Logo
FULL SITE MENU

3.5hp carb problems

B

barrell

New member
So my two year old 3.5 was acting up and wouldn't get above 1/2 rpms without choking out. I took it to a certified Tohatsu dealer who cleaned out carb. Said it was fixed but it wasn't. Took it back to him and this time he said I needed a carb rebuild kit as the needle was a bit scratched, but he didn't have any kits so I paid him a second time and motor still didn't run. I ordered my own kit and installed it. Seemed pretty simple to do. Now motor is idling at two to three times normal rpms (I don't have tach) I didn't change anything on the two cables. The idle screw isn't even making contact so if anything it should be idling too low. Im stumped. I hate this dam Tohatsu. Even the certified mechanic I paid $200 to cant get it right.
 
First, in order to help you best, we need the exact model. I am guessing is is an MFS3.5B. Secondly, why did you pay the dealer a second time, when he was unable to work on the motor? Thirdly, you must have a tach in order to adjust the idle speed.

Since the throttle plate is advanced above idle, that is why the throttle stop screw is not seated. You will need to determine why the throttle is so high. For example, if the choke is even partially on, that adds throttle. Likewise, if you did not reassemble the two gaskets and insulator between the carb and the intake, that could throw off the geometry. Likewise, if the throttle drum and or throttle opener is not assembled correctly, that could cause a problem. If you neglected to install one of the spacer collars, that could also goof things up. If the throttle plats was removed and reinstalled on the shaft, it could mis-aligned as well. And those types of things are why it requires training to be an outboard mechanic. If you could post a couple of pics of the setup, we might be able to identify what is wrong.

Odds are that you were not running the carb dry at the end of every day it was used. That would allow crud to accumulate in the carb. It is quite a common issue. Modern, EPA-rated 4-stroke outboards of all sizes and manufacturers run very lean, so the fuel systems must be maintained in spotless condition, or they will be too lean to work well. I'm not sure about how a viton float valve needle could become "scratched", so I don't really know what the mechanic was referring to. What method did he use to clean the carb in the first place? What were the symptoms after the technician worked on the motor?

Motor for motor, Tohatsu makes the most outboards of any manufacturer. Think of it: every Nissan, Evinrude 20 and below, Mercury 30 and below, are all Tohatsu motors. Their reliability is by far the best in the business. So I guess you hate Nissan, Evinrude/Johnson, and Mercury as well. Maybe you need to get a Torqeedo.
 
pvanv said:
First, in order to help you best, we need the exact model. I am guessing is is an MFS3.5B. Secondly, why did you pay the dealer a second time, when he was unable to work on the motor? Thirdly, you must have a tach in order to adjust the idle speed.

Since the throttle plate is advanced above idle, that is why the throttle stop screw is not seated. You will need to determine why the throttle is so high. For example, if the choke is even partially on, that adds throttle. Likewise, if you did not reassemble the two gaskets and insulator between the carb and the intake, that could throw off the geometry. Likewise, if the throttle drum and or throttle opener is not assembled correctly, that could cause a problem. If you neglected to install one of the spacer collars, that could also goof things up. If the throttle plats was removed and reinstalled on the shaft, it could mis-aligned as well. And those types of things are why it requires training to be an outboard mechanic. If you could post a couple of pics of the setup, we might be able to identify what is wrong.

Odds are that you were not running the carb dry at the end of every day it was used. That would allow crud to accumulate in the carb. It is quite a common issue. Modern, EPA-rated 4-stroke outboards of all sizes and manufacturers run very lean, so the fuel systems must be maintained in spotless condition, or they will be too lean to work well. I'm not sure about how a viton float valve needle could become "scratched", so I don't really know what the mechanic was referring to. What method did he use to clean the carb in the first place? What were the symptoms after the technician worked on the motor?

Motor for motor, Tohatsu makes the most outboards of any manufacturer. Think of it: every Nissan, Evinrude 20 and below, Mercury 30 and below, are all Tohatsu motors. Their reliability is by far the best in the business. So I guess you hate Nissan, Evinrude/Johnson, and Mercury as well. Maybe you need to get a Torqeedo.
Click to expand...
Mechanic insisted I pay him for looking at it and analyzing it needed a carb rebuild kit If I didnt pay him he wouldn't give me my motor. He did not stock carb kits. Yes its a B and yes I hate all those brands. I am a Suzuki guy and have owned 4 of them and not one ever needed to see a dealer after I left with them. Almost 14,000 hours on four them and they always started on first turn of key and ran perfectly. I just bought a new 4p Suzuki (my 5th) for my solo skiff and Im trying to get rid of this Tohatsu on Craigslist but I need to get it running right to dump it.
I didn't mess with the throttle plate. I only replaced the parts that came with the kit.
Mechanic supposedly cleaned the carb on the first trip there but why he didn't see the needle was scratched , you will have to ask him. I don't think he ever took it apart the first time as his helper told me he just sprayed carb cleaner in it and ran it for hours. He is a certified Tohatsu mechanic in Margate, NJ
Does the little plate that supports the needle need to be bent to adjust it?. I installed it as I came out of the bag. was carefull not to bend it or the spring. Yes reinstalled it with the two gaskets on the engine side.
 
Last edited:
That dealer mechanic sounds like a jerk.
All the older, non-EPA motors ran richer, hence more reliably.
If he did not disassemble the carb and do a 4-hour soak in carb dip, he did not actually clean the carb. Spraying acetone-type spray down the throat merely makes it shiny.
Yes, you should check float height whenever you change either the float or the needle. They are usually perfect out of the box, but it is good practice to check it.

At this point, assuming nothing you (or that technician) did damaged the carb, it may very well still need to be cleaned, if that was actually the original issue. Typically, if the needle is damaged, the motor runs too rich, which wasn't your original symptom. Check over the linkages and attachment points to see if anything is holding the throttle above idle. These are incredibly simple motors to service, so even a dolt should be able to figure it out. There are 5 dealers within 50 miles of Margate, so perhaps you may want to see one of the others. You are still under warranty, as long as the issue was not caused by operator abure (such as leaving gas in the carn). Oh, and I would also consider reporting your problem with that unnamed dealer in Margate to Tohatsu America at 214 420 6440.

Please let us know how it goes.
 
barrell said:
And how do you adjust needle height? Bend the stainless L channel? Stretch the spring?
Click to expand...
You need to seek the assistance of a qualified mechanic.
Odds are the float level is correct. Is the float parallel with the casting when the carb is held inverted? If so, you are OK.
Did you ever resolve why the throttle would not return to the idle stop?
 
pvanv said:
You need to seek the assistance of a qualified mechanic.
Odds are the float level is correct. Is the float parallel with the casting when the carb is held inverted? If so, you are OK.
Did you ever resolve why the throttle would not return to the idle stop?
Click to expand...
I took it to a certified Tohatsu dealer and mechanic. There is no problem with the throttle returning it just wont idle. The idle screw is almost touching the block but when I start it now it turns maybe 2,000 rpms that's as low as I can get it. I am about to wack this POS with a hammer. There are literaly thousands of complaints about this motor and its carb problems all over the internet. wish I had read them before buying it. My nephew just bought a solo skiff off me and went out and ought a brand new Mercury/Tohatsu 3.5. It wont run right . Keeps stalling and the merc dealer blames him and cant seem to get running. motor is two weeks old.
 
So it does NOT return to the idle stop. That is a mechanical malfunction of some sort. Somewhere, the throttle plate is jammed above idle, or it would return to the idle stop. Probably incorrectly installed. Regardless, if you are able to get the carb throttle lower, and then it won't run below 2000 RPM, odds are that the low-speed circuit is fouled with crud. In other words, it probably still needs to be cleaned. In severe cases, ordinary cleaning may not be adequate, and the carb would then need to be replaced.

Your nephew's situation is on a different motor, and may well be a different issue, and he is in warranty.

For that matter, so are you. If there is a manufacturer's defect, Tohatsu will happily repair it. If you have an incorrectly installed carb, or one that was otherwise subjected to consumer abuse, that problem is not a warranty issue.

There are 4 other dealers within 50 miles of the one who apparently was not willing/able to help you. You may wish to contact one of them.
 
pvanv said:
So it does NOT return to the idle stop. That is a mechanical malfunction of some sort. Somewhere, the throttle plate is jammed above idle, or it would return to the idle stop. Probably incorrectly installed. Regardless, if you are able to get the carb throttle lower, and then it won't run below 2000 RPM, odds are that the low-speed circuit is fouled with crud. In other words, it probably still needs to be cleaned. In severe cases, ordinary cleaning may not be adequate, and the carb would then need to be replaced.

Your nephew's situation is on a different motor, and may well be a different issue, and he is in warranty.

For that matter, so are you. If there is a manufacturer's defect, Tohatsu will happily repair it. If you have an incorrectly installed carb, or one that was otherwise subjected to consumer abuse, that problem is not a warranty issue.

There are 4 other dealers within 50 miles of the one who apparently was not willing/able to help you. You may wish to contact one of them.
Click to expand...
Maybe I don't understand but the throttle is completely closing. The idle control screw is almost touching the plate when adjusted all the way out. The Mercury dealer has had my nephews motor two weeks ad still cant get it to run right. That's the point about theese motors, even certified mechanics try, try, and try again and cant get these carbs running right. I run a business. I dont have time to drive 50 miles and have already paid a mechanic 1/4 the cost of the motor and its still f##cked up.
 
If the throttle were in fact completely closed, the motor would not be running at all, so you are mistaken. The fact that it idles at 2K RPM tells me what I already diagnosed (although it's admittedly an educated guess, as I am not looking at the motor).

Your nephew has a different motor, and his issue may not even be fuel related. His dealer may want to just swap it out if they can't repair it; they would need to call Tohatsu America in Dallas to get that approval.

In my years of turning wrenches on Tohatsu motors, I have never has a carb for a 3.5 that I could not get working correctly.

If you "don't have time", and just want to bad-mouth your frustrations on the forum, I cannot assist you. Those dealers (I trust you can use the dealer locator function on the Tohatsu website) are all LESS than 50 miles from the other dealer. If all you want to do is complain, go ahead.

If you want to get your motor working, either take the advice you get from the forum (for free), or see a dealer.
 
On the outside the throttle is clearly closed. I will post a picture. Obviously on the inside something is wrong that's its operating at such high rpms. That what this post is all about. How do you know those other mechanics are any good? Im tired of paying and paying a certified Tohatsu mechanic that doesn't know what hes doing or was just to lazy to do the proper job the first time. I have 5 or 6 marine mechanics in the town I live in. I went out of my way to take the motor to a certified Tohatsu mechanic. I thought my nephews new Mercury was identical to my Nissan?
 
No. You clearly do not understand how a carburetor works. There is no "on the outside" to the throttle.
You definitely need the assistance of a mechanic. Pick one and see what happens.
Yes, Merc motors are made by Tohatsu. That does not mean that an issue on your nephew's motor is even slightly similar to a problem you have.
 
Ok I came here looking for assistance. Your only answer is take it 50 miles to another authorized mechanic. The whole idea is to avoid getting ripped off again by an authorized mechanic. I was referring to the throttle control lever on the outside of the carb that the throttle cable operates. It is fully closed. maybe internaly the throttle is still pe so How doI realign the external lever wit the internal control?
 
Again, it is clear that you have not been educated in the workings of carburetion. Therefore, I recommend you seek the assistance of someone who is skilled in that technology.

Although you may be well-intended, it seems that you prefer to be argumentative, rather than take expert advice.

It is not possible to "realign the external lever with the internal control".
 
pvanv said:
If the throttle were in fact completely closed, the motor would not be running at all, so you are mistaken. The fact that it idles at 2K RPM tells me what I already diagnosed (although it's admittedly an educated guess, as I am not looking at the motor).

Your nephew has a different motor, and his issue may not even be fuel related. His dealer may want to just swap it out if they can't repair it; they would need to call Tohatsu America in Dallas to get that approval.

In my years of turning wrenches on Tohatsu motors, I have never has a carb for a 3.5 that I could not get working correctly.

If you "don't have time", and just want to bad-mouth your frustrations on the forum, I cannot assist you. Those dealers (I trust you can use the dealer locator function on the Tohatsu website) are all LESS than 50 miles from the other dealer. If all you want to do is complain, go ahead.

If you want to get your motor working, either take the advice you get from the forum (for free), or see a dealer.
Click to expand...

In all my years of turning wrenches I have had nothing BUT fuel issues with Tohatsu. That 3.5 carburetor is such a fickle little POS!
If anyone reads this before they buy one just tie a prop on a weed whacker, it'll work better
 
Patrick. said:
In all my years of turning wrenches I have had nothing BUT fuel issues with Tohatsu. That 3.5 carburetor is such a fickle little POS!
If anyone reads this before they buy one just tie a prop on a weed whacker, it'll work better
Click to expand...

You do realize that this issue is from two years ago, right?
 
Back
Top