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Hi all,

I bought a 1999 Suzuki King Quad a few months ago and it had a bit of a high idle issue. I would need to play with the choke and leave it just ever so slightly engaged so prevent the machine from dying and it would randomly climb in idle.

Today I rebuilt the carb in it thinking things might have been a bit gunked up. They were a bit. On first startup she was actually running a bit worse, popping and backfiring. We attributed it to possibly being the air fuel screw. I had read to screw it all the way in counting the rotations and then remove and install the new screw all the way in backing it out the recorded number of rotations before. So we backed it out 2.5 turns. When I pulled the spark plug after a few minutes of running and revving it up the plug tip was white (was black before). The throttle would not remain stable, meaning it would stable out nice and low, then randomly crawl back up to being high if we touched the throttle cable at all, anywhere.

Thinking maybe there was an issue with the cable as there was a bit of a sharp bend to the routing to the carb, we pulled the carb out reran the throttle cable so it didn't have any funky bends. We also cranked the airfuel screw out a 1/2 turn. This time around we fired it up without the air box attached. She sounded like she was falling on her face when we revved it up. The machine appears to be backfiring through the carb as it would spit gas out versus sucking it in.

We then repeated the previous step one more time but put the air box loosely on not clamped down and it appears to make things a little better - idle isn't quite as low as it should be and we have backed the throttle cables off on both the carb and hand throttle as well as backing off the set screw. The machine searches a little bit for idle but it is way better than it was to start.

Questions I have:

- The rubber diaphram on top of the carb (under the 2 screws) - does that play into the idle at all? It was swollen when we removed it and we had a hard time lining it back up. We ended up using RTV in the grove to hold the diaphram properly in place so we could screw the cap back down.
- Does having the airbox on vs not being on impact how the machine runs? (the second time we opted not to install the box as it is a pain in the rear end to get on and off and we were diagnosing issues) However, when we covered part of the throttle with our hand it appeared to make the machine run a little better - possibly indicating the air box plays a vital role in smooth operation? Weird as this is a carb and it is not like fuel injection where unmetered air might be traveling past a MAF sensor causing a lean condition?
- Is there some kind of trick to adjusting the air fuel ratio? Including any tricks to adjust the screw without having to tear the carburetor out and flip it upside down?
- What else could cause a rough idle? The idle raises sometimes on its own but it typically happens when it goes into a sputter? If you watch the gas in the fuel filter it appears to "hiccup" every time the machine sputters as well.

Thanks all!
 

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When adjusting the fuel mixture screws there is no easy option to adjust them while on the atv. Unfortunately it needs to be removed each time. Only one which is easy enough to adjust is the idle screw while on the atv. As for the air box, it does play a vital role. I wouldn’t recommend riding the atv without it. Testing it without won’t harm things.

As for the diaphragm in the top of the carb. If it is damaged in any way, cracked, a pin hole, etc. Then that will cause running issues. And I wouldn’t recommend leaving the RTV silicone there either.

One thing I would check however just to rule it out is the fuel petcock. With the atv off, pull the vacuum line off at the fuel petcock. If the line is wet or fuel comes out the line or port where you removed that line then the fuel petcock is bad and needs replacing. As for adjusting the carb properly. If you know the exact carb specs for your Atv. Take each screw and screw them in till they are lightly seated. Then back them out the appropriate amount of turns. Example: 2-1/2 turns, 1-1/2 turns, etc.


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Discussion Starter #3
When adjusting the fuel mixture screws there is no easy option to adjust them while on the atv. Unfortunately it needs to be removed each time. Only one which is easy enough to adjust is the idle screw while on the atv. As for the air box, it does play a vital role. I wouldn’t recommend riding the atv without it. Testing it without won’t harm things.

As for the diaphragm in the top of the carb. If it is damaged in any way, cracked, a pin hole, etc. Then that will cause running issues. And I wouldn’t recommend leaving the RTV silicone there either.

One thing I would check however just to rule it out is the fuel petcock. With the atv off, pull the vacuum line off at the fuel petcock. If the line is wet or fuel comes out the line or port where you removed that line then the fuel petcock is bad and needs replacing. As for adjusting the carb properly. If you know the exact carb specs for your Atv. Take each screw and screw then in till they are lightly seated. Then back them out the appropriate amount of turns. Example: 2-1/2 turns, 1-1/2 turns, etc.


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Thanks - We didn't leave the airbox off with the intention of riding around, just for diagnostic purposes where it didn't leave the paved driveway. However, we seemed to notice that the machine runs differently with the airbox attached vs unattached and I am not sure why that is either?

Why would you not leave RTV around the edge of the diaphram? As far as I can tell it appears there is no fluids that come in contact with the rubber diaphragm and it is strictly for vacuum operation?

I will check on the fuel petcock - thank you.

Do you know where I can find the exact carb specs for the 99 King Quad 300? We did seat the screw lightly and then back it out 2.5 turns, however it didn't seem to run right. The original screw that was in there was backed off 2.5 turns from the seat so that threw us off.
 

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I believe I have the carb specs somewhere on my PC. I’ll check for them tomorrow afternoon unless someone beats me to it.

And yes the diaphragm is for vacuum. Though I don’t believe the RTV may help. Might even interfere. Might be wrong though. I’ve never really heard of anyone else using RTV or anything else around the diaphragm. Not a common practice. So I’m not sure if that’s having any I’ll affect on your running issues.


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If you could grab those specs it would be much appreciated - thank you!

The rtv was used just to hold the edges in place. Because it was swollen the diaphragm became "too big". By using RTV around the outer edge we were able to hold the lip in place so the cap/spring was put back on without it shifting. The rtv was applied to the "grooved" area only and therefore is pinched between the cap - it should not interfere with the body of the diaphragm moving up and down at all.

We tried the heating trick to shrink it back down without any luck.

I looked at getting a new one for the heck of it, but what should cost about $5 is about $40-$60 everywhere I am been able to find.
 

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Here ya go:



Carburetor Specs



Carburetor Type: MIKUNI BSR29SS

Bore Type: 29 mm

I.D. No. 3902

Idle/r/min: 1500 +/- 100 r/min

Float Height: 13 +/- 0.5 mm (0.51 +/- 0.02 in)

Main Jet: #117.5

Jet Needle: 5D112-2nd

Needle Jet: P-0M

Throttle Valve: #105

Pilot Jet: #15

Starter Jet: #70

Pilot Screw: 2 1/4 Turns Back

Pilot Air Jet: #160

Throttle Cable Play: 3 - 5 mm (0.12 - 0.20 in)



Spark Plug Specs



DENSO: x22ESR-U

NGK: DR7EA

Gap: 0.6 - 0.7 (0.024 - 0.028)
 

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The big diaphram should be replaced if its all distorted. They are readily available. It sounds like you've got a vacuum leak that is causing a lean condition. I have had issues with the rubber intake mount leaking. You can check for leaks by running the motor and spraying carb cleaner around the mount flanges. If the motor speeds up or smooths out you have found your leak. RTV on the diaphram is not a good long term fix. Get a new one.

Hi all,

I bought a 1999 Suzuki King Quad a few months ago and it had a bit of a high idle issue. I would need to play with the choke and leave it just ever so slightly engaged so prevent the machine from dying and it would randomly climb in idle.

Today I rebuilt the carb in it thinking things might have been a bit gunked up. They were a bit. On first startup she was actually running a bit worse, popping and backfiring. We attributed it to possibly being the air fuel screw. I had read to screw it all the way in counting the rotations and then remove and install the new screw all the way in backing it out the recorded number of rotations before. So we backed it out 2.5 turns. When I pulled the spark plug after a few minutes of running and revving it up the plug tip was white (was black before). The throttle would not remain stable, meaning it would stable out nice and low, then randomly crawl back up to being high if we touched the throttle cable at all, anywhere.

Thinking maybe there was an issue with the cable as there was a bit of a sharp bend to the routing to the carb, we pulled the carb out reran the throttle cable so it didn't have any funky bends. We also cranked the airfuel screw out a 1/2 turn. This time around we fired it up without the air box attached. She sounded like she was falling on her face when we revved it up. The machine appears to be backfiring through the carb as it would spit gas out versus sucking it in.

We then repeated the previous step one more time but put the air box loosely on not clamped down and it appears to make things a little better - idle isn't quite as low as it should be and we have backed the throttle cables off on both the carb and hand throttle as well as backing off the set screw. The machine searches a little bit for idle but it is way better than it was to start.

Questions I have:

- The rubber diaphram on top of the carb (under the 2 screws) - does that play into the idle at all? It was swollen when we removed it and we had a hard time lining it back up. We ended up using RTV in the grove to hold the diaphram properly in place so we could screw the cap back down.
- Does having the airbox on vs not being on impact how the machine runs? (the second time we opted not to install the box as it is a pain in the rear end to get on and off and we were diagnosing issues) However, when we covered part of the throttle with our hand it appeared to make the machine run a little better - possibly indicating the air box plays a vital role in smooth operation? Weird as this is a carb and it is not like fuel injection where unmetered air might be traveling past a MAF sensor causing a lean condition?
- Is there some kind of trick to adjusting the air fuel ratio? Including any tricks to adjust the screw without having to tear the carburetor out and flip it upside down?
- What else could cause a rough idle? The idle raises sometimes on its own but it typically happens when it goes into a sputter? If you watch the gas in the fuel filter it appears to "hiccup" every time the machine sputters as well.

Thanks all!
 

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I would just replce the vacuum diaphragm And sort out the carb .
If the air cleaner is dirty its restrictive and could make engine run different when its taken on or off. Especially if you have a vacuum leak. Wouldn't hurt too clean the air filter .
If fixing and tuning the carburetor doesn't do it. I agree with FLHTK . Sounds like vacuum leaks. Spraying carb clean on intake and vacuum lines is easy way to find them.
 
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