1994 70 HP Yamaha...Help

[palmettoe]

Any help appreciated, I've tried everything I can think of at least once. Appears to be fuel starvation when powering up from idle ( intermittent). Sometimes runs ok, sometimes requires finesse with throttle to get to plane, sometimes will only get to 3500 rpm and starves when more throttle applied. I've checked carbs, jets, needle and seats, all like new. Swapped entire fuel tank, line and bulb, even though bulbs stays fully pumped. Installed new fitting on motor (fuel), new plugs even though missing wasn't apparent, checked all fuel lines to pump, carbs, filter, (cleaned), replaced both diaphrams in pump. No missing, backfires or the like, no indication of overheating, etc. Fresh new fuel. Any ideas? Thanks in advance, John PS Winning advice gets a free ultralight aircraft demo flight lesson in Georgetown, SC, lol

 

[Trent]

Re: 1994 70 HP Yamaha...Help

You say you cleaned the fuel filter? If its the plastic kind I am thinking about, replace it.<br /><br />Remove your fuel lines on the engine and look down them to make sure the inside of the hoses are not comming apart/causing a restriction. <br /><br />Im sure you have also looked at the fuel lines for kinks?<br /><br />Also another thing...And its hard to hear over the internet...Are you shure its not trying to stay in the "slow mode" due to overheating/or low oil (if oil injected)??? <br />What kind of ultralight..

 

[palmettoe]

Re: 1994 70 HP Yamaha...Help

Thanks for your reply, Yes I looked inside of fuel lines and also checked for kinks and obstructions. However you may have something on the filter. It is the factory one on the engine, plastic, with a mesh (plastic?) screen, Are you saying the screen could be collasping?<br /> Flightstar IISC and an X-Air. Thanks again, John<br />Just saw the rest of your post, sorry. No indication of overheat or low oil. On occassion I can finesse the throttle to run at 5500 and normally will stay there until you move the throttle again.

 

[Trent]

Re: 1994 70 HP Yamaha...Help

Im saying those filters (the ones Im thinking about) are not to be cleaned. THey are to be thrown away.<br /><br />My dad's got a Flightstar II. <br /><br />I put a Jabaru (80HP) couple of years ago on one..Man would she go!

 

[palmettoe]

Re: 1994 70 HP Yamaha...Help

Thanks Trent,<br /> I'll remove the screen and try that and get back to you.<br /> Yes, the Jabiru is quite an impressive engine but expensive. Guess I'll have to continue to poke around with the 582 Rotax.<br /> John

 

[JohnnyVero]

Re: 1994 70 HP Yamaha...Help

It's diffinitly not anything to do with oil or overheat, both functions are alarmed and also will shut down to 1500 rpm's automaticly. Check your compression, it should be around 135 lbs with a 10pct tolerance, also I had the same problem with one of my twin 1988 70hp Yamaha's and it was a pinhole corrosion hole by the sparkplug, also check for gasket leak....Good luck

 

[palmettoe]

Re: 1994 70 HP Yamaha...Help

Johnny,<br /> Thanks for your help. Checked the compression a few days ago and all 3 cylinders exactly the same, however only 120 lbs. Low time engine and runs as strong as ever on top when you can sneak up on it with the throttle. Whadda you think?<br /> John

 

[Trent]

Re: 1994 70 HP Yamaha...Help

Keep an eye on your oil tank for the engine..(rotax) Iv got alot of time on the 582. Make sure before any flight their is no water in the oil tank or the tank itself is not "blown up" by steam.

 

[Trent]

Re: 1994 70 HP Yamaha...Help

Alarms fail..<br /><br />Just a thought..JohnnyVero <br /><br />Palmettoe.. Your compression is fine, No worries their. I would just for kicks check the alarm system, If its a C- model their is no automatic check when the key is turned on and you must ground manually the sensors to make sure they are working.

 

[russthemuss]

Re: 1994 70 HP Yamaha...Help

uummmmm have you checked the diaphram in the accelerator pump? Is fuel tank vented? Can you get it to pick up when its starving by using the choke?

 

[JohnnyVero]

Re: 1994 70 HP Yamaha...Help

Even thought your might have a defective alarm buzzer which is not likely (yamaha's have a twin check system which makes that failure highly unlikely) your in line computer would shut your engine down to 1500RPM's and no higher, it sure sound like you have a gasket problem somewhere. If you hear a something that sounds like AIR PUFFING than it's a compression leak. Check the gasket on your head plate, (thin plate where your spark plugs are)Well the guys before me covered everything else, so good luck, and when you find the problem please let me know, I have twin 70's myself. (JohnnyVero@aol.com)

 

[palmettoe]

Re: 1994 70 HP Yamaha...Help

Russ, accelerator pump? You mean fuel pump? Yes, replaced diaphrams even though old ones looked ok.Yes, tanks vented. To be sure, even changed entire fule line, tank, bulb. Engine has no key switch push choke or lift lever type, all automatic. I think Trent may have it on the fuel filter screen even though it looks clean. I'll try it today and advise. Thanks

 

[palmettoe]

Re: 1994 70 HP Yamaha...Help

Johnny, will most certainly let all you guys know when I find it! Thanks again for all your help. John

 

[palmettoe]

Re: 1994 70 HP Yamaha...Help

Well the mystery continues. Not the filter screen,did the same thing with it removed and no filter at all. Don't know why, but seems like it could be timimg related. Also the pee water is cool, but the local Yamaha mech said that is sometime normal and again, no alarm or indication on guage (tach). I have checked the thermostat and it opens just before boiling temp and even ran it without and no change. Didn't want to run much past 4900 today and once it started acting up 3900 or so. If you added throttle there it would die back. Back to the pee water which was strong even though cool, the engine felt pretty warm if not hot. Internal blockage? and not showing up on guage and not backing down to the 1500? Hmmmmmmm, really whipping me! Thanks again for everyone's help so far,

 

[palmettoe]

Re: 1994 70 HP Yamaha...Help

Just in case anyone goes this far back......finally found problem! Timing too far advanced, don't know how it got that way. Retarded 2 turns on linkage, problem went away.<br /> John