DT75 trouble

[troutrvr]

I have a 95' DT75. At idle all seems to run OK, head seems normal to the touch, after the hole shot 3-4 seconds on plane I start getting surges and at WOT it is bogging down. I have inspected the fuel system from cleaning the tank, pick up tube, replacing primer bulb, had the fuel pump apart, rebuilt all carbs,(which looked very clean to me)I have a water seperater . Tried pumping the bulb when running on the water and that didnt help. Ran a timing light while under power, it was reading around 24 deg BTDC (hard to tell by my self). Does this motor have an over heating circuit that acks as a governer to save the motor?

 

[jim dozier]

Re: DT75 trouble

Try choking it when it bogs down. If it picks up you will need to go back into the carbs. You wouldn't be the first to have to redo a rebuild. The carbs don't have to just look clean they have to BE clean. One speck of crud in the jet is all it takes. Clean with carb cleaner AND compressed air. Install rebuild kit and set float height and idle air screw to manual specs.

 

[troutrvr]

Re: DT75 trouble

Thanks for the speedy reply, I'm waiting on an impeller from iboats and I'll give a try.

 

[troutrvr]

Re: DT75 trouble

Well, I ran the boat last Saturday to test what I have done so far. After going through the carbs again completely with cleaner and compressed air, changing fuel/water separator, water pump impeller. It did show slight difference at mid and WOT but didn’t fix my original problem. I did notice something else, at idle, after the motor has ran I'm getting allot more smoke. Also, in the water I noticed a small oil slick around my motor. I though maybe it was from tilting but there has been oil under the carbs allot more than usual. I tried to look for a leak in the lines but nothing obvious and I found the plugs were wet with oil. Does the motor have an oil sensor that detects oil starving and would govern at high rpms.? Sorry so long, but I'm really close to taking it in, but I'm not convinced it's not something simple.

 

[jafa]

Re: DT75 trouble

Have you checked spark on the all cylinders. Unbolt the fuel pump from the block and pressurise the system with the bulb , if fuel leaks out the back , the rubber diaphrams have ruptured dumping fuel into the block.

 

[troutrvr]

Re: DT75 trouble

Yes, getting spark to all cylinders. I had the fuel pump apart and checked both diaphrams. But, it's an easy test so I'll try it. Is it commen to have worn pump diaphrams but not ruptured? Thanks for the reply.

 

[jafa]

Re: DT75 trouble

Anythings possible whats the rpm at WOT ?

 

[troutrvr]

Re: DT75 trouble

I seen that coming......<br /> I don't have a tach. I bought the boat ( a 17' center consol) in perfect condition in 98'. It for the most part has been trouble free. Then lately the motor started bogging down after getting on plane. Then would run fine for the rest of the day. It progressively got worse, and some surging after a few secounds on plane, now leads to bogging so bad I have to throttle back to smooth the motor out enough to cruise slightly on plane. I thought going through the carbs (twice) would fix it, but no joy. I'm thinking of running it with the gas cap off the 18 gal. portable tank to see if it was not venting properly. But then again it would have drawn in the bulb I would think.

 

[jafa]

Re: DT75 trouble

Your right it would have sucked the bulb in. Did you try choking it when it bogs down. If rpms pick up the mixture has gone lean (restriction)if its kills it then you have too much fuel getting in (flooding). When you went through the carbs did you clean out the lines and the tank pickup. All sorts of crud seems to get in there even though its sealed.

 

[troutrvr]

Re: DT75 trouble

I did remove the pick up tube and clean. I also cleaned the quick disconnect to the motor which was fozen in place. I was able to clean it up and the seals still looked sevicable, but I was also looking at replacing it because of the age of the seals or just getting rid of it and fuel filter on the motor like I had read in a previous forum. I was wondering about my fuel lines. They seemed to be a bit small(1/4") never a problem before, but they are 10 years old I'm sure they might be worth changing. Would a larger 3/8" line be a problem for a DT75? I did try choking each carb when the motor was bogging and it would (kill) Bogg down even more. I also tried the fuel pump leak test by pumping the bulb, no leaking gas.

 

[jafa]

Re: DT75 trouble

Did you install new carb kits when you overhauled them , those needle valves are 10 years old and may not be seating properly. What float height did you set. Have you done the link and synch as per the manual.

 

[troutrvr]

Re: DT75 trouble

I did install new needle and seats. The bowl highth was not adjusted. Since I dont have a manual I called the shop where I bought the kit and the tech said with the carb upside the float should be level (Parallel) with the carb. I have not fooled with the linkage at all.

 

[troutrvr]

Re: DT75 trouble

update: found oil leak coming from motor tilt actuator seal while trouble shooting tilt pump motor not working. After taping pump motor with hammer, it would operate but not for more than 1 or two cycles. Looks like water intrusion maybe the problem. Can the cover for the tilt motor be removed w/out taking the tilt assembly apart?<br />(Well, after taking the motor apart and cleaning up corroded parts looks to be salvagable.)

 

[troutrvr]

Re: DT75 trouble

After braking down and taking into local shop, they found bad gas(which realy looked bad), and a bad spark plug that was causing #2 cyclinder dropping off at full throttle. Total cost seemed fair for the work they did and I didnt feel like I had been raped. And after all the work I did it was a big relief. But man I felt like an A-- for not changing the plugs out when I should've. Leason learned. Thanks for the replies.