F40TLR Problems Running

[howardrya]

My 2001 Yamaha F40TLR outboard is having a few problems running. I just had the carbs professionally cleaned and synchronized by a mechanic. However, when I push the throttle too quickly or let off too quickly, the motor stalls. It seems like this is a common problem with these F40 motors. It runs fine once I get it up to higher rpms. Next, I’m only seeing 4700 rpms at what is supposed to be WOT. The Manual says it should be 5000-6000 rpms. It looks like the butterflies on the carbs are opening up all the way. The prop is the OEM standard prop, and has no obvious bends or damages. I’m running good new fuel through a new water separator filter. I’m pretty good at working on marine engines, like rebuilding them, but when it comes to carbs I struggle. Is there a carb adjustment somewhere that I should play with? I’d like to try to remedy this myself, as bringing it back to the mechanic will be difficult and expensive.

[howardrya]

Thanks a lot that opens some possibilities.
The dash pot diaphragm on the carbs looks like it could be the culprit for the engine dieing when the throttle is let off, but could it also be the reason it dies under a quick increase in throttle?

There's nothing in the manual for testing it, is there a guide somewhere online you could point me towards?

[99yam40]

i think the F40 has accelerator pump, somewhat like the carbs on old automotive motors.
when you move the throttle it squirts a little gas to help transition to a higher RPM

maybe plugged up passage or other malfunction.

hopefully Rodbolt or someone that knows the F40 will chime in

[howardrya]

I'm really thinking this dashpot is bad. However, I'm still not sure how to test it with a vacuum pump as it has no hose barbs. It also looks different than the one linked with a picture. Should there be some vacuum connection to the carbs?

As of yesterday, my motor had a high idle (up to 1500 from 750), which happened very suddenly. I didn't change anything, I left the dock at normal idle, and when I returned it was high. While observing the dashpot work today, it seems like its not extending back out all the way, which is keeping the butterflys open just enough to increase the idle. If I give that arm a little push, the motor settles down to idle.

I adjusted the dashpot as recommended by Yamaha, and while it was out of spec, the adjustment didn't fix any problems.

Am I right to assume the dashpot should extend back out all the way?

[rodbolt17]

is this real mechanic wearing a master tech hat?
does this real mechcanic actually have Yamaha school certs for fuel systems on the wall>
if the answer is no find a real mechanic.
the dashpot only works on closing throttle.
each carb has an accelerator pump.

[rodbolt17]

because without a clue you are lost.
without the proper tools and training you are lost.
I see way to many so called shops without proper tools and training that will work on anything and charge for it.
that is why you do not go to a proctologist with a brain tumor.

that year F40 used 3 carbs and was a mercury motor with silver blue paint.

each carb has an accelerator pump circuit.
the dashpot simply helps prevent a stall at rapid throttle closing.

[boscoe99]

The accelerator pump in this model is somewhat problematic. Gunk gets in the bottom of the carburetor bowl and causes it to not work so well. Also, the pump outlet nozzle has a hole the size of a gnat's arse. It too can clog up and not spray gasoline into the carburetor throat as it is supposed to. Gunk that gets in is hard to get out. Maybe impossible.

F40 carburetors are known to whip master mechanics arse's and Yamaha field service technicians arse's. The Yam man more times than not will simply install a completely new set of carburetors.

[boscoe99]

[panasonic]

Great diagram....all should understand this type of carb better now. This is how we learn...pictures are worth a thousand words a lot of the time.

Thanks for sharing it.

[99yam40]

dash pot will not have vacuum fittings, just a diaphragm with a small orifice to slowly let the diaphragm move

[rodbolt17]

hey zues H Christ.
dashpots have been used since at least the 1920's.
accelerator pumps have been around even longer.
never had a carb,Q-jet , or others whoop me.
that is cause I tend to grab an SM and get an understanding of how it works and why.
if the SM calls for a specific tool for tuning you either buy the tool or take it to someone who bought said tool.

does one have to be a master tech to fix something?
NO.
but one does have to have a clue.

ya really want a challenge.
do a triple set of SU carbs.
or maybe the VV carbs ford used back in the day.

[rodbolt17]

now I am gonna chunk ya a curveball.
some of the Yamaha dashpots are also ACCELERATOR pumps.

some of the systems modify fuel bowl air pressure to accelerate and slow the throttle closing on deaccelerate.
not difficult.

I did my first carter/Rochester carb school in Hayward CA in 1977.
followed that with an AC/Delco school a few weeks later.

it is also why I have spent most of a lifetime studying how and why things work.
it is also why I don't reply much to posts talking about poor desine waaaa waaa waaa.

now the Fv8 and the F150 balancer, piss poor desighn.

I will warrenty I have done more q-jets than you have ever seen.

[pstephens46]

I had a Pinto one time. Think it had a 1 and 1/2 barrel carb. When that 1/2 kicked in, all hell broke loose. I just peed myself remembering it.

[rodbolt17]

depended on the pinto motor.
the 1.6L used a single barrel.
the 2.0 and 2.3 used w 2bbl.
I still have the bent box end that I made to remove/install the 2bbl.

[pstephens46]

depended on the pinto motor.
the 1.6L used a single barrel.
the 2.0 and 2.3 used w 2bbl.
I still have the bent box end that I made to remove/install the 2bbl.

I did have a Pinto. I was being sarcastic about the rest....

We also had a Ford wagon with the VV carb. My father finally found someone willing to fix that carb versus replacing with new.