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I have a 2007 Yamaha Grizzly 450 4x4 that will start and

Idle great. Fresh gas...
I have a 2007 Yamaha Grizzly 450 4x4 that will start and Idle great. Fresh gas with no flow issues and new carburetor, spark plug, and air filter. The problem I'm having is the atv will bog and die when the throttle is pressed near 1/4 or so. I'm at a loss. I've also checked the rubber boots around carb and intake for vacuum leak and it seems fine in that aspect. Could the intake valve need adjusting?
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Customer reply replied 2 months ago
Also bike has 963 miles and about 250 hours
Answered in 18 minutes by:
10/10/2017
Louie
Louie, Technician
Category: Motorcycle
Satisfied Customers: 12,882
Experience: 25+ yrs. experience
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Hi and welcome to JustAnswer, I’m Louie. Sorry you had to wait awhile but I’ll do my best to help.
Initially, what is the burn color of the old spark plug? ...of the new?

Is the new air filter an original element? ...or a whole / new / aftermarket air filter assembly?
And to avoid asking you to do something you've already tried, can you please tell me what / any and all troubleshooting / specific steps you've already attempted other than / to address the above.

This is an independent site and members of this online community provide information, repair tips, technical assistance as a form of paid Q & A service.

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Customer reply replied 2 months ago
The air filter assembly is all stock except foam part is aftermarket. I have not done much except what has been listed.
Customer reply replied 2 months ago
Also, It runs worse with air filter removed.

Appreciate the post back.

Have you tried using the old air filter and the original air box?

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Customer reply replied 2 months ago
The air box is original and the issue existed with the old foam filter.

Let's try an experiment; add a layer of generic foam over the air filter element. The idea is to further restrict air entry through the carb.

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Customer reply replied 2 months ago
I don't have any foam so I layed a microfiber rag over the filter and same thing, except a small backfire came through the filter.

Continuing the experiment; how about folding the microfiber rag making only half of the air filter covered?

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Customer reply replied 2 months ago
Ok, I was able to partially cover the snorkel with my hand and rev it up without stalling

Very significant; "...further restrict air entry through the carb..." = rev it up without stalling.

This would make the mix lean.

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Proposed workarounds:

  • change air filter to something denser or experiment with layer(s) of generic foam air filter;
  • raise the needle height.
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Customer reply replied 2 months ago
I heavily coated the foam with yamalube grease. Tested and still bogs with throttle. Is it normal to have to adjust the needle height on a new carb?

Adjusting needle height is an acceptable method of compensating for lean mix. This is the reason most versions of carbs have a needle with several notches and a removable circlip type of a lock.

In some others, small thin washers may be added.

Incidentally, ensure that the air box/coupling is tightly fitted with no possibility of an air leak.

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Hi again,

Is further assistance/information still needed with the Grizzly?

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Customer reply replied 2 months ago
I was able to add the washers to raise the needle and get it running better, however I have now noticed that fuel line will start to dry up faster than it is refilled during riding. When I detach the fuel line from the carb, it seems to flow good from the petcock but when reconnected to the carb its like air gets in the line and causes fuel flow to slow way down from the petcock. Any ideas? The petcock has the strainers in the tank but I also have an inline clear filer with the gold looking element inside. Couldn't determine if that or the extra fuel lines were contributing to allowing air to get trapped in or something.

Great! Good to hear that the Grizzly is "...running better...", congratulations.

And if you haven’t done so, please provide a positive rating (3 to 5 stars) at the top of your page.

On this new issue, a possibility to consider is that the tank vent is clogged. There is vacuum developing in the tank while riding/as the fuel is used up. Try opening the gas cap when this happens and note if air can be heard rushing in.

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Customer reply replied 2 months ago
I tried the opening the gas cap and no noticeable improvement.

Is the "...inline clear filer..." an aftermarket? ...and have you tried bypassing / removing?

Louie
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Category: Motorcycle
Satisfied Customers: 12,882
Experience: 25+ yrs. experience
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Customer reply replied 2 months ago
The only difference from how I bought it is that I installed the briggs and stratton shut off valve and new gas lines (black rubber style material). The shut off valve was added because the original petcock did not completely shut off the fuel supply. It appears that the restriction is not in the filter or lines because it flows when disconnected from the carb. I will pick up some clear tubing to be able to watch the flow and isolate possible issues with the current assembly. I'm thinking something is happening with the petcock or problems due to the length of fuel line, due to the way the filter seems to get an air bubble and eventually dry up until the lean condition appears from fuel starvation. If left alone for long enough the filter will slowly fill back up with gas. Thank you for your help with this.
Customer reply replied 2 months ago
Also, I would like your opinion regarding how many washers you think are too many. I added 2 thin metal ones and a plastic one that is about as thick as 2 of the metal ones and I'm not unsure that another metal one would make the mix too rich. What would you expect for a new carb and I'm at sea level. It is an aftermarket carb off amazon for about $40

Consider adding washers to make the mix just a bit rich. This can be determine by the burn color of the spark plug tip; just a shade over brownish.

Another possibility would be the float height needing adjustment.

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Louie
Louie
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