85 Suzuki DT 115 Excessive Gas Consumption

[jlynn37174]

My 1985 ST115 seems to be consuming close to a gallon per mile. I ran a compression check and all 4 cylinders were around 70 psi. The engine starts and runs well. It has yet to let me down, but I can go through a 12 gallon tank of gas in an hour just cruising. Am I just kidding my self, does the engine need to be overhauled or is there something I can do to improve the gas consumption?

 

[deejaycee_2000]

Re: 85 Suzuki DT 115 Excessive Gas Consumption

damn that is really heavy on gas ...... 70 is really low compression, you can get the motor overhauled, redone .....

 

[jlynn37174]

Re: 85 Suzuki DT 115 Excessive Gas Consumption

Since I'm not a mechanic, what should I expect to pay to have it overhauled?

 

[Johnshan1]

Re: 85 Suzuki DT 115 Excessive Gas Consumption

Your gauge might be off, 70 psi is low, but the fact that they are all the same is more important.

 

[jlynn37174]

Re: 85 Suzuki DT 115 Excessive Gas Consumption

How long should I turn over the engine to measure PSI? I just bumped it so that it wouldn't start.

 

[tommays]

Re: 85 Suzuki DT 115 Excessive Gas Consumption

You need to pull all the plugs ,kill the ignition ,have the throttle wide open and i would give each cylinder a good 3 cycles to get a reading



Tommays

 

[deejaycee_2000]

Re: 85 Suzuki DT 115 Excessive Gas Consumption

agreed, do that again and give us the reading .....

 

[jlynn37174]

Re: 85 Suzuki DT 115 Excessive Gas Consumption

I did as you suggested. I removed all 4 plugs and move the throttle to full. The compression on all 4 was around 125.

 

[Big Keepers]

Re: 85 Suzuki DT 115 Excessive Gas Consumption

Now that is more like it. Typically you want to put the motor through 5 compressions. Not sure why the WOT is necessary. I do my checks with closed throttle. Check your spark, make sure all the cylinders are getting a good, clean spark. What did the plugs look like when you removed them? This is important. Keep the plugs in cylinder order so you know what each cylinder is doing. After that I'd do a visual inspection of the fuel system. Make sure there are no leaks or anything. A fuel vacuum and pressure test of the system would not hurt either.

How do you operate your boat? This could come into play as well. Is it loaded down with gear and stuff? Do you go WOT often?

The boat seems to need a check up it sounds like. I'd start running down the list of what could be wrong and eliminate even the mundane silly stuff like battery cables, battery, wiring between motor and remote control, see what may be different from what you remember. Is it propped correctly? Is it at the proper operating temperature?

 

[deejaycee_2000]

Re: 85 Suzuki DT 115 Excessive Gas Consumption

that is a much better reading .... so your motor runs well, it is just heavy on fuel? That is strange ..... does it idle well, perform well at WOT everything? You sure there is no hole in your fuel tank? Nothing smelling like fuel after operating?

 

[jlynn37174]

Re: 85 Suzuki DT 115 Excessive Gas Consumption

The boat has it's original metal external tank, but since it was consuming so much gas I purchased an additional plastic tank. It uses the same amount from either. Therre no signs of a gas leak. The boat does idle a little rough.

 

[jlynn37174]

Re: 85 Suzuki DT 115 Excessive Gas Consumption

I did change the plugs this week but haven't tested it since. Since I pulled the plugs I don't know what cylinder they came out of. They all seemed to have some oil residue on them. They all looked the same. The boat runs great at high speeds. It will run in low 30's mph without being at WOT. It is a 20 hurricane deck boat. It's a tri-hull type. My most recent outing had only my wife, son and I on the boat. About 400 pounds of people and nothing else other than life jackets. It still really sucked the gas.

 

[deejaycee_2000]

Re: 85 Suzuki DT 115 Excessive Gas Consumption

Well the only thing I can think of is .... to make sure your spark plug gaps are correct, adjust your carbs a little, seeing that you say it is running a bit rough, so it seams it is running a bit rich seeing that your carbs had alot of oil residue on them ... the ideal setting is 1 & 1/2 turns and then lightly till perfect from there ..... also it will be worth looking at you reed valves to make sure they are all still good ...... that could be the reason your motor is so heavy on fuel ....

 

[jlynn37174]

Re: 85 Suzuki DT 115 Excessive Gas Consumption

What are reed valves and where would I find them?

 

[deejaycee_2000]

Re: 85 Suzuki DT 115 Excessive Gas Consumption

Reed valves consist of thin flexible metal or fiberglass strips fixed on one end that open and close upon changing pressures across opposite sides of the valve much like heart valves do. They are intended to restrict flow to a single direction. Reed valves are commonly used in two-stroke engines to control the fuel-air mixture that is admitted to the engine crankcase. As the piston rises in the cylinder the resulting vacuum opens the valve and admits the fuel-air mixture. As the piston descends, it raises the crankcase pressure causing the valve to close to retain the mixture and pressurize it for its eventual transfer through to the combustion chamber .....

If take your carbs off, you will find them behind the carbs .... see the part breakdown here .....

http://store.brownspoint.com/dt115/fig004-1158601.asp

 

[jlynn37174]

Re: 85 Suzuki DT 115 Excessive Gas Consumption

Is this a DIY type of project or should I seek professional help? I'm not afraid to tackle it. Are the reed valves part of a carb rebuild kit or can they be purchased separately?

 

[deejaycee_2000]

Re: 85 Suzuki DT 115 Excessive Gas Consumption

they need to be purchased separately and they are not part of the carb re-build kit ..... first check if they seem to look in good order before you just buy new ones, cause they are expensive .....