Author Topic: Runs fine but bogs when first started  (Read 181 times)

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Offline Spruce_Goose

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Runs fine but bogs when first started
« on: March 08, 2015, 09:31:14 pm »
I'm having a little trouble with a 357xp. When I start it, it tends to bog down / stall when I try to give it throttle. If I work the throttle gently and allow the fuel to get flowing, it runs fine and then cuts fine the rest of the run. This does not only happen when I FIRST start it but oftentimes when I start it still warm not many minutes later.

I have been tinkering very mildly with the low-end carb adjustment, but I can't seem to easily get at the problem with that. Seeing as it is only happening when starting it makes me think it may be a pumping issue? It is a new fuel line. Not a new pulse line but i checked it and as far as i can tell looks fine. Perhaps diaphragm pump? Or maybe when I replaced the line I didn't get a tight fit on one of the nipples...

Hopefully the fact that it bogs only after being started is clue for someone.

Thanks for any help,
Spruce_goose

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Offline 660magnum

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Re: Runs fine but bogs when first started
« Reply #1 on: March 08, 2015, 09:46:01 pm »
Have you removed the travel limiters from the needle valves?
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Offline Spruce_Goose

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Re: Runs fine but bogs when first started
« Reply #2 on: March 10, 2015, 10:59:24 am »
The carb is supposedly not the stock (as per someone on this forum I believe) and is a zama (its an older 357 that came stock with walbro i guess) and has no limiters. I think it is possible its just a carb adjustment and I'm just new to tuning and haven't had the time to really get it worked out just right.

Offline 660magnum

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Re: Runs fine but bogs when first started
« Reply #3 on: March 10, 2015, 11:38:02 am »
My 357XP has a Walbro HDA-499 accelerator pump carb. It is sensitive to the outside air temperature and requires re-adjustment everytime  I go to use it in a different season of the year. The factory OEM replacement carb for one of these is a Zama.

Bogging usually requires opening of the needle valves.
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Online srcarr52

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Re: Runs fine but bogs when first started
« Reply #4 on: March 10, 2015, 11:56:44 am »
I have a 359 with the HDA199 that does the same thing when you first start it. About a minute of idle and light blips and it will come out of it. It's having a hard time getting fuel, could be stiff diaphragms, sticky needle valve, slightly too high of pop off pressure. Anyway, I don't mess with it because it runs fine all day after the first start up.

Offline JohnG28

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Re: Runs fine but bogs when first started
« Reply #5 on: March 10, 2015, 07:02:49 pm »
If you replaced the fuel line did you rebuild the carb? Usually good to do hand in hand, get it all at once. Stiff diaphragms could cause it to pull hard until it gets going and fuel flowing. Did you replace the fuel filter? Carb strainer could be blocked up also. Hope you figure it out.

Offline Spruce_Goose

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Re: Runs fine but bogs when first started
« Reply #6 on: March 11, 2015, 05:02:30 pm »
thanks all for the advice.

Fuel filter was replaced fairly recently. Carb was not rebuilt, but the screen is clean. I am considering rebuilding it, just not sure how to know if it is necessary or overkill.

It was definitely running different a couple days ago in this warmer weather. The problem actually shifted from bogging after start to straight up dying after start (occasionally) unless set to start at high idle. Especially when its been running hard for a while. Not sure if this problem is indicative more of lean or rich settings (or another problem all together). It almost seems like the opposite problem in a way - needing more throttle after start as opposed to bogging with throttle.

I'll play some more with the carb, especially now its warmed up (maine) and consider a rebuild if I don't get anywhere.

thanks again

Offline 660magnum

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Re: Runs fine but bogs when first started
« Reply #7 on: March 11, 2015, 08:20:37 pm »
I always start at high idle hot or cold.
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