Engine Bog

[Jason2tpa]

Before I recently pulled carbs for cleaning and after, the motor will occasionally bog down as I throttle up from idle. But it will only do this after motor has been off for a considerable amount of time, like long enough to go cold. For example, 1st throttle up of the day; when throttling up after fishing in one spot for awhile.

If I cut engine and restart 10-15min later and throttle up, no issues. So it seems to be occasionally happening only when motor is not at normal operating temp. Important to note, when it does experience this bog down the motor does not cut off or "bog down". If I maintain the same rpms as this is happening, the hp starts kicking in and within a few seconds the bog is gone. It's a deep "throaty" sound.

Do I have her too lean, too rich, or some other adjustment? And if so, could you explain what mechanical process is occurring as it's experiencing this bog. Thanks.

[TownsendsFJR1300]

Generally, bogging down is lack of fuel. A cold engine requires more fuel (IE choke).

The throaty sound is likely simply the intake your hearing with the butterfly's open (but the engine RPMs NOT increasing..

I know you have a butterfly choke, does it have any type of accelerator pump (didn't see any in the parts section).

How long has the issue been? Recent?


I know you don't want to hear it, but I'd try some RF, shock dose, should there be a little bit of crap in there you missed.

*Just finished cleaning an Echo, commercial weed eater carb (cleaning). Got it running but it ran pretty crappy. Did a RF treatment, ran it, let it sit
for a couple of days, NOW (doing nothing else), it starts on the first pull, idles great (wouldn't do either before). The owner picked it up yesterday.

[DennisG01]

From what you have posted, this could be normal. It's normal for carb'd engines to experience (more-so when cold) "carb lag". Meaning, if you throttle up too quickly the carb's aren't keeping up with the "demanded" fuel usage to match the air. If you throttle up slower/smoother it should keep up with the demand. But if you "nail it", it will bog down for a second or two before ramping back up. This has been my experience, anyways, with all carb'd engines I've owned.

[99yam40]

small 2 strokes like weed eaters, chainsaws,etc. tend to drop off like that when running too lean at idle to transition up to higher rpm
even they have off idle ports that get exposed as the throttle plats move past them

[Jason2tpa]

Generally, bogging down is lack of fuel. A cold engine requires more fuel (IE choke).

The throaty sound is likely simply the intake your hearing with the butterfly's open (but the engine RPMs NOT increasing..

I know you have a butterfly choke, does it have any type of accelerator pump (didn't see any in the parts section).

How long has the issue been? Recent?


I know you don't want to hear it, but I'd try some RF, shock dose, should there be a little bit of crap in there you missed.

*Just finished cleaning an Echo, commercial weed eater carb (cleaning). Got it running but it ran pretty crappy. Did a RF treatment, ran it, let it sit
for a couple of days, NOW (doing nothing else), it starts on the first pull, idles great (wouldn't do either before). The owner picked it up yesterday.

No accelerator pump...fuel enrichment valve activated via pushing in ignition switch. I didn't think of it till this moment, perhaps activating the choke when experiencing this bog corrects the issue. And if it does, this would imply the lack of full as you suggested and a lean idle mix as 99yam suggested. Is this an accurate assessment....your thoughts?

[Jason2tpa]

From what you have posted, this could be normal. It's normal for carb'd engines to experience (more-so when cold) "carb lag". Meaning, if you throttle up too quickly the carb's aren't keeping up with the "demanded" fuel usage to match the air. If you throttle up slower/smoother it should keep up with the demand. But if you "nail it", it will bog down for a second or two before ramping back up. This has been my experience, anyways, with all carb'd engines I've owned.

I understand what you're saying and in some instances it might be true. This bog is definitely not normal for my engine and the pace by which I throttle up prior to experiencing bog is slow.

[99yam40]

If I remember correctly, Rodbolt or Boscoe said that the enrichment system on some of those motors provides not only extra fuel for cold start, but also during acceleration

[Jason2tpa]

If I remember correctly, Rodbolt or Boscoe said that the enrichment system on some of those motors provides io only extra fuel for cold start, but also during acceleration

I was told by I think boscoe the choke system is technically called fuel enrichment. Its a soleniod that when activated pulls up the choke lever which in turn closes the carb flaps. If what you say is true, I wondering how the choke engages upon acceleration without me activating it.

#19
https://www.boats.net/catalog/yamaha...w/electrical-2

[DennisG01]

You mentioned in your first post that the motor did the bog both before and after the carb cleaning... are you instead saying this bog is different than before? It's hard to evaluate how much of a bog is there (and again, some bog is normal) via the info given and the fact that we only have words here. But if it's more than normal, then maybe a throttle/carb adjustment is needed... which is not my specialty so I won't even start to advise what specifically to do - and there are much more knowledgeable guys here than me when it comes to carb adjustment.

[99yam40]

I was told by I think boscoe the choke system is technically called fuel enrichment. Its a soleniod that when activated pulls up the choke lever which in turn closes the carb flaps. If what you say is true, I wondering how the choke engages upon acceleration without me activating it.

#19
https://www.boats.net/catalog/yamaha...w/electrical-2

nope wrong wording, I thought it was a enrichment system, but it is just a electric choke

[TownsendsFJR1300]

Every two stroke, (or 4 stroke) I've had or worked on, does NOT bog when accelerating if everything is working properly.

Mentioned earlier in the thread was small engines(weed wackers, chain saws, etc). Most have low speed screw that can be adjusted slightly richer that will eliminate any bog.
If the high speed adjustment is also set too lean (common, thanks EPA), that'll also affect it.

As mentioned earlier, I'll let a small machine sit over night will a strong dose of RF with SIGNICANT improvement in performance a day or two later (JUST SITTING).
I then have to re-adjust the HS and LS adjusters for max performance, and INSTANT acceleration..

Something is too lean, whether it be a clogged orifice, low speed fuel screw setting, etc.

The choke solenoid will NOT close automatically when accelerating.

[Jason2tpa]

There is only 1 screw per carb that will effect the idle mix (lean/rich) that can be adjusted...the air adjustment screw.

[TownsendsFJR1300]

There is only 1 screw per carb that will effect the idle mix (lean/rich) that can be adjusted...the air adjustment screw.

That's correct, I was answering 99Yams post.

I was also inferring that with the correct mixture (not lean) , you won't have that bog... It is NOT normal.

[Jason2tpa]

... It is NOT normal.

Couldn't agree with you more there.

[DennisG01]

Geez, I dunno guys. Every single carb'd engine I've ever had... cars... boats (4-stroke and 2-stroke)... etc, etc. Has always had some type of bog on a cold engine and quick acceleration. I've owned quite a few boats, but I've run literally hundreds with my job. On smooth, con*****ed acceleration - no bog. But on quicker acceleration, yes.