Quick Idiotic Question.-

[Sea Rider]

If a carb has a slow jet with issues and doesn't want to stay ON at idle rpm once sufficiently warmed up, will OB miss throughout the ramaining throttle range ? Slow jet has nothing to do, are separate fuel systems if you can call that, right ?

Happy Boating

 

[pvanv]

nope. slow jet will affect all speeds. less at high speeds.

 

[alldodge]

Slow jet

Not an OB guy but a carb is a carb

IMO, there is no such thing as a "slow" jet. The fuel bowl fills with fuel to a preset level. The intake stroke of the piston creates a vacuum which draws air across the venturi which pulls fuel out of the fuel bowl. The amount of fuel pulled out of the bowl depends on the amount of air drawn past. size of venturi and idle adjustment screw (idle only).

Once motor gets above idle circuit the main jet size takes over, but amount still stays at a given ratio based on jet size.

As for your symptoms, it sounds like your float is not set correctly or its a bit clogged

When cold the choke runs richer allowing more fuel. Once warmed up, choke opens fully and there is less fuel

 

[ahicks]

Later carb designs all feature multiple fuel paths/stages for fuel to flow. A late model 4 stroke may have 4 (low, medium low, mid range, and high)! These different fuel stages are used/activated by the carb's butterfly and the amount of air flowing through the carb. As the butterfly opens early in it's travel it exposes more of the tiny holes in the carb's throat (very near the butterfly). The tiny holes are fed by increasingly larger jets.

All that to say that while those tiny holes in the carb's throat aren't pulling as much fuel at wide open throttle as when the throttle butterfly is directly over them, as long as there a vacuum in the carb, they will (should) be flowing fuel. I would temper that comment by saying the percentage of fuel they are supplying at wide open throttle is not that high.

So, if your engine has a noticeable miss from idle to wide open, I'm not real sure I'd be quick to point at the carb. Knowing there's an issue on the low speed, that's where I would start when it comes to repairing this engine. Getting that right eliminates that issue as the potential reason for the miss at higher rpms....

 

[Sea Rider]

Sorry, Paul and I speak same OB language. A slow Jet exists as such, happens to be the tiny jet close to the Main Jet. The story behind this inquired issue is : Recently made a huge maintenance to an OB that was ready to be used as an anchor as shade tree pseudo mechanics could not make OB to run well.

When all was set to factory specs, OB was found with less than 100 PSI during a cylinder compression test, was hard to start or restart without choke. Once sufficiently warmed up would stay ON while idle rpm were adjusted bit higher than normal. Carb was cleaned to spotless perfection, float, needle and needle plug are in excellent shape. Float is fixed and non adjustable.

If OB doesn't miss a bit at any other throttle setting passed idle, then it's not a Slow Jet related issue, right ? That OB needs new piston rings or a combo of piston rings and pistosns whether standard or super ones, will depend on how much wear is detected on both cylinders at a machine shop.

Owner has decided going for a second opinion and has taken OB to another experienced shade tree mechanic that says it's a carb issue, doesn't know that low compression issues will give those symptoms.

Happy Boating

 

[ahicks]

<<<If OB doesn't miss a bit at any other throttle setting passed idle, then it's not a Slow Jet related issue, right ?>>>

You can't make that assumption, sorry. From a likelihood perspective it would be one of the most common.

And if we're working on a 2 stroke, you can't assume low compression is a piston/ring issue either. As you seem to rely on Paul and he talks your language, ask him about reed valves, and what the symptoms of a bad/damaged one might cause?

Point being, if there is no obvious damage apparent when you pull the head, before you get too far into it, checking the reed valves for apparent damage could save a lot of time and money....

 

[Sea Rider]

According to a buddy that has been repairing 2 strokes motorcycles for the past 30 years, having bad reed valves gives symptoms such as a puff/spit from the carb. Why would reeds go bad if you haven't messed them up and after only max 150 worked hours.

Have seen same symptom on other OB, a new piston and ring with spot on bored cylinder walls along new gasket kit cured it. Would be interesting for Paul to chime in and give the on line audience his interesting tech point of view regarding bad reeds symptoms..

Happy Boating

 

[ahicks]

<<<Why would reeds go bad if you haven't messed them up and after only max 150 worked hours.>>>

I'd happily answer that question, but you would likely come up with somebody else you know with contradictory information. Maybe you could look into it yourself and learn something. I'm done wasting my time with you. Have a good life.

 

[pvanv]

Play nice, guys. Luis found, as is sometimes the case, that carboning of the rings can lower compression. It can also lead to detonation, depending on how bad it is, and whether it's on the head or on the piston. Seldom do reeds go bad on Tohatsu motors, and when they do, it's usually obvious... but it never hurts to check them, as it's easy to do.

 

[Sea Rider]

I'd happily answer that question, but you would likely come up with somebody else you know with contradictory information. Maybe you could look into it yourself and learn something. I'm done wasting my time with you. Have a good life.

In reality don't need to disasemble intake manifold assy to check reed valves just to please you. As Paul stated with proven knowlidge and experience, Tohatsu reed valves seldom go bad. In 12 years selling, servicingTohatsu OB's have never found a reed valve issue but found descompression issues.

This is the third time you have been picky and discourteous with my posts. The issue with you is that you like wild guessing, assuming, badly diagnosing things, not addressing the point on time. Besides nobody asked for your advise along bad mood...

Happy Boating

 

[ahicks]

Play nice, guys. Luis found, as is sometimes the case, that carboning of the rings can lower compression. It can also lead to detonation, depending on how bad it is, and whether it's on the head or on the piston. Seldom do reeds go bad on Tohatsu motors, and when they do, it's usually obvious... but it never hurts to check them, as it's easy to do.

Paul, as I'm sure you know, it takes time to think an issue through and type out an answer. Maybe it's my imagination, but every time I try to provide some guidance to what seems like a rookie question from this man (14 year old kid?), he comes up with contradictory advice from some questionable source. Good or bad, anything to discredit my time....

In the case of a generic engine (I wasn't speaking of Tohatsu specifically), let's talk about that obviously bad reed valve for instance. That very well could influence a compression reading, no? Due to loss of crankcase pressure? What symptoms would be most obvious? How about difficult to start? In the case of a partially damaged reed, how about a low speed miss that disappears as the rpms increase? Even if the reeds seldom go bad, there's still a chance something has been ingested and is now fouled in the reed cage preventing a reed from closing.

Yes, been around long enough to know the chance is remote, but at the same time, been around long enough to have learned not to make quick assumptions regarding loss of compression on an outboard. I'm not going to pull one of those down until I've checked all other possibilities. Easy stuff first logic......

Been around this stuff a long time, well over 50 years. Getting older gives me the right to be grouchy on occasion - like regarding the lack of respect shown by our OP. As mentioned, going to eliminate this source of aggravation pretty easily.

-Al

 

[Sea Rider]

Gee, who aggravates who in the first place, as always fully justifying your posts ? Man you need to locate yourself in time and space, we're talking about "Tohatsu Outboards" which you don't have any proven experience with. Why compare this supposedly reed valve issue with other brand ones ? It's as simple as to each his own brand issue, period.

Why check my back yard garden when I'm having a front garden flood. Guess what, OB has been disassembled, reed valves are 101% operational, power head was sent to a machine shop and probably will have cylinders bored to next piston/ring size which is 0.5 as there's too much cylinder wear to install standard parts.

Have read near all your posts on different forum topics, are full of comparisons, assumptions which doesn't fix anything any time soon nor contribute a bit for a correct and precise tech diagnose. Everything else it's just good for 6 o'clock tea talk. If you feel you're being mistreated, offended with my answers after having read and replied yours, simply ignore my threads/posts and voilá..

Happy Boating

 

[GA_Boater]

Warning - Please, don't make this personal.

Offered advice doesn't not need to be followed. If you feel like your input is not welcome, ignore the thread and stop commenting.

 

[ahicks]

Precisely what I've offered (see post # 8). Thank you for your input.

 

[Sea Rider]

For me this thread is Closed, the culprit has already been found and action taken.

Happy Boating