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Air Vent Screw Prob

Vinden M.B.

New member
My Tohatsu 3.5 was running perfectly, however, I forgot to open the air vent screw and when it started to sputter I realized the problem and opened it, while the engine was still running. There was a sucking noise as the pressure was relieved, but afterwards my engine will not rev. It just putters when I start it. I drained the fuel tank, carb and fuel lines, but it still just sputters. Help.
 
The vacuum in the tank probably sucked the float needle shut, damaging it. Check that first.
 
Thanks for responding so quickly. I took apart the carb and checked the float. Not sure what to look for as needle damage. The float seemed to work properly, however, when I put it all back, it was still sputtering.
 
Is the fuel definitely OK, or could there be some water in it? Does the fuel flow OK by gravity to the carb inlet? If the needle seems to operate correctly, and the float height is proper (parallel to the casting when the carb is held inverted), you may have a different, non-fuel-related issue.
 
Thanks a lot for your help Paul. Next weekend I will look at the float assembly again to see if it is parallel. Fuel flows ok. Fuel is fine.
 
Is the fuel definitely OK, or could there be some water in it? Does the fuel flow OK by gravity to the carb inlet? If the needle seems to operate correctly, and the float height is proper (parallel to the casting when the carb is held inverted), you may have a different, non-fuel-related issue.

Paul,

I am attaching photos of my carb. The float is NOT parallel to the casting. Perhaps the metal tab is bent?

Bob
 

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Looks off to me. You must check it when inverted. When inverted, the float should be parallel, It is adjusted by bending the tab. That's the shutoff point for the gas. When upright, it needs to drop down in order for the needle to open and the fuel to flow.
 
Is the fuel definitely OK, or could there be some water in it? Does the fuel flow OK by gravity to the carb inlet? If the needle seems to operate correctly, and the float height is proper (parallel to the casting when the carb is held inverted), you may have a different, non-fuel-related issue.

Paul,

How about those Jets?!

I am sorry to say that after taking my carb apart again and adjusting it, as you suggested, still no change.

One of your other posts suggested checking the float needle for damange. How do I check it?

Thanks,

Bob
 
Time to go through the motor systems methodically. Your problem and the fuel vent event may be coincidental. Check the spark plug color. Black soot is way too rich, white is way too lean. Should be tan. You didn't specify exact model -- If this is a 4-stroke (carb looks it), check crankcase oil level. Must not be even a drop over filled. As for the needle, if it completely shuts off flow when the carb is inverted, and flows freely when upright, it should be OK -- but if you see an indentation in the viton tip where it was jammed against the seat, it should be replaced.
 
Paul,

Thanks again for your guidance. Wish I had checked the spark plug way back. After I pulled the carb apart again to check the needle (which looked ok), I pulled the plug and found it to be way fouled - black. Put her all back together with a new plug and am hoping when I crank it that I'll find a positive change. The guy at the auto parts store I got the new plug from didn't have a NGK so I took an Autolite, even though he said it wouldn't last as long.

Bob

Bob
 
Hopefully it works out for you, Someone may have left the choke out, or the carb float may have been set way too rich to cause that fouling. Also... There is no other plug that will work as well as the NGK DCPR6E (available from any dealer, including me) in Tohatsu 4-stroke motors.
 
Hey Paul,

Well it might be time for me to cart my engine to a professional. After filling the tank with fresh gas and replacing the spark plug, she still just sputters. Do you know a good mechanic in the Miami area? I think that I will do as you suggested and drain a bit of oil, though she worked fine for weeks after I changed the oil the last time.

Thanks for you assistance,

Bob
 
See http://www.tohatsu.com/dealersearch/index.html to find your local dealers. Since the plug was so fouled, and the motor still sputters, you are probably WAY rich... though it could be a few other things. Time for a Tohatsu mechanic to have a peek at it.

Hey Paul,

I called all the dealers in my area and can't get it in until Monday. So I tried a few other things, cause I have really spent a lot of time on this engine. Cleaned out the carb, again, and also cleaned the fuel filter, which was pretty dirty. Well, still won't go, so I video taped it in case you could see/hear a problem.

Here is the You Tube link:
http://www.youtube.com/watch?v=sOvCR-Onpjk

Last resort,

Bob
 
Sounds like it's probably either really lean (carb backfire), or maybe the ignition is off time (non-adjustable on these). What is the date of purchase? You may well be in warranty.
 
I odered a repair manual from Tohatsu and am still waiting. The engine was purchased several years ago. Is there a fuel pump on these? A mechanic mentioned that the fuel pump diaphram might be bad... If off time, and not adjustable, what then? Thanks
 
I odered a repair manual from Tohatsu and am still waiting. The engine was purchased several years ago. Is there a fuel pump on these? A mechanic mentioned that the fuel pump diaphram might be bad... If off time, and not adjustable, what then? Thanks

You can check the timing with a timing light. There are marks on the flywheel. If the ignition is firing out of time, odds are the CD has a problem. The ignition advance curve is hard coded into the CD module. This is not a very common problem.

But... we're getting ahead of ourselves here. Based on your video, it's just as likely that you still have a carb or fuel delivery problem. Did you replace the fuel cock? That has the long cylindrical fuel filter attached to the inlet side. If the filter is stopped up with junk, it could limit fuel flow, allowing an OK idle, but insufficient fuel to run much above idle. Not an uncommon problem on motors that sit a while or are fed some cheap gas. If you have the 3.5A, you will need a lot of patience to change the fuel cock; The B model is a bit easier.
 
Just guessing; I have seen on several small engines (new and old) in the carbs "fuel bowl" that the needle will have a wear-ring on it.
It occurs where the needle meets the seat causing the needle to either get stuck in the seat or not seal tight enough to stop the fuel
when the floats rise.
 
Paul,

I had cleaned the fuel filter a while ago and it was really dirty. Think I found the problem! Going over everything again this weekend, found out the main line into the carb is blocked. Could not blow air through it. I have seen on other online threads that compressed air is the way to go. Does that brass fitting come off?

Bob
 
Bob,

The brass nipple of the fuel inlet of the carb is pressed in, and is not intended to be removed. The inlet will be shut off if/when the float is up (carb bowl is full) and the needle is pressed up to shut off the gas. That's how fuel flow is regulated in a float-type carburetor.
 
Hi Paul,

It has been a while, however, I have been waiting over three weeks for the local Tohatsu repair facility to repair my engine. Called them last week and was told that they could not fix it. They had tried replacing a jet but they still could not get the engine to do anything but sputter.

The service manager said that they were going to call Tohatsu for advice.

What do you think about that?

Bob
 
Bob,

I have full confidence in the Tohatsu reps that your dealer will call. They have a lot of experience, especially with the newer small 4-strokes, which is an area where many OB mechanics lack experience. Assuming compression is OK and ignition is firing on time (need to check those items), we come back to fuel.

The motor can always be tested with a new carb. Depending on whether you have an A or B model motor, the appropriate carb costs about $145.30 (for the A model) or $110.97 for the B model. If it runs correctly with a new carb, then we have confirmed that the issue is in your carb. If it runs the same, we know the carb is not the problem. Many shops keep a spare carb handy to do that kind of testing, as it's a quick way to verify what we already suspect.
 
Hi Paul,

Bad News. The authorized Tohatsu Dealer in Coconut Grove, FL could not repair my engine! After having it for three months he has given up and is returning it to me... Any suggestions?

Bob
 
Sheesh. Anything can be fixed. What work did they do? What were the results? We must go back to basics. There are 3 systems that need to work: Mechanical, Fuel and Ignition. Inspect each system one at a time, with ridiculous meticulous precision. Check compression and leak-down. Verify ignition and valve timing. If that all looks good, we come back to fuel. If the tank, filter, and shutoff cock and OK, we come to the carb.
 
Take it to a Mercury dealer...Or a Tohatsu dealer...Or another Nissan dealer...Or start throwing parts at it by simply replacing the carburetor or ignitor. Since it doesn't look like anyone is running any tests on the systems it is probably one or the other.
 
Take it to a Mercury dealer...Or a Tohatsu dealer...Or another Nissan dealer...Or start throwing parts at it by simply replacing the carburetor or ignitor. Since it doesn't look like anyone is running any tests on the systems it is probably one or the other.

Yes. It needs to be diagnosed properly -- always did. And it appears that no one has done that so far. 99% chance the issue is either with the carb or ignitor. Perhaps a different dealer (Nissan, Tohatsu, or Mercury) is willing to do a few simple tests to diagnose it correctly... Or at least swap in a "known good" test part to confirm or rule out that bit.
 
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