system is new including the gas, what on earth could it be? It sounds like a fuel delivery problem, but I know for a fact that the fuel pump diaphragms are brand new as well as all the fuel lines.

For reference, my starting procedure was this:

-Pump the primer bulb until it was hard. (It never got THAT hard though?)
-Pump the throttle lever twice and return to neutral
-Push the key in to choke the engine (this didn't always work for some reason - occasionally I had to flick the choke plates closed by hand when the key was pushed in)
-Crank the engine. Sometimes it would fire, sometimes it wouldn't. I wouldn't crank it for more than 5-10 seconds at a time. Sometimes it would fire without closing the choke, but most of the time it wouldn't.

The primer bulb not getting that hard worries me, but I haven't been able to find any fuel leaks anywhere. I was using a portable fuel tank and the vent was open.

I'm very close to giving up, because this thing has been nothing but a nightmare and its beginning to turn me off to boating in general. I've NEVER had this much trouble with any other type of engine, so the problems I am having now are largely a mystery to me.

 

[Gas Giant]

Re: DT75 - can't get it to stay running

Slight update: i was messing with it some more, and I noticed gas leaks out of the top carburetor after it dies.

Perhaps the floats aren't set right?

I also noticed a very small fuel leak on top of the fuel filter housing when I squeeze the primer bulb.

 

[99yam40]

Re: DT75 - can't get it to stay running

Sounds like trash in the fuel system holding needle open on top carb maybe or float stuck or out of adjustment, along with the fuel delivery system sucking air.If fuel leaks out before the pump. the pump will suck air instead of all fuel
Who have you had working on this thing?
Maybe time to find someone else

 

[bernieb]

Re: DT75 - can't get it to stay running

For the time being ,forget about the carbs. check to see if you have fire on all cylinders ,if you dont have a timing light, you can buy a simple spark tester at local auto parts store for less than 10 bucks. I'm not a pro but it sounds like an ignition problem, which means if you dont have fire on one or more plugs,you need to back track right up to the flywheel area where the voltages are generated. Try boats.net for your engine and hit on the magnito top right. Although they didn't list a dt75 in year 88, but it may be the same for the 115. I had the identical problem with dripping carb, slightly running then quiting, but it was a 87 mercury and the problem was the switchbox (dont know if you have a switchbox).

 

[James R]

Re: DT75 - can't get it to stay running

A simple test for sparks.
Pull the plugs. take some stiff copper wire, that found as the ground wire in 3-12, 3-16 or similar house wire.
Twist a loop in the wire for each plug threaded part. attach one end to the block by unscrewing a bolt and putting the wire under it and retightening. Connect the plugs to their wires and fit the plugs tightly in the loops.
Have someone turn the motor over and look for your sparks. If those show good then go to your fuel side. Eliminate one thing first.
Suzukis tend to have very reliable electrics.

 

[Gas Giant]

Re: DT75 - can't get it to stay running

Hey guys, sorry for the delay.

Before I read this, I actually took the carbs off myself and cleaned them out. Sprayed carb cleaner through every passage, jet and valve in them. I also set the floats to the setting listed in the Clymers manual. (One carb was out of spec, the other two were right).

I also took off every fuel line and blew carb cleaner though it.

I reassembled it, and all that cleaning made no difference. Would run with the choke closed, but as soon as I would open it, it would speed up and die. On one occasion I was able to close the choke in time to save it, and it ran until I let go of it again.

Only now when it is running, its running worse than it was before.

I also installed a cheap clear fuel filter temporarily to eliminate the pinhole leak problem - made no difference.

I managed to get it to start two or three times, and then I couldn't even get it to sputter. I had my brother check the spark while I was cranking it, and it was sparking. I squeezed the primer bulb until it was hard, but it wouldn't even sputter.

That is about where I got mad and quit for the day. I'm pretty much out of ideas, fuel wise. Perhaps crank it with a bottle on the end of the fuel line to see if the fuel pump is spraying gas?

If it is, can I assume that I DO have an electronic problem?

This engine is about to find itself in a junkyard.

 

[58rude]

Re: DT75 - can't get it to stay running

Verify spark first. If you have spark then go ahead and spray some premix in the carbs to see if it will run off the spray. If it runs on the spray, then you know you have a fuel issue. Did you do the lync and sync?

 

[Gas Giant]

Re: DT75 - can't get it to stay running

I'm not sure what lync and synch is. I've been checking over the Clymers manual - it mentions balancing (which sounds well beyond my capability), but I haven't come across anything called lync and sync.

I haven't done anything else to it today; I went inside and pouted for awhile.

 

[James R]

Re: DT75 - can't get it to stay running

There is no link and Sync on this motor. The advance retard is done electronically based on throttle position and RPM. This will not cause the motor to fail to start and Idle.
The fuel check by using a spray bottle filled with 50:1 mix sprayed into the carb intakes while turning the motor over will prove or disprove the fuel issue. Frankly it sounds like a fuel issue. To eliminate everything before the carbs disconnect the output hose from the fuel pump. Invest in a new bulb and hose. Connect the output of the new hose to the hose from the fuel pump to the carbs. Stick the input end of the new bulb/hose assy in a gallon jug filled with 50:1 mix. Pump up the fuel and test run. Use the bulb as your fuel pump to keep the motor running. If this works then you know you have a fuel pump problem, hose problem or tank problem.
Oh, by the way, is your bulb fitted correctly, with the arrow pointing toward the motor.
Another issue overlooked is wear on the throttle spindles. Had a similar problem with a DT30.
Put newer carbs on and no more problem.

 

[Gas Giant]

Re: DT75 - can't get it to stay running

Sounds like a good test.

The bulb is facing the right way; I know this because the first time I installed it, it was facing the wrong way. The hose/bulb assembly are probably a month old.

 

[99yam40]

Re: DT75 - can't get it to stay running

I would think that if that motor has more than one carb on it they should be synchronized and all linkage adjusted properly.

A fuel pressure/vacuum gauge hooked into the pump output with a tee fitting will tell you if it is pumping properly and on the inlet it will tell if there is a restriction.The primer bulb will pump fuel through the pump and into the carbs without taking the pump out of the system.
a piece of clear tubing put in between pump and carbs (for testing only)will show if you are getting air in the system.
A timing light hooked to the plug wires will show if it is getting spark or get a spark tester or make one.

You need good compression and good spark at the correct time (timing), and the proper fuel/air ratio to fire the cylinders. could be too much fuel or too little to fire

Always make sure each of the ones you can test are good and then chase the fuel/air ratio problems that are not as easy to test

 

[James R]

Re: DT75 - can't get it to stay running

Suzuki three carb systems have one adjustment screw on the middle throttle butterfly to set it closed and top and bottom have individual plate screws to set those at closed. All three should then be at closed together. No other adjustment is available other than Idle mixture setting on each carb.

 

[Gas Giant]

Re: DT75 - can't get it to stay running

I picked up a spark tester yesterday, one with an adjustable gap. I'm going to test the spark tonight since I'll have access to a helper. (My arms aren't long enough to crank the ignition switch from behind the boat and I don't have a remote starter switch).

I'll post the results. I don't have a vacuum or pressure gauge, but I can get ahold of clear tubing to check for air bubbles in the fuel.

I don't think I am going to get a chance to test run the engine using me as the fuel pump until Sunday, but I'll post the results of that too.

Also, I found out I have access to an ultrasonic cleaner at work, so I am going to try to borrow that and plop the disassembled carbs in it. Any suggestions on a cleaning fluid? Any reason to NOT use carb cleaner?

 

[Gas Giant]

Re: DT75 - can't get it to stay running

Ok, the results of the spark test are in. I have blue spark on all 3 spark plugs during cranking.

I also increased the gap on the spark plug tester to 0.50", and it was able to arc across that large gap on all 3 spark plugs.

She's sparkin pretty good, she shocked me on the first test and it hurt like hell.

 

[99yam40]

Re: DT75 - can't get it to stay running

Ok, the results of the spark test are in. I have blue spark on all 3 spark plugs during cranking.

I also increased the gap on the spark plug tester to 0.50", and it was able to arc across that large gap on all 3 spark plugs.

She's sparkin pretty good, she shocked me on the first test and it hurt like hell.

Buck up guy, that short pulse of electricity don't realy hurt it just shocks you and makes you jump and hit yourself on something that can hurt

Testing things is the best way to go

 

[Silvertip]

Re: DT75 - can't get it to stay running

Have you checked the timing. A backfire at one time or another can partially shear a flywheel key which thows the engine out of time. If the engine "tries" to run with the choke closed, you have a fuel delivery problem. Leaks must be fixed. Are the idle and high speed jets adjustable? If so, are they adjusted correctly? If the choke is not working with the key, fix it. Pumping the throttle does nothing. The carbs don't have accelerator pumps. The engine will likely not stay running unless you use the fast idle feature which depending on the type of control you have is either a separate lever at the top of the control box or you push a button to release the shifter from the throttle and move the throttle forward. It may also have a box on which you grasp the lever and pull it toward the center of the boat then forward to get fast idle.

 

[Gas Giant]

Re: DT75 - can't get it to stay running

99ym40 - you're right. I have a push-pole platform over my engine, which as it turns out is perfect for bumping into.

Silvertip, I don't know for sure, but I don't think any jets are adjustable. Here is a diagram of the carbs:

http://store.brownspoint.com/DT75/fig004-758897.asp

The only jets I know if are the pilot jet (#4), and the main jet (#17 or #26). I can't see how they are adjustable, but maybe they are. I haven't seen anything in the Cylmers manual about adjusting them; the only adjustments in the carb listed are the float height.

Unfortunately, the pilot jets on two of my carbs are broken in such a way that I can't take them out. When I had the carbs apart, I sprayed carb cleaner though the main jets, and got a strong spray into the throat of the carb in each carb.

I don't know where the idle jets or passages are; the only reference to an idle circuit in the diagram is the pilot air screw (#6) which is called an idle air screw in the Cylmers manual. I think this only lets air in, but again I am a novice.

Actually, I re-read what James R posted, and it looks like the only carb adjustments on this engine are the idle screw setting and adjustments to get the butterflies to close together.

The idle speed is controlled by a switch on the front of the engine; I've been using the Fast Idle setting for all my tests. The choke does work with the key; I was just complaining that it is annoying to sit there pushing the key in for minutes on end to keep the engine running. NOTE: I forgot what I posted earlier about the choke being flighty; when I took the carbs off and reinstalled them the choke seems to be working much better.

I am going to try and borrow an ultrasonic cleaner from work this weekend and re-clean the carbs in it. I'll blow the passages out with compressed air, and post what happens.

 

[James R]

Re: DT75 - can't get it to stay running

I did not know the procedure you had used for cleaning your carbs but now you have told me the story and probably the problem.
Suzuki carbs are very precise and are sensitive to contamination.
Go buy a Gallon can "Kit" Carb and parts cleaner by Gunk. Available at auto parts stores.
I use this on every carb that comes through my shop including Suzuki's.
Never failed yet. Follow the instructions. May take two soakings and two rinsings and two blowings out with compressed air, but they will be clean.
Will not harm plastics. Remove all gaskets and hoses before soaking.
When all is done be sure to use Stabil in your fuel to avoid all this crap again.

 

[99yam40]

Re: DT75 - can't get it to stay running

You really need to remover those screws and all other parts from the carbs when cleaning to make sure you clean all passages and the readjust as the manual states

 

[Silvertip]

Re: DT75 - can't get it to stay running

Again -- if you have to hold the choke closed (via the key) to keep the engine running, you have a fuel delivery problem. Do the basics. VERIFY that the fuel line is delivering fuel. Remove the fitting at the end of the hose and squeeze the bulb. Good fuel flow you have a good delivery system to that point. Disconnect the output of the fuel pump and spin the engine while catching the fuel in can or soda bottle. If there is good flow, then the problem is in one or more of the carbs.