120 hp tohatsu idle issues

[polar_bear]

hey everybody, im new here and hope to gain alot of knowledge from yall. i bought a new motor today, a 94 2-stroke tohatsu 120 horse, it ran fine when i went to look at it for probablly 15 minutes, i looked everything else over, ran a compression test, and checked prop run-out. gave the guy 900 bucks. got home and mounted it. i transported it standing up. now, when i start it the sound reminds me of an old 2 stroke dirtbike, but really the only way to express the sound is to try to hear this noise, lol whan an whan an whan an whan. now if you can hear that noise in your head then were on the same page. ive checked ignition and all plugs are poppin hot, but im not sure if theyre poppim at the right time, ive narrowed it to either that or fuel delivery, maybe 1 carb out of whack? ive been a diesel mechanic for a few years but im not an expert when it comes to ignition systems and carburetors. so any input or possible fixes from someone whos had the same problem is greatly appreciated, ill be tinkering with it more tomorrow but some general area to look at would help alot. oh and also i called the previous owner and he told me its done that once before and his mechanic changed some pressure switch on the side of the block and it corrected it "maybe the water pressure switch?" is what he told me... does this sound right? thanks for any help guys

 

[pvanv]

Re: 120 hp tohatsu idle issues

Are you running on the hose, or in the water? If you want to get into the carbs, get a Factory service manual (skip the aftermarket ones), at any dealer, including me.

I assume you have the control box as well... Does any alarm sound? Are you running a water separator? Do you have fresh fuel? Did you verify no leaks in the fuel system? Start with the basics... make sure you have clean fuel at the carbs. Maybe even pull the drain plugs on the carbs to see what comes out.

If the problem is at idle only, it's likely some crud in the low speed passages, but could be a lot of other things. So get on firm ground with the fuel system first.

 

[polar_bear]

Re: 120 hp tohatsu idle issues

i was running it on the hose with clean fresh fuel. the seller actually gave me a factory service manual and parts manual but i havent even opened them yet so i will start there. and yes i do have the control box but it was not completely hooked up, that is my first task this morning, so i probably wouldnt hear any buzzers, i wouldnt think so any way. and now that you mentioned it i do have a small seepage of fuel at the 3rd Tee towards the bottom, are carburetors sensitive to air?

and on another note, i have tuned carbs before, mainly just my truck and a few lawn mowers that come in to the shop, but how in the world do you get 4 carbs yuned the exact same?!

thanks in advance


EDIT: and it does all the way through the throttle range until absolutlet WOT then it smooths out for the most part

 

[polar_bear]

Re: 120 hp tohatsu idle issues

update:
i played around with the mixture screw (im assuming?) on each carb. backed them out 1 full turn and it made it run fine at idle, but as soon as you rev it up any it continues to do the same thing, even at idle. shut er down, fire er back up again and same situation, its like once it misses one time it cant pull itsself back out of the irratic idle. it misses so bad the motor swings back and forth about 1 turn of the steering wheel. any help is appreciated

 

[pvanv]

Re: 120 hp tohatsu idle issues

Yes, since carbs mix air with fuel, they are sensitive to air. The pilot screw initial setting is about 1-3/4 or 2 turns out. You may have a number of different problems to cause those symptoms. I would go through the motor methodically, with the help of the trusty Factory service manual. Pick one system (fuel first, probably), verify everything from the fuel pickup in the tank all the way to the carbs... and then go on to electrical, and finally mechanical (since you already confirmed compression).

 

[polar_bear]

Re: 120 hp tohatsu idle issues

ok, i recollected today and started fresh, checked spark, at idle and while idled up, good hard spark, and the mechanical advance is operating. then checked fuel, have a good strong fuel flow out of the pulse pump, so im assuming it is the carbs, called a local shop and its 340 plus parts to rebuild them, does that sound about right to you pvanv? and is the pilot screw the one with the spring on it that goes to a point on the right side of the carb when facing thew prop of the engine? and also how much is the service manual for this engine from you? you have my business if i decide top buy one. thanks

 

[pvanv]

Re: 120 hp tohatsu idle issues

Figure shop rates of $75 to $125 an hour... Figure pulling and disassembling and soaking, then reassembling and setting up. Might be a little on the high side, depending on how much time they expect to spend on diagnosis and final testing. The Factory service manual is Part# 003-21036-1, $44.17, available from any dealer, including me. BTW, the carb kit is Part# 3C7871221M $193.07, and does all 4 carbs.

If you are going to a shop, don't just dictate "clean the carbs", but rather see if you can get them to diagnose your issue... after all, it's possible that you missed a symptom that they might catch right away... 2 heads being better than one, as they say. Then if they confirm a carb issue, cool.

 

[polar_bear]

Re: 120 hp tohatsu idle issues

i appreciate all your advice sir, and thanks for the part numbers. i messed with it more earlier and tightened up the linkage for the ignition advance because it was advancing a few degrees before mating with the throttle linkage and that made it run good for about two seconds then it would start screwin up again, so now im thinkin ignition probs. my neighbors mobile boat mechanic is gonna take a gander tomorrow. ill follow up with what he finds.